| 1 | <!DOCTYPE html |
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| 2 | PUBLIC "-//W3C//DTD HTML 4.01//EN"> |
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| 3 | <html lang="en"> |
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| 4 | <head profile="http://dublincore.org/documents/2008/08/04/dc-html/"> |
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| 5 | <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> |
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| 6 | <title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title><script> |
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| 7 | var buttonsAdded = false; |
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| 8 | |
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| 9 | function init() { |
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| 10 | var fb = document.createElement("div"); |
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| 11 | fb.className = "feedback noprint"; |
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| 12 | fb.setAttribute("onclick", "feedback();"); |
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| 13 | fb.appendChild(document.createTextNode("feedback")); |
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| 14 | |
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| 15 | var bodyl = document.getElementsByTagName("body"); |
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| 16 | bodyl.item(0).appendChild(fb); |
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| 17 | } |
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| 18 | |
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| 19 | function feedback() { |
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| 20 | toggleButtonsToElementsByName("h1"); |
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| 21 | toggleButtonsToElementsByName("h2"); |
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| 22 | toggleButtonsToElementsByName("h3"); |
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| 23 | toggleButtonsToElementsByName("h4"); |
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| 24 | |
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| 25 | buttonsAdded = !buttonsAdded; |
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| 26 | } |
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| 27 | |
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| 28 | function toggleButtonsToElementsByName(name) { |
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| 29 | var list = document.getElementsByTagName(name); |
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| 30 | for (var i = 0; i < list.length; i++) { |
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| 31 | toggleButton(list.item(i)); |
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| 32 | } |
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| 33 | } |
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| 34 | |
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| 35 | function toggleButton(node) { |
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| 36 | if (! buttonsAdded) { |
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| 37 | |
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| 38 | // docname |
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| 39 | var template = "mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&body=<{ref}>:"; |
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| 40 | |
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| 41 | var id = node.getAttribute("id"); |
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| 42 | // better id available? |
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| 43 | var titlelinks = node.getElementsByTagName("a"); |
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| 44 | for (var i = 0; i < titlelinks.length; i++) { |
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| 45 | var tl = titlelinks.item(i); |
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| 46 | if (tl.getAttribute("id")) { |
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| 47 | id = tl.getAttribute("id"); |
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| 48 | } |
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| 49 | } |
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| 50 | |
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| 51 | // ref |
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| 52 | var ref = window.location.toString(); |
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| 53 | var hash = ref.indexOf("#"); |
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| 54 | if (hash != -1) { |
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| 55 | ref = ref.substring(0, hash); |
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| 56 | } |
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| 57 | if (id != "") { |
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| 58 | ref += "#" + id; |
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| 59 | } |
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| 60 | |
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| 61 | // docname |
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| 62 | var docname = "draft-ietf-httpbis-p6-cache-latest"; |
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| 63 | |
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| 64 | // section |
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| 65 | var section = node.textContent; |
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| 66 | section = section.replace("\u00a0", " "); |
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| 67 | |
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| 68 | // build URI from template |
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| 69 | var uri = template.replace("{docname}", encodeURIComponent(docname)); |
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| 70 | uri = uri.replace("{section}", encodeURIComponent(section)); |
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| 71 | uri = uri.replace("{ref}", encodeURIComponent(ref)); |
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| 72 | |
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| 73 | var button = document.createElement("a"); |
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| 74 | button.className = "fbbutton noprint"; |
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| 75 | button.setAttribute("href", uri); |
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| 76 | button.appendChild(document.createTextNode("send feedback")); |
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| 77 | node.appendChild(button); |
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| 78 | } |
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| 79 | else { |
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| 80 | var buttons = node.getElementsByTagName("a"); |
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| 81 | for (var i = 0; i < buttons.length; i++) { |
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| 82 | var b = buttons.item(i); |
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| 83 | if (b.className == "fbbutton noprint") { |
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| 84 | node.removeChild(b); |
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| 85 | } |
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| 86 | } |
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| 87 | } |
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| 88 | }</script><style type="text/css" title="Xml2Rfc (sans serif)"> |
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| 89 | a { |
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| 90 | text-decoration: none; |
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| 91 | } |
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| 92 | a.smpl { |
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| 93 | color: black; |
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| 94 | } |
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| 95 | a:hover { |
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| 96 | text-decoration: underline; |
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| 97 | } |
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| 98 | a:active { |
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| 99 | text-decoration: underline; |
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| 100 | } |
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| 101 | address { |
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| 102 | margin-top: 1em; |
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| 103 | margin-left: 2em; |
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| 104 | font-style: normal; |
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| 105 | } |
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| 106 | body { |
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| 107 | color: black; |
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| 108 | font-family: cambria, helvetica, arial, sans-serif; |
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| 109 | font-size: 11pt; |
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| 110 | margin-right: 2em; |
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| 111 | } |
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| 112 | cite { |
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| 113 | font-style: normal; |
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| 114 | } |
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| 115 | div.note { |
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| 116 | margin-left: 2em; |
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| 117 | } |
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| 118 | dl { |
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| 119 | margin-left: 2em; |
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| 120 | } |
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| 121 | ul.empty { |
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| 122 | list-style-type: none; |
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| 123 | } |
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| 124 | ul.empty li { |
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| 125 | margin-top: .5em; |
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| 126 | } |
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| 127 | dl p { |
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| 128 | margin-left: 0em; |
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| 129 | } |
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| 130 | dt { |
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| 131 | margin-top: .5em; |
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| 132 | } |
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| 133 | h1 { |
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| 134 | font-size: 130%; |
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| 135 | line-height: 21pt; |
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| 136 | page-break-after: avoid; |
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| 137 | } |
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| 138 | h1.np { |
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| 139 | page-break-before: always; |
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| 140 | } |
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| 141 | h2 { |
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| 142 | font-size: 120%; |
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| 143 | line-height: 15pt; |
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| 144 | page-break-after: avoid; |
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| 145 | } |
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| 146 | h3, h4, h5, h6 { |
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| 147 | font-size: 110%; |
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| 148 | page-break-after: avoid; |
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| 149 | } |
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| 150 | h1 a, h2 a, h3 a, h4 a, h5 a, h6 a { |
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| 151 | color: black; |
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| 152 | } |
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| 153 | img { |
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| 154 | margin-left: 3em; |
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| 155 | } |
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| 156 | li { |
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| 157 | margin-left: 2em; |
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| 158 | } |
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| 159 | ol { |
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| 160 | margin-left: 2em; |
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| 161 | } |
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| 162 | ol.la { |
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| 163 | list-style-type: lower-alpha; |
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| 164 | } |
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| 165 | ol.ua { |
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| 166 | list-style-type: upper-alpha; |
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| 167 | } |
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| 168 | ol p { |
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| 169 | margin-left: 0em; |
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| 170 | } |
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| 171 | p { |
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| 172 | margin-left: 2em; |
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| 173 | } |
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| 174 | pre { |
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| 175 | margin-left: 3em; |
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| 176 | background-color: lightyellow; |
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| 177 | padding: .25em; |
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| 178 | page-break-inside: avoid; |
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| 179 | } |
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| 180 | pre.text2 { |
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| 181 | border-style: dotted; |
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| 182 | border-width: 1px; |
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| 183 | background-color: #f0f0f0; |
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| 184 | width: 69em; |
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| 185 | } |
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| 186 | pre.inline { |
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| 187 | background-color: white; |
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| 188 | padding: 0em; |
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| 189 | } |
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| 190 | pre.text { |
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| 191 | border-style: dotted; |
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| 192 | border-width: 1px; |
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| 193 | background-color: #f8f8f8; |
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| 194 | width: 69em; |
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| 195 | } |
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| 196 | pre.drawing { |
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| 197 | border-style: solid; |
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| 198 | border-width: 1px; |
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| 199 | background-color: #f8f8f8; |
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| 200 | padding: 2em; |
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| 201 | } |
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| 202 | sup { |
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| 203 | font-size: 60%; |
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| 204 | } |
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| 205 | table { |
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| 206 | margin-left: 2em; |
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| 207 | } |
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| 208 | table.tt { |
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| 209 | vertical-align: top; |
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| 210 | } |
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| 211 | table.full { |
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| 212 | border-style: outset; |
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| 213 | border-width: 1px; |
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| 214 | } |
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| 215 | table.headers { |
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| 216 | border-style: outset; |
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| 217 | border-width: 1px; |
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| 218 | } |
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| 219 | table.tt td { |
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| 220 | vertical-align: top; |
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| 221 | } |
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| 222 | table.full td { |
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| 223 | border-style: inset; |
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| 224 | border-width: 1px; |
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| 225 | } |
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| 226 | table.tt th { |
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| 227 | vertical-align: top; |
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| 228 | } |
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| 229 | table.full th { |
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| 230 | border-style: inset; |
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| 231 | border-width: 1px; |
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| 232 | } |
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| 233 | table.headers th { |
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| 234 | border-style: none none inset none; |
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| 235 | border-width: 1px; |
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| 236 | } |
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| 237 | table.left { |
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| 238 | margin-right: auto; |
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| 239 | } |
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| 240 | table.right { |
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| 241 | margin-left: auto; |
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| 242 | } |
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| 243 | table.center { |
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| 244 | margin-left: auto; |
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| 245 | margin-right: auto; |
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| 246 | } |
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| 247 | caption { |
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| 248 | caption-side: bottom; |
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| 249 | font-weight: bold; |
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| 250 | font-size: 10pt; |
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| 251 | margin-top: .5em; |
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| 252 | } |
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| 253 | |
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| 254 | table.header { |
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| 255 | border-spacing: 1px; |
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| 256 | width: 95%; |
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| 257 | font-size: 11pt; |
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| 258 | color: white; |
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| 259 | } |
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| 260 | td.top { |
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| 261 | vertical-align: top; |
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| 262 | } |
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| 263 | td.topnowrap { |
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| 264 | vertical-align: top; |
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| 265 | white-space: nowrap; |
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| 266 | } |
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| 267 | table.header td { |
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| 268 | background-color: gray; |
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| 269 | width: 50%; |
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| 270 | } |
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| 271 | table.header a { |
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| 272 | color: white; |
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| 273 | } |
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| 274 | td.reference { |
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| 275 | vertical-align: top; |
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| 276 | white-space: nowrap; |
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| 277 | padding-right: 1em; |
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| 278 | } |
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| 279 | thead { |
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| 280 | display:table-header-group; |
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| 281 | } |
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| 282 | ul.toc, ul.toc ul { |
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| 283 | list-style: none; |
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| 284 | margin-left: 1.5em; |
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| 285 | padding-left: 0em; |
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| 286 | } |
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| 287 | ul.toc li { |
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| 288 | line-height: 150%; |
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| 289 | font-weight: bold; |
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| 290 | margin-left: 0em; |
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| 291 | } |
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| 292 | ul.toc li li { |
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| 293 | line-height: normal; |
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| 294 | font-weight: normal; |
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| 295 | font-size: 10pt; |
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| 296 | margin-left: 0em; |
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| 297 | } |
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| 298 | li.excluded { |
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| 299 | font-size: 0pt; |
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| 300 | } |
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| 301 | ul p { |
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| 302 | margin-left: 0em; |
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| 303 | } |
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| 304 | .title, .filename, h1, h2, h3, h4 { |
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| 305 | font-family: candara, helvetica, arial, sans-serif; |
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| 306 | } |
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| 307 | samp, tt, code, pre { |
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| 308 | font: consolas, monospace; |
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| 309 | } |
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| 310 | ul.ind, ul.ind ul { |
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| 311 | list-style: none; |
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| 312 | margin-left: 1.5em; |
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| 313 | padding-left: 0em; |
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| 314 | page-break-before: avoid; |
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| 315 | } |
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| 316 | ul.ind li { |
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| 317 | font-weight: bold; |
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| 318 | line-height: 200%; |
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| 319 | margin-left: 0em; |
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| 320 | } |
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| 321 | ul.ind li li { |
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| 322 | font-weight: normal; |
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| 323 | line-height: 150%; |
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| 324 | margin-left: 0em; |
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| 325 | } |
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| 326 | .avoidbreak { |
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| 327 | page-break-inside: avoid; |
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| 328 | } |
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| 329 | .bcp14 { |
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| 330 | font-style: normal; |
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| 331 | text-transform: lowercase; |
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| 332 | font-variant: small-caps; |
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| 333 | } |
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| 334 | .comment { |
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| 335 | background-color: yellow; |
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| 336 | } |
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| 337 | .center { |
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| 338 | text-align: center; |
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| 339 | } |
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| 340 | .error { |
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| 341 | color: red; |
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| 342 | font-style: italic; |
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| 343 | font-weight: bold; |
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| 344 | } |
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| 345 | .figure { |
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| 346 | font-weight: bold; |
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| 347 | text-align: center; |
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| 348 | font-size: 10pt; |
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| 349 | } |
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| 350 | .filename { |
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| 351 | color: #333333; |
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| 352 | font-size: 75%; |
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| 353 | font-weight: bold; |
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| 354 | line-height: 21pt; |
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| 355 | text-align: center; |
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| 356 | } |
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| 357 | .fn { |
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| 358 | font-weight: bold; |
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| 359 | } |
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| 360 | .left { |
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| 361 | text-align: left; |
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| 362 | } |
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| 363 | .right { |
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| 364 | text-align: right; |
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| 365 | } |
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| 366 | .title { |
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| 367 | color: green; |
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| 368 | font-size: 150%; |
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| 369 | line-height: 18pt; |
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| 370 | font-weight: bold; |
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| 371 | text-align: center; |
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| 372 | margin-top: 36pt; |
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| 373 | } |
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| 374 | .warning { |
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| 375 | font-size: 130%; |
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| 376 | background-color: yellow; |
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| 377 | } |
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| 378 | .feedback { |
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| 379 | position: fixed; |
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| 380 | bottom: 1%; |
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| 381 | right: 1%; |
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| 382 | padding: 3px 5px; |
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| 383 | color: white; |
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| 384 | border-radius: 5px; |
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| 385 | background: #a00000; |
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| 386 | border: 1px solid silver; |
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| 387 | } |
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| 388 | .fbbutton { |
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| 389 | margin-left: 1em; |
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| 390 | color: #303030; |
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| 391 | font-size: small; |
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| 392 | font-weight: normal; |
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| 393 | background: #d0d000; |
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| 394 | padding: 1px 4px; |
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| 395 | border: 1px solid silver; |
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| 396 | border-radius: 5px; |
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| 397 | } |
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| 398 | |
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| 399 | @media print { |
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| 400 | .noprint { |
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| 401 | display: none; |
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| 402 | } |
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| 403 | |
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| 404 | a { |
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| 405 | color: black; |
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| 406 | text-decoration: none; |
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| 407 | } |
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| 408 | |
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| 409 | table.header { |
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| 410 | width: 90%; |
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| 411 | } |
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| 412 | |
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| 413 | td.header { |
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| 414 | width: 50%; |
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| 415 | color: black; |
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| 416 | background-color: white; |
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| 417 | vertical-align: top; |
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| 418 | font-size: 110%; |
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| 419 | } |
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| 420 | |
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| 421 | ul.toc a:nth-child(2)::after { |
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| 422 | content: leader('.') target-counter(attr(href), page); |
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| 423 | } |
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| 424 | |
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| 425 | ul.ind li li a { |
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| 426 | content: target-counter(attr(href), page); |
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| 427 | } |
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| 428 | |
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| 429 | .print2col { |
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| 430 | column-count: 2; |
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| 431 | -moz-column-count: 2; |
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| 432 | column-fill: auto; |
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| 433 | } |
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| 434 | } |
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| 435 | |
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| 436 | @page { |
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| 437 | @top-left { |
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| 438 | content: "Internet-Draft"; |
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| 439 | } |
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| 440 | @top-right { |
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| 441 | content: "October 2013"; |
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| 442 | } |
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| 443 | @top-center { |
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| 444 | content: "HTTP/1.1 Caching"; |
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| 445 | } |
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| 446 | @bottom-left { |
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| 447 | content: "Fielding, et al."; |
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| 448 | } |
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| 449 | @bottom-center { |
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| 450 | content: "Expires April 14, 2014"; |
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| 451 | } |
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| 452 | @bottom-right { |
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| 453 | content: "[Page " counter(page) "]"; |
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| 454 | } |
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| 455 | } |
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| 456 | |
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| 457 | @page:first { |
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| 458 | @top-left { |
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| 459 | content: normal; |
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| 460 | } |
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| 461 | @top-right { |
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| 462 | content: normal; |
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| 463 | } |
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| 464 | @top-center { |
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| 465 | content: normal; |
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| 466 | } |
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| 467 | } |
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| 468 | </style><link rel="Contents" href="#rfc.toc"> |
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| 469 | <link rel="Author" href="#rfc.authors"> |
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| 470 | <link rel="Copyright" href="#rfc.copyrightnotice"> |
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| 471 | <link rel="Index" href="#rfc.index"> |
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| 472 | <link rel="Chapter" title="1 Introduction" href="#rfc.section.1"> |
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| 473 | <link rel="Chapter" title="2 Overview of Cache Operation" href="#rfc.section.2"> |
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| 474 | <link rel="Chapter" title="3 Storing Responses in Caches" href="#rfc.section.3"> |
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| 475 | <link rel="Chapter" title="4 Constructing Responses from Caches" href="#rfc.section.4"> |
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| 476 | <link rel="Chapter" title="5 Header Field Definitions" href="#rfc.section.5"> |
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| 477 | <link rel="Chapter" title="6 History Lists" href="#rfc.section.6"> |
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| 478 | <link rel="Chapter" title="7 IANA Considerations" href="#rfc.section.7"> |
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| 479 | <link rel="Chapter" title="8 Security Considerations" href="#rfc.section.8"> |
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| 480 | <link rel="Chapter" title="9 Acknowledgments" href="#rfc.section.9"> |
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| 481 | <link rel="Chapter" href="#rfc.section.10" title="10 References"> |
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| 482 | <link rel="Appendix" title="A Changes from RFC 2616" href="#rfc.section.A"> |
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| 483 | <link rel="Appendix" title="B Imported ABNF" href="#rfc.section.B"> |
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| 484 | <link rel="Appendix" title="C Collected ABNF" href="#rfc.section.C"> |
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| 485 | <link rel="Appendix" title="D Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.D"> |
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| 486 | <link href="p5-range.html" rel="prev"> |
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| 487 | <link href="p7-auth.html" rel="next"> |
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| 488 | <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.603, 2013/09/18 20:22:25, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/"> |
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| 489 | <link rel="schema.dct" href="http://purl.org/dc/terms/"> |
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| 490 | <meta name="dct.creator" content="Fielding, R."> |
|---|
| 491 | <meta name="dct.creator" content="Nottingham, M."> |
|---|
| 492 | <meta name="dct.creator" content="Reschke, J. F."> |
|---|
| 493 | <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p6-cache-latest"> |
|---|
| 494 | <meta name="dct.issued" scheme="ISO8601" content="2013-10-11"> |
|---|
| 495 | <meta name="dct.replaces" content="urn:ietf:rfc:2616"> |
|---|
| 496 | <meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information systems. This document defines requirements on HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages."> |
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| 497 | <meta name="description" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information systems. This document defines requirements on HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages."> |
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| 498 | </head> |
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| 499 | <body onload="init();"> |
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| 500 | <table class="header"> |
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| 501 | <tbody> |
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| 502 | <tr> |
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| 503 | <td class="left">HTTPbis Working Group</td> |
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| 504 | <td class="right">R. Fielding, Editor</td> |
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| 505 | </tr> |
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| 506 | <tr> |
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| 507 | <td class="left">Internet-Draft</td> |
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| 508 | <td class="right">Adobe</td> |
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| 509 | </tr> |
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| 510 | <tr> |
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| 511 | <td class="left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved) |
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| 512 | </td> |
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| 513 | <td class="right">M. Nottingham, Editor</td> |
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| 514 | </tr> |
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| 515 | <tr> |
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| 516 | <td class="left">Intended status: Standards Track</td> |
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| 517 | <td class="right">Akamai</td> |
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| 518 | </tr> |
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| 519 | <tr> |
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| 520 | <td class="left">Expires: April 14, 2014</td> |
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| 521 | <td class="right">J. Reschke, Editor</td> |
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| 522 | </tr> |
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| 523 | <tr> |
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| 524 | <td class="left"></td> |
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| 525 | <td class="right">greenbytes</td> |
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| 526 | </tr> |
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| 527 | <tr> |
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| 528 | <td class="left"></td> |
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| 529 | <td class="right">October 11, 2013</td> |
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| 530 | </tr> |
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| 531 | </tbody> |
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| 532 | </table> |
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| 533 | <p class="title">Hypertext Transfer Protocol (HTTP/1.1): Caching<br><span class="filename">draft-ietf-httpbis-p6-cache-latest</span></p> |
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| 534 | <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1> |
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| 535 | <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information |
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| 536 | systems. This document defines requirements on HTTP caches and the associated header fields that control cache behavior or |
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| 537 | indicate cacheable response messages. |
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| 538 | </p> |
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| 539 | <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1> |
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| 540 | <p>Discussion of this draft takes place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org), which is archived at <<a href="http://lists.w3.org/Archives/Public/ietf-http-wg/">http://lists.w3.org/Archives/Public/ietf-http-wg/</a>>. |
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| 541 | </p> |
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| 542 | <p>The current issues list is at <<a href="http://tools.ietf.org/wg/httpbis/trac/report/3">http://tools.ietf.org/wg/httpbis/trac/report/3</a>> and related documents (including fancy diffs) can be found at <<a href="http://tools.ietf.org/wg/httpbis/">http://tools.ietf.org/wg/httpbis/</a>>. |
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| 543 | </p> |
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| 544 | <p>The changes in this draft are summarized in <a href="#changes.since.24" title="Since draft-ietf-httpbis-p6-cache-24">Appendix D.6</a>. |
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| 545 | </p> |
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| 546 | <div id="rfc.status"> |
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| 547 | <h1><a href="#rfc.status">Status of This Memo</a></h1> |
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| 548 | <p>This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.</p> |
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| 549 | <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute |
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| 550 | working documents as Internet-Drafts. The list of current Internet-Drafts is at <a href="http://datatracker.ietf.org/drafts/current/">http://datatracker.ietf.org/drafts/current/</a>. |
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| 551 | </p> |
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| 552 | <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other |
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| 553 | documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work |
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| 554 | in progress”. |
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| 555 | </p> |
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| 556 | <p>This Internet-Draft will expire on April 14, 2014.</p> |
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| 557 | </div> |
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| 558 | <div id="rfc.copyrightnotice"> |
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| 559 | <h1><a href="#rfc.copyrightnotice">Copyright Notice</a></h1> |
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| 560 | <p>Copyright © 2013 IETF Trust and the persons identified as the document authors. All rights reserved.</p> |
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| 561 | <p>This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights |
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| 562 | and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License |
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| 563 | text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified |
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| 564 | BSD License. |
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| 565 | </p> |
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| 566 | <p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November |
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| 567 | 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to |
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| 568 | allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) |
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| 569 | controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative |
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| 570 | works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate |
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| 571 | it into languages other than English. |
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| 572 | </p> |
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| 573 | </div> |
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| 574 | <hr class="noprint"> |
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| 575 | <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1> |
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| 576 | <ul class="toc"> |
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| 577 | <li><a href="#rfc.section.1">1.</a> <a href="#caching">Introduction</a><ul> |
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| 578 | <li><a href="#rfc.section.1.1">1.1</a> <a href="#conformance">Conformance and Error Handling</a></li> |
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| 579 | <li><a href="#rfc.section.1.2">1.2</a> <a href="#notation">Syntax Notation</a><ul> |
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| 580 | <li><a href="#rfc.section.1.2.1">1.2.1</a> <a href="#delta-seconds">Delta Seconds</a></li> |
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| 581 | </ul> |
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| 582 | </li> |
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| 583 | </ul> |
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| 584 | </li> |
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| 585 | <li><a href="#rfc.section.2">2.</a> <a href="#caching.overview">Overview of Cache Operation</a></li> |
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| 586 | <li><a href="#rfc.section.3">3.</a> <a href="#response.cacheability">Storing Responses in Caches</a><ul> |
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| 587 | <li><a href="#rfc.section.3.1">3.1</a> <a href="#incomplete.responses">Storing Incomplete Responses</a></li> |
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| 588 | <li><a href="#rfc.section.3.2">3.2</a> <a href="#caching.authenticated.responses">Storing Responses to Authenticated Requests</a></li> |
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| 589 | <li><a href="#rfc.section.3.3">3.3</a> <a href="#combining.responses">Combining Partial Content</a></li> |
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| 590 | </ul> |
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| 591 | </li> |
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| 592 | <li><a href="#rfc.section.4">4.</a> <a href="#constructing.responses.from.caches">Constructing Responses from Caches</a><ul> |
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| 593 | <li><a href="#rfc.section.4.1">4.1</a> <a href="#caching.negotiated.responses">Calculating Secondary Keys with Vary</a></li> |
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| 594 | <li><a href="#rfc.section.4.2">4.2</a> <a href="#expiration.model">Freshness</a><ul> |
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| 595 | <li><a href="#rfc.section.4.2.1">4.2.1</a> <a href="#calculating.freshness.lifetime">Calculating Freshness Lifetime</a></li> |
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| 596 | <li><a href="#rfc.section.4.2.2">4.2.2</a> <a href="#heuristic.freshness">Calculating Heuristic Freshness</a></li> |
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| 597 | <li><a href="#rfc.section.4.2.3">4.2.3</a> <a href="#age.calculations">Calculating Age</a></li> |
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| 598 | <li><a href="#rfc.section.4.2.4">4.2.4</a> <a href="#serving.stale.responses">Serving Stale Responses</a></li> |
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| 599 | </ul> |
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| 600 | </li> |
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| 601 | <li><a href="#rfc.section.4.3">4.3</a> <a href="#validation.model">Validation</a><ul> |
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| 602 | <li><a href="#rfc.section.4.3.1">4.3.1</a> <a href="#validation.sent">Sending a Validation Request</a></li> |
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| 603 | <li><a href="#rfc.section.4.3.2">4.3.2</a> <a href="#validation.received">Handling a Received Validation Request</a></li> |
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| 604 | <li><a href="#rfc.section.4.3.3">4.3.3</a> <a href="#validation.response">Handling a Validation Response</a></li> |
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| 605 | <li><a href="#rfc.section.4.3.4">4.3.4</a> <a href="#freshening.responses">Freshening Stored Responses upon Validation</a></li> |
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| 606 | <li><a href="#rfc.section.4.3.5">4.3.5</a> <a href="#head.effects">Freshening Responses via HEAD</a></li> |
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| 607 | </ul> |
|---|
| 608 | </li> |
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| 609 | <li><a href="#rfc.section.4.4">4.4</a> <a href="#invalidation">Invalidation</a></li> |
|---|
| 610 | </ul> |
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| 611 | </li> |
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| 612 | <li><a href="#rfc.section.5">5.</a> <a href="#header.field.definitions">Header Field Definitions</a><ul> |
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| 613 | <li><a href="#rfc.section.5.1">5.1</a> <a href="#header.age">Age</a></li> |
|---|
| 614 | <li><a href="#rfc.section.5.2">5.2</a> <a href="#header.cache-control">Cache-Control</a><ul> |
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| 615 | <li><a href="#rfc.section.5.2.1">5.2.1</a> <a href="#cache-request-directive">Request Cache-Control Directives</a><ul> |
|---|
| 616 | <li><a href="#rfc.section.5.2.1.1">5.2.1.1</a> <a href="#cache-request-directive.max-age">max-age</a></li> |
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| 617 | <li><a href="#rfc.section.5.2.1.2">5.2.1.2</a> <a href="#cache-request-directive.max-stale">max-stale</a></li> |
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| 618 | <li><a href="#rfc.section.5.2.1.3">5.2.1.3</a> <a href="#cache-request-directive.min-fresh">min-fresh</a></li> |
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| 619 | <li><a href="#rfc.section.5.2.1.4">5.2.1.4</a> <a href="#cache-request-directive.no-cache">no-cache</a></li> |
|---|
| 620 | <li><a href="#rfc.section.5.2.1.5">5.2.1.5</a> <a href="#cache-request-directive.no-store">no-store</a></li> |
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| 621 | <li><a href="#rfc.section.5.2.1.6">5.2.1.6</a> <a href="#cache-request-directive.no-transform">no-transform</a></li> |
|---|
| 622 | <li><a href="#rfc.section.5.2.1.7">5.2.1.7</a> <a href="#cache-request-directive.only-if-cached">only-if-cached</a></li> |
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| 623 | </ul> |
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| 624 | </li> |
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| 625 | <li><a href="#rfc.section.5.2.2">5.2.2</a> <a href="#cache-response-directive">Response Cache-Control Directives</a><ul> |
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| 626 | <li><a href="#rfc.section.5.2.2.1">5.2.2.1</a> <a href="#cache-response-directive.must-revalidate">must-revalidate</a></li> |
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| 627 | <li><a href="#rfc.section.5.2.2.2">5.2.2.2</a> <a href="#cache-response-directive.no-cache">no-cache</a></li> |
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| 628 | <li><a href="#rfc.section.5.2.2.3">5.2.2.3</a> <a href="#cache-response-directive.no-store">no-store</a></li> |
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| 629 | <li><a href="#rfc.section.5.2.2.4">5.2.2.4</a> <a href="#cache-response-directive.no-transform">no-transform</a></li> |
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| 630 | <li><a href="#rfc.section.5.2.2.5">5.2.2.5</a> <a href="#cache-response-directive.public">public</a></li> |
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| 631 | <li><a href="#rfc.section.5.2.2.6">5.2.2.6</a> <a href="#cache-response-directive.private">private</a></li> |
|---|
| 632 | <li><a href="#rfc.section.5.2.2.7">5.2.2.7</a> <a href="#cache-response-directive.proxy-revalidate">proxy-revalidate</a></li> |
|---|
| 633 | <li><a href="#rfc.section.5.2.2.8">5.2.2.8</a> <a href="#cache-response-directive.max-age">max-age</a></li> |
|---|
| 634 | <li><a href="#rfc.section.5.2.2.9">5.2.2.9</a> <a href="#cache-response-directive.s-maxage">s-maxage</a></li> |
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| 635 | </ul> |
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| 636 | </li> |
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| 637 | <li><a href="#rfc.section.5.2.3">5.2.3</a> <a href="#cache.control.extensions">Cache Control Extensions</a></li> |
|---|
| 638 | </ul> |
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| 639 | </li> |
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| 640 | <li><a href="#rfc.section.5.3">5.3</a> <a href="#header.expires">Expires</a></li> |
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| 641 | <li><a href="#rfc.section.5.4">5.4</a> <a href="#header.pragma">Pragma</a></li> |
|---|
| 642 | <li><a href="#rfc.section.5.5">5.5</a> <a href="#header.warning">Warning</a><ul> |
|---|
| 643 | <li><a href="#rfc.section.5.5.1">5.5.1</a> <a href="#warn.110">Warning: 110 - "Response is Stale"</a></li> |
|---|
| 644 | <li><a href="#rfc.section.5.5.2">5.5.2</a> <a href="#warn.111">Warning: 111 - "Revalidation Failed"</a></li> |
|---|
| 645 | <li><a href="#rfc.section.5.5.3">5.5.3</a> <a href="#warn.112">Warning: 112 - "Disconnected Operation"</a></li> |
|---|
| 646 | <li><a href="#rfc.section.5.5.4">5.5.4</a> <a href="#warn.113">Warning: 113 - "Heuristic Expiration"</a></li> |
|---|
| 647 | <li><a href="#rfc.section.5.5.5">5.5.5</a> <a href="#warn.199">Warning: 199 - "Miscellaneous Warning"</a></li> |
|---|
| 648 | <li><a href="#rfc.section.5.5.6">5.5.6</a> <a href="#warn.214">Warning: 214 - "Transformation Applied"</a></li> |
|---|
| 649 | <li><a href="#rfc.section.5.5.7">5.5.7</a> <a href="#warn.299">Warning: 299 - "Miscellaneous Persistent Warning"</a></li> |
|---|
| 650 | </ul> |
|---|
| 651 | </li> |
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| 652 | </ul> |
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| 653 | </li> |
|---|
| 654 | <li><a href="#rfc.section.6">6.</a> <a href="#history.lists">History Lists</a></li> |
|---|
| 655 | <li><a href="#rfc.section.7">7.</a> <a href="#iana.considerations">IANA Considerations</a><ul> |
|---|
| 656 | <li><a href="#rfc.section.7.1">7.1</a> <a href="#cache.directive.registry">Cache Directive Registry</a><ul> |
|---|
| 657 | <li><a href="#rfc.section.7.1.1">7.1.1</a> <a href="#cache.directive.registry.procedure">Procedure</a></li> |
|---|
| 658 | <li><a href="#rfc.section.7.1.2">7.1.2</a> <a href="#cache.directive.considerations">Considerations for New Cache Control Directives</a></li> |
|---|
| 659 | <li><a href="#rfc.section.7.1.3">7.1.3</a> <a href="#cache.directive.registration">Registrations</a></li> |
|---|
| 660 | </ul> |
|---|
| 661 | </li> |
|---|
| 662 | <li><a href="#rfc.section.7.2">7.2</a> <a href="#warn.code.registry">Warn Code Registry</a><ul> |
|---|
| 663 | <li><a href="#rfc.section.7.2.1">7.2.1</a> <a href="#warn.code.registry.procedure">Procedure</a></li> |
|---|
| 664 | <li><a href="#rfc.section.7.2.2">7.2.2</a> <a href="#warn.code.registration">Registrations</a></li> |
|---|
| 665 | </ul> |
|---|
| 666 | </li> |
|---|
| 667 | <li><a href="#rfc.section.7.3">7.3</a> <a href="#header.field.registration">Header Field Registration</a></li> |
|---|
| 668 | </ul> |
|---|
| 669 | </li> |
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| 670 | <li><a href="#rfc.section.8">8.</a> <a href="#security.considerations">Security Considerations</a></li> |
|---|
| 671 | <li><a href="#rfc.section.9">9.</a> <a href="#acks">Acknowledgments</a></li> |
|---|
| 672 | <li><a href="#rfc.section.10">10.</a> <a href="#rfc.references">References</a><ul> |
|---|
| 673 | <li><a href="#rfc.section.10.1">10.1</a> <a href="#rfc.references.1">Normative References</a></li> |
|---|
| 674 | <li><a href="#rfc.section.10.2">10.2</a> <a href="#rfc.references.2">Informative References</a></li> |
|---|
| 675 | </ul> |
|---|
| 676 | </li> |
|---|
| 677 | <li><a href="#rfc.authors">Authors' Addresses</a></li> |
|---|
| 678 | <li><a href="#rfc.section.A">A.</a> <a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li> |
|---|
| 679 | <li><a href="#rfc.section.B">B.</a> <a href="#imported.abnf">Imported ABNF</a></li> |
|---|
| 680 | <li><a href="#rfc.section.C">C.</a> <a href="#collected.abnf">Collected ABNF</a></li> |
|---|
| 681 | <li><a href="#rfc.section.D">D.</a> <a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul> |
|---|
| 682 | <li><a href="#rfc.section.D.1">D.1</a> <a href="#changes.since.19">Since draft-ietf-httpbis-p6-cache-19</a></li> |
|---|
| 683 | <li><a href="#rfc.section.D.2">D.2</a> <a href="#changes.since.20">Since draft-ietf-httpbis-p6-cache-20</a></li> |
|---|
| 684 | <li><a href="#rfc.section.D.3">D.3</a> <a href="#changes.since.21">Since draft-ietf-httpbis-p6-cache-21</a></li> |
|---|
| 685 | <li><a href="#rfc.section.D.4">D.4</a> <a href="#changes.since.22">Since draft-ietf-httpbis-p6-cache-22</a></li> |
|---|
| 686 | <li><a href="#rfc.section.D.5">D.5</a> <a href="#changes.since.23">Since draft-ietf-httpbis-p6-cache-23</a></li> |
|---|
| 687 | <li><a href="#rfc.section.D.6">D.6</a> <a href="#changes.since.24">Since draft-ietf-httpbis-p6-cache-24</a></li> |
|---|
| 688 | </ul> |
|---|
| 689 | </li> |
|---|
| 690 | <li><a href="#rfc.index">Index</a></li> |
|---|
| 691 | </ul> |
|---|
| 692 | <div id="caching"> |
|---|
| 693 | <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a> <a href="#caching">Introduction</a></h1> |
|---|
| 694 | <p id="rfc.section.1.p.1">HTTP is typically used for distributed information systems, where performance can be improved by the use of response caches. |
|---|
| 695 | This document defines aspects of HTTP/1.1 related to caching and reusing response messages. |
|---|
| 696 | </p> |
|---|
| 697 | <div id="rfc.iref.c.1"></div> |
|---|
| 698 | <p id="rfc.section.1.p.2">An HTTP <dfn>cache</dfn> is a local store of response messages and the subsystem that controls storage, retrieval, and deletion of messages in it. |
|---|
| 699 | A cache stores cacheable responses in order to reduce the response time and network bandwidth consumption on future, equivalent |
|---|
| 700 | requests. Any client or server <em class="bcp14">MAY</em> employ a cache, though a cache cannot be used by a server that is acting as a tunnel. |
|---|
| 701 | </p> |
|---|
| 702 | <div id="rfc.iref.s.1"></div> |
|---|
| 703 | <div id="rfc.iref.p.1"></div> |
|---|
| 704 | <div id="shared.and.private.caches"> |
|---|
| 705 | <p id="rfc.section.1.p.3">A <dfn>shared cache</dfn> is a cache that stores responses to be reused by more than one user; shared caches are usually (but not always) deployed as |
|---|
| 706 | a part of an intermediary. A <dfn>private cache</dfn>, in contrast, is dedicated to a single user. |
|---|
| 707 | </p> |
|---|
| 708 | </div> |
|---|
| 709 | <p id="rfc.section.1.p.4">The goal of caching in HTTP/1.1 is to significantly improve performance by reusing a prior response message to satisfy a current |
|---|
| 710 | request. A stored response is considered "fresh", as defined in <a href="#expiration.model" title="Freshness">Section 4.2</a>, if the response can be reused without "validation" (checking with the origin server to see if the cached response remains |
|---|
| 711 | valid for this request). A fresh response can therefore reduce both latency and network overhead each time it is reused. When |
|---|
| 712 | a cached response is not fresh, it might still be reusable if it can be freshened by validation (<a href="#validation.model" title="Validation">Section 4.3</a>) or if the origin is unavailable (<a href="#serving.stale.responses" title="Serving Stale Responses">Section 4.2.4</a>). |
|---|
| 713 | </p> |
|---|
| 714 | <div id="conformance"> |
|---|
| 715 | <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a> <a href="#conformance">Conformance and Error Handling</a></h2> |
|---|
| 716 | <p id="rfc.section.1.1.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" |
|---|
| 717 | in this document are to be interpreted as described in <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>. |
|---|
| 718 | </p> |
|---|
| 719 | <p id="rfc.section.1.1.p.2">Conformance criteria and considerations regarding error handling are defined in <a href="p1-messaging.html#conformance" title="Conformance and Error Handling">Section 2.5</a> of <a href="#Part1" id="rfc.xref.Part1.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>. |
|---|
| 720 | </p> |
|---|
| 721 | </div> |
|---|
| 722 | <div id="notation"> |
|---|
| 723 | <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a> <a href="#notation">Syntax Notation</a></h2> |
|---|
| 724 | <p id="rfc.section.1.2.p.1">This specification uses the Augmented Backus-Naur Form (ABNF) notation of <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a> with the list rule extension defined in <a href="p1-messaging.html#abnf.extension" title="ABNF list extension: #rule">Section 7</a> of <a href="#Part1" id="rfc.xref.Part1.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>. <a href="#imported.abnf" title="Imported ABNF">Appendix B</a> describes rules imported from other documents. <a href="#collected.abnf" title="Collected ABNF">Appendix C</a> shows the collected ABNF with the list rule expanded. |
|---|
| 725 | </p> |
|---|
| 726 | <div id="delta-seconds"> |
|---|
| 727 | <h3 id="rfc.section.1.2.1"><a href="#rfc.section.1.2.1">1.2.1</a> <a href="#delta-seconds">Delta Seconds</a></h3> |
|---|
| 728 | <p id="rfc.section.1.2.1.p.1">The delta-seconds rule specifies a non-negative integer, representing time in seconds.</p> |
|---|
| 729 | <div id="rfc.figure.u.1"></div><pre class="inline"><span id="rfc.iref.g.1"></span> <a href="#delta-seconds" class="smpl">delta-seconds</a> = 1*<a href="#imported.abnf" class="smpl">DIGIT</a> |
|---|
| 730 | </pre><p id="rfc.section.1.2.1.p.3">If a cache receives a delta-seconds value larger than the largest positive integer it can represent, or if any of its subsequent |
|---|
| 731 | calculations overflows, the cache <em class="bcp14">MUST</em> consider the value to be 2147483648 (2<sup>31</sup>). A recipient parsing a delta-seconds value <em class="bcp14">MUST</em> use an arithmetic type of at least 31 bits of range, and a sender <em class="bcp14">MUST NOT</em> generate delta-seconds with a value greater than 2147483648. |
|---|
| 732 | </p> |
|---|
| 733 | </div> |
|---|
| 734 | </div> |
|---|
| 735 | </div> |
|---|
| 736 | <div id="caching.overview"> |
|---|
| 737 | <div id="rfc.iref.c.2"></div> |
|---|
| 738 | <div id="rfc.iref.c.3"></div> |
|---|
| 739 | <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a href="#caching.overview">Overview of Cache Operation</a></h1> |
|---|
| 740 | <p id="rfc.section.2.p.1">Proper cache operation preserves the semantics of HTTP transfers (<a href="#Part2" id="rfc.xref.Part2.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[Part2]</cite></a>) while eliminating the transfer of information already held in the cache. Although caching is an entirely <em class="bcp14">OPTIONAL</em> feature of HTTP, we assume that reusing the cached response is desirable and that such reuse is the default behavior when |
|---|
| 741 | no requirement or local configuration prevents it. Therefore, HTTP cache requirements are focused on preventing a cache from |
|---|
| 742 | either storing a non-reusable response or reusing a stored response inappropriately, rather than mandating that caches always |
|---|
| 743 | store and reuse particular responses. |
|---|
| 744 | </p> |
|---|
| 745 | <p id="rfc.section.2.p.2">Each <dfn>cache entry</dfn> consists of a cache key and one or more HTTP responses corresponding to prior requests that used the same key. The most common |
|---|
| 746 | form of cache entry is a successful result of a retrieval request: i.e., a <a href="p2-semantics.html#status.200" class="smpl">200 (OK)</a> response to a GET request, which contains a representation of the resource identified by the request target (<a href="p2-semantics.html#GET" title="GET">Section 4.3.1</a> of <a href="#Part2" id="rfc.xref.Part2.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[Part2]</cite></a>). However, it is also possible to cache permanent redirects, negative results (e.g., <a href="p2-semantics.html#status.404" class="smpl">404 (Not Found)</a>), incomplete results (e.g., <a href="p5-range.html#status.206" class="smpl">206 (Partial Content)</a>), and responses to methods other than GET if the method's definition allows such caching and defines something suitable for |
|---|
| 747 | use as a cache key. |
|---|
| 748 | </p> |
|---|
| 749 | <div id="rfc.iref.c.4"></div> |
|---|
| 750 | <p id="rfc.section.2.p.3">The primary <dfn>cache key</dfn> consists of the request method and target URI. However, since HTTP caches in common use today are typically limited to caching |
|---|
| 751 | responses to GET, many caches simply decline other methods and use only the URI as the primary cache key. |
|---|
| 752 | </p> |
|---|
| 753 | <p id="rfc.section.2.p.4">If a request target is subject to content negotiation, its cache entry might consist of multiple stored responses, each differentiated |
|---|
| 754 | by a secondary key for the values of the original request's selecting header fields (<a href="#caching.negotiated.responses" title="Calculating Secondary Keys with Vary">Section 4.1</a>). |
|---|
| 755 | </p> |
|---|
| 756 | </div> |
|---|
| 757 | <div id="response.cacheability"> |
|---|
| 758 | <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a> <a href="#response.cacheability">Storing Responses in Caches</a></h1> |
|---|
| 759 | <p id="rfc.section.3.p.1">A cache <em class="bcp14">MUST NOT</em> store a response to any request, unless: |
|---|
| 760 | </p> |
|---|
| 761 | <ul> |
|---|
| 762 | <li>The request method is understood by the cache and defined as being cacheable, and</li> |
|---|
| 763 | <li>the response status code is understood by the cache, and</li> |
|---|
| 764 | <li>the "no-store" cache directive (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.1" title="Cache-Control">Section 5.2</a>) does not appear in request or response header fields, and |
|---|
| 765 | </li> |
|---|
| 766 | <li>the "private" cache response directive (see <a href="#cache-response-directive.private" title="private">Section 5.2.2.6</a>) does not appear in the response, if the cache is shared, and |
|---|
| 767 | </li> |
|---|
| 768 | <li>the <a href="p7-auth.html#header.authorization" class="smpl">Authorization</a> header field (see <a href="p7-auth.html#header.authorization" title="Authorization">Section 4.1</a> of <a href="#Part7" id="rfc.xref.Part7.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[Part7]</cite></a>) does not appear in the request, if the cache is shared, unless the response explicitly allows it (see <a href="#caching.authenticated.responses" title="Storing Responses to Authenticated Requests">Section 3.2</a>), and |
|---|
| 769 | </li> |
|---|
| 770 | <li>the response either: |
|---|
| 771 | <ul> |
|---|
| 772 | <li>contains an <a href="#header.expires" class="smpl">Expires</a> header field (see <a href="#header.expires" id="rfc.xref.header.expires.1" title="Expires">Section 5.3</a>), or |
|---|
| 773 | </li> |
|---|
| 774 | <li>contains a max-age response cache directive (see <a href="#cache-response-directive.max-age" title="max-age">Section 5.2.2.8</a>), or |
|---|
| 775 | </li> |
|---|
| 776 | <li>contains a s-maxage response cache directive (see <a href="#cache-response-directive.s-maxage" title="s-maxage">Section 5.2.2.9</a>) and the cache is shared, or |
|---|
| 777 | </li> |
|---|
| 778 | <li>contains a Cache Control Extension (see <a href="#cache.control.extensions" title="Cache Control Extensions">Section 5.2.3</a>) that allows it to be cached, or |
|---|
| 779 | </li> |
|---|
| 780 | <li>has a status code that is defined as cacheable (see <a href="#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a>), or |
|---|
| 781 | </li> |
|---|
| 782 | <li>contains a public response cache directive (see <a href="#cache-response-directive.public" title="public">Section 5.2.2.5</a>). |
|---|
| 783 | </li> |
|---|
| 784 | </ul> |
|---|
| 785 | </li> |
|---|
| 786 | </ul> |
|---|
| 787 | <p id="rfc.section.3.p.2">Note that any of the requirements listed above can be overridden by a cache-control extension; see <a href="#cache.control.extensions" title="Cache Control Extensions">Section 5.2.3</a>. |
|---|
| 788 | </p> |
|---|
| 789 | <p id="rfc.section.3.p.3">In this context, a cache has "understood" a request method or a response status code if it recognizes it and implements all |
|---|
| 790 | specified caching-related behavior. |
|---|
| 791 | </p> |
|---|
| 792 | <p id="rfc.section.3.p.4">Note that, in normal operation, some caches will not store a response that has neither a cache validator nor an explicit expiration |
|---|
| 793 | time, as such responses are not usually useful to store. However, caches are not prohibited from storing such responses. |
|---|
| 794 | </p> |
|---|
| 795 | <div id="incomplete.responses"> |
|---|
| 796 | <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a> <a href="#incomplete.responses">Storing Incomplete Responses</a></h2> |
|---|
| 797 | <p id="rfc.section.3.1.p.1">A response message is considered complete when all of the octets indicated by the message framing (<a href="#Part1" id="rfc.xref.Part1.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>) are received prior to the connection being closed. If the request method is GET, the response status code is <a href="p2-semantics.html#status.200" class="smpl">200 (OK)</a>, and the entire response header section has been received, a cache <em class="bcp14">MAY</em> store an incomplete response message body if the cache entry is recorded as incomplete. Likewise, a <a href="p5-range.html#status.206" class="smpl">206 (Partial Content)</a> response <em class="bcp14">MAY</em> be stored as if it were an incomplete <a href="p2-semantics.html#status.200" class="smpl">200 |
|---|
| 798 | (OK)</a> cache entry. However, a cache <em class="bcp14">MUST NOT</em> store incomplete or partial content responses if it does not support the <a href="p5-range.html#header.range" class="smpl">Range</a> and <a href="p5-range.html#header.content-range" class="smpl">Content-Range</a> header fields or if it does not understand the range units used in those fields. |
|---|
| 799 | </p> |
|---|
| 800 | <p id="rfc.section.3.1.p.2">A cache <em class="bcp14">MAY</em> complete a stored incomplete response by making a subsequent range request (<a href="#Part5" id="rfc.xref.Part5.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[Part5]</cite></a>) and combining the successful response with the stored entry, as defined in <a href="#combining.responses" title="Combining Partial Content">Section 3.3</a>. A cache <em class="bcp14">MUST NOT</em> use an incomplete response to answer requests unless the response has been made complete or the request is partial and specifies |
|---|
| 801 | a range that is wholly within the incomplete response. A cache <em class="bcp14">MUST NOT</em> send a partial response to a client without explicitly marking it as such using the <a href="p5-range.html#status.206" class="smpl">206 (Partial Content)</a> status code. |
|---|
| 802 | </p> |
|---|
| 803 | </div> |
|---|
| 804 | <div id="caching.authenticated.responses"> |
|---|
| 805 | <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a> <a href="#caching.authenticated.responses">Storing Responses to Authenticated Requests</a></h2> |
|---|
| 806 | <p id="rfc.section.3.2.p.1">A shared cache <em class="bcp14">MUST NOT</em> use a cached response to a request with an <a href="p7-auth.html#header.authorization" class="smpl">Authorization</a> header field (<a href="p7-auth.html#header.authorization" title="Authorization">Section 4.1</a> of <a href="#Part7" id="rfc.xref.Part7.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[Part7]</cite></a>) to satisfy any subsequent request unless a cache directive that allows such responses to be stored is present in the response. |
|---|
| 807 | </p> |
|---|
| 808 | <p id="rfc.section.3.2.p.2">In this specification, the following <a href="#header.cache-control" class="smpl">Cache-Control</a> response directives (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section 5.2.2</a>) have such an effect: must-revalidate, public, s-maxage. |
|---|
| 809 | </p> |
|---|
| 810 | <p id="rfc.section.3.2.p.3">Note that cached responses that contain the "must-revalidate" and/or "s-maxage" response directives are not allowed to be |
|---|
| 811 | served stale (<a href="#serving.stale.responses" title="Serving Stale Responses">Section 4.2.4</a>) by shared caches. In particular, a response with either "max-age=0, must-revalidate" or "s-maxage=0" cannot be used to satisfy |
|---|
| 812 | a subsequent request without revalidating it on the origin server. |
|---|
| 813 | </p> |
|---|
| 814 | </div> |
|---|
| 815 | <div id="combining.responses"> |
|---|
| 816 | <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a> <a href="#combining.responses">Combining Partial Content</a></h2> |
|---|
| 817 | <p id="rfc.section.3.3.p.1">A response might transfer only a partial representation if the connection closed prematurely or if the request used one or |
|---|
| 818 | more Range specifiers (<a href="#Part5" id="rfc.xref.Part5.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[Part5]</cite></a>). After several such transfers, a cache might have received several ranges of the same representation. A cache <em class="bcp14">MAY</em> combine these ranges into a single stored response, and reuse that response to satisfy later requests, if they all share the |
|---|
| 819 | same strong validator and the cache complies with the client requirements in <a href="p5-range.html#combining.byte.ranges" title="Combining Ranges">Section 4.3</a> of <a href="#Part5" id="rfc.xref.Part5.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[Part5]</cite></a>. |
|---|
| 820 | </p> |
|---|
| 821 | <p id="rfc.section.3.3.p.2">When combining the new response with one or more stored responses, a cache <em class="bcp14">MUST</em>: |
|---|
| 822 | </p> |
|---|
| 823 | <ul> |
|---|
| 824 | <li>delete any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.1" title="Warning">Section 5.5</a>); |
|---|
| 825 | </li> |
|---|
| 826 | <li>retain any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 2xx; and, |
|---|
| 827 | </li> |
|---|
| 828 | <li>use other header fields provided in the new response, aside from <a href="p5-range.html#header.content-range" class="smpl">Content-Range</a>, to replace all instances of the corresponding header fields in the stored response. |
|---|
| 829 | </li> |
|---|
| 830 | </ul> |
|---|
| 831 | </div> |
|---|
| 832 | </div> |
|---|
| 833 | <div id="constructing.responses.from.caches"> |
|---|
| 834 | <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a> <a href="#constructing.responses.from.caches">Constructing Responses from Caches</a></h1> |
|---|
| 835 | <p id="rfc.section.4.p.1">When presented with a request, a cache <em class="bcp14">MUST NOT</em> reuse a stored response, unless: |
|---|
| 836 | </p> |
|---|
| 837 | <ul> |
|---|
| 838 | <li>The presented effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</a> of <a href="#Part1" id="rfc.xref.Part1.4"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>) and that of the stored response match, and |
|---|
| 839 | </li> |
|---|
| 840 | <li>the request method associated with the stored response allows it to be used for the presented request, and</li> |
|---|
| 841 | <li>selecting header fields nominated by the stored response (if any) match those presented (see <a href="#caching.negotiated.responses" title="Calculating Secondary Keys with Vary">Section 4.1</a>), and |
|---|
| 842 | </li> |
|---|
| 843 | <li>the presented request does not contain the no-cache pragma (<a href="#header.pragma" id="rfc.xref.header.pragma.1" title="Pragma">Section 5.4</a>), nor the no-cache cache directive (<a href="#cache-request-directive" title="Request Cache-Control Directives">Section 5.2.1</a>), unless the stored response is successfully validated (<a href="#validation.model" title="Validation">Section 4.3</a>), and |
|---|
| 844 | </li> |
|---|
| 845 | <li>the stored response does not contain the no-cache cache directive (<a href="#cache-response-directive.no-cache" title="no-cache">Section 5.2.2.2</a>), unless it is successfully validated (<a href="#validation.model" title="Validation">Section 4.3</a>), and |
|---|
| 846 | </li> |
|---|
| 847 | <li>the stored response is either: |
|---|
| 848 | <ul> |
|---|
| 849 | <li>fresh (see <a href="#expiration.model" title="Freshness">Section 4.2</a>), or |
|---|
| 850 | </li> |
|---|
| 851 | <li>allowed to be served stale (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section 4.2.4</a>), or |
|---|
| 852 | </li> |
|---|
| 853 | <li>successfully validated (see <a href="#validation.model" title="Validation">Section 4.3</a>). |
|---|
| 854 | </li> |
|---|
| 855 | </ul> |
|---|
| 856 | </li> |
|---|
| 857 | </ul> |
|---|
| 858 | <p id="rfc.section.4.p.2">Note that any of the requirements listed above can be overridden by a cache-control extension; see <a href="#cache.control.extensions" title="Cache Control Extensions">Section 5.2.3</a>. |
|---|
| 859 | </p> |
|---|
| 860 | <p id="rfc.section.4.p.3">When a stored response is used to satisfy a request without validation, a cache <em class="bcp14">MUST</em> generate an <a href="#header.age" class="smpl">Age</a> header field (<a href="#header.age" id="rfc.xref.header.age.1" title="Age">Section 5.1</a>), replacing any present in the response with a value equal to the stored response's current_age; see <a href="#age.calculations" title="Calculating Age">Section 4.2.3</a>. |
|---|
| 861 | </p> |
|---|
| 862 | <p id="rfc.section.4.p.4">A cache <em class="bcp14">MUST</em> write through requests with methods that are unsafe (<a href="p2-semantics.html#safe.methods" title="Safe Methods">Section 4.2.1</a> of <a href="#Part2" id="rfc.xref.Part2.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[Part2]</cite></a>) to the origin server; i.e., a cache is not allowed to generate a reply to such a request before having forwarded the request |
|---|
| 863 | and having received a corresponding response. |
|---|
| 864 | </p> |
|---|
| 865 | <p id="rfc.section.4.p.5">Also, note that unsafe requests might invalidate already stored responses; see <a href="#invalidation" title="Invalidation">Section 4.4</a>. |
|---|
| 866 | </p> |
|---|
| 867 | <p id="rfc.section.4.p.6">When more than one suitable response is stored, a cache <em class="bcp14">MUST</em> use the most recent response (as determined by the <a href="p2-semantics.html#header.date" class="smpl">Date</a> header field). It can also forward the request with "Cache-Control: max-age=0" or "Cache-Control: no-cache" to disambiguate |
|---|
| 868 | which response to use. |
|---|
| 869 | </p> |
|---|
| 870 | <p id="rfc.section.4.p.7">A cache that does not have a clock available <em class="bcp14">MUST NOT</em> use stored responses without revalidating them upon every use. |
|---|
| 871 | </p> |
|---|
| 872 | <div id="caching.negotiated.responses"> |
|---|
| 873 | <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a> <a href="#caching.negotiated.responses">Calculating Secondary Keys with Vary</a></h2> |
|---|
| 874 | <p id="rfc.section.4.1.p.1">When a cache receives a request that can be satisfied by a stored response that has a <a href="p2-semantics.html#header.vary" class="smpl">Vary</a> header field (<a href="p2-semantics.html#header.vary" title="Vary">Section 7.1.4</a> of <a href="#Part2" id="rfc.xref.Part2.4"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[Part2]</cite></a>), it <em class="bcp14">MUST NOT</em> use that response unless all of the selecting header fields nominated by the Vary header field match in both the original |
|---|
| 875 | request (i.e., that associated with the stored response), and the presented request. |
|---|
| 876 | </p> |
|---|
| 877 | <p id="rfc.section.4.1.p.2">The selecting header fields from two requests are defined to match if and only if those in the first request can be transformed |
|---|
| 878 | to those in the second request by applying any of the following: |
|---|
| 879 | </p> |
|---|
| 880 | <ul> |
|---|
| 881 | <li>adding or removing whitespace, where allowed in the header field's syntax</li> |
|---|
| 882 | <li>combining multiple header fields with the same field name (see <a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#Part1" id="rfc.xref.Part1.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>) |
|---|
| 883 | </li> |
|---|
| 884 | <li>normalizing both header field values in a way that is known to have identical semantics, according to the header field's specification |
|---|
| 885 | (e.g., re-ordering field values when order is not significant; case-normalization, where values are defined to be case-insensitive) |
|---|
| 886 | </li> |
|---|
| 887 | </ul> |
|---|
| 888 | <p id="rfc.section.4.1.p.3">If (after any normalization that might take place) a header field is absent from a request, it can only match another request |
|---|
| 889 | if it is also absent there. |
|---|
| 890 | </p> |
|---|
| 891 | <p id="rfc.section.4.1.p.4">A <a href="p2-semantics.html#header.vary" class="smpl">Vary</a> header field-value of "*" always fails to match. |
|---|
| 892 | </p> |
|---|
| 893 | <p id="rfc.section.4.1.p.5">The stored response with matching selecting header fields is known as the selected response.</p> |
|---|
| 894 | <p id="rfc.section.4.1.p.6">If multiple selected responses are available (potentially including responses without a Vary header field), the cache will |
|---|
| 895 | need to choose one to use. When a selecting header field has a known mechanism for doing so (e.g., qvalues on <a href="p2-semantics.html#header.accept" class="smpl">Accept</a> and similar request header fields), that mechanism <em class="bcp14">MAY</em> be used to select preferred responses; of the remainder, the most recent response (as determined by the <a href="p2-semantics.html#header.date" class="smpl">Date</a> header field) is used, as per <a href="#constructing.responses.from.caches" title="Constructing Responses from Caches">Section 4</a>. |
|---|
| 896 | </p> |
|---|
| 897 | <p id="rfc.section.4.1.p.7">If no selected response is available, the cache cannot satisfy the presented request. Typically, it is forwarded to the origin |
|---|
| 898 | server in a (possibly conditional; see <a href="#validation.model" title="Validation">Section 4.3</a>) request. |
|---|
| 899 | </p> |
|---|
| 900 | </div> |
|---|
| 901 | <div id="expiration.model"> |
|---|
| 902 | <div id="rfc.iref.f.1"></div> |
|---|
| 903 | <div id="rfc.iref.s.2"></div> |
|---|
| 904 | <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a> <a href="#expiration.model">Freshness</a></h2> |
|---|
| 905 | <p id="rfc.section.4.2.p.1">A <dfn>fresh</dfn> response is one whose age has not yet exceeded its freshness lifetime. Conversely, a <dfn>stale</dfn> response is one where it has. |
|---|
| 906 | </p> |
|---|
| 907 | <div id="rfc.iref.f.2"></div> |
|---|
| 908 | <div id="rfc.iref.e.1"></div> |
|---|
| 909 | <div id="rfc.iref.h.1"></div> |
|---|
| 910 | <p id="rfc.section.4.2.p.2">A response's <dfn>freshness lifetime</dfn> is the length of time between its generation by the origin server and its expiration time. An <dfn>explicit expiration time</dfn> is the time at which the origin server intends that a stored response can no longer be used by a cache without further validation, |
|---|
| 911 | whereas a <dfn>heuristic expiration time</dfn> is assigned by a cache when no explicit expiration time is available. |
|---|
| 912 | </p> |
|---|
| 913 | <div id="rfc.iref.a.1"></div> |
|---|
| 914 | <p id="rfc.section.4.2.p.3">A response's <dfn>age</dfn> is the time that has passed since it was generated by, or successfully validated with, the origin server. |
|---|
| 915 | </p> |
|---|
| 916 | <p id="rfc.section.4.2.p.4">When a response is "fresh" in the cache, it can be used to satisfy subsequent requests without contacting the origin server, |
|---|
| 917 | thereby improving efficiency. |
|---|
| 918 | </p> |
|---|
| 919 | <p id="rfc.section.4.2.p.5">The primary mechanism for determining freshness is for an origin server to provide an explicit expiration time in the future, |
|---|
| 920 | using either the <a href="#header.expires" class="smpl">Expires</a> header field (<a href="#header.expires" id="rfc.xref.header.expires.2" title="Expires">Section 5.3</a>) or the max-age response cache directive (<a href="#cache-response-directive.max-age" title="max-age">Section 5.2.2.8</a>). Generally, origin servers will assign future explicit expiration times to responses in the belief that the representation |
|---|
| 921 | is not likely to change in a semantically significant way before the expiration time is reached. |
|---|
| 922 | </p> |
|---|
| 923 | <p id="rfc.section.4.2.p.6">If an origin server wishes to force a cache to validate every request, it can assign an explicit expiration time in the past |
|---|
| 924 | to indicate that the response is already stale. Compliant caches will normally validate a stale cached response before reusing |
|---|
| 925 | it for subsequent requests (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section 4.2.4</a>). |
|---|
| 926 | </p> |
|---|
| 927 | <p id="rfc.section.4.2.p.7">Since origin servers do not always provide explicit expiration times, caches are also allowed to use a heuristic to determine |
|---|
| 928 | an expiration time under certain circumstances (see <a href="#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a>). |
|---|
| 929 | </p> |
|---|
| 930 | <div id="rfc.figure.u.2"></div> |
|---|
| 931 | <p>The calculation to determine if a response is fresh is:</p><pre class="text"> response_is_fresh = (freshness_lifetime > current_age) |
|---|
| 932 | </pre><p id="rfc.section.4.2.p.9">freshness_lifetime is defined in <a href="#calculating.freshness.lifetime" title="Calculating Freshness Lifetime">Section 4.2.1</a>; current_age is defined in <a href="#age.calculations" title="Calculating Age">Section 4.2.3</a>. |
|---|
| 933 | </p> |
|---|
| 934 | <p id="rfc.section.4.2.p.10">Clients can send the max-age or min-fresh cache directives in a request to constrain or relax freshness calculations for the |
|---|
| 935 | corresponding response (<a href="#cache-request-directive" title="Request Cache-Control Directives">Section 5.2.1</a>). |
|---|
| 936 | </p> |
|---|
| 937 | <p id="rfc.section.4.2.p.11">When calculating freshness, to avoid common problems in date parsing:</p> |
|---|
| 938 | <p id="rfc.section.4.2.p.12"></p> |
|---|
| 939 | <ul> |
|---|
| 940 | <li>Although all date formats are specified to be case-sensitive, a cache recipient <em class="bcp14">SHOULD</em> match day, week, and timezone names case-insensitively. |
|---|
| 941 | </li> |
|---|
| 942 | <li>If a cache recipient's internal implementation of time has less resolution than the value of an HTTP-date, the recipient <em class="bcp14">MUST</em> internally represent a parsed <a href="#header.expires" class="smpl">Expires</a> date as the nearest time equal to or earlier than the received value. |
|---|
| 943 | </li> |
|---|
| 944 | <li>A cache recipient <em class="bcp14">MUST NOT</em> allow local time zones to influence the calculation or comparison of an age or expiration time. |
|---|
| 945 | </li> |
|---|
| 946 | <li>A cache recipient <em class="bcp14">SHOULD</em> consider a date with a zone abbreviation other than GMT or UTC to be invalid for calculating expiration. |
|---|
| 947 | </li> |
|---|
| 948 | </ul> |
|---|
| 949 | <p id="rfc.section.4.2.p.13">Note that freshness applies only to cache operation; it cannot be used to force a user agent to refresh its display or reload |
|---|
| 950 | a resource. See <a href="#history.lists" title="History Lists">Section 6</a> for an explanation of the difference between caches and history mechanisms. |
|---|
| 951 | </p> |
|---|
| 952 | <div id="calculating.freshness.lifetime"> |
|---|
| 953 | <h3 id="rfc.section.4.2.1"><a href="#rfc.section.4.2.1">4.2.1</a> <a href="#calculating.freshness.lifetime">Calculating Freshness Lifetime</a></h3> |
|---|
| 954 | <p id="rfc.section.4.2.1.p.1">A cache can calculate the freshness lifetime (denoted as freshness_lifetime) of a response by using the first match of: </p> |
|---|
| 955 | <ul> |
|---|
| 956 | <li>If the cache is shared and the s-maxage response cache directive (<a href="#cache-response-directive.s-maxage" title="s-maxage">Section 5.2.2.9</a>) is present, use its value, or |
|---|
| 957 | </li> |
|---|
| 958 | <li>If the max-age response cache directive (<a href="#cache-response-directive.max-age" title="max-age">Section 5.2.2.8</a>) is present, use its value, or |
|---|
| 959 | </li> |
|---|
| 960 | <li>If the <a href="#header.expires" class="smpl">Expires</a> response header field (<a href="#header.expires" id="rfc.xref.header.expires.3" title="Expires">Section 5.3</a>) is present, use its value minus the value of the <a href="p2-semantics.html#header.date" class="smpl">Date</a> response header field, or |
|---|
| 961 | </li> |
|---|
| 962 | <li>Otherwise, no explicit expiration time is present in the response. A heuristic freshness lifetime might be applicable; see <a href="#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a>. |
|---|
| 963 | </li> |
|---|
| 964 | </ul> |
|---|
| 965 | <p id="rfc.section.4.2.1.p.2">Note that this calculation is not vulnerable to clock skew, since all of the information comes from the origin server.</p> |
|---|
| 966 | <p id="rfc.section.4.2.1.p.3">When there is more than one value present for a given directive (e.g., two <a href="#header.expires" class="smpl">Expires</a> header fields, multiple Cache-Control: max-age directives), the directive's value is considered invalid. Caches are encouraged |
|---|
| 967 | to consider responses that have invalid freshness information to be stale. |
|---|
| 968 | </p> |
|---|
| 969 | </div> |
|---|
| 970 | <div id="heuristic.freshness"> |
|---|
| 971 | <h3 id="rfc.section.4.2.2"><a href="#rfc.section.4.2.2">4.2.2</a> <a href="#heuristic.freshness">Calculating Heuristic Freshness</a></h3> |
|---|
| 972 | <p id="rfc.section.4.2.2.p.1">Since origin servers do not always provide explicit expiration times, a cache <em class="bcp14">MAY</em> assign a heuristic expiration time when an explicit time is not specified, employing algorithms that use other header field |
|---|
| 973 | values (such as the <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> time) to estimate a plausible expiration time. This specification does not provide specific algorithms, but does impose worst-case |
|---|
| 974 | constraints on their results. |
|---|
| 975 | </p> |
|---|
| 976 | <p id="rfc.section.4.2.2.p.2">A cache <em class="bcp14">MUST NOT</em> use heuristics to determine freshness when an explicit expiration time is present in the stored response. Because of the requirements |
|---|
| 977 | in <a href="#response.cacheability" title="Storing Responses in Caches">Section 3</a>, this means that, effectively, heuristics can only be used on responses without explicit freshness whose status codes are |
|---|
| 978 | defined as cacheable, and responses without explicit freshness that have been marked as explicitly cacheable (e.g., with a |
|---|
| 979 | "public" response cache directive). |
|---|
| 980 | </p> |
|---|
| 981 | <p id="rfc.section.4.2.2.p.3">If the response has a <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> header field (<a href="p4-conditional.html#header.last-modified" title="Last-Modified">Section 2.2</a> of <a href="#Part4" id="rfc.xref.Part4.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[Part4]</cite></a>), caches are encouraged to use a heuristic expiration value that is no more than some fraction of the interval since that |
|---|
| 982 | time. A typical setting of this fraction might be 10%. |
|---|
| 983 | </p> |
|---|
| 984 | <p id="rfc.section.4.2.2.p.4">When a heuristic is used to calculate freshness lifetime, a cache <em class="bcp14">SHOULD</em> generate a <a href="#header.warning" class="smpl">Warning</a> header field with a 113 warn-code (see <a href="#warn.113" id="rfc.xref.warn.113.1" title="Warning: 113 - "Heuristic Expiration"">Section 5.5.4</a>) in the response if its current_age is more than 24 hours and such a warning is not already present. |
|---|
| 985 | </p> |
|---|
| 986 | <div class="note" id="rfc.section.4.2.2.p.5"> |
|---|
| 987 | <p><b>Note:</b> <a href="http://tools.ietf.org/html/rfc2616#section-13.9">Section 13.9</a> of <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a> prohibited caches from calculating heuristic freshness for URIs with query components (i.e., those containing '?'). In practice, |
|---|
| 988 | this has not been widely implemented. Therefore, origin servers are encouraged to send explicit directives (e.g., Cache-Control: |
|---|
| 989 | no-cache) if they wish to preclude caching. |
|---|
| 990 | </p> |
|---|
| 991 | </div> |
|---|
| 992 | </div> |
|---|
| 993 | <div id="age.calculations"> |
|---|
| 994 | <h3 id="rfc.section.4.2.3"><a href="#rfc.section.4.2.3">4.2.3</a> <a href="#age.calculations">Calculating Age</a></h3> |
|---|
| 995 | <p id="rfc.section.4.2.3.p.1">The <a href="#header.age" class="smpl">Age</a> header field is used to convey an estimated age of the response message when obtained from a cache. The Age field value is |
|---|
| 996 | the cache's estimate of the number of seconds since the response was generated or validated by the origin server. In essence, |
|---|
| 997 | the Age value is the sum of the time that the response has been resident in each of the caches along the path from the origin |
|---|
| 998 | server, plus the amount of time it has been in transit along network paths. |
|---|
| 999 | </p> |
|---|
| 1000 | <p id="rfc.section.4.2.3.p.2">The following data is used for the age calculation:</p> |
|---|
| 1001 | <p id="rfc.section.4.2.3.p.3"><dfn>age_value</dfn> |
|---|
| 1002 | </p> |
|---|
| 1003 | <ul class="empty"> |
|---|
| 1004 | <li>The term "age_value" denotes the value of the <a href="#header.age" class="smpl">Age</a> header field (<a href="#header.age" id="rfc.xref.header.age.2" title="Age">Section 5.1</a>), in a form appropriate for arithmetic operation; or 0, if not available. |
|---|
| 1005 | </li> |
|---|
| 1006 | </ul> |
|---|
| 1007 | <p id="rfc.section.4.2.3.p.4"><dfn>date_value</dfn> |
|---|
| 1008 | </p> |
|---|
| 1009 | <ul class="empty"> |
|---|
| 1010 | <li>The term "date_value" denotes the value of the Date header field, in a form appropriate for arithmetic operations. See <a href="p2-semantics.html#header.date" title="Date">Section 7.1.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[Part2]</cite></a> for the definition of the Date header field, and for requirements regarding responses without it. |
|---|
| 1011 | </li> |
|---|
| 1012 | </ul> |
|---|
| 1013 | <p id="rfc.section.4.2.3.p.5"><dfn>now</dfn> |
|---|
| 1014 | </p> |
|---|
| 1015 | <ul class="empty"> |
|---|
| 1016 | <li>The term "now" means "the current value of the clock at the host performing the calculation". A host ought to use NTP (<a href="#RFC5905" id="rfc.xref.RFC5905.1"><cite title="Network Time Protocol Version 4: Protocol and Algorithms Specification">[RFC5905]</cite></a>) or some similar protocol to synchronize its clocks to Coordinated Universal Time. |
|---|
| 1017 | </li> |
|---|
| 1018 | </ul> |
|---|
| 1019 | <p id="rfc.section.4.2.3.p.6"><dfn>request_time</dfn> |
|---|
| 1020 | </p> |
|---|
| 1021 | <ul class="empty"> |
|---|
| 1022 | <li>The current value of the clock at the host at the time the request resulting in the stored response was made.</li> |
|---|
| 1023 | </ul> |
|---|
| 1024 | <p id="rfc.section.4.2.3.p.7"><dfn>response_time</dfn> |
|---|
| 1025 | </p> |
|---|
| 1026 | <ul class="empty"> |
|---|
| 1027 | <li>The current value of the clock at the host at the time the response was received.</li> |
|---|
| 1028 | </ul> |
|---|
| 1029 | <p id="rfc.section.4.2.3.p.8">A response's age can be calculated in two entirely independent ways: </p> |
|---|
| 1030 | <ol> |
|---|
| 1031 | <li>the "apparent_age": response_time minus date_value, if the local clock is reasonably well synchronized to the origin server's |
|---|
| 1032 | clock. If the result is negative, the result is replaced by zero. |
|---|
| 1033 | </li> |
|---|
| 1034 | <li>the "corrected_age_value", if all of the caches along the response path implement HTTP/1.1. A cache <em class="bcp14">MUST</em> interpret this value relative to the time the request was initiated, not the time that the response was received. |
|---|
| 1035 | </li> |
|---|
| 1036 | </ol> |
|---|
| 1037 | <div id="rfc.figure.u.3"></div><pre class="text"> apparent_age = max(0, response_time - date_value); |
|---|
| 1038 | |
|---|
| 1039 | response_delay = response_time - request_time; |
|---|
| 1040 | corrected_age_value = age_value + response_delay; |
|---|
| 1041 | </pre><div id="rfc.figure.u.4"></div> |
|---|
| 1042 | <p>These are combined as</p><pre class="text"> corrected_initial_age = max(apparent_age, corrected_age_value); |
|---|
| 1043 | </pre><p id="rfc.section.4.2.3.p.11">unless the cache is confident in the value of the <a href="#header.age" class="smpl">Age</a> header field (e.g., because there are no HTTP/1.0 hops in the <a href="p1-messaging.html#header.via" class="smpl">Via</a> header field), in which case the corrected_age_value <em class="bcp14">MAY</em> be used as the corrected_initial_age. |
|---|
| 1044 | </p> |
|---|
| 1045 | <p id="rfc.section.4.2.3.p.12">The current_age of a stored response can then be calculated by adding the amount of time (in seconds) since the stored response |
|---|
| 1046 | was last validated by the origin server to the corrected_initial_age. |
|---|
| 1047 | </p> |
|---|
| 1048 | <div id="rfc.figure.u.5"></div><pre class="text"> resident_time = now - response_time; |
|---|
| 1049 | current_age = corrected_initial_age + resident_time; |
|---|
| 1050 | </pre></div> |
|---|
| 1051 | <div id="serving.stale.responses"> |
|---|
| 1052 | <h3 id="rfc.section.4.2.4"><a href="#rfc.section.4.2.4">4.2.4</a> <a href="#serving.stale.responses">Serving Stale Responses</a></h3> |
|---|
| 1053 | <p id="rfc.section.4.2.4.p.1">A "stale" response is one that either has explicit expiry information or is allowed to have heuristic expiry calculated, but |
|---|
| 1054 | is not fresh according to the calculations in <a href="#expiration.model" title="Freshness">Section 4.2</a>. |
|---|
| 1055 | </p> |
|---|
| 1056 | <p id="rfc.section.4.2.4.p.2">A cache <em class="bcp14">MUST NOT</em> generate a stale response if it is prohibited by an explicit in-protocol directive (e.g., by a "no-store" or "no-cache" cache |
|---|
| 1057 | directive, a "must-revalidate" cache-response-directive, or an applicable "s-maxage" or "proxy-revalidate" cache-response-directive; |
|---|
| 1058 | see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 5.2.2</a>). |
|---|
| 1059 | </p> |
|---|
| 1060 | <p id="rfc.section.4.2.4.p.3">A cache <em class="bcp14">MUST NOT</em> send stale responses unless it is disconnected (i.e., it cannot contact the origin server or otherwise find a forward path) |
|---|
| 1061 | or doing so is explicitly allowed (e.g., by the max-stale request directive; see <a href="#cache-request-directive" title="Request Cache-Control Directives">Section 5.2.1</a>). |
|---|
| 1062 | </p> |
|---|
| 1063 | <p id="rfc.section.4.2.4.p.4">A cache <em class="bcp14">SHOULD</em> generate a <a href="#header.warning" class="smpl">Warning</a> header field with the 110 warn-code (see <a href="#warn.110" id="rfc.xref.warn.110.1" title="Warning: 110 - "Response is Stale"">Section 5.5.1</a>) in stale responses. Likewise, a cache <em class="bcp14">SHOULD</em> generate a 112 warn-code (see <a href="#warn.112" id="rfc.xref.warn.112.1" title="Warning: 112 - "Disconnected Operation"">Section 5.5.3</a>) in stale responses if the cache is disconnected. |
|---|
| 1064 | </p> |
|---|
| 1065 | <p id="rfc.section.4.2.4.p.5">A cache <em class="bcp14">SHOULD NOT</em> generate a new <a href="#header.warning" class="smpl">Warning</a> header field when forwarding a response that does not have an <a href="#header.age" class="smpl">Age</a> header field, even if the response is already stale. A cache need not validate a response that merely became stale in transit. |
|---|
| 1066 | </p> |
|---|
| 1067 | </div> |
|---|
| 1068 | </div> |
|---|
| 1069 | <div id="validation.model"> |
|---|
| 1070 | <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a> <a href="#validation.model">Validation</a></h2> |
|---|
| 1071 | <p id="rfc.section.4.3.p.1">When a cache has one or more stored responses for a requested URI, but cannot serve any of them (e.g., because they are not |
|---|
| 1072 | fresh, or one cannot be selected; see <a href="#caching.negotiated.responses" title="Calculating Secondary Keys with Vary">Section 4.1</a>), it can use the conditional request mechanism <a href="#Part4" id="rfc.xref.Part4.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[Part4]</cite></a> in the forwarded request to give the next inbound server an opportunity to select a valid stored response to use, updating |
|---|
| 1073 | the stored metadata in the process, or to replace the stored response(s) with a new response. This process is known as "validating" |
|---|
| 1074 | or "revalidating" the stored response. |
|---|
| 1075 | </p> |
|---|
| 1076 | <div id="validation.sent"> |
|---|
| 1077 | <div id="rfc.iref.v.1"></div> |
|---|
| 1078 | <h3 id="rfc.section.4.3.1"><a href="#rfc.section.4.3.1">4.3.1</a> <a href="#validation.sent">Sending a Validation Request</a></h3> |
|---|
| 1079 | <p id="rfc.section.4.3.1.p.1">When sending a conditional request for cache validation, a cache sends one or more precondition header fields containing <dfn>validator</dfn> metadata from its stored response(s), which is then compared by recipients to determine whether a stored response is equivalent |
|---|
| 1080 | to a current representation of the resource. |
|---|
| 1081 | </p> |
|---|
| 1082 | <p id="rfc.section.4.3.1.p.2">One such validator is the timestamp given in a <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> header field (<a href="p4-conditional.html#header.last-modified" title="Last-Modified">Section 2.2</a> of <a href="#Part4" id="rfc.xref.Part4.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[Part4]</cite></a>), which can be used in an <a href="p4-conditional.html#header.if-modified-since" class="smpl">If-Modified-Since</a> header field for response validation, or in an <a href="p4-conditional.html#header.if-unmodified-since" class="smpl">If-Unmodified-Since</a> or <a href="p5-range.html#header.if-range" class="smpl">If-Range</a> header field for representation selection (i.e., the client is referring specifically to a previously obtained representation |
|---|
| 1083 | with that timestamp). |
|---|
| 1084 | </p> |
|---|
| 1085 | <p id="rfc.section.4.3.1.p.3">Another validator is the entity-tag given in an <a href="p4-conditional.html#header.etag" class="smpl">ETag</a> header field (<a href="p4-conditional.html#header.etag" title="ETag">Section 2.3</a> of <a href="#Part4" id="rfc.xref.Part4.4"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[Part4]</cite></a>). One or more entity-tags, indicating one or more stored responses, can be used in an <a href="p4-conditional.html#header.if-none-match" class="smpl">If-None-Match</a> header field for response validation, or in an <a href="p4-conditional.html#header.if-match" class="smpl">If-Match</a> or <a href="p5-range.html#header.if-range" class="smpl">If-Range</a> header field for representation selection (i.e., the client is referring specifically to one or more previously obtained representations |
|---|
| 1086 | with the listed entity-tags). |
|---|
| 1087 | </p> |
|---|
| 1088 | </div> |
|---|
| 1089 | <div id="validation.received"> |
|---|
| 1090 | <h3 id="rfc.section.4.3.2"><a href="#rfc.section.4.3.2">4.3.2</a> <a href="#validation.received">Handling a Received Validation Request</a></h3> |
|---|
| 1091 | <p id="rfc.section.4.3.2.p.1">Each client in the request chain may have its own cache, so it is common for a cache at an intermediary to receive conditional |
|---|
| 1092 | requests from other (outbound) caches. Likewise, some user agents make use of conditional requests to limit data transfers |
|---|
| 1093 | to recently modified representations or to complete the transfer of a partially retrieved representation. |
|---|
| 1094 | </p> |
|---|
| 1095 | <p id="rfc.section.4.3.2.p.2">If a cache receives a request that can be satisfied by reusing one of its stored <a href="p2-semantics.html#status.200" class="smpl">200 (OK)</a> or <a href="p5-range.html#status.206" class="smpl">206 (Partial Content)</a> responses, the cache <em class="bcp14">SHOULD</em> evaluate any applicable conditional header field preconditions received in that request with respect to the corresponding |
|---|
| 1096 | validators contained within the selected response. A cache <em class="bcp14">MUST NOT</em> evaluate conditional header fields that are only applicable to an origin server, found in a request with semantics that cannot |
|---|
| 1097 | be satisfied with a cached response, or applied to a target resource for which it has no stored responses; such preconditions |
|---|
| 1098 | are likely intended for some other (inbound) server. |
|---|
| 1099 | </p> |
|---|
| 1100 | <p id="rfc.section.4.3.2.p.3">The proper evaluation of conditional requests by a cache depends on the received precondition header fields and their precedence, |
|---|
| 1101 | as defined in <a href="p4-conditional.html#precedence" title="Precedence">Section 6</a> of <a href="#Part4" id="rfc.xref.Part4.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[Part4]</cite></a>. The <a href="p4-conditional.html#header.if-match" class="smpl">If-Match</a> and <a href="p4-conditional.html#header.if-unmodified-since" class="smpl">If-Unmodified-Since</a> conditional header fields are not applicable to a cache. |
|---|
| 1102 | </p> |
|---|
| 1103 | <p id="rfc.section.4.3.2.p.4">A request containing an <a href="p4-conditional.html#header.if-none-match" class="smpl">If-None-Match</a> header field (<a href="p4-conditional.html#header.if-none-match" title="If-None-Match">Section 3.2</a> of <a href="#Part4" id="rfc.xref.Part4.6"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[Part4]</cite></a>) indicates that the client wants to validate one or more of its own stored responses in comparison to whichever stored response |
|---|
| 1104 | is selected by the cache. If the field-value is "*", or if the field-value is a list of entity-tags and at least one of them |
|---|
| 1105 | match the entity-tag of the selected stored response, a cache recipient <em class="bcp14">SHOULD</em> generate a <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> response (using the metadata of the selected stored response) instead of sending that stored response. |
|---|
| 1106 | </p> |
|---|
| 1107 | <p id="rfc.section.4.3.2.p.5">When a cache decides to revalidate its own stored responses for a request that contains an <a href="p4-conditional.html#header.if-none-match" class="smpl">If-None-Match</a> list of entity-tags, the cache <em class="bcp14">MAY</em> combine the received list with a list of entity-tags from its own stored set of responses (fresh or stale) and send the union |
|---|
| 1108 | of the two lists as a replacement <a href="p4-conditional.html#header.if-none-match" class="smpl">If-None-Match</a> header field value in the forwarded request. If a stored response contains only partial content, the cache <em class="bcp14">MUST NOT</em> include its entity-tag in the union unless the request is for a range that would be fully satisfied by that partial stored |
|---|
| 1109 | response. If the response to the forwarded request is <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> and has an ETag header field value with an entity-tag that is not in the client's list, the cache <em class="bcp14">MUST</em> generate a <a href="p2-semantics.html#status.200" class="smpl">200 (OK)</a> response for the client by reusing its corresponding stored response, as updated by the 304 response metadata (<a href="#freshening.responses" title="Freshening Stored Responses upon Validation">Section 4.3.4</a>). |
|---|
| 1110 | </p> |
|---|
| 1111 | <p id="rfc.section.4.3.2.p.6">If an <a href="p4-conditional.html#header.if-none-match" class="smpl">If-None-Match</a> header field is not present, a request containing an <a href="p4-conditional.html#header.if-modified-since" class="smpl">If-Modified-Since</a> header field (<a href="p4-conditional.html#header.if-modified-since" title="If-Modified-Since">Section 3.3</a> of <a href="#Part4" id="rfc.xref.Part4.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[Part4]</cite></a>) indicates that the client wants to validate one or more of its own stored responses by modification date. A cache recipient <em class="bcp14">SHOULD</em> generate a <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> response (using the metadata of the selected stored response) if one of the following cases is true: 1) the selected stored |
|---|
| 1112 | response has a <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> field-value that is earlier than or equal to the conditional timestamp; 2) no <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> field is present in the selected stored response, but it has a <a href="p2-semantics.html#header.date" class="smpl">Date</a> field-value that is earlier than or equal to the conditional timestamp; or, 3) neither <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> nor <a href="p2-semantics.html#header.date" class="smpl">Date</a> is present in the selected stored response, but the cache recorded it as having been received at a time earlier than or equal |
|---|
| 1113 | to the conditional timestamp. |
|---|
| 1114 | </p> |
|---|
| 1115 | <p id="rfc.section.4.3.2.p.7">A cache that implements partial responses to range requests, as defined in <a href="#Part5" id="rfc.xref.Part5.4"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[Part5]</cite></a>, also needs to evaluate a received <a href="p5-range.html#header.if-range" class="smpl">If-Range</a> header field (<a href="p5-range.html#header.if-range" title="If-Range">Section 3.2</a> of <a href="#Part5" id="rfc.xref.Part5.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[Part5]</cite></a>) with respect to its selected stored response. |
|---|
| 1116 | </p> |
|---|
| 1117 | </div> |
|---|
| 1118 | <div id="validation.response"> |
|---|
| 1119 | <h3 id="rfc.section.4.3.3"><a href="#rfc.section.4.3.3">4.3.3</a> <a href="#validation.response">Handling a Validation Response</a></h3> |
|---|
| 1120 | <p id="rfc.section.4.3.3.p.1">Cache handling of a response to a conditional request is dependent upon its status code:</p> |
|---|
| 1121 | <p id="rfc.section.4.3.3.p.2"></p> |
|---|
| 1122 | <ul> |
|---|
| 1123 | <li>A <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> response status code indicates that the stored response can be updated and reused; see <a href="#freshening.responses" title="Freshening Stored Responses upon Validation">Section 4.3.4</a>. |
|---|
| 1124 | </li> |
|---|
| 1125 | <li>A full response (i.e., one with a payload body) indicates that none of the stored responses nominated in the conditional request |
|---|
| 1126 | is suitable. Instead, the cache <em class="bcp14">MUST</em> use the full response to satisfy the request and <em class="bcp14">MAY</em> replace the stored response(s). |
|---|
| 1127 | </li> |
|---|
| 1128 | <li>However, if a cache receives a <a href="p2-semantics.html#status.5xx" class="smpl">5xx (Server Error)</a> response while attempting to validate a response, it can either forward this response to the requesting client, or act as |
|---|
| 1129 | if the server failed to respond. In the latter case, the cache <em class="bcp14">MAY</em> send a previously stored response (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section 4.2.4</a>). |
|---|
| 1130 | </li> |
|---|
| 1131 | </ul> |
|---|
| 1132 | </div> |
|---|
| 1133 | <div id="freshening.responses"> |
|---|
| 1134 | <h3 id="rfc.section.4.3.4"><a href="#rfc.section.4.3.4">4.3.4</a> <a href="#freshening.responses">Freshening Stored Responses upon Validation</a></h3> |
|---|
| 1135 | <p id="rfc.section.4.3.4.p.1">When a cache receives a <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> response and already has one or more stored <a href="p2-semantics.html#status.200" class="smpl">200 (OK)</a> responses for the same cache key, the cache needs to identify which of the stored responses are updated by this new response |
|---|
| 1136 | and then update the stored response(s) with the new information provided in the <a href="p4-conditional.html#status.304" class="smpl">304</a> response. |
|---|
| 1137 | </p> |
|---|
| 1138 | <div id="rfc.iref.s.3"></div> |
|---|
| 1139 | <p id="rfc.section.4.3.4.p.2">The stored response to update is identified by using the first match (if any) of: </p> |
|---|
| 1140 | <ul> |
|---|
| 1141 | <li>If the new response contains a <dfn>strong validator</dfn> (see <a href="p4-conditional.html#weak.and.strong.validators" title="Weak versus Strong">Section 2.1</a> of <a href="#Part4" id="rfc.xref.Part4.8"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[Part4]</cite></a>), then that strong validator identifies the selected representation for update. All of the stored responses with the same |
|---|
| 1142 | strong validator are selected. If none of the stored responses contain the same strong validator, then the cache <em class="bcp14">MUST NOT</em> use the new response to update any stored responses. |
|---|
| 1143 | </li> |
|---|
| 1144 | <li>If the new response contains a weak validator and that validator corresponds to one of the cache's stored responses, then |
|---|
| 1145 | the most recent of those matching stored responses is selected for update. |
|---|
| 1146 | </li> |
|---|
| 1147 | <li>If the new response does not include any form of validator (such as in the case where a client generates an If-Modified-Since |
|---|
| 1148 | request from a source other than the Last-Modified response header field), and there is only one stored response, and that |
|---|
| 1149 | stored response also lacks a validator, then that stored response is selected for update. |
|---|
| 1150 | </li> |
|---|
| 1151 | </ul> |
|---|
| 1152 | <p id="rfc.section.4.3.4.p.3">If a stored response is selected for update, the cache <em class="bcp14">MUST</em>: |
|---|
| 1153 | </p> |
|---|
| 1154 | <ul> |
|---|
| 1155 | <li>delete any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.2" title="Warning">Section 5.5</a>); |
|---|
| 1156 | </li> |
|---|
| 1157 | <li>retain any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 2xx; and, |
|---|
| 1158 | </li> |
|---|
| 1159 | <li>use other header fields provided in the <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> response to replace all instances of the corresponding header fields in the stored response. |
|---|
| 1160 | </li> |
|---|
| 1161 | </ul> |
|---|
| 1162 | </div> |
|---|
| 1163 | <div id="head.effects"> |
|---|
| 1164 | <h3 id="rfc.section.4.3.5"><a href="#rfc.section.4.3.5">4.3.5</a> <a href="#head.effects">Freshening Responses via HEAD</a></h3> |
|---|
| 1165 | <p id="rfc.section.4.3.5.p.1">A response to the HEAD method is identical to what an equivalent request made with a GET would have been, except it lacks |
|---|
| 1166 | a body. This property of HEAD responses can be used to invalidate or update a cached GET response if the more efficient conditional |
|---|
| 1167 | GET request mechanism is not available (due to no validators being present in the stored response) or if transmission of the |
|---|
| 1168 | representation body is not desired even if it has changed. |
|---|
| 1169 | </p> |
|---|
| 1170 | <p id="rfc.section.4.3.5.p.2">When a cache makes an inbound HEAD request for a given request target and receives a <a href="p2-semantics.html#status.200" class="smpl">200 (OK)</a> response, the cache <em class="bcp14">SHOULD</em> update or invalidate each of its stored GET responses that could have been selected for that request (see <a href="#caching.negotiated.responses" title="Calculating Secondary Keys with Vary">Section 4.1</a>). |
|---|
| 1171 | </p> |
|---|
| 1172 | <p id="rfc.section.4.3.5.p.3">For each of the stored responses that could have been selected, if the stored response and HEAD response have matching values |
|---|
| 1173 | for any received validator fields (<a href="p4-conditional.html#header.etag" class="smpl">ETag</a> and <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a>) and, if the HEAD response has a <a href="p1-messaging.html#header.content-length" class="smpl">Content-Length</a> header field, the value of <a href="p1-messaging.html#header.content-length" class="smpl">Content-Length</a> matches that of the stored response, the cache <em class="bcp14">SHOULD</em> update the stored response a described below; otherwise, the cache <em class="bcp14">SHOULD</em> consider the stored response to be stale. |
|---|
| 1174 | </p> |
|---|
| 1175 | <p id="rfc.section.4.3.5.p.4">If a cache updates a stored response with the metadata provided in a HEAD response, the cache <em class="bcp14">MUST</em>: |
|---|
| 1176 | </p> |
|---|
| 1177 | <ul> |
|---|
| 1178 | <li>delete any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.3" title="Warning">Section 5.5</a>); |
|---|
| 1179 | </li> |
|---|
| 1180 | <li>retain any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 2xx; and, |
|---|
| 1181 | </li> |
|---|
| 1182 | <li>use other header fields provided in the HEAD response to replace all instances of the corresponding header fields in the stored |
|---|
| 1183 | response and append new header fields to the stored response's header section unless otherwise restricted by the <a href="#header.cache-control" class="smpl">Cache-Control</a> header field. |
|---|
| 1184 | </li> |
|---|
| 1185 | </ul> |
|---|
| 1186 | </div> |
|---|
| 1187 | </div> |
|---|
| 1188 | <div id="invalidation"> |
|---|
| 1189 | <h2 id="rfc.section.4.4"><a href="#rfc.section.4.4">4.4</a> <a href="#invalidation">Invalidation</a></h2> |
|---|
| 1190 | <p id="rfc.section.4.4.p.1">Because unsafe request methods (<a href="p2-semantics.html#safe.methods" title="Safe Methods">Section 4.2.1</a> of <a href="#Part2" id="rfc.xref.Part2.6"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[Part2]</cite></a>) such as PUT, POST or DELETE have the potential for changing state on the origin server, intervening caches can use them |
|---|
| 1191 | to keep their contents up-to-date. |
|---|
| 1192 | </p> |
|---|
| 1193 | <p id="rfc.section.4.4.p.2">A cache <em class="bcp14">MUST</em> invalidate the effective Request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</a> of <a href="#Part1" id="rfc.xref.Part1.6"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>) as well as the URI(s) in the <a href="p2-semantics.html#header.location" class="smpl">Location</a> and <a href="p2-semantics.html#header.content-location" class="smpl">Content-Location</a> response header fields (if present) when a non-error status code is received in response to an unsafe request method. |
|---|
| 1194 | </p> |
|---|
| 1195 | <p id="rfc.section.4.4.p.3">However, a cache <em class="bcp14">MUST NOT</em> invalidate a URI from a <a href="p2-semantics.html#header.location" class="smpl">Location</a> or <a href="p2-semantics.html#header.content-location" class="smpl">Content-Location</a> response header field if the host part of that URI differs from the host part in the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</a> of <a href="#Part1" id="rfc.xref.Part1.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>). This helps prevent denial of service attacks. |
|---|
| 1196 | </p> |
|---|
| 1197 | <p id="rfc.section.4.4.p.4">A cache <em class="bcp14">MUST</em> invalidate the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</a> of <a href="#Part1" id="rfc.xref.Part1.8"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>) when it receives a non-error response to a request with a method whose safety is unknown. |
|---|
| 1198 | </p> |
|---|
| 1199 | <p id="rfc.section.4.4.p.5">Here, a "non-error response" is one with a <a href="p2-semantics.html#status.2xx" class="smpl">2xx (Successful)</a> or <a href="p2-semantics.html#status.3xx" class="smpl">3xx (Redirection)</a> status code. "Invalidate" means that the cache will either remove all stored responses related to the effective request URI, |
|---|
| 1200 | or will mark these as "invalid" and in need of a mandatory validation before they can be sent in response to a subsequent |
|---|
| 1201 | request. |
|---|
| 1202 | </p> |
|---|
| 1203 | <p id="rfc.section.4.4.p.6">Note that this does not guarantee that all appropriate responses are invalidated. For example, a state-changing request might |
|---|
| 1204 | invalidate responses in the caches it travels through, but relevant responses still might be stored in other caches that it |
|---|
| 1205 | has not. |
|---|
| 1206 | </p> |
|---|
| 1207 | </div> |
|---|
| 1208 | </div> |
|---|
| 1209 | <div id="header.field.definitions"> |
|---|
| 1210 | <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a> <a href="#header.field.definitions">Header Field Definitions</a></h1> |
|---|
| 1211 | <p id="rfc.section.5.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to caching.</p> |
|---|
| 1212 | <div id="header.age"> |
|---|
| 1213 | <div id="rfc.iref.a.2"></div> |
|---|
| 1214 | <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a> <a href="#header.age">Age</a></h2> |
|---|
| 1215 | <p id="rfc.section.5.1.p.1">The "Age" header field conveys the sender's estimate of the amount of time since the response was generated or successfully |
|---|
| 1216 | validated at the origin server. Age values are calculated as specified in <a href="#age.calculations" title="Calculating Age">Section 4.2.3</a>. |
|---|
| 1217 | </p> |
|---|
| 1218 | <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.2"></span> <a href="#header.age" class="smpl">Age</a> = <a href="#delta-seconds" class="smpl">delta-seconds</a> |
|---|
| 1219 | </pre><p id="rfc.section.5.1.p.3">The Age field-value is a non-negative integer, representing time in seconds (see <a href="#delta-seconds" title="Delta Seconds">Section 1.2.1</a>). |
|---|
| 1220 | </p> |
|---|
| 1221 | <p id="rfc.section.5.1.p.4">The presence of an Age header field implies that the response was not generated or validated by the origin server for this |
|---|
| 1222 | request. However, lack of an Age header field does not imply the origin was contacted, since the response might have been |
|---|
| 1223 | received from an HTTP/1.0 cache that does not implement Age. |
|---|
| 1224 | </p> |
|---|
| 1225 | </div> |
|---|
| 1226 | <div id="header.cache-control"> |
|---|
| 1227 | <div id="rfc.iref.c.5"></div> |
|---|
| 1228 | <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a> <a href="#header.cache-control">Cache-Control</a></h2> |
|---|
| 1229 | <p id="rfc.section.5.2.p.1">The "Cache-Control" header field is used to specify directives for caches along the request/response chain. Such cache directives |
|---|
| 1230 | are unidirectional in that the presence of a directive in a request does not imply that the same directive is to be given |
|---|
| 1231 | in the response. |
|---|
| 1232 | </p> |
|---|
| 1233 | <p id="rfc.section.5.2.p.2">A cache <em class="bcp14">MUST</em> obey the requirements of the Cache-Control directives defined in this section. See <a href="#cache.control.extensions" title="Cache Control Extensions">Section 5.2.3</a> for information about how Cache-Control directives defined elsewhere are handled. |
|---|
| 1234 | </p> |
|---|
| 1235 | <div class="note" id="rfc.section.5.2.p.3"> |
|---|
| 1236 | <p><b>Note:</b> Some HTTP/1.0 caches might not implement Cache-Control. |
|---|
| 1237 | </p> |
|---|
| 1238 | </div> |
|---|
| 1239 | <p id="rfc.section.5.2.p.4">A proxy, whether or not it implements a cache, <em class="bcp14">MUST</em> pass cache directives through in forwarded messages, regardless of their significance to that application, since the directives |
|---|
| 1240 | might be applicable to all recipients along the request/response chain. It is not possible to target a directive to a specific |
|---|
| 1241 | cache. |
|---|
| 1242 | </p> |
|---|
| 1243 | <p id="rfc.section.5.2.p.5">Cache directives are identified by a token, to be compared case-insensitively, and have an optional argument, that can use |
|---|
| 1244 | both token and quoted-string syntax. For the directives defined below that define arguments, recipients ought to accept both |
|---|
| 1245 | forms, even if one is documented to be preferred. For any directive not defined by this specification, a recipient <em class="bcp14">MUST</em> accept both forms. |
|---|
| 1246 | </p> |
|---|
| 1247 | <div id="rfc.figure.u.7"></div><pre class="inline"><span id="rfc.iref.g.3"></span><span id="rfc.iref.g.4"></span> <a href="#header.cache-control" class="smpl">Cache-Control</a> = 1#<a href="#header.cache-control" class="smpl">cache-directive</a> |
|---|
| 1248 | |
|---|
| 1249 | <a href="#header.cache-control" class="smpl">cache-directive</a> = <a href="#imported.abnf" class="smpl">token</a> [ "=" ( <a href="#imported.abnf" class="smpl">token</a> / <a href="#imported.abnf" class="smpl">quoted-string</a> ) ] |
|---|
| 1250 | </pre><p id="rfc.section.5.2.p.7">For the cache directives defined below, no argument is defined (nor allowed) unless stated otherwise.</p> |
|---|
| 1251 | <div id="cache-request-directive"> |
|---|
| 1252 | <h3 id="rfc.section.5.2.1"><a href="#rfc.section.5.2.1">5.2.1</a> <a href="#cache-request-directive">Request Cache-Control Directives</a></h3> |
|---|
| 1253 | <div id="cache-request-directive.max-age"> |
|---|
| 1254 | <div id="rfc.iref.m.1"></div> |
|---|
| 1255 | <h4 id="rfc.section.5.2.1.1"><a href="#rfc.section.5.2.1.1">5.2.1.1</a> <a href="#cache-request-directive.max-age">max-age</a></h4> |
|---|
| 1256 | <p id="rfc.section.5.2.1.1.p.1">Argument syntax: </p> |
|---|
| 1257 | <ul class="empty"> |
|---|
| 1258 | <li><a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section 1.2.1</a>) |
|---|
| 1259 | </li> |
|---|
| 1260 | </ul> |
|---|
| 1261 | <p id="rfc.section.5.2.1.1.p.2">The "max-age" request directive indicates that the client is unwilling to accept a response whose age is greater than the |
|---|
| 1262 | specified number of seconds. Unless the max-stale request directive is also present, the client is not willing to accept a |
|---|
| 1263 | stale response. |
|---|
| 1264 | </p> |
|---|
| 1265 | <p id="rfc.section.5.2.1.1.p.3"><b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'max-age=5', not 'max-age="5"'. A sender <em class="bcp14">SHOULD NOT</em> generate the quoted-string form. |
|---|
| 1266 | </p> |
|---|
| 1267 | </div> |
|---|
| 1268 | <div id="cache-request-directive.max-stale"> |
|---|
| 1269 | <div id="rfc.iref.m.2"></div> |
|---|
| 1270 | <h4 id="rfc.section.5.2.1.2"><a href="#rfc.section.5.2.1.2">5.2.1.2</a> <a href="#cache-request-directive.max-stale">max-stale</a></h4> |
|---|
| 1271 | <p id="rfc.section.5.2.1.2.p.1">Argument syntax: </p> |
|---|
| 1272 | <ul class="empty"> |
|---|
| 1273 | <li><a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section 1.2.1</a>) |
|---|
| 1274 | </li> |
|---|
| 1275 | </ul> |
|---|
| 1276 | <p id="rfc.section.5.2.1.2.p.2">The "max-stale" request directive indicates that the client is willing to accept a response that has exceeded its freshness |
|---|
| 1277 | lifetime. If max-stale is assigned a value, then the client is willing to accept a response that has exceeded its freshness |
|---|
| 1278 | lifetime by no more than the specified number of seconds. If no value is assigned to max-stale, then the client is willing |
|---|
| 1279 | to accept a stale response of any age. |
|---|
| 1280 | </p> |
|---|
| 1281 | <p id="rfc.section.5.2.1.2.p.3"><b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'max-stale=10', not 'max-stale="10"'. A sender <em class="bcp14">SHOULD NOT</em> generate the quoted-string form. |
|---|
| 1282 | </p> |
|---|
| 1283 | </div> |
|---|
| 1284 | <div id="cache-request-directive.min-fresh"> |
|---|
| 1285 | <div id="rfc.iref.m.3"></div> |
|---|
| 1286 | <h4 id="rfc.section.5.2.1.3"><a href="#rfc.section.5.2.1.3">5.2.1.3</a> <a href="#cache-request-directive.min-fresh">min-fresh</a></h4> |
|---|
| 1287 | <p id="rfc.section.5.2.1.3.p.1">Argument syntax: </p> |
|---|
| 1288 | <ul class="empty"> |
|---|
| 1289 | <li><a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section 1.2.1</a>) |
|---|
| 1290 | </li> |
|---|
| 1291 | </ul> |
|---|
| 1292 | <p id="rfc.section.5.2.1.3.p.2">The "min-fresh" request directive indicates that the client is willing to accept a response whose freshness lifetime is no |
|---|
| 1293 | less than its current age plus the specified time in seconds. That is, the client wants a response that will still be fresh |
|---|
| 1294 | for at least the specified number of seconds. |
|---|
| 1295 | </p> |
|---|
| 1296 | <p id="rfc.section.5.2.1.3.p.3"><b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'min-fresh=20', not 'min-fresh="20"'. A sender <em class="bcp14">SHOULD NOT</em> generate the quoted-string form. |
|---|
| 1297 | </p> |
|---|
| 1298 | </div> |
|---|
| 1299 | <div id="cache-request-directive.no-cache"> |
|---|
| 1300 | <div id="rfc.iref.n.1"></div> |
|---|
| 1301 | <h4 id="rfc.section.5.2.1.4"><a href="#rfc.section.5.2.1.4">5.2.1.4</a> <a href="#cache-request-directive.no-cache">no-cache</a></h4> |
|---|
| 1302 | <p id="rfc.section.5.2.1.4.p.1">The "no-cache" request directive indicates that a cache <em class="bcp14">MUST NOT</em> use a stored response to satisfy the request without successful validation on the origin server. |
|---|
| 1303 | </p> |
|---|
| 1304 | </div> |
|---|
| 1305 | <div id="cache-request-directive.no-store"> |
|---|
| 1306 | <div id="rfc.iref.n.2"></div> |
|---|
| 1307 | <h4 id="rfc.section.5.2.1.5"><a href="#rfc.section.5.2.1.5">5.2.1.5</a> <a href="#cache-request-directive.no-store">no-store</a></h4> |
|---|
| 1308 | <p id="rfc.section.5.2.1.5.p.1">The "no-store" request directive indicates that a cache <em class="bcp14">MUST NOT</em> store any part of either this request or any response to it. This directive applies to both private and shared caches. "<em class="bcp14">MUST NOT</em> store" in this context means that the cache <em class="bcp14">MUST NOT</em> intentionally store the information in non-volatile storage, and <em class="bcp14">MUST</em> make a best-effort attempt to remove the information from volatile storage as promptly as possible after forwarding it. |
|---|
| 1309 | </p> |
|---|
| 1310 | <p id="rfc.section.5.2.1.5.p.2">This directive is NOT a reliable or sufficient mechanism for ensuring privacy. In particular, malicious or compromised caches |
|---|
| 1311 | might not recognize or obey this directive, and communications networks might be vulnerable to eavesdropping. |
|---|
| 1312 | </p> |
|---|
| 1313 | <p id="rfc.section.5.2.1.5.p.3">Note that if a request containing this directive is satisfied from a cache, the no-store request directive does not apply |
|---|
| 1314 | to the already stored response. |
|---|
| 1315 | </p> |
|---|
| 1316 | </div> |
|---|
| 1317 | <div id="cache-request-directive.no-transform"> |
|---|
| 1318 | <div id="rfc.iref.n.3"></div> |
|---|
| 1319 | <h4 id="rfc.section.5.2.1.6"><a href="#rfc.section.5.2.1.6">5.2.1.6</a> <a href="#cache-request-directive.no-transform">no-transform</a></h4> |
|---|
| 1320 | <p id="rfc.section.5.2.1.6.p.1">The "no-transform" request directive indicates that an intermediary (whether or not it implements a cache) <em class="bcp14">MUST NOT</em> transform the payload, as defined in <a href="p1-messaging.html#message.transformations" title="Transformations">Section 5.7.2</a> of <a href="#Part1" id="rfc.xref.Part1.9"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>. |
|---|
| 1321 | </p> |
|---|
| 1322 | </div> |
|---|
| 1323 | <div id="cache-request-directive.only-if-cached"> |
|---|
| 1324 | <div id="rfc.iref.o.1"></div> |
|---|
| 1325 | <h4 id="rfc.section.5.2.1.7"><a href="#rfc.section.5.2.1.7">5.2.1.7</a> <a href="#cache-request-directive.only-if-cached">only-if-cached</a></h4> |
|---|
| 1326 | <p id="rfc.section.5.2.1.7.p.1">The "only-if-cached" request directive indicates that the client only wishes to obtain a stored response. If it receives this |
|---|
| 1327 | directive, a cache <em class="bcp14">SHOULD</em> either respond using a stored response that is consistent with the other constraints of the request, or respond with a <a href="p2-semantics.html#status.504" class="smpl">504 (Gateway |
|---|
| 1328 | Timeout)</a> status code. If a group of caches is being operated as a unified system with good internal connectivity, a member cache <em class="bcp14">MAY</em> forward such a request within that group of caches. |
|---|
| 1329 | </p> |
|---|
| 1330 | </div> |
|---|
| 1331 | </div> |
|---|
| 1332 | <div id="cache-response-directive"> |
|---|
| 1333 | <h3 id="rfc.section.5.2.2"><a href="#rfc.section.5.2.2">5.2.2</a> <a href="#cache-response-directive">Response Cache-Control Directives</a></h3> |
|---|
| 1334 | <div id="cache-response-directive.must-revalidate"> |
|---|
| 1335 | <div id="rfc.iref.m.4"></div> |
|---|
| 1336 | <h4 id="rfc.section.5.2.2.1"><a href="#rfc.section.5.2.2.1">5.2.2.1</a> <a href="#cache-response-directive.must-revalidate">must-revalidate</a></h4> |
|---|
| 1337 | <p id="rfc.section.5.2.2.1.p.1">The "must-revalidate" response directive indicates that once it has become stale, a cache <em class="bcp14">MUST NOT</em> use the response to satisfy subsequent requests without successful validation on the origin server. |
|---|
| 1338 | </p> |
|---|
| 1339 | <p id="rfc.section.5.2.2.1.p.2">The must-revalidate directive is necessary to support reliable operation for certain protocol features. In all circumstances |
|---|
| 1340 | a cache <em class="bcp14">MUST</em> obey the must-revalidate directive; in particular, if a cache cannot reach the origin server for any reason, it <em class="bcp14">MUST</em> generate a <a href="p2-semantics.html#status.504" class="smpl">504 (Gateway Timeout)</a> response. |
|---|
| 1341 | </p> |
|---|
| 1342 | <p id="rfc.section.5.2.2.1.p.3">The must-revalidate directive ought to be used by servers if and only if failure to validate a request on the representation |
|---|
| 1343 | could result in incorrect operation, such as a silently unexecuted financial transaction. |
|---|
| 1344 | </p> |
|---|
| 1345 | </div> |
|---|
| 1346 | <div id="cache-response-directive.no-cache"> |
|---|
| 1347 | <div id="rfc.iref.n.4"></div> |
|---|
| 1348 | <h4 id="rfc.section.5.2.2.2"><a href="#rfc.section.5.2.2.2">5.2.2.2</a> <a href="#cache-response-directive.no-cache">no-cache</a></h4> |
|---|
| 1349 | <p id="rfc.section.5.2.2.2.p.1">Argument syntax: </p> |
|---|
| 1350 | <ul class="empty"> |
|---|
| 1351 | <li>#<a href="#imported.abnf" class="smpl">field-name</a> |
|---|
| 1352 | </li> |
|---|
| 1353 | </ul> |
|---|
| 1354 | <p id="rfc.section.5.2.2.2.p.2">The "no-cache" response directive indicates that the response <em class="bcp14">MUST NOT</em> be used to satisfy a subsequent request without successful validation on the origin server. This allows an origin server to |
|---|
| 1355 | prevent a cache from using it to satisfy a request without contacting it, even by caches that have been configured to send |
|---|
| 1356 | stale responses. |
|---|
| 1357 | </p> |
|---|
| 1358 | <p id="rfc.section.5.2.2.2.p.3">If the no-cache response directive specifies one or more field-names, then a cache <em class="bcp14">MAY</em> use the response to satisfy a subsequent request, subject to any other restrictions on caching. However, any header fields |
|---|
| 1359 | in the response that have the field-name(s) listed <em class="bcp14">MUST NOT</em> be sent in the response to a subsequent request without successful revalidation with the origin server. This allows an origin |
|---|
| 1360 | server to prevent the re-use of certain header fields in a response, while still allowing caching of the rest of the response. |
|---|
| 1361 | </p> |
|---|
| 1362 | <p id="rfc.section.5.2.2.2.p.4">The field-names given are not limited to the set of header fields defined by this specification. Field names are case-insensitive.</p> |
|---|
| 1363 | <p id="rfc.section.5.2.2.2.p.5"><b>Note:</b> Although it has been back-ported to many implementations, some HTTP/1.0 caches will not recognize or obey this directive. |
|---|
| 1364 | Also, no-cache response directives with field-names are often handled by caches as if an unqualified no-cache directive was |
|---|
| 1365 | received; i.e., the special handling for the qualified form is not widely implemented. |
|---|
| 1366 | </p> |
|---|
| 1367 | <p id="rfc.section.5.2.2.2.p.6"><b>Note:</b> This directive uses the quoted-string form of the argument syntax. A sender <em class="bcp14">SHOULD NOT</em> generate the token form (even if quoting appears not to be needed for single-entry lists). |
|---|
| 1368 | </p> |
|---|
| 1369 | </div> |
|---|
| 1370 | <div id="cache-response-directive.no-store"> |
|---|
| 1371 | <div id="rfc.iref.n.5"></div> |
|---|
| 1372 | <h4 id="rfc.section.5.2.2.3"><a href="#rfc.section.5.2.2.3">5.2.2.3</a> <a href="#cache-response-directive.no-store">no-store</a></h4> |
|---|
| 1373 | <p id="rfc.section.5.2.2.3.p.1">The "no-store" response directive indicates that a cache <em class="bcp14">MUST NOT</em> store any part of either the immediate request or response. This directive applies to both private and shared caches. "<em class="bcp14">MUST NOT</em> store" in this context means that the cache <em class="bcp14">MUST NOT</em> intentionally store the information in non-volatile storage, and <em class="bcp14">MUST</em> make a best-effort attempt to remove the information from volatile storage as promptly as possible after forwarding it. |
|---|
| 1374 | </p> |
|---|
| 1375 | <p id="rfc.section.5.2.2.3.p.2">This directive is NOT a reliable or sufficient mechanism for ensuring privacy. In particular, malicious or compromised caches |
|---|
| 1376 | might not recognize or obey this directive, and communications networks might be vulnerable to eavesdropping. |
|---|
| 1377 | </p> |
|---|
| 1378 | </div> |
|---|
| 1379 | <div id="cache-response-directive.no-transform"> |
|---|
| 1380 | <div id="rfc.iref.n.6"></div> |
|---|
| 1381 | <h4 id="rfc.section.5.2.2.4"><a href="#rfc.section.5.2.2.4">5.2.2.4</a> <a href="#cache-response-directive.no-transform">no-transform</a></h4> |
|---|
| 1382 | <p id="rfc.section.5.2.2.4.p.1">The "no-transform" response directive indicates that an intermediary (regardless of whether it implements a cache) <em class="bcp14">MUST NOT</em> transform the payload, as defined in <a href="p1-messaging.html#message.transformations" title="Transformations">Section 5.7.2</a> of <a href="#Part1" id="rfc.xref.Part1.10"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>. |
|---|
| 1383 | </p> |
|---|
| 1384 | </div> |
|---|
| 1385 | <div id="cache-response-directive.public"> |
|---|
| 1386 | <div id="rfc.iref.p.2"></div> |
|---|
| 1387 | <h4 id="rfc.section.5.2.2.5"><a href="#rfc.section.5.2.2.5">5.2.2.5</a> <a href="#cache-response-directive.public">public</a></h4> |
|---|
| 1388 | <p id="rfc.section.5.2.2.5.p.1">The "public" response directive indicates that any cache <em class="bcp14">MAY</em> store the response, even if the response would normally be non-cacheable or cacheable only within a private cache. (See <a href="#caching.authenticated.responses" title="Storing Responses to Authenticated Requests">Section 3.2</a> for additional details related to the use of public in response to a request containing <a href="p7-auth.html#header.authorization" class="smpl">Authorization</a>, and <a href="#response.cacheability" title="Storing Responses in Caches">Section 3</a> for details of how public affects responses that would normally not be stored, due to their status codes not being defined |
|---|
| 1389 | as cacheable.) |
|---|
| 1390 | </p> |
|---|
| 1391 | </div> |
|---|
| 1392 | <div id="cache-response-directive.private"> |
|---|
| 1393 | <div id="rfc.iref.p.3"></div> |
|---|
| 1394 | <h4 id="rfc.section.5.2.2.6"><a href="#rfc.section.5.2.2.6">5.2.2.6</a> <a href="#cache-response-directive.private">private</a></h4> |
|---|
| 1395 | <p id="rfc.section.5.2.2.6.p.1">Argument syntax: </p> |
|---|
| 1396 | <ul class="empty"> |
|---|
| 1397 | <li>#<a href="#imported.abnf" class="smpl">field-name</a> |
|---|
| 1398 | </li> |
|---|
| 1399 | </ul> |
|---|
| 1400 | <p id="rfc.section.5.2.2.6.p.2">The "private" response directive indicates that the response message is intended for a single user and <em class="bcp14">MUST NOT</em> be stored by a shared cache. A private cache <em class="bcp14">MAY</em> store the response and reuse it for later requests, even if the response would normally be non-cacheable. |
|---|
| 1401 | </p> |
|---|
| 1402 | <p id="rfc.section.5.2.2.6.p.3">If the private response directive specifies one or more field-names, this requirement is limited to the field-values associated |
|---|
| 1403 | with the listed response header fields. That is, a shared cache <em class="bcp14">MUST NOT</em> store the specified field-names(s), whereas it <em class="bcp14">MAY</em> store the remainder of the response message. |
|---|
| 1404 | </p> |
|---|
| 1405 | <p id="rfc.section.5.2.2.6.p.4">The field-names given are not limited to the set of header fields defined by this specification. Field names are case-insensitive.</p> |
|---|
| 1406 | <p id="rfc.section.5.2.2.6.p.5"><b>Note:</b> This usage of the word "private" only controls where the response can be stored; it cannot ensure the privacy of the message |
|---|
| 1407 | content. Also, private response directives with field-names are often handled by caches as if an unqualified private directive |
|---|
| 1408 | was received; i.e., the special handling for the qualified form is not widely implemented. |
|---|
| 1409 | </p> |
|---|
| 1410 | <p id="rfc.section.5.2.2.6.p.6"><b>Note:</b> This directive uses the quoted-string form of the argument syntax. A sender <em class="bcp14">SHOULD NOT</em> generate the token form (even if quoting appears not to be needed for single-entry lists). |
|---|
| 1411 | </p> |
|---|
| 1412 | </div> |
|---|
| 1413 | <div id="cache-response-directive.proxy-revalidate"> |
|---|
| 1414 | <div id="rfc.iref.p.4"></div> |
|---|
| 1415 | <h4 id="rfc.section.5.2.2.7"><a href="#rfc.section.5.2.2.7">5.2.2.7</a> <a href="#cache-response-directive.proxy-revalidate">proxy-revalidate</a></h4> |
|---|
| 1416 | <p id="rfc.section.5.2.2.7.p.1">The "proxy-revalidate" response directive has the same meaning as the must-revalidate response directive, except that it does |
|---|
| 1417 | not apply to private caches. |
|---|
| 1418 | </p> |
|---|
| 1419 | </div> |
|---|
| 1420 | <div id="cache-response-directive.max-age"> |
|---|
| 1421 | <div id="rfc.iref.m.5"></div> |
|---|
| 1422 | <h4 id="rfc.section.5.2.2.8"><a href="#rfc.section.5.2.2.8">5.2.2.8</a> <a href="#cache-response-directive.max-age">max-age</a></h4> |
|---|
| 1423 | <p id="rfc.section.5.2.2.8.p.1">Argument syntax: </p> |
|---|
| 1424 | <ul class="empty"> |
|---|
| 1425 | <li><a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section 1.2.1</a>) |
|---|
| 1426 | </li> |
|---|
| 1427 | </ul> |
|---|
| 1428 | <p id="rfc.section.5.2.2.8.p.2">The "max-age" response directive indicates that the response is to be considered stale after its age is greater than the specified |
|---|
| 1429 | number of seconds. |
|---|
| 1430 | </p> |
|---|
| 1431 | <p id="rfc.section.5.2.2.8.p.3"><b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'max-age=5', not 'max-age="5"'. A sender <em class="bcp14">SHOULD NOT</em> generate the quoted-string form. |
|---|
| 1432 | </p> |
|---|
| 1433 | </div> |
|---|
| 1434 | <div id="cache-response-directive.s-maxage"> |
|---|
| 1435 | <div id="rfc.iref.s.4"></div> |
|---|
| 1436 | <h4 id="rfc.section.5.2.2.9"><a href="#rfc.section.5.2.2.9">5.2.2.9</a> <a href="#cache-response-directive.s-maxage">s-maxage</a></h4> |
|---|
| 1437 | <p id="rfc.section.5.2.2.9.p.1">Argument syntax: </p> |
|---|
| 1438 | <ul class="empty"> |
|---|
| 1439 | <li><a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section 1.2.1</a>) |
|---|
| 1440 | </li> |
|---|
| 1441 | </ul> |
|---|
| 1442 | <p id="rfc.section.5.2.2.9.p.2">The "s-maxage" response directive indicates that, in shared caches, the maximum age specified by this directive overrides |
|---|
| 1443 | the maximum age specified by either the max-age directive or the <a href="#header.expires" class="smpl">Expires</a> header field. The s-maxage directive also implies the semantics of the proxy-revalidate response directive. |
|---|
| 1444 | </p> |
|---|
| 1445 | <p id="rfc.section.5.2.2.9.p.3"><b>Note:</b> This directive uses the token form of the argument syntax; e.g., 's-maxage=10', not 's-maxage="10"'. A sender <em class="bcp14">SHOULD NOT</em> generate the quoted-string form. |
|---|
| 1446 | </p> |
|---|
| 1447 | </div> |
|---|
| 1448 | </div> |
|---|
| 1449 | <div id="cache.control.extensions"> |
|---|
| 1450 | <h3 id="rfc.section.5.2.3"><a href="#rfc.section.5.2.3">5.2.3</a> <a href="#cache.control.extensions">Cache Control Extensions</a></h3> |
|---|
| 1451 | <p id="rfc.section.5.2.3.p.1">The Cache-Control header field can be extended through the use of one or more cache-extension tokens, each with an optional |
|---|
| 1452 | value. |
|---|
| 1453 | </p> |
|---|
| 1454 | <p id="rfc.section.5.2.3.p.2">Informational extensions (those that do not require a change in cache behavior) can be added without changing the semantics |
|---|
| 1455 | of other directives. Behavioral extensions are designed to work by acting as modifiers to the existing base of cache directives. |
|---|
| 1456 | </p> |
|---|
| 1457 | <p id="rfc.section.5.2.3.p.3">Both the new directive and the standard directive are supplied, such that applications that do not understand the new directive |
|---|
| 1458 | will default to the behavior specified by the standard directive, and those that understand the new directive will recognize |
|---|
| 1459 | it as modifying the requirements associated with the standard directive. In this way, extensions to the cache-control directives |
|---|
| 1460 | can be made without requiring changes to the base protocol. |
|---|
| 1461 | </p> |
|---|
| 1462 | <p id="rfc.section.5.2.3.p.4">This extension mechanism depends on an HTTP cache obeying all of the cache-control directives defined for its native HTTP-version, |
|---|
| 1463 | obeying certain extensions, and ignoring all directives that it does not understand. |
|---|
| 1464 | </p> |
|---|
| 1465 | <p id="rfc.section.5.2.3.p.5">For example, consider a hypothetical new response directive called "community" that acts as a modifier to the private directive. |
|---|
| 1466 | We define this new directive to mean that, in addition to any private cache, any cache that is shared only by members of the |
|---|
| 1467 | community named within its value is allowed to cache the response. An origin server wishing to allow the UCI community to |
|---|
| 1468 | use an otherwise private response in their shared cache(s) could do so by including |
|---|
| 1469 | </p> |
|---|
| 1470 | <div id="rfc.figure.u.8"></div><pre class="text"> Cache-Control: private, community="UCI" |
|---|
| 1471 | </pre><p id="rfc.section.5.2.3.p.7">A cache seeing this header field will act correctly even if the cache does not understand the community cache-extension, since |
|---|
| 1472 | it will also see and understand the private directive and thus default to the safe behavior. |
|---|
| 1473 | </p> |
|---|
| 1474 | <p id="rfc.section.5.2.3.p.8">A cache <em class="bcp14">MUST</em> ignore unrecognized cache directives; it is assumed that any cache directive likely to be unrecognized by an HTTP/1.1 cache |
|---|
| 1475 | will be combined with standard directives (or the response's default cacheability) such that the cache behavior will remain |
|---|
| 1476 | minimally correct even if the cache does not understand the extension(s). |
|---|
| 1477 | </p> |
|---|
| 1478 | </div> |
|---|
| 1479 | </div> |
|---|
| 1480 | <div id="header.expires"> |
|---|
| 1481 | <div id="rfc.iref.e.2"></div> |
|---|
| 1482 | <h2 id="rfc.section.5.3"><a href="#rfc.section.5.3">5.3</a> <a href="#header.expires">Expires</a></h2> |
|---|
| 1483 | <p id="rfc.section.5.3.p.1">The "Expires" header field gives the date/time after which the response is considered stale. See <a href="#expiration.model" title="Freshness">Section 4.2</a> for further discussion of the freshness model. |
|---|
| 1484 | </p> |
|---|
| 1485 | <p id="rfc.section.5.3.p.2">The presence of an Expires field does not imply that the original resource will change or cease to exist at, before, or after |
|---|
| 1486 | that time. |
|---|
| 1487 | </p> |
|---|
| 1488 | <p id="rfc.section.5.3.p.3">The Expires value is an HTTP-date timestamp, as defined in <a href="p2-semantics.html#http.date" title="Date/Time Formats">Section 7.1.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[Part2]</cite></a>. |
|---|
| 1489 | </p> |
|---|
| 1490 | <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.5"></span> <a href="#header.expires" class="smpl">Expires</a> = <a href="#imported.abnf" class="smpl">HTTP-date</a> |
|---|
| 1491 | </pre><div id="rfc.figure.u.10"></div> |
|---|
| 1492 | <p>For example</p><pre class="text"> Expires: Thu, 01 Dec 1994 16:00:00 GMT |
|---|
| 1493 | </pre><p id="rfc.section.5.3.p.6">A cache recipient <em class="bcp14">MUST</em> interpret invalid date formats, especially the value "0", as representing a time in the past (i.e., "already expired"). |
|---|
| 1494 | </p> |
|---|
| 1495 | <p id="rfc.section.5.3.p.7">If a response includes a <a href="#header.cache-control" class="smpl">Cache-Control</a> field with the max-age directive (<a href="#cache-response-directive.max-age" title="max-age">Section 5.2.2.8</a>), a recipient <em class="bcp14">MUST</em> ignore the Expires field. Likewise, if a response includes the s-maxage directive (<a href="#cache-response-directive.s-maxage" title="s-maxage">Section 5.2.2.9</a>), a shared cache recipient <em class="bcp14">MUST</em> ignore the Expires field. In both these cases, the value in Expires is only intended for recipients that have not yet implemented |
|---|
| 1496 | the Cache-Control field. |
|---|
| 1497 | </p> |
|---|
| 1498 | <p id="rfc.section.5.3.p.8">An origin server without a clock <em class="bcp14">MUST NOT</em> generate an Expires field unless its value represents a fixed time in the past (always expired) or its value has been associated |
|---|
| 1499 | with the resource by a system or user with a reliable clock. |
|---|
| 1500 | </p> |
|---|
| 1501 | <p id="rfc.section.5.3.p.9">Historically, HTTP required the Expires field-value to be no more than a year in the future. While longer freshness lifetimes |
|---|
| 1502 | are no longer prohibited, extremely large values have been demonstrated to cause problems (e.g., clock overflows due to use |
|---|
| 1503 | of 32-bit integers for time values), and many caches will evict a response far sooner than that. |
|---|
| 1504 | </p> |
|---|
| 1505 | </div> |
|---|
| 1506 | <div id="header.pragma"> |
|---|
| 1507 | <div id="rfc.iref.p.5"></div> |
|---|
| 1508 | <h2 id="rfc.section.5.4"><a href="#rfc.section.5.4">5.4</a> <a href="#header.pragma">Pragma</a></h2> |
|---|
| 1509 | <p id="rfc.section.5.4.p.1">The "Pragma" header field allows backwards compatibility with HTTP/1.0 caches, so that clients can specify a "no-cache" request |
|---|
| 1510 | that they will understand (as <a href="#header.cache-control" class="smpl">Cache-Control</a> was not defined until HTTP/1.1). When the Cache-Control header field is also present and understood in a request, Pragma is |
|---|
| 1511 | ignored. |
|---|
| 1512 | </p> |
|---|
| 1513 | <p id="rfc.section.5.4.p.2">In HTTP/1.0, Pragma was defined as an extensible field for implementation-specified directives for recipients. This specification |
|---|
| 1514 | deprecates such extensions to improve interoperability. |
|---|
| 1515 | </p> |
|---|
| 1516 | <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.6"></span><span id="rfc.iref.g.7"></span><span id="rfc.iref.g.8"></span> <a href="#header.pragma" class="smpl">Pragma</a> = 1#<a href="#header.pragma" class="smpl">pragma-directive</a> |
|---|
| 1517 | <a href="#header.pragma" class="smpl">pragma-directive</a> = "no-cache" / <a href="#header.pragma" class="smpl">extension-pragma</a> |
|---|
| 1518 | <a href="#header.pragma" class="smpl">extension-pragma</a> = <a href="#imported.abnf" class="smpl">token</a> [ "=" ( <a href="#imported.abnf" class="smpl">token</a> / <a href="#imported.abnf" class="smpl">quoted-string</a> ) ] |
|---|
| 1519 | </pre><p id="rfc.section.5.4.p.4">When the <a href="#header.cache-control" class="smpl">Cache-Control</a> header field is not present in a request, caches <em class="bcp14">MUST</em> consider the no-cache request pragma-directive as having the same effect as if "Cache-Control: no-cache" were present (see <a href="#cache-request-directive" title="Request Cache-Control Directives">Section 5.2.1</a>). |
|---|
| 1520 | </p> |
|---|
| 1521 | <p id="rfc.section.5.4.p.5">When sending a no-cache request, a client ought to include both the pragma and cache-control directives, unless Cache-Control: |
|---|
| 1522 | no-cache is purposefully omitted to target other <a href="#header.cache-control" class="smpl">Cache-Control</a> response directives at HTTP/1.1 caches. For example: |
|---|
| 1523 | </p> |
|---|
| 1524 | <div id="rfc.figure.u.12"></div><pre class="text">GET / HTTP/1.1 |
|---|
| 1525 | Host: www.example.com |
|---|
| 1526 | Cache-Control: max-age=30 |
|---|
| 1527 | Pragma: no-cache |
|---|
| 1528 | |
|---|
| 1529 | </pre><p id="rfc.section.5.4.p.7">will constrain HTTP/1.1 caches to serve a response no older than 30 seconds, while precluding implementations that do not |
|---|
| 1530 | understand <a href="#header.cache-control" class="smpl">Cache-Control</a> from serving a cached response. |
|---|
| 1531 | </p> |
|---|
| 1532 | <div class="note" id="rfc.section.5.4.p.8"> |
|---|
| 1533 | <p><b>Note:</b> Because the meaning of "Pragma: no-cache" in responses is not specified, it does not provide a reliable replacement for "Cache-Control: |
|---|
| 1534 | no-cache" in them. |
|---|
| 1535 | </p> |
|---|
| 1536 | </div> |
|---|
| 1537 | </div> |
|---|
| 1538 | <div id="header.warning"> |
|---|
| 1539 | <div id="rfc.iref.w.1"></div> |
|---|
| 1540 | <h2 id="rfc.section.5.5"><a href="#rfc.section.5.5">5.5</a> <a href="#header.warning">Warning</a></h2> |
|---|
| 1541 | <p id="rfc.section.5.5.p.1">The "Warning" header field is used to carry additional information about the status or transformation of a message that might |
|---|
| 1542 | not be reflected in the status code. This information is typically used to warn about possible incorrectness introduced by |
|---|
| 1543 | caching operations or transformations applied to the payload of the message. |
|---|
| 1544 | </p> |
|---|
| 1545 | <p id="rfc.section.5.5.p.2">Warnings can be used for other purposes, both cache-related and otherwise. The use of a warning, rather than an error status |
|---|
| 1546 | code, distinguishes these responses from true failures. |
|---|
| 1547 | </p> |
|---|
| 1548 | <p id="rfc.section.5.5.p.3">Warning header fields can in general be applied to any message, however some warn-codes are specific to caches and can only |
|---|
| 1549 | be applied to response messages. |
|---|
| 1550 | </p> |
|---|
| 1551 | <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.9"></span><span id="rfc.iref.g.10"></span><span id="rfc.iref.g.11"></span><span id="rfc.iref.g.12"></span><span id="rfc.iref.g.13"></span><span id="rfc.iref.g.14"></span> <a href="#header.warning" class="smpl">Warning</a> = 1#<a href="#header.warning" class="smpl">warning-value</a> |
|---|
| 1552 | |
|---|
| 1553 | <a href="#header.warning" class="smpl">warning-value</a> = <a href="#header.warning" class="smpl">warn-code</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#header.warning" class="smpl">warn-agent</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#header.warning" class="smpl">warn-text</a> |
|---|
| 1554 | [ <a href="#imported.abnf" class="smpl">SP</a> <a href="#header.warning" class="smpl">warn-date</a> ] |
|---|
| 1555 | |
|---|
| 1556 | <a href="#header.warning" class="smpl">warn-code</a> = 3<a href="#imported.abnf" class="smpl">DIGIT</a> |
|---|
| 1557 | <a href="#header.warning" class="smpl">warn-agent</a> = ( <a href="#imported.abnf" class="smpl">uri-host</a> [ ":" <a href="#imported.abnf" class="smpl">port</a> ] ) / <a href="#imported.abnf" class="smpl">pseudonym</a> |
|---|
| 1558 | ; the name or pseudonym of the server adding |
|---|
| 1559 | ; the Warning header field, for use in debugging |
|---|
| 1560 | ; a single "-" is recommended when agent unknown |
|---|
| 1561 | <a href="#header.warning" class="smpl">warn-text</a> = <a href="#imported.abnf" class="smpl">quoted-string</a> |
|---|
| 1562 | <a href="#header.warning" class="smpl">warn-date</a> = <a href="#imported.abnf" class="smpl">DQUOTE</a> <a href="#imported.abnf" class="smpl">HTTP-date</a> <a href="#imported.abnf" class="smpl">DQUOTE</a> |
|---|
| 1563 | </pre><p id="rfc.section.5.5.p.5">Multiple warnings can be generated in a response (either by the origin server or by a cache), including multiple warnings |
|---|
| 1564 | with the same warn-code number that only differ in warn-text. |
|---|
| 1565 | </p> |
|---|
| 1566 | <p id="rfc.section.5.5.p.6">A user agent that receives one or more Warning header fields <em class="bcp14">SHOULD</em> inform the user of as many of them as possible, in the order that they appear in the response. Senders that generate multiple |
|---|
| 1567 | Warning header fields are encouraged to order them with this user agent behavior in mind. A sender that generates new Warning |
|---|
| 1568 | header fields <em class="bcp14">MUST</em> append them after any existing Warning header fields. |
|---|
| 1569 | </p> |
|---|
| 1570 | <p id="rfc.section.5.5.p.7">Warnings are assigned three digit warn-codes. The first digit indicates whether the Warning is required to be deleted from |
|---|
| 1571 | a stored response after validation: |
|---|
| 1572 | </p> |
|---|
| 1573 | <ul> |
|---|
| 1574 | <li>1xx warn-codes describe the freshness or validation status of the response, and so <em class="bcp14">MUST</em> be deleted by a cache after validation. They can only be generated by a cache when validating a cached entry, and <em class="bcp14">MUST NOT</em> be generated in any other situation. |
|---|
| 1575 | </li> |
|---|
| 1576 | <li>2xx warn-codes describe some aspect of the representation that is not rectified by a validation (for example, a lossy compression |
|---|
| 1577 | of the representation) and <em class="bcp14">MUST NOT</em> be deleted by a cache after validation, unless a full response is sent, in which case they <em class="bcp14">MUST</em> be. |
|---|
| 1578 | </li> |
|---|
| 1579 | </ul> |
|---|
| 1580 | <p id="rfc.section.5.5.p.8">If a sender generates one or more 1xx warn-codes in a message to be sent to a recipient known to implement only HTTP/1.0, |
|---|
| 1581 | the sender <em class="bcp14">MUST</em> include in each corresponding warning-value a warn-date that matches the <a href="p2-semantics.html#header.date" class="smpl">Date</a> header field in the message. For example: |
|---|
| 1582 | </p> |
|---|
| 1583 | <div id="rfc.figure.u.14"></div><pre class="text">HTTP/1.1 200 OK |
|---|
| 1584 | Date: Sat, 25 Aug 2012 23:34:45 GMT |
|---|
| 1585 | Warning: 112 - "network down" "Sat, 25 Aug 2012 23:34:45 GMT" |
|---|
| 1586 | |
|---|
| 1587 | </pre><p id="rfc.section.5.5.p.10">If a recipient that uses, evaluates, or displays Warning header fields receives a warn-date that is different from the <a href="p2-semantics.html#header.date" class="smpl">Date</a> value in the same message, the recipient <em class="bcp14">MUST</em> exclude the warning-value containing that warn-date before storing, forwarding, or using the message. This allows recipients |
|---|
| 1588 | to exclude warning-values that were improperly retained after a cache validation. If all of the warning-values are excluded, |
|---|
| 1589 | the recipient <em class="bcp14">MUST</em> exclude the Warning header field as well. |
|---|
| 1590 | </p> |
|---|
| 1591 | <p id="rfc.section.5.5.p.11">The following warn-codes are defined by this specification, each with a recommended warn-text in English, and a description |
|---|
| 1592 | of its meaning. The procedure for defining additional warn codes is described in <a href="#warn.code.registry.procedure" title="Procedure">Section 7.2.1</a>. |
|---|
| 1593 | </p> |
|---|
| 1594 | <div id="warn.110"> |
|---|
| 1595 | <div id="rfc.iref.49"></div> |
|---|
| 1596 | <div id="rfc.iref.r.1"></div> |
|---|
| 1597 | <h3 id="rfc.section.5.5.1"><a href="#rfc.section.5.5.1">5.5.1</a> <a href="#warn.110">Warning: 110 - "Response is Stale"</a></h3> |
|---|
| 1598 | <p id="rfc.section.5.5.1.p.1">A cache <em class="bcp14">SHOULD</em> generate this whenever the sent response is stale. |
|---|
| 1599 | </p> |
|---|
| 1600 | </div> |
|---|
| 1601 | <div id="warn.111"> |
|---|
| 1602 | <div id="rfc.iref.50"></div> |
|---|
| 1603 | <div id="rfc.iref.r.2"></div> |
|---|
| 1604 | <h3 id="rfc.section.5.5.2"><a href="#rfc.section.5.5.2">5.5.2</a> <a href="#warn.111">Warning: 111 - "Revalidation Failed"</a></h3> |
|---|
| 1605 | <p id="rfc.section.5.5.2.p.1">A cache <em class="bcp14">SHOULD</em> generate this when sending a stale response because an attempt to validate the response failed, due to an inability to reach |
|---|
| 1606 | the server. |
|---|
| 1607 | </p> |
|---|
| 1608 | </div> |
|---|
| 1609 | <div id="warn.112"> |
|---|
| 1610 | <div id="rfc.iref.51"></div> |
|---|
| 1611 | <div id="rfc.iref.d.1"></div> |
|---|
| 1612 | <h3 id="rfc.section.5.5.3"><a href="#rfc.section.5.5.3">5.5.3</a> <a href="#warn.112">Warning: 112 - "Disconnected Operation"</a></h3> |
|---|
| 1613 | <p id="rfc.section.5.5.3.p.1">A cache <em class="bcp14">SHOULD</em> generate this if it is intentionally disconnected from the rest of the network for a period of time. |
|---|
| 1614 | </p> |
|---|
| 1615 | </div> |
|---|
| 1616 | <div id="warn.113"> |
|---|
| 1617 | <div id="rfc.iref.52"></div> |
|---|
| 1618 | <div id="rfc.iref.h.2"></div> |
|---|
| 1619 | <h3 id="rfc.section.5.5.4"><a href="#rfc.section.5.5.4">5.5.4</a> <a href="#warn.113">Warning: 113 - "Heuristic Expiration"</a></h3> |
|---|
| 1620 | <p id="rfc.section.5.5.4.p.1">A cache <em class="bcp14">SHOULD</em> generate this if it heuristically chose a freshness lifetime greater than 24 hours and the response's age is greater than |
|---|
| 1621 | 24 hours. |
|---|
| 1622 | </p> |
|---|
| 1623 | </div> |
|---|
| 1624 | <div id="warn.199"> |
|---|
| 1625 | <div id="rfc.iref.53"></div> |
|---|
| 1626 | <div id="rfc.iref.m.6"></div> |
|---|
| 1627 | <h3 id="rfc.section.5.5.5"><a href="#rfc.section.5.5.5">5.5.5</a> <a href="#warn.199">Warning: 199 - "Miscellaneous Warning"</a></h3> |
|---|
| 1628 | <p id="rfc.section.5.5.5.p.1">The warning text can include arbitrary information to be presented to a human user, or logged. A system receiving this warning <em class="bcp14">MUST NOT</em> take any automated action, besides presenting the warning to the user. |
|---|
| 1629 | </p> |
|---|
| 1630 | </div> |
|---|
| 1631 | <div id="warn.214"> |
|---|
| 1632 | <div id="rfc.iref.54"></div> |
|---|
| 1633 | <div id="rfc.iref.t.1"></div> |
|---|
| 1634 | <h3 id="rfc.section.5.5.6"><a href="#rfc.section.5.5.6">5.5.6</a> <a href="#warn.214">Warning: 214 - "Transformation Applied"</a></h3> |
|---|
| 1635 | <p id="rfc.section.5.5.6.p.1"><em class="bcp14">MUST</em> be added by a proxy if it applies any transformation to the representation, such as changing the content-coding, media-type, |
|---|
| 1636 | or modifying the representation data, unless this Warning code already appears in the response. |
|---|
| 1637 | </p> |
|---|
| 1638 | </div> |
|---|
| 1639 | <div id="warn.299"> |
|---|
| 1640 | <div id="rfc.iref.55"></div> |
|---|
| 1641 | <div id="rfc.iref.m.7"></div> |
|---|
| 1642 | <h3 id="rfc.section.5.5.7"><a href="#rfc.section.5.5.7">5.5.7</a> <a href="#warn.299">Warning: 299 - "Miscellaneous Persistent Warning"</a></h3> |
|---|
| 1643 | <p id="rfc.section.5.5.7.p.1">The warning text can include arbitrary information to be presented to a human user, or logged. A system receiving this warning <em class="bcp14">MUST NOT</em> take any automated action. |
|---|
| 1644 | </p> |
|---|
| 1645 | </div> |
|---|
| 1646 | </div> |
|---|
| 1647 | </div> |
|---|
| 1648 | <div id="history.lists"> |
|---|
| 1649 | <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a> <a href="#history.lists">History Lists</a></h1> |
|---|
| 1650 | <p id="rfc.section.6.p.1">User agents often have history mechanisms, such as "Back" buttons and history lists, that can be used to redisplay a representation |
|---|
| 1651 | retrieved earlier in a session. |
|---|
| 1652 | </p> |
|---|
| 1653 | <p id="rfc.section.6.p.2">The freshness model (<a href="#expiration.model" title="Freshness">Section 4.2</a>) does not necessarily apply to history mechanisms. I.e., a history mechanism can display a previous representation even if |
|---|
| 1654 | it has expired. |
|---|
| 1655 | </p> |
|---|
| 1656 | <p id="rfc.section.6.p.3">This does not prohibit the history mechanism from telling the user that a view might be stale, or from honoring cache directives |
|---|
| 1657 | (e.g., Cache-Control: no-store). |
|---|
| 1658 | </p> |
|---|
| 1659 | </div> |
|---|
| 1660 | <div id="iana.considerations"> |
|---|
| 1661 | <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a> <a href="#iana.considerations">IANA Considerations</a></h1> |
|---|
| 1662 | <div id="cache.directive.registry"> |
|---|
| 1663 | <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a> <a href="#cache.directive.registry">Cache Directive Registry</a></h2> |
|---|
| 1664 | <p id="rfc.section.7.1.p.1">The HTTP Cache Directive Registry defines the name space for the cache directives. It will be created and maintained at (the |
|---|
| 1665 | suggested URI) <<a href="http://www.iana.org/assignments/http-cache-directives">http://www.iana.org/assignments/http-cache-directives</a>>. |
|---|
| 1666 | </p> |
|---|
| 1667 | <div id="cache.directive.registry.procedure"> |
|---|
| 1668 | <h3 id="rfc.section.7.1.1"><a href="#rfc.section.7.1.1">7.1.1</a> <a href="#cache.directive.registry.procedure">Procedure</a></h3> |
|---|
| 1669 | <p id="rfc.section.7.1.1.p.1">A registration <em class="bcp14">MUST</em> include the following fields: |
|---|
| 1670 | </p> |
|---|
| 1671 | <ul> |
|---|
| 1672 | <li>Cache Directive Name</li> |
|---|
| 1673 | <li>Pointer to specification text</li> |
|---|
| 1674 | </ul> |
|---|
| 1675 | <p id="rfc.section.7.1.1.p.2">Values to be added to this name space require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.1"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>). |
|---|
| 1676 | </p> |
|---|
| 1677 | </div> |
|---|
| 1678 | <div id="cache.directive.considerations"> |
|---|
| 1679 | <h3 id="rfc.section.7.1.2"><a href="#rfc.section.7.1.2">7.1.2</a> <a href="#cache.directive.considerations">Considerations for New Cache Control Directives</a></h3> |
|---|
| 1680 | <p id="rfc.section.7.1.2.p.1">New extension directives ought to consider defining:</p> |
|---|
| 1681 | <p id="rfc.section.7.1.2.p.2"></p> |
|---|
| 1682 | <ul> |
|---|
| 1683 | <li>What it means for a directive to be specified multiple times,</li> |
|---|
| 1684 | <li>When the directive does not take an argument, what it means when an argument is present,</li> |
|---|
| 1685 | <li>When the directive requires an argument, what it means when it is missing,</li> |
|---|
| 1686 | <li>Whether the directive is specific to requests, responses, or able to be used in either.</li> |
|---|
| 1687 | </ul> |
|---|
| 1688 | <p id="rfc.section.7.1.2.p.3">See also <a href="#cache.control.extensions" title="Cache Control Extensions">Section 5.2.3</a>. |
|---|
| 1689 | </p> |
|---|
| 1690 | </div> |
|---|
| 1691 | <div id="cache.directive.registration"> |
|---|
| 1692 | <h3 id="rfc.section.7.1.3"><a href="#rfc.section.7.1.3">7.1.3</a> <a href="#cache.directive.registration">Registrations</a></h3> |
|---|
| 1693 | <p id="rfc.section.7.1.3.p.1">The HTTP Cache Directive Registry shall be populated with the registrations below:</p> |
|---|
| 1694 | <div id="rfc.table.1"> |
|---|
| 1695 | <div id="iana.cache.directive.registration.table"></div> |
|---|
| 1696 | <table class="tt full left" cellpadding="3" cellspacing="0"> |
|---|
| 1697 | <thead> |
|---|
| 1698 | <tr> |
|---|
| 1699 | <th>Cache Directive</th> |
|---|
| 1700 | <th>Reference</th> |
|---|
| 1701 | </tr> |
|---|
| 1702 | </thead> |
|---|
| 1703 | <tbody> |
|---|
| 1704 | <tr> |
|---|
| 1705 | <td class="left">max-age</td> |
|---|
| 1706 | <td class="left"><a href="#cache-request-directive.max-age" title="max-age">Section 5.2.1.1</a>, <a href="#cache-response-directive.max-age" title="max-age">Section 5.2.2.8</a> |
|---|
| 1707 | </td> |
|---|
| 1708 | </tr> |
|---|
| 1709 | <tr> |
|---|
| 1710 | <td class="left">max-stale</td> |
|---|
| 1711 | <td class="left"><a href="#cache-request-directive.max-stale" title="max-stale">Section 5.2.1.2</a> |
|---|
| 1712 | </td> |
|---|
| 1713 | </tr> |
|---|
| 1714 | <tr> |
|---|
| 1715 | <td class="left">min-fresh</td> |
|---|
| 1716 | <td class="left"><a href="#cache-request-directive.min-fresh" title="min-fresh">Section 5.2.1.3</a> |
|---|
| 1717 | </td> |
|---|
| 1718 | </tr> |
|---|
| 1719 | <tr> |
|---|
| 1720 | <td class="left">must-revalidate</td> |
|---|
| 1721 | <td class="left"><a href="#cache-response-directive.must-revalidate" title="must-revalidate">Section 5.2.2.1</a> |
|---|
| 1722 | </td> |
|---|
| 1723 | </tr> |
|---|
| 1724 | <tr> |
|---|
| 1725 | <td class="left">no-cache</td> |
|---|
| 1726 | <td class="left"><a href="#cache-request-directive.no-cache" title="no-cache">Section 5.2.1.4</a>, <a href="#cache-response-directive.no-cache" title="no-cache">Section 5.2.2.2</a> |
|---|
| 1727 | </td> |
|---|
| 1728 | </tr> |
|---|
| 1729 | <tr> |
|---|
| 1730 | <td class="left">no-store</td> |
|---|
| 1731 | <td class="left"><a href="#cache-request-directive.no-store" title="no-store">Section 5.2.1.5</a>, <a href="#cache-response-directive.no-store" title="no-store">Section 5.2.2.3</a> |
|---|
| 1732 | </td> |
|---|
| 1733 | </tr> |
|---|
| 1734 | <tr> |
|---|
| 1735 | <td class="left">no-transform</td> |
|---|
| 1736 | <td class="left"><a href="#cache-request-directive.no-transform" title="no-transform">Section 5.2.1.6</a>, <a href="#cache-response-directive.no-transform" title="no-transform">Section 5.2.2.4</a> |
|---|
| 1737 | </td> |
|---|
| 1738 | </tr> |
|---|
| 1739 | <tr> |
|---|
| 1740 | <td class="left">only-if-cached</td> |
|---|
| 1741 | <td class="left"><a href="#cache-request-directive.only-if-cached" title="only-if-cached">Section 5.2.1.7</a> |
|---|
| 1742 | </td> |
|---|
| 1743 | </tr> |
|---|
| 1744 | <tr> |
|---|
| 1745 | <td class="left">private</td> |
|---|
| 1746 | <td class="left"><a href="#cache-response-directive.private" title="private">Section 5.2.2.6</a> |
|---|
| 1747 | </td> |
|---|
| 1748 | </tr> |
|---|
| 1749 | <tr> |
|---|
| 1750 | <td class="left">proxy-revalidate</td> |
|---|
| 1751 | <td class="left"><a href="#cache-response-directive.proxy-revalidate" title="proxy-revalidate">Section 5.2.2.7</a> |
|---|
| 1752 | </td> |
|---|
| 1753 | </tr> |
|---|
| 1754 | <tr> |
|---|
| 1755 | <td class="left">public</td> |
|---|
| 1756 | <td class="left"><a href="#cache-response-directive.public" title="public">Section 5.2.2.5</a> |
|---|
| 1757 | </td> |
|---|
| 1758 | </tr> |
|---|
| 1759 | <tr> |
|---|
| 1760 | <td class="left">s-maxage</td> |
|---|
| 1761 | <td class="left"><a href="#cache-response-directive.s-maxage" title="s-maxage">Section 5.2.2.9</a> |
|---|
| 1762 | </td> |
|---|
| 1763 | </tr> |
|---|
| 1764 | <tr> |
|---|
| 1765 | <td class="left">stale-if-error</td> |
|---|
| 1766 | <td class="left"><a href="#RFC5861" id="rfc.xref.RFC5861.1"><cite title="HTTP Cache-Control Extensions for Stale Content">[RFC5861]</cite></a>, <a href="http://tools.ietf.org/html/rfc5861#section-4">Section 4</a> |
|---|
| 1767 | </td> |
|---|
| 1768 | </tr> |
|---|
| 1769 | <tr> |
|---|
| 1770 | <td class="left">stale-while-revalidate</td> |
|---|
| 1771 | <td class="left"><a href="#RFC5861" id="rfc.xref.RFC5861.2"><cite title="HTTP Cache-Control Extensions for Stale Content">[RFC5861]</cite></a>, <a href="http://tools.ietf.org/html/rfc5861#section-3">Section 3</a> |
|---|
| 1772 | </td> |
|---|
| 1773 | </tr> |
|---|
| 1774 | </tbody> |
|---|
| 1775 | </table> |
|---|
| 1776 | </div> |
|---|
| 1777 | </div> |
|---|
| 1778 | </div> |
|---|
| 1779 | <div id="warn.code.registry"> |
|---|
| 1780 | <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a> <a href="#warn.code.registry">Warn Code Registry</a></h2> |
|---|
| 1781 | <p id="rfc.section.7.2.p.1">The HTTP Warn Code Registry defines the name space for warn codes. It will be created and maintained at (the suggested URI) <<a href="http://www.iana.org/assignments/http-warn-codes">http://www.iana.org/assignments/http-warn-codes</a>>. |
|---|
| 1782 | </p> |
|---|
| 1783 | <div id="warn.code.registry.procedure"> |
|---|
| 1784 | <h3 id="rfc.section.7.2.1"><a href="#rfc.section.7.2.1">7.2.1</a> <a href="#warn.code.registry.procedure">Procedure</a></h3> |
|---|
| 1785 | <p id="rfc.section.7.2.1.p.1">A registration <em class="bcp14">MUST</em> include the following fields: |
|---|
| 1786 | </p> |
|---|
| 1787 | <ul> |
|---|
| 1788 | <li>Warn Code (3 digits)</li> |
|---|
| 1789 | <li>Short Description</li> |
|---|
| 1790 | <li>Pointer to specification text</li> |
|---|
| 1791 | </ul> |
|---|
| 1792 | <p id="rfc.section.7.2.1.p.2">Values to be added to this name space require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.2"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>). |
|---|
| 1793 | </p> |
|---|
| 1794 | </div> |
|---|
| 1795 | <div id="warn.code.registration"> |
|---|
| 1796 | <h3 id="rfc.section.7.2.2"><a href="#rfc.section.7.2.2">7.2.2</a> <a href="#warn.code.registration">Registrations</a></h3> |
|---|
| 1797 | <p id="rfc.section.7.2.2.p.1">The HTTP Warn Code Registry shall be populated with the registrations below:</p> |
|---|
| 1798 | <div id="rfc.table.2"> |
|---|
| 1799 | <div id="iana.warn.code.registration.table"></div> |
|---|
| 1800 | <table class="tt full left" cellpadding="3" cellspacing="0"> |
|---|
| 1801 | <thead> |
|---|
| 1802 | <tr> |
|---|
| 1803 | <th>Warn Code</th> |
|---|
| 1804 | <th>Short Description</th> |
|---|
| 1805 | <th>Reference</th> |
|---|
| 1806 | </tr> |
|---|
| 1807 | </thead> |
|---|
| 1808 | <tbody> |
|---|
| 1809 | <tr> |
|---|
| 1810 | <td class="left">110</td> |
|---|
| 1811 | <td class="left">Response is Stale</td> |
|---|
| 1812 | <td class="left"><a href="#warn.110" id="rfc.xref.warn.110.2" title="Warning: 110 - "Response is Stale"">Section 5.5.1</a> |
|---|
| 1813 | </td> |
|---|
| 1814 | </tr> |
|---|
| 1815 | <tr> |
|---|
| 1816 | <td class="left">111</td> |
|---|
| 1817 | <td class="left">Revalidation Failed</td> |
|---|
| 1818 | <td class="left"><a href="#warn.111" id="rfc.xref.warn.111.1" title="Warning: 111 - "Revalidation Failed"">Section 5.5.2</a> |
|---|
| 1819 | </td> |
|---|
| 1820 | </tr> |
|---|
| 1821 | <tr> |
|---|
| 1822 | <td class="left">112</td> |
|---|
| 1823 | <td class="left">Disconnected Operation</td> |
|---|
| 1824 | <td class="left"><a href="#warn.112" id="rfc.xref.warn.112.2" title="Warning: 112 - "Disconnected Operation"">Section 5.5.3</a> |
|---|
| 1825 | </td> |
|---|
| 1826 | </tr> |
|---|
| 1827 | <tr> |
|---|
| 1828 | <td class="left">113</td> |
|---|
| 1829 | <td class="left">Heuristic Expiration</td> |
|---|
| 1830 | <td class="left"><a href="#warn.113" id="rfc.xref.warn.113.2" title="Warning: 113 - "Heuristic Expiration"">Section 5.5.4</a> |
|---|
| 1831 | </td> |
|---|
| 1832 | </tr> |
|---|
| 1833 | <tr> |
|---|
| 1834 | <td class="left">199</td> |
|---|
| 1835 | <td class="left">Miscellaneous Warning</td> |
|---|
| 1836 | <td class="left"><a href="#warn.199" id="rfc.xref.warn.199.1" title="Warning: 199 - "Miscellaneous Warning"">Section 5.5.5</a> |
|---|
| 1837 | </td> |
|---|
| 1838 | </tr> |
|---|
| 1839 | <tr> |
|---|
| 1840 | <td class="left">214</td> |
|---|
| 1841 | <td class="left">Transformation Applied</td> |
|---|
| 1842 | <td class="left"><a href="#warn.214" id="rfc.xref.warn.214.1" title="Warning: 214 - "Transformation Applied"">Section 5.5.6</a> |
|---|
| 1843 | </td> |
|---|
| 1844 | </tr> |
|---|
| 1845 | <tr> |
|---|
| 1846 | <td class="left">299</td> |
|---|
| 1847 | <td class="left">Miscellaneous Persistent Warning</td> |
|---|
| 1848 | <td class="left"><a href="#warn.299" id="rfc.xref.warn.299.1" title="Warning: 299 - "Miscellaneous Persistent Warning"">Section 5.5.7</a> |
|---|
| 1849 | </td> |
|---|
| 1850 | </tr> |
|---|
| 1851 | </tbody> |
|---|
| 1852 | </table> |
|---|
| 1853 | </div> |
|---|
| 1854 | </div> |
|---|
| 1855 | </div> |
|---|
| 1856 | <div id="header.field.registration"> |
|---|
| 1857 | <h2 id="rfc.section.7.3"><a href="#rfc.section.7.3">7.3</a> <a href="#header.field.registration">Header Field Registration</a></h2> |
|---|
| 1858 | <p id="rfc.section.7.3.p.1">HTTP header fields are registered within the Message Header Field Registry maintained at <<a href="http://www.iana.org/assignments/message-headers/message-header-index.html">http://www.iana.org/assignments/message-headers/message-header-index.html</a>>. |
|---|
| 1859 | </p> |
|---|
| 1860 | <p id="rfc.section.7.3.p.2">This document defines the following HTTP header fields, so their associated registry entries shall be updated according to |
|---|
| 1861 | the permanent registrations below (see <a href="#BCP90" id="rfc.xref.BCP90.1"><cite title="Registration Procedures for Message Header Fields">[BCP90]</cite></a>): |
|---|
| 1862 | </p> |
|---|
| 1863 | <div id="rfc.table.3"> |
|---|
| 1864 | <div id="iana.header.registration.table"></div> |
|---|
| 1865 | <table class="tt full left" cellpadding="3" cellspacing="0"> |
|---|
| 1866 | <thead> |
|---|
| 1867 | <tr> |
|---|
| 1868 | <th>Header Field Name</th> |
|---|
| 1869 | <th>Protocol</th> |
|---|
| 1870 | <th>Status</th> |
|---|
| 1871 | <th>Reference</th> |
|---|
| 1872 | </tr> |
|---|
| 1873 | </thead> |
|---|
| 1874 | <tbody> |
|---|
| 1875 | <tr> |
|---|
| 1876 | <td class="left">Age</td> |
|---|
| 1877 | <td class="left">http</td> |
|---|
| 1878 | <td class="left">standard</td> |
|---|
| 1879 | <td class="left"><a href="#header.age" id="rfc.xref.header.age.3" title="Age">Section 5.1</a> |
|---|
| 1880 | </td> |
|---|
| 1881 | </tr> |
|---|
| 1882 | <tr> |
|---|
| 1883 | <td class="left">Cache-Control</td> |
|---|
| 1884 | <td class="left">http</td> |
|---|
| 1885 | <td class="left">standard</td> |
|---|
| 1886 | <td class="left"><a href="#header.cache-control" id="rfc.xref.header.cache-control.2" title="Cache-Control">Section 5.2</a> |
|---|
| 1887 | </td> |
|---|
| 1888 | </tr> |
|---|
| 1889 | <tr> |
|---|
| 1890 | <td class="left">Expires</td> |
|---|
| 1891 | <td class="left">http</td> |
|---|
| 1892 | <td class="left">standard</td> |
|---|
| 1893 | <td class="left"><a href="#header.expires" id="rfc.xref.header.expires.4" title="Expires">Section 5.3</a> |
|---|
| 1894 | </td> |
|---|
| 1895 | </tr> |
|---|
| 1896 | <tr> |
|---|
| 1897 | <td class="left">Pragma</td> |
|---|
| 1898 | <td class="left">http</td> |
|---|
| 1899 | <td class="left">standard</td> |
|---|
| 1900 | <td class="left"><a href="#header.pragma" id="rfc.xref.header.pragma.2" title="Pragma">Section 5.4</a> |
|---|
| 1901 | </td> |
|---|
| 1902 | </tr> |
|---|
| 1903 | <tr> |
|---|
| 1904 | <td class="left">Warning</td> |
|---|
| 1905 | <td class="left">http</td> |
|---|
| 1906 | <td class="left">standard</td> |
|---|
| 1907 | <td class="left"><a href="#header.warning" id="rfc.xref.header.warning.4" title="Warning">Section 5.5</a> |
|---|
| 1908 | </td> |
|---|
| 1909 | </tr> |
|---|
| 1910 | </tbody> |
|---|
| 1911 | </table> |
|---|
| 1912 | </div> |
|---|
| 1913 | <p id="rfc.section.7.3.p.3">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p> |
|---|
| 1914 | </div> |
|---|
| 1915 | </div> |
|---|
| 1916 | <div id="security.considerations"> |
|---|
| 1917 | <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a> <a href="#security.considerations">Security Considerations</a></h1> |
|---|
| 1918 | <p id="rfc.section.8.p.1">This section is meant to inform developers, information providers, and users of known security concerns specific to HTTP/1.1 |
|---|
| 1919 | caching. More general security considerations are addressed in HTTP messaging <a href="#Part1" id="rfc.xref.Part1.11"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a> and semantics <a href="#Part2" id="rfc.xref.Part2.8"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[Part2]</cite></a>. |
|---|
| 1920 | </p> |
|---|
| 1921 | <p id="rfc.section.8.p.2">Caches expose additional potential vulnerabilities, since the contents of the cache represent an attractive target for malicious |
|---|
| 1922 | exploitation. Because cache contents persist after an HTTP request is complete, an attack on the cache can reveal information |
|---|
| 1923 | long after a user believes that the information has been removed from the network. Therefore, cache contents need to be protected |
|---|
| 1924 | as sensitive information. |
|---|
| 1925 | </p> |
|---|
| 1926 | <p id="rfc.section.8.p.3">Furthermore, the very use of a cache can bring about privacy concerns. For example, if two users share a cache, and the first |
|---|
| 1927 | one browses to a site, the second may be able to detect that the other has been to that site, because the resources from it |
|---|
| 1928 | load more quickly, thanks to the cache. |
|---|
| 1929 | </p> |
|---|
| 1930 | <p id="rfc.section.8.p.4">Implementation flaws might allow attackers to insert content into a cache ("cache poisoning"), leading to compromise of clients |
|---|
| 1931 | that trust that content. Because of their nature, these attacks are difficult to mitigate. |
|---|
| 1932 | </p> |
|---|
| 1933 | <p id="rfc.section.8.p.5">Likewise, implementation flaws (as well as misunderstanding of cache operation) might lead to caching of sensitive information |
|---|
| 1934 | (e.g., authentication credentials) that is thought to be private, exposing it to unauthorized parties. |
|---|
| 1935 | </p> |
|---|
| 1936 | <p id="rfc.section.8.p.6">Note that the Set-Cookie response header field <a href="#RFC6265" id="rfc.xref.RFC6265.1"><cite title="HTTP State Management Mechanism">[RFC6265]</cite></a> does not inhibit caching; a cacheable response with a Set-Cookie header field can be (and often is) used to satisfy subsequent |
|---|
| 1937 | requests to caches. Servers who wish to control caching of these responses are encouraged to emit appropriate Cache-Control |
|---|
| 1938 | response header fields. |
|---|
| 1939 | </p> |
|---|
| 1940 | </div> |
|---|
| 1941 | <div id="acks"> |
|---|
| 1942 | <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a> <a href="#acks">Acknowledgments</a></h1> |
|---|
| 1943 | <p id="rfc.section.9.p.1">See <a href="p1-messaging.html#acks" title="Acknowledgments">Section 10</a> of <a href="#Part1" id="rfc.xref.Part1.12"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>. |
|---|
| 1944 | </p> |
|---|
| 1945 | </div> |
|---|
| 1946 | <h1 id="rfc.references"><a id="rfc.section.10" href="#rfc.section.10">10.</a> References |
|---|
| 1947 | </h1> |
|---|
| 1948 | <h2 id="rfc.references.1"><a href="#rfc.section.10.1" id="rfc.section.10.1">10.1</a> Normative References |
|---|
| 1949 | </h2> |
|---|
| 1950 | <table> |
|---|
| 1951 | <tr> |
|---|
| 1952 | <td class="reference"><b id="Part1">[Part1]</b></td> |
|---|
| 1953 | <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a> and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-latest">Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</a>”, Internet-Draft draft-ietf-httpbis-p1-messaging-latest (work in progress), October 2013. |
|---|
| 1954 | </td> |
|---|
| 1955 | </tr> |
|---|
| 1956 | <tr> |
|---|
| 1957 | <td class="reference"><b id="Part2">[Part2]</b></td> |
|---|
| 1958 | <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a> and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-latest">Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</a>”, Internet-Draft draft-ietf-httpbis-p2-semantics-latest (work in progress), October 2013. |
|---|
| 1959 | </td> |
|---|
| 1960 | </tr> |
|---|
| 1961 | <tr> |
|---|
| 1962 | <td class="reference"><b id="Part4">[Part4]</b></td> |
|---|
| 1963 | <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a> and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p4-conditional-latest">Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</a>”, Internet-Draft draft-ietf-httpbis-p4-conditional-latest (work in progress), October 2013. |
|---|
| 1964 | </td> |
|---|
| 1965 | </tr> |
|---|
| 1966 | <tr> |
|---|
| 1967 | <td class="reference"><b id="Part5">[Part5]</b></td> |
|---|
| 1968 | <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p5-range-latest">Hypertext Transfer Protocol (HTTP/1.1): Range Requests</a>”, Internet-Draft draft-ietf-httpbis-p5-range-latest (work in progress), October 2013. |
|---|
| 1969 | </td> |
|---|
| 1970 | </tr> |
|---|
| 1971 | <tr> |
|---|
| 1972 | <td class="reference"><b id="Part7">[Part7]</b></td> |
|---|
| 1973 | <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a> and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p7-auth-latest">Hypertext Transfer Protocol (HTTP/1.1): Authentication</a>”, Internet-Draft draft-ietf-httpbis-p7-auth-latest (work in progress), October 2013. |
|---|
| 1974 | </td> |
|---|
| 1975 | </tr> |
|---|
| 1976 | <tr> |
|---|
| 1977 | <td class="reference"><b id="RFC2119">[RFC2119]</b></td> |
|---|
| 1978 | <td class="top"><a href="mailto:sob@harvard.edu" title="Harvard University">Bradner, S.</a>, “<a href="http://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>”, BCP 14, RFC 2119, March 1997. |
|---|
| 1979 | </td> |
|---|
| 1980 | </tr> |
|---|
| 1981 | <tr> |
|---|
| 1982 | <td class="reference"><b id="RFC5234">[RFC5234]</b></td> |
|---|
| 1983 | <td class="top"><a href="mailto:dcrocker@bbiw.net" title="Brandenburg InternetWorking">Crocker, D., Ed.</a> and <a href="mailto:paul.overell@thus.net" title="THUS plc.">P. Overell</a>, “<a href="http://tools.ietf.org/html/rfc5234">Augmented BNF for Syntax Specifications: ABNF</a>”, STD 68, RFC 5234, January 2008. |
|---|
| 1984 | </td> |
|---|
| 1985 | </tr> |
|---|
| 1986 | </table> |
|---|
| 1987 | <h2 id="rfc.references.2"><a href="#rfc.section.10.2" id="rfc.section.10.2">10.2</a> Informative References |
|---|
| 1988 | </h2> |
|---|
| 1989 | <table> |
|---|
| 1990 | <tr> |
|---|
| 1991 | <td class="reference"><b id="BCP90">[BCP90]</b></td> |
|---|
| 1992 | <td class="top"><a href="mailto:GK-IETF@ninebynine.org" title="Nine by Nine">Klyne, G.</a>, <a href="mailto:mnot@pobox.com" title="BEA Systems">Nottingham, M.</a>, and <a href="mailto:JeffMogul@acm.org" title="HP Labs">J. Mogul</a>, “<a href="http://tools.ietf.org/html/rfc3864">Registration Procedures for Message Header Fields</a>”, BCP 90, RFC 3864, September 2004. |
|---|
| 1993 | </td> |
|---|
| 1994 | </tr> |
|---|
| 1995 | <tr> |
|---|
| 1996 | <td class="reference"><b id="RFC2616">[RFC2616]</b></td> |
|---|
| 1997 | <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="W3C">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Compaq Computer Corporation">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Frystyk, H.</a>, <a href="mailto:masinter@parc.xerox.com" title="Xerox Corporation">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" title="W3C">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/rfc2616">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC 2616, June 1999. |
|---|
| 1998 | </td> |
|---|
| 1999 | </tr> |
|---|
| 2000 | <tr> |
|---|
| 2001 | <td class="reference"><b id="RFC5226">[RFC5226]</b></td> |
|---|
| 2002 | <td class="top"><a href="mailto:narten@us.ibm.com" title="IBM">Narten, T.</a> and <a href="mailto:Harald@Alvestrand.no" title="Google">H. Alvestrand</a>, “<a href="http://tools.ietf.org/html/rfc5226">Guidelines for Writing an IANA Considerations Section in RFCs</a>”, BCP 26, RFC 5226, May 2008. |
|---|
| 2003 | </td> |
|---|
| 2004 | </tr> |
|---|
| 2005 | <tr> |
|---|
| 2006 | <td class="reference"><b id="RFC5861">[RFC5861]</b></td> |
|---|
| 2007 | <td class="top"><a href="mailto:mnot@yahoo-inc.com" title="Yahoo! Inc.">Nottingham, M.</a>, “<a href="http://tools.ietf.org/html/rfc5861">HTTP Cache-Control Extensions for Stale Content</a>”, RFC 5861, April 2010. |
|---|
| 2008 | </td> |
|---|
| 2009 | </tr> |
|---|
| 2010 | <tr> |
|---|
| 2011 | <td class="reference"><b id="RFC5905">[RFC5905]</b></td> |
|---|
| 2012 | <td class="top">Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, “<a href="http://tools.ietf.org/html/rfc5905">Network Time Protocol Version 4: Protocol and Algorithms Specification</a>”, RFC 5905, June 2010. |
|---|
| 2013 | </td> |
|---|
| 2014 | </tr> |
|---|
| 2015 | <tr> |
|---|
| 2016 | <td class="reference"><b id="RFC6265">[RFC6265]</b></td> |
|---|
| 2017 | <td class="top"><a href="mailto:abarth@eecs.berkeley.edu" title="
 University of California, Berkeley
 ">Barth, A.</a>, “<a href="http://tools.ietf.org/html/rfc6265">HTTP State Management Mechanism</a>”, RFC 6265, April 2011. |
|---|
| 2018 | </td> |
|---|
| 2019 | </tr> |
|---|
| 2020 | </table> |
|---|
| 2021 | <div class="avoidbreak"> |
|---|
| 2022 | <h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1> |
|---|
| 2023 | <p><b>Roy T. Fielding</b> |
|---|
| 2024 | (editor) |
|---|
| 2025 | <br>Adobe Systems Incorporated<br>345 Park Ave<br>San Jose, CA 95110<br>USA<br>Email: <a href="mailto:fielding@gbiv.com">fielding@gbiv.com</a><br>URI: <a href="http://roy.gbiv.com/">http://roy.gbiv.com/</a></p> |
|---|
| 2026 | <p><b>Mark Nottingham</b> |
|---|
| 2027 | (editor) |
|---|
| 2028 | <br>Akamai<br>Email: <a href="mailto:mnot@mnot.net">mnot@mnot.net</a><br>URI: <a href="http://www.mnot.net/">http://www.mnot.net/</a></p> |
|---|
| 2029 | <p><b>Julian F. Reschke</b> |
|---|
| 2030 | (editor) |
|---|
| 2031 | <br>greenbytes GmbH<br>Hafenweg 16<br>Muenster, NW 48155<br>Germany<br>Email: <a href="mailto:julian.reschke@greenbytes.de">julian.reschke@greenbytes.de</a><br>URI: <a href="http://greenbytes.de/tech/webdav/">http://greenbytes.de/tech/webdav/</a></p> |
|---|
| 2032 | </div> |
|---|
| 2033 | <div id="changes.from.rfc.2616"> |
|---|
| 2034 | <h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a> <a href="#changes.from.rfc.2616">Changes from RFC 2616</a></h1> |
|---|
| 2035 | <p id="rfc.section.A.p.1">The specification has been substantially rewritten for clarity.</p> |
|---|
| 2036 | <p id="rfc.section.A.p.2">The conditions under which an authenticated response can be cached have been clarified. (<a href="#caching.authenticated.responses" title="Storing Responses to Authenticated Requests">Section 3.2</a>) |
|---|
| 2037 | </p> |
|---|
| 2038 | <p id="rfc.section.A.p.3">New status codes can now define that caches are allowed to use heuristic freshness with them. Caches are now allowed to calculate |
|---|
| 2039 | heuristic freshness for URIs with query components. (<a href="#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a>) |
|---|
| 2040 | </p> |
|---|
| 2041 | <p id="rfc.section.A.p.4">The algorithm for calculating age is now less conservative. Caches are now required to handle dates with timezones as if they're |
|---|
| 2042 | invalid, because it's not possible to accurately guess. (<a href="#age.calculations" title="Calculating Age">Section 4.2.3</a>) |
|---|
| 2043 | </p> |
|---|
| 2044 | <p id="rfc.section.A.p.5">The <a href="p2-semantics.html#header.content-location" class="smpl">Content-Location</a> response header field is no longer used to determine the appropriate response to use when validating. (<a href="#validation.model" title="Validation">Section 4.3</a>) |
|---|
| 2045 | </p> |
|---|
| 2046 | <p id="rfc.section.A.p.6">The algorithm for selecting a cached negotiated response to use has been clarified in several ways. In particular, it now |
|---|
| 2047 | explicitly allows header-specific canonicalization when processing selecting header fields. (<a href="#caching.negotiated.responses" title="Calculating Secondary Keys with Vary">Section 4.1</a>) |
|---|
| 2048 | </p> |
|---|
| 2049 | <p id="rfc.section.A.p.7">Requirements regarding denial of service attack avoidance when performing invalidation have been clarified. (<a href="#invalidation" title="Invalidation">Section 4.4</a>) |
|---|
| 2050 | </p> |
|---|
| 2051 | <p id="rfc.section.A.p.8">Cache invalidation only occurs when a successful response is received. (<a href="#invalidation" title="Invalidation">Section 4.4</a>) |
|---|
| 2052 | </p> |
|---|
| 2053 | <p id="rfc.section.A.p.9">Cache directives are explicitly defined to be case-insensitive. Handling of multiple instances of cache directives when only |
|---|
| 2054 | one is expected is now defined. (<a href="#header.cache-control" id="rfc.xref.header.cache-control.3" title="Cache-Control">Section 5.2</a>) |
|---|
| 2055 | </p> |
|---|
| 2056 | <p id="rfc.section.A.p.10">The "no-store" cache request directive doesn't apply to responses; i.e., a cache can satisfy a request with no-store on it, |
|---|
| 2057 | and does not invalidate it. (<a href="#cache-request-directive.no-store" title="no-store">Section 5.2.1.5</a>) |
|---|
| 2058 | </p> |
|---|
| 2059 | <p id="rfc.section.A.p.11">The qualified forms of the private and no-cache cache directives are noted to not be widely implemented; e.g., "private=foo" |
|---|
| 2060 | is interpreted by many caches as simply "private". Additionally, the meaning of the qualified form of no-cache has been clarified. |
|---|
| 2061 | (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section 5.2.2</a>) |
|---|
| 2062 | </p> |
|---|
| 2063 | <p id="rfc.section.A.p.12">The "no-cache" response cache directive's meaning has been clarified. (<a href="#cache-response-directive.no-cache" title="no-cache">Section 5.2.2.2</a>) |
|---|
| 2064 | </p> |
|---|
| 2065 | <p id="rfc.section.A.p.13">The one-year limit on <a href="#header.expires" class="smpl">Expires</a> header field values has been removed; instead, the reasoning for using a sensible value is given. (<a href="#header.expires" id="rfc.xref.header.expires.5" title="Expires">Section 5.3</a>) |
|---|
| 2066 | </p> |
|---|
| 2067 | <p id="rfc.section.A.p.14">The <a href="#header.pragma" class="smpl">Pragma</a> header field is now only defined for backwards compatibility; future pragmas are deprecated. (<a href="#header.pragma" id="rfc.xref.header.pragma.3" title="Pragma">Section 5.4</a>) |
|---|
| 2068 | </p> |
|---|
| 2069 | <p id="rfc.section.A.p.15">Some requirements regarding production and processing of the <a href="#header.warning" class="smpl">Warning</a> header fields have been relaxed, as it is not widely implemented. Furthermore, the <a href="#header.warning" class="smpl">Warning</a> header field no longer uses RFC 2047 encoding, nor allows multiple languages, as these aspects were not implemented. (<a href="#header.warning" id="rfc.xref.header.warning.5" title="Warning">Section 5.5</a>) |
|---|
| 2070 | </p> |
|---|
| 2071 | <p id="rfc.section.A.p.16">This specification introduces the Cache Directive and Warn Code Registries, and defines considerations for new cache directives. |
|---|
| 2072 | (<a href="#cache.directive.registry" title="Cache Directive Registry">Section 7.1</a> and <a href="#warn.code.registry" title="Warn Code Registry">Section 7.2</a>) |
|---|
| 2073 | </p> |
|---|
| 2074 | </div> |
|---|
| 2075 | <div id="imported.abnf"> |
|---|
| 2076 | <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a> <a href="#imported.abnf">Imported ABNF</a></h1> |
|---|
| 2077 | <p id="rfc.section.B.p.1">The following core rules are included by reference, as defined in <a href="http://tools.ietf.org/html/rfc5234#appendix-B.1">Appendix B.1</a> of <a href="#RFC5234" id="rfc.xref.RFC5234.2"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>: ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), HEXDIG |
|---|
| 2078 | (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit sequence of data), SP (space), and VCHAR (any visible US-ASCII |
|---|
| 2079 | character). |
|---|
| 2080 | </p> |
|---|
| 2081 | <p id="rfc.section.B.p.2">The rules below are defined in <a href="#Part1" id="rfc.xref.Part1.13"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>: |
|---|
| 2082 | </p> |
|---|
| 2083 | <div id="rfc.figure.u.15"></div><pre class="inline"> <a href="#imported.abnf" class="smpl">OWS</a> = <OWS, defined in <a href="#Part1" id="rfc.xref.Part1.14"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>, <a href="p1-messaging.html#whitespace" title="Whitespace">Section 3.2.3</a>> |
|---|
| 2084 | <a href="#imported.abnf" class="smpl">field-name</a> = <field-name, defined in <a href="#Part1" id="rfc.xref.Part1.15"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>, <a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a>> |
|---|
| 2085 | <a href="#imported.abnf" class="smpl">quoted-string</a> = <quoted-string, defined in <a href="#Part1" id="rfc.xref.Part1.16"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>, <a href="p1-messaging.html#field.components" title="Field value components">Section 3.2.6</a>> |
|---|
| 2086 | <a href="#imported.abnf" class="smpl">token</a> = <token, defined in <a href="#Part1" id="rfc.xref.Part1.17"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>, <a href="p1-messaging.html#field.components" title="Field value components">Section 3.2.6</a>> |
|---|
| 2087 | |
|---|
| 2088 | <a href="#imported.abnf" class="smpl">port</a> = <port, defined in <a href="#Part1" id="rfc.xref.Part1.18"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>, <a href="p1-messaging.html#uri" title="Uniform Resource Identifiers">Section 2.7</a>> |
|---|
| 2089 | <a href="#imported.abnf" class="smpl">pseudonym</a> = <pseudonym, defined in <a href="#Part1" id="rfc.xref.Part1.19"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>, <a href="p1-messaging.html#header.via" title="Via">Section 5.7.1</a>> |
|---|
| 2090 | <a href="#imported.abnf" class="smpl">uri-host</a> = <uri-host, defined in <a href="#Part1" id="rfc.xref.Part1.20"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>, <a href="p1-messaging.html#uri" title="Uniform Resource Identifiers">Section 2.7</a>> |
|---|
| 2091 | </pre><p id="rfc.section.B.p.4">The rules below are defined in other parts:</p> |
|---|
| 2092 | <div id="rfc.figure.u.16"></div><pre class="inline"> <a href="#imported.abnf" class="smpl">HTTP-date</a> = <HTTP-date, defined in <a href="#Part2" id="rfc.xref.Part2.9"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[Part2]</cite></a>, <a href="p2-semantics.html#http.date" title="Date/Time Formats">Section 7.1.1.1</a>> |
|---|
| 2093 | </pre></div> |
|---|
| 2094 | <div id="collected.abnf"> |
|---|
| 2095 | <h1 id="rfc.section.C"><a href="#rfc.section.C">C.</a> <a href="#collected.abnf">Collected ABNF</a></h1> |
|---|
| 2096 | <p id="rfc.section.C.p.1">In the collected ABNF below, list rules are expanded as per <a href="p1-messaging.html#notation" title="Syntax Notation">Section 1.2</a> of <a href="#Part1" id="rfc.xref.Part1.21"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[Part1]</cite></a>. |
|---|
| 2097 | </p> |
|---|
| 2098 | <div id="rfc.figure.u.17"></div><pre class="inline"><a href="#header.age" class="smpl">Age</a> = delta-seconds |
|---|
| 2099 | |
|---|
| 2100 | <a href="#header.cache-control" class="smpl">Cache-Control</a> = *( "," OWS ) cache-directive *( OWS "," [ OWS |
|---|
| 2101 | cache-directive ] ) |
|---|
| 2102 | |
|---|
| 2103 | <a href="#header.expires" class="smpl">Expires</a> = HTTP-date |
|---|
| 2104 | |
|---|
| 2105 | <a href="#imported.abnf" class="smpl">HTTP-date</a> = <HTTP-date, defined in [Part2], Section 7.1.1.1> |
|---|
| 2106 | |
|---|
| 2107 | <a href="#imported.abnf" class="smpl">OWS</a> = <OWS, defined in [Part1], Section 3.2.3> |
|---|
| 2108 | |
|---|
| 2109 | <a href="#header.pragma" class="smpl">Pragma</a> = *( "," OWS ) pragma-directive *( OWS "," [ OWS |
|---|
| 2110 | pragma-directive ] ) |
|---|
| 2111 | |
|---|
| 2112 | <a href="#header.warning" class="smpl">Warning</a> = *( "," OWS ) warning-value *( OWS "," [ OWS warning-value ] |
|---|
| 2113 | ) |
|---|
| 2114 | |
|---|
| 2115 | <a href="#header.cache-control" class="smpl">cache-directive</a> = token [ "=" ( token / quoted-string ) ] |
|---|
| 2116 | |
|---|
| 2117 | <a href="#delta-seconds" class="smpl">delta-seconds</a> = 1*DIGIT |
|---|
| 2118 | |
|---|
| 2119 | <a href="#header.pragma" class="smpl">extension-pragma</a> = token [ "=" ( token / quoted-string ) ] |
|---|
| 2120 | |
|---|
| 2121 | <a href="#imported.abnf" class="smpl">field-name</a> = <field-name, defined in [Part1], Section 3.2> |
|---|
| 2122 | |
|---|
| 2123 | <a href="#imported.abnf" class="smpl">port</a> = <port, defined in [Part1], Section 2.7> |
|---|
| 2124 | <a href="#header.pragma" class="smpl">pragma-directive</a> = "no-cache" / extension-pragma |
|---|
| 2125 | <a href="#imported.abnf" class="smpl">pseudonym</a> = <pseudonym, defined in [Part1], Section 5.7.1> |
|---|
| 2126 | |
|---|
| 2127 | <a href="#imported.abnf" class="smpl">quoted-string</a> = <quoted-string, defined in [Part1], Section 3.2.6> |
|---|
| 2128 | |
|---|
| 2129 | <a href="#imported.abnf" class="smpl">token</a> = <token, defined in [Part1], Section 3.2.6> |
|---|
| 2130 | |
|---|
| 2131 | <a href="#imported.abnf" class="smpl">uri-host</a> = <uri-host, defined in [Part1], Section 2.7> |
|---|
| 2132 | |
|---|
| 2133 | <a href="#header.warning" class="smpl">warn-agent</a> = ( uri-host [ ":" port ] ) / pseudonym |
|---|
| 2134 | <a href="#header.warning" class="smpl">warn-code</a> = 3DIGIT |
|---|
| 2135 | <a href="#header.warning" class="smpl">warn-date</a> = DQUOTE HTTP-date DQUOTE |
|---|
| 2136 | <a href="#header.warning" class="smpl">warn-text</a> = quoted-string |
|---|
| 2137 | <a href="#header.warning" class="smpl">warning-value</a> = warn-code SP warn-agent SP warn-text [ SP warn-date |
|---|
| 2138 | ] |
|---|
| 2139 | </pre></div> |
|---|
| 2140 | <div id="change.log"> |
|---|
| 2141 | <h1 id="rfc.section.D"><a href="#rfc.section.D">D.</a> <a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a></h1> |
|---|
| 2142 | <p id="rfc.section.D.p.1">Changes up to the first Working Group Last Call draft are summarized in <<a href="http://trac.tools.ietf.org/html/draft-ietf-httpbis-p6-cache-19#appendix-C">http://trac.tools.ietf.org/html/draft-ietf-httpbis-p6-cache-19#appendix-C</a>>. |
|---|
| 2143 | </p> |
|---|
| 2144 | <div id="changes.since.19"> |
|---|
| 2145 | <h2 id="rfc.section.D.1"><a href="#rfc.section.D.1">D.1</a> <a href="#changes.since.19">Since draft-ietf-httpbis-p6-cache-19</a></h2> |
|---|
| 2146 | <p id="rfc.section.D.1.p.1">Closed issues: </p> |
|---|
| 2147 | <ul> |
|---|
| 2148 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/307">http://tools.ietf.org/wg/httpbis/trac/ticket/307</a>>: "untangle Cache-Control ABNF" |
|---|
| 2149 | </li> |
|---|
| 2150 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/353">http://tools.ietf.org/wg/httpbis/trac/ticket/353</a>>: "Multiple values in Cache-Control header fields" |
|---|
| 2151 | </li> |
|---|
| 2152 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/355">http://tools.ietf.org/wg/httpbis/trac/ticket/355</a>>: "Case sensitivity of header fields in CC values" |
|---|
| 2153 | </li> |
|---|
| 2154 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/356">http://tools.ietf.org/wg/httpbis/trac/ticket/356</a>>: "Spurious 'MAYs'" |
|---|
| 2155 | </li> |
|---|
| 2156 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/360">http://tools.ietf.org/wg/httpbis/trac/ticket/360</a>>: "enhance considerations for new cache control directives" |
|---|
| 2157 | </li> |
|---|
| 2158 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/361">http://tools.ietf.org/wg/httpbis/trac/ticket/361</a>>: "ABNF requirements for recipients" |
|---|
| 2159 | </li> |
|---|
| 2160 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/368">http://tools.ietf.org/wg/httpbis/trac/ticket/368</a>>: "note introduction of new IANA registries as normative changes" |
|---|
| 2161 | </li> |
|---|
| 2162 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/373">http://tools.ietf.org/wg/httpbis/trac/ticket/373</a>>: "broken prose in description of 'Vary'" |
|---|
| 2163 | </li> |
|---|
| 2164 | </ul> |
|---|
| 2165 | </div> |
|---|
| 2166 | <div id="changes.since.20"> |
|---|
| 2167 | <h2 id="rfc.section.D.2"><a href="#rfc.section.D.2">D.2</a> <a href="#changes.since.20">Since draft-ietf-httpbis-p6-cache-20</a></h2> |
|---|
| 2168 | <p id="rfc.section.D.2.p.1">Closed issues: </p> |
|---|
| 2169 | <ul> |
|---|
| 2170 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/375">http://tools.ietf.org/wg/httpbis/trac/ticket/375</a>>: "'Most Conservative'" |
|---|
| 2171 | </li> |
|---|
| 2172 | </ul> |
|---|
| 2173 | <p id="rfc.section.D.2.p.2">Other changes: </p> |
|---|
| 2174 | <ul> |
|---|
| 2175 | <li>Conformance criteria and considerations regarding error handling are now defined in Part 1.</li> |
|---|
| 2176 | <li>Move definition of "Vary" header field into Part 2.</li> |
|---|
| 2177 | <li>Add security considerations with respect to cache poisoning and the "Set-Cookie" header field.</li> |
|---|
| 2178 | </ul> |
|---|
| 2179 | </div> |
|---|
| 2180 | <div id="changes.since.21"> |
|---|
| 2181 | <h2 id="rfc.section.D.3"><a href="#rfc.section.D.3">D.3</a> <a href="#changes.since.21">Since draft-ietf-httpbis-p6-cache-21</a></h2> |
|---|
| 2182 | <p id="rfc.section.D.3.p.1">Closed issues: </p> |
|---|
| 2183 | <ul> |
|---|
| 2184 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/223">http://tools.ietf.org/wg/httpbis/trac/ticket/223</a>>: "Allowing heuristic caching for new status codes" |
|---|
| 2185 | </li> |
|---|
| 2186 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/406">http://tools.ietf.org/wg/httpbis/trac/ticket/406</a>>: "304 without validator" |
|---|
| 2187 | </li> |
|---|
| 2188 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/418">http://tools.ietf.org/wg/httpbis/trac/ticket/418</a>>: "No-Transform" |
|---|
| 2189 | </li> |
|---|
| 2190 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/430">http://tools.ietf.org/wg/httpbis/trac/ticket/430</a>>: "definition public cache-control directive is incompatible with RFC2616" - revert prior change to the meaning of the public |
|---|
| 2191 | cache response directive. |
|---|
| 2192 | </li> |
|---|
| 2193 | </ul> |
|---|
| 2194 | </div> |
|---|
| 2195 | <div id="changes.since.22"> |
|---|
| 2196 | <h2 id="rfc.section.D.4"><a href="#rfc.section.D.4">D.4</a> <a href="#changes.since.22">Since draft-ietf-httpbis-p6-cache-22</a></h2> |
|---|
| 2197 | <p id="rfc.section.D.4.p.1">Closed issues: </p> |
|---|
| 2198 | <ul> |
|---|
| 2199 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/436">http://tools.ietf.org/wg/httpbis/trac/ticket/436</a>>: "explain list expansion in ABNF appendices" |
|---|
| 2200 | </li> |
|---|
| 2201 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/453">http://tools.ietf.org/wg/httpbis/trac/ticket/453</a>>: "Returning the freshest response" |
|---|
| 2202 | </li> |
|---|
| 2203 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/464">http://tools.ietf.org/wg/httpbis/trac/ticket/464</a>>: "placement of extension point considerations" |
|---|
| 2204 | </li> |
|---|
| 2205 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/469">http://tools.ietf.org/wg/httpbis/trac/ticket/469</a>>: "Editorial notes for p6" |
|---|
| 2206 | </li> |
|---|
| 2207 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/471">http://tools.ietf.org/wg/httpbis/trac/ticket/471</a>>: "Vary and future requests" |
|---|
| 2208 | </li> |
|---|
| 2209 | </ul> |
|---|
| 2210 | </div> |
|---|
| 2211 | <div id="changes.since.23"> |
|---|
| 2212 | <h2 id="rfc.section.D.5"><a href="#rfc.section.D.5">D.5</a> <a href="#changes.since.23">Since draft-ietf-httpbis-p6-cache-23</a></h2> |
|---|
| 2213 | <p id="rfc.section.D.5.p.1">Closed issues: </p> |
|---|
| 2214 | <ul> |
|---|
| 2215 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/486">http://tools.ietf.org/wg/httpbis/trac/ticket/486</a>>: "Requiring proxies to process warn-date" |
|---|
| 2216 | </li> |
|---|
| 2217 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/496">http://tools.ietf.org/wg/httpbis/trac/ticket/496</a>>: "add Warning header field examples" |
|---|
| 2218 | </li> |
|---|
| 2219 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/498">http://tools.ietf.org/wg/httpbis/trac/ticket/498</a>>: "Conditionals and caches" |
|---|
| 2220 | </li> |
|---|
| 2221 | </ul> |
|---|
| 2222 | </div> |
|---|
| 2223 | <div id="changes.since.24"> |
|---|
| 2224 | <h2 id="rfc.section.D.6"><a href="#rfc.section.D.6">D.6</a> <a href="#changes.since.24">Since draft-ietf-httpbis-p6-cache-24</a></h2> |
|---|
| 2225 | <p id="rfc.section.D.6.p.1">Closed issues: </p> |
|---|
| 2226 | <ul> |
|---|
| 2227 | <li><<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/499">http://tools.ietf.org/wg/httpbis/trac/ticket/499</a>>: "RFC 1305 ref needs to be updated to 5905" |
|---|
| 2228 | </li> |
|---|
| 2229 | </ul> |
|---|
| 2230 | </div> |
|---|
| 2231 | </div> |
|---|
| 2232 | <h1 id="rfc.index"><a href="#rfc.index">Index</a></h1> |
|---|
| 2233 | <p class="noprint"><a href="#rfc.index.1">1</a> <a href="#rfc.index.2">2</a> <a href="#rfc.index.A">A</a> <a href="#rfc.index.B">B</a> <a href="#rfc.index.C">C</a> <a href="#rfc.index.D">D</a> <a href="#rfc.index.E">E</a> <a href="#rfc.index.F">F</a> <a href="#rfc.index.G">G</a> <a href="#rfc.index.H">H</a> <a href="#rfc.index.M">M</a> <a href="#rfc.index.N">N</a> <a href="#rfc.index.O">O</a> <a href="#rfc.index.P">P</a> <a href="#rfc.index.R">R</a> <a href="#rfc.index.S">S</a> <a href="#rfc.index.T">T</a> <a href="#rfc.index.V">V</a> <a href="#rfc.index.W">W</a> |
|---|
| 2234 | </p> |
|---|
| 2235 | <div class="print2col"> |
|---|
| 2236 | <ul class="ind"> |
|---|
| 2237 | <li><a id="rfc.index.1" href="#rfc.index.1"><b>1</b></a><ul> |
|---|
| 2238 | <li>110 (warn-code) <a href="#rfc.xref.warn.110.1">4.2.4</a>, <a href="#rfc.iref.49"><b>5.5.1</b></a>, <a href="#rfc.xref.warn.110.2">7.2.2</a></li> |
|---|
| 2239 | <li>111 (warn-code) <a href="#rfc.iref.50"><b>5.5.2</b></a>, <a href="#rfc.xref.warn.111.1">7.2.2</a></li> |
|---|
| 2240 | <li>112 (warn-code) <a href="#rfc.xref.warn.112.1">4.2.4</a>, <a href="#rfc.iref.51"><b>5.5.3</b></a>, <a href="#rfc.xref.warn.112.2">7.2.2</a></li> |
|---|
| 2241 | <li>113 (warn-code) <a href="#rfc.xref.warn.113.1">4.2.2</a>, <a href="#rfc.iref.52"><b>5.5.4</b></a>, <a href="#rfc.xref.warn.113.2">7.2.2</a></li> |
|---|
| 2242 | <li>199 (warn-code) <a href="#rfc.iref.53"><b>5.5.5</b></a>, <a href="#rfc.xref.warn.199.1">7.2.2</a></li> |
|---|
| 2243 | </ul> |
|---|
| 2244 | </li> |
|---|
| 2245 | <li><a id="rfc.index.2" href="#rfc.index.2"><b>2</b></a><ul> |
|---|
| 2246 | <li>214 (warn-code) <a href="#rfc.iref.54"><b>5.5.6</b></a>, <a href="#rfc.xref.warn.214.1">7.2.2</a></li> |
|---|
| 2247 | <li>299 (warn-code) <a href="#rfc.iref.55"><b>5.5.7</b></a>, <a href="#rfc.xref.warn.299.1">7.2.2</a></li> |
|---|
| 2248 | </ul> |
|---|
| 2249 | </li> |
|---|
| 2250 | <li><a id="rfc.index.A" href="#rfc.index.A"><b>A</b></a><ul> |
|---|
| 2251 | <li>age <a href="#rfc.iref.a.1">4.2</a></li> |
|---|
| 2252 | <li>Age header field <a href="#rfc.xref.header.age.1">4</a>, <a href="#rfc.xref.header.age.2">4.2.3</a>, <a href="#rfc.iref.a.2"><b>5.1</b></a>, <a href="#rfc.xref.header.age.3">7.3</a></li> |
|---|
| 2253 | </ul> |
|---|
| 2254 | </li> |
|---|
| 2255 | <li><a id="rfc.index.B" href="#rfc.index.B"><b>B</b></a><ul> |
|---|
| 2256 | <li><em>BCP90</em> <a href="#rfc.xref.BCP90.1">7.3</a>, <a href="#BCP90"><b>10.2</b></a></li> |
|---|
| 2257 | </ul> |
|---|
| 2258 | </li> |
|---|
| 2259 | <li><a id="rfc.index.C" href="#rfc.index.C"><b>C</b></a><ul> |
|---|
| 2260 | <li>cache <a href="#rfc.iref.c.1">1</a></li> |
|---|
| 2261 | <li>cache entry <a href="#rfc.iref.c.2">2</a></li> |
|---|
| 2262 | <li>cache key <a href="#rfc.iref.c.3">2</a>, <a href="#rfc.iref.c.4">2</a></li> |
|---|
| 2263 | <li>Cache-Control header field <a href="#rfc.xref.header.cache-control.1">3</a>, <a href="#rfc.iref.c.5"><b>5.2</b></a>, <a href="#rfc.xref.header.cache-control.2">7.3</a>, <a href="#rfc.xref.header.cache-control.3">A</a></li> |
|---|
| 2264 | </ul> |
|---|
| 2265 | </li> |
|---|
| 2266 | <li><a id="rfc.index.D" href="#rfc.index.D"><b>D</b></a><ul> |
|---|
| 2267 | <li>Disconnected Operation (warn-text) <a href="#rfc.xref.warn.112.1">4.2.4</a>, <a href="#rfc.iref.d.1"><b>5.5.3</b></a>, <a href="#rfc.xref.warn.112.2">7.2.2</a></li> |
|---|
| 2268 | </ul> |
|---|
| 2269 | </li> |
|---|
| 2270 | <li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul> |
|---|
| 2271 | <li>Expires header field <a href="#rfc.xref.header.expires.1">3</a>, <a href="#rfc.xref.header.expires.2">4.2</a>, <a href="#rfc.xref.header.expires.3">4.2.1</a>, <a href="#rfc.iref.e.2"><b>5.3</b></a>, <a href="#rfc.xref.header.expires.4">7.3</a>, <a href="#rfc.xref.header.expires.5">A</a></li> |
|---|
| 2272 | <li>explicit expiration time <a href="#rfc.iref.e.1">4.2</a></li> |
|---|
| 2273 | </ul> |
|---|
| 2274 | </li> |
|---|
| 2275 | <li><a id="rfc.index.F" href="#rfc.index.F"><b>F</b></a><ul> |
|---|
| 2276 | <li>fresh <a href="#rfc.iref.f.1">4.2</a></li> |
|---|
| 2277 | <li>freshness lifetime <a href="#rfc.iref.f.2">4.2</a></li> |
|---|
| 2278 | </ul> |
|---|
| 2279 | </li> |
|---|
| 2280 | <li><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul> |
|---|
| 2281 | <li><tt>Grammar</tt> |
|---|
| 2282 | <ul> |
|---|
| 2283 | <li><tt>Age</tt> <a href="#rfc.iref.g.2"><b>5.1</b></a></li> |
|---|
| 2284 | <li><tt>Cache-Control</tt> <a href="#rfc.iref.g.3"><b>5.2</b></a></li> |
|---|
| 2285 | <li><tt>cache-directive</tt> <a href="#rfc.iref.g.4"><b>5.2</b></a></li> |
|---|
| 2286 | <li><tt>delta-seconds</tt> <a href="#rfc.iref.g.1"><b>1.2.1</b></a></li> |
|---|
| 2287 | <li><tt>Expires</tt> <a href="#rfc.iref.g.5"><b>5.3</b></a></li> |
|---|
| 2288 | <li><tt>extension-pragma</tt> <a href="#rfc.iref.g.8"><b>5.4</b></a></li> |
|---|
| 2289 | <li><tt>Pragma</tt> <a href="#rfc.iref.g.6"><b>5.4</b></a></li> |
|---|
| 2290 | <li><tt>pragma-directive</tt> <a href="#rfc.iref.g.7"><b>5.4</b></a></li> |
|---|
| 2291 | <li><tt>warn-agent</tt> <a href="#rfc.iref.g.12"><b>5.5</b></a></li> |
|---|
| 2292 | <li><tt>warn-code</tt> <a href="#rfc.iref.g.11"><b>5.5</b></a></li> |
|---|
| 2293 | <li><tt>warn-date</tt> <a href="#rfc.iref.g.14"><b>5.5</b></a></li> |
|---|
| 2294 | <li><tt>warn-text</tt> <a href="#rfc.iref.g.13"><b>5.5</b></a></li> |
|---|
| 2295 | <li><tt>Warning</tt> <a href="#rfc.iref.g.9"><b>5.5</b></a></li> |
|---|
| 2296 | <li><tt>warning-value</tt> <a href="#rfc.iref.g.10"><b>5.5</b></a></li> |
|---|
| 2297 | </ul> |
|---|
| 2298 | </li> |
|---|
| 2299 | </ul> |
|---|
| 2300 | </li> |
|---|
| 2301 | <li><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul> |
|---|
| 2302 | <li>Heuristic Expiration (warn-text) <a href="#rfc.xref.warn.113.1">4.2.2</a>, <a href="#rfc.iref.h.2"><b>5.5.4</b></a>, <a href="#rfc.xref.warn.113.2">7.2.2</a></li> |
|---|
| 2303 | <li>heuristic expiration time <a href="#rfc.iref.h.1">4.2</a></li> |
|---|
| 2304 | </ul> |
|---|
| 2305 | </li> |
|---|
| 2306 | <li><a id="rfc.index.M" href="#rfc.index.M"><b>M</b></a><ul> |
|---|
| 2307 | <li>max-age (cache directive) <a href="#rfc.iref.m.1"><b>5.2.1.1</b></a>, <a href="#rfc.iref.m.5"><b>5.2.2.8</b></a></li> |
|---|
| 2308 | <li>max-stale (cache directive) <a href="#rfc.iref.m.2"><b>5.2.1.2</b></a></li> |
|---|
| 2309 | <li>min-fresh (cache directive) <a href="#rfc.iref.m.3"><b>5.2.1.3</b></a></li> |
|---|
| 2310 | <li>Miscellaneous Persistent Warning (warn-text) <a href="#rfc.iref.m.7"><b>5.5.7</b></a>, <a href="#rfc.xref.warn.299.1">7.2.2</a></li> |
|---|
| 2311 | <li>Miscellaneous Warning (warn-text) <a href="#rfc.iref.m.6"><b>5.5.5</b></a>, <a href="#rfc.xref.warn.199.1">7.2.2</a></li> |
|---|
| 2312 | <li>must-revalidate (cache directive) <a href="#rfc.iref.m.4"><b>5.2.2.1</b></a></li> |
|---|
| 2313 | </ul> |
|---|
| 2314 | </li> |
|---|
| 2315 | <li><a id="rfc.index.N" href="#rfc.index.N"><b>N</b></a><ul> |
|---|
| 2316 | <li>no-cache (cache directive) <a href="#rfc.iref.n.1"><b>5.2.1.4</b></a>, <a href="#rfc.iref.n.4"><b>5.2.2.2</b></a></li> |
|---|
| 2317 | <li>no-store (cache directive) <a href="#rfc.iref.n.2"><b>5.2.1.5</b></a>, <a href="#rfc.iref.n.5"><b>5.2.2.3</b></a></li> |
|---|
| 2318 | <li>no-transform (cache directive) <a href="#rfc.iref.n.3"><b>5.2.1.6</b></a>, <a href="#rfc.iref.n.6"><b>5.2.2.4</b></a></li> |
|---|
| 2319 | </ul> |
|---|
| 2320 | </li> |
|---|
| 2321 | <li><a id="rfc.index.O" href="#rfc.index.O"><b>O</b></a><ul> |
|---|
| 2322 | <li>only-if-cached (cache directive) <a href="#rfc.iref.o.1"><b>5.2.1.7</b></a></li> |
|---|
| 2323 | </ul> |
|---|
| 2324 | </li> |
|---|
| 2325 | <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul> |
|---|
| 2326 | <li><em>Part1</em> <a href="#rfc.xref.Part1.1">1.1</a>, <a href="#rfc.xref.Part1.2">1.2</a>, <a href="#rfc.xref.Part1.3">3.1</a>, <a href="#rfc.xref.Part1.4">4</a>, <a href="#rfc.xref.Part1.5">4.1</a>, <a href="#rfc.xref.Part1.6">4.4</a>, <a href="#rfc.xref.Part1.7">4.4</a>, <a href="#rfc.xref.Part1.8">4.4</a>, <a href="#rfc.xref.Part1.9">5.2.1.6</a>, <a href="#rfc.xref.Part1.10">5.2.2.4</a>, <a href="#rfc.xref.Part1.11">8</a>, <a href="#rfc.xref.Part1.12">9</a>, <a href="#Part1"><b>10.1</b></a>, <a href="#rfc.xref.Part1.13">B</a>, <a href="#rfc.xref.Part1.14">B</a>, <a href="#rfc.xref.Part1.15">B</a>, <a href="#rfc.xref.Part1.16">B</a>, <a href="#rfc.xref.Part1.17">B</a>, <a href="#rfc.xref.Part1.18">B</a>, <a href="#rfc.xref.Part1.19">B</a>, <a href="#rfc.xref.Part1.20">B</a>, <a href="#rfc.xref.Part1.21">C</a><ul> |
|---|
| 2327 | <li><em>Section 1.2</em> <a href="#rfc.xref.Part1.21">C</a></li> |
|---|
| 2328 | <li><em>Section 2.5</em> <a href="#rfc.xref.Part1.1">1.1</a></li> |
|---|
| 2329 | <li><em>Section 2.7</em> <a href="#rfc.xref.Part1.18">B</a>, <a href="#rfc.xref.Part1.20">B</a></li> |
|---|
| 2330 | <li><em>Section 3.2</em> <a href="#rfc.xref.Part1.5">4.1</a>, <a href="#rfc.xref.Part1.15">B</a></li> |
|---|
| 2331 | <li><em>Section 3.2.3</em> <a href="#rfc.xref.Part1.14">B</a></li> |
|---|
| 2332 | <li><em>Section 3.2.6</em> <a href="#rfc.xref.Part1.16">B</a>, <a href="#rfc.xref.Part1.17">B</a></li> |
|---|
| 2333 | <li><em>Section 5.5</em> <a href="#rfc.xref.Part1.4">4</a>, <a href="#rfc.xref.Part1.6">4.4</a>, <a href="#rfc.xref.Part1.7">4.4</a>, <a href="#rfc.xref.Part1.8">4.4</a></li> |
|---|
| 2334 | <li><em>Section 5.7.1</em> <a href="#rfc.xref.Part1.19">B</a></li> |
|---|
| 2335 | <li><em>Section 5.7.2</em> <a href="#rfc.xref.Part1.9">5.2.1.6</a>, <a href="#rfc.xref.Part1.10">5.2.2.4</a></li> |
|---|
| 2336 | <li><em>Section 7</em> <a href="#rfc.xref.Part1.2">1.2</a></li> |
|---|
| 2337 | <li><em>Section 10</em> <a href="#rfc.xref.Part1.12">9</a></li> |
|---|
| 2338 | </ul> |
|---|
| 2339 | </li> |
|---|
| 2340 | <li><em>Part2</em> <a href="#rfc.xref.Part2.1">2</a>, <a href="#rfc.xref.Part2.2">2</a>, <a href="#rfc.xref.Part2.3">4</a>, <a href="#rfc.xref.Part2.4">4.1</a>, <a href="#rfc.xref.Part2.5">4.2.3</a>, <a href="#rfc.xref.Part2.6">4.4</a>, <a href="#rfc.xref.Part2.7">5.3</a>, <a href="#rfc.xref.Part2.8">8</a>, <a href="#Part2"><b>10.1</b></a>, <a href="#rfc.xref.Part2.9">B</a><ul> |
|---|
| 2341 | <li><em>Section 4.2.1</em> <a href="#rfc.xref.Part2.3">4</a>, <a href="#rfc.xref.Part2.6">4.4</a></li> |
|---|
| 2342 | <li><em>Section 4.3.1</em> <a href="#rfc.xref.Part2.2">2</a></li> |
|---|
| 2343 | <li><em>Section 7.1.1.1</em> <a href="#rfc.xref.Part2.7">5.3</a>, <a href="#rfc.xref.Part2.9">B</a></li> |
|---|
| 2344 | <li><em>Section 7.1.1.2</em> <a href="#rfc.xref.Part2.5">4.2.3</a></li> |
|---|
| 2345 | <li><em>Section 7.1.4</em> <a href="#rfc.xref.Part2.4">4.1</a></li> |
|---|
| 2346 | </ul> |
|---|
| 2347 | </li> |
|---|
| 2348 | <li><em>Part4</em> <a href="#rfc.xref.Part4.1">4.2.2</a>, <a href="#rfc.xref.Part4.2">4.3</a>, <a href="#rfc.xref.Part4.3">4.3.1</a>, <a href="#rfc.xref.Part4.4">4.3.1</a>, <a href="#rfc.xref.Part4.5">4.3.2</a>, <a href="#rfc.xref.Part4.6">4.3.2</a>, <a href="#rfc.xref.Part4.7">4.3.2</a>, <a href="#rfc.xref.Part4.8">4.3.4</a>, <a href="#Part4"><b>10.1</b></a><ul> |
|---|
| 2349 | <li><em>Section 2.1</em> <a href="#rfc.xref.Part4.8">4.3.4</a></li> |
|---|
| 2350 | <li><em>Section 2.2</em> <a href="#rfc.xref.Part4.1">4.2.2</a>, <a href="#rfc.xref.Part4.3">4.3.1</a></li> |
|---|
| 2351 | <li><em>Section 2.3</em> <a href="#rfc.xref.Part4.4">4.3.1</a></li> |
|---|
| 2352 | <li><em>Section 3.2</em> <a href="#rfc.xref.Part4.6">4.3.2</a></li> |
|---|
| 2353 | <li><em>Section 3.3</em> <a href="#rfc.xref.Part4.7">4.3.2</a></li> |
|---|
| 2354 | <li><em>Section 6</em> <a href="#rfc.xref.Part4.5">4.3.2</a></li> |
|---|
| 2355 | </ul> |
|---|
| 2356 | </li> |
|---|
| 2357 | <li><em>Part5</em> <a href="#rfc.xref.Part5.1">3.1</a>, <a href="#rfc.xref.Part5.2">3.3</a>, <a href="#rfc.xref.Part5.3">3.3</a>, <a href="#rfc.xref.Part5.4">4.3.2</a>, <a href="#rfc.xref.Part5.5">4.3.2</a>, <a href="#Part5"><b>10.1</b></a><ul> |
|---|
| 2358 | <li><em>Section 3.2</em> <a href="#rfc.xref.Part5.5">4.3.2</a></li> |
|---|
| 2359 | <li><em>Section 4.3</em> <a href="#rfc.xref.Part5.3">3.3</a></li> |
|---|
| 2360 | </ul> |
|---|
| 2361 | </li> |
|---|
| 2362 | <li><em>Part7</em> <a href="#rfc.xref.Part7.1">3</a>, <a href="#rfc.xref.Part7.2">3.2</a>, <a href="#Part7"><b>10.1</b></a><ul> |
|---|
| 2363 | <li><em>Section 4.1</em> <a href="#rfc.xref.Part7.1">3</a>, <a href="#rfc.xref.Part7.2">3.2</a></li> |
|---|
| 2364 | </ul> |
|---|
| 2365 | </li> |
|---|
| 2366 | <li>Pragma header field <a href="#rfc.xref.header.pragma.1">4</a>, <a href="#rfc.iref.p.5"><b>5.4</b></a>, <a href="#rfc.xref.header.pragma.2">7.3</a>, <a href="#rfc.xref.header.pragma.3">A</a></li> |
|---|
| 2367 | <li>private (cache directive) <a href="#rfc.iref.p.3"><b>5.2.2.6</b></a></li> |
|---|
| 2368 | <li>private cache <a href="#rfc.iref.p.1">1</a></li> |
|---|
| 2369 | <li>proxy-revalidate (cache directive) <a href="#rfc.iref.p.4"><b>5.2.2.7</b></a></li> |
|---|
| 2370 | <li>public (cache directive) <a href="#rfc.iref.p.2"><b>5.2.2.5</b></a></li> |
|---|
| 2371 | </ul> |
|---|
| 2372 | </li> |
|---|
| 2373 | <li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul> |
|---|
| 2374 | <li>Response is Stale (warn-text) <a href="#rfc.xref.warn.110.1">4.2.4</a>, <a href="#rfc.iref.r.1"><b>5.5.1</b></a>, <a href="#rfc.xref.warn.110.2">7.2.2</a></li> |
|---|
| 2375 | <li>Revalidation Failed (warn-text) <a href="#rfc.iref.r.2"><b>5.5.2</b></a>, <a href="#rfc.xref.warn.111.1">7.2.2</a></li> |
|---|
| 2376 | <li><em>RFC2119</em> <a href="#rfc.xref.RFC2119.1">1.1</a>, <a href="#RFC2119"><b>10.1</b></a></li> |
|---|
| 2377 | <li><em>RFC2616</em> <a href="#rfc.xref.RFC2616.1">4.2.2</a>, <a href="#RFC2616"><b>10.2</b></a><ul> |
|---|
| 2378 | <li><em>Section 13.9</em> <a href="#rfc.xref.RFC2616.1">4.2.2</a></li> |
|---|
| 2379 | </ul> |
|---|
| 2380 | </li> |
|---|
| 2381 | <li><em>RFC5226</em> <a href="#rfc.xref.RFC5226.1">7.1.1</a>, <a href="#rfc.xref.RFC5226.2">7.2.1</a>, <a href="#RFC5226"><b>10.2</b></a><ul> |
|---|
| 2382 | <li><em>Section 4.1</em> <a href="#rfc.xref.RFC5226.1">7.1.1</a>, <a href="#rfc.xref.RFC5226.2">7.2.1</a></li> |
|---|
| 2383 | </ul> |
|---|
| 2384 | </li> |
|---|
| 2385 | <li><em>RFC5234</em> <a href="#rfc.xref.RFC5234.1">1.2</a>, <a href="#RFC5234"><b>10.1</b></a>, <a href="#rfc.xref.RFC5234.2">B</a><ul> |
|---|
| 2386 | <li><em>Appendix B.1</em> <a href="#rfc.xref.RFC5234.2">B</a></li> |
|---|
| 2387 | </ul> |
|---|
| 2388 | </li> |
|---|
| 2389 | <li><em>RFC5861</em> <a href="#rfc.xref.RFC5861.1">7.1.3</a>, <a href="#rfc.xref.RFC5861.2">7.1.3</a>, <a href="#RFC5861"><b>10.2</b></a><ul> |
|---|
| 2390 | <li><em>Section 3</em> <a href="#rfc.xref.RFC5861.2">7.1.3</a></li> |
|---|
| 2391 | <li><em>Section 4</em> <a href="#rfc.xref.RFC5861.1">7.1.3</a></li> |
|---|
| 2392 | </ul> |
|---|
| 2393 | </li> |
|---|
| 2394 | <li><em>RFC5905</em> <a href="#rfc.xref.RFC5905.1">4.2.3</a>, <a href="#RFC5905"><b>10.2</b></a></li> |
|---|
| 2395 | <li><em>RFC6265</em> <a href="#rfc.xref.RFC6265.1">8</a>, <a href="#RFC6265"><b>10.2</b></a></li> |
|---|
| 2396 | </ul> |
|---|
| 2397 | </li> |
|---|
| 2398 | <li><a id="rfc.index.S" href="#rfc.index.S"><b>S</b></a><ul> |
|---|
| 2399 | <li>s-maxage (cache directive) <a href="#rfc.iref.s.4"><b>5.2.2.9</b></a></li> |
|---|
| 2400 | <li>shared cache <a href="#rfc.iref.s.1">1</a></li> |
|---|
| 2401 | <li>stale <a href="#rfc.iref.s.2">4.2</a></li> |
|---|
| 2402 | <li>strong validator <a href="#rfc.iref.s.3">4.3.4</a></li> |
|---|
| 2403 | </ul> |
|---|
| 2404 | </li> |
|---|
| 2405 | <li><a id="rfc.index.T" href="#rfc.index.T"><b>T</b></a><ul> |
|---|
| 2406 | <li>Transformation Applied (warn-text) <a href="#rfc.iref.t.1"><b>5.5.6</b></a>, <a href="#rfc.xref.warn.214.1">7.2.2</a></li> |
|---|
| 2407 | </ul> |
|---|
| 2408 | </li> |
|---|
| 2409 | <li><a id="rfc.index.V" href="#rfc.index.V"><b>V</b></a><ul> |
|---|
| 2410 | <li>validator <a href="#rfc.iref.v.1">4.3.1</a></li> |
|---|
| 2411 | </ul> |
|---|
| 2412 | </li> |
|---|
| 2413 | <li><a id="rfc.index.W" href="#rfc.index.W"><b>W</b></a><ul> |
|---|
| 2414 | <li>Warning header field <a href="#rfc.xref.header.warning.1">3.3</a>, <a href="#rfc.xref.header.warning.2">4.3.4</a>, <a href="#rfc.xref.header.warning.3">4.3.5</a>, <a href="#rfc.iref.w.1"><b>5.5</b></a>, <a href="#rfc.xref.header.warning.4">7.3</a>, <a href="#rfc.xref.header.warning.5">A</a></li> |
|---|
| 2415 | </ul> |
|---|
| 2416 | </li> |
|---|
| 2417 | </ul> |
|---|
| 2418 | </div> |
|---|
| 2419 | </body> |
|---|
| 2420 | </html> |
|---|
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