| 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://www.w3.org/2006/03/hcard 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: verdana, helvetica, arial, sans-serif; |
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| 109 | font-size: 10pt; |
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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: 14pt; |
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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 | h1 a { |
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| 142 | color: #333333; |
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| 143 | } |
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| 144 | h2 { |
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| 145 | font-size: 12pt; |
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| 146 | line-height: 15pt; |
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| 147 | page-break-after: avoid; |
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| 148 | } |
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| 149 | h3, h4, h5, h6 { |
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| 150 | font-size: 10pt; |
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| 151 | page-break-after: avoid; |
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| 152 | } |
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| 153 | h2 a, h3 a, h4 a, h5 a, h6 a { |
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| 154 | color: black; |
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| 155 | } |
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| 156 | img { |
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| 157 | margin-left: 3em; |
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| 158 | } |
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| 159 | li { |
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| 160 | margin-left: 2em; |
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| 161 | } |
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| 162 | ol { |
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| 163 | margin-left: 2em; |
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| 164 | } |
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| 165 | ol.la { |
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| 166 | list-style-type: lower-alpha; |
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| 167 | } |
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| 168 | ol.ua { |
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| 169 | list-style-type: upper-alpha; |
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| 170 | } |
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| 171 | ol p { |
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| 172 | margin-left: 0em; |
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| 173 | } |
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| 174 | p { |
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| 175 | margin-left: 2em; |
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| 176 | } |
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| 177 | pre { |
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| 178 | margin-left: 3em; |
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| 179 | background-color: lightyellow; |
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| 180 | padding: .25em; |
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| 181 | page-break-inside: avoid; |
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| 182 | } |
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| 183 | pre.text2 { |
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| 184 | border-style: dotted; |
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| 185 | border-width: 1px; |
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| 186 | background-color: #f0f0f0; |
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| 187 | width: 69em; |
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| 188 | } |
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| 189 | pre.inline { |
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| 190 | background-color: white; |
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| 191 | padding: 0em; |
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| 192 | } |
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| 193 | pre.text { |
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| 194 | border-style: dotted; |
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| 195 | border-width: 1px; |
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| 196 | background-color: #f8f8f8; |
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| 197 | width: 69em; |
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| 198 | } |
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| 199 | pre.drawing { |
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| 200 | border-style: solid; |
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| 201 | border-width: 1px; |
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| 202 | background-color: #f8f8f8; |
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| 203 | padding: 2em; |
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| 204 | } |
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| 205 | sup { |
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| 206 | font-size: 60%; |
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| 207 | } |
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| 208 | table { |
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| 209 | margin-left: 2em; |
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| 210 | } |
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| 211 | table.tt { |
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| 212 | vertical-align: top; |
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| 213 | } |
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| 214 | table.full { |
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| 215 | border-style: outset; |
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| 216 | border-width: 1px; |
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| 217 | } |
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| 218 | table.headers { |
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| 219 | border-style: outset; |
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| 220 | border-width: 1px; |
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| 221 | } |
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| 222 | table.tt td { |
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| 223 | vertical-align: top; |
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| 224 | } |
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| 225 | table.full td { |
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| 226 | border-style: inset; |
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| 227 | border-width: 1px; |
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| 228 | } |
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| 229 | table.tt th { |
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| 230 | vertical-align: top; |
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| 231 | } |
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| 232 | table.full th { |
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| 233 | border-style: inset; |
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| 234 | border-width: 1px; |
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| 235 | } |
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| 236 | table.headers th { |
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| 237 | border-style: none none inset none; |
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| 238 | border-width: 1px; |
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| 239 | } |
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| 240 | table.left { |
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| 241 | margin-right: auto; |
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| 242 | } |
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| 243 | table.right { |
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| 244 | margin-left: auto; |
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| 245 | } |
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| 246 | table.center { |
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| 247 | margin-left: auto; |
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| 248 | margin-right: auto; |
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| 249 | } |
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| 250 | caption { |
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| 251 | caption-side: bottom; |
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| 252 | font-weight: bold; |
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| 253 | font-size: 9pt; |
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| 254 | margin-top: .5em; |
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| 255 | } |
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| 256 | |
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| 257 | table.header { |
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| 258 | border-spacing: 1px; |
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| 259 | width: 95%; |
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| 260 | font-size: 10pt; |
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| 261 | color: white; |
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| 262 | } |
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| 263 | td.top { |
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| 264 | vertical-align: top; |
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| 265 | } |
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| 266 | td.topnowrap { |
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| 267 | vertical-align: top; |
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| 268 | white-space: nowrap; |
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| 269 | } |
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| 270 | table.header td { |
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| 271 | background-color: gray; |
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| 272 | width: 50%; |
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| 273 | } |
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| 274 | table.header a { |
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| 275 | color: white; |
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| 276 | } |
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| 277 | td.reference { |
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| 278 | vertical-align: top; |
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| 279 | white-space: nowrap; |
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| 280 | padding-right: 1em; |
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| 281 | } |
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| 282 | thead { |
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| 283 | display:table-header-group; |
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| 284 | } |
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| 285 | ul.toc, ul.toc ul { |
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| 286 | list-style: none; |
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| 287 | margin-left: 1.5em; |
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| 288 | padding-left: 0em; |
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| 289 | } |
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| 290 | ul.toc li { |
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| 291 | line-height: 150%; |
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| 292 | font-weight: bold; |
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| 293 | font-size: 10pt; |
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| 294 | margin-left: 0em; |
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| 295 | } |
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| 296 | ul.toc li li { |
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| 297 | line-height: normal; |
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| 298 | font-weight: normal; |
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| 299 | font-size: 9pt; |
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| 300 | margin-left: 0em; |
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| 301 | } |
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| 302 | li.excluded { |
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| 303 | font-size: 0pt; |
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| 304 | } |
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| 305 | ul p { |
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| 306 | margin-left: 0em; |
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| 307 | } |
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| 308 | ul.ind, ul.ind ul { |
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| 309 | list-style: none; |
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| 310 | margin-left: 1.5em; |
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| 311 | padding-left: 0em; |
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| 312 | page-break-before: avoid; |
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| 313 | } |
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| 314 | ul.ind li { |
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| 315 | font-weight: bold; |
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| 316 | line-height: 200%; |
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| 317 | margin-left: 0em; |
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| 318 | } |
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| 319 | ul.ind li li { |
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| 320 | font-weight: normal; |
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| 321 | line-height: 150%; |
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| 322 | margin-left: 0em; |
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| 323 | } |
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| 324 | .avoidbreak { |
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| 325 | page-break-inside: avoid; |
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| 326 | } |
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| 327 | .bcp14 { |
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| 328 | font-style: normal; |
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| 329 | text-transform: lowercase; |
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| 330 | font-variant: small-caps; |
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| 331 | } |
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| 332 | .comment { |
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| 333 | background-color: yellow; |
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| 334 | } |
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| 335 | .center { |
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| 336 | text-align: center; |
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| 337 | } |
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| 338 | .error { |
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| 339 | color: red; |
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| 340 | font-style: italic; |
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| 341 | font-weight: bold; |
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| 342 | } |
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| 343 | .figure { |
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| 344 | font-weight: bold; |
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| 345 | text-align: center; |
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| 346 | font-size: 9pt; |
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| 347 | } |
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| 348 | .filename { |
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| 349 | color: #333333; |
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| 350 | font-weight: bold; |
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| 351 | font-size: 12pt; |
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| 352 | line-height: 21pt; |
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| 353 | text-align: center; |
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| 354 | } |
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| 355 | .fn { |
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| 356 | font-weight: bold; |
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| 357 | } |
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| 358 | .hidden { |
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| 359 | display: none; |
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| 360 | } |
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| 361 | .left { |
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| 362 | text-align: left; |
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| 363 | } |
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| 364 | .right { |
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| 365 | text-align: right; |
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| 366 | } |
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| 367 | .title { |
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| 368 | color: #990000; |
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| 369 | font-size: 18pt; |
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| 370 | line-height: 18pt; |
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| 371 | font-weight: bold; |
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| 372 | text-align: center; |
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| 373 | margin-top: 36pt; |
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| 374 | } |
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| 375 | .vcardline { |
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| 376 | display: block; |
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| 377 | } |
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| 378 | .warning { |
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| 379 | font-size: 14pt; |
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| 380 | background-color: yellow; |
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| 381 | } |
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| 382 | .feedback { |
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| 383 | position: fixed; |
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| 384 | bottom: 1%; |
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| 385 | right: 1%; |
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| 386 | padding: 3px 5px; |
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| 387 | color: white; |
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| 388 | border-radius: 5px; |
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| 389 | background: #a00000; |
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| 390 | border: 1px solid silver; |
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| 391 | } |
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| 392 | .fbbutton { |
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| 393 | margin-left: 1em; |
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| 394 | color: #303030; |
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| 395 | font-size: small; |
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| 396 | font-weight: normal; |
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| 397 | background: #d0d000; |
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| 398 | padding: 1px 4px; |
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| 399 | border: 1px solid silver; |
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| 400 | border-radius: 5px; |
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| 401 | } |
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| 402 | |
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| 403 | @media print { |
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| 404 | .noprint { |
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| 405 | display: none; |
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| 406 | } |
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| 407 | |
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| 408 | a { |
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| 409 | color: black; |
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| 410 | text-decoration: none; |
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| 411 | } |
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| 412 | |
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| 413 | table.header { |
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| 414 | width: 90%; |
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| 415 | } |
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| 416 | |
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| 417 | td.header { |
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| 418 | width: 50%; |
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| 419 | color: black; |
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| 420 | background-color: white; |
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| 421 | vertical-align: top; |
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| 422 | font-size: 12pt; |
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| 423 | } |
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| 424 | |
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| 425 | ul.toc a:nth-child(2)::after { |
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| 426 | content: leader('.') target-counter(attr(href), page); |
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| 427 | } |
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| 428 | |
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| 429 | ul.ind li li a { |
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| 430 | content: target-counter(attr(href), page); |
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| 431 | } |
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| 432 | |
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| 433 | .print2col { |
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| 434 | column-count: 2; |
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| 435 | -moz-column-count: 2; |
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| 436 | column-fill: auto; |
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| 437 | } |
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| 438 | } |
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| 439 | |
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| 440 | @page { |
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| 441 | @top-left { |
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| 442 | content: "Internet-Draft"; |
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| 443 | } |
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| 444 | @top-right { |
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| 445 | content: "February 2013"; |
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| 446 | } |
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| 447 | @top-center { |
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| 448 | content: "HTTP/1.1 Caching"; |
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| 449 | } |
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| 450 | @bottom-left { |
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| 451 | content: "Fielding, et al."; |
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| 452 | } |
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| 453 | @bottom-center { |
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| 454 | content: "Expires August 27, 2013"; |
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| 455 | } |
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| 456 | @bottom-right { |
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| 457 | content: "[Page " counter(page) "]"; |
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| 458 | } |
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| 459 | } |
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| 460 | |
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| 461 | @page:first { |
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| 462 | @top-left { |
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| 463 | content: normal; |
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| 464 | } |
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| 465 | @top-right { |
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| 466 | content: normal; |
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| 467 | } |
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| 468 | @top-center { |
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| 469 | content: normal; |
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| 470 | } |
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| 471 | } |
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| 472 | </style><link rel="Contents" href="#rfc.toc"> |
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| 473 | <link rel="Author" href="#rfc.authors"> |
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| 474 | <link rel="Copyright" href="#rfc.copyrightnotice"> |
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| 475 | <link rel="Index" href="#rfc.index"> |
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| 476 | <link rel="Chapter" title="1 Introduction" href="#rfc.section.1"> |
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| 477 | <link rel="Chapter" title="2 Overview of Cache Operation" href="#rfc.section.2"> |
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| 478 | <link rel="Chapter" title="3 Storing Responses in Caches" href="#rfc.section.3"> |
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| 479 | <link rel="Chapter" title="4 Constructing Responses from Caches" href="#rfc.section.4"> |
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| 480 | <link rel="Chapter" title="5 Updating Caches with HEAD Responses" href="#rfc.section.5"> |
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| 481 | <link rel="Chapter" title="6 Request Methods that Invalidate" href="#rfc.section.6"> |
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| 482 | <link rel="Chapter" title="7 Header Field Definitions" href="#rfc.section.7"> |
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| 483 | <link rel="Chapter" title="8 History Lists" href="#rfc.section.8"> |
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| 484 | <link rel="Chapter" title="9 IANA Considerations" href="#rfc.section.9"> |
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| 485 | <link rel="Chapter" title="10 Security Considerations" href="#rfc.section.10"> |
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| 486 | <link rel="Chapter" title="11 Acknowledgments" href="#rfc.section.11"> |
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| 487 | <link rel="Chapter" href="#rfc.section.12" title="12 References"> |
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| 488 | <link rel="Appendix" title="A Changes from RFC 2616" href="#rfc.section.A"> |
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| 489 | <link rel="Appendix" title="B Imported ABNF" href="#rfc.section.B"> |
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| 490 | <link rel="Appendix" title="C Collected ABNF" href="#rfc.section.C"> |
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| 491 | <link rel="Appendix" title="D Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.D"> |
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| 492 | <link href="p5-range.html" rel="prev"> |
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| 493 | <link href="p7-auth.html" rel="next"> |
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| 494 | <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.590, 2013/01/23 17:59:36, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/"> |
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| 495 | <link rel="schema.dct" href="http://purl.org/dc/terms/"> |
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| 496 | <meta name="dct.creator" content="Fielding, R."> |
|---|
| 497 | <meta name="dct.creator" content="Nottingham, M."> |
|---|
| 498 | <meta name="dct.creator" content="Reschke, J. F."> |
|---|
| 499 | <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p6-cache-latest"> |
|---|
| 500 | <meta name="dct.issued" scheme="ISO8601" content="2013-02-23"> |
|---|
| 501 | <meta name="dct.replaces" content="urn:ietf:rfc:2616"> |
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| 502 | <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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| 503 | <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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| 504 | </head> |
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| 505 | <body onload="init();"> |
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| 506 | <table class="header"> |
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| 507 | <tbody> |
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| 508 | <tr> |
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| 509 | <td class="left">HTTPbis Working Group</td> |
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| 510 | <td class="right">R. Fielding, Editor</td> |
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| 511 | </tr> |
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| 512 | <tr> |
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| 513 | <td class="left">Internet-Draft</td> |
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| 514 | <td class="right">Adobe</td> |
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| 515 | </tr> |
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| 516 | <tr> |
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| 517 | <td class="left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved) |
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| 518 | </td> |
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| 519 | <td class="right">M. Nottingham, Editor</td> |
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| 520 | </tr> |
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| 521 | <tr> |
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| 522 | <td class="left">Intended status: Standards Track</td> |
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| 523 | <td class="right">Akamai</td> |
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| 524 | </tr> |
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| 525 | <tr> |
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| 526 | <td class="left">Expires: August 27, 2013</td> |
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| 527 | <td class="right">J. Reschke, Editor</td> |
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| 528 | </tr> |
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| 529 | <tr> |
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| 530 | <td class="left"></td> |
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| 531 | <td class="right">greenbytes</td> |
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| 532 | </tr> |
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| 533 | <tr> |
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| 534 | <td class="left"></td> |
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| 535 | <td class="right">February 23, 2013</td> |
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| 536 | </tr> |
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| 537 | </tbody> |
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| 538 | </table> |
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| 539 | <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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| 540 | <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1> |
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| 541 | <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information |
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| 542 | systems. This document defines requirements on HTTP caches and the associated header fields that control cache behavior or |
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| 543 | indicate cacheable response messages. |
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| 544 | </p> |
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| 545 | <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1> |
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| 546 | <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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| 547 | </p> |
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| 548 | <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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| 549 | </p> |
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| 550 | <p>The changes in this draft are summarized in <a href="#changes.since.22" title="Since draft-ietf-httpbis-p6-cache-22">Appendix D.4</a>. |
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| 551 | </p> |
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| 552 | <h1><a id="rfc.status" href="#rfc.status">Status of This Memo</a></h1> |
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| 553 | <p>This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.</p> |
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| 554 | <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute |
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| 555 | 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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| 556 | </p> |
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| 557 | <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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| 558 | 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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| 559 | in progress”. |
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| 560 | </p> |
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| 561 | <p>This Internet-Draft will expire on August 27, 2013.</p> |
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| 562 | <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1> |
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| 563 | <p>Copyright © 2013 IETF Trust and the persons identified as the document authors. All rights reserved.</p> |
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| 564 | <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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| 565 | and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License |
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| 566 | 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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| 567 | BSD License. |
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| 568 | </p> |
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| 569 | <p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November |
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| 570 | 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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| 571 | allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) |
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| 572 | controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative |
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| 573 | 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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| 574 | it into languages other than English. |
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| 575 | </p> |
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| 576 | <hr class="noprint"> |
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| 577 | <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1> |
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| 578 | <ul class="toc"> |
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| 579 | <li><a href="#rfc.section.1">1.</a> <a href="#caching">Introduction</a><ul> |
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| 580 | <li><a href="#rfc.section.1.1">1.1</a> <a href="#intro.purpose">Purpose</a></li> |
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| 581 | <li><a href="#rfc.section.1.2">1.2</a> <a href="#intro.terminology">Terminology</a></li> |
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| 582 | <li><a href="#rfc.section.1.3">1.3</a> <a href="#conformance">Conformance and Error Handling</a></li> |
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| 583 | <li><a href="#rfc.section.1.4">1.4</a> <a href="#notation">Syntax Notation</a><ul> |
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| 584 | <li><a href="#rfc.section.1.4.1">1.4.1</a> <a href="#delta-seconds">Delta Seconds</a></li> |
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| 585 | </ul> |
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| 586 | </li> |
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| 587 | </ul> |
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| 588 | </li> |
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| 589 | <li><a href="#rfc.section.2">2.</a> <a href="#caching.overview">Overview of Cache Operation</a></li> |
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| 590 | <li><a href="#rfc.section.3">3.</a> <a href="#response.cacheability">Storing Responses in Caches</a><ul> |
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| 591 | <li><a href="#rfc.section.3.1">3.1</a> <a href="#incomplete.responses">Storing Incomplete Responses</a></li> |
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| 592 | <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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| 593 | </ul> |
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| 594 | </li> |
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| 595 | <li><a href="#rfc.section.4">4.</a> <a href="#constructing.responses.from.caches">Constructing Responses from Caches</a><ul> |
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| 596 | <li><a href="#rfc.section.4.1">4.1</a> <a href="#expiration.model">Freshness Model</a><ul> |
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| 597 | <li><a href="#rfc.section.4.1.1">4.1.1</a> <a href="#calculating.freshness.lifetime">Calculating Freshness Lifetime</a></li> |
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| 598 | <li><a href="#rfc.section.4.1.2">4.1.2</a> <a href="#heuristic.freshness">Calculating Heuristic Freshness</a></li> |
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| 599 | <li><a href="#rfc.section.4.1.3">4.1.3</a> <a href="#age.calculations">Calculating Age</a></li> |
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| 600 | <li><a href="#rfc.section.4.1.4">4.1.4</a> <a href="#serving.stale.responses">Serving Stale Responses</a></li> |
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| 601 | </ul> |
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| 602 | </li> |
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| 603 | <li><a href="#rfc.section.4.2">4.2</a> <a href="#validation.model">Validation Model</a><ul> |
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| 604 | <li><a href="#rfc.section.4.2.1">4.2.1</a> <a href="#freshening.responses">Freshening Responses with 304 Not Modified</a></li> |
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| 605 | </ul> |
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| 606 | </li> |
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| 607 | <li><a href="#rfc.section.4.3">4.3</a> <a href="#caching.negotiated.responses">Using Negotiated Responses</a></li> |
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| 608 | <li><a href="#rfc.section.4.4">4.4</a> <a href="#combining.responses">Combining Partial Content</a></li> |
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| 609 | </ul> |
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| 610 | </li> |
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| 611 | <li><a href="#rfc.section.5">5.</a> <a href="#head.effects">Updating Caches with HEAD Responses</a></li> |
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| 612 | <li><a href="#rfc.section.6">6.</a> <a href="#invalidation.after.updates.or.deletions">Request Methods that Invalidate</a></li> |
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| 613 | <li><a href="#rfc.section.7">7.</a> <a href="#header.field.definitions">Header Field Definitions</a><ul> |
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| 614 | <li><a href="#rfc.section.7.1">7.1</a> <a href="#header.age">Age</a></li> |
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| 615 | <li><a href="#rfc.section.7.2">7.2</a> <a href="#header.cache-control">Cache-Control</a><ul> |
|---|
| 616 | <li><a href="#rfc.section.7.2.1">7.2.1</a> <a href="#cache-request-directive">Request Cache-Control Directives</a><ul> |
|---|
| 617 | <li><a href="#rfc.section.7.2.1.1">7.2.1.1</a> <a href="#cache-request-directive.no-cache">no-cache</a></li> |
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| 618 | <li><a href="#rfc.section.7.2.1.2">7.2.1.2</a> <a href="#cache-request-directive.no-store">no-store</a></li> |
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| 619 | <li><a href="#rfc.section.7.2.1.3">7.2.1.3</a> <a href="#cache-request-directive.max-age">max-age</a></li> |
|---|
| 620 | <li><a href="#rfc.section.7.2.1.4">7.2.1.4</a> <a href="#cache-request-directive.max-stale">max-stale</a></li> |
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| 621 | <li><a href="#rfc.section.7.2.1.5">7.2.1.5</a> <a href="#cache-request-directive.min-fresh">min-fresh</a></li> |
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| 622 | <li><a href="#rfc.section.7.2.1.6">7.2.1.6</a> <a href="#cache-request-directive.no-transform">no-transform</a></li> |
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| 623 | <li><a href="#rfc.section.7.2.1.7">7.2.1.7</a> <a href="#cache-request-directive.only-if-cached">only-if-cached</a></li> |
|---|
| 624 | </ul> |
|---|
| 625 | </li> |
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| 626 | <li><a href="#rfc.section.7.2.2">7.2.2</a> <a href="#cache-response-directive">Response Cache-Control Directives</a><ul> |
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| 627 | <li><a href="#rfc.section.7.2.2.1">7.2.2.1</a> <a href="#cache-response-directive.public">public</a></li> |
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| 628 | <li><a href="#rfc.section.7.2.2.2">7.2.2.2</a> <a href="#cache-response-directive.private">private</a></li> |
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| 629 | <li><a href="#rfc.section.7.2.2.3">7.2.2.3</a> <a href="#cache-response-directive.no-cache">no-cache</a></li> |
|---|
| 630 | <li><a href="#rfc.section.7.2.2.4">7.2.2.4</a> <a href="#cache-response-directive.no-store">no-store</a></li> |
|---|
| 631 | <li><a href="#rfc.section.7.2.2.5">7.2.2.5</a> <a href="#cache-response-directive.must-revalidate">must-revalidate</a></li> |
|---|
| 632 | <li><a href="#rfc.section.7.2.2.6">7.2.2.6</a> <a href="#cache-response-directive.proxy-revalidate">proxy-revalidate</a></li> |
|---|
| 633 | <li><a href="#rfc.section.7.2.2.7">7.2.2.7</a> <a href="#cache-response-directive.max-age">max-age</a></li> |
|---|
| 634 | <li><a href="#rfc.section.7.2.2.8">7.2.2.8</a> <a href="#cache-response-directive.s-maxage">s-maxage</a></li> |
|---|
| 635 | <li><a href="#rfc.section.7.2.2.9">7.2.2.9</a> <a href="#cache-response-directive.no-transform">no-transform</a></li> |
|---|
| 636 | </ul> |
|---|
| 637 | </li> |
|---|
| 638 | <li><a href="#rfc.section.7.2.3">7.2.3</a> <a href="#cache.control.extensions">Cache Control Extensions</a></li> |
|---|
| 639 | </ul> |
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| 640 | </li> |
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| 641 | <li><a href="#rfc.section.7.3">7.3</a> <a href="#header.expires">Expires</a></li> |
|---|
| 642 | <li><a href="#rfc.section.7.4">7.4</a> <a href="#header.pragma">Pragma</a></li> |
|---|
| 643 | <li><a href="#rfc.section.7.5">7.5</a> <a href="#header.warning">Warning</a><ul> |
|---|
| 644 | <li><a href="#rfc.section.7.5.1">7.5.1</a> <a href="#warn.110">110 Response is Stale</a></li> |
|---|
| 645 | <li><a href="#rfc.section.7.5.2">7.5.2</a> <a href="#warn.111">111 Revalidation Failed</a></li> |
|---|
| 646 | <li><a href="#rfc.section.7.5.3">7.5.3</a> <a href="#warn.112">112 Disconnected Operation</a></li> |
|---|
| 647 | <li><a href="#rfc.section.7.5.4">7.5.4</a> <a href="#warn.113">113 Heuristic Expiration</a></li> |
|---|
| 648 | <li><a href="#rfc.section.7.5.5">7.5.5</a> <a href="#warn.199">199 Miscellaneous Warning</a></li> |
|---|
| 649 | <li><a href="#rfc.section.7.5.6">7.5.6</a> <a href="#warn.214">214 Transformation Applied</a></li> |
|---|
| 650 | <li><a href="#rfc.section.7.5.7">7.5.7</a> <a href="#warn.299">299 Miscellaneous Persistent Warning</a></li> |
|---|
| 651 | <li><a href="#rfc.section.7.5.8">7.5.8</a> <a href="#warn.code.extensions">Warn Code Extensions</a></li> |
|---|
| 652 | </ul> |
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| 653 | </li> |
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| 654 | </ul> |
|---|
| 655 | </li> |
|---|
| 656 | <li><a href="#rfc.section.8">8.</a> <a href="#history.lists">History Lists</a></li> |
|---|
| 657 | <li><a href="#rfc.section.9">9.</a> <a href="#IANA.considerations">IANA Considerations</a><ul> |
|---|
| 658 | <li><a href="#rfc.section.9.1">9.1</a> <a href="#cache.directive.registration">Cache Directive Registry</a></li> |
|---|
| 659 | <li><a href="#rfc.section.9.2">9.2</a> <a href="#warn.code.registration">Warn Code Registry</a></li> |
|---|
| 660 | <li><a href="#rfc.section.9.3">9.3</a> <a href="#header.field.registration">Header Field Registration</a></li> |
|---|
| 661 | </ul> |
|---|
| 662 | </li> |
|---|
| 663 | <li><a href="#rfc.section.10">10.</a> <a href="#security.considerations">Security Considerations</a></li> |
|---|
| 664 | <li><a href="#rfc.section.11">11.</a> <a href="#acks">Acknowledgments</a></li> |
|---|
| 665 | <li><a href="#rfc.section.12">12.</a> <a href="#rfc.references">References</a><ul> |
|---|
| 666 | <li><a href="#rfc.section.12.1">12.1</a> <a href="#rfc.references.1">Normative References</a></li> |
|---|
| 667 | <li><a href="#rfc.section.12.2">12.2</a> <a href="#rfc.references.2">Informative References</a></li> |
|---|
| 668 | </ul> |
|---|
| 669 | </li> |
|---|
| 670 | <li><a href="#rfc.authors">Authors' Addresses</a></li> |
|---|
| 671 | <li><a href="#rfc.section.A">A.</a> <a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li> |
|---|
| 672 | <li><a href="#rfc.section.B">B.</a> <a href="#imported.abnf">Imported ABNF</a></li> |
|---|
| 673 | <li><a href="#rfc.section.C">C.</a> <a href="#collected.abnf">Collected ABNF</a></li> |
|---|
| 674 | <li><a href="#rfc.section.D">D.</a> <a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul> |
|---|
| 675 | <li><a href="#rfc.section.D.1">D.1</a> <a href="#changes.since.19">Since draft-ietf-httpbis-p6-cache-19</a></li> |
|---|
| 676 | <li><a href="#rfc.section.D.2">D.2</a> <a href="#changes.since.20">Since draft-ietf-httpbis-p6-cache-20</a></li> |
|---|
| 677 | <li><a href="#rfc.section.D.3">D.3</a> <a href="#changes.since.21">Since draft-ietf-httpbis-p6-cache-21</a></li> |
|---|
| 678 | <li><a href="#rfc.section.D.4">D.4</a> <a href="#changes.since.22">Since draft-ietf-httpbis-p6-cache-22</a></li> |
|---|
| 679 | </ul> |
|---|
| 680 | </li> |
|---|
| 681 | <li><a href="#rfc.index">Index</a></li> |
|---|
| 682 | </ul> |
|---|
| 683 | <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a> <a id="caching" href="#caching">Introduction</a></h1> |
|---|
| 684 | <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. |
|---|
| 685 | This document defines aspects of HTTP/1.1 related to caching and reusing response messages. |
|---|
| 686 | </p> |
|---|
| 687 | <div id="rfc.iref.c.1"></div> |
|---|
| 688 | <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a> <a id="intro.purpose" href="#intro.purpose">Purpose</a></h2> |
|---|
| 689 | <p id="rfc.section.1.1.p.1">An HTTP <dfn>cache</dfn> is a local store of response messages and the subsystem that controls its message storage, retrieval, and deletion. A cache |
|---|
| 690 | stores cacheable responses in order to reduce the response time and network bandwidth consumption on future, equivalent requests. |
|---|
| 691 | 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. |
|---|
| 692 | </p> |
|---|
| 693 | <p id="rfc.section.1.1.p.2">The goal of caching in HTTP/1.1 is to significantly improve performance by reusing a prior response message to satisfy a current |
|---|
| 694 | request. A stored response is considered "fresh", as defined in <a href="#expiration.model" title="Freshness Model">Section 4.1</a>, if the response can be reused without "validation" (checking with the origin server to see if the cached response remains |
|---|
| 695 | valid for this request). A fresh cache response can therefore reduce both latency and network transfers each time it is reused. |
|---|
| 696 | When a cached response is not fresh, it might still be reusable if it can be freshened by validation (<a href="#validation.model" title="Validation Model">Section 4.2</a>) or if the origin is unavailable. |
|---|
| 697 | </p> |
|---|
| 698 | <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a> <a id="intro.terminology" href="#intro.terminology">Terminology</a></h2> |
|---|
| 699 | <p id="rfc.section.1.2.p.1">This specification uses a number of terms to refer to the roles played by participants in, and objects of, HTTP caching.</p> |
|---|
| 700 | <p id="rfc.section.1.2.p.2"> <span id="rfc.iref.c.2"></span> <dfn>cache</dfn> |
|---|
| 701 | </p> |
|---|
| 702 | <ul class="empty"> |
|---|
| 703 | <li>A conformant implementation of an HTTP cache. Note that this implies an HTTP/1.1 cache; this specification does not define |
|---|
| 704 | conformance for HTTP/1.0 caches. |
|---|
| 705 | </li> |
|---|
| 706 | </ul> |
|---|
| 707 | <div id="shared.and.non-shared.caches"> |
|---|
| 708 | <p id="rfc.section.1.2.p.3"> <span id="rfc.iref.s.1"></span> <dfn>shared cache</dfn> |
|---|
| 709 | </p> |
|---|
| 710 | <ul class="empty"> |
|---|
| 711 | <li>A cache that stores responses to be reused by more than one user; usually (but not always) deployed as part of an intermediary.</li> |
|---|
| 712 | </ul> |
|---|
| 713 | </div> |
|---|
| 714 | <p id="rfc.section.1.2.p.4"> <span id="rfc.iref.p.1"></span> <dfn>private cache</dfn> |
|---|
| 715 | </p> |
|---|
| 716 | <ul class="empty"> |
|---|
| 717 | <li>A cache that is dedicated to a single user.</li> |
|---|
| 718 | </ul> |
|---|
| 719 | <p id="rfc.section.1.2.p.5"> <span id="rfc.iref.c.3"></span> <dfn>cacheable</dfn> |
|---|
| 720 | </p> |
|---|
| 721 | <ul class="empty"> |
|---|
| 722 | <li>A response is cacheable if a cache is allowed to store a copy of the response message for use in answering subsequent requests. |
|---|
| 723 | Even when a response is cacheable, there might be additional constraints on whether a cache can use the stored copy to satisfy |
|---|
| 724 | a particular request. |
|---|
| 725 | </li> |
|---|
| 726 | </ul> |
|---|
| 727 | <p id="rfc.section.1.2.p.6"> <span id="rfc.iref.e.1"></span> <dfn>explicit expiration time</dfn> |
|---|
| 728 | </p> |
|---|
| 729 | <ul class="empty"> |
|---|
| 730 | <li>The time at which the origin server intends that a stored response no longer be used by a cache without further validation.</li> |
|---|
| 731 | </ul> |
|---|
| 732 | <p id="rfc.section.1.2.p.7"> <span id="rfc.iref.h.1"></span> <dfn>heuristic expiration time</dfn> |
|---|
| 733 | </p> |
|---|
| 734 | <ul class="empty"> |
|---|
| 735 | <li>An expiration time assigned by a cache when no explicit expiration time is available.</li> |
|---|
| 736 | </ul> |
|---|
| 737 | <p id="rfc.section.1.2.p.8"> <span id="rfc.iref.a.1"></span> <dfn>age</dfn> |
|---|
| 738 | </p> |
|---|
| 739 | <ul class="empty"> |
|---|
| 740 | <li>The age of a response is the time since it was sent by, or successfully validated with, the origin server.</li> |
|---|
| 741 | </ul> |
|---|
| 742 | <p id="rfc.section.1.2.p.9"> <span id="rfc.iref.f.1"></span> <dfn>first-hand</dfn> |
|---|
| 743 | </p> |
|---|
| 744 | <ul class="empty"> |
|---|
| 745 | <li>A response is first-hand if the freshness model is not in use; i.e., its age is 0.</li> |
|---|
| 746 | </ul> |
|---|
| 747 | <p id="rfc.section.1.2.p.10"> <span id="rfc.iref.f.2"></span> <dfn>freshness lifetime</dfn> |
|---|
| 748 | </p> |
|---|
| 749 | <ul class="empty"> |
|---|
| 750 | <li>The length of time between the generation of a response and its expiration time.</li> |
|---|
| 751 | </ul> |
|---|
| 752 | <p id="rfc.section.1.2.p.11"> <span id="rfc.iref.f.3"></span> <dfn>fresh</dfn> |
|---|
| 753 | </p> |
|---|
| 754 | <ul class="empty"> |
|---|
| 755 | <li>A response is fresh if its age has not yet exceeded its freshness lifetime.</li> |
|---|
| 756 | </ul> |
|---|
| 757 | <p id="rfc.section.1.2.p.12"> <span id="rfc.iref.s.2"></span> <dfn>stale</dfn> |
|---|
| 758 | </p> |
|---|
| 759 | <ul class="empty"> |
|---|
| 760 | <li>A response is stale if its age has passed its freshness lifetime (either explicit or heuristic).</li> |
|---|
| 761 | </ul> |
|---|
| 762 | <p id="rfc.section.1.2.p.13"> <span id="rfc.iref.v.1"></span> <dfn>validator</dfn> |
|---|
| 763 | </p> |
|---|
| 764 | <ul class="empty"> |
|---|
| 765 | <li>A protocol element (e.g., an entity-tag or a <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> time) that is used to find out whether a stored response is an equivalent copy of a representation. 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.Part4.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[Part4]</cite></a>. |
|---|
| 766 | </li> |
|---|
| 767 | </ul> |
|---|
| 768 | <p id="rfc.section.1.2.p.14"> <span id="rfc.iref.s.3"></span> <span id="rfc.iref.v.2"></span> <dfn>strong validator</dfn> |
|---|
| 769 | </p> |
|---|
| 770 | <ul class="empty"> |
|---|
| 771 | <li>A validator that is defined by the origin server such that its current value will change if the representation data changes; |
|---|
| 772 | i.e., an entity-tag that is not marked as weak (<a href="p4-conditional.html#header.etag" title="ETag">Section 2.3</a> of <a href="#Part4" id="rfc.xref.Part4.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[Part4]</cite></a>) or, if no entity-tag is provided, a <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> value that is strong in the sense defined by <a href="p4-conditional.html#lastmod.comparison" title="Comparison">Section 2.2.2</a> of <a href="#Part4" id="rfc.xref.Part4.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[Part4]</cite></a>. |
|---|
| 773 | </li> |
|---|
| 774 | </ul> |
|---|
| 775 | <h2 id="rfc.section.1.3"><a href="#rfc.section.1.3">1.3</a> <a id="conformance" href="#conformance">Conformance and Error Handling</a></h2> |
|---|
| 776 | <p id="rfc.section.1.3.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" |
|---|
| 777 | 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>. |
|---|
| 778 | </p> |
|---|
| 779 | <p id="rfc.section.1.3.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>. |
|---|
| 780 | </p> |
|---|
| 781 | <h2 id="rfc.section.1.4"><a href="#rfc.section.1.4">1.4</a> <a id="notation" href="#notation">Syntax Notation</a></h2> |
|---|
| 782 | <p id="rfc.section.1.4.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#notation" title="Syntax Notation">Section 1.2</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. |
|---|
| 783 | </p> |
|---|
| 784 | <h3 id="rfc.section.1.4.1"><a href="#rfc.section.1.4.1">1.4.1</a> <a id="delta-seconds" href="#delta-seconds">Delta Seconds</a></h3> |
|---|
| 785 | <p id="rfc.section.1.4.1.p.1">The delta-seconds rule specifies a non-negative integer, representing time in seconds.</p> |
|---|
| 786 | <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> |
|---|
| 787 | </pre><p id="rfc.section.1.4.1.p.3">If an implementation receives a delta-seconds value larger than the largest positive integer it can represent, or if any of |
|---|
| 788 | its subsequent calculations overflows, it <em class="bcp14">MUST</em> consider the value to be 2147483648 (2<sup>31</sup>). Recipients parsing a delta-seconds value <em class="bcp14">MUST</em> use an arithmetic type of at least 31 bits of range, and senders <em class="bcp14">MUST NOT</em> send delta-seconds with a value greater than 2147483648. |
|---|
| 789 | </p> |
|---|
| 790 | <div id="rfc.iref.c.4"></div> |
|---|
| 791 | <div id="rfc.iref.c.5"></div> |
|---|
| 792 | <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a id="caching.overview" href="#caching.overview">Overview of Cache Operation</a></h1> |
|---|
| 793 | <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 |
|---|
| 794 | no requirement or locally-desired configuration prevents it. Therefore, HTTP cache requirements are focused on preventing |
|---|
| 795 | a cache from either storing a non-reusable response or reusing a stored response inappropriately. |
|---|
| 796 | </p> |
|---|
| 797 | <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 |
|---|
| 798 | 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 |
|---|
| 799 | use as a cache key. |
|---|
| 800 | </p> |
|---|
| 801 | <p id="rfc.section.2.p.3">The default <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 |
|---|
| 802 | responses to GET, many implementations simply decline other methods and use only the URI as the key. |
|---|
| 803 | </p> |
|---|
| 804 | <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 |
|---|
| 805 | by a secondary key for the values of the original request's selecting header fields (<a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section 4.3</a>). |
|---|
| 806 | </p> |
|---|
| 807 | <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a> <a id="response.cacheability" href="#response.cacheability">Storing Responses in Caches</a></h1> |
|---|
| 808 | <p id="rfc.section.3.p.1">A cache <em class="bcp14">MUST NOT</em> store a response to any request, unless: |
|---|
| 809 | </p> |
|---|
| 810 | <ul> |
|---|
| 811 | <li>The request method is understood by the cache and defined as being cacheable, and</li> |
|---|
| 812 | <li>the response status code is understood by the cache, and</li> |
|---|
| 813 | <li>the "no-store" cache directive (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.1" title="Cache-Control">Section 7.2</a>) does not appear in request or response header fields, and |
|---|
| 814 | </li> |
|---|
| 815 | <li>the "private" cache response directive (see <a href="#cache-response-directive.private" title="private">Section 7.2.2.2</a>) does not appear in the response, if the cache is shared, and |
|---|
| 816 | </li> |
|---|
| 817 | <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 |
|---|
| 818 | </li> |
|---|
| 819 | <li>the response either: |
|---|
| 820 | <ul> |
|---|
| 821 | <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 7.3</a>), or |
|---|
| 822 | </li> |
|---|
| 823 | <li>contains a max-age response cache directive (see <a href="#cache-response-directive.max-age" title="max-age">Section 7.2.2.7</a>), or |
|---|
| 824 | </li> |
|---|
| 825 | <li>contains a s-maxage response cache directive and the cache is shared, or</li> |
|---|
| 826 | <li>contains a Cache Control Extension (see <a href="#cache.control.extensions" title="Cache Control Extensions">Section 7.2.3</a>) that allows it to be cached, or |
|---|
| 827 | </li> |
|---|
| 828 | <li>has a status code that is defined as cacheable (see <a href="#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.1.2</a>), or |
|---|
| 829 | </li> |
|---|
| 830 | <li>contains a public response cache directive (see <a href="#cache-response-directive.public" title="public">Section 7.2.2.1</a>). |
|---|
| 831 | </li> |
|---|
| 832 | </ul> |
|---|
| 833 | </li> |
|---|
| 834 | </ul> |
|---|
| 835 | <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 7.2.3</a>. |
|---|
| 836 | </p> |
|---|
| 837 | <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 any |
|---|
| 838 | cache-specific behavior. |
|---|
| 839 | </p> |
|---|
| 840 | <p id="rfc.section.3.p.4">Note that, in normal operation, many caches will not store a response that has neither a cache validator nor an explicit expiration |
|---|
| 841 | time, as such responses are not usually useful to store. However, caches are not prohibited from storing such responses. |
|---|
| 842 | </p> |
|---|
| 843 | <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a> <a id="incomplete.responses" href="#incomplete.responses">Storing Incomplete Responses</a></h2> |
|---|
| 844 | <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 is GET, the response status is <a href="p2-semantics.html#status.200" class="smpl">200 |
|---|
| 845 | (OK)</a>, and the entire response header block 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 |
|---|
| 846 | (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. |
|---|
| 847 | </p> |
|---|
| 848 | <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 4.4</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 |
|---|
| 849 | 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. |
|---|
| 850 | </p> |
|---|
| 851 | <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a> <a id="caching.authenticated.responses" href="#caching.authenticated.responses">Storing Responses to Authenticated Requests</a></h2> |
|---|
| 852 | <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. |
|---|
| 853 | </p> |
|---|
| 854 | <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 7.2.2</a>) have such an effect: must-revalidate, public, s-maxage. |
|---|
| 855 | </p> |
|---|
| 856 | <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 |
|---|
| 857 | served stale (<a href="#serving.stale.responses" title="Serving Stale Responses">Section 4.1.4</a>) by shared caches. In particular, a response with either "max-age=0, must-revalidate" or "s-maxage=0" cannot be used to satisfy |
|---|
| 858 | a subsequent request without revalidating it on the origin server. |
|---|
| 859 | </p> |
|---|
| 860 | <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a> <a id="constructing.responses.from.caches" href="#constructing.responses.from.caches">Constructing Responses from Caches</a></h1> |
|---|
| 861 | <p id="rfc.section.4.p.1">For a presented request, a cache <em class="bcp14">MUST NOT</em> send a stored response, unless: |
|---|
| 862 | </p> |
|---|
| 863 | <ul> |
|---|
| 864 | <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 |
|---|
| 865 | </li> |
|---|
| 866 | <li>the request method associated with the stored response allows it to be used for the presented request, and</li> |
|---|
| 867 | <li>selecting header fields nominated by the stored response (if any) match those presented (see <a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section 4.3</a>), and |
|---|
| 868 | </li> |
|---|
| 869 | <li>the presented request does not contain the no-cache pragma (<a href="#header.pragma" id="rfc.xref.header.pragma.1" title="Pragma">Section 7.4</a>), nor the no-cache cache directive (<a href="#cache-request-directive" title="Request Cache-Control Directives">Section 7.2.1</a>), unless the stored response is successfully validated (<a href="#validation.model" title="Validation Model">Section 4.2</a>), and |
|---|
| 870 | </li> |
|---|
| 871 | <li>the stored response does not contain the no-cache cache directive (<a href="#cache-response-directive.no-cache" title="no-cache">Section 7.2.2.3</a>), unless it is successfully validated (<a href="#validation.model" title="Validation Model">Section 4.2</a>), and |
|---|
| 872 | </li> |
|---|
| 873 | <li>the stored response is either: |
|---|
| 874 | <ul> |
|---|
| 875 | <li>fresh (see <a href="#expiration.model" title="Freshness Model">Section 4.1</a>), or |
|---|
| 876 | </li> |
|---|
| 877 | <li>allowed to be served stale (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section 4.1.4</a>), or |
|---|
| 878 | </li> |
|---|
| 879 | <li>successfully validated (see <a href="#validation.model" title="Validation Model">Section 4.2</a>). |
|---|
| 880 | </li> |
|---|
| 881 | </ul> |
|---|
| 882 | </li> |
|---|
| 883 | </ul> |
|---|
| 884 | <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 7.2.3</a>. |
|---|
| 885 | </p> |
|---|
| 886 | <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> send a single <a href="#header.age" class="smpl">Age</a> header field (<a href="#header.age" id="rfc.xref.header.age.1" title="Age">Section 7.1</a>) in the response with a value equal to the stored response's current_age; see <a href="#age.calculations" title="Calculating Age">Section 4.1.3</a>. |
|---|
| 887 | </p> |
|---|
| 888 | <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 |
|---|
| 889 | and having received a corresponding response. |
|---|
| 890 | </p> |
|---|
| 891 | <p id="rfc.section.4.p.5">Also, note that unsafe requests might invalidate already stored responses; see <a href="#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section 6</a>. |
|---|
| 892 | </p> |
|---|
| 893 | <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 a request with "Cache-Control: max-age=0" or "Cache-Control: no-cache" to disambiguate |
|---|
| 894 | which response to use. |
|---|
| 895 | </p> |
|---|
| 896 | <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 on every use. |
|---|
| 897 | </p> |
|---|
| 898 | <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a> <a id="expiration.model" href="#expiration.model">Freshness Model</a></h2> |
|---|
| 899 | <p id="rfc.section.4.1.p.1">When a response is "fresh" in the cache, it can be used to satisfy subsequent requests without contacting the origin server, |
|---|
| 900 | thereby improving efficiency. |
|---|
| 901 | </p> |
|---|
| 902 | <p id="rfc.section.4.1.p.2">The primary mechanism for determining freshness is for an origin server to provide an explicit expiration time in the future, |
|---|
| 903 | 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 7.3</a>) or the max-age response cache directive (<a href="#cache-response-directive.max-age" title="max-age">Section 7.2.2.7</a>). Generally, origin servers will assign future explicit expiration times to responses in the belief that the representation |
|---|
| 904 | is not likely to change in a semantically significant way before the expiration time is reached. |
|---|
| 905 | </p> |
|---|
| 906 | <p id="rfc.section.4.1.p.3">If an origin server wishes to force a cache to validate every request, it can assign an explicit expiration time in the past |
|---|
| 907 | to indicate that the response is already stale. Compliant caches will normally validate a stale cached response before reusing |
|---|
| 908 | it for subsequent requests (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section 4.1.4</a>). |
|---|
| 909 | </p> |
|---|
| 910 | <p id="rfc.section.4.1.p.4">Since origin servers do not always provide explicit expiration times, caches are also allowed to use a heuristic to determine |
|---|
| 911 | an expiration time under certain circumstances (see <a href="#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.1.2</a>). |
|---|
| 912 | </p> |
|---|
| 913 | <div id="rfc.figure.u.2"></div> |
|---|
| 914 | <p>The calculation to determine if a response is fresh is:</p> <pre class="text"> response_is_fresh = (freshness_lifetime > current_age) |
|---|
| 915 | </pre> <p id="rfc.section.4.1.p.6">The freshness_lifetime is defined in <a href="#calculating.freshness.lifetime" title="Calculating Freshness Lifetime">Section 4.1.1</a>; the current_age is defined in <a href="#age.calculations" title="Calculating Age">Section 4.1.3</a>. |
|---|
| 916 | </p> |
|---|
| 917 | <p id="rfc.section.4.1.p.7">Clients can send the max-age or min-fresh cache directives in a request to constrain or relax freshness calculations for the |
|---|
| 918 | corresponding response (<a href="#cache-request-directive" title="Request Cache-Control Directives">Section 7.2.1</a>). |
|---|
| 919 | </p> |
|---|
| 920 | <p id="rfc.section.4.1.p.8">Note that freshness applies only to cache operation; it cannot be used to force a user agent to refresh its display or reload |
|---|
| 921 | a resource. See <a href="#history.lists" title="History Lists">Section 8</a> for an explanation of the difference between caches and history mechanisms. |
|---|
| 922 | </p> |
|---|
| 923 | <h3 id="rfc.section.4.1.1"><a href="#rfc.section.4.1.1">4.1.1</a> <a id="calculating.freshness.lifetime" href="#calculating.freshness.lifetime">Calculating Freshness Lifetime</a></h3> |
|---|
| 924 | <p id="rfc.section.4.1.1.p.1">A cache can calculate the freshness lifetime (denoted as freshness_lifetime) of a response by using the first match of: </p> |
|---|
| 925 | <ul> |
|---|
| 926 | <li>If the cache is shared and the s-maxage response cache directive (<a href="#cache-response-directive.s-maxage" title="s-maxage">Section 7.2.2.8</a>) is present, use its value, or |
|---|
| 927 | </li> |
|---|
| 928 | <li>If the max-age response cache directive (<a href="#cache-response-directive.max-age" title="max-age">Section 7.2.2.7</a>) is present, use its value, or |
|---|
| 929 | </li> |
|---|
| 930 | <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 7.3</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 |
|---|
| 931 | </li> |
|---|
| 932 | <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 4.1.2</a>. |
|---|
| 933 | </li> |
|---|
| 934 | </ul> |
|---|
| 935 | <p id="rfc.section.4.1.1.p.2">Note that this calculation is not vulnerable to clock skew, since all of the information comes from the origin server.</p> |
|---|
| 936 | <p id="rfc.section.4.1.1.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), it is considered invalid. Caches are encouraged to consider responses |
|---|
| 937 | that have invalid freshness information to be stale. |
|---|
| 938 | </p> |
|---|
| 939 | <h3 id="rfc.section.4.1.2"><a href="#rfc.section.4.1.2">4.1.2</a> <a id="heuristic.freshness" href="#heuristic.freshness">Calculating Heuristic Freshness</a></h3> |
|---|
| 940 | <p id="rfc.section.4.1.2.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 |
|---|
| 941 | 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 |
|---|
| 942 | constraints on their results. |
|---|
| 943 | </p> |
|---|
| 944 | <p id="rfc.section.4.1.2.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 |
|---|
| 945 | 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 |
|---|
| 946 | defined as cacheable, and responses without explicit freshness that have been marked as explicitly cacheable (e.g., with a |
|---|
| 947 | "public" response cache directive). |
|---|
| 948 | </p> |
|---|
| 949 | <p id="rfc.section.4.1.2.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.Part4.4"><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 |
|---|
| 950 | time. A typical setting of this fraction might be 10%. |
|---|
| 951 | </p> |
|---|
| 952 | <p id="rfc.section.4.1.2.p.4">When a heuristic is used to calculate freshness lifetime, a cache <em class="bcp14">SHOULD</em> attach a <a href="#header.warning" class="smpl">Warning</a> header field with a 113 warn-code to the response if its current_age is more than 24 hours and such a warning is not already |
|---|
| 953 | present. |
|---|
| 954 | </p> |
|---|
| 955 | <div class="note" id="rfc.section.4.1.2.p.5"> |
|---|
| 956 | <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, |
|---|
| 957 | this has not been widely implemented. Therefore, servers are encouraged to send explicit directives (e.g., Cache-Control: |
|---|
| 958 | no-cache) if they wish to preclude caching. |
|---|
| 959 | </p> |
|---|
| 960 | </div> |
|---|
| 961 | <h3 id="rfc.section.4.1.3"><a href="#rfc.section.4.1.3">4.1.3</a> <a id="age.calculations" href="#age.calculations">Calculating Age</a></h3> |
|---|
| 962 | <p id="rfc.section.4.1.3.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 |
|---|
| 963 | the cache's estimate of the number of seconds since the response was generated or validated by the origin server. In essence, |
|---|
| 964 | 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 |
|---|
| 965 | server, plus the amount of time it has been in transit along network paths. |
|---|
| 966 | </p> |
|---|
| 967 | <p id="rfc.section.4.1.3.p.2">The following data is used for the age calculation:</p> |
|---|
| 968 | <p id="rfc.section.4.1.3.p.3"> <dfn>age_value</dfn> |
|---|
| 969 | </p> |
|---|
| 970 | <ul class="empty"> |
|---|
| 971 | <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 7.1</a>), in a form appropriate for arithmetic operation; or 0, if not available. |
|---|
| 972 | </li> |
|---|
| 973 | </ul> |
|---|
| 974 | <p id="rfc.section.4.1.3.p.4"> <dfn>date_value</dfn> |
|---|
| 975 | </p> |
|---|
| 976 | <ul class="empty"> |
|---|
| 977 | <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.Part2.4"><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. |
|---|
| 978 | </li> |
|---|
| 979 | </ul> |
|---|
| 980 | <p id="rfc.section.4.1.3.p.5"> <dfn>now</dfn> |
|---|
| 981 | </p> |
|---|
| 982 | <ul class="empty"> |
|---|
| 983 | <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="#RFC1305" id="rfc.xref.RFC1305.1"><cite title="Network Time Protocol (Version 3) Specification, Implementation">[RFC1305]</cite></a>) or some similar protocol to synchronize its clocks to Coordinated Universal Time. |
|---|
| 984 | </li> |
|---|
| 985 | </ul> |
|---|
| 986 | <p id="rfc.section.4.1.3.p.6"> <dfn>request_time</dfn> |
|---|
| 987 | </p> |
|---|
| 988 | <ul class="empty"> |
|---|
| 989 | <li>The current value of the clock at the host at the time the request resulting in the stored response was made.</li> |
|---|
| 990 | </ul> |
|---|
| 991 | <p id="rfc.section.4.1.3.p.7"> <dfn>response_time</dfn> |
|---|
| 992 | </p> |
|---|
| 993 | <ul class="empty"> |
|---|
| 994 | <li>The current value of the clock at the host at the time the response was received.</li> |
|---|
| 995 | </ul> |
|---|
| 996 | <p id="rfc.section.4.1.3.p.8">A response's age can be calculated in two entirely independent ways: </p> |
|---|
| 997 | <ol> |
|---|
| 998 | <li>the "apparent_age": response_time minus date_value, if the local clock is reasonably well synchronized to the origin server's |
|---|
| 999 | clock. If the result is negative, the result is replaced by zero. |
|---|
| 1000 | </li> |
|---|
| 1001 | <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. |
|---|
| 1002 | </li> |
|---|
| 1003 | </ol> |
|---|
| 1004 | <div id="rfc.figure.u.3"></div> <pre class="text"> apparent_age = max(0, response_time - date_value); |
|---|
| 1005 | |
|---|
| 1006 | response_delay = response_time - request_time; |
|---|
| 1007 | corrected_age_value = age_value + response_delay; |
|---|
| 1008 | </pre> <div id="rfc.figure.u.4"></div> |
|---|
| 1009 | <p>These <em class="bcp14">SHOULD</em> be combined as |
|---|
| 1010 | </p> <pre class="text"> corrected_initial_age = max(apparent_age, corrected_age_value); |
|---|
| 1011 | </pre><p id="rfc.section.4.1.3.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. |
|---|
| 1012 | </p> |
|---|
| 1013 | <p id="rfc.section.4.1.3.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 |
|---|
| 1014 | was last validated by the origin server to the corrected_initial_age. |
|---|
| 1015 | </p> |
|---|
| 1016 | <div id="rfc.figure.u.5"></div><pre class="text"> resident_time = now - response_time; |
|---|
| 1017 | current_age = corrected_initial_age + resident_time; |
|---|
| 1018 | </pre><p id="rfc.section.4.1.3.p.14">Additionally, to avoid common problems in date parsing:</p> |
|---|
| 1019 | <p id="rfc.section.4.1.3.p.15"> </p> |
|---|
| 1020 | <ul> |
|---|
| 1021 | <li>Although all date formats are specified to be case-sensitive, cache recipients <em class="bcp14">SHOULD</em> match day, week and timezone names case-insensitively. |
|---|
| 1022 | </li> |
|---|
| 1023 | <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. |
|---|
| 1024 | </li> |
|---|
| 1025 | <li>Cache recipients <em class="bcp14">MUST NOT</em> allow local time zones to influence the calculation or comparison of an age or expiration time. |
|---|
| 1026 | </li> |
|---|
| 1027 | <li>Cache recipients <em class="bcp14">SHOULD</em> consider a date with a zone abbreviation other than "GMT" to be invalid for calculating expiration. |
|---|
| 1028 | </li> |
|---|
| 1029 | </ul> |
|---|
| 1030 | <h3 id="rfc.section.4.1.4"><a href="#rfc.section.4.1.4">4.1.4</a> <a id="serving.stale.responses" href="#serving.stale.responses">Serving Stale Responses</a></h3> |
|---|
| 1031 | <p id="rfc.section.4.1.4.p.1">A "stale" response is one that either has explicit expiry information or is allowed to have heuristic expiry calculated, but |
|---|
| 1032 | is not fresh according to the calculations in <a href="#expiration.model" title="Freshness Model">Section 4.1</a>. |
|---|
| 1033 | </p> |
|---|
| 1034 | <p id="rfc.section.4.1.4.p.2">A cache <em class="bcp14">MUST NOT</em> send a stale response if it is prohibited by an explicit in-protocol directive (e.g., by a "no-store" or "no-cache" cache |
|---|
| 1035 | directive, a "must-revalidate" cache-response-directive, or an applicable "s-maxage" or "proxy-revalidate" cache-response-directive; |
|---|
| 1036 | see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 7.2.2</a>). |
|---|
| 1037 | </p> |
|---|
| 1038 | <p id="rfc.section.4.1.4.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) |
|---|
| 1039 | 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 7.2.1</a>). |
|---|
| 1040 | </p> |
|---|
| 1041 | <p id="rfc.section.4.1.4.p.4">A cache <em class="bcp14">SHOULD</em> append a <a href="#header.warning" class="smpl">Warning</a> header field with the 110 warn-code (see <a href="#header.warning" id="rfc.xref.header.warning.1" title="Warning">Section 7.5</a>) to stale responses. Likewise, a cache <em class="bcp14">SHOULD</em> add the 112 warn-code to stale responses if the cache is disconnected. |
|---|
| 1042 | </p> |
|---|
| 1043 | <p id="rfc.section.4.1.4.p.5">If a cache receives a first-hand response (either an entire response, or a <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> response) that it would normally forward to the requesting client, and the received response is no longer fresh, the cache |
|---|
| 1044 | can forward it to the requesting client without adding a new <a href="#header.warning" class="smpl">Warning</a> (but without removing any existing Warning header fields). A cache shouldn't attempt to validate a response simply because |
|---|
| 1045 | that response became stale in transit. |
|---|
| 1046 | </p> |
|---|
| 1047 | <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a> <a id="validation.model" href="#validation.model">Validation Model</a></h2> |
|---|
| 1048 | <p id="rfc.section.4.2.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 |
|---|
| 1049 | fresh, or one cannot be selected; see <a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section 4.3</a>), it can use the conditional request mechanism <a href="#Part4" id="rfc.xref.Part4.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[Part4]</cite></a> in the forwarded request to give the origin server an opportunity to both select a valid stored response to be used, and to |
|---|
| 1050 | update it. This process is known as "validating" or "revalidating" the stored response. |
|---|
| 1051 | </p> |
|---|
| 1052 | <p id="rfc.section.4.2.p.2">When sending such a conditional request, a cache adds an <a href="p4-conditional.html#header.if-modified-since" class="smpl">If-Modified-Since</a> header field whose value is that of the <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> header field from the selected (see <a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section 4.3</a>) stored response, if available. |
|---|
| 1053 | </p> |
|---|
| 1054 | <p id="rfc.section.4.2.p.3">Additionally, a cache can add an <a href="p4-conditional.html#header.if-none-match" class="smpl">If-None-Match</a> header field whose value is that of the <a href="p4-conditional.html#header.etag" class="smpl">ETag</a> header field(s) from all responses stored for the requested URI, if present. However, if any of the stored responses contains |
|---|
| 1055 | only partial content, the cache shouldn't include its entity-tag in the If-None-Match header field unless the request is for |
|---|
| 1056 | a range that would be fully satisfied by that stored response. |
|---|
| 1057 | </p> |
|---|
| 1058 | <p id="rfc.section.4.2.p.4">Cache handling of a response to a conditional request is dependent upon its status code:</p> |
|---|
| 1059 | <p id="rfc.section.4.2.p.5"> </p> |
|---|
| 1060 | <ul> |
|---|
| 1061 | <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 Responses with 304 Not Modified">Section 4.2.1</a>. |
|---|
| 1062 | </li> |
|---|
| 1063 | <li>A full response (i.e., one with a payload body) indicates that none of the stored responses nominated in the conditional request |
|---|
| 1064 | is suitable. Instead, the cache can use the full response to satisfy the request and <em class="bcp14">MAY</em> replace the stored response(s). |
|---|
| 1065 | </li> |
|---|
| 1066 | <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 |
|---|
| 1067 | if the server failed to respond. In the latter case, it can send a previously stored response (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section 4.1.4</a>). |
|---|
| 1068 | </li> |
|---|
| 1069 | </ul> |
|---|
| 1070 | <h3 id="rfc.section.4.2.1"><a href="#rfc.section.4.2.1">4.2.1</a> <a id="freshening.responses" href="#freshening.responses">Freshening Responses with 304 Not Modified</a></h3> |
|---|
| 1071 | <p id="rfc.section.4.2.1.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 |
|---|
| 1072 | 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. |
|---|
| 1073 | </p> |
|---|
| 1074 | <p id="rfc.section.4.2.1.p.2">The stored response to update is identified by using the first match (if any) of: </p> |
|---|
| 1075 | <ul> |
|---|
| 1076 | <li>If the new response contains a strong validator, then that strong validator identifies the selected representation. All of |
|---|
| 1077 | the stored responses with the same strong validator are selected. If none of the stored responses contain the same strong |
|---|
| 1078 | validator, then the new response <em class="bcp14">MUST NOT</em> be used to update any stored responses. |
|---|
| 1079 | </li> |
|---|
| 1080 | <li>If the new response contains a weak validator and that validator corresponds to one of the cache's stored responses, then |
|---|
| 1081 | the most recent of those matching stored responses is selected. |
|---|
| 1082 | </li> |
|---|
| 1083 | <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 |
|---|
| 1084 | request from a source other than the Last-Modified response header field), and there is only one stored response, and that |
|---|
| 1085 | stored response also lacks a validator, then that stored response is selected. |
|---|
| 1086 | </li> |
|---|
| 1087 | </ul> |
|---|
| 1088 | <p id="rfc.section.4.2.1.p.3">If a stored response is selected for update, the cache <em class="bcp14">MUST</em>: |
|---|
| 1089 | </p> |
|---|
| 1090 | <ul> |
|---|
| 1091 | <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 7.5</a>); |
|---|
| 1092 | </li> |
|---|
| 1093 | <li>retain any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 2xx; and, |
|---|
| 1094 | </li> |
|---|
| 1095 | <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. |
|---|
| 1096 | </li> |
|---|
| 1097 | </ul> |
|---|
| 1098 | <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a> <a id="caching.negotiated.responses" href="#caching.negotiated.responses">Using Negotiated Responses</a></h2> |
|---|
| 1099 | <p id="rfc.section.4.3.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.Part2.5"><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 |
|---|
| 1100 | request (i.e., that associated with the stored response), and the presented request. |
|---|
| 1101 | </p> |
|---|
| 1102 | <p id="rfc.section.4.3.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 |
|---|
| 1103 | to those in the second request by applying any of the following: |
|---|
| 1104 | </p> |
|---|
| 1105 | <ul> |
|---|
| 1106 | <li>adding or removing whitespace, where allowed in the header field's syntax</li> |
|---|
| 1107 | <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>) |
|---|
| 1108 | </li> |
|---|
| 1109 | <li>normalizing both header field values in a way that is known to have identical semantics, according to the header field's specification |
|---|
| 1110 | (e.g., re-ordering field values when order is not significant; case-normalization, where values are defined to be case-insensitive) |
|---|
| 1111 | </li> |
|---|
| 1112 | </ul> |
|---|
| 1113 | <p id="rfc.section.4.3.p.3">If (after any normalization that might take place) a header field is absent from a request, it can only match another request |
|---|
| 1114 | if it is also absent there. |
|---|
| 1115 | </p> |
|---|
| 1116 | <p id="rfc.section.4.3.p.4">A <a href="p2-semantics.html#header.vary" class="smpl">Vary</a> header field-value of "*" always fails to match, and subsequent requests to that resource can only be properly interpreted |
|---|
| 1117 | by the origin server. |
|---|
| 1118 | </p> |
|---|
| 1119 | <p id="rfc.section.4.3.p.5">The stored response with matching selecting header fields is known as the selected response.</p> |
|---|
| 1120 | <p id="rfc.section.4.3.p.6">If multiple selected responses are available, the most recent response (as determined by the <a href="p2-semantics.html#header.date" class="smpl">Date</a> header field) is used; see <a href="#constructing.responses.from.caches" title="Constructing Responses from Caches">Section 4</a>. |
|---|
| 1121 | </p> |
|---|
| 1122 | <p id="rfc.section.4.3.p.7">If no selected response is available, the cache cannot satisfy the presented request. Typically, it is forwarded to the origin |
|---|
| 1123 | server in a (possibly conditional; see <a href="#validation.model" title="Validation Model">Section 4.2</a>) request. |
|---|
| 1124 | </p> |
|---|
| 1125 | <h2 id="rfc.section.4.4"><a href="#rfc.section.4.4">4.4</a> <a id="combining.responses" href="#combining.responses">Combining Partial Content</a></h2> |
|---|
| 1126 | <p id="rfc.section.4.4.p.1">A response might transfer only a partial representation if the connection closed prematurely or if the request used one or |
|---|
| 1127 | 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 |
|---|
| 1128 | 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>. |
|---|
| 1129 | </p> |
|---|
| 1130 | <p id="rfc.section.4.4.p.2">When combining the new response with one or more stored responses, a cache <em class="bcp14">MUST</em>: |
|---|
| 1131 | </p> |
|---|
| 1132 | <ul> |
|---|
| 1133 | <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 7.5</a>); |
|---|
| 1134 | </li> |
|---|
| 1135 | <li>retain any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 2xx; and, |
|---|
| 1136 | </li> |
|---|
| 1137 | <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. |
|---|
| 1138 | </li> |
|---|
| 1139 | </ul> |
|---|
| 1140 | <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a> <a id="head.effects" href="#head.effects">Updating Caches with HEAD Responses</a></h1> |
|---|
| 1141 | <p id="rfc.section.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 |
|---|
| 1142 | a body. This property of HEAD responses is used to both invalidate and update cached GET responses. |
|---|
| 1143 | </p> |
|---|
| 1144 | <p id="rfc.section.5.p.2">If one or more stored GET responses can be selected (as per <a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section 4.3</a>) for a HEAD request, and the <a href="p1-messaging.html#header.content-length" class="smpl">Content-Length</a>, <a href="p4-conditional.html#header.etag" class="smpl">ETag</a> or <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> value of a HEAD response differs from that in a selected GET response, the cache <em class="bcp14">MUST</em> consider that selected response to be stale. |
|---|
| 1145 | </p> |
|---|
| 1146 | <p id="rfc.section.5.p.3">If the <a href="p1-messaging.html#header.content-length" class="smpl">Content-Length</a>, <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> values of a HEAD response (when present) are the same as that in a selected GET response (as per <a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section 4.3</a>), the cache <em class="bcp14">SHOULD</em> update the remaining header fields in the stored response using the following rules: |
|---|
| 1147 | </p> |
|---|
| 1148 | <ul> |
|---|
| 1149 | <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.4" title="Warning">Section 7.5</a>); |
|---|
| 1150 | </li> |
|---|
| 1151 | <li>retain any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 2xx; and, |
|---|
| 1152 | </li> |
|---|
| 1153 | <li>use other header fields provided in the response to replace all instances of the corresponding header fields in the stored |
|---|
| 1154 | response. |
|---|
| 1155 | </li> |
|---|
| 1156 | </ul> |
|---|
| 1157 | <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a> <a id="invalidation.after.updates.or.deletions" href="#invalidation.after.updates.or.deletions">Request Methods that Invalidate</a></h1> |
|---|
| 1158 | <p id="rfc.section.6.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 |
|---|
| 1159 | to keep their contents up-to-date. |
|---|
| 1160 | </p> |
|---|
| 1161 | <p id="rfc.section.6.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 response to a request with an unsafe method is received. |
|---|
| 1162 | </p> |
|---|
| 1163 | <p id="rfc.section.6.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. |
|---|
| 1164 | </p> |
|---|
| 1165 | <p id="rfc.section.6.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. |
|---|
| 1166 | </p> |
|---|
| 1167 | <p id="rfc.section.6.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, |
|---|
| 1168 | or will mark these as "invalid" and in need of a mandatory validation before they can be sent in response to a subsequent |
|---|
| 1169 | request. |
|---|
| 1170 | </p> |
|---|
| 1171 | <p id="rfc.section.6.p.6">Note that this does not guarantee that all appropriate responses are invalidated. For example, the request that caused the |
|---|
| 1172 | change at the origin server might not have gone through the cache where a response is stored. |
|---|
| 1173 | </p> |
|---|
| 1174 | <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a> <a id="header.field.definitions" href="#header.field.definitions">Header Field Definitions</a></h1> |
|---|
| 1175 | <p id="rfc.section.7.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to caching.</p> |
|---|
| 1176 | <div id="rfc.iref.a.2"></div> |
|---|
| 1177 | <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a> <a id="header.age" href="#header.age">Age</a></h2> |
|---|
| 1178 | <p id="rfc.section.7.1.p.1">The "Age" header field conveys the sender's estimate of the amount of time since the response was generated or successfully |
|---|
| 1179 | validated at the origin server. Age values are calculated as specified in <a href="#age.calculations" title="Calculating Age">Section 4.1.3</a>. |
|---|
| 1180 | </p> |
|---|
| 1181 | <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> |
|---|
| 1182 | </pre><p id="rfc.section.7.1.p.3">Age field-values are non-negative integers, representing time in seconds (see <a href="#delta-seconds" title="Delta Seconds">Section 1.4.1</a>). |
|---|
| 1183 | </p> |
|---|
| 1184 | <p id="rfc.section.7.1.p.4">The presence of an Age header field in a response implies that a response is not first-hand. However, the converse is not |
|---|
| 1185 | true, since HTTP/1.0 caches might not implement the Age header field. |
|---|
| 1186 | </p> |
|---|
| 1187 | <div id="rfc.iref.c.6"></div> |
|---|
| 1188 | <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a> <a id="header.cache-control" href="#header.cache-control">Cache-Control</a></h2> |
|---|
| 1189 | <p id="rfc.section.7.2.p.1">The "Cache-Control" header field is used to specify directives for caches along the request/response chain. Such cache directives |
|---|
| 1190 | are unidirectional in that the presence of a directive in a request does not imply that the same directive is to be given |
|---|
| 1191 | in the response. |
|---|
| 1192 | </p> |
|---|
| 1193 | <p id="rfc.section.7.2.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 7.2.3</a> for information about how Cache-Control directives defined elsewhere are handled. |
|---|
| 1194 | </p> |
|---|
| 1195 | <div class="note" id="rfc.section.7.2.p.3"> |
|---|
| 1196 | <p> <b>Note:</b> HTTP/1.0 caches might not implement Cache-Control and might only implement Pragma: no-cache (see <a href="#header.pragma" id="rfc.xref.header.pragma.2" title="Pragma">Section 7.4</a>). |
|---|
| 1197 | </p> |
|---|
| 1198 | </div> |
|---|
| 1199 | <p id="rfc.section.7.2.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 |
|---|
| 1200 | might be applicable to all recipients along the request/response chain. It is not possible to target a directive to a specific |
|---|
| 1201 | cache. |
|---|
| 1202 | </p> |
|---|
| 1203 | <p id="rfc.section.7.2.p.5">Cache directives are identified by a token, to be compared case-insensitively, and have an optional argument, that can use |
|---|
| 1204 | both token and quoted-string syntax. For the directives defined below that define arguments, recipients ought to accept both |
|---|
| 1205 | forms, even if one is documented to be preferred. For any directive not defined by this specification, recipients <em class="bcp14">MUST</em> accept both forms. |
|---|
| 1206 | </p> |
|---|
| 1207 | <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> |
|---|
| 1208 | |
|---|
| 1209 | <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> ) ] |
|---|
| 1210 | </pre><p id="rfc.section.7.2.p.7">For the cache directives defined below, no argument is defined (nor allowed) otherwise stated otherwise.</p> |
|---|
| 1211 | <h3 id="rfc.section.7.2.1"><a href="#rfc.section.7.2.1">7.2.1</a> <a id="cache-request-directive" href="#cache-request-directive">Request Cache-Control Directives</a></h3> |
|---|
| 1212 | <div id="rfc.iref.n.1"></div> |
|---|
| 1213 | <h4 id="rfc.section.7.2.1.1"><a href="#rfc.section.7.2.1.1">7.2.1.1</a> <a id="cache-request-directive.no-cache" href="#cache-request-directive.no-cache">no-cache</a></h4> |
|---|
| 1214 | <p id="rfc.section.7.2.1.1.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. |
|---|
| 1215 | </p> |
|---|
| 1216 | <div id="rfc.iref.n.2"></div> |
|---|
| 1217 | <h4 id="rfc.section.7.2.1.2"><a href="#rfc.section.7.2.1.2">7.2.1.2</a> <a id="cache-request-directive.no-store" href="#cache-request-directive.no-store">no-store</a></h4> |
|---|
| 1218 | <p id="rfc.section.7.2.1.2.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. |
|---|
| 1219 | </p> |
|---|
| 1220 | <p id="rfc.section.7.2.1.2.p.2">This directive is NOT a reliable or sufficient mechanism for ensuring privacy. In particular, malicious or compromised caches |
|---|
| 1221 | might not recognize or obey this directive, and communications networks might be vulnerable to eavesdropping. |
|---|
| 1222 | </p> |
|---|
| 1223 | <p id="rfc.section.7.2.1.2.p.3">Note that if a request containing this directive is satisfied from a cache, the no-store request directive does not apply |
|---|
| 1224 | to the already stored response. |
|---|
| 1225 | </p> |
|---|
| 1226 | <div id="rfc.iref.m.1"></div> |
|---|
| 1227 | <h4 id="rfc.section.7.2.1.3"><a href="#rfc.section.7.2.1.3">7.2.1.3</a> <a id="cache-request-directive.max-age" href="#cache-request-directive.max-age">max-age</a></h4> |
|---|
| 1228 | <p id="rfc.section.7.2.1.3.p.1">Argument syntax: </p> |
|---|
| 1229 | <ul class="empty"> |
|---|
| 1230 | <li> <a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section 1.4.1</a>) |
|---|
| 1231 | </li> |
|---|
| 1232 | </ul> |
|---|
| 1233 | <p id="rfc.section.7.2.1.3.p.2">The "max-age" request directive indicates that the client is unwilling to accept a response whose age is greater than the |
|---|
| 1234 | specified number of seconds. Unless the max-stale request directive is also present, the client is not willing to accept a |
|---|
| 1235 | stale response. |
|---|
| 1236 | </p> |
|---|
| 1237 | <p id="rfc.section.7.2.1.3.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'max-age=5', not 'max-age="5"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form. |
|---|
| 1238 | </p> |
|---|
| 1239 | <div id="rfc.iref.m.2"></div> |
|---|
| 1240 | <h4 id="rfc.section.7.2.1.4"><a href="#rfc.section.7.2.1.4">7.2.1.4</a> <a id="cache-request-directive.max-stale" href="#cache-request-directive.max-stale">max-stale</a></h4> |
|---|
| 1241 | <p id="rfc.section.7.2.1.4.p.1">Argument syntax: </p> |
|---|
| 1242 | <ul class="empty"> |
|---|
| 1243 | <li> <a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section 1.4.1</a>) |
|---|
| 1244 | </li> |
|---|
| 1245 | </ul> |
|---|
| 1246 | <p id="rfc.section.7.2.1.4.p.2">The "max-stale" request directive indicates that the client is willing to accept a response that has exceeded its expiration |
|---|
| 1247 | time. If max-stale is assigned a value, then the client is willing to accept a response that has exceeded its expiration time |
|---|
| 1248 | by no more than the specified number of seconds. If no value is assigned to max-stale, then the client is willing to accept |
|---|
| 1249 | a stale response of any age. |
|---|
| 1250 | </p> |
|---|
| 1251 | <p id="rfc.section.7.2.1.4.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'max-stale=10', not 'max-stale="10"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form. |
|---|
| 1252 | </p> |
|---|
| 1253 | <div id="rfc.iref.m.3"></div> |
|---|
| 1254 | <h4 id="rfc.section.7.2.1.5"><a href="#rfc.section.7.2.1.5">7.2.1.5</a> <a id="cache-request-directive.min-fresh" href="#cache-request-directive.min-fresh">min-fresh</a></h4> |
|---|
| 1255 | <p id="rfc.section.7.2.1.5.p.1">Argument syntax: </p> |
|---|
| 1256 | <ul class="empty"> |
|---|
| 1257 | <li> <a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section 1.4.1</a>) |
|---|
| 1258 | </li> |
|---|
| 1259 | </ul> |
|---|
| 1260 | <p id="rfc.section.7.2.1.5.p.2">The "min-fresh" request directive indicates that the client is willing to accept a response whose freshness lifetime is no |
|---|
| 1261 | less than its current age plus the specified time in seconds. That is, the client wants a response that will still be fresh |
|---|
| 1262 | for at least the specified number of seconds. |
|---|
| 1263 | </p> |
|---|
| 1264 | <p id="rfc.section.7.2.1.5.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'min-fresh=20', not 'min-fresh="20"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form. |
|---|
| 1265 | </p> |
|---|
| 1266 | <div id="rfc.iref.n.3"></div> |
|---|
| 1267 | <h4 id="rfc.section.7.2.1.6"><a href="#rfc.section.7.2.1.6">7.2.1.6</a> <a id="cache-request-directive.no-transform" href="#cache-request-directive.no-transform">no-transform</a></h4> |
|---|
| 1268 | <p id="rfc.section.7.2.1.6.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>. |
|---|
| 1269 | </p> |
|---|
| 1270 | <div id="rfc.iref.o.1"></div> |
|---|
| 1271 | <h4 id="rfc.section.7.2.1.7"><a href="#rfc.section.7.2.1.7">7.2.1.7</a> <a id="cache-request-directive.only-if-cached" href="#cache-request-directive.only-if-cached">only-if-cached</a></h4> |
|---|
| 1272 | <p id="rfc.section.7.2.1.7.p.1">The "only-if-cached" request directive indicates that the client only wishes to obtain a stored response. If it receives this |
|---|
| 1273 | 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 |
|---|
| 1274 | 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. |
|---|
| 1275 | </p> |
|---|
| 1276 | <h3 id="rfc.section.7.2.2"><a href="#rfc.section.7.2.2">7.2.2</a> <a id="cache-response-directive" href="#cache-response-directive">Response Cache-Control Directives</a></h3> |
|---|
| 1277 | <div id="rfc.iref.p.2"></div> |
|---|
| 1278 | <h4 id="rfc.section.7.2.2.1"><a href="#rfc.section.7.2.2.1">7.2.2.1</a> <a id="cache-response-directive.public" href="#cache-response-directive.public">public</a></h4> |
|---|
| 1279 | <p id="rfc.section.7.2.2.1.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 non-shared 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 |
|---|
| 1280 | as cacheable.) |
|---|
| 1281 | </p> |
|---|
| 1282 | <div id="rfc.iref.p.3"></div> |
|---|
| 1283 | <h4 id="rfc.section.7.2.2.2"><a href="#rfc.section.7.2.2.2">7.2.2.2</a> <a id="cache-response-directive.private" href="#cache-response-directive.private">private</a></h4> |
|---|
| 1284 | <p id="rfc.section.7.2.2.2.p.1">Argument syntax: </p> |
|---|
| 1285 | <ul class="empty"> |
|---|
| 1286 | <li>#<a href="#imported.abnf" class="smpl">field-name</a> |
|---|
| 1287 | </li> |
|---|
| 1288 | </ul> |
|---|
| 1289 | <p id="rfc.section.7.2.2.2.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. |
|---|
| 1290 | </p> |
|---|
| 1291 | <p id="rfc.section.7.2.2.2.p.3">If the private response directive specifies one or more field-names, this requirement is limited to the field-values associated |
|---|
| 1292 | 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. |
|---|
| 1293 | </p> |
|---|
| 1294 | <p id="rfc.section.7.2.2.2.p.4">The field-names given are not limited to the set of standard header fields defined by this specification. Field names are |
|---|
| 1295 | case-insensitive. |
|---|
| 1296 | </p> |
|---|
| 1297 | <p id="rfc.section.7.2.2.2.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 |
|---|
| 1298 | content. Also, private response directives with field-names are often handled by implementations as if an unqualified private |
|---|
| 1299 | directive was received; i.e., the special handling for the qualified form is not widely implemented. |
|---|
| 1300 | </p> |
|---|
| 1301 | <p id="rfc.section.7.2.2.2.p.6"> <b>Note:</b> This directive uses the quoted-string form of the argument syntax. Senders <em class="bcp14">SHOULD NOT</em> use the token form (even if quoting appears not to be needed for single-entry lists). |
|---|
| 1302 | </p> |
|---|
| 1303 | <div id="rfc.iref.n.4"></div> |
|---|
| 1304 | <h4 id="rfc.section.7.2.2.3"><a href="#rfc.section.7.2.2.3">7.2.2.3</a> <a id="cache-response-directive.no-cache" href="#cache-response-directive.no-cache">no-cache</a></h4> |
|---|
| 1305 | <p id="rfc.section.7.2.2.3.p.1">Argument syntax: </p> |
|---|
| 1306 | <ul class="empty"> |
|---|
| 1307 | <li>#<a href="#imported.abnf" class="smpl">field-name</a> |
|---|
| 1308 | </li> |
|---|
| 1309 | </ul> |
|---|
| 1310 | <p id="rfc.section.7.2.2.3.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 |
|---|
| 1311 | prevent a cache from using it to satisfy a request without contacting it, even by caches that have been configured to send |
|---|
| 1312 | stale responses. |
|---|
| 1313 | </p> |
|---|
| 1314 | <p id="rfc.section.7.2.2.3.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 |
|---|
| 1315 | 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 |
|---|
| 1316 | server to prevent the re-use of certain header fields in a response, while still allowing caching of the rest of the response. |
|---|
| 1317 | </p> |
|---|
| 1318 | <p id="rfc.section.7.2.2.3.p.4">The field-names given are not limited to the set of standard header fields defined by this specification. Field names are |
|---|
| 1319 | case-insensitive. |
|---|
| 1320 | </p> |
|---|
| 1321 | <p id="rfc.section.7.2.2.3.p.5"> <b>Note:</b> Many HTTP/1.0 caches will not recognize or obey this directive. Also, no-cache response directives with field-names are often |
|---|
| 1322 | handled by implementations as if an unqualified no-cache directive was received; i.e., the special handling for the qualified |
|---|
| 1323 | form is not widely implemented. |
|---|
| 1324 | </p> |
|---|
| 1325 | <p id="rfc.section.7.2.2.3.p.6"> <b>Note:</b> This directive uses the quoted-string form of the argument syntax. Senders <em class="bcp14">SHOULD NOT</em> use the token form (even if quoting appears not to be needed for single-entry lists). |
|---|
| 1326 | </p> |
|---|
| 1327 | <div id="rfc.iref.n.5"></div> |
|---|
| 1328 | <h4 id="rfc.section.7.2.2.4"><a href="#rfc.section.7.2.2.4">7.2.2.4</a> <a id="cache-response-directive.no-store" href="#cache-response-directive.no-store">no-store</a></h4> |
|---|
| 1329 | <p id="rfc.section.7.2.2.4.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. |
|---|
| 1330 | </p> |
|---|
| 1331 | <p id="rfc.section.7.2.2.4.p.2">This directive is NOT a reliable or sufficient mechanism for ensuring privacy. In particular, malicious or compromised caches |
|---|
| 1332 | might not recognize or obey this directive, and communications networks might be vulnerable to eavesdropping. |
|---|
| 1333 | </p> |
|---|
| 1334 | <div id="rfc.iref.m.4"></div> |
|---|
| 1335 | <h4 id="rfc.section.7.2.2.5"><a href="#rfc.section.7.2.2.5">7.2.2.5</a> <a id="cache-response-directive.must-revalidate" href="#cache-response-directive.must-revalidate">must-revalidate</a></h4> |
|---|
| 1336 | <p id="rfc.section.7.2.2.5.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. |
|---|
| 1337 | </p> |
|---|
| 1338 | <p id="rfc.section.7.2.2.5.p.2">The must-revalidate directive is necessary to support reliable operation for certain protocol features. In all circumstances |
|---|
| 1339 | 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. |
|---|
| 1340 | </p> |
|---|
| 1341 | <p id="rfc.section.7.2.2.5.p.3">The must-revalidate directive ought to be used by servers if and only if failure to validate a request on the representation |
|---|
| 1342 | could result in incorrect operation, such as a silently unexecuted financial transaction. |
|---|
| 1343 | </p> |
|---|
| 1344 | <div id="rfc.iref.p.4"></div> |
|---|
| 1345 | <h4 id="rfc.section.7.2.2.6"><a href="#rfc.section.7.2.2.6">7.2.2.6</a> <a id="cache-response-directive.proxy-revalidate" href="#cache-response-directive.proxy-revalidate">proxy-revalidate</a></h4> |
|---|
| 1346 | <p id="rfc.section.7.2.2.6.p.1">The "proxy-revalidate" response directive has the same meaning as the must-revalidate response directive, except that it does |
|---|
| 1347 | not apply to private caches. |
|---|
| 1348 | </p> |
|---|
| 1349 | <div id="rfc.iref.m.5"></div> |
|---|
| 1350 | <h4 id="rfc.section.7.2.2.7"><a href="#rfc.section.7.2.2.7">7.2.2.7</a> <a id="cache-response-directive.max-age" href="#cache-response-directive.max-age">max-age</a></h4> |
|---|
| 1351 | <p id="rfc.section.7.2.2.7.p.1">Argument syntax: </p> |
|---|
| 1352 | <ul class="empty"> |
|---|
| 1353 | <li> <a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section 1.4.1</a>) |
|---|
| 1354 | </li> |
|---|
| 1355 | </ul> |
|---|
| 1356 | <p id="rfc.section.7.2.2.7.p.2">The "max-age" response directive indicates that the response is to be considered stale after its age is greater than the specified |
|---|
| 1357 | number of seconds. |
|---|
| 1358 | </p> |
|---|
| 1359 | <p id="rfc.section.7.2.2.7.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'max-age=5', not 'max-age="5"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form. |
|---|
| 1360 | </p> |
|---|
| 1361 | <div id="rfc.iref.s.4"></div> |
|---|
| 1362 | <h4 id="rfc.section.7.2.2.8"><a href="#rfc.section.7.2.2.8">7.2.2.8</a> <a id="cache-response-directive.s-maxage" href="#cache-response-directive.s-maxage">s-maxage</a></h4> |
|---|
| 1363 | <p id="rfc.section.7.2.2.8.p.1">Argument syntax: </p> |
|---|
| 1364 | <ul class="empty"> |
|---|
| 1365 | <li> <a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section 1.4.1</a>) |
|---|
| 1366 | </li> |
|---|
| 1367 | </ul> |
|---|
| 1368 | <p id="rfc.section.7.2.2.8.p.2">The "s-maxage" response directive indicates that, in shared caches, the maximum age specified by this directive overrides |
|---|
| 1369 | 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. |
|---|
| 1370 | </p> |
|---|
| 1371 | <p id="rfc.section.7.2.2.8.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 's-maxage=10', not 's-maxage="10"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form. |
|---|
| 1372 | </p> |
|---|
| 1373 | <div id="rfc.iref.n.6"></div> |
|---|
| 1374 | <h4 id="rfc.section.7.2.2.9"><a href="#rfc.section.7.2.2.9">7.2.2.9</a> <a id="cache-response-directive.no-transform" href="#cache-response-directive.no-transform">no-transform</a></h4> |
|---|
| 1375 | <p id="rfc.section.7.2.2.9.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>. |
|---|
| 1376 | </p> |
|---|
| 1377 | <h3 id="rfc.section.7.2.3"><a href="#rfc.section.7.2.3">7.2.3</a> <a id="cache.control.extensions" href="#cache.control.extensions">Cache Control Extensions</a></h3> |
|---|
| 1378 | <p id="rfc.section.7.2.3.p.1">The Cache-Control header field can be extended through the use of one or more cache-extension tokens, each with an optional |
|---|
| 1379 | value. Informational extensions (those that do not require a change in cache behavior) can be added without changing the semantics |
|---|
| 1380 | of other directives. Behavioral extensions are designed to work by acting as modifiers to the existing base of cache directives. |
|---|
| 1381 | Both the new directive and the standard directive are supplied, such that applications that do not understand the new directive |
|---|
| 1382 | will default to the behavior specified by the standard directive, and those that understand the new directive will recognize |
|---|
| 1383 | it as modifying the requirements associated with the standard directive. In this way, extensions to the cache-control directives |
|---|
| 1384 | can be made without requiring changes to the base protocol. |
|---|
| 1385 | </p> |
|---|
| 1386 | <p id="rfc.section.7.2.3.p.2">This extension mechanism depends on an HTTP cache obeying all of the cache-control directives defined for its native HTTP-version, |
|---|
| 1387 | obeying certain extensions, and ignoring all directives that it does not understand. |
|---|
| 1388 | </p> |
|---|
| 1389 | <p id="rfc.section.7.2.3.p.3">For example, consider a hypothetical new response directive called "community" that acts as a modifier to the private directive. |
|---|
| 1390 | We define this new directive to mean that, in addition to any private cache, any cache that is shared only by members of the |
|---|
| 1391 | community named within its value is allowed to cache the response. An origin server wishing to allow the UCI community to |
|---|
| 1392 | use an otherwise private response in their shared cache(s) could do so by including |
|---|
| 1393 | </p> |
|---|
| 1394 | <div id="rfc.figure.u.8"></div><pre class="text"> Cache-Control: private, community="UCI" |
|---|
| 1395 | </pre><p id="rfc.section.7.2.3.p.5">A cache seeing this header field will act correctly even if the cache does not understand the community cache-extension, since |
|---|
| 1396 | it will also see and understand the private directive and thus default to the safe behavior. |
|---|
| 1397 | </p> |
|---|
| 1398 | <p id="rfc.section.7.2.3.p.6">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 |
|---|
| 1399 | will be combined with standard directives (or the response's default cacheability) such that the cache behavior will remain |
|---|
| 1400 | minimally correct even if the cache does not understand the extension(s). |
|---|
| 1401 | </p> |
|---|
| 1402 | <p id="rfc.section.7.2.3.p.7">New extension directives ought to consider defining:</p> |
|---|
| 1403 | <p id="rfc.section.7.2.3.p.8"> </p> |
|---|
| 1404 | <ul> |
|---|
| 1405 | <li>What it means for a directive to be specified multiple times,</li> |
|---|
| 1406 | <li>When the directive does not take an argument, what it means when an argument is present,</li> |
|---|
| 1407 | <li>When the directive requires an argument, what it means when it is missing.</li> |
|---|
| 1408 | </ul> |
|---|
| 1409 | <p id="rfc.section.7.2.3.p.9">The HTTP Cache Directive Registry defines the name space for the cache directives.</p> |
|---|
| 1410 | <p id="rfc.section.7.2.3.p.10">A registration <em class="bcp14">MUST</em> include the following fields: |
|---|
| 1411 | </p> |
|---|
| 1412 | <ul> |
|---|
| 1413 | <li>Cache Directive Name</li> |
|---|
| 1414 | <li>Pointer to specification text</li> |
|---|
| 1415 | </ul> |
|---|
| 1416 | <p id="rfc.section.7.2.3.p.11">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>). |
|---|
| 1417 | </p> |
|---|
| 1418 | <p id="rfc.section.7.2.3.p.12">The registry itself is maintained at <<a href="http://www.iana.org/assignments/http-cache-directives">http://www.iana.org/assignments/http-cache-directives</a>>. |
|---|
| 1419 | </p> |
|---|
| 1420 | <div id="rfc.iref.e.2"></div> |
|---|
| 1421 | <h2 id="rfc.section.7.3"><a href="#rfc.section.7.3">7.3</a> <a id="header.expires" href="#header.expires">Expires</a></h2> |
|---|
| 1422 | <p id="rfc.section.7.3.p.1">The "Expires" header field gives the date/time after which the response is considered stale. See <a href="#expiration.model" title="Freshness Model">Section 4.1</a> for further discussion of the freshness model. |
|---|
| 1423 | </p> |
|---|
| 1424 | <p id="rfc.section.7.3.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 |
|---|
| 1425 | that time. |
|---|
| 1426 | </p> |
|---|
| 1427 | <p id="rfc.section.7.3.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>. |
|---|
| 1428 | </p> |
|---|
| 1429 | <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> |
|---|
| 1430 | </pre><div id="rfc.figure.u.10"></div> |
|---|
| 1431 | <p>For example</p> <pre class="text"> Expires: Thu, 01 Dec 1994 16:00:00 GMT |
|---|
| 1432 | </pre><p id="rfc.section.7.3.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"). |
|---|
| 1433 | </p> |
|---|
| 1434 | <p id="rfc.section.7.3.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 7.2.2.7</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 7.2.2.8</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 |
|---|
| 1435 | the Cache-Control field. |
|---|
| 1436 | </p> |
|---|
| 1437 | <p id="rfc.section.7.3.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 |
|---|
| 1438 | with the resource by a system or user with a reliable clock. |
|---|
| 1439 | </p> |
|---|
| 1440 | <p id="rfc.section.7.3.p.9">Historically, HTTP required the Expires field-value to be no more than a year in the future. While longer freshness lifetimes |
|---|
| 1441 | are no longer prohibited, extremely large values have been demonstrated to cause problems (e.g., clock overflows due to use |
|---|
| 1442 | of 32-bit integers for time values), and many caches will evict a response far sooner than that. |
|---|
| 1443 | </p> |
|---|
| 1444 | <div id="rfc.iref.p.5"></div> |
|---|
| 1445 | <h2 id="rfc.section.7.4"><a href="#rfc.section.7.4">7.4</a> <a id="header.pragma" href="#header.pragma">Pragma</a></h2> |
|---|
| 1446 | <p id="rfc.section.7.4.p.1">The "Pragma" header field allows backwards compatibility with HTTP/1.0 caches, so that clients can specify a "no-cache" request |
|---|
| 1447 | 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 |
|---|
| 1448 | ignored. |
|---|
| 1449 | </p> |
|---|
| 1450 | <p id="rfc.section.7.4.p.2">In HTTP/1.0, Pragma was defined as an extensible field for implementation-specified directives for recipients. This specification |
|---|
| 1451 | deprecates such extensions to improve interoperability. |
|---|
| 1452 | </p> |
|---|
| 1453 | <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> |
|---|
| 1454 | <a href="#header.pragma" class="smpl">pragma-directive</a> = "no-cache" / <a href="#header.pragma" class="smpl">extension-pragma</a> |
|---|
| 1455 | <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> ) ] |
|---|
| 1456 | </pre><p id="rfc.section.7.4.p.4">When the <a href="#header.cache-control" class="smpl">Cache-Control</a> header field is not present in a request, the no-cache request pragma-directive <em class="bcp14">MUST</em> have the same effect on caches as if "Cache-Control: no-cache" were present (see <a href="#cache-request-directive" title="Request Cache-Control Directives">Section 7.2.1</a>). |
|---|
| 1457 | </p> |
|---|
| 1458 | <p id="rfc.section.7.4.p.5">When sending a no-cache request, a client ought to include both the pragma and cache-control directives, unless Cache-Control: |
|---|
| 1459 | 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: |
|---|
| 1460 | </p> |
|---|
| 1461 | <div id="rfc.figure.u.12"></div> <pre class="text">GET / HTTP/1.1 |
|---|
| 1462 | Host: www.example.com |
|---|
| 1463 | Cache-Control: max-age=30 |
|---|
| 1464 | Pragma: no-cache |
|---|
| 1465 | |
|---|
| 1466 | </pre> <p id="rfc.section.7.4.p.7">will constrain HTTP/1.1 caches to serve a response no older than 30 seconds, while precluding implementations that do not |
|---|
| 1467 | understand <a href="#header.cache-control" class="smpl">Cache-Control</a> from serving a cached response. |
|---|
| 1468 | </p> |
|---|
| 1469 | <div class="note" id="rfc.section.7.4.p.8"> |
|---|
| 1470 | <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: |
|---|
| 1471 | no-cache" in them. |
|---|
| 1472 | </p> |
|---|
| 1473 | </div> |
|---|
| 1474 | <div id="rfc.iref.w.1"></div> |
|---|
| 1475 | <h2 id="rfc.section.7.5"><a href="#rfc.section.7.5">7.5</a> <a id="header.warning" href="#header.warning">Warning</a></h2> |
|---|
| 1476 | <p id="rfc.section.7.5.p.1">The "Warning" header field is used to carry additional information about the status or transformation of a message that might |
|---|
| 1477 | not be reflected in the message. This information is typically used to warn about possible incorrectness introduced by caching |
|---|
| 1478 | operations or transformations applied to the payload of the message. |
|---|
| 1479 | </p> |
|---|
| 1480 | <p id="rfc.section.7.5.p.2">Warnings can be used for other purposes, both cache-related and otherwise. The use of a warning, rather than an error status |
|---|
| 1481 | code, distinguishes these responses from true failures. |
|---|
| 1482 | </p> |
|---|
| 1483 | <p id="rfc.section.7.5.p.3">Warning header fields can in general be applied to any message, however some warn-codes are specific to caches and can only |
|---|
| 1484 | be applied to response messages. |
|---|
| 1485 | </p> |
|---|
| 1486 | <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> |
|---|
| 1487 | |
|---|
| 1488 | <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> |
|---|
| 1489 | [<a href="#imported.abnf" class="smpl">SP</a> <a href="#header.warning" class="smpl">warn-date</a>] |
|---|
| 1490 | |
|---|
| 1491 | <a href="#header.warning" class="smpl">warn-code</a> = 3<a href="#imported.abnf" class="smpl">DIGIT</a> |
|---|
| 1492 | <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> |
|---|
| 1493 | ; the name or pseudonym of the server adding |
|---|
| 1494 | ; the Warning header field, for use in debugging |
|---|
| 1495 | <a href="#header.warning" class="smpl">warn-text</a> = <a href="#imported.abnf" class="smpl">quoted-string</a> |
|---|
| 1496 | <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> |
|---|
| 1497 | </pre><p id="rfc.section.7.5.p.5">Multiple warnings can be attached to a response (either by the origin server or by a cache), including multiple warnings with |
|---|
| 1498 | the same code number, only differing in warn-text. |
|---|
| 1499 | </p> |
|---|
| 1500 | <p id="rfc.section.7.5.p.6">When this occurs, the user agent <em class="bcp14">SHOULD</em> inform the user of as many of them as possible, in the order that they appear in the response. |
|---|
| 1501 | </p> |
|---|
| 1502 | <p id="rfc.section.7.5.p.7">Systems that generate multiple Warning header fields are encouraged to order them with this user agent behavior in mind. New |
|---|
| 1503 | Warning header fields are added after any existing Warning header fields. |
|---|
| 1504 | </p> |
|---|
| 1505 | <p id="rfc.section.7.5.p.8">Warnings are assigned three digit warn-codes. The first digit indicates whether the Warning is required to be deleted from |
|---|
| 1506 | a stored response after validation: |
|---|
| 1507 | </p> |
|---|
| 1508 | <ul> |
|---|
| 1509 | <li>1xx Warnings 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. |
|---|
| 1510 | </li> |
|---|
| 1511 | <li>2xx Warnings describe some aspect of the representation that is not rectified by a validation (for example, a lossy compression |
|---|
| 1512 | 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. |
|---|
| 1513 | </li> |
|---|
| 1514 | </ul> |
|---|
| 1515 | <p id="rfc.section.7.5.p.9">If an implementation sends a message with one or more Warning header fields to a receiver whose version is HTTP/1.0 or lower, |
|---|
| 1516 | then the sender <em class="bcp14">MUST</em> include in each warning-value a warn-date that matches the <a href="p2-semantics.html#header.date" class="smpl">Date</a> header field in the message. |
|---|
| 1517 | </p> |
|---|
| 1518 | <p id="rfc.section.7.5.p.10">If a system receives a message with a warning-value that includes a warn-date, and that warn-date is different from the <a href="p2-semantics.html#header.date" class="smpl">Date</a> value in the response, then that warning-value <em class="bcp14">MUST</em> be deleted from the message before storing, forwarding, or using it. (preventing the consequences of naive caching of Warning |
|---|
| 1519 | header fields.) If all of the warning-values are deleted for this reason, the Warning header field <em class="bcp14">MUST</em> be deleted as well. |
|---|
| 1520 | </p> |
|---|
| 1521 | <p id="rfc.section.7.5.p.11">The following warn-codes are defined by this specification, each with a recommended warn-text in English, and a description |
|---|
| 1522 | of its meaning. |
|---|
| 1523 | </p> |
|---|
| 1524 | <div id="rfc.iref.52"></div> |
|---|
| 1525 | <h3 id="rfc.section.7.5.1"><a href="#rfc.section.7.5.1">7.5.1</a> <a id="warn.110" href="#warn.110">110 Response is Stale</a></h3> |
|---|
| 1526 | <p id="rfc.section.7.5.1.p.1">A cache <em class="bcp14">SHOULD</em> generate this whenever the sent response is stale. |
|---|
| 1527 | </p> |
|---|
| 1528 | <div id="rfc.iref.52"></div> |
|---|
| 1529 | <h3 id="rfc.section.7.5.2"><a href="#rfc.section.7.5.2">7.5.2</a> <a id="warn.111" href="#warn.111">111 Revalidation Failed</a></h3> |
|---|
| 1530 | <p id="rfc.section.7.5.2.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 |
|---|
| 1531 | the server. |
|---|
| 1532 | </p> |
|---|
| 1533 | <div id="rfc.iref.52"></div> |
|---|
| 1534 | <h3 id="rfc.section.7.5.3"><a href="#rfc.section.7.5.3">7.5.3</a> <a id="warn.112" href="#warn.112">112 Disconnected Operation</a></h3> |
|---|
| 1535 | <p id="rfc.section.7.5.3.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. |
|---|
| 1536 | </p> |
|---|
| 1537 | <div id="rfc.iref.52"></div> |
|---|
| 1538 | <h3 id="rfc.section.7.5.4"><a href="#rfc.section.7.5.4">7.5.4</a> <a id="warn.113" href="#warn.113">113 Heuristic Expiration</a></h3> |
|---|
| 1539 | <p id="rfc.section.7.5.4.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 |
|---|
| 1540 | 24 hours. |
|---|
| 1541 | </p> |
|---|
| 1542 | <div id="rfc.iref.52"></div> |
|---|
| 1543 | <h3 id="rfc.section.7.5.5"><a href="#rfc.section.7.5.5">7.5.5</a> <a id="warn.199" href="#warn.199">199 Miscellaneous Warning</a></h3> |
|---|
| 1544 | <p id="rfc.section.7.5.5.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. |
|---|
| 1545 | </p> |
|---|
| 1546 | <div id="rfc.iref.52"></div> |
|---|
| 1547 | <h3 id="rfc.section.7.5.6"><a href="#rfc.section.7.5.6">7.5.6</a> <a id="warn.214" href="#warn.214">214 Transformation Applied</a></h3> |
|---|
| 1548 | <p id="rfc.section.7.5.6.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, |
|---|
| 1549 | or modifying the representation data, unless this Warning code already appears in the response. |
|---|
| 1550 | </p> |
|---|
| 1551 | <div id="rfc.iref.52"></div> |
|---|
| 1552 | <h3 id="rfc.section.7.5.7"><a href="#rfc.section.7.5.7">7.5.7</a> <a id="warn.299" href="#warn.299">299 Miscellaneous Persistent Warning</a></h3> |
|---|
| 1553 | <p id="rfc.section.7.5.7.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. |
|---|
| 1554 | </p> |
|---|
| 1555 | <h3 id="rfc.section.7.5.8"><a href="#rfc.section.7.5.8">7.5.8</a> <a id="warn.code.extensions" href="#warn.code.extensions">Warn Code Extensions</a></h3> |
|---|
| 1556 | <p id="rfc.section.7.5.8.p.1">The HTTP Warn Code Registry defines the name space for warn codes.</p> |
|---|
| 1557 | <p id="rfc.section.7.5.8.p.2">A registration <em class="bcp14">MUST</em> include the following fields: |
|---|
| 1558 | </p> |
|---|
| 1559 | <ul> |
|---|
| 1560 | <li>Warn Code (3 digits)</li> |
|---|
| 1561 | <li>Short Description</li> |
|---|
| 1562 | <li>Pointer to specification text</li> |
|---|
| 1563 | </ul> |
|---|
| 1564 | <p id="rfc.section.7.5.8.p.3">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>). |
|---|
| 1565 | </p> |
|---|
| 1566 | <p id="rfc.section.7.5.8.p.4">The registry itself is maintained at <<a href="http://www.iana.org/assignments/http-warn-codes">http://www.iana.org/assignments/http-warn-codes</a>>. |
|---|
| 1567 | </p> |
|---|
| 1568 | <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a> <a id="history.lists" href="#history.lists">History Lists</a></h1> |
|---|
| 1569 | <p id="rfc.section.8.p.1">User agents often have history mechanisms, such as "Back" buttons and history lists, that can be used to redisplay a representation |
|---|
| 1570 | retrieved earlier in a session. |
|---|
| 1571 | </p> |
|---|
| 1572 | <p id="rfc.section.8.p.2">The freshness model (<a href="#expiration.model" title="Freshness Model">Section 4.1</a>) does not necessarily apply to history mechanisms. I.e., a history mechanism can display a previous representation even if |
|---|
| 1573 | it has expired. |
|---|
| 1574 | </p> |
|---|
| 1575 | <p id="rfc.section.8.p.3">This does not prohibit the history mechanism from telling the user that a view might be stale, or from honoring cache directives |
|---|
| 1576 | (e.g., Cache-Control: no-store). |
|---|
| 1577 | </p> |
|---|
| 1578 | <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a> <a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1> |
|---|
| 1579 | <h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a> <a id="cache.directive.registration" href="#cache.directive.registration">Cache Directive Registry</a></h2> |
|---|
| 1580 | <p id="rfc.section.9.1.p.1">The registration procedure for HTTP Cache Directives is defined by <a href="#cache.control.extensions" title="Cache Control Extensions">Section 7.2.3</a> of this document. |
|---|
| 1581 | </p> |
|---|
| 1582 | <p id="rfc.section.9.1.p.2">The HTTP Cache Directive Registry shall be created at <<a href="http://www.iana.org/assignments/http-cache-directives">http://www.iana.org/assignments/http-cache-directives</a>> and be populated with the registrations below: |
|---|
| 1583 | </p> |
|---|
| 1584 | <div id="rfc.table.1"> |
|---|
| 1585 | <div id="iana.cache.directive.registration.table"></div> |
|---|
| 1586 | <table class="tt full left" cellpadding="3" cellspacing="0"> |
|---|
| 1587 | <thead> |
|---|
| 1588 | <tr> |
|---|
| 1589 | <th>Cache Directive</th> |
|---|
| 1590 | <th>Reference</th> |
|---|
| 1591 | </tr> |
|---|
| 1592 | </thead> |
|---|
| 1593 | <tbody> |
|---|
| 1594 | <tr> |
|---|
| 1595 | <td class="left">max-age</td> |
|---|
| 1596 | <td class="left"> <a href="#cache-request-directive.max-age" title="max-age">Section 7.2.1.3</a>, <a href="#cache-response-directive.max-age" title="max-age">Section 7.2.2.7</a> |
|---|
| 1597 | </td> |
|---|
| 1598 | </tr> |
|---|
| 1599 | <tr> |
|---|
| 1600 | <td class="left">max-stale</td> |
|---|
| 1601 | <td class="left"> <a href="#cache-request-directive.max-stale" title="max-stale">Section 7.2.1.4</a> |
|---|
| 1602 | </td> |
|---|
| 1603 | </tr> |
|---|
| 1604 | <tr> |
|---|
| 1605 | <td class="left">min-fresh</td> |
|---|
| 1606 | <td class="left"> <a href="#cache-request-directive.min-fresh" title="min-fresh">Section 7.2.1.5</a> |
|---|
| 1607 | </td> |
|---|
| 1608 | </tr> |
|---|
| 1609 | <tr> |
|---|
| 1610 | <td class="left">must-revalidate</td> |
|---|
| 1611 | <td class="left"> <a href="#cache-response-directive.must-revalidate" title="must-revalidate">Section 7.2.2.5</a> |
|---|
| 1612 | </td> |
|---|
| 1613 | </tr> |
|---|
| 1614 | <tr> |
|---|
| 1615 | <td class="left">no-cache</td> |
|---|
| 1616 | <td class="left"> <a href="#cache-request-directive.no-cache" title="no-cache">Section 7.2.1.1</a>, <a href="#cache-response-directive.no-cache" title="no-cache">Section 7.2.2.3</a> |
|---|
| 1617 | </td> |
|---|
| 1618 | </tr> |
|---|
| 1619 | <tr> |
|---|
| 1620 | <td class="left">no-store</td> |
|---|
| 1621 | <td class="left"> <a href="#cache-request-directive.no-store" title="no-store">Section 7.2.1.2</a>, <a href="#cache-response-directive.no-store" title="no-store">Section 7.2.2.4</a> |
|---|
| 1622 | </td> |
|---|
| 1623 | </tr> |
|---|
| 1624 | <tr> |
|---|
| 1625 | <td class="left">no-transform</td> |
|---|
| 1626 | <td class="left"> <a href="#cache-request-directive.no-transform" title="no-transform">Section 7.2.1.6</a>, <a href="#cache-response-directive.no-transform" title="no-transform">Section 7.2.2.9</a> |
|---|
| 1627 | </td> |
|---|
| 1628 | </tr> |
|---|
| 1629 | <tr> |
|---|
| 1630 | <td class="left">only-if-cached</td> |
|---|
| 1631 | <td class="left"> <a href="#cache-request-directive.only-if-cached" title="only-if-cached">Section 7.2.1.7</a> |
|---|
| 1632 | </td> |
|---|
| 1633 | </tr> |
|---|
| 1634 | <tr> |
|---|
| 1635 | <td class="left">private</td> |
|---|
| 1636 | <td class="left"> <a href="#cache-response-directive.private" title="private">Section 7.2.2.2</a> |
|---|
| 1637 | </td> |
|---|
| 1638 | </tr> |
|---|
| 1639 | <tr> |
|---|
| 1640 | <td class="left">proxy-revalidate</td> |
|---|
| 1641 | <td class="left"> <a href="#cache-response-directive.proxy-revalidate" title="proxy-revalidate">Section 7.2.2.6</a> |
|---|
| 1642 | </td> |
|---|
| 1643 | </tr> |
|---|
| 1644 | <tr> |
|---|
| 1645 | <td class="left">public</td> |
|---|
| 1646 | <td class="left"> <a href="#cache-response-directive.public" title="public">Section 7.2.2.1</a> |
|---|
| 1647 | </td> |
|---|
| 1648 | </tr> |
|---|
| 1649 | <tr> |
|---|
| 1650 | <td class="left">s-maxage</td> |
|---|
| 1651 | <td class="left"> <a href="#cache-response-directive.s-maxage" title="s-maxage">Section 7.2.2.8</a> |
|---|
| 1652 | </td> |
|---|
| 1653 | </tr> |
|---|
| 1654 | <tr> |
|---|
| 1655 | <td class="left">stale-if-error</td> |
|---|
| 1656 | <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> |
|---|
| 1657 | </td> |
|---|
| 1658 | </tr> |
|---|
| 1659 | <tr> |
|---|
| 1660 | <td class="left">stale-while-revalidate</td> |
|---|
| 1661 | <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> |
|---|
| 1662 | </td> |
|---|
| 1663 | </tr> |
|---|
| 1664 | </tbody> |
|---|
| 1665 | </table> |
|---|
| 1666 | </div> |
|---|
| 1667 | <h2 id="rfc.section.9.2"><a href="#rfc.section.9.2">9.2</a> <a id="warn.code.registration" href="#warn.code.registration">Warn Code Registry</a></h2> |
|---|
| 1668 | <p id="rfc.section.9.2.p.1">The registration procedure for HTTP Warn Codes is defined by <a href="#warn.code.extensions" title="Warn Code Extensions">Section 7.5.8</a> of this document. |
|---|
| 1669 | </p> |
|---|
| 1670 | <p id="rfc.section.9.2.p.2">The HTTP Warn Code Registry shall be created at <<a href="http://www.iana.org/assignments/http-cache-directives">http://www.iana.org/assignments/http-cache-directives</a>> and be populated with the registrations below: |
|---|
| 1671 | </p> |
|---|
| 1672 | <div id="rfc.table.2"> |
|---|
| 1673 | <div id="iana.warn.code.registration.table"></div> |
|---|
| 1674 | <table class="tt full left" cellpadding="3" cellspacing="0"> |
|---|
| 1675 | <thead> |
|---|
| 1676 | <tr> |
|---|
| 1677 | <th>Warn Code</th> |
|---|
| 1678 | <th>Short Description</th> |
|---|
| 1679 | <th>Reference</th> |
|---|
| 1680 | </tr> |
|---|
| 1681 | </thead> |
|---|
| 1682 | <tbody> |
|---|
| 1683 | <tr> |
|---|
| 1684 | <td class="left">110</td> |
|---|
| 1685 | <td class="left">Response is Stale</td> |
|---|
| 1686 | <td class="left"> <a href="#warn.110" id="rfc.xref.warn.110.1" title="110 Response is Stale">Section 7.5.1</a> |
|---|
| 1687 | </td> |
|---|
| 1688 | </tr> |
|---|
| 1689 | <tr> |
|---|
| 1690 | <td class="left">111</td> |
|---|
| 1691 | <td class="left">Revalidation Failed</td> |
|---|
| 1692 | <td class="left"> <a href="#warn.111" id="rfc.xref.warn.111.1" title="111 Revalidation Failed">Section 7.5.2</a> |
|---|
| 1693 | </td> |
|---|
| 1694 | </tr> |
|---|
| 1695 | <tr> |
|---|
| 1696 | <td class="left">112</td> |
|---|
| 1697 | <td class="left">Disconnected Operation</td> |
|---|
| 1698 | <td class="left"> <a href="#warn.112" id="rfc.xref.warn.112.1" title="112 Disconnected Operation">Section 7.5.3</a> |
|---|
| 1699 | </td> |
|---|
| 1700 | </tr> |
|---|
| 1701 | <tr> |
|---|
| 1702 | <td class="left">113</td> |
|---|
| 1703 | <td class="left">Heuristic Expiration</td> |
|---|
| 1704 | <td class="left"> <a href="#warn.113" id="rfc.xref.warn.113.1" title="113 Heuristic Expiration">Section 7.5.4</a> |
|---|
| 1705 | </td> |
|---|
| 1706 | </tr> |
|---|
| 1707 | <tr> |
|---|
| 1708 | <td class="left">199</td> |
|---|
| 1709 | <td class="left">Miscellaneous Warning</td> |
|---|
| 1710 | <td class="left"> <a href="#warn.199" id="rfc.xref.warn.199.1" title="199 Miscellaneous Warning">Section 7.5.5</a> |
|---|
| 1711 | </td> |
|---|
| 1712 | </tr> |
|---|
| 1713 | <tr> |
|---|
| 1714 | <td class="left">214</td> |
|---|
| 1715 | <td class="left">Transformation Applied</td> |
|---|
| 1716 | <td class="left"> <a href="#warn.214" id="rfc.xref.warn.214.1" title="214 Transformation Applied">Section 7.5.6</a> |
|---|
| 1717 | </td> |
|---|
| 1718 | </tr> |
|---|
| 1719 | <tr> |
|---|
| 1720 | <td class="left">299</td> |
|---|
| 1721 | <td class="left">Miscellaneous Persistent Warning</td> |
|---|
| 1722 | <td class="left"> <a href="#warn.299" id="rfc.xref.warn.299.1" title="299 Miscellaneous Persistent Warning">Section 7.5.7</a> |
|---|
| 1723 | </td> |
|---|
| 1724 | </tr> |
|---|
| 1725 | </tbody> |
|---|
| 1726 | </table> |
|---|
| 1727 | </div> |
|---|
| 1728 | <h2 id="rfc.section.9.3"><a href="#rfc.section.9.3">9.3</a> <a id="header.field.registration" href="#header.field.registration">Header Field Registration</a></h2> |
|---|
| 1729 | <p id="rfc.section.9.3.p.1">The Message Header Field Registry located 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>> shall be updated with the permanent registrations below (see <a href="#BCP90" id="rfc.xref.BCP90.1"><cite title="Registration Procedures for Message Header Fields">[BCP90]</cite></a>): |
|---|
| 1730 | </p> |
|---|
| 1731 | <div id="rfc.table.3"> |
|---|
| 1732 | <div id="iana.header.registration.table"></div> |
|---|
| 1733 | <table class="tt full left" cellpadding="3" cellspacing="0"> |
|---|
| 1734 | <thead> |
|---|
| 1735 | <tr> |
|---|
| 1736 | <th>Header Field Name</th> |
|---|
| 1737 | <th>Protocol</th> |
|---|
| 1738 | <th>Status</th> |
|---|
| 1739 | <th>Reference</th> |
|---|
| 1740 | </tr> |
|---|
| 1741 | </thead> |
|---|
| 1742 | <tbody> |
|---|
| 1743 | <tr> |
|---|
| 1744 | <td class="left">Age</td> |
|---|
| 1745 | <td class="left">http</td> |
|---|
| 1746 | <td class="left">standard</td> |
|---|
| 1747 | <td class="left"> <a href="#header.age" id="rfc.xref.header.age.3" title="Age">Section 7.1</a> |
|---|
| 1748 | </td> |
|---|
| 1749 | </tr> |
|---|
| 1750 | <tr> |
|---|
| 1751 | <td class="left">Cache-Control</td> |
|---|
| 1752 | <td class="left">http</td> |
|---|
| 1753 | <td class="left">standard</td> |
|---|
| 1754 | <td class="left"> <a href="#header.cache-control" id="rfc.xref.header.cache-control.2" title="Cache-Control">Section 7.2</a> |
|---|
| 1755 | </td> |
|---|
| 1756 | </tr> |
|---|
| 1757 | <tr> |
|---|
| 1758 | <td class="left">Expires</td> |
|---|
| 1759 | <td class="left">http</td> |
|---|
| 1760 | <td class="left">standard</td> |
|---|
| 1761 | <td class="left"> <a href="#header.expires" id="rfc.xref.header.expires.4" title="Expires">Section 7.3</a> |
|---|
| 1762 | </td> |
|---|
| 1763 | </tr> |
|---|
| 1764 | <tr> |
|---|
| 1765 | <td class="left">Pragma</td> |
|---|
| 1766 | <td class="left">http</td> |
|---|
| 1767 | <td class="left">standard</td> |
|---|
| 1768 | <td class="left"> <a href="#header.pragma" id="rfc.xref.header.pragma.3" title="Pragma">Section 7.4</a> |
|---|
| 1769 | </td> |
|---|
| 1770 | </tr> |
|---|
| 1771 | <tr> |
|---|
| 1772 | <td class="left">Warning</td> |
|---|
| 1773 | <td class="left">http</td> |
|---|
| 1774 | <td class="left">standard</td> |
|---|
| 1775 | <td class="left"> <a href="#header.warning" id="rfc.xref.header.warning.5" title="Warning">Section 7.5</a> |
|---|
| 1776 | </td> |
|---|
| 1777 | </tr> |
|---|
| 1778 | </tbody> |
|---|
| 1779 | </table> |
|---|
| 1780 | </div> |
|---|
| 1781 | <p id="rfc.section.9.3.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p> |
|---|
| 1782 | <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a> <a id="security.considerations" href="#security.considerations">Security Considerations</a></h1> |
|---|
| 1783 | <p id="rfc.section.10.p.1">This section is meant to inform developers, information providers, and users of known security concerns specific to HTTP/1.1 |
|---|
| 1784 | 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>. |
|---|
| 1785 | </p> |
|---|
| 1786 | <p id="rfc.section.10.p.2">Caches expose additional potential vulnerabilities, since the contents of the cache represent an attractive target for malicious |
|---|
| 1787 | exploitation. Because cache contents persist after an HTTP request is complete, an attack on the cache can reveal information |
|---|
| 1788 | long after a user believes that the information has been removed from the network. Therefore, cache contents need to be protected |
|---|
| 1789 | as sensitive information. |
|---|
| 1790 | </p> |
|---|
| 1791 | <p id="rfc.section.10.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 |
|---|
| 1792 | 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 |
|---|
| 1793 | load more quickly, thanks to the cache. |
|---|
| 1794 | </p> |
|---|
| 1795 | <p id="rfc.section.10.p.4">Implementation flaws might allow attackers to insert content into a cache ("cache poisoning"), leading to compromise of clients |
|---|
| 1796 | that trust that content. Because of their nature, these attacks are difficult to mitigate. |
|---|
| 1797 | </p> |
|---|
| 1798 | <p id="rfc.section.10.p.5">Likewise, implementation flaws (as well as misunderstanding of cache operation) might lead to caching of sensitive information |
|---|
| 1799 | (e.g., authentication credentials) that is thought to be private, exposing it to unauthorized parties. |
|---|
| 1800 | </p> |
|---|
| 1801 | <p id="rfc.section.10.p.6">Note that the Set-Cookie response header <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 can be (and often is) used to satisfy subsequent requests |
|---|
| 1802 | to caches. Servers who wish to control caching of these responses are encouraged to emit appropriate Cache-Control response |
|---|
| 1803 | headers. |
|---|
| 1804 | </p> |
|---|
| 1805 | <h1 id="rfc.section.11"><a href="#rfc.section.11">11.</a> <a id="acks" href="#acks">Acknowledgments</a></h1> |
|---|
| 1806 | <p id="rfc.section.11.p.1">See <a href="p1-messaging.html#acks" title="Acknowledgments">Section 9</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>. |
|---|
| 1807 | </p> |
|---|
| 1808 | <h1 id="rfc.references"><a id="rfc.section.12" href="#rfc.section.12">12.</a> References |
|---|
| 1809 | </h1> |
|---|
| 1810 | <h2 id="rfc.references.1"><a href="#rfc.section.12.1" id="rfc.section.12.1">12.1</a> Normative References |
|---|
| 1811 | </h2> |
|---|
| 1812 | <table> |
|---|
| 1813 | <tr> |
|---|
| 1814 | <td class="reference"><b id="Part1">[Part1]</b></td> |
|---|
| 1815 | <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), February 2013. |
|---|
| 1816 | </td> |
|---|
| 1817 | </tr> |
|---|
| 1818 | <tr> |
|---|
| 1819 | <td class="reference"><b id="Part2">[Part2]</b></td> |
|---|
| 1820 | <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), February 2013. |
|---|
| 1821 | </td> |
|---|
| 1822 | </tr> |
|---|
| 1823 | <tr> |
|---|
| 1824 | <td class="reference"><b id="Part4">[Part4]</b></td> |
|---|
| 1825 | <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), February 2013. |
|---|
| 1826 | </td> |
|---|
| 1827 | </tr> |
|---|
| 1828 | <tr> |
|---|
| 1829 | <td class="reference"><b id="Part5">[Part5]</b></td> |
|---|
| 1830 | <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), February 2013. |
|---|
| 1831 | </td> |
|---|
| 1832 | </tr> |
|---|
| 1833 | <tr> |
|---|
| 1834 | <td class="reference"><b id="Part7">[Part7]</b></td> |
|---|
| 1835 | <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), February 2013. |
|---|
| 1836 | </td> |
|---|
| 1837 | </tr> |
|---|
| 1838 | <tr> |
|---|
| 1839 | <td class="reference"><b id="RFC2119">[RFC2119]</b></td> |
|---|
| 1840 | <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. |
|---|
| 1841 | </td> |
|---|
| 1842 | </tr> |
|---|
| 1843 | <tr> |
|---|
| 1844 | <td class="reference"><b id="RFC5234">[RFC5234]</b></td> |
|---|
| 1845 | <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. |
|---|
| 1846 | </td> |
|---|
| 1847 | </tr> |
|---|
| 1848 | </table> |
|---|
| 1849 | <h2 id="rfc.references.2"><a href="#rfc.section.12.2" id="rfc.section.12.2">12.2</a> Informative References |
|---|
| 1850 | </h2> |
|---|
| 1851 | <table> |
|---|
| 1852 | <tr> |
|---|
| 1853 | <td class="reference"><b id="BCP90">[BCP90]</b></td> |
|---|
| 1854 | <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. |
|---|
| 1855 | </td> |
|---|
| 1856 | </tr> |
|---|
| 1857 | <tr> |
|---|
| 1858 | <td class="reference"><b id="RFC1305">[RFC1305]</b></td> |
|---|
| 1859 | <td class="top"><a href="mailto:mills@udel.edu" title="University of Delaware, Electrical Engineering Department">Mills, D.</a>, “<a href="http://tools.ietf.org/html/rfc1305">Network Time Protocol (Version 3) Specification, Implementation</a>”, RFC 1305, March 1992. |
|---|
| 1860 | </td> |
|---|
| 1861 | </tr> |
|---|
| 1862 | <tr> |
|---|
| 1863 | <td class="reference"><b id="RFC2616">[RFC2616]</b></td> |
|---|
| 1864 | <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. |
|---|
| 1865 | </td> |
|---|
| 1866 | </tr> |
|---|
| 1867 | <tr> |
|---|
| 1868 | <td class="reference"><b id="RFC5226">[RFC5226]</b></td> |
|---|
| 1869 | <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. |
|---|
| 1870 | </td> |
|---|
| 1871 | </tr> |
|---|
| 1872 | <tr> |
|---|
| 1873 | <td class="reference"><b id="RFC5861">[RFC5861]</b></td> |
|---|
| 1874 | <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. |
|---|
| 1875 | </td> |
|---|
| 1876 | </tr> |
|---|
| 1877 | <tr> |
|---|
| 1878 | <td class="reference"><b id="RFC6265">[RFC6265]</b></td> |
|---|
| 1879 | <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. |
|---|
| 1880 | </td> |
|---|
| 1881 | </tr> |
|---|
| 1882 | </table> |
|---|
| 1883 | <div class="avoidbreak"> |
|---|
| 1884 | <h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1> |
|---|
| 1885 | <address class="vcard"><span class="vcardline"><span class="fn">Roy T. Fielding</span> |
|---|
| 1886 | (editor) |
|---|
| 1887 | <span class="n hidden"><span class="family-name">Fielding</span><span class="given-name">Roy T.</span></span></span><span class="org vcardline">Adobe Systems Incorporated</span><span class="adr"><span class="street-address vcardline">345 Park Ave</span><span class="vcardline"><span class="locality">San Jose</span>, <span class="region">CA</span> <span class="postal-code">95110</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">Email: <a href="mailto:fielding@gbiv.com"><span class="email">fielding@gbiv.com</span></a></span><span class="vcardline">URI: <a href="http://roy.gbiv.com/" class="url">http://roy.gbiv.com/</a></span></address> |
|---|
| 1888 | <address class="vcard"><span class="vcardline"><span class="fn">Mark Nottingham</span> |
|---|
| 1889 | (editor) |
|---|
| 1890 | <span class="n hidden"><span class="family-name">Nottingham</span><span class="given-name">Mark</span></span></span><span class="org vcardline">Akamai</span><span class="vcardline">Email: <a href="mailto:mnot@mnot.net"><span class="email">mnot@mnot.net</span></a></span><span class="vcardline">URI: <a href="http://www.mnot.net/" class="url">http://www.mnot.net/</a></span></address> |
|---|
| 1891 | <address class="vcard"><span class="vcardline"><span class="fn">Julian F. Reschke</span> |
|---|
| 1892 | (editor) |
|---|
| 1893 | <span class="n hidden"><span class="family-name">Reschke</span><span class="given-name">Julian F.</span></span></span><span class="org vcardline">greenbytes GmbH</span><span class="adr"><span class="street-address vcardline">Hafenweg 16</span><span class="vcardline"><span class="locality">Muenster</span>, <span class="region">NW</span> <span class="postal-code">48155</span></span><span class="country-name vcardline">Germany</span></span><span class="vcardline">Email: <a href="mailto:julian.reschke@greenbytes.de"><span class="email">julian.reschke@greenbytes.de</span></a></span><span class="vcardline">URI: <a href="http://greenbytes.de/tech/webdav/" class="url">http://greenbytes.de/tech/webdav/</a></span></address> |
|---|
| 1894 | </div> |
|---|
| 1895 | <h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a> <a id="changes.from.rfc.2616" href="#changes.from.rfc.2616">Changes from RFC 2616</a></h1> |
|---|
| 1896 | <p id="rfc.section.A.p.1">Caching-related text has been substantially rewritten for clarity.</p> |
|---|
| 1897 | <p id="rfc.section.A.p.2">The algorithm for calculating age is now less conservative. (<a href="#age.calculations" title="Calculating Age">Section 4.1.3</a>) |
|---|
| 1898 | </p> |
|---|
| 1899 | <p id="rfc.section.A.p.3">Caches are now required to handle dates with timezones as if they're invalid, because it's not possible to accurately guess. |
|---|
| 1900 | (<a href="#age.calculations" title="Calculating Age">Section 4.1.3</a>) |
|---|
| 1901 | </p> |
|---|
| 1902 | <p id="rfc.section.A.p.4">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 Model">Section 4.2</a>) |
|---|
| 1903 | </p> |
|---|
| 1904 | <p id="rfc.section.A.p.5">The algorithm for selecting a cached negotiated response to use has been clarified in several ways. In particular, it now |
|---|
| 1905 | explicitly allows header-specific canonicalization when processing selecting header fields. (<a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section 4.3</a>) |
|---|
| 1906 | </p> |
|---|
| 1907 | <p id="rfc.section.A.p.6">Requirements regarding denial of service attack avoidance when performing invalidation have been clarified. (<a href="#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section 6</a>) |
|---|
| 1908 | </p> |
|---|
| 1909 | <p id="rfc.section.A.p.7">Cache invalidation only occurs when a successful response is received. (<a href="#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section 6</a>) |
|---|
| 1910 | </p> |
|---|
| 1911 | <p id="rfc.section.A.p.8">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>) |
|---|
| 1912 | </p> |
|---|
| 1913 | <p id="rfc.section.A.p.9">The one-year limit on Expires header field values has been removed; instead, the reasoning for using a sensible value is given. |
|---|
| 1914 | (<a href="#header.expires" id="rfc.xref.header.expires.5" title="Expires">Section 7.3</a>) |
|---|
| 1915 | </p> |
|---|
| 1916 | <p id="rfc.section.A.p.10">The Pragma header field is now only defined for backwards compatibility; future pragmas are deprecated. (<a href="#header.pragma" id="rfc.xref.header.pragma.4" title="Pragma">Section 7.4</a>) |
|---|
| 1917 | </p> |
|---|
| 1918 | <p id="rfc.section.A.p.11">Cache directives are explicitly defined to be case-insensitive. (<a href="#header.cache-control" id="rfc.xref.header.cache-control.3" title="Cache-Control">Section 7.2</a>) |
|---|
| 1919 | </p> |
|---|
| 1920 | <p id="rfc.section.A.p.12">Handling of multiple instances of cache directives when only one is expected is now defined. (<a href="#header.cache-control" id="rfc.xref.header.cache-control.4" title="Cache-Control">Section 7.2</a>) |
|---|
| 1921 | </p> |
|---|
| 1922 | <p id="rfc.section.A.p.13">The qualified forms of the private and no-cache cache directives are noted to not be widely implemented; e.g., "private=foo" |
|---|
| 1923 | is interpreted by many caches as simply "private". Additionally, the meaning of the qualified form of no-cache has been clarified. |
|---|
| 1924 | (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section 7.2.2</a>) |
|---|
| 1925 | </p> |
|---|
| 1926 | <p id="rfc.section.A.p.14">The "no-store" cache request directive doesn't apply to responses; i.e., a cache can satisfy a request with no-store on it, |
|---|
| 1927 | and does not invalidate it. (<a href="#cache-request-directive.no-store" title="no-store">Section 7.2.1.2</a>) |
|---|
| 1928 | </p> |
|---|
| 1929 | <p id="rfc.section.A.p.15">The "no-cache" response cache directive's meaning has been clarified. (<a href="#cache-response-directive.no-cache" title="no-cache">Section 7.2.2.3</a>) |
|---|
| 1930 | </p> |
|---|
| 1931 | <p id="rfc.section.A.p.16">New status codes can now define that caches are allowed to use heuristic freshness with them. (<a href="#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.1.2</a>) |
|---|
| 1932 | </p> |
|---|
| 1933 | <p id="rfc.section.A.p.17">Caches are now allow to calculate heuristic freshness for URLs with query components. (<a href="#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.1.2</a>) |
|---|
| 1934 | </p> |
|---|
| 1935 | <p id="rfc.section.A.p.18">Some requirements regarding production of the <a href="#header.warning" class="smpl">Warning</a> header have been relaxed, as it is not widely implemented. (<a href="#header.warning" id="rfc.xref.header.warning.6" title="Warning">Section 7.5</a>) |
|---|
| 1936 | </p> |
|---|
| 1937 | <p id="rfc.section.A.p.19">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.7" title="Warning">Section 7.5</a>) |
|---|
| 1938 | </p> |
|---|
| 1939 | <p id="rfc.section.A.p.20">This specification introduces the Cache Directive and Warn Code Registries, and defines considerations for new cache directives. |
|---|
| 1940 | (<a href="#cache.control.extensions" title="Cache Control Extensions">Section 7.2.3</a> and <a href="#warn.code.extensions" title="Warn Code Extensions">Section 7.5.8</a>) |
|---|
| 1941 | </p> |
|---|
| 1942 | <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a> <a id="imported.abnf" href="#imported.abnf">Imported ABNF</a></h1> |
|---|
| 1943 | <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 |
|---|
| 1944 | (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 |
|---|
| 1945 | character). |
|---|
| 1946 | </p> |
|---|
| 1947 | <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>: |
|---|
| 1948 | </p> |
|---|
| 1949 | <div id="rfc.figure.u.14"></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>> |
|---|
| 1950 | <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>> |
|---|
| 1951 | <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>> |
|---|
| 1952 | <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>> |
|---|
| 1953 | |
|---|
| 1954 | <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>> |
|---|
| 1955 | <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>> |
|---|
| 1956 | <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>> |
|---|
| 1957 | </pre><p id="rfc.section.B.p.4">The rules below are defined in other parts:</p> |
|---|
| 1958 | <div id="rfc.figure.u.15"></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>> |
|---|
| 1959 | </pre><h1 id="rfc.section.C"><a href="#rfc.section.C">C.</a> <a id="collected.abnf" href="#collected.abnf">Collected ABNF</a></h1> |
|---|
| 1960 | <div id="rfc.figure.u.16"></div> <pre class="inline"><a href="#header.age" class="smpl">Age</a> = delta-seconds |
|---|
| 1961 | |
|---|
| 1962 | <a href="#header.cache-control" class="smpl">Cache-Control</a> = *( "," OWS ) cache-directive *( OWS "," [ OWS |
|---|
| 1963 | cache-directive ] ) |
|---|
| 1964 | |
|---|
| 1965 | <a href="#header.expires" class="smpl">Expires</a> = HTTP-date |
|---|
| 1966 | |
|---|
| 1967 | <a href="#imported.abnf" class="smpl">HTTP-date</a> = <HTTP-date, defined in [Part2], Section 7.1.1.1> |
|---|
| 1968 | |
|---|
| 1969 | <a href="#imported.abnf" class="smpl">OWS</a> = <OWS, defined in [Part1], Section 3.2.3> |
|---|
| 1970 | |
|---|
| 1971 | <a href="#header.pragma" class="smpl">Pragma</a> = *( "," OWS ) pragma-directive *( OWS "," [ OWS |
|---|
| 1972 | pragma-directive ] ) |
|---|
| 1973 | |
|---|
| 1974 | <a href="#header.warning" class="smpl">Warning</a> = *( "," OWS ) warning-value *( OWS "," [ OWS warning-value ] |
|---|
| 1975 | ) |
|---|
| 1976 | |
|---|
| 1977 | <a href="#header.cache-control" class="smpl">cache-directive</a> = token [ "=" ( token / quoted-string ) ] |
|---|
| 1978 | |
|---|
| 1979 | <a href="#delta-seconds" class="smpl">delta-seconds</a> = 1*DIGIT |
|---|
| 1980 | |
|---|
| 1981 | <a href="#header.pragma" class="smpl">extension-pragma</a> = token [ "=" ( token / quoted-string ) ] |
|---|
| 1982 | |
|---|
| 1983 | <a href="#imported.abnf" class="smpl">field-name</a> = <field-name, defined in [Part1], Section 3.2> |
|---|
| 1984 | |
|---|
| 1985 | <a href="#imported.abnf" class="smpl">port</a> = <port, defined in [Part1], Section 2.7> |
|---|
| 1986 | <a href="#header.pragma" class="smpl">pragma-directive</a> = "no-cache" / extension-pragma |
|---|
| 1987 | <a href="#imported.abnf" class="smpl">pseudonym</a> = <pseudonym, defined in [Part1], Section 5.7.1> |
|---|
| 1988 | |
|---|
| 1989 | <a href="#imported.abnf" class="smpl">quoted-string</a> = <quoted-string, defined in [Part1], Section 3.2.6> |
|---|
| 1990 | |
|---|
| 1991 | <a href="#imported.abnf" class="smpl">token</a> = <token, defined in [Part1], Section 3.2.6> |
|---|
| 1992 | |
|---|
| 1993 | <a href="#imported.abnf" class="smpl">uri-host</a> = <uri-host, defined in [Part1], Section 2.7> |
|---|
| 1994 | |
|---|
| 1995 | <a href="#header.warning" class="smpl">warn-agent</a> = ( uri-host [ ":" port ] ) / pseudonym |
|---|
| 1996 | <a href="#header.warning" class="smpl">warn-code</a> = 3DIGIT |
|---|
| 1997 | <a href="#header.warning" class="smpl">warn-date</a> = DQUOTE HTTP-date DQUOTE |
|---|
| 1998 | <a href="#header.warning" class="smpl">warn-text</a> = quoted-string |
|---|
| 1999 | <a href="#header.warning" class="smpl">warning-value</a> = warn-code SP warn-agent SP warn-text [ SP warn-date |
|---|
| 2000 | ] |
|---|
| 2001 | </pre> <h1 id="rfc.section.D"><a href="#rfc.section.D">D.</a> <a id="change.log" href="#change.log">Change Log (to be removed by RFC Editor before publication)</a></h1> |
|---|
| 2002 | <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>>. |
|---|
| 2003 | </p> |
|---|
| 2004 | <h2 id="rfc.section.D.1"><a href="#rfc.section.D.1">D.1</a> <a id="changes.since.19" href="#changes.since.19">Since draft-ietf-httpbis-p6-cache-19</a></h2> |
|---|
| 2005 | <p id="rfc.section.D.1.p.1">Closed issues: </p> |
|---|
| 2006 | <ul> |
|---|
| 2007 | <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" |
|---|
| 2008 | </li> |
|---|
| 2009 | <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" |
|---|
| 2010 | </li> |
|---|
| 2011 | <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" |
|---|
| 2012 | </li> |
|---|
| 2013 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/356">http://tools.ietf.org/wg/httpbis/trac/ticket/356</a>>: "Spurious 'MAYs'" |
|---|
| 2014 | </li> |
|---|
| 2015 | <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" |
|---|
| 2016 | </li> |
|---|
| 2017 | <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" |
|---|
| 2018 | </li> |
|---|
| 2019 | <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" |
|---|
| 2020 | </li> |
|---|
| 2021 | <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'" |
|---|
| 2022 | </li> |
|---|
| 2023 | </ul> |
|---|
| 2024 | <h2 id="rfc.section.D.2"><a href="#rfc.section.D.2">D.2</a> <a id="changes.since.20" href="#changes.since.20">Since draft-ietf-httpbis-p6-cache-20</a></h2> |
|---|
| 2025 | <p id="rfc.section.D.2.p.1">Closed issues: </p> |
|---|
| 2026 | <ul> |
|---|
| 2027 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/375">http://tools.ietf.org/wg/httpbis/trac/ticket/375</a>>: "'Most Conservative'" |
|---|
| 2028 | </li> |
|---|
| 2029 | </ul> |
|---|
| 2030 | <p id="rfc.section.D.2.p.2">Other changes: </p> |
|---|
| 2031 | <ul> |
|---|
| 2032 | <li>Conformance criteria and considerations regarding error handling are now defined in Part 1.</li> |
|---|
| 2033 | <li>Move definition of "Vary" header field into Part 2.</li> |
|---|
| 2034 | <li>Add security considerations with respect to cache poisoning and the "Set-Cookie" header field.</li> |
|---|
| 2035 | </ul> |
|---|
| 2036 | <h2 id="rfc.section.D.3"><a href="#rfc.section.D.3">D.3</a> <a id="changes.since.21" href="#changes.since.21">Since draft-ietf-httpbis-p6-cache-21</a></h2> |
|---|
| 2037 | <p id="rfc.section.D.3.p.1">Closed issues: </p> |
|---|
| 2038 | <ul> |
|---|
| 2039 | <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" |
|---|
| 2040 | </li> |
|---|
| 2041 | <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" |
|---|
| 2042 | </li> |
|---|
| 2043 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/418">http://tools.ietf.org/wg/httpbis/trac/ticket/418</a>>: "No-Transform" |
|---|
| 2044 | </li> |
|---|
| 2045 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/430">http://tools.ietf.org/wg/httpbis/trac/ticket/430</a>>: "Revert prior change to the meaning of the public cache response directive. |
|---|
| 2046 | </li> |
|---|
| 2047 | </ul> |
|---|
| 2048 | <h2 id="rfc.section.D.4"><a href="#rfc.section.D.4">D.4</a> <a id="changes.since.22" href="#changes.since.22">Since draft-ietf-httpbis-p6-cache-22</a></h2> |
|---|
| 2049 | <p id="rfc.section.D.4.p.1">None yet.</p> |
|---|
| 2050 | <h1 id="rfc.index"><a href="#rfc.index">Index</a></h1> |
|---|
| 2051 | <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.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.V">V</a> <a href="#rfc.index.W">W</a> |
|---|
| 2052 | </p> |
|---|
| 2053 | <div class="print2col"> |
|---|
| 2054 | <ul class="ind"> |
|---|
| 2055 | <li><a id="rfc.index.1" href="#rfc.index.1"><b>1</b></a><ul> |
|---|
| 2056 | <li>110 Response is Stale (warn code) <a href="#rfc.iref.52"><b>7.5.1</b></a>, <a href="#rfc.xref.warn.110.1">9.2</a></li> |
|---|
| 2057 | <li>111 Revalidation Failed (warn code) <a href="#rfc.iref.52"><b>7.5.2</b></a>, <a href="#rfc.xref.warn.111.1">9.2</a></li> |
|---|
| 2058 | <li>112 Disconnected Operation (warn code) <a href="#rfc.iref.52"><b>7.5.3</b></a>, <a href="#rfc.xref.warn.112.1">9.2</a></li> |
|---|
| 2059 | <li>113 Heuristic Expiration (warn code) <a href="#rfc.iref.52"><b>7.5.4</b></a>, <a href="#rfc.xref.warn.113.1">9.2</a></li> |
|---|
| 2060 | <li>199 Miscellaneous Warning (warn code) <a href="#rfc.iref.52"><b>7.5.5</b></a>, <a href="#rfc.xref.warn.199.1">9.2</a></li> |
|---|
| 2061 | </ul> |
|---|
| 2062 | </li> |
|---|
| 2063 | <li><a id="rfc.index.2" href="#rfc.index.2"><b>2</b></a><ul> |
|---|
| 2064 | <li>214 Transformation Applied (warn code) <a href="#rfc.iref.52"><b>7.5.6</b></a>, <a href="#rfc.xref.warn.214.1">9.2</a></li> |
|---|
| 2065 | <li>299 Miscellaneous Persistent Warning (warn code) <a href="#rfc.iref.52"><b>7.5.7</b></a>, <a href="#rfc.xref.warn.299.1">9.2</a></li> |
|---|
| 2066 | </ul> |
|---|
| 2067 | </li> |
|---|
| 2068 | <li><a id="rfc.index.A" href="#rfc.index.A"><b>A</b></a><ul> |
|---|
| 2069 | <li>age <a href="#rfc.iref.a.1">1.2</a></li> |
|---|
| 2070 | <li>Age header field <a href="#rfc.xref.header.age.1">4</a>, <a href="#rfc.xref.header.age.2">4.1.3</a>, <a href="#rfc.iref.a.2"><b>7.1</b></a>, <a href="#rfc.xref.header.age.3">9.3</a></li> |
|---|
| 2071 | </ul> |
|---|
| 2072 | </li> |
|---|
| 2073 | <li><a id="rfc.index.B" href="#rfc.index.B"><b>B</b></a><ul> |
|---|
| 2074 | <li><em>BCP90</em> <a href="#rfc.xref.BCP90.1">9.3</a>, <a href="#BCP90"><b>12.2</b></a></li> |
|---|
| 2075 | </ul> |
|---|
| 2076 | </li> |
|---|
| 2077 | <li><a id="rfc.index.C" href="#rfc.index.C"><b>C</b></a><ul> |
|---|
| 2078 | <li>cache <a href="#rfc.iref.c.1">1.1</a>, <a href="#rfc.iref.c.2">1.2</a></li> |
|---|
| 2079 | <li>cache entry <a href="#rfc.iref.c.4">2</a></li> |
|---|
| 2080 | <li>cache key <a href="#rfc.iref.c.5">2</a></li> |
|---|
| 2081 | <li>Cache-Control header field <a href="#rfc.xref.header.cache-control.1">3</a>, <a href="#rfc.iref.c.6"><b>7.2</b></a>, <a href="#rfc.xref.header.cache-control.2">9.3</a>, <a href="#rfc.xref.header.cache-control.3">A</a>, <a href="#rfc.xref.header.cache-control.4">A</a></li> |
|---|
| 2082 | <li>cacheable <a href="#rfc.iref.c.3">1.2</a></li> |
|---|
| 2083 | </ul> |
|---|
| 2084 | </li> |
|---|
| 2085 | <li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul> |
|---|
| 2086 | <li>Expires header field <a href="#rfc.xref.header.expires.1">3</a>, <a href="#rfc.xref.header.expires.2">4.1</a>, <a href="#rfc.xref.header.expires.3">4.1.1</a>, <a href="#rfc.iref.e.2"><b>7.3</b></a>, <a href="#rfc.xref.header.expires.4">9.3</a>, <a href="#rfc.xref.header.expires.5">A</a></li> |
|---|
| 2087 | <li>explicit expiration time <a href="#rfc.iref.e.1">1.2</a></li> |
|---|
| 2088 | </ul> |
|---|
| 2089 | </li> |
|---|
| 2090 | <li><a id="rfc.index.F" href="#rfc.index.F"><b>F</b></a><ul> |
|---|
| 2091 | <li>first-hand <a href="#rfc.iref.f.1">1.2</a></li> |
|---|
| 2092 | <li>fresh <a href="#rfc.iref.f.3">1.2</a></li> |
|---|
| 2093 | <li>freshness lifetime <a href="#rfc.iref.f.2">1.2</a></li> |
|---|
| 2094 | </ul> |
|---|
| 2095 | </li> |
|---|
| 2096 | <li><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul> |
|---|
| 2097 | <li><tt>Grammar</tt> |
|---|
| 2098 | <ul> |
|---|
| 2099 | <li><tt>Age</tt> <a href="#rfc.iref.g.2"><b>7.1</b></a></li> |
|---|
| 2100 | <li><tt>Cache-Control</tt> <a href="#rfc.iref.g.3"><b>7.2</b></a></li> |
|---|
| 2101 | <li><tt>cache-directive</tt> <a href="#rfc.iref.g.4"><b>7.2</b></a></li> |
|---|
| 2102 | <li><tt>delta-seconds</tt> <a href="#rfc.iref.g.1"><b>1.4.1</b></a></li> |
|---|
| 2103 | <li><tt>Expires</tt> <a href="#rfc.iref.g.5"><b>7.3</b></a></li> |
|---|
| 2104 | <li><tt>extension-pragma</tt> <a href="#rfc.iref.g.8"><b>7.4</b></a></li> |
|---|
| 2105 | <li><tt>Pragma</tt> <a href="#rfc.iref.g.6"><b>7.4</b></a></li> |
|---|
| 2106 | <li><tt>pragma-directive</tt> <a href="#rfc.iref.g.7"><b>7.4</b></a></li> |
|---|
| 2107 | <li><tt>warn-agent</tt> <a href="#rfc.iref.g.12"><b>7.5</b></a></li> |
|---|
| 2108 | <li><tt>warn-code</tt> <a href="#rfc.iref.g.11"><b>7.5</b></a></li> |
|---|
| 2109 | <li><tt>warn-date</tt> <a href="#rfc.iref.g.14"><b>7.5</b></a></li> |
|---|
| 2110 | <li><tt>warn-text</tt> <a href="#rfc.iref.g.13"><b>7.5</b></a></li> |
|---|
| 2111 | <li><tt>Warning</tt> <a href="#rfc.iref.g.9"><b>7.5</b></a></li> |
|---|
| 2112 | <li><tt>warning-value</tt> <a href="#rfc.iref.g.10"><b>7.5</b></a></li> |
|---|
| 2113 | </ul> |
|---|
| 2114 | </li> |
|---|
| 2115 | </ul> |
|---|
| 2116 | </li> |
|---|
| 2117 | <li><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul> |
|---|
| 2118 | <li>heuristic expiration time <a href="#rfc.iref.h.1">1.2</a></li> |
|---|
| 2119 | </ul> |
|---|
| 2120 | </li> |
|---|
| 2121 | <li><a id="rfc.index.M" href="#rfc.index.M"><b>M</b></a><ul> |
|---|
| 2122 | <li>max-age (cache directive) <a href="#rfc.iref.m.1"><b>7.2.1.3</b></a>, <a href="#rfc.iref.m.5"><b>7.2.2.7</b></a></li> |
|---|
| 2123 | <li>max-stale (cache directive) <a href="#rfc.iref.m.2"><b>7.2.1.4</b></a></li> |
|---|
| 2124 | <li>min-fresh (cache directive) <a href="#rfc.iref.m.3"><b>7.2.1.5</b></a></li> |
|---|
| 2125 | <li>must-revalidate (cache directive) <a href="#rfc.iref.m.4"><b>7.2.2.5</b></a></li> |
|---|
| 2126 | </ul> |
|---|
| 2127 | </li> |
|---|
| 2128 | <li><a id="rfc.index.N" href="#rfc.index.N"><b>N</b></a><ul> |
|---|
| 2129 | <li>no-cache (cache directive) <a href="#rfc.iref.n.1"><b>7.2.1.1</b></a>, <a href="#rfc.iref.n.4"><b>7.2.2.3</b></a></li> |
|---|
| 2130 | <li>no-store (cache directive) <a href="#rfc.iref.n.2"><b>7.2.1.2</b></a>, <a href="#rfc.iref.n.5"><b>7.2.2.4</b></a></li> |
|---|
| 2131 | <li>no-transform (cache directive) <a href="#rfc.iref.n.3"><b>7.2.1.6</b></a>, <a href="#rfc.iref.n.6"><b>7.2.2.9</b></a></li> |
|---|
| 2132 | </ul> |
|---|
| 2133 | </li> |
|---|
| 2134 | <li><a id="rfc.index.O" href="#rfc.index.O"><b>O</b></a><ul> |
|---|
| 2135 | <li>only-if-cached (cache directive) <a href="#rfc.iref.o.1"><b>7.2.1.7</b></a></li> |
|---|
| 2136 | </ul> |
|---|
| 2137 | </li> |
|---|
| 2138 | <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul> |
|---|
| 2139 | <li><em>Part1</em> <a href="#rfc.xref.Part1.1">1.3</a>, <a href="#rfc.xref.Part1.2">1.4</a>, <a href="#rfc.xref.Part1.3">3.1</a>, <a href="#rfc.xref.Part1.4">4</a>, <a href="#rfc.xref.Part1.5">4.3</a>, <a href="#rfc.xref.Part1.6">6</a>, <a href="#rfc.xref.Part1.7">6</a>, <a href="#rfc.xref.Part1.8">6</a>, <a href="#rfc.xref.Part1.9">7.2.1.6</a>, <a href="#rfc.xref.Part1.10">7.2.2.9</a>, <a href="#rfc.xref.Part1.11">10</a>, <a href="#rfc.xref.Part1.12">11</a>, <a href="#Part1"><b>12.1</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><ul> |
|---|
| 2140 | <li><em>Section 1.2</em> <a href="#rfc.xref.Part1.2">1.4</a></li> |
|---|
| 2141 | <li><em>Section 2.5</em> <a href="#rfc.xref.Part1.1">1.3</a></li> |
|---|
| 2142 | <li><em>Section 2.7</em> <a href="#rfc.xref.Part1.18">B</a>, <a href="#rfc.xref.Part1.20">B</a></li> |
|---|
| 2143 | <li><em>Section 3.2</em> <a href="#rfc.xref.Part1.5">4.3</a>, <a href="#rfc.xref.Part1.15">B</a></li> |
|---|
| 2144 | <li><em>Section 3.2.3</em> <a href="#rfc.xref.Part1.14">B</a></li> |
|---|
| 2145 | <li><em>Section 3.2.6</em> <a href="#rfc.xref.Part1.16">B</a>, <a href="#rfc.xref.Part1.17">B</a></li> |
|---|
| 2146 | <li><em>Section 5.5</em> <a href="#rfc.xref.Part1.4">4</a>, <a href="#rfc.xref.Part1.6">6</a>, <a href="#rfc.xref.Part1.7">6</a>, <a href="#rfc.xref.Part1.8">6</a></li> |
|---|
| 2147 | <li><em>Section 5.7.1</em> <a href="#rfc.xref.Part1.19">B</a></li> |
|---|
| 2148 | <li><em>Section 5.7.2</em> <a href="#rfc.xref.Part1.9">7.2.1.6</a>, <a href="#rfc.xref.Part1.10">7.2.2.9</a></li> |
|---|
| 2149 | <li><em>Section 9</em> <a href="#rfc.xref.Part1.12">11</a></li> |
|---|
| 2150 | </ul> |
|---|
| 2151 | </li> |
|---|
| 2152 | <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">4.1.3</a>, <a href="#rfc.xref.Part2.5">4.3</a>, <a href="#rfc.xref.Part2.6">6</a>, <a href="#rfc.xref.Part2.7">7.3</a>, <a href="#rfc.xref.Part2.8">10</a>, <a href="#Part2"><b>12.1</b></a>, <a href="#rfc.xref.Part2.9">B</a><ul> |
|---|
| 2153 | <li><em>Section 4.2.1</em> <a href="#rfc.xref.Part2.3">4</a>, <a href="#rfc.xref.Part2.6">6</a></li> |
|---|
| 2154 | <li><em>Section 4.3.1</em> <a href="#rfc.xref.Part2.2">2</a></li> |
|---|
| 2155 | <li><em>Section 7.1.1.1</em> <a href="#rfc.xref.Part2.7">7.3</a>, <a href="#rfc.xref.Part2.9">B</a></li> |
|---|
| 2156 | <li><em>Section 7.1.1.2</em> <a href="#rfc.xref.Part2.4">4.1.3</a></li> |
|---|
| 2157 | <li><em>Section 7.1.4</em> <a href="#rfc.xref.Part2.5">4.3</a></li> |
|---|
| 2158 | </ul> |
|---|
| 2159 | </li> |
|---|
| 2160 | <li><em>Part4</em> <a href="#rfc.xref.Part4.1">1.2</a>, <a href="#rfc.xref.Part4.2">1.2</a>, <a href="#rfc.xref.Part4.3">1.2</a>, <a href="#rfc.xref.Part4.4">4.1.2</a>, <a href="#rfc.xref.Part4.5">4.2</a>, <a href="#Part4"><b>12.1</b></a><ul> |
|---|
| 2161 | <li><em>Section 2.1</em> <a href="#rfc.xref.Part4.1">1.2</a></li> |
|---|
| 2162 | <li><em>Section 2.2</em> <a href="#rfc.xref.Part4.4">4.1.2</a></li> |
|---|
| 2163 | <li><em>Section 2.2.2</em> <a href="#rfc.xref.Part4.3">1.2</a></li> |
|---|
| 2164 | <li><em>Section 2.3</em> <a href="#rfc.xref.Part4.2">1.2</a></li> |
|---|
| 2165 | </ul> |
|---|
| 2166 | </li> |
|---|
| 2167 | <li><em>Part5</em> <a href="#rfc.xref.Part5.1">3.1</a>, <a href="#rfc.xref.Part5.2">4.4</a>, <a href="#rfc.xref.Part5.3">4.4</a>, <a href="#Part5"><b>12.1</b></a><ul> |
|---|
| 2168 | <li><em>Section 4.3</em> <a href="#rfc.xref.Part5.3">4.4</a></li> |
|---|
| 2169 | </ul> |
|---|
| 2170 | </li> |
|---|
| 2171 | <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>12.1</b></a><ul> |
|---|
| 2172 | <li><em>Section 4.1</em> <a href="#rfc.xref.Part7.1">3</a>, <a href="#rfc.xref.Part7.2">3.2</a></li> |
|---|
| 2173 | </ul> |
|---|
| 2174 | </li> |
|---|
| 2175 | <li>Pragma header field <a href="#rfc.xref.header.pragma.1">4</a>, <a href="#rfc.xref.header.pragma.2">7.2</a>, <a href="#rfc.iref.p.5"><b>7.4</b></a>, <a href="#rfc.xref.header.pragma.3">9.3</a>, <a href="#rfc.xref.header.pragma.4">A</a></li> |
|---|
| 2176 | <li>private (cache directive) <a href="#rfc.iref.p.3"><b>7.2.2.2</b></a></li> |
|---|
| 2177 | <li>private cache <a href="#rfc.iref.p.1">1.2</a></li> |
|---|
| 2178 | <li>proxy-revalidate (cache directive) <a href="#rfc.iref.p.4"><b>7.2.2.6</b></a></li> |
|---|
| 2179 | <li>public (cache directive) <a href="#rfc.iref.p.2"><b>7.2.2.1</b></a></li> |
|---|
| 2180 | </ul> |
|---|
| 2181 | </li> |
|---|
| 2182 | <li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul> |
|---|
| 2183 | <li><em>RFC1305</em> <a href="#rfc.xref.RFC1305.1">4.1.3</a>, <a href="#RFC1305"><b>12.2</b></a></li> |
|---|
| 2184 | <li><em>RFC2119</em> <a href="#rfc.xref.RFC2119.1">1.3</a>, <a href="#RFC2119"><b>12.1</b></a></li> |
|---|
| 2185 | <li><em>RFC2616</em> <a href="#rfc.xref.RFC2616.1">4.1.2</a>, <a href="#RFC2616"><b>12.2</b></a><ul> |
|---|
| 2186 | <li><em>Section 13.9</em> <a href="#rfc.xref.RFC2616.1">4.1.2</a></li> |
|---|
| 2187 | </ul> |
|---|
| 2188 | </li> |
|---|
| 2189 | <li><em>RFC5226</em> <a href="#rfc.xref.RFC5226.1">7.2.3</a>, <a href="#rfc.xref.RFC5226.2">7.5.8</a>, <a href="#RFC5226"><b>12.2</b></a><ul> |
|---|
| 2190 | <li><em>Section 4.1</em> <a href="#rfc.xref.RFC5226.1">7.2.3</a>, <a href="#rfc.xref.RFC5226.2">7.5.8</a></li> |
|---|
| 2191 | </ul> |
|---|
| 2192 | </li> |
|---|
| 2193 | <li><em>RFC5234</em> <a href="#rfc.xref.RFC5234.1">1.4</a>, <a href="#RFC5234"><b>12.1</b></a>, <a href="#rfc.xref.RFC5234.2">B</a><ul> |
|---|
| 2194 | <li><em>Appendix B.1</em> <a href="#rfc.xref.RFC5234.2">B</a></li> |
|---|
| 2195 | </ul> |
|---|
| 2196 | </li> |
|---|
| 2197 | <li><em>RFC5861</em> <a href="#rfc.xref.RFC5861.1">9.1</a>, <a href="#rfc.xref.RFC5861.2">9.1</a>, <a href="#RFC5861"><b>12.2</b></a><ul> |
|---|
| 2198 | <li><em>Section 3</em> <a href="#rfc.xref.RFC5861.2">9.1</a></li> |
|---|
| 2199 | <li><em>Section 4</em> <a href="#rfc.xref.RFC5861.1">9.1</a></li> |
|---|
| 2200 | </ul> |
|---|
| 2201 | </li> |
|---|
| 2202 | <li><em>RFC6265</em> <a href="#rfc.xref.RFC6265.1">10</a>, <a href="#RFC6265"><b>12.2</b></a></li> |
|---|
| 2203 | </ul> |
|---|
| 2204 | </li> |
|---|
| 2205 | <li><a id="rfc.index.S" href="#rfc.index.S"><b>S</b></a><ul> |
|---|
| 2206 | <li>s-maxage (cache directive) <a href="#rfc.iref.s.4"><b>7.2.2.8</b></a></li> |
|---|
| 2207 | <li>shared cache <a href="#rfc.iref.s.1">1.2</a></li> |
|---|
| 2208 | <li>stale <a href="#rfc.iref.s.2">1.2</a></li> |
|---|
| 2209 | <li>strong validator <a href="#rfc.iref.s.3">1.2</a></li> |
|---|
| 2210 | </ul> |
|---|
| 2211 | </li> |
|---|
| 2212 | <li><a id="rfc.index.V" href="#rfc.index.V"><b>V</b></a><ul> |
|---|
| 2213 | <li>validator <a href="#rfc.iref.v.1">1.2</a><ul> |
|---|
| 2214 | <li>strong <a href="#rfc.iref.v.2">1.2</a></li> |
|---|
| 2215 | </ul> |
|---|
| 2216 | </li> |
|---|
| 2217 | </ul> |
|---|
| 2218 | </li> |
|---|
| 2219 | <li><a id="rfc.index.W" href="#rfc.index.W"><b>W</b></a><ul> |
|---|
| 2220 | <li>Warning header field <a href="#rfc.xref.header.warning.1">4.1.4</a>, <a href="#rfc.xref.header.warning.2">4.2.1</a>, <a href="#rfc.xref.header.warning.3">4.4</a>, <a href="#rfc.xref.header.warning.4">5</a>, <a href="#rfc.iref.w.1"><b>7.5</b></a>, <a href="#rfc.xref.header.warning.5">9.3</a>, <a href="#rfc.xref.header.warning.6">A</a>, <a href="#rfc.xref.header.warning.7">A</a></li> |
|---|
| 2221 | </ul> |
|---|
| 2222 | </li> |
|---|
| 2223 | </ul> |
|---|
| 2224 | </div> |
|---|
| 2225 | </body> |
|---|
| 2226 | </html> |
|---|
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