| [52] | 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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| [573] | 4 | <head profile="http://www.w3.org/2006/03/hcard http://dublincore.org/documents/2008/08/04/dc-html/"> |
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| [52] | 5 | <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> |
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| [1522] | 6 | <title>HTTP/1.1, part 4: Conditional Requests</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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| [1528] | 11 | fb.className = "feedback noprint"; |
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| [1522] | 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-p4-conditional-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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| [1528] | 66 | section = section.replace("\u00a0", " "); |
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| [1522] | 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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| [1528] | 74 | button.className = "fbbutton noprint"; |
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| [1522] | 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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| [1528] | 83 | if (b.className == "fbbutton noprint") { |
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| [1522] | 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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| [52] | 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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| [1667] | 110 | margin-right: 2em; |
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| [52] | 111 | } |
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| 112 | cite { |
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| 113 | font-style: normal; |
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| 114 | } |
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| [563] | 115 | div.note { |
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| 116 | margin-left: 2em; |
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| 117 | } |
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| [52] | 118 | dl { |
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| 119 | margin-left: 2em; |
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| 120 | } |
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| [729] | 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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| [52] | 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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| [446] | 149 | h3, h4, h5, h6 { |
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| [52] | 150 | font-size: 10pt; |
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| 151 | page-break-after: avoid; |
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| 152 | } |
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| [446] | 153 | h2 a, h3 a, h4 a, h5 a, h6 a { |
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| [52] | 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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| [1145] | 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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| [52] | 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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| [1667] | 181 | page-break-inside: avoid; |
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| [52] | 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 | table { |
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| 206 | margin-left: 2em; |
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| 207 | } |
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| [253] | 208 | table.tt { |
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| 209 | vertical-align: top; |
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| 210 | } |
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| 211 | table.full { |
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| 212 | border-style: outset; |
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| 213 | border-width: 1px; |
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| 214 | } |
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| 215 | table.headers { |
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| 216 | border-style: outset; |
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| 217 | border-width: 1px; |
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| 218 | } |
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| 219 | table.tt td { |
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| 220 | vertical-align: top; |
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| 221 | } |
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| 222 | table.full td { |
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| 223 | border-style: inset; |
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| 224 | border-width: 1px; |
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| 225 | } |
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| 226 | table.tt th { |
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| 227 | vertical-align: top; |
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| 228 | } |
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| 229 | table.full th { |
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| 230 | border-style: inset; |
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| 231 | border-width: 1px; |
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| 232 | } |
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| 233 | table.headers th { |
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| 234 | border-style: none none inset none; |
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| 235 | border-width: 1px; |
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| 236 | } |
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| [675] | 237 | table.left { |
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| 238 | margin-right: auto; |
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| 239 | } |
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| 240 | table.right { |
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| 241 | margin-left: auto; |
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| 242 | } |
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| 243 | table.center { |
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| 244 | margin-left: auto; |
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| 245 | margin-right: auto; |
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| 246 | } |
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| [454] | 247 | caption { |
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| 248 | caption-side: bottom; |
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| 249 | font-weight: bold; |
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| 250 | font-size: 9pt; |
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| 251 | margin-top: .5em; |
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| 252 | } |
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| 253 | |
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| [52] | 254 | table.header { |
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| [729] | 255 | border-spacing: 1px; |
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| [52] | 256 | width: 95%; |
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| 257 | font-size: 10pt; |
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| 258 | color: white; |
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| 259 | } |
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| 260 | td.top { |
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| 261 | vertical-align: top; |
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| 262 | } |
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| 263 | td.topnowrap { |
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| 264 | vertical-align: top; |
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| 265 | white-space: nowrap; |
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| 266 | } |
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| [729] | 267 | table.header td { |
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| [52] | 268 | background-color: gray; |
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| 269 | width: 50%; |
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| 270 | } |
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| [729] | 271 | table.header a { |
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| [227] | 272 | color: white; |
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| 273 | } |
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| [52] | 274 | td.reference { |
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| 275 | vertical-align: top; |
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| 276 | white-space: nowrap; |
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| 277 | padding-right: 1em; |
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| 278 | } |
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| 279 | thead { |
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| 280 | display:table-header-group; |
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| 281 | } |
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| [1072] | 282 | ul.toc, ul.toc ul { |
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| [52] | 283 | list-style: none; |
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| 284 | margin-left: 1.5em; |
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| 285 | padding-left: 0em; |
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| 286 | } |
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| [1072] | 287 | ul.toc li { |
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| [52] | 288 | line-height: 150%; |
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| 289 | font-weight: bold; |
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| 290 | font-size: 10pt; |
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| 291 | margin-left: 0em; |
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| 292 | } |
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| [1072] | 293 | ul.toc li li { |
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| [52] | 294 | line-height: normal; |
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| 295 | font-weight: normal; |
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| 296 | font-size: 9pt; |
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| 297 | margin-left: 0em; |
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| 298 | } |
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| [1072] | 299 | li.excluded { |
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| [52] | 300 | font-size: 0pt; |
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| 301 | } |
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| 302 | ul p { |
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| 303 | margin-left: 0em; |
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| 304 | } |
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| [1095] | 305 | ul.ind, ul.ind ul { |
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| [52] | 306 | list-style: none; |
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| 307 | margin-left: 1.5em; |
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| 308 | padding-left: 0em; |
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| [440] | 309 | page-break-before: avoid; |
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| [52] | 310 | } |
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| [1072] | 311 | ul.ind li { |
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| [52] | 312 | font-weight: bold; |
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| 313 | line-height: 200%; |
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| 314 | margin-left: 0em; |
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| 315 | } |
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| [1072] | 316 | ul.ind li li { |
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| [52] | 317 | font-weight: normal; |
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| 318 | line-height: 150%; |
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| 319 | margin-left: 0em; |
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| 320 | } |
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| [662] | 321 | .avoidbreak { |
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| 322 | page-break-inside: avoid; |
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| 323 | } |
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| [52] | 324 | .bcp14 { |
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| 325 | font-style: normal; |
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| 326 | text-transform: lowercase; |
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| 327 | font-variant: small-caps; |
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| 328 | } |
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| 329 | .comment { |
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| 330 | background-color: yellow; |
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| 331 | } |
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| 332 | .center { |
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| 333 | text-align: center; |
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| 334 | } |
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| 335 | .error { |
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| 336 | color: red; |
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| 337 | font-style: italic; |
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| 338 | font-weight: bold; |
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| 339 | } |
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| 340 | .figure { |
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| 341 | font-weight: bold; |
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| 342 | text-align: center; |
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| 343 | font-size: 9pt; |
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| 344 | } |
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| 345 | .filename { |
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| 346 | color: #333333; |
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| 347 | font-weight: bold; |
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| 348 | font-size: 12pt; |
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| 349 | line-height: 21pt; |
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| 350 | text-align: center; |
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| 351 | } |
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| 352 | .fn { |
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| 353 | font-weight: bold; |
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| 354 | } |
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| 355 | .hidden { |
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| 356 | display: none; |
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| 357 | } |
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| 358 | .left { |
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| 359 | text-align: left; |
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| 360 | } |
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| 361 | .right { |
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| 362 | text-align: right; |
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| 363 | } |
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| 364 | .title { |
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| 365 | color: #990000; |
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| 366 | font-size: 18pt; |
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| 367 | line-height: 18pt; |
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| 368 | font-weight: bold; |
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| 369 | text-align: center; |
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| 370 | margin-top: 36pt; |
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| 371 | } |
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| 372 | .vcardline { |
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| 373 | display: block; |
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| 374 | } |
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| 375 | .warning { |
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| 376 | font-size: 14pt; |
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| 377 | background-color: yellow; |
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| 378 | } |
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| [1522] | 379 | .feedback { |
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| 380 | position: fixed; |
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| 381 | bottom: 1%; |
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| 382 | right: 1%; |
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| 383 | padding: 3px 5px; |
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| 384 | color: white; |
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| 385 | border-radius: 5px; |
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| 386 | background: #a00000; |
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| 387 | border: 1px solid silver; |
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| 388 | } |
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| 389 | .fbbutton { |
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| 390 | margin-left: 1em; |
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| 391 | color: #303030; |
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| 392 | font-size: small; |
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| 393 | font-weight: normal; |
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| 394 | background: #d0d000; |
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| 395 | padding: 1px 4px; |
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| 396 | border: 1px solid silver; |
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| 397 | border-radius: 5px; |
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| 398 | } |
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| [52] | 399 | |
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| 400 | @media print { |
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| 401 | .noprint { |
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| 402 | display: none; |
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| 403 | } |
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| 404 | |
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| 405 | a { |
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| 406 | color: black; |
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| 407 | text-decoration: none; |
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| 408 | } |
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| 409 | |
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| 410 | table.header { |
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| 411 | width: 90%; |
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| 412 | } |
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| 413 | |
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| 414 | td.header { |
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| 415 | width: 50%; |
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| 416 | color: black; |
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| 417 | background-color: white; |
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| 418 | vertical-align: top; |
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| 419 | font-size: 12pt; |
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| 420 | } |
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| 421 | |
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| 422 | ul.toc a::after { |
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| 423 | content: leader('.') target-counter(attr(href), page); |
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| 424 | } |
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| 425 | |
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| [1072] | 426 | ul.ind li li a { |
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| [52] | 427 | content: target-counter(attr(href), page); |
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| 428 | } |
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| 429 | |
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| 430 | .print2col { |
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| 431 | column-count: 2; |
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| [1528] | 432 | -moz-column-count: 2; |
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| [52] | 433 | column-fill: auto; |
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| 434 | } |
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| 435 | } |
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| 436 | |
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| 437 | @page { |
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| 438 | @top-left { |
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| [754] | 439 | content: "Internet-Draft"; |
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| [52] | 440 | } |
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| 441 | @top-right { |
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| [1667] | 442 | content: "June 2012"; |
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| [52] | 443 | } |
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| 444 | @top-center { |
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| [120] | 445 | content: "HTTP/1.1, Part 4"; |
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| [52] | 446 | } |
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| 447 | @bottom-left { |
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| 448 | content: "Fielding, et al."; |
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| 449 | } |
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| 450 | @bottom-center { |
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| [1691] | 451 | content: "Expires December 25, 2012"; |
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| [52] | 452 | } |
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| 453 | @bottom-right { |
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| 454 | content: "[Page " counter(page) "]"; |
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| 455 | } |
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| 456 | } |
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| 457 | |
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| 458 | @page:first { |
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| 459 | @top-left { |
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| 460 | content: normal; |
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| 461 | } |
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| 462 | @top-right { |
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| 463 | content: normal; |
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| 464 | } |
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| 465 | @top-center { |
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| 466 | content: normal; |
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| 467 | } |
|---|
| 468 | } |
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| 469 | </style><link rel="Contents" href="#rfc.toc"> |
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| 470 | <link rel="Author" href="#rfc.authors"> |
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| [754] | 471 | <link rel="Copyright" href="#rfc.copyrightnotice"> |
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| [52] | 472 | <link rel="Index" href="#rfc.index"> |
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| 473 | <link rel="Chapter" title="1 Introduction" href="#rfc.section.1"> |
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| [1381] | 474 | <link rel="Chapter" title="2 Validators" href="#rfc.section.2"> |
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| [1253] | 475 | <link rel="Chapter" title="3 Precondition Header Fields" href="#rfc.section.3"> |
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| 476 | <link rel="Chapter" title="4 Status Code Definitions" href="#rfc.section.4"> |
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| 477 | <link rel="Chapter" title="5 IANA Considerations" href="#rfc.section.5"> |
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| 478 | <link rel="Chapter" title="6 Security Considerations" href="#rfc.section.6"> |
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| 479 | <link rel="Chapter" title="7 Acknowledgments" href="#rfc.section.7"> |
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| 480 | <link rel="Chapter" href="#rfc.section.8" title="8 References"> |
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| [912] | 481 | <link rel="Appendix" title="A Changes from RFC 2616" href="#rfc.section.A"> |
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| [421] | 482 | <link rel="Appendix" title="B Collected ABNF" href="#rfc.section.B"> |
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| 483 | <link rel="Appendix" title="C Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.C"> |
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| [1472] | 484 | <link href="p3-payload.html" rel="prev"> |
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| 485 | <link href="p5-range.html" rel="next"> |
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| [1667] | 486 | <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.579, 2012-05-24 20:24:05, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/"> |
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| [754] | 487 | <link rel="schema.dct" href="http://purl.org/dc/terms/"> |
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| 488 | <meta name="dct.creator" content="Fielding, R."> |
|---|
| 489 | <meta name="dct.creator" content="Lafon, Y."> |
|---|
| 490 | <meta name="dct.creator" content="Reschke, J. F."> |
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| 491 | <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p4-conditional-latest"> |
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| [1691] | 492 | <meta name="dct.issued" scheme="ISO8601" content="2012-06-23"> |
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| [754] | 493 | <meta name="dct.replaces" content="urn:ietf:rfc:2616"> |
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| [1373] | 494 | <meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 4 of the seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 4 defines request header fields for indicating conditional requests and the rules for constructing responses to those requests."> |
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| 495 | <meta name="description" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 4 of the seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 4 defines request header fields for indicating conditional requests and the rules for constructing responses to those requests."> |
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| [52] | 496 | </head> |
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| [1522] | 497 | <body onload="init();"> |
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| [729] | 498 | <table class="header"> |
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| 499 | <tbody> |
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| 500 | <tr> |
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| 501 | <td class="left">HTTPbis Working Group</td> |
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| 502 | <td class="right">R. Fielding, Editor</td> |
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| 503 | </tr> |
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| 504 | <tr> |
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| [754] | 505 | <td class="left">Internet-Draft</td> |
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| [1106] | 506 | <td class="right">Adobe</td> |
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| [729] | 507 | </tr> |
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| 508 | <tr> |
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| [741] | 509 | <td class="left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved) |
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| [729] | 510 | </td> |
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| [1586] | 511 | <td class="right">Y. Lafon, Editor</td> |
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| [729] | 512 | </tr> |
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| 513 | <tr> |
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| [741] | 514 | <td class="left">Intended status: Standards Track</td> |
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| [729] | 515 | <td class="right">W3C</td> |
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| 516 | </tr> |
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| 517 | <tr> |
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| [1691] | 518 | <td class="left">Expires: December 25, 2012</td> |
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| [832] | 519 | <td class="right">J. Reschke, Editor</td> |
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| [729] | 520 | </tr> |
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| 521 | <tr> |
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| 522 | <td class="left"></td> |
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| 523 | <td class="right">greenbytes</td> |
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| 524 | </tr> |
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| 525 | <tr> |
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| 526 | <td class="left"></td> |
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| [1691] | 527 | <td class="right">June 23, 2012</td> |
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| [729] | 528 | </tr> |
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| 529 | </tbody> |
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| [52] | 530 | </table> |
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| 531 | <p class="title">HTTP/1.1, part 4: Conditional Requests<br><span class="filename">draft-ietf-httpbis-p4-conditional-latest</span></p> |
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| [723] | 532 | <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1> |
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| [1373] | 533 | <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information |
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| [723] | 534 | systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 4 of the |
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| [1373] | 535 | seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. |
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| 536 | </p> |
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| 537 | <p>Part 4 defines request header fields for indicating conditional requests and the rules for constructing responses to those |
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| 538 | requests. |
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| [723] | 539 | </p> |
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| 540 | <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1> |
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| [1685] | 541 | <p>Discussion of this draft ought to take place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org), which is archived |
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| [1268] | 542 | 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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| [723] | 543 | </p> |
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| [1268] | 544 | <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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| 545 | </p> |
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| [1624] | 546 | <p>The changes in this draft are summarized in <a href="#changes.since.19" title="Since draft-ietf-httpbis-p4-conditional-19">Appendix C.1</a>. |
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| [723] | 547 | </p> |
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| [799] | 548 | <h1><a id="rfc.status" href="#rfc.status">Status of This Memo</a></h1> |
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| 549 | <p>This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.</p> |
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| 550 | <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute |
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| 551 | 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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| [52] | 552 | </p> |
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| 553 | <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other |
|---|
| 554 | 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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| 555 | in progress”. |
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| 556 | </p> |
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| [1691] | 557 | <p>This Internet-Draft will expire on December 25, 2012.</p> |
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| [446] | 558 | <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1> |
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| [1497] | 559 | <p>Copyright © 2012 IETF Trust and the persons identified as the document authors. All rights reserved.</p> |
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| [723] | 560 | <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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| 561 | and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License |
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| [799] | 562 | text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified |
|---|
| 563 | BSD License. |
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| [446] | 564 | </p> |
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| [723] | 565 | <p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November |
|---|
| 566 | 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to |
|---|
| 567 | allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) |
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| 568 | controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative |
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| 569 | 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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| 570 | it into languages other than English. |
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| 571 | </p> |
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| [52] | 572 | <hr class="noprint"> |
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| 573 | <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1> |
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| 574 | <ul class="toc"> |
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| [1072] | 575 | <li>1. <a href="#introduction">Introduction</a><ul> |
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| [1452] | 576 | <li>1.1 <a href="#intro.conformance.and.error.handling">Conformance and Error Handling</a></li> |
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| [1251] | 577 | <li>1.2 <a href="#notation">Syntax Notation</a></li> |
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| 578 | </ul> |
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| 579 | </li> |
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| [1381] | 580 | <li>2. <a href="#validators">Validators</a><ul> |
|---|
| 581 | <li>2.1 <a href="#weak.and.strong.validators">Weak versus Strong</a></li> |
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| 582 | <li>2.2 <a href="#header.last-modified">Last-Modified</a><ul> |
|---|
| 583 | <li>2.2.1 <a href="#lastmod.generation">Generation</a></li> |
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| 584 | <li>2.2.2 <a href="#lastmod.comparison">Comparison</a></li> |
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| [424] | 585 | </ul> |
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| 586 | </li> |
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| [1381] | 587 | <li>2.3 <a href="#header.etag">ETag</a><ul> |
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| 588 | <li>2.3.1 <a href="#entity.tag.generation">Generation</a></li> |
|---|
| 589 | <li>2.3.2 <a href="#entity.tag.comparison">Comparison</a></li> |
|---|
| 590 | <li>2.3.3 <a href="#example.entity.tag.vs.conneg">Example: Entity-tags varying on Content-Negotiated Resources</a></li> |
|---|
| [1260] | 591 | </ul> |
|---|
| 592 | </li> |
|---|
| [1381] | 593 | <li>2.4 <a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity-tags and Last-Modified Dates</a></li> |
|---|
| [96] | 594 | </ul> |
|---|
| 595 | </li> |
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| [1415] | 596 | <li>3. <a href="#header.field.definitions">Precondition Header Fields</a><ul> |
|---|
| [1253] | 597 | <li>3.1 <a href="#header.if-match">If-Match</a></li> |
|---|
| 598 | <li>3.2 <a href="#header.if-none-match">If-None-Match</a></li> |
|---|
| 599 | <li>3.3 <a href="#header.if-modified-since">If-Modified-Since</a></li> |
|---|
| 600 | <li>3.4 <a href="#header.if-unmodified-since">If-Unmodified-Since</a></li> |
|---|
| [1260] | 601 | <li>3.5 <a href="#header.if-range">If-Range</a></li> |
|---|
| [52] | 602 | </ul> |
|---|
| 603 | </li> |
|---|
| [1253] | 604 | <li>4. <a href="#status.code.definitions">Status Code Definitions</a><ul> |
|---|
| 605 | <li>4.1 <a href="#status.304">304 Not Modified</a></li> |
|---|
| 606 | <li>4.2 <a href="#status.412">412 Precondition Failed</a></li> |
|---|
| [52] | 607 | </ul> |
|---|
| 608 | </li> |
|---|
| [1253] | 609 | <li>5. <a href="#IANA.considerations">IANA Considerations</a><ul> |
|---|
| 610 | <li>5.1 <a href="#status.code.registration">Status Code Registration</a></li> |
|---|
| 611 | <li>5.2 <a href="#header.field.registration">Header Field Registration</a></li> |
|---|
| [253] | 612 | </ul> |
|---|
| 613 | </li> |
|---|
| [1253] | 614 | <li>6. <a href="#security.considerations">Security Considerations</a></li> |
|---|
| [1364] | 615 | <li>7. <a href="#acks">Acknowledgments</a></li> |
|---|
| [1253] | 616 | <li>8. <a href="#rfc.references">References</a><ul> |
|---|
| 617 | <li>8.1 <a href="#rfc.references.1">Normative References</a></li> |
|---|
| 618 | <li>8.2 <a href="#rfc.references.2">Informative References</a></li> |
|---|
| [119] | 619 | </ul> |
|---|
| 620 | </li> |
|---|
| [1072] | 621 | <li><a href="#rfc.authors">Authors' Addresses</a></li> |
|---|
| 622 | <li>A. <a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li> |
|---|
| 623 | <li>B. <a href="#collected.abnf">Collected ABNF</a></li> |
|---|
| 624 | <li>C. <a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul> |
|---|
| [1624] | 625 | <li>C.1 <a href="#changes.since.19">Since draft-ietf-httpbis-p4-conditional-19</a></li> |
|---|
| [115] | 626 | </ul> |
|---|
| 627 | </li> |
|---|
| [1072] | 628 | <li><a href="#rfc.index">Index</a></li> |
|---|
| [52] | 629 | </ul> |
|---|
| 630 | <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a> <a id="introduction" href="#introduction">Introduction</a></h1> |
|---|
| [1381] | 631 | <p id="rfc.section.1.p.1">This document defines the HTTP/1.1 conditional request mechanisms, including both metadata for indicating/observing changes |
|---|
| 632 | in resource representations and request header fields that specify preconditions on that metadata be checked before performing |
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| 633 | the request method. Conditional GET requests are the most efficient mechanism for HTTP cache updates <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>. Conditionals can also be applied to state-changing methods, such as PUT and DELETE, to prevent the "lost update" problem: |
|---|
| [1260] | 634 | one client accidentally overwriting the work of another client that has been acting in parallel. |
|---|
| [52] | 635 | </p> |
|---|
| [1251] | 636 | <p id="rfc.section.1.p.2">Conditional request preconditions are based on the state of the target resource as a whole (its current value set) or the |
|---|
| 637 | state as observed in a previously obtained representation (one value in that set). A resource might have multiple current |
|---|
| 638 | representations, each with its own observable state. The conditional request mechanisms assume that the mapping of requests |
|---|
| 639 | to corresponding representations will be consistent over time if the server intends to take advantage of conditionals. Regardless, |
|---|
| 640 | if the mapping is inconsistent and the server is unable to select the appropriate representation, then no harm will result |
|---|
| 641 | when the precondition evaluates to false. |
|---|
| [1223] | 642 | </p> |
|---|
| [1251] | 643 | <p id="rfc.section.1.p.3"><span id="rfc.iref.s.1"></span> We use the term "<dfn>selected representation</dfn>" to refer to the current representation of the target resource that would have been selected in a successful response if |
|---|
| 644 | the same request had used the method GET and had excluded all of the conditional request header fields. The conditional request |
|---|
| 645 | preconditions are evaluated by comparing the values provided in the request header fields to the current metadata for the |
|---|
| 646 | selected representation. |
|---|
| [163] | 647 | </p> |
|---|
| [1452] | 648 | <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a> <a id="intro.conformance.and.error.handling" href="#intro.conformance.and.error.handling">Conformance and Error Handling</a></h2> |
|---|
| [96] | 649 | <p id="rfc.section.1.1.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" |
|---|
| 650 | 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>. |
|---|
| 651 | </p> |
|---|
| [1452] | 652 | <p id="rfc.section.1.1.p.2">This document defines conformance criteria for several roles in HTTP communication, including Senders, Recipients, Clients, |
|---|
| 653 | Servers, User-Agents, Origin Servers, Intermediaries, Proxies and Gateways. See <a href="p1-messaging.html#architecture" title="Architecture">Section 2</a> of <a href="#Part1" id="rfc.xref.Part1.1"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> for definitions of these terms. |
|---|
| [96] | 654 | </p> |
|---|
| [1452] | 655 | <p id="rfc.section.1.1.p.3">An implementation is considered conformant if it complies with all of the requirements associated with its role(s). Note that |
|---|
| 656 | SHOULD-level requirements are relevant here, unless one of the documented exceptions is applicable. |
|---|
| 657 | </p> |
|---|
| 658 | <p id="rfc.section.1.1.p.4">This document also uses ABNF to define valid protocol elements (<a href="#notation" title="Syntax Notation">Section 1.2</a>). In addition to the prose requirements placed upon them, Senders <em class="bcp14">MUST NOT</em> generate protocol elements that are invalid. |
|---|
| 659 | </p> |
|---|
| [1682] | 660 | <p id="rfc.section.1.1.p.5">Unless noted otherwise, Recipients <em class="bcp14">MUST</em> be able to parse all protocol elements matching the ABNF rules defined for them and <em class="bcp14">MAY</em> take steps to recover a usable protocol element from an invalid construct. However, HTTP does not define specific error handling |
|---|
| [1452] | 661 | mechanisms, except in cases where it has direct impact on security. This is because different uses of the protocol require |
|---|
| [1684] | 662 | different error handling strategies; for example, a Web browser might wish to transparently recover from a response where |
|---|
| 663 | the Location header field doesn't parse according to the ABNF, whereby in a systems control protocol using HTTP, this type |
|---|
| 664 | of error recovery could lead to dangerous consequences. |
|---|
| [1452] | 665 | </p> |
|---|
| [424] | 666 | <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a> <a id="notation" href="#notation">Syntax Notation</a></h2> |
|---|
| [1519] | 667 | <p id="rfc.section.1.2.p.1">This specification uses the Augmented Backus-Naur Form (ABNF) notation of <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a> with the list rule extension defined in <a href="p1-messaging.html#notation" title="Syntax Notation">Section 1.2</a> of <a href="#Part1" id="rfc.xref.Part1.2"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. <a href="#collected.abnf" title="Collected ABNF">Appendix B</a> shows the collected ABNF with the list rule expanded. |
|---|
| [543] | 668 | </p> |
|---|
| 669 | <p id="rfc.section.1.2.p.2">The following core rules are included by reference, as defined in <a href="#RFC5234" id="rfc.xref.RFC5234.2"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>, <a href="http://tools.ietf.org/html/rfc5234#appendix-B.1">Appendix B.1</a>: ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), HEXDIG |
|---|
| [1425] | 670 | (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 |
|---|
| 671 | character). |
|---|
| [52] | 672 | </p> |
|---|
| [1452] | 673 | <p id="rfc.section.1.2.p.3">The ABNF rules below are defined in <a href="#Part1" id="rfc.xref.Part1.3"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> and <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>: |
|---|
| [1396] | 674 | </p> |
|---|
| [1519] | 675 | <div id="rfc.figure.u.1"></div><pre class="inline"> <a href="#notation" class="smpl">OWS</a> = <OWS, defined in <a href="#Part1" id="rfc.xref.Part1.4"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#whitespace" title="Whitespace">Section 3.2.1</a>> |
|---|
| 676 | <a href="#notation" class="smpl">obs-text</a> = <obs-text, defined in <a href="#Part1" id="rfc.xref.Part1.5"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#field.components" title="Field value components">Section 3.2.4</a>> |
|---|
| [1650] | 677 | <a href="#notation" class="smpl">HTTP-date</a> = <HTTP-date, defined in <a href="#Part2" id="rfc.xref.Part2.2"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#http.date" title="Date/Time Formats">Section 5.1</a>> |
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| [1253] | 678 | </pre><div id="rfc.iref.m.1"></div> |
|---|
| 679 | <div id="rfc.iref.v.1"></div> |
|---|
| [1381] | 680 | <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a id="validators" href="#validators">Validators</a></h1> |
|---|
| [1251] | 681 | <p id="rfc.section.2.p.1">This specification defines two forms of metadata that are commonly used to observe resource state and test for preconditions: |
|---|
| 682 | modification dates and opaque entity tags. Additional metadata that reflects resource state has been defined by various extensions |
|---|
| [1260] | 683 | of HTTP, such as WebDAV <a href="#RFC4918" id="rfc.xref.RFC4918.1"><cite title="HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)">[RFC4918]</cite></a>, that are beyond the scope of this specification. A resource metadata value is referred to as a "<dfn>validator</dfn>" when it is used within a precondition. |
|---|
| [424] | 684 | </p> |
|---|
| [1381] | 685 | <div id="rfc.iref.v.2"></div> |
|---|
| 686 | <div id="rfc.iref.v.3"></div> |
|---|
| 687 | <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a> <a id="weak.and.strong.validators" href="#weak.and.strong.validators">Weak versus Strong</a></h2> |
|---|
| 688 | <p id="rfc.section.2.1.p.1">Validators come in two flavors: strong or weak. Weak validators are easy to generate but are far less useful for comparisons. |
|---|
| 689 | Strong validators are ideal for comparisons but can be very difficult (and occasionally impossible) to generate efficiently. |
|---|
| 690 | Rather than impose that all forms of resource adhere to the same strength of validator, HTTP exposes the type of validator |
|---|
| 691 | in use and imposes restrictions on when weak validators can be used as preconditions. |
|---|
| 692 | </p> |
|---|
| 693 | <p id="rfc.section.2.1.p.2">A "strong validator" is a representation metadata value that <em class="bcp14">MUST</em> be changed to a new, previously unused or guaranteed unique, value whenever a change occurs to the representation data such |
|---|
| 694 | that a change would be observable in the payload body of a 200 response to GET. A strong validator <em class="bcp14">MAY</em> be changed for other reasons, such as when a semantically significant part of the representation metadata is changed (e.g., |
|---|
| 695 | Content-Type), but it is in the best interests of the origin server to only change the value when it is necessary to invalidate |
|---|
| 696 | the stored responses held by remote caches and authoring tools. A strong validator <em class="bcp14">MUST</em> be unique across all representations of a given resource, such that no two representations of that resource share the same |
|---|
| 697 | validator unless their payload body would be identical. |
|---|
| 698 | </p> |
|---|
| 699 | <p id="rfc.section.2.1.p.3">Cache entries might persist for arbitrarily long periods, regardless of expiration times. Thus, a cache might attempt to validate |
|---|
| 700 | an entry using a validator that it obtained in the distant past. A strong validator <em class="bcp14">MUST</em> be unique across all versions of all representations associated with a particular resource over time. However, there is no |
|---|
| 701 | implication of uniqueness across representations of different resources (i.e., the same strong validator might be in use for |
|---|
| 702 | representations of multiple resources at the same time and does not imply that those representations are equivalent). |
|---|
| 703 | </p> |
|---|
| 704 | <p id="rfc.section.2.1.p.4">There are a variety of strong validators used in practice. The best are based on strict revision control, wherein each change |
|---|
| 705 | to a representation always results in a unique node name and revision identifier being assigned before the representation |
|---|
| 706 | is made accessible to GET. A cryptographic hash function applied to the representation data is also sufficient if the data |
|---|
| 707 | is available prior to the response header fields being sent and the digest does not need to be recalculated every time a validation |
|---|
| 708 | request is received. However, if a resource has distinct representations that differ only in their metadata, such as might |
|---|
| [1691] | 709 | occur with content negotiation over media types that happen to share the same data format, then the origin server <em class="bcp14">SHOULD</em> incorporate additional information in the validator to distinguish those representations and avoid confusing cache behavior. |
|---|
| [1381] | 710 | </p> |
|---|
| 711 | <p id="rfc.section.2.1.p.5">In contrast, a "weak validator" is a representation metadata value that might not be changed for every change to the representation |
|---|
| 712 | data. This weakness might be due to limitations in how the value is calculated, such as clock resolution or an inability to |
|---|
| 713 | ensure uniqueness for all possible representations of the resource, or due to a desire by the resource owner to group representations |
|---|
| [1691] | 714 | by some self-determined set of equivalency rather than unique sequences of data. An origin server <em class="bcp14">SHOULD</em> change a weak entity-tag whenever it considers prior representations to be unacceptable as a substitute for the current representation. |
|---|
| 715 | In other words, a weak entity-tag ought to change whenever the origin server wants caches to invalidate old responses. |
|---|
| [1381] | 716 | </p> |
|---|
| 717 | <p id="rfc.section.2.1.p.6">For example, the representation of a weather report that changes in content every second, based on dynamic measurements, might |
|---|
| 718 | be grouped into sets of equivalent representations (from the origin server's perspective) with the same weak validator in |
|---|
| 719 | order to allow cached representations to be valid for a reasonable period of time (perhaps adjusted dynamically based on server |
|---|
| 720 | load or weather quality). Likewise, a representation's modification time, if defined with only one-second resolution, might |
|---|
| 721 | be a weak validator if it is possible for the representation to be modified twice during a single second and retrieved between |
|---|
| 722 | those modifications. |
|---|
| 723 | </p> |
|---|
| 724 | <p id="rfc.section.2.1.p.7">A "use" of a validator occurs when either a client generates a request and includes the validator in a precondition or when |
|---|
| 725 | a server compares two validators. Weak validators are only usable in contexts that do not depend on exact equality of a representation's |
|---|
| 726 | payload body. Strong validators are usable and preferred for all conditional requests, including cache validation, partial |
|---|
| 727 | content ranges, and "lost update" avoidance. |
|---|
| 728 | </p> |
|---|
| [1253] | 729 | <div id="rfc.iref.l.1"></div> |
|---|
| 730 | <div id="rfc.iref.h.1"></div> |
|---|
| [1381] | 731 | <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a> <a id="header.last-modified" href="#header.last-modified">Last-Modified</a></h2> |
|---|
| 732 | <p id="rfc.section.2.2.p.1">The "Last-Modified" header field indicates the date and time at which the origin server believes the selected representation |
|---|
| [1260] | 733 | was last modified. |
|---|
| [205] | 734 | </p> |
|---|
| [1253] | 735 | <div id="rfc.figure.u.2"></div><pre class="inline"><span id="rfc.iref.g.1"></span> <a href="#header.last-modified" class="smpl">Last-Modified</a> = <a href="#notation" class="smpl">HTTP-date</a> |
|---|
| [1381] | 736 | </pre><p id="rfc.section.2.2.p.3">An example of its use is</p> |
|---|
| [1253] | 737 | <div id="rfc.figure.u.3"></div><pre class="text"> Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT |
|---|
| [1381] | 738 | </pre><h3 id="rfc.section.2.2.1"><a href="#rfc.section.2.2.1">2.2.1</a> <a id="lastmod.generation" href="#lastmod.generation">Generation</a></h3> |
|---|
| 739 | <p id="rfc.section.2.2.1.p.1">Origin servers <em class="bcp14">SHOULD</em> send Last-Modified for any selected representation for which a last modification date can be reasonably and consistently determined, |
|---|
| [1260] | 740 | since its use in conditional requests and evaluating cache freshness (<a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) results in a substantial reduction of HTTP traffic on the Internet and can be a significant factor in improving service |
|---|
| 741 | scalability and reliability. |
|---|
| 742 | </p> |
|---|
| [1381] | 743 | <p id="rfc.section.2.2.1.p.2">A representation is typically the sum of many parts behind the resource interface. The last-modified time would usually be |
|---|
| [1253] | 744 | the most recent time that any of those parts were changed. How that value is determined for any given resource is an implementation |
|---|
| 745 | detail beyond the scope of this specification. What matters to HTTP is how recipients of the Last-Modified header field can |
|---|
| 746 | use its value to make conditional requests and test the validity of locally cached responses. |
|---|
| 747 | </p> |
|---|
| [1381] | 748 | <p id="rfc.section.2.2.1.p.3">An origin server <em class="bcp14">SHOULD</em> obtain the Last-Modified value of the representation as close as possible to the time that it generates the Date field-value |
|---|
| [1260] | 749 | for its response. This allows a recipient to make an accurate assessment of the representation's modification time, especially |
|---|
| [1253] | 750 | if the representation changes near the time that the response is generated. |
|---|
| 751 | </p> |
|---|
| [1381] | 752 | <p id="rfc.section.2.2.1.p.4">An origin server with a clock <em class="bcp14">MUST NOT</em> send a Last-Modified date that is later than the server's time of message origination (Date). If the last modification time |
|---|
| [1260] | 753 | is derived from implementation-specific metadata that evaluates to some time in the future, according to the origin server's |
|---|
| 754 | clock, then the origin server <em class="bcp14">MUST</em> replace that value with the message origination date. This prevents a future modification date from having an adverse impact |
|---|
| 755 | on cache validation. |
|---|
| [1253] | 756 | </p> |
|---|
| [1436] | 757 | <p id="rfc.section.2.2.1.p.5">An origin server without a clock <em class="bcp14">MUST NOT</em> assign Last-Modified values to a response unless these values were associated with the resource by some other system or user |
|---|
| 758 | with a reliable clock. |
|---|
| 759 | </p> |
|---|
| [1381] | 760 | <h3 id="rfc.section.2.2.2"><a href="#rfc.section.2.2.2">2.2.2</a> <a id="lastmod.comparison" href="#lastmod.comparison">Comparison</a></h3> |
|---|
| 761 | <p id="rfc.section.2.2.2.p.1">A Last-Modified time, when used as a validator in a request, is implicitly weak unless it is possible to deduce that it is |
|---|
| [1260] | 762 | strong, using the following rules: |
|---|
| [1253] | 763 | </p> |
|---|
| [1260] | 764 | <ul> |
|---|
| 765 | <li>The validator is being compared by an origin server to the actual current validator for the representation and,</li> |
|---|
| 766 | <li>That origin server reliably knows that the associated representation did not change twice during the second covered by the |
|---|
| 767 | presented validator. |
|---|
| 768 | </li> |
|---|
| 769 | </ul> |
|---|
| [1381] | 770 | <p id="rfc.section.2.2.2.p.2">or </p> |
|---|
| [1260] | 771 | <ul> |
|---|
| [1339] | 772 | <li>The validator is about to be used by a client in an If-Modified-Since, If-Unmodified-Since header field, because the client |
|---|
| 773 | has a cache entry, or If-Range for the associated representation, and |
|---|
| [1260] | 774 | </li> |
|---|
| 775 | <li>That cache entry includes a Date value, which gives the time when the origin server sent the original response, and</li> |
|---|
| 776 | <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li> |
|---|
| 777 | </ul> |
|---|
| [1381] | 778 | <p id="rfc.section.2.2.2.p.3">or </p> |
|---|
| [1260] | 779 | <ul> |
|---|
| 780 | <li>The validator is being compared by an intermediate cache to the validator stored in its cache entry for the representation, |
|---|
| 781 | and |
|---|
| 782 | </li> |
|---|
| 783 | <li>That cache entry includes a Date value, which gives the time when the origin server sent the original response, and</li> |
|---|
| 784 | <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li> |
|---|
| 785 | </ul> |
|---|
| [1381] | 786 | <p id="rfc.section.2.2.2.p.4">This method relies on the fact that if two different responses were sent by the origin server during the same second, but |
|---|
| [1260] | 787 | both had the same Last-Modified time, then at least one of those responses would have a Date value equal to its Last-Modified |
|---|
| 788 | time. The arbitrary 60-second limit guards against the possibility that the Date and Last-Modified values are generated from |
|---|
| 789 | different clocks, or at somewhat different times during the preparation of the response. An implementation <em class="bcp14">MAY</em> use a value larger than 60 seconds, if it is believed that 60 seconds is too short. |
|---|
| [1253] | 790 | </p> |
|---|
| 791 | <div id="rfc.iref.e.1"></div> |
|---|
| 792 | <div id="rfc.iref.h.2"></div> |
|---|
| [1381] | 793 | <h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a> <a id="header.etag" href="#header.etag">ETag</a></h2> |
|---|
| 794 | <p id="rfc.section.2.3.p.1">The ETag header field provides the current entity-tag for the selected representation. An entity-tag is an opaque validator |
|---|
| [1260] | 795 | for differentiating between multiple representations of the same resource, regardless of whether those multiple representations |
|---|
| 796 | are due to resource state changes over time, content negotiation resulting in multiple representations being valid at the |
|---|
| 797 | same time, or both. An entity-tag consists of an opaque quoted string, possibly prefixed by a weakness indicator. |
|---|
| [800] | 798 | </p> |
|---|
| [1470] | 799 | <div id="rfc.figure.u.4"></div><pre class="inline"><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span><span id="rfc.iref.g.4"></span><span id="rfc.iref.g.5"></span><span id="rfc.iref.g.6"></span> <a href="#header.etag" class="smpl">ETag</a> = <a href="#header.etag" class="smpl">entity-tag</a> |
|---|
| [1260] | 800 | |
|---|
| 801 | <a href="#header.etag" class="smpl">entity-tag</a> = [ <a href="#header.etag" class="smpl">weak</a> ] <a href="#header.etag" class="smpl">opaque-tag</a> |
|---|
| 802 | <a href="#header.etag" class="smpl">weak</a> = %x57.2F ; "W/", case-sensitive |
|---|
| [1470] | 803 | <a href="#header.etag" class="smpl">opaque-tag</a> = <a href="#notation" class="smpl">DQUOTE</a> *<a href="#header.etag" class="smpl">etagc</a> <a href="#notation" class="smpl">DQUOTE</a> |
|---|
| 804 | <a href="#header.etag" class="smpl">etagc</a> = %x21 / %x23-7E / <a href="#notation" class="smpl">obs-text</a> |
|---|
| [1482] | 805 | ; <a href="#notation" class="smpl">VCHAR</a> except double quotes, plus obs-text |
|---|
| [1470] | 806 | </pre><div class="note" id="rfc.section.2.3.p.3"> |
|---|
| 807 | <p> <b>Note:</b> Previously, opaque-tag was defined to be a quoted-string (<a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>, <a href="http://tools.ietf.org/html/rfc2616#section-3.11">Section 3.11</a>), thus some recipients might perform backslash unescaping. Servers therefore ought to avoid backslash characters in entity |
|---|
| 808 | tags. |
|---|
| 809 | </p> |
|---|
| 810 | </div> |
|---|
| 811 | <p id="rfc.section.2.3.p.4">An entity-tag can be more reliable for validation than a modification date in situations where it is inconvenient to store |
|---|
| [1260] | 812 | modification dates, where the one-second resolution of HTTP date values is not sufficient, or where modification dates are |
|---|
| 813 | not consistently maintained. |
|---|
| 814 | </p> |
|---|
| 815 | <div id="rfc.figure.u.5"></div> |
|---|
| [1253] | 816 | <p>Examples:</p> <pre class="text"> ETag: "xyzzy" |
|---|
| 817 | ETag: W/"xyzzy" |
|---|
| 818 | ETag: "" |
|---|
| [1470] | 819 | </pre><p id="rfc.section.2.3.p.6">An entity-tag can be either a weak or strong validator, with strong being the default. If an origin server provides an entity-tag |
|---|
| [1381] | 820 | for a representation and the generation of that entity-tag does not satisfy the requirements for a strong validator (<a href="#weak.and.strong.validators" title="Weak versus Strong">Section 2.1</a>), then that entity-tag <em class="bcp14">MUST</em> be marked as weak by prefixing its opaque value with "W/" (case-sensitive). |
|---|
| 821 | </p> |
|---|
| 822 | <h3 id="rfc.section.2.3.1"><a href="#rfc.section.2.3.1">2.3.1</a> <a id="entity.tag.generation" href="#entity.tag.generation">Generation</a></h3> |
|---|
| 823 | <p id="rfc.section.2.3.1.p.1">The principle behind entity-tags is that only the service author knows the implementation of a resource well enough to select |
|---|
| [1260] | 824 | the most accurate and efficient validation mechanism for that resource, and that any such mechanism can be mapped to a simple |
|---|
| 825 | sequence of octets for easy comparison. Since the value is opaque, there is no need for the client to be aware of how each |
|---|
| 826 | entity-tag is constructed. |
|---|
| [1253] | 827 | </p> |
|---|
| [1381] | 828 | <p id="rfc.section.2.3.1.p.2">For example, a resource that has implementation-specific versioning applied to all changes might use an internal revision |
|---|
| [1260] | 829 | number, perhaps combined with a variance identifier for content negotiation, to accurately differentiate between representations. |
|---|
| 830 | Other implementations might use a stored hash of representation content, a combination of various filesystem attributes, or |
|---|
| 831 | a modification timestamp that has sub-second resolution. |
|---|
| [1253] | 832 | </p> |
|---|
| [1381] | 833 | <p id="rfc.section.2.3.1.p.3">Origin servers <em class="bcp14">SHOULD</em> send ETag for any selected representation for which detection of changes can be reasonably and consistently determined, since |
|---|
| [1260] | 834 | the entity-tag's use in conditional requests and evaluating cache freshness (<a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) can result in a substantial reduction of HTTP network traffic and can be a significant factor in improving service scalability |
|---|
| 835 | and reliability. |
|---|
| [1253] | 836 | </p> |
|---|
| [1381] | 837 | <h3 id="rfc.section.2.3.2"><a href="#rfc.section.2.3.2">2.3.2</a> <a id="entity.tag.comparison" href="#entity.tag.comparison">Comparison</a></h3> |
|---|
| 838 | <p id="rfc.section.2.3.2.p.1">There are two entity-tag comparison functions, depending on whether the comparison context allows the use of weak validators |
|---|
| [1260] | 839 | or not: |
|---|
| 840 | </p> |
|---|
| [52] | 841 | <ul> |
|---|
| [298] | 842 | <li>The strong comparison function: in order to be considered equal, both opaque-tags <em class="bcp14">MUST</em> be identical character-by-character, and both <em class="bcp14">MUST NOT</em> be weak. |
|---|
| [52] | 843 | </li> |
|---|
| [610] | 844 | <li>The weak comparison function: in order to be considered equal, both opaque-tags <em class="bcp14">MUST</em> be identical character-by-character, but either or both of them <em class="bcp14">MAY</em> be tagged as "weak" without affecting the result. |
|---|
| [52] | 845 | </li> |
|---|
| 846 | </ul> |
|---|
| [1381] | 847 | <p id="rfc.section.2.3.2.p.2">The example below shows the results for a set of entity-tag pairs, and both the weak and strong comparison function results:</p> |
|---|
| [298] | 848 | <div id="rfc.table.u.1"> |
|---|
| [675] | 849 | <table class="tt full left" cellpadding="3" cellspacing="0"> |
|---|
| [298] | 850 | <thead> |
|---|
| 851 | <tr> |
|---|
| 852 | <th>ETag 1</th> |
|---|
| 853 | <th>ETag 2</th> |
|---|
| 854 | <th>Strong Comparison</th> |
|---|
| 855 | <th>Weak Comparison</th> |
|---|
| 856 | </tr> |
|---|
| 857 | </thead> |
|---|
| 858 | <tbody> |
|---|
| 859 | <tr> |
|---|
| [704] | 860 | <td class="left">W/"1"</td> |
|---|
| 861 | <td class="left">W/"1"</td> |
|---|
| 862 | <td class="left">no match</td> |
|---|
| 863 | <td class="left">match</td> |
|---|
| [298] | 864 | </tr> |
|---|
| 865 | <tr> |
|---|
| [704] | 866 | <td class="left">W/"1"</td> |
|---|
| 867 | <td class="left">W/"2"</td> |
|---|
| 868 | <td class="left">no match</td> |
|---|
| 869 | <td class="left">no match</td> |
|---|
| [298] | 870 | </tr> |
|---|
| 871 | <tr> |
|---|
| [704] | 872 | <td class="left">W/"1"</td> |
|---|
| 873 | <td class="left">"1"</td> |
|---|
| 874 | <td class="left">no match</td> |
|---|
| 875 | <td class="left">match</td> |
|---|
| [298] | 876 | </tr> |
|---|
| 877 | <tr> |
|---|
| [704] | 878 | <td class="left">"1"</td> |
|---|
| 879 | <td class="left">"1"</td> |
|---|
| 880 | <td class="left">match</td> |
|---|
| 881 | <td class="left">match</td> |
|---|
| [298] | 882 | </tr> |
|---|
| 883 | </tbody> |
|---|
| 884 | </table> |
|---|
| 885 | </div> |
|---|
| [1381] | 886 | <h3 id="rfc.section.2.3.3"><a href="#rfc.section.2.3.3">2.3.3</a> <a id="example.entity.tag.vs.conneg" href="#example.entity.tag.vs.conneg">Example: Entity-tags varying on Content-Negotiated Resources</a></h3> |
|---|
| [1650] | 887 | <p id="rfc.section.2.3.3.p.1">Consider a resource that is subject to content negotiation (<a href="p2-semantics.html#content.negotiation" title="Content Negotiation">Section 8</a> of <a href="#Part2" id="rfc.xref.Part2.3"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>), and where the representations returned upon a GET request vary based on the Accept-Encoding request header field (<a href="p2-semantics.html#header.accept-encoding" title="Accept-Encoding">Section 9.3</a> of <a href="#Part2" id="rfc.xref.Part2.4"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>): |
|---|
| [1381] | 888 | </p> |
|---|
| 889 | <div id="rfc.figure.u.6"></div> |
|---|
| 890 | <p>>> Request:</p><pre class="text2">GET /index HTTP/1.1 |
|---|
| 891 | Host: www.example.com |
|---|
| 892 | Accept-Encoding: gzip |
|---|
| 893 | |
|---|
| 894 | </pre><p id="rfc.section.2.3.3.p.3">In this case, the response might or might not use the gzip content coding. If it does not, the response might look like:</p> |
|---|
| 895 | <div id="rfc.figure.u.7"></div> |
|---|
| 896 | <p>>> Response:</p><pre class="text">HTTP/1.1 200 OK |
|---|
| 897 | Date: Thu, 26 Mar 2010 00:05:00 GMT |
|---|
| 898 | ETag: "123-a" |
|---|
| 899 | Content-Length: 70 |
|---|
| 900 | Vary: Accept-Encoding |
|---|
| 901 | Content-Type: text/plain |
|---|
| 902 | |
|---|
| 903 | <span id="exbody">Hello World! |
|---|
| 904 | Hello World! |
|---|
| 905 | Hello World! |
|---|
| 906 | Hello World! |
|---|
| 907 | Hello World! |
|---|
| 908 | </span></pre><p id="rfc.section.2.3.3.p.5">An alternative representation that does use gzip content coding would be:</p> |
|---|
| 909 | <div id="rfc.figure.u.8"></div> |
|---|
| 910 | <p>>> Response:</p><pre class="text">HTTP/1.1 200 OK |
|---|
| 911 | Date: Thu, 26 Mar 2010 00:05:00 GMT |
|---|
| 912 | ETag: "123-b" |
|---|
| 913 | Content-Length: 43 |
|---|
| 914 | Vary: Accept-Encoding |
|---|
| 915 | Content-Type: text/plain |
|---|
| 916 | Content-Encoding: gzip |
|---|
| 917 | |
|---|
| 918 | <em>...binary data...</em></pre><div class="note" id="rfc.section.2.3.3.p.7"> |
|---|
| [1604] | 919 | <p> <b>Note:</b> Content codings are a property of the representation, so therefore an entity-tag of an encoded representation has to be distinct |
|---|
| [1381] | 920 | from an unencoded representation to prevent conflicts during cache updates and range requests. In contrast, transfer codings |
|---|
| [1580] | 921 | (<a href="p1-messaging.html#transfer.codings" title="Transfer Codings">Section 4</a> of <a href="#Part1" id="rfc.xref.Part1.6"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) apply only during message transfer and do not require distinct entity-tags. |
|---|
| [1381] | 922 | </p> |
|---|
| 923 | </div> |
|---|
| 924 | <h2 id="rfc.section.2.4"><a href="#rfc.section.2.4">2.4</a> <a id="rules.for.when.to.use.entity.tags.and.last-modified.dates" href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity-tags and Last-Modified Dates</a></h2> |
|---|
| 925 | <p id="rfc.section.2.4.p.1">We adopt a set of rules and recommendations for origin servers, clients, and caches regarding when various validator types |
|---|
| [52] | 926 | ought to be used, and for what purposes. |
|---|
| 927 | </p> |
|---|
| [1381] | 928 | <p id="rfc.section.2.4.p.2">HTTP/1.1 origin servers: </p> |
|---|
| [52] | 929 | <ul> |
|---|
| [875] | 930 | <li><em class="bcp14">SHOULD</em> send an entity-tag validator unless it is not feasible to generate one. |
|---|
| [52] | 931 | </li> |
|---|
| [875] | 932 | <li><em class="bcp14">MAY</em> send a weak entity-tag instead of a strong entity-tag, if performance considerations support the use of weak entity-tags, |
|---|
| 933 | or if it is unfeasible to send a strong entity-tag. |
|---|
| [52] | 934 | </li> |
|---|
| [1223] | 935 | <li><em class="bcp14">SHOULD</em> send a Last-Modified value if it is feasible to send one. |
|---|
| [52] | 936 | </li> |
|---|
| 937 | </ul> |
|---|
| [1381] | 938 | <p id="rfc.section.2.4.p.3">In other words, the preferred behavior for an HTTP/1.1 origin server is to send both a strong entity-tag and a Last-Modified |
|---|
| [52] | 939 | value. |
|---|
| 940 | </p> |
|---|
| [1381] | 941 | <p id="rfc.section.2.4.p.4">HTTP/1.1 clients: </p> |
|---|
| [52] | 942 | <ul> |
|---|
| [875] | 943 | <li><em class="bcp14">MUST</em> use that entity-tag in any cache-conditional request (using If-Match or If-None-Match) if an entity-tag has been provided |
|---|
| [755] | 944 | by the origin server. |
|---|
| [52] | 945 | </li> |
|---|
| [755] | 946 | <li><em class="bcp14">SHOULD</em> use the Last-Modified value in non-subrange cache-conditional requests (using If-Modified-Since) if only a Last-Modified value |
|---|
| 947 | has been provided by the origin server. |
|---|
| [52] | 948 | </li> |
|---|
| [755] | 949 | <li><em class="bcp14">MAY</em> use the Last-Modified value in subrange cache-conditional requests (using If-Unmodified-Since) if only a Last-Modified value |
|---|
| 950 | has been provided by an HTTP/1.0 origin server. The user agent <em class="bcp14">SHOULD</em> provide a way to disable this, in case of difficulty. |
|---|
| [52] | 951 | </li> |
|---|
| [875] | 952 | <li><em class="bcp14">SHOULD</em> use both validators in cache-conditional requests if both an entity-tag and a Last-Modified value have been provided by the |
|---|
| [755] | 953 | origin server. This allows both HTTP/1.0 and HTTP/1.1 caches to respond appropriately. |
|---|
| [52] | 954 | </li> |
|---|
| 955 | </ul> |
|---|
| [1381] | 956 | <p id="rfc.section.2.4.p.5">An HTTP/1.1 origin server, upon receiving a conditional request that includes both a Last-Modified date (e.g., in an If-Modified-Since |
|---|
| [875] | 957 | or If-Unmodified-Since header field) and one or more entity-tags (e.g., in an If-Match, If-None-Match, or If-Range header |
|---|
| [928] | 958 | field) as cache validators, <em class="bcp14">MUST NOT</em> return a response status code of 304 (Not Modified) unless doing so is consistent with all of the conditional header fields |
|---|
| 959 | in the request. |
|---|
| [52] | 960 | </p> |
|---|
| [1381] | 961 | <p id="rfc.section.2.4.p.6">An HTTP/1.1 caching proxy, upon receiving a conditional request that includes both a Last-Modified date and one or more entity-tags |
|---|
| [875] | 962 | as cache validators, <em class="bcp14">MUST NOT</em> return a locally cached response to the client unless that cached response is consistent with all of the conditional header |
|---|
| [52] | 963 | fields in the request. |
|---|
| 964 | </p> |
|---|
| [729] | 965 | <ul class="empty"> |
|---|
| [970] | 966 | <li> <b>Note:</b> The general principle behind these rules is that HTTP/1.1 servers and clients ought to transmit as much non-redundant information |
|---|
| [52] | 967 | as is available in their responses and requests. HTTP/1.1 systems receiving this information will make the most conservative |
|---|
| 968 | assumptions about the validators they receive. |
|---|
| [729] | 969 | </li> |
|---|
| [1109] | 970 | <li>HTTP/1.0 clients and caches might ignore entity-tags. Generally, last-modified values received or used by these systems will |
|---|
| [1691] | 971 | support transparent and efficient caching, and so HTTP/1.1 origin servers still ought to provide Last-Modified values. In |
|---|
| 972 | those rare cases where the use of a Last-Modified value as a validator by an HTTP/1.0 system could result in a serious problem, |
|---|
| 973 | then HTTP/1.1 origin servers should not provide one. |
|---|
| [729] | 974 | </li> |
|---|
| 975 | </ul> |
|---|
| [1415] | 976 | <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a> <a id="header.field.definitions" href="#header.field.definitions">Precondition Header Fields</a></h1> |
|---|
| [1253] | 977 | <p id="rfc.section.3.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields for applying preconditions on requests.</p> |
|---|
| [183] | 978 | <div id="rfc.iref.i.1"></div> |
|---|
| [1253] | 979 | <div id="rfc.iref.h.3"></div> |
|---|
| 980 | <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a> <a id="header.if-match" href="#header.if-match">If-Match</a></h2> |
|---|
| [1691] | 981 | <p id="rfc.section.3.1.p.1">The "If-Match" header field can be used to make a request method conditional on the current existence or value of an entity-tag |
|---|
| 982 | for one or more representations of the target resource. If-Match is generally useful for resource update requests, such as |
|---|
| 983 | PUT requests, as a means for protecting against accidental overwrites when multiple clients are acting in parallel on the |
|---|
| 984 | same resource (i.e., the "lost update" problem). An If-Match field-value of "*" places the precondition on the existence of |
|---|
| 985 | any current representation for the target resource. |
|---|
| [52] | 986 | </p> |
|---|
| [1470] | 987 | <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.7"></span> <a href="#header.if-match" class="smpl">If-Match</a> = "*" / 1#<a href="#header.etag" class="smpl">entity-tag</a> |
|---|
| [1381] | 988 | </pre><p id="rfc.section.3.1.p.3">If any of the entity-tags listed in the If-Match field value match (as per <a href="#entity.tag.comparison" title="Comparison">Section 2.3.2</a>) the entity-tag of the selected representation for the target resource, or if "*" is given and any current representation |
|---|
| [1262] | 989 | exists for the target resource, then the server <em class="bcp14">MAY</em> perform the request method as if the If-Match header field was not present. |
|---|
| [52] | 990 | </p> |
|---|
| [1253] | 991 | <p id="rfc.section.3.1.p.4">If none of the entity-tags match, or if "*" is given and no current representation exists, the server <em class="bcp14">MUST NOT</em> perform the requested method. Instead, the server <em class="bcp14">MUST</em> respond with the 412 (Precondition Failed) status code. |
|---|
| [52] | 992 | </p> |
|---|
| [1253] | 993 | <p id="rfc.section.3.1.p.5">If the request would, without the If-Match header field, result in anything other than a 2xx or 412 status code, then the |
|---|
| [994] | 994 | If-Match header field <em class="bcp14">MUST</em> be ignored. |
|---|
| [52] | 995 | </p> |
|---|
| [1253] | 996 | <p id="rfc.section.3.1.p.6">Examples:</p> |
|---|
| [1260] | 997 | <div id="rfc.figure.u.10"></div><pre class="text"> If-Match: "xyzzy" |
|---|
| [362] | 998 | If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz" |
|---|
| 999 | If-Match: * |
|---|
| [1514] | 1000 | </pre><p id="rfc.section.3.1.p.8">The result of a request having both an If-Match header field and either an If-None-Match or an If-Modified-Since header field |
|---|
| [52] | 1001 | is undefined by this specification. |
|---|
| 1002 | </p> |
|---|
| 1003 | <div id="rfc.iref.i.2"></div> |
|---|
| [1253] | 1004 | <div id="rfc.iref.h.4"></div> |
|---|
| 1005 | <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a> <a id="header.if-none-match" href="#header.if-none-match">If-None-Match</a></h2> |
|---|
| [1691] | 1006 | <p id="rfc.section.3.2.p.1">The "If-None-Match" header field can be used to make a request method conditional on not matching any of the current entity-tag |
|---|
| 1007 | values for representations of the target resource. If-None-Match is primarily used in conditional GET requests to enable efficient |
|---|
| 1008 | updates of cached information with a minimum amount of transaction overhead. A client that has one or more representations |
|---|
| 1009 | previously obtained from the target resource can send If-None-Match with a list of the associated entity-tags in the hope |
|---|
| 1010 | of receiving a 304 response if at least one of those representations matches the selected representation. |
|---|
| [1253] | 1011 | </p> |
|---|
| [1691] | 1012 | <p id="rfc.section.3.2.p.2">If-None-Match can also be used with a value of "*" to prevent an unsafe request method (e.g., PUT) from inadvertently modifying |
|---|
| 1013 | an existing representation of the target resource when the client believes that the resource does not have a current representation. |
|---|
| 1014 | This is a variation on the "lost update" problem that might arise if more than one client attempts to create an initial representation |
|---|
| [1253] | 1015 | for the target resource. |
|---|
| 1016 | </p> |
|---|
| [1470] | 1017 | <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.8"></span> <a href="#header.if-none-match" class="smpl">If-None-Match</a> = "*" / 1#<a href="#header.etag" class="smpl">entity-tag</a> |
|---|
| [1381] | 1018 | </pre><p id="rfc.section.3.2.p.4">If any of the entity-tags listed in the If-None-Match field-value match (as per <a href="#entity.tag.comparison" title="Comparison">Section 2.3.2</a>) the entity-tag of the selected representation, or if "*" is given and any current representation exists for that resource, |
|---|
| [1262] | 1019 | then the server <em class="bcp14">MUST NOT</em> perform the requested method. Instead, if the request method was GET or HEAD, the server <em class="bcp14">SHOULD</em> respond with a 304 (Not Modified) status code, including the cache-related header fields (particularly ETag) of the selected |
|---|
| [1253] | 1020 | representation that has a matching entity-tag. For all other request methods, the server <em class="bcp14">MUST</em> respond with a 412 (Precondition Failed) status code. |
|---|
| 1021 | </p> |
|---|
| 1022 | <p id="rfc.section.3.2.p.5">If none of the entity-tags match, then the server <em class="bcp14">MAY</em> perform the requested method as if the If-None-Match header field did not exist, but <em class="bcp14">MUST</em> also ignore any If-Modified-Since header field(s) in the request. That is, if no entity-tags match, then the server <em class="bcp14">MUST NOT</em> return a 304 (Not Modified) response. |
|---|
| 1023 | </p> |
|---|
| 1024 | <p id="rfc.section.3.2.p.6">If the request would, without the If-None-Match header field, result in anything other than a 2xx or 304 status code, then |
|---|
| [1381] | 1025 | the If-None-Match header field <em class="bcp14">MUST</em> be ignored. (See <a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates" title="Rules for When to Use Entity-tags and Last-Modified Dates">Section 2.4</a> for a discussion of server behavior when both If-Modified-Since and If-None-Match appear in the same request.) |
|---|
| [1253] | 1026 | </p> |
|---|
| 1027 | <p id="rfc.section.3.2.p.7">Examples:</p> |
|---|
| [1260] | 1028 | <div id="rfc.figure.u.12"></div><pre class="text"> If-None-Match: "xyzzy" |
|---|
| [1253] | 1029 | If-None-Match: W/"xyzzy" |
|---|
| 1030 | If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz" |
|---|
| 1031 | If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz" |
|---|
| 1032 | If-None-Match: * |
|---|
| 1033 | </pre><p id="rfc.section.3.2.p.9">The result of a request having both an If-None-Match header field and either an If-Match or an If-Unmodified-Since header |
|---|
| [1514] | 1034 | field is undefined by this specification. |
|---|
| [1253] | 1035 | </p> |
|---|
| 1036 | <div id="rfc.iref.i.3"></div> |
|---|
| 1037 | <div id="rfc.iref.h.5"></div> |
|---|
| 1038 | <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a> <a id="header.if-modified-since" href="#header.if-modified-since">If-Modified-Since</a></h2> |
|---|
| [1691] | 1039 | <p id="rfc.section.3.3.p.1">The "If-Modified-Since" header field can be used to make a request method conditional by modification date: if the selected |
|---|
| 1040 | representation has not been modified since the time specified in this field, then do not perform the request method; instead, |
|---|
| 1041 | respond as detailed below. |
|---|
| [52] | 1042 | </p> |
|---|
| [1470] | 1043 | <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.9"></span> <a href="#header.if-modified-since" class="smpl">If-Modified-Since</a> = <a href="#notation" class="smpl">HTTP-date</a> |
|---|
| [1253] | 1044 | </pre><p id="rfc.section.3.3.p.3">An example of the field is:</p> |
|---|
| [1260] | 1045 | <div id="rfc.figure.u.14"></div><pre class="text"> If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT |
|---|
| [1253] | 1046 | </pre><p id="rfc.section.3.3.p.5">A GET method with an If-Modified-Since header field and no Range header field requests that the selected representation be |
|---|
| [1223] | 1047 | transferred only if it has been modified since the date given by the If-Modified-Since header field. The algorithm for determining |
|---|
| 1048 | this includes the following cases: |
|---|
| [52] | 1049 | </p> |
|---|
| 1050 | <ol> |
|---|
| [928] | 1051 | <li>If the request would normally result in anything other than a 200 (OK) status code, or if the passed If-Modified-Since date |
|---|
| 1052 | is invalid, the response is exactly the same as for a normal GET. A date which is later than the server's current time is |
|---|
| 1053 | invalid. |
|---|
| [52] | 1054 | </li> |
|---|
| [1223] | 1055 | <li>If the selected representation has been modified since the If-Modified-Since date, the response is exactly the same as for |
|---|
| 1056 | a normal GET. |
|---|
| [52] | 1057 | </li> |
|---|
| [1223] | 1058 | <li>If the selected representation has not been modified since a valid If-Modified-Since date, the server <em class="bcp14">SHOULD</em> return a 304 (Not Modified) response. |
|---|
| [861] | 1059 | </li> |
|---|
| [52] | 1060 | </ol> |
|---|
| [1253] | 1061 | <p id="rfc.section.3.3.p.6">The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction overhead. </p> |
|---|
| [729] | 1062 | <ul class="empty"> |
|---|
| [1260] | 1063 | <li> <b>Note:</b> The Range header field modifies the meaning of If-Modified-Since; see <a href="p5-range.html#header.range" title="Range">Section 5.4</a> of <a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a> for full details. |
|---|
| [729] | 1064 | </li> |
|---|
| 1065 | <li> <b>Note:</b> If-Modified-Since times are interpreted by the server, whose clock might not be synchronized with the client. |
|---|
| 1066 | </li> |
|---|
| 1067 | <li> <b>Note:</b> When handling an If-Modified-Since header field, some servers will use an exact date comparison function, rather than a less-than |
|---|
| [52] | 1068 | function, for deciding whether to send a 304 (Not Modified) response. To get best results when sending an If-Modified-Since |
|---|
| 1069 | header field for cache validation, clients are advised to use the exact date string received in a previous Last-Modified header |
|---|
| 1070 | field whenever possible. |
|---|
| [729] | 1071 | </li> |
|---|
| [994] | 1072 | <li> <b>Note:</b> If a client uses an arbitrary date in the If-Modified-Since header field instead of a date taken from the Last-Modified header |
|---|
| 1073 | field for the same request, the client needs to be aware that this date is interpreted in the server's understanding of time. |
|---|
| 1074 | Unsynchronized clocks and rounding problems, due to the different encodings of time between the client and server, are concerns. |
|---|
| 1075 | This includes the possibility of race conditions if the document has changed between the time it was first requested and the |
|---|
| 1076 | If-Modified-Since date of a subsequent request, and the possibility of clock-skew-related problems if the If-Modified-Since |
|---|
| 1077 | date is derived from the client's clock without correction to the server's clock. Corrections for different time bases between |
|---|
| 1078 | client and server are at best approximate due to network latency. |
|---|
| [729] | 1079 | </li> |
|---|
| 1080 | </ul> |
|---|
| [1253] | 1081 | <p id="rfc.section.3.3.p.7">The result of a request having both an If-Modified-Since header field and either an If-Match or an If-Unmodified-Since header |
|---|
| [1514] | 1082 | field is undefined by this specification. |
|---|
| [52] | 1083 | </p> |
|---|
| 1084 | <div id="rfc.iref.i.4"></div> |
|---|
| [1253] | 1085 | <div id="rfc.iref.h.6"></div> |
|---|
| 1086 | <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a> <a id="header.if-unmodified-since" href="#header.if-unmodified-since">If-Unmodified-Since</a></h2> |
|---|
| [1691] | 1087 | <p id="rfc.section.3.4.p.1">The "If-Unmodified-Since" header field can be used to make a request method conditional by modification date: if the selected |
|---|
| 1088 | representation has been modified since the time specified in this field, then the server <em class="bcp14">MUST NOT</em> perform the requested operation and <em class="bcp14">MUST</em> instead respond with the 412 (Precondition Failed) status code. If the selected representation has not been modified since |
|---|
| [1223] | 1089 | the time specified in this field, the server <em class="bcp14">SHOULD</em> perform the request method as if the If-Unmodified-Since header field were not present. |
|---|
| [52] | 1090 | </p> |
|---|
| [1470] | 1091 | <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.10"></span> <a href="#header.if-unmodified-since" class="smpl">If-Unmodified-Since</a> = <a href="#notation" class="smpl">HTTP-date</a> |
|---|
| [1253] | 1092 | </pre><p id="rfc.section.3.4.p.3">An example of the field is:</p> |
|---|
| [1260] | 1093 | <div id="rfc.figure.u.16"></div><pre class="text"> If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT |
|---|
| [1691] | 1094 | </pre><p id="rfc.section.3.4.p.5">If a request normally (i.e., in absence of the If-Unmodified-Since header field) would result in anything other than a 2xx |
|---|
| 1095 | or 412 status code, the If-Unmodified-Since header field <em class="bcp14">SHOULD</em> be ignored. |
|---|
| [52] | 1096 | </p> |
|---|
| [1253] | 1097 | <p id="rfc.section.3.4.p.6">If the specified date is invalid, the header field <em class="bcp14">MUST</em> be ignored. |
|---|
| [1223] | 1098 | </p> |
|---|
| [1253] | 1099 | <p id="rfc.section.3.4.p.7">The result of a request having both an If-Unmodified-Since header field and either an If-None-Match or an If-Modified-Since |
|---|
| [1514] | 1100 | header field is undefined by this specification. |
|---|
| [52] | 1101 | </p> |
|---|
| [1260] | 1102 | <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a> <a id="header.if-range" href="#header.if-range">If-Range</a></h2> |
|---|
| 1103 | <p id="rfc.section.3.5.p.1">The If-Range header field provides a special conditional request mechanism that is similar to If-Match and If-Unmodified-Since |
|---|
| 1104 | but specific to HTTP range requests. If-Range is defined in <a href="p5-range.html#header.if-range" title="If-Range">Section 5.3</a> of <a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>. |
|---|
| 1105 | </p> |
|---|
| [1253] | 1106 | <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a> <a id="status.code.definitions" href="#status.code.definitions">Status Code Definitions</a></h1> |
|---|
| [1470] | 1107 | <div id="rfc.iref.27"></div> |
|---|
| [1253] | 1108 | <div id="rfc.iref.s.2"></div> |
|---|
| 1109 | <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a> <a id="status.304" href="#status.304">304 Not Modified</a></h2> |
|---|
| 1110 | <p id="rfc.section.4.1.p.1">The 304 status code indicates that a conditional GET request has been received and would have resulted in a 200 (OK) response |
|---|
| 1111 | if it were not for the fact that the condition has evaluated to false. In other words, there is no need for the server to |
|---|
| 1112 | transfer a representation of the target resource because the client's request indicates that it already has a valid representation, |
|---|
| 1113 | as indicated by the 304 response header fields, and is therefore redirecting the client to make use of that stored representation |
|---|
| 1114 | as if it were the payload of a 200 response. The 304 response <em class="bcp14">MUST NOT</em> contain a message-body, and thus is always terminated by the first empty line after the header fields. |
|---|
| [52] | 1115 | </p> |
|---|
| [1650] | 1116 | <p id="rfc.section.4.1.p.2">A 304 response <em class="bcp14">MUST</em> include a Date header field (<a href="p2-semantics.html#header.date" title="Date">Section 9.10</a> of <a href="#Part2" id="rfc.xref.Part2.5"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) unless the origin server does not have a clock that can provide a reasonable approximation of the current time. If a 200 |
|---|
| [1436] | 1117 | response to the same request would have included any of the header fields Cache-Control, Content-Location, ETag, Expires, |
|---|
| [1545] | 1118 | or Vary, then those same header fields <em class="bcp14">MUST</em> be sent in a 304 response. |
|---|
| [52] | 1119 | </p> |
|---|
| [1253] | 1120 | <p id="rfc.section.4.1.p.3">Since the goal of a 304 response is to minimize information transfer when the recipient already has one or more cached representations, |
|---|
| 1121 | the response <em class="bcp14">SHOULD NOT</em> include representation metadata other than the above listed fields unless said metadata exists for the purpose of guiding |
|---|
| 1122 | cache updates (e.g., future HTTP extensions). |
|---|
| [52] | 1123 | </p> |
|---|
| [1253] | 1124 | <p id="rfc.section.4.1.p.4">If the recipient of a 304 response does not have a cached representation corresponding to the entity-tag indicated by the |
|---|
| 1125 | 304 response, then the recipient <em class="bcp14">MUST NOT</em> use the 304 to update its own cache. If this conditional request originated with an outbound client, such as a user agent |
|---|
| 1126 | with its own cache sending a conditional GET to a shared proxy, then the 304 response <em class="bcp14">MAY</em> be forwarded to the outbound client. Otherwise, the recipient <em class="bcp14">MUST</em> disregard the 304 response and repeat the request without any preconditions. |
|---|
| [52] | 1127 | </p> |
|---|
| [1253] | 1128 | <p id="rfc.section.4.1.p.5">If a cache uses a received 304 response to update a cache entry, the cache <em class="bcp14">MUST</em> update the entry to reflect any new field values given in the response. |
|---|
| [52] | 1129 | </p> |
|---|
| [1470] | 1130 | <div id="rfc.iref.28"></div> |
|---|
| [1253] | 1131 | <div id="rfc.iref.s.3"></div> |
|---|
| 1132 | <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a> <a id="status.412" href="#status.412">412 Precondition Failed</a></h2> |
|---|
| 1133 | <p id="rfc.section.4.2.p.1">The 412 status code indicates that one or more preconditions given in the request header fields evaluated to false when tested |
|---|
| 1134 | on the server. This response code allows the client to place preconditions on the current resource state (its current representations |
|---|
| 1135 | and metadata) and thus prevent the request method from being applied if the target resource is in an unexpected state. |
|---|
| [183] | 1136 | </p> |
|---|
| [1253] | 1137 | <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a> <a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1> |
|---|
| 1138 | <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a> <a id="status.code.registration" href="#status.code.registration">Status Code Registration</a></h2> |
|---|
| 1139 | <p id="rfc.section.5.1.p.1">The HTTP Status Code Registry located at <<a href="http://www.iana.org/assignments/http-status-codes">http://www.iana.org/assignments/http-status-codes</a>> shall be updated with the registrations below: |
|---|
| [203] | 1140 | </p> |
|---|
| [290] | 1141 | <div id="rfc.table.1"> |
|---|
| [700] | 1142 | <div id="iana.status.code.registration.table"></div> |
|---|
| 1143 | <table class="tt full left" cellpadding="3" cellspacing="0"> |
|---|
| 1144 | <thead> |
|---|
| 1145 | <tr> |
|---|
| 1146 | <th>Value</th> |
|---|
| 1147 | <th>Description</th> |
|---|
| 1148 | <th>Reference</th> |
|---|
| 1149 | </tr> |
|---|
| 1150 | </thead> |
|---|
| 1151 | <tbody> |
|---|
| 1152 | <tr> |
|---|
| [704] | 1153 | <td class="left">304</td> |
|---|
| 1154 | <td class="left">Not Modified</td> |
|---|
| [1253] | 1155 | <td class="left"> <a href="#status.304" id="rfc.xref.status.304.1" title="304 Not Modified">Section 4.1</a> |
|---|
| [700] | 1156 | </td> |
|---|
| 1157 | </tr> |
|---|
| 1158 | <tr> |
|---|
| [704] | 1159 | <td class="left">412</td> |
|---|
| 1160 | <td class="left">Precondition Failed</td> |
|---|
| [1253] | 1161 | <td class="left"> <a href="#status.412" id="rfc.xref.status.412.1" title="412 Precondition Failed">Section 4.2</a> |
|---|
| [700] | 1162 | </td> |
|---|
| 1163 | </tr> |
|---|
| 1164 | </tbody> |
|---|
| 1165 | </table> |
|---|
| 1166 | </div> |
|---|
| [1253] | 1167 | <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a> <a id="header.field.registration" href="#header.field.registration">Header Field Registration</a></h2> |
|---|
| 1168 | <p id="rfc.section.5.2.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="#RFC3864" id="rfc.xref.RFC3864.1"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>): |
|---|
| [700] | 1169 | </p> |
|---|
| 1170 | <div id="rfc.table.2"> |
|---|
| [290] | 1171 | <div id="iana.header.registration.table"></div> |
|---|
| [675] | 1172 | <table class="tt full left" cellpadding="3" cellspacing="0"> |
|---|
| [253] | 1173 | <thead> |
|---|
| 1174 | <tr> |
|---|
| 1175 | <th>Header Field Name</th> |
|---|
| 1176 | <th>Protocol</th> |
|---|
| 1177 | <th>Status</th> |
|---|
| 1178 | <th>Reference</th> |
|---|
| 1179 | </tr> |
|---|
| 1180 | </thead> |
|---|
| 1181 | <tbody> |
|---|
| 1182 | <tr> |
|---|
| [704] | 1183 | <td class="left">ETag</td> |
|---|
| 1184 | <td class="left">http</td> |
|---|
| 1185 | <td class="left">standard</td> |
|---|
| [1381] | 1186 | <td class="left"> <a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section 2.3</a> |
|---|
| [253] | 1187 | </td> |
|---|
| 1188 | </tr> |
|---|
| 1189 | <tr> |
|---|
| [704] | 1190 | <td class="left">If-Match</td> |
|---|
| 1191 | <td class="left">http</td> |
|---|
| 1192 | <td class="left">standard</td> |
|---|
| [1260] | 1193 | <td class="left"> <a href="#header.if-match" id="rfc.xref.header.if-match.1" title="If-Match">Section 3.1</a> |
|---|
| [253] | 1194 | </td> |
|---|
| 1195 | </tr> |
|---|
| 1196 | <tr> |
|---|
| [704] | 1197 | <td class="left">If-Modified-Since</td> |
|---|
| 1198 | <td class="left">http</td> |
|---|
| 1199 | <td class="left">standard</td> |
|---|
| [1253] | 1200 | <td class="left"> <a href="#header.if-modified-since" id="rfc.xref.header.if-modified-since.1" title="If-Modified-Since">Section 3.3</a> |
|---|
| [253] | 1201 | </td> |
|---|
| 1202 | </tr> |
|---|
| 1203 | <tr> |
|---|
| [704] | 1204 | <td class="left">If-None-Match</td> |
|---|
| 1205 | <td class="left">http</td> |
|---|
| 1206 | <td class="left">standard</td> |
|---|
| [1260] | 1207 | <td class="left"> <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.1" title="If-None-Match">Section 3.2</a> |
|---|
| [253] | 1208 | </td> |
|---|
| 1209 | </tr> |
|---|
| 1210 | <tr> |
|---|
| [704] | 1211 | <td class="left">If-Unmodified-Since</td> |
|---|
| 1212 | <td class="left">http</td> |
|---|
| 1213 | <td class="left">standard</td> |
|---|
| [1253] | 1214 | <td class="left"> <a href="#header.if-unmodified-since" id="rfc.xref.header.if-unmodified-since.1" title="If-Unmodified-Since">Section 3.4</a> |
|---|
| [253] | 1215 | </td> |
|---|
| 1216 | </tr> |
|---|
| 1217 | <tr> |
|---|
| [704] | 1218 | <td class="left">Last-Modified</td> |
|---|
| 1219 | <td class="left">http</td> |
|---|
| 1220 | <td class="left">standard</td> |
|---|
| [1381] | 1221 | <td class="left"> <a href="#header.last-modified" id="rfc.xref.header.last-modified.1" title="Last-Modified">Section 2.2</a> |
|---|
| [253] | 1222 | </td> |
|---|
| 1223 | </tr> |
|---|
| 1224 | </tbody> |
|---|
| 1225 | </table> |
|---|
| 1226 | </div> |
|---|
| [1253] | 1227 | <p id="rfc.section.5.2.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p> |
|---|
| 1228 | <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a> <a id="security.considerations" href="#security.considerations">Security Considerations</a></h1> |
|---|
| [1452] | 1229 | <p id="rfc.section.6.p.1">No additional security considerations have been identified beyond those applicable to HTTP in general <a href="#Part1" id="rfc.xref.Part1.7"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. |
|---|
| [52] | 1230 | </p> |
|---|
| [1364] | 1231 | <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a> <a id="acks" href="#acks">Acknowledgments</a></h1> |
|---|
| [1586] | 1232 | <p id="rfc.section.7.p.1">See <a href="p1-messaging.html#acks" title="Acknowledgments">Section 9</a> of <a href="#Part1" id="rfc.xref.Part1.8"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. |
|---|
| [1364] | 1233 | </p> |
|---|
| [1253] | 1234 | <h1 id="rfc.references"><a id="rfc.section.8" href="#rfc.section.8">8.</a> References |
|---|
| [52] | 1235 | </h1> |
|---|
| [1253] | 1236 | <h2 id="rfc.references.1"><a href="#rfc.section.8.1" id="rfc.section.8.1">8.1</a> Normative References |
|---|
| [119] | 1237 | </h2> |
|---|
| [1643] | 1238 | <table> |
|---|
| [52] | 1239 | <tr> |
|---|
| 1240 | <td class="reference"><b id="Part1">[Part1]</b></td> |
|---|
| [1667] | 1241 | <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-p1-messaging-latest">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</a>”, Internet-Draft draft-ietf-httpbis-p1-messaging-latest (work in progress), June 2012. |
|---|
| [52] | 1242 | </td> |
|---|
| 1243 | </tr> |
|---|
| 1244 | <tr> |
|---|
| [1436] | 1245 | <td class="reference"><b id="Part2">[Part2]</b></td> |
|---|
| [1667] | 1246 | <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-p2-semantics-latest">HTTP/1.1, part 2: Message Semantics</a>”, Internet-Draft draft-ietf-httpbis-p2-semantics-latest (work in progress), June 2012. |
|---|
| [1436] | 1247 | </td> |
|---|
| 1248 | </tr> |
|---|
| 1249 | <tr> |
|---|
| [52] | 1250 | <td class="reference"><b id="Part5">[Part5]</b></td> |
|---|
| [1667] | 1251 | <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">HTTP/1.1, part 5: Range Requests and Partial Responses</a>”, Internet-Draft draft-ietf-httpbis-p5-range-latest (work in progress), June 2012. |
|---|
| [52] | 1252 | </td> |
|---|
| 1253 | </tr> |
|---|
| 1254 | <tr> |
|---|
| 1255 | <td class="reference"><b id="Part6">[Part6]</b></td> |
|---|
| [1667] | 1256 | <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>, <a href="mailto:mnot@mnot.net" title="Rackspace">Nottingham, M., 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-p6-cache-latest">HTTP/1.1, part 6: Caching</a>”, Internet-Draft draft-ietf-httpbis-p6-cache-latest (work in progress), June 2012. |
|---|
| [52] | 1257 | </td> |
|---|
| 1258 | </tr> |
|---|
| 1259 | <tr> |
|---|
| [119] | 1260 | <td class="reference"><b id="RFC2119">[RFC2119]</b></td> |
|---|
| [704] | 1261 | <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. |
|---|
| [52] | 1262 | </td> |
|---|
| 1263 | </tr> |
|---|
| [425] | 1264 | <tr> |
|---|
| 1265 | <td class="reference"><b id="RFC5234">[RFC5234]</b></td> |
|---|
| [704] | 1266 | <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. |
|---|
| [425] | 1267 | </td> |
|---|
| 1268 | </tr> |
|---|
| [119] | 1269 | </table> |
|---|
| [1253] | 1270 | <h2 id="rfc.references.2"><a href="#rfc.section.8.2" id="rfc.section.8.2">8.2</a> Informative References |
|---|
| [119] | 1271 | </h2> |
|---|
| [1251] | 1272 | <table> |
|---|
| [52] | 1273 | <tr> |
|---|
| 1274 | <td class="reference"><b id="RFC2616">[RFC2616]</b></td> |
|---|
| [704] | 1275 | <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. |
|---|
| [52] | 1276 | </td> |
|---|
| 1277 | </tr> |
|---|
| [253] | 1278 | <tr> |
|---|
| 1279 | <td class="reference"><b id="RFC3864">[RFC3864]</b></td> |
|---|
| [704] | 1280 | <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. |
|---|
| [253] | 1281 | </td> |
|---|
| 1282 | </tr> |
|---|
| [1251] | 1283 | <tr> |
|---|
| 1284 | <td class="reference"><b id="RFC4918">[RFC4918]</b></td> |
|---|
| 1285 | <td class="top"><a href="mailto:ldusseault@commerce.net" title="CommerceNet">Dusseault, L., Ed.</a>, “<a href="http://tools.ietf.org/html/rfc4918">HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)</a>”, RFC 4918, June 2007. |
|---|
| 1286 | </td> |
|---|
| 1287 | </tr> |
|---|
| [52] | 1288 | </table> |
|---|
| [662] | 1289 | <div class="avoidbreak"> |
|---|
| 1290 | <h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1> |
|---|
| 1291 | <address class="vcard"><span class="vcardline"><span class="fn">Roy T. Fielding</span> |
|---|
| 1292 | (editor) |
|---|
| [1106] | 1293 | <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> |
|---|
| [662] | 1294 | <address class="vcard"><span class="vcardline"><span class="fn">Yves Lafon</span> |
|---|
| 1295 | (editor) |
|---|
| [799] | 1296 | <span class="n hidden"><span class="family-name">Lafon</span><span class="given-name">Yves</span></span></span><span class="org vcardline">World Wide Web Consortium</span><span class="adr"><span class="street-address vcardline">W3C / ERCIM</span><span class="street-address vcardline">2004, rte des Lucioles</span><span class="vcardline"><span class="locality">Sophia-Antipolis</span>, <span class="region">AM</span> <span class="postal-code">06902</span></span><span class="country-name vcardline">France</span></span><span class="vcardline">Email: <a href="mailto:ylafon@w3.org"><span class="email">ylafon@w3.org</span></a></span><span class="vcardline">URI: <a href="http://www.raubacapeu.net/people/yves/" class="url">http://www.raubacapeu.net/people/yves/</a></span></address> |
|---|
| [662] | 1297 | <address class="vcard"><span class="vcardline"><span class="fn">Julian F. Reschke</span> |
|---|
| 1298 | (editor) |
|---|
| [1689] | 1299 | <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> |
|---|
| [662] | 1300 | </div> |
|---|
| [912] | 1301 | <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> |
|---|
| [1381] | 1302 | <p id="rfc.section.A.p.1">Allow weak entity-tags in all requests except range requests (Sections <a href="#weak.and.strong.validators" title="Weak versus Strong">2.1</a> and <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.2" title="If-None-Match">3.2</a>). |
|---|
| [245] | 1303 | </p> |
|---|
| [1470] | 1304 | <p id="rfc.section.A.p.2">Change ETag header field ABNF not to use quoted-string, thus avoiding escaping issues. (<a href="#header.etag" id="rfc.xref.header.etag.2" title="ETag">Section 2.3</a>) |
|---|
| [1233] | 1305 | </p> |
|---|
| [1470] | 1306 | <p id="rfc.section.A.p.3">Change ABNF productions for header fields to only define the field value. (<a href="#header.field.definitions" title="Precondition Header Fields">Section 3</a>) |
|---|
| 1307 | </p> |
|---|
| [421] | 1308 | <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a> <a id="collected.abnf" href="#collected.abnf">Collected ABNF</a></h1> |
|---|
| [1260] | 1309 | <div id="rfc.figure.u.17"></div> <pre class="inline"><a href="#header.etag" class="smpl">ETag</a> = entity-tag |
|---|
| [427] | 1310 | |
|---|
| [1663] | 1311 | <a href="#notation" class="smpl">HTTP-date</a> = <HTTP-date, defined in [Part2], Section 5.1> |
|---|
| [427] | 1312 | |
|---|
| [1233] | 1313 | <a href="#header.if-match" class="smpl">If-Match</a> = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS |
|---|
| [421] | 1314 | entity-tag ] ) ) |
|---|
| [1233] | 1315 | <a href="#header.if-modified-since" class="smpl">If-Modified-Since</a> = HTTP-date |
|---|
| 1316 | <a href="#header.if-none-match" class="smpl">If-None-Match</a> = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS |
|---|
| [421] | 1317 | entity-tag ] ) ) |
|---|
| [1233] | 1318 | <a href="#header.if-unmodified-since" class="smpl">If-Unmodified-Since</a> = HTTP-date |
|---|
| [427] | 1319 | |
|---|
| [1233] | 1320 | <a href="#header.last-modified" class="smpl">Last-Modified</a> = HTTP-date |
|---|
| [427] | 1321 | |
|---|
| [1523] | 1322 | <a href="#notation" class="smpl">OWS</a> = <OWS, defined in [Part1], Section 3.2.1> |
|---|
| [427] | 1323 | |
|---|
| [1260] | 1324 | <a href="#header.etag" class="smpl">entity-tag</a> = [ weak ] opaque-tag |
|---|
| [1470] | 1325 | <a href="#header.etag" class="smpl">etagc</a> = "!" / %x23-7E ; '#'-'~' |
|---|
| 1326 | / obs-text |
|---|
| [427] | 1327 | |
|---|
| [1523] | 1328 | <a href="#notation" class="smpl">obs-text</a> = <obs-text, defined in [Part1], Section 3.2.4> |
|---|
| [1470] | 1329 | <a href="#header.etag" class="smpl">opaque-tag</a> = DQUOTE *etagc DQUOTE |
|---|
| [427] | 1330 | |
|---|
| [1260] | 1331 | <a href="#header.etag" class="smpl">weak</a> = %x57.2F ; W/ |
|---|
| 1332 | </pre> <div id="rfc.figure.u.18"></div> |
|---|
| [454] | 1333 | <p>ABNF diagnostics:</p><pre class="inline">; ETag defined but not used |
|---|
| [421] | 1334 | ; If-Match defined but not used |
|---|
| 1335 | ; If-Modified-Since defined but not used |
|---|
| 1336 | ; If-None-Match defined but not used |
|---|
| 1337 | ; If-Unmodified-Since defined but not used |
|---|
| 1338 | ; Last-Modified defined but not used |
|---|
| [454] | 1339 | </pre><h1 id="rfc.section.C"><a href="#rfc.section.C">C.</a> <a id="change.log" href="#change.log">Change Log (to be removed by RFC Editor before publication)</a></h1> |
|---|
| [1624] | 1340 | <p id="rfc.section.C.p.1">Changes up to the first Working Group Last Call draft are summarized in <<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p4-conditional-19#appendix-C">http://tools.ietf.org/html/draft-ietf-httpbis-p4-conditional-19#appendix-C</a>>. |
|---|
| [115] | 1341 | </p> |
|---|
| [1624] | 1342 | <h2 id="rfc.section.C.1"><a href="#rfc.section.C.1">C.1</a> <a id="changes.since.19" href="#changes.since.19">Since draft-ietf-httpbis-p4-conditional-19</a></h2> |
|---|
| [1682] | 1343 | <p id="rfc.section.C.1.p.1">Closed issues: </p> |
|---|
| 1344 | <ul> |
|---|
| 1345 | <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" |
|---|
| 1346 | </li> |
|---|
| 1347 | </ul> |
|---|
| [52] | 1348 | <h1 id="rfc.index"><a href="#rfc.index">Index</a></h1> |
|---|
| [1253] | 1349 | <p class="noprint"><a href="#rfc.index.3">3</a> <a href="#rfc.index.4">4</a> <a href="#rfc.index.E">E</a> <a href="#rfc.index.G">G</a> <a href="#rfc.index.H">H</a> <a href="#rfc.index.I">I</a> <a href="#rfc.index.L">L</a> <a href="#rfc.index.M">M</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> |
|---|
| [52] | 1350 | </p> |
|---|
| 1351 | <div class="print2col"> |
|---|
| 1352 | <ul class="ind"> |
|---|
| [1072] | 1353 | <li><a id="rfc.index.3" href="#rfc.index.3"><b>3</b></a><ul> |
|---|
| [1470] | 1354 | <li>304 Not Modified (status code) <a href="#rfc.iref.27"><b>4.1</b></a>, <a href="#rfc.xref.status.304.1">5.1</a></li> |
|---|
| [52] | 1355 | </ul> |
|---|
| 1356 | </li> |
|---|
| [1072] | 1357 | <li><a id="rfc.index.4" href="#rfc.index.4"><b>4</b></a><ul> |
|---|
| [1470] | 1358 | <li>412 Precondition Failed (status code) <a href="#rfc.iref.28"><b>4.2</b></a>, <a href="#rfc.xref.status.412.1">5.1</a></li> |
|---|
| [52] | 1359 | </ul> |
|---|
| 1360 | </li> |
|---|
| [1072] | 1361 | <li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul> |
|---|
| [1470] | 1362 | <li>ETag header field <a href="#rfc.iref.e.1"><b>2.3</b></a>, <a href="#rfc.xref.header.etag.1">5.2</a>, <a href="#rfc.xref.header.etag.2">A</a></li> |
|---|
| [52] | 1363 | </ul> |
|---|
| 1364 | </li> |
|---|
| [1072] | 1365 | <li><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul> |
|---|
| 1366 | <li><tt>Grammar</tt> |
|---|
| 1367 | <ul> |
|---|
| [1381] | 1368 | <li><tt>entity-tag</tt> <a href="#rfc.iref.g.3"><b>2.3</b></a></li> |
|---|
| 1369 | <li><tt>ETag</tt> <a href="#rfc.iref.g.2"><b>2.3</b></a></li> |
|---|
| [1470] | 1370 | <li><tt>etagc</tt> <a href="#rfc.iref.g.6"><b>2.3</b></a></li> |
|---|
| 1371 | <li><tt>If-Match</tt> <a href="#rfc.iref.g.7"><b>3.1</b></a></li> |
|---|
| 1372 | <li><tt>If-Modified-Since</tt> <a href="#rfc.iref.g.9"><b>3.3</b></a></li> |
|---|
| 1373 | <li><tt>If-None-Match</tt> <a href="#rfc.iref.g.8"><b>3.2</b></a></li> |
|---|
| 1374 | <li><tt>If-Unmodified-Since</tt> <a href="#rfc.iref.g.10"><b>3.4</b></a></li> |
|---|
| [1381] | 1375 | <li><tt>Last-Modified</tt> <a href="#rfc.iref.g.1"><b>2.2</b></a></li> |
|---|
| 1376 | <li><tt>opaque-tag</tt> <a href="#rfc.iref.g.5"><b>2.3</b></a></li> |
|---|
| 1377 | <li><tt>weak</tt> <a href="#rfc.iref.g.4"><b>2.3</b></a></li> |
|---|
| [52] | 1378 | </ul> |
|---|
| 1379 | </li> |
|---|
| 1380 | </ul> |
|---|
| 1381 | </li> |
|---|
| [1072] | 1382 | <li><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul> |
|---|
| [1120] | 1383 | <li>Header Fields |
|---|
| [1072] | 1384 | <ul> |
|---|
| [1470] | 1385 | <li>ETag <a href="#rfc.iref.h.2"><b>2.3</b></a>, <a href="#rfc.xref.header.etag.1">5.2</a>, <a href="#rfc.xref.header.etag.2">A</a></li> |
|---|
| [1260] | 1386 | <li>If-Match <a href="#rfc.iref.h.3"><b>3.1</b></a>, <a href="#rfc.xref.header.if-match.1">5.2</a></li> |
|---|
| [1253] | 1387 | <li>If-Modified-Since <a href="#rfc.iref.h.5"><b>3.3</b></a>, <a href="#rfc.xref.header.if-modified-since.1">5.2</a></li> |
|---|
| [1260] | 1388 | <li>If-None-Match <a href="#rfc.iref.h.4"><b>3.2</b></a>, <a href="#rfc.xref.header.if-none-match.1">5.2</a>, <a href="#rfc.xref.header.if-none-match.2">A</a></li> |
|---|
| [1253] | 1389 | <li>If-Unmodified-Since <a href="#rfc.iref.h.6"><b>3.4</b></a>, <a href="#rfc.xref.header.if-unmodified-since.1">5.2</a></li> |
|---|
| [1381] | 1390 | <li>Last-Modified <a href="#rfc.iref.h.1"><b>2.2</b></a>, <a href="#rfc.xref.header.last-modified.1">5.2</a></li> |
|---|
| [52] | 1391 | </ul> |
|---|
| 1392 | </li> |
|---|
| 1393 | </ul> |
|---|
| 1394 | </li> |
|---|
| [1072] | 1395 | <li><a id="rfc.index.I" href="#rfc.index.I"><b>I</b></a><ul> |
|---|
| [1260] | 1396 | <li>If-Match header field <a href="#rfc.iref.i.1"><b>3.1</b></a>, <a href="#rfc.xref.header.if-match.1">5.2</a></li> |
|---|
| [1253] | 1397 | <li>If-Modified-Since header field <a href="#rfc.iref.i.3"><b>3.3</b></a>, <a href="#rfc.xref.header.if-modified-since.1">5.2</a></li> |
|---|
| [1260] | 1398 | <li>If-None-Match header field <a href="#rfc.iref.i.2"><b>3.2</b></a>, <a href="#rfc.xref.header.if-none-match.1">5.2</a>, <a href="#rfc.xref.header.if-none-match.2">A</a></li> |
|---|
| [1253] | 1399 | <li>If-Unmodified-Since header field <a href="#rfc.iref.i.4"><b>3.4</b></a>, <a href="#rfc.xref.header.if-unmodified-since.1">5.2</a></li> |
|---|
| [52] | 1400 | </ul> |
|---|
| 1401 | </li> |
|---|
| [1072] | 1402 | <li><a id="rfc.index.L" href="#rfc.index.L"><b>L</b></a><ul> |
|---|
| [1381] | 1403 | <li>Last-Modified header field <a href="#rfc.iref.l.1"><b>2.2</b></a>, <a href="#rfc.xref.header.last-modified.1">5.2</a></li> |
|---|
| [52] | 1404 | </ul> |
|---|
| 1405 | </li> |
|---|
| [1253] | 1406 | <li><a id="rfc.index.M" href="#rfc.index.M"><b>M</b></a><ul> |
|---|
| 1407 | <li>metadata <a href="#rfc.iref.m.1"><b>2</b></a></li> |
|---|
| 1408 | </ul> |
|---|
| 1409 | </li> |
|---|
| [1072] | 1410 | <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul> |
|---|
| [1452] | 1411 | <li><em>Part1</em> <a href="#rfc.xref.Part1.1">1.1</a>, <a href="#rfc.xref.Part1.2">1.2</a>, <a href="#rfc.xref.Part1.3">1.2</a>, <a href="#rfc.xref.Part1.4">1.2</a>, <a href="#rfc.xref.Part1.5">1.2</a>, <a href="#rfc.xref.Part1.6">2.3.3</a>, <a href="#rfc.xref.Part1.7">6</a>, <a href="#rfc.xref.Part1.8">7</a>, <a href="#Part1"><b>8.1</b></a><ul> |
|---|
| 1412 | <li><em>Section 1.2</em> <a href="#rfc.xref.Part1.2">1.2</a></li> |
|---|
| 1413 | <li><em>Section 2</em> <a href="#rfc.xref.Part1.1">1.1</a></li> |
|---|
| [1519] | 1414 | <li><em>Section 3.2.1</em> <a href="#rfc.xref.Part1.4">1.2</a></li> |
|---|
| 1415 | <li><em>Section 3.2.4</em> <a href="#rfc.xref.Part1.5">1.2</a></li> |
|---|
| [1580] | 1416 | <li><em>Section 4</em> <a href="#rfc.xref.Part1.6">2.3.3</a></li> |
|---|
| [1586] | 1417 | <li><em>Section 9</em> <a href="#rfc.xref.Part1.8">7</a></li> |
|---|
| [52] | 1418 | </ul> |
|---|
| 1419 | </li> |
|---|
| [1643] | 1420 | <li><em>Part2</em> <a href="#rfc.xref.Part2.1">1.2</a>, <a href="#rfc.xref.Part2.2">1.2</a>, <a href="#rfc.xref.Part2.3">2.3.3</a>, <a href="#rfc.xref.Part2.4">2.3.3</a>, <a href="#rfc.xref.Part2.5">4.1</a>, <a href="#Part2"><b>8.1</b></a><ul> |
|---|
| [1650] | 1421 | <li><em>Section 5.1</em> <a href="#rfc.xref.Part2.2">1.2</a></li> |
|---|
| 1422 | <li><em>Section 8</em> <a href="#rfc.xref.Part2.3">2.3.3</a></li> |
|---|
| 1423 | <li><em>Section 9.3</em> <a href="#rfc.xref.Part2.4">2.3.3</a></li> |
|---|
| 1424 | <li><em>Section 9.10</em> <a href="#rfc.xref.Part2.5">4.1</a></li> |
|---|
| [1436] | 1425 | </ul> |
|---|
| 1426 | </li> |
|---|
| [1260] | 1427 | <li><em>Part5</em> <a href="#rfc.xref.Part5.1">3.3</a>, <a href="#rfc.xref.Part5.2">3.5</a>, <a href="#Part5"><b>8.1</b></a><ul> |
|---|
| 1428 | <li><em>Section 5.3</em> <a href="#rfc.xref.Part5.2">3.5</a></li> |
|---|
| 1429 | <li><em>Section 5.4</em> <a href="#rfc.xref.Part5.1">3.3</a></li> |
|---|
| [52] | 1430 | </ul> |
|---|
| 1431 | </li> |
|---|
| [1381] | 1432 | <li><em>Part6</em> <a href="#rfc.xref.Part6.1">1</a>, <a href="#rfc.xref.Part6.2">2.2.1</a>, <a href="#rfc.xref.Part6.3">2.3.1</a>, <a href="#Part6"><b>8.1</b></a></li> |
|---|
| [52] | 1433 | </ul> |
|---|
| 1434 | </li> |
|---|
| [1072] | 1435 | <li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul> |
|---|
| [1253] | 1436 | <li><em>RFC2119</em> <a href="#rfc.xref.RFC2119.1">1.1</a>, <a href="#RFC2119"><b>8.1</b></a></li> |
|---|
| [1624] | 1437 | <li><em>RFC2616</em> <a href="#rfc.xref.RFC2616.1">2.3</a>, <a href="#RFC2616"><b>8.2</b></a><ul> |
|---|
| [1470] | 1438 | <li><em>Section 3.11</em> <a href="#rfc.xref.RFC2616.1">2.3</a></li> |
|---|
| 1439 | </ul> |
|---|
| 1440 | </li> |
|---|
| [1253] | 1441 | <li><em>RFC3864</em> <a href="#rfc.xref.RFC3864.1">5.2</a>, <a href="#RFC3864"><b>8.2</b></a></li> |
|---|
| 1442 | <li><em>RFC4918</em> <a href="#rfc.xref.RFC4918.1">2</a>, <a href="#RFC4918"><b>8.2</b></a></li> |
|---|
| 1443 | <li><em>RFC5234</em> <a href="#rfc.xref.RFC5234.1">1.2</a>, <a href="#rfc.xref.RFC5234.2">1.2</a>, <a href="#RFC5234"><b>8.1</b></a><ul> |
|---|
| [1072] | 1444 | <li><em>Appendix B.1</em> <a href="#rfc.xref.RFC5234.2">1.2</a></li> |
|---|
| [425] | 1445 | </ul> |
|---|
| 1446 | </li> |
|---|
| [52] | 1447 | </ul> |
|---|
| 1448 | </li> |
|---|
| [1072] | 1449 | <li><a id="rfc.index.S" href="#rfc.index.S"><b>S</b></a><ul> |
|---|
| [1224] | 1450 | <li>selected representation <a href="#rfc.iref.s.1"><b>1</b></a></li> |
|---|
| [1072] | 1451 | <li>Status Codes |
|---|
| 1452 | <ul> |
|---|
| [1253] | 1453 | <li>304 Not Modified <a href="#rfc.iref.s.2"><b>4.1</b></a>, <a href="#rfc.xref.status.304.1">5.1</a></li> |
|---|
| 1454 | <li>412 Precondition Failed <a href="#rfc.iref.s.3"><b>4.2</b></a>, <a href="#rfc.xref.status.412.1">5.1</a></li> |
|---|
| [52] | 1455 | </ul> |
|---|
| 1456 | </li> |
|---|
| 1457 | </ul> |
|---|
| 1458 | </li> |
|---|
| [1253] | 1459 | <li><a id="rfc.index.V" href="#rfc.index.V"><b>V</b></a><ul> |
|---|
| [1381] | 1460 | <li>validator <a href="#rfc.iref.v.1"><b>2</b></a><ul> |
|---|
| 1461 | <li>strong <a href="#rfc.iref.v.3"><b>2.1</b></a></li> |
|---|
| 1462 | <li>weak <a href="#rfc.iref.v.2"><b>2.1</b></a></li> |
|---|
| 1463 | </ul> |
|---|
| 1464 | </li> |
|---|
| [1253] | 1465 | </ul> |
|---|
| 1466 | </li> |
|---|
| [52] | 1467 | </ul> |
|---|
| 1468 | </div> |
|---|
| 1469 | </body> |
|---|
| 1470 | </html> |
|---|
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