source: draft-ietf-httpbis/latest/p5-range.xml @ 2401

Last change on this file since 2401 was 2401, checked in by fielding@…, 7 years ago

uniform terminology for header section instead of header block; this and [2400] addresses #234

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "September">
16  <!ENTITY ID-YEAR "2013">
17  <!ENTITY Note "<x:h xmlns:x='http://purl.org/net/xml2rfc/ext'>Note:</x:h>">
18  <!ENTITY architecture               "<xref target='Part1' x:rel='#architecture' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY conformance                "<xref target='Part1' x:rel='#conformance' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY abnf-extension             "<xref target='Part1' x:rel='#abnf.extension' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY whitespace                 "<xref target='Part1' x:rel='#whitespace' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY field-components           "<xref target='Part1' x:rel='#field.components' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY semantics                  "<xref target='Part2' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY http-date                  "<xref target='Part2' x:rel='#http.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY representation             "<xref target='Part2' x:rel='#representations' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY entity-tags                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY weak-and-strong-validators "<xref target='Part4' x:rel='#weak.and.strong.validators' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY entity-tag-comparison      "<xref target='Part4' x:rel='#entity.tag.comparison' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY lastmod-comparison         "<xref target='Part4' x:rel='#lastmod.comparison' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY p6-heuristic               "<xref target='Part6' x:rel='#heuristic.freshness' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34]>
35<?rfc toc="yes" ?>
36<?rfc symrefs="yes" ?>
37<?rfc sortrefs="yes" ?>
38<?rfc compact="yes"?>
39<?rfc subcompact="no" ?>
40<?rfc linkmailto="no" ?>
41<?rfc editing="no" ?>
42<?rfc comments="yes"?>
43<?rfc inline="yes"?>
44<?rfc rfcedstyle="yes"?>
45<?rfc-ext allow-markup-in-artwork="yes" ?>
46<?rfc-ext include-references-in-index="yes" ?>
47<rfc obsoletes="2616" category="std" x:maturity-level="proposed"
48     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p5-range-&ID-VERSION;"
49     xmlns:x='http://purl.org/net/xml2rfc/ext'>
50<x:link rel="prev" basename="p4-conditional"/>
51<x:link rel="next" basename="p6-cache"/>
52<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
53<front>
54
55  <title abbrev="HTTP/1.1 Range Requests">Hypertext Transfer Protocol (HTTP/1.1): Range Requests</title>
56
57  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
58    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
59    <address>
60      <postal>
61        <street>345 Park Ave</street>
62        <city>San Jose</city>
63        <region>CA</region>
64        <code>95110</code>
65        <country>USA</country>
66      </postal>
67      <email>fielding@gbiv.com</email>
68      <uri>http://roy.gbiv.com/</uri>
69    </address>
70  </author>
71
72  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
73    <organization abbrev="W3C">World Wide Web Consortium</organization>
74    <address>
75      <postal>
76        <street>W3C / ERCIM</street>
77        <street>2004, rte des Lucioles</street>
78        <city>Sophia-Antipolis</city>
79        <region>AM</region>
80        <code>06902</code>
81        <country>France</country>
82      </postal>
83      <email>ylafon@w3.org</email>
84      <uri>http://www.raubacapeu.net/people/yves/</uri>
85    </address>
86  </author>
87
88  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
89    <organization abbrev="greenbytes">greenbytes GmbH</organization>
90    <address>
91      <postal>
92        <street>Hafenweg 16</street>
93        <city>Muenster</city><region>NW</region><code>48155</code>
94        <country>Germany</country>
95      </postal>
96      <email>julian.reschke@greenbytes.de</email>
97      <uri>http://greenbytes.de/tech/webdav/</uri>
98    </address>
99  </author>
100
101  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
102  <workgroup>HTTPbis Working Group</workgroup>
103
104<abstract>
105<t>
106   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
107   distributed, collaborative, hypertext information systems. This document
108   defines range requests and the rules for constructing and combining
109   responses to those requests.
110</t>
111</abstract>
112
113<note title="Editorial Note (To be removed by RFC Editor)">
114  <t>
115    Discussion of this draft takes place on the HTTPBIS working group
116    mailing list (ietf-http-wg@w3.org), which is archived at
117    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
118  </t>
119  <t>
120    The current issues list is at
121    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
122    documents (including fancy diffs) can be found at
123    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
124  </t>
125  <t>
126    The changes in this draft are summarized in <xref target="changes.since.23"/>.
127  </t>
128</note>
129</front>
130<middle>
131<section title="Introduction" anchor="introduction">
132<t>
133   Hypertext Transfer Protocol (HTTP) clients often encounter interrupted data
134   transfers as a result of canceled requests or dropped connections. When a
135   client has stored a partial representation, it is desirable to request the
136   remainder of that representation in a subsequent request rather than
137   transfer the entire representation. Likewise, devices with limited local
138   storage might benefit from being able to request only a subset of a larger
139   representation, such as a single page of a very large document, or the
140   dimensions of an embedded image.
141</t>
142<t>
143   This document defines HTTP/1.1 range requests, partial responses, and the
144   multipart/byteranges media type. Range requests are an &OPTIONAL; feature
145   of HTTP, designed so that recipients not implementing this feature (or not
146   supporting it for the target resource) can respond as if it is a normal
147   GET request without impacting interoperability. Partial responses are
148   indicated by a distinct status code to not be mistaken for full responses
149   by caches that might not implement the feature.
150</t>
151<t>
152   Although the range request mechanism is designed to allow for
153   extensible range types, this specification only defines requests for
154   byte ranges.
155</t>
156
157<section title="Conformance and Error Handling" anchor="conformance">
158<t>
159   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
160   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
161   document are to be interpreted as described in <xref target="RFC2119"/>.
162</t>
163<t>
164   Conformance criteria and considerations regarding error handling
165   are defined in &conformance;.
166</t>
167</section>
168
169<section title="Syntax Notation" anchor="notation">
170<t>
171   This specification uses the Augmented Backus-Naur Form (ABNF) notation
172   of <xref target="RFC5234"/> with the list rule extension defined in
173   &abnf-extension;. <xref target="imported.abnf"/> describes rules imported from
174   other documents. <xref target="collected.abnf"/> shows the collected ABNF
175   with the list rule expanded.
176</t>
177</section>
178</section>
179
180
181<section title="Range Units" anchor="range.units">
182  <x:anchor-alias value="range-unit"/>
183  <x:anchor-alias value="range unit"/>
184<t>
185   A representation can be partitioned into subranges according to various
186   structural units, depending on the structure inherent in the
187   representation's media type. This "<x:dfn>range unit</x:dfn>" is used
188   in the <x:ref>Accept-Ranges</x:ref> (<xref target="header.accept-ranges"/>)
189   response header field to advertise support for range requests, the
190   <x:ref>Range</x:ref> (<xref target="header.range"/>) request header field
191   to delineate the parts of a representation that are requested, and the
192   <x:ref>Content-Range</x:ref> (<xref target="header.content-range"/>)
193   payload header field to describe which part of a representation is being
194   transferred.
195</t>
196<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="range-unit"/><iref item="Grammar" subitem="bytes-unit"/><iref item="Grammar" subitem="other-range-unit"/>
197  <x:ref>range-unit</x:ref>       = <x:ref>bytes-unit</x:ref> / <x:ref>other-range-unit</x:ref>
198</artwork></figure>
199
200<section title="Byte Ranges" anchor="byte.ranges">
201  <x:anchor-alias value="bytes-unit"/>
202<t>
203   Since representation data is transferred in payloads as a sequence of
204   octets, a byte range is a meaningful substructure for any representation
205   transferable over HTTP (&representation;). We define the "bytes" range
206   unit for expressing subranges of the data's octet sequence.
207</t>
208<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="bytes-unit"/>
209  <x:ref>bytes-unit</x:ref>       = "bytes"
210</artwork></figure>
211<t anchor="rule.ranges-specifier">
212  <x:anchor-alias value="byte-range-set"/>
213  <x:anchor-alias value="byte-range-spec"/>
214  <x:anchor-alias value="byte-ranges-specifier"/>
215  <x:anchor-alias value="first-byte-pos"/>
216  <x:anchor-alias value="last-byte-pos"/>
217  <x:anchor-alias value="ranges-specifier"/>
218  <x:anchor-alias value="suffix-byte-range-spec"/>
219  <x:anchor-alias value="suffix-length"/>
220   A byte range request can specify a single range of bytes, or a set
221   of ranges within a single representation.
222</t>
223<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="ranges-specifier"/><iref primary="true" item="Grammar" subitem="byte-ranges-specifier"/><iref primary="true" item="Grammar" subitem="byte-range-set"/><iref primary="true" item="Grammar" subitem="byte-range-spec"/><iref primary="true" item="Grammar" subitem="first-byte-pos"/><iref primary="true" item="Grammar" subitem="last-byte-pos"/>
224  <x:ref>byte-ranges-specifier</x:ref> = <x:ref>bytes-unit</x:ref> "=" <x:ref>byte-range-set</x:ref>
225  <x:ref>byte-range-set</x:ref>  = 1#( <x:ref>byte-range-spec</x:ref> / <x:ref>suffix-byte-range-spec</x:ref> )
226  <x:ref>byte-range-spec</x:ref> = <x:ref>first-byte-pos</x:ref> "-" [ <x:ref>last-byte-pos</x:ref> ]
227  <x:ref>first-byte-pos</x:ref>  = 1*<x:ref>DIGIT</x:ref>
228  <x:ref>last-byte-pos</x:ref>   = 1*<x:ref>DIGIT</x:ref>
229</artwork></figure>
230<t>
231   The <x:ref>first-byte-pos</x:ref> value in a <x:ref>byte-range-spec</x:ref>
232   gives the byte-offset of the first byte in a range.
233   The <x:ref>last-byte-pos</x:ref> value gives the byte-offset of the last
234   byte in the range; that is, the byte positions specified are inclusive.
235   Byte offsets start at zero.
236</t>
237<t>
238   Examples of <x:ref>byte-ranges-specifier</x:ref> values:
239  <list style="symbols">
240     <t>The first 500 bytes (byte offsets 0-499, inclusive):
241<figure><artwork type="example" x:indent-with="   ">
242  bytes=0-499
243</artwork></figure>
244    </t>
245     <t>The second 500 bytes (byte offsets 500-999, inclusive):
246<figure><artwork type="example" x:indent-with="   ">
247  bytes=500-999
248</artwork></figure>
249    </t>
250  </list>
251</t>
252<t>
253   A <x:ref>byte-range-spec</x:ref> is invalid if the
254   <x:ref>last-byte-pos</x:ref> value is present and less than the
255   <x:ref>first-byte-pos</x:ref>.
256</t>
257<t>
258   A client can limit the number of bytes requested without knowing the size
259   of the selected representation.
260   If the <x:ref>last-byte-pos</x:ref> value is absent, or if the value is
261   greater than or equal to the current length of the representation data, the
262   byte range is interpreted as the remainder of the representation (i.e., the
263   server replaces the value of <x:ref>last-byte-pos</x:ref> with a value that
264   is one less than the current length of the selected representation).
265</t>
266<t>
267   A client can request the last N bytes of the selected representation using
268   a <x:ref>suffix-byte-range-spec</x:ref>.
269</t>
270<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="suffix-byte-range-spec"/><iref primary="true" item="Grammar" subitem="suffix-length"/>
271  <x:ref>suffix-byte-range-spec</x:ref> = "-" <x:ref>suffix-length</x:ref>
272  <x:ref>suffix-length</x:ref> = 1*<x:ref>DIGIT</x:ref>
273</artwork></figure>
274<t>
275   If the selected representation is shorter than the specified
276   <x:ref>suffix-length</x:ref>, the entire representation is used.
277</t>
278<t>  
279   Additional examples, assuming a representation of length 10000:
280  <list style="symbols">
281     <t>The final 500 bytes (byte offsets 9500-9999, inclusive):
282<figure><artwork type="example" x:indent-with="   ">
283  bytes=-500
284</artwork></figure>
285    Or:
286<figure><artwork type="example" x:indent-with="   ">
287  bytes=9500-
288</artwork></figure>
289    </t>
290     <t>The first and last bytes only (bytes 0 and 9999):
291<figure><artwork type="example" x:indent-with="   ">
292  bytes=0-0,-1
293</artwork></figure>
294     </t>
295     <t>Other valid (but not canonical) specifications of the second 500
296        bytes (byte offsets 500-999, inclusive):
297<figure><artwork type="example" x:indent-with="   ">
298  bytes=500-600,601-999
299  bytes=500-700,601-999
300</artwork></figure>
301     </t>
302  </list>
303</t>
304<t>
305   If a valid <x:ref>byte-range-set</x:ref> includes at least one
306   <x:ref>byte-range-spec</x:ref> with a <x:ref>first-byte-pos</x:ref> that is
307   less than the current length of the representation, or at least one
308   <x:ref>suffix-byte-range-spec</x:ref> with a non-zero
309   <x:ref>suffix-length</x:ref>, then the <x:ref>byte-range-set</x:ref> is
310   satisfiable. Otherwise, the <x:ref>byte-range-set</x:ref> is unsatisfiable.
311</t>
312<t>
313   In the byte range syntax, <x:ref>first-byte-pos</x:ref>,
314   <x:ref>last-byte-pos</x:ref>, and <x:ref>suffix-length</x:ref> are
315   expressed as decimal number of octets. Since there is no predefined limit
316   to the length of a payload, recipients ought to anticipate potentially
317   large decimal numerals and prevent parsing errors due to integer conversion
318   overflows.
319</t>
320</section>
321
322<section title="Other Range Units" anchor="range.units.other">
323  <x:anchor-alias value="other-range-unit"/>
324<t>
325  Range units are intended to be extensible.  New range units ought to be
326  registered with IANA, as defined in <xref target="range.unit.registry"/>.
327</t>
328<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="other-range-unit"/>
329  <x:ref>other-range-unit</x:ref> = <x:ref>token</x:ref>
330</artwork></figure>
331</section>
332
333<section title="Accept-Ranges" anchor="header.accept-ranges">
334  <iref primary="true" item="Accept-Ranges header field" x:for-anchor=""/>
335  <x:anchor-alias value="Accept-Ranges"/>
336  <x:anchor-alias value="acceptable-ranges"/>
337<t>
338   The "Accept-Ranges" header field allows a server to indicate that it
339   supports range requests for the target resource.
340</t>
341<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Ranges"/><iref primary="true" item="Grammar" subitem="acceptable-ranges"/>
342  <x:ref>Accept-Ranges</x:ref>     = <x:ref>acceptable-ranges</x:ref>
343  <x:ref>acceptable-ranges</x:ref> = 1#<x:ref>range-unit</x:ref> / "none"
344</artwork></figure>
345<t>
346   Origin servers that support byte-range requests &MAY; send
347</t>
348<figure><artwork type="example">
349  Accept-Ranges: bytes
350</artwork></figure>
351<t>
352   but are not required to do so. Clients &MAY; generate range
353   requests without having received this header field for the resource
354   involved. Range units are defined in <xref target="range.units"/>.
355</t>
356<t>
357   Servers that do not support any kind of range request for the target
358   resource resource &MAY; send
359</t>
360<figure><artwork type="example">
361  Accept-Ranges: none
362</artwork></figure>
363<t>
364   to advise the client not to attempt a range request.
365</t>
366</section>
367</section>
368
369
370<section title="Range Requests" anchor="range.requests">
371<section title="Range" anchor="header.range">
372  <iref primary="true" item="Range header field" x:for-anchor=""/>
373  <x:anchor-alias value="Range"/>
374  <x:anchor-alias value="other-ranges-specifier"/>
375  <x:anchor-alias value="other-range-set"/>
376<t>
377   The "Range" header field on a GET request modifies the method semantics to
378   request transfer of only one or more subranges of the selected
379   representation data, rather than the entire selected representation data.
380</t>
381<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Range"/>
382  <x:ref>Range</x:ref> = <x:ref>byte-ranges-specifier</x:ref> / <x:ref>other-ranges-specifier</x:ref>
383  <x:ref>other-ranges-specifier</x:ref> = <x:ref>other-range-unit</x:ref> "=" <x:ref>other-range-set</x:ref>
384  <x:ref>other-range-set</x:ref> = 1*<x:ref>CHAR</x:ref>
385</artwork></figure>
386<t>
387   A server &MAY; ignore the Range header field. However, origin servers and
388   intermediate caches ought to support byte ranges when possible, since Range
389   supports efficient recovery from partially failed transfers and partial
390   retrieval of large representations. A server &MUST; ignore a Range header
391   field received with a request method other than GET.
392</t>
393<t>
394   An origin server &MUST; ignore a Range header field that contains a range
395   unit it does not understand. A proxy &MAY; discard a Range header
396   field that contains a range unit it does not understand.
397</t>
398<t>
399   A server that supports range requests &MAY; ignore or reject a
400   <x:ref>Range</x:ref> header field that consists of more than two
401   overlapping ranges, or a set of many small ranges that are not listed
402   in ascending order, since both are indications of either a broken client or
403   a deliberate denial of service attack (<xref target="overlapping.ranges"/>).
404   A client &SHOULD-NOT; request multiple ranges that are inherently less
405   efficient to process and transfer than a single range that encompasses the
406   same data.
407</t>
408<t>
409   A client that is requesting multiple ranges &SHOULD; list those ranges in
410   ascending order (the order in which they would typically be received in a
411   complete representation) unless there is a specific need to request a later
412   part earlier. For example, a user agent processing a large representation
413   with an internal catalog of parts might need to request later parts first,
414   particularly if the representation consists of pages stored in reverse
415   order and the user agent wishes to transfer one page at a time.
416</t>
417<t>
418   The Range header field is evaluated after evaluating the precondition header
419   fields defined in <xref target="Part4"/>, and only if the result in absence
420   of the Range header field would be a <x:ref>200 (OK)</x:ref> response. In
421   other words, Range is ignored when a conditional GET would result in a
422   <x:ref>304 (Not Modified)</x:ref> response.
423</t>
424<t>
425   The If-Range header field (<xref target="header.if-range"/>) can be used as
426   a precondition to applying the Range header field.
427</t>
428<t>
429   If all of the preconditions are true, the server supports the Range header
430   field for the target resource, and the specified range(s) are valid and
431   satisfiable (as defined in <xref target="byte.ranges"/>), the
432   server &SHOULD; send a <x:ref>206 (Partial Content)</x:ref> response with a
433   payload containing one or more partial representations that correspond to
434   the satisfiable ranges requested, as defined in
435   <xref target="range.response"/>.
436</t>
437<t>
438   If all of the preconditions are true, the server supports the Range header
439   field for the target resource, and the specified range(s) are invalid or
440   unsatisfiable, the server &SHOULD; send a
441   <x:ref>416 (Range Not Satisfiable)</x:ref> response.
442</t>
443</section>
444
445<section title="If-Range" anchor="header.if-range">
446  <iref primary="true" item="If-Range header field" x:for-anchor=""/>
447  <x:anchor-alias value="If-Range"/>
448<t>
449   If a client has a partial copy of a representation and wishes
450   to have an up-to-date copy of the entire representation, it could use the
451   <x:ref>Range</x:ref> header field with a conditional GET (using
452   either or both of <x:ref>If-Unmodified-Since</x:ref> and
453   <x:ref>If-Match</x:ref>.) However, if the precondition fails because the
454   representation has been modified, the client would then have to make a
455   second request to obtain the entire current representation.
456</t>
457<t>
458   The "If-Range" header field allows a client to "short-circuit" the second
459   request. Informally, its meaning is: if the representation is unchanged,
460   send me the part(s) that I am requesting in Range; otherwise, send me the
461   entire representation.
462</t>
463<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-Range"/>
464  <x:ref>If-Range</x:ref> = <x:ref>entity-tag</x:ref> / <x:ref>HTTP-date</x:ref>
465</artwork></figure>
466<t>
467   A client &MUST-NOT; generate an If-Range header field in a request that
468   does not contain a <x:ref>Range</x:ref> header field.
469   A server &MUST; ignore an If-Range header field received in a request that
470   does not contain a <x:ref>Range</x:ref> header field.
471   An origin server &MUST; ignore an If-Range header field received in a
472   request for a target resource that does not support Range requests.
473</t>
474<t>
475   A client &MUST-NOT; generate an If-Range header field containing an
476   entity-tag that is marked as weak.
477   A client &MUST-NOT; generate an If-Range header field containing an
478   <x:ref>HTTP-date</x:ref> unless the client has no entity-tag for
479   the corresponding representation and the date is a strong validator
480   in the sense defined by &lastmod-comparison;.
481</t>
482<t>
483   A server that evaluates an If-Range precondition &MUST; use the strong
484   comparison function when comparing entity-tags (&entity-tag-comparison;)
485   and &MUST; evaluate the condition as false if an <x:ref>HTTP-date</x:ref>
486   validator is provided that is not a strong validator in the sense defined
487   by &lastmod-comparison;.
488   (A server can distinguish between a valid <x:ref>HTTP-date</x:ref> and any
489   form of entity-tag by examining the first two characters.)
490</t>
491<t>
492   If the validator given in the If-Range header field matches the current
493   validator for the selected representation of the target resource, then
494   the server &SHOULD; process the <x:ref>Range</x:ref> header field as
495   requested. If the validator does not match, the server &MUST; ignore the
496   <x:ref>Range</x:ref> header field.
497</t>
498</section>
499</section>
500
501
502<section title="Responses to a Range Request" anchor="range.response">
503
504<section title="206 Partial Content" anchor="status.206">
505  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
506  <x:anchor-alias value="206"/>
507  <x:anchor-alias value="206 (Partial Content)"/>
508<t>
509   The <x:dfn>206 (Partial Content)</x:dfn> status code indicates that the
510   server is successfully fulfilling a range request for the target resource
511   by transferring one or more parts of the selected representation that
512   correspond to the satisfiable ranges found in the request's
513   <x:ref>Range</x:ref> header field (<xref target="header.range"/>).
514</t>
515<t>
516   If a single part is being transferred, the server generating the 206
517   response &MUST; generate a <x:ref>Content-Range</x:ref> header field,
518   describing what range of the selected representation is enclosed, and a
519   payload consisting of the range. For example:
520</t>
521<figure><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
522HTTP/1.1 206 Partial Content
523Date: Wed, 15 Nov 1995 06:25:24 GMT
524Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
525Content-Range: bytes 21010-47021/47022
526Content-Length: 26012
527Content-Type: image/gif
528
529... 26012 bytes of partial image data ...
530</artwork></figure>
531<t>
532   If multiple parts are being transferred, the server generating the 206
533   response &MUST; generate a "multipart/byteranges" payload, as defined
534   in <xref target="internet.media.type.multipart.byteranges"/>, and a
535   <x:ref>Content-Type</x:ref> header field containing the
536   multipart/byteranges media type and its required boundary parameter.
537   To avoid confusion with single part responses, a server &MUST-NOT; generate
538   a <x:ref>Content-Range</x:ref> header field in the HTTP header section of a
539   multiple part response (this field will be sent in each part instead).
540</t>
541<t>
542   Within the header area of each body part in the multipart payload, the
543   server &MUST; generate a <x:ref>Content-Range</x:ref> header field
544   corresponding to the range being enclosed in that body part.
545   If the selected representation would have had a <x:ref>Content-Type</x:ref>
546   header field in a <x:ref>200 (OK)</x:ref> response, the server &SHOULD;
547   generate that same <x:ref>Content-Type</x:ref> field in the header area of
548   each body part. For example:
549</t>
550<figure><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
551HTTP/1.1 206 Partial Content
552Date: Wed, 15 Nov 1995 06:25:24 GMT
553Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
554Content-Length: 1741
555Content-Type: multipart/byteranges; boundary=THIS_STRING_SEPARATES
556
557--THIS_STRING_SEPARATES
558Content-Type: application/pdf
559Content-Range: bytes 500-999/8000
560
561...the first range...
562--THIS_STRING_SEPARATES
563Content-Type: application/pdf
564Content-Range: bytes 7000-7999/8000
565
566...the second range
567--THIS_STRING_SEPARATES--
568</artwork></figure>
569<t>
570   When multiple ranges are requested, a server &MAY; coalesce any of the
571   ranges that overlap or that are separated by a gap that is smaller than the
572   overhead of sending multiple parts, regardless of the order in which the
573   corresponding byte-range-spec appeared in the received <x:ref>Range</x:ref>
574   header field. Since the typical overhead between parts of a
575   multipart/byteranges payload is around 80 bytes, depending on the selected
576   representation's media type and the chosen boundary parameter length, it
577   can be less efficient to transfer many small disjoint parts than it is to
578   transfer the entire selected representation.
579</t>
580<t>
581   A server &MUST-NOT; generate a multipart response to a request for a single
582   range, since a client that does not request multiple parts might not
583   support multipart responses. However, a server &MAY; generate a
584   multipart/byteranges payload with only a single body part if multiple
585   ranges were requested and only one range was found to be satisfiable or
586   only one range remained after coalescing.
587   A client that cannot process a multipart/byteranges response &MUST-NOT;
588   generate a request that asks for multiple ranges.
589</t>
590<t>
591   When a multipart response payload is generated, the server &SHOULD; send
592   the parts in the same order that the corresponding byte-range-spec appeared
593   in the received <x:ref>Range</x:ref> header field, excluding those ranges
594   that were deemed unsatisfiable or that were coalesced into other ranges.
595   A client that receives a multipart response &MUST; inspect the
596   <x:ref>Content-Range</x:ref> header field present in each body part in
597   order to determine which range is contained in that body part; a client
598   cannot rely on receiving the same ranges that it requested, nor the same
599   order that it requested.
600</t>
601<t>
602   When a 206 response is generated, the server &MUST; generate the following
603   header fields, in addition to those required above, if the field would
604   have been sent in a <x:ref>200 (OK)</x:ref> response to the same request:
605   <x:ref>Date</x:ref>, <x:ref>Cache-Control</x:ref>, <x:ref>ETag</x:ref>,
606   <x:ref>Expires</x:ref>, <x:ref>Content-Location</x:ref>, and
607   <x:ref>Vary</x:ref>.
608</t>
609<t>
610   If a 206 is generated in response to a request with an <x:ref>If-Range</x:ref>
611   header field, the sender &SHOULD-NOT; generate other representation header
612   fields beyond those required above, because the client is understood to
613   already have a prior response containing those header fields.
614   Otherwise, the sender &MUST; generate all of the representation header
615   fields that would have been sent in a <x:ref>200 (OK)</x:ref> response
616   to the same request.
617</t>
618<t>
619   A 206 response is cacheable unless otherwise indicated by
620   explicit cache controls (see &p6-heuristic;).
621</t>
622</section>
623
624<section title="Content-Range" anchor="header.content-range">
625  <iref primary="true" item="Content-Range header field" x:for-anchor=""/>
626  <x:anchor-alias value="Content-Range"/>
627  <x:anchor-alias value="byte-content-range"/>
628  <x:anchor-alias value="byte-range-resp"/>
629  <x:anchor-alias value="byte-range"/>
630  <x:anchor-alias value="unsatisfied-range"/>
631  <x:anchor-alias value="complete-length"/>
632  <x:anchor-alias value="other-content-range"/>
633  <x:anchor-alias value="other-range-resp"/>
634<t>
635   The "Content-Range" header field is sent in a single part
636   <x:ref>206 (Partial Content)</x:ref> response to indicate the partial range
637   of the selected representation enclosed as the message payload, sent in
638   each part of a multipart 206 response to indicate the range enclosed within
639   each body part, and sent in <x:ref>416 (Range Not Satisfiable)</x:ref>
640   responses to provide information about the selected representation.
641</t>
642<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Range"/><iref primary="true" item="Grammar" subitem="byte-content-range"/><iref primary="true" item="Grammar" subitem="byte-range-resp"/><iref primary="true" item="Grammar" subitem="byte-range"/><iref primary="true" item="Grammar" subitem="unsatisfied-range"/><iref primary="true" item="Grammar" subitem="other-content-range"/><iref primary="true" item="Grammar" subitem="other-range-resp"/><iref primary="true" item="Grammar" subitem="complete-length"/>
643  <x:ref>Content-Range</x:ref>       = <x:ref>byte-content-range</x:ref>
644                      / <x:ref>other-content-range</x:ref>
645                         
646  <x:ref>byte-content-range</x:ref>  = <x:ref>bytes-unit</x:ref> <x:ref>SP</x:ref>
647                        ( <x:ref>byte-range-resp</x:ref> / <x:ref>unsatisfied-range</x:ref> )
648
649  <x:ref>byte-range-resp</x:ref>     = <x:ref>byte-range</x:ref> "/" ( <x:ref>complete-length</x:ref> / "*" )
650  <x:ref>byte-range</x:ref>          = <x:ref>first-byte-pos</x:ref> "-" <x:ref>last-byte-pos</x:ref>
651  <x:ref>unsatisfied-range</x:ref>   = "*/" <x:ref>complete-length</x:ref>
652                         
653  <x:ref>complete-length</x:ref>     = 1*<x:ref>DIGIT</x:ref>
654 
655  <x:ref>other-content-range</x:ref> = <x:ref>other-range-unit</x:ref> <x:ref>SP</x:ref> <x:ref>other-range-resp</x:ref>
656  <x:ref>other-range-resp</x:ref>    = *<x:ref>CHAR</x:ref>
657</artwork></figure>
658<t>  
659   If a <x:ref>206 (Partial Content)</x:ref> response contains a
660   <x:ref>Content-Range</x:ref> header field with a <x:ref>range unit</x:ref>
661   (<xref target="range.units"/>) that the recipient does not understand, the
662   recipient &MUST-NOT; attempt to recombine it with a stored representation.
663   A proxy that receives such a message &SHOULD; forward it downstream.
664</t>
665<t>
666   For byte ranges, a sender &SHOULD; indicate the complete length of the
667   representation from which the range has been extracted, unless the complete
668   length is unknown or difficult to determine. An asterisk character ("*") in
669   place of the complete-length indicates that the representation length was
670   unknown when the header field was generated.
671</t>
672<t>
673   The following example illustrates when the complete length of the selected
674   representation is known by the sender to be 1234 bytes:
675</t>
676<figure><artwork type="example">
677  Content-Range: bytes 42-1233/1234
678</artwork></figure>
679<t>
680   and this second example illustrates when the complete length is unknown:
681</t>
682<figure><artwork type="example">
683  Content-Range: bytes 42-1233/*
684</artwork></figure>
685<t>
686   A Content-Range field value is invalid if it contains a
687   <x:ref>byte-range-resp</x:ref> that has a <x:ref>last-byte-pos</x:ref>
688   value less than its <x:ref>first-byte-pos</x:ref> value, or a
689   <x:ref>complete-length</x:ref> value less than or equal to its
690   <x:ref>last-byte-pos</x:ref> value. The recipient of an invalid
691   <x:ref>Content-Range</x:ref> &MUST-NOT; attempt to recombine the received
692   content with a stored representation.
693</t>
694<t>
695   A server generating a <x:ref>416 (Range Not Satisfiable)</x:ref> response
696   to a byte range request &SHOULD; send a Content-Range header field with an
697   <x:ref>unsatisfied-range</x:ref> value, as in the following example:
698</t>
699<figure><artwork type="example">
700  Content-Range: bytes */1234
701</artwork></figure>
702<t>
703   The complete-length in a 416 response indicates the current length of the
704   selected representation.
705</t>
706<t>
707   The "Content-Range" header field has no meaning for status codes that do
708   not explicitly describe its semantic. For this specification, only the
709   <x:ref>206 (Partial Content)</x:ref> and
710   <x:ref>416 (Range Not Satisfiable)</x:ref> status codes describe a meaning
711   for Content-Range.
712</t>
713<t>
714   The following are examples of Content-Range values in which the
715   selected representation contains a total of 1234 bytes:
716   <list style="symbols">
717      <t>
718        The first 500 bytes:
719<figure><artwork type="example" x:indent-with="   ">
720  Content-Range: bytes 0-499/1234
721</artwork></figure>
722      </t>   
723      <t>
724        The second 500 bytes:
725<figure><artwork type="example" x:indent-with="   ">
726  Content-Range: bytes 500-999/1234
727</artwork></figure>
728      </t>   
729      <t>
730        All except for the first 500 bytes:
731<figure><artwork type="example" x:indent-with="   ">
732  Content-Range: bytes 500-1233/1234
733</artwork></figure>
734      </t>   
735      <t>
736        The last 500 bytes:
737<figure><artwork type="example" x:indent-with="   ">
738  Content-Range: bytes 734-1233/1234
739</artwork></figure>
740      </t>   
741   </list>
742</t>
743</section>
744
745<section title="Combining Ranges" anchor="combining.byte.ranges">
746<t>
747   A response might transfer only a subrange of a representation if the
748   connection closed prematurely or if the request used one or more Range
749   specifications.  After several such transfers, a client might have
750   received several ranges of the same representation.  These ranges can only
751   be safely combined if they all have in common the same strong validator
752   (&weak-and-strong-validators;).
753</t>
754<t>
755   A client that has received multiple partial responses to GET requests on a
756   target resource &MAY; combine those responses into a larger continuous
757   range if they share the same strong validator.
758</t>
759<t>
760   If the most recent response is an incomplete <x:ref>200 (OK)</x:ref>
761   response, then the header fields of that response are used for any
762   combined response and replace those of the matching stored responses.
763</t>
764<t>
765   If the most recent response is a <x:ref>206 (Partial Content)</x:ref>
766   response and at least one of the matching stored responses is a
767   <x:ref>200 (OK)</x:ref>, then the combined response header fields consist
768   of the most recent 200 response's header fields. If all of the matching
769   stored responses are 206 responses, then the stored response with the most
770   recent header fields is used as the source of header fields for the
771   combined response, except that the client &MUST; use other header fields
772   provided in the new response, aside from <x:ref>Content-Range</x:ref>, to
773   replace all instances of the corresponding header fields in the stored
774   response.
775</t>
776<t>
777   The combined response message body consists of the union of partial
778   content ranges in the new response and each of the selected responses.
779   If the union consists of the entire range of the representation, then the
780   client &MUST; process the combined response as if it were a complete
781   <x:ref>200 (OK)</x:ref> response, including a <x:ref>Content-Length</x:ref>
782   header field that reflects the complete length.
783   Otherwise, the client &MUST; process the set of continuous ranges as one of
784   the following:
785   an incomplete <x:ref>200 (OK)</x:ref> response if the combined response is
786   a prefix of the representation,
787   a single <x:ref>206 (Partial Content)</x:ref> response containing a
788   multipart/byteranges body, or
789   multiple <x:ref>206 (Partial Content)</x:ref> responses, each with one
790   continuous range that is indicated by a <x:ref>Content-Range</x:ref> header
791   field.
792</t>
793</section>
794
795<section title="416 Range Not Satisfiable" anchor="status.416">
796  <iref primary="true" item="416 Range Not Satisfiable (status code)" x:for-anchor=""/>
797  <x:anchor-alias value="416 (Range Not Satisfiable)"/>
798<t>
799   The <x:dfn>416 (Range Not Satisfiable)</x:dfn> status code indicates that
800   none of the ranges in the request's <x:ref>Range</x:ref> header field
801   (<xref target="header.range"/>) overlap the current extent of the selected
802   resource or that the set of ranges requested has been rejected due to
803   invalid ranges or an excessive request of small or overlapping ranges.
804</t>
805<t>
806   For byte ranges, failing to overlap the current extent means that the
807   <x:ref>first-byte-pos</x:ref> of all of the <x:ref>byte-range-spec</x:ref>
808   values were greater than the current length of the selected representation.
809   When this status code is generated in response to a byte range request, the
810   sender &SHOULD; generate a <x:ref>Content-Range</x:ref> header field
811   specifying the current length of the selected representation
812   (<xref target="header.content-range"/>).
813</t>
814<figure>
815<preamble>For example:</preamble>
816<artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
817HTTP/1.1 416 Range Not Satisfiable
818Date: Fri, 20 Jan 2012 15:41:54 GMT
819Content-Range: bytes */47022
820</artwork></figure>
821<x:note>
822  <t>
823    &Note; Because servers are free to ignore <x:ref>Range</x:ref>, many
824    implementations will simply respond with the entire selected representation
825    in a <x:ref>200 (OK)</x:ref> response. That is partly because
826    most clients are prepared to receive a <x:ref>200 (OK)</x:ref> to
827    complete the task (albeit less efficiently) and partly because clients
828    might not stop making an invalid partial request until they have received
829    a complete representation. Thus, clients cannot depend on receiving a
830    <x:ref>416 (Range Not Satisfiable)</x:ref> response even when it is most
831    appropriate.
832  </t>
833</x:note>
834</section>
835</section>
836
837<section title="IANA Considerations" anchor="IANA.considerations">
838
839<section title="Range Unit Registry" anchor="range.unit.registry">
840<t>
841   The HTTP Range Unit Registry defines the name space for the range
842   unit names and refers to their corresponding specifications.
843   The registry will be created and maintained at
844   <eref target="http://www.iana.org/assignments/http-parameters"/>.
845</t>
846
847<section title="Procedure" anchor="range.unit.registry.procedure">
848<t>
849   Registration of an HTTP Range Unit &MUST; include the following fields:
850   <list style="symbols">
851     <t>Name</t>
852     <t>Description</t>
853     <t>Pointer to specification text</t>
854   </list>
855</t>
856<t>
857  Values to be added to this name space require IETF Review
858  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
859</t>
860</section>
861
862<section title="Registrations" anchor="range.unit.registration">
863<t>
864   The initial HTTP Range Unit Registry shall contain the registrations
865   below:
866</t>
867<texttable align="left" suppress-title="true" anchor="iana.range.units.table">
868   <ttcol>Range Unit Name</ttcol>
869   <ttcol>Description</ttcol>
870   <ttcol>Reference</ttcol>
871
872   <c>bytes</c>
873   <c>a range of octets</c>
874   <c><xref target="byte.ranges"/></c>
875
876   <c>none</c>
877   <c>reserved as keyword, indicating no ranges are supported</c>
878   <c><xref target="header.accept-ranges"/></c>
879</texttable>
880<t>
881   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
882</t>
883</section>
884</section>
885
886<section title="Status Code Registration" anchor="status.code.registration">
887<t>
888   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
889   shall be updated with the registrations below:
890</t>
891<?BEGININC p5-range.iana-status-codes ?>
892<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
893<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
894   <ttcol>Value</ttcol>
895   <ttcol>Description</ttcol>
896   <ttcol>Reference</ttcol>
897   <c>206</c>
898   <c>Partial Content</c>
899   <c>
900      <xref target="status.206"/>
901   </c>
902   <c>416</c>
903   <c>Range Not Satisfiable</c>
904   <c>
905      <xref target="status.416"/>
906   </c>
907</texttable>
908<!--(END)-->
909<?ENDINC p5-range.iana-status-codes ?>
910</section>
911
912<section title="Header Field Registration" anchor="header.field.registration">
913<t>
914   HTTP header fields are registered within the Message Header Field Registry
915   maintained at
916   <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>.
917</t>
918<t>
919   This document defines the following HTTP header fields, so their
920   associated registry entries shall be updated according to the permanent
921   registrations below (see <xref target="BCP90"/>):
922</t>
923<?BEGININC p5-range.iana-headers ?>
924<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
925<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
926   <ttcol>Header Field Name</ttcol>
927   <ttcol>Protocol</ttcol>
928   <ttcol>Status</ttcol>
929   <ttcol>Reference</ttcol>
930
931   <c>Accept-Ranges</c>
932   <c>http</c>
933   <c>standard</c>
934   <c>
935      <xref target="header.accept-ranges"/>
936   </c>
937   <c>Content-Range</c>
938   <c>http</c>
939   <c>standard</c>
940   <c>
941      <xref target="header.content-range"/>
942   </c>
943   <c>If-Range</c>
944   <c>http</c>
945   <c>standard</c>
946   <c>
947      <xref target="header.if-range"/>
948   </c>
949   <c>Range</c>
950   <c>http</c>
951   <c>standard</c>
952   <c>
953      <xref target="header.range"/>
954   </c>
955</texttable>
956<!--(END)-->
957<?ENDINC p5-range.iana-headers ?>
958<t>
959   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
960</t>
961</section>
962
963</section>
964
965<section title="Security Considerations" anchor="security.considerations">
966<t>
967   This section is meant to inform developers, information providers, and
968   users of known security concerns specific to the HTTP/1.1 range
969   request mechanisms. More general security considerations are addressed
970   in HTTP messaging &messaging; and semantics &semantics;.
971</t>
972
973<section title="Denial of Service Attacks using Range" anchor="overlapping.ranges">
974<t>
975   Unconstrained multiple range requests are susceptible to denial of service
976   attacks because the effort required to request many overlapping ranges of
977   the same data is tiny compared to the time, memory, and bandwidth consumed
978   by attempting to serve the requested data in many parts.
979   Servers ought to ignore, coalesce, or reject egregious range requests, such
980   as requests for more than two overlapping ranges or for many small ranges
981   in a single set, particularly when the ranges are requested out of order
982   for no apparent reason. Multipart range requests are not designed to
983   support random access.
984</t>
985</section>
986</section>
987
988<section title="Acknowledgments" anchor="acks">
989<t>
990  See &acks;.
991</t>
992</section>
993</middle>
994<back>
995
996<references title="Normative References">
997
998<reference anchor="Part1">
999  <front>
1000    <title>Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</title>
1001    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1002      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1003      <address><email>fielding@gbiv.com</email></address>
1004    </author>
1005    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1006      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1007      <address><email>julian.reschke@greenbytes.de</email></address>
1008    </author>
1009    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1010  </front>
1011  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1012  <x:source href="p1-messaging.xml" basename="p1-messaging">
1013    <x:defines>Content-Length</x:defines>
1014  </x:source>
1015</reference>
1016
1017<reference anchor="Part2">
1018  <front>
1019    <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
1020    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1021      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1022      <address><email>fielding@gbiv.com</email></address>
1023    </author>
1024    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1025      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1026      <address><email>julian.reschke@greenbytes.de</email></address>
1027    </author>
1028    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1029  </front>
1030  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1031  <x:source href="p2-semantics.xml" basename="p2-semantics">
1032    <x:defines>200 (OK)</x:defines>
1033    <x:defines>410 (Gone)</x:defines>
1034    <x:defines>Content-Location</x:defines>
1035    <x:defines>Content-Type</x:defines>
1036    <x:defines>Date</x:defines>
1037    <x:defines>Location</x:defines>
1038    <x:defines>Vary</x:defines>
1039  </x:source>
1040</reference>
1041
1042<reference anchor="Part4">
1043  <front>
1044    <title>Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</title>
1045    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1046      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1047      <address><email>fielding@gbiv.com</email></address>
1048    </author>
1049    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1050      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1051      <address><email>julian.reschke@greenbytes.de</email></address>
1052    </author>
1053    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1054  </front>
1055  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1056  <x:source href="p4-conditional.xml" basename="p4-conditional">
1057    <x:defines>304 (Not Modified)</x:defines>
1058    <x:defines>ETag</x:defines>
1059    <x:defines>If-Match</x:defines>
1060    <x:defines>If-Modified-Since</x:defines>
1061    <x:defines>If-None-Match</x:defines>
1062    <x:defines>If-Unmodified-Since</x:defines>
1063    <x:defines>Last-Modified</x:defines>
1064  </x:source>
1065</reference>
1066
1067<reference anchor="Part6">
1068  <front>
1069    <title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
1070    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1071      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1072      <address><email>fielding@gbiv.com</email></address>
1073    </author>
1074    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1075      <organization>Akamai</organization>
1076      <address><email>mnot@mnot.net</email></address>
1077    </author>
1078    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1079      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1080      <address><email>julian.reschke@greenbytes.de</email></address>
1081    </author>
1082    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1083  </front>
1084  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1085  <x:source href="p6-cache.xml" basename="p6-cache">
1086    <x:defines>Cache-Control</x:defines>
1087    <x:defines>Expires</x:defines>
1088  </x:source>
1089</reference>
1090
1091<reference anchor="RFC2046">
1092  <front>
1093    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
1094    <author initials="N." surname="Freed" fullname="Ned Freed">
1095      <organization>Innosoft International, Inc.</organization>
1096      <address><email>ned@innosoft.com</email></address>
1097    </author>
1098    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1099      <organization>First Virtual Holdings</organization>
1100      <address><email>nsb@nsb.fv.com</email></address>
1101    </author>
1102    <date month="November" year="1996"/>
1103  </front>
1104  <seriesInfo name="RFC" value="2046"/>
1105</reference>
1106
1107<reference anchor="RFC2119">
1108  <front>
1109    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
1110    <author initials="S." surname="Bradner" fullname="Scott Bradner">
1111      <organization>Harvard University</organization>
1112      <address><email>sob@harvard.edu</email></address>
1113    </author>
1114    <date month="March" year="1997"/>
1115  </front>
1116  <seriesInfo name="BCP" value="14"/>
1117  <seriesInfo name="RFC" value="2119"/>
1118</reference>
1119
1120<reference anchor="RFC5234">
1121  <front>
1122    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
1123    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
1124      <organization>Brandenburg InternetWorking</organization>
1125      <address>
1126        <email>dcrocker@bbiw.net</email>
1127      </address> 
1128    </author>
1129    <author initials="P." surname="Overell" fullname="Paul Overell">
1130      <organization>THUS plc.</organization>
1131      <address>
1132        <email>paul.overell@thus.net</email>
1133      </address>
1134    </author>
1135    <date month="January" year="2008"/>
1136  </front>
1137  <seriesInfo name="STD" value="68"/>
1138  <seriesInfo name="RFC" value="5234"/>
1139</reference>
1140
1141</references>
1142
1143<references title="Informative References">
1144
1145<reference anchor="RFC2616">
1146  <front>
1147    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
1148    <author initials="R." surname="Fielding" fullname="R. Fielding">
1149      <organization>University of California, Irvine</organization>
1150      <address><email>fielding@ics.uci.edu</email></address>
1151    </author>
1152    <author initials="J." surname="Gettys" fullname="J. Gettys">
1153      <organization>W3C</organization>
1154      <address><email>jg@w3.org</email></address>
1155    </author>
1156    <author initials="J." surname="Mogul" fullname="J. Mogul">
1157      <organization>Compaq Computer Corporation</organization>
1158      <address><email>mogul@wrl.dec.com</email></address>
1159    </author>
1160    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
1161      <organization>MIT Laboratory for Computer Science</organization>
1162      <address><email>frystyk@w3.org</email></address>
1163    </author>
1164    <author initials="L." surname="Masinter" fullname="L. Masinter">
1165      <organization>Xerox Corporation</organization>
1166      <address><email>masinter@parc.xerox.com</email></address>
1167    </author>
1168    <author initials="P." surname="Leach" fullname="P. Leach">
1169      <organization>Microsoft Corporation</organization>
1170      <address><email>paulle@microsoft.com</email></address>
1171    </author>
1172    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
1173      <organization>W3C</organization>
1174      <address><email>timbl@w3.org</email></address>
1175    </author>
1176    <date month="June" year="1999"/>
1177  </front>
1178  <seriesInfo name="RFC" value="2616"/>
1179</reference>
1180
1181<reference anchor='BCP90'>
1182  <front>
1183    <title>Registration Procedures for Message Header Fields</title>
1184    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
1185      <organization>Nine by Nine</organization>
1186      <address><email>GK-IETF@ninebynine.org</email></address>
1187    </author>
1188    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
1189      <organization>BEA Systems</organization>
1190      <address><email>mnot@pobox.com</email></address>
1191    </author>
1192    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
1193      <organization>HP Labs</organization>
1194      <address><email>JeffMogul@acm.org</email></address>
1195    </author>
1196    <date year='2004' month='September' />
1197  </front>
1198  <seriesInfo name='BCP' value='90' />
1199  <seriesInfo name='RFC' value='3864' />
1200</reference>
1201
1202<reference anchor="BCP13">
1203  <front>
1204    <title>Media Type Specifications and Registration Procedures</title>
1205    <author initials="N." surname="Freed" fullname="Ned Freed">
1206      <organization>Oracle</organization>
1207      <address>
1208        <email>ned+ietf@mrochek.com</email>
1209      </address>
1210    </author>
1211    <author initials="J." surname="Klensin" fullname="John C. Klensin">
1212      <address>
1213        <email>john+ietf@jck.com</email>
1214      </address>
1215    </author>
1216    <author initials="T." surname="Hansen" fullname="Tony Hansen">
1217      <organization>AT&amp;T Laboratories</organization>
1218      <address>
1219        <email>tony+mtsuffix@maillennium.att.com</email>
1220      </address>
1221    </author>
1222    <date year="2013" month="January"/>
1223  </front>
1224  <seriesInfo name="BCP" value="13"/>
1225  <seriesInfo name="RFC" value="6838"/>
1226</reference>
1227
1228<reference anchor='RFC5226'>
1229  <front>
1230    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
1231    <author initials='T.' surname='Narten' fullname='T. Narten'>
1232      <organization>IBM</organization>
1233      <address><email>narten@us.ibm.com</email></address>
1234    </author>
1235    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
1236      <organization>Google</organization>
1237      <address><email>Harald@Alvestrand.no</email></address>
1238    </author>
1239    <date year='2008' month='May' />
1240  </front>
1241  <seriesInfo name='BCP' value='26' />
1242  <seriesInfo name='RFC' value='5226' />
1243</reference>
1244
1245</references>
1246
1247<section title="Internet Media Type multipart/byteranges" anchor="internet.media.type.multipart.byteranges">
1248<iref item="Media Type" subitem="multipart/byteranges" primary="true"/>
1249<iref item="multipart/byteranges Media Type" primary="true"/>
1250<t>
1251   When a <x:ref>206 (Partial Content)</x:ref> response message includes the
1252   content of multiple ranges, they are transmitted as body parts in a
1253   multipart message body (<xref target="RFC2046" x:fmt="," x:sec="5.1"/>)
1254   with the media type of "multipart/byteranges".  The following definition is
1255   to be registered with IANA <xref target="BCP13"/>.
1256</t>
1257<t>
1258   The multipart/byteranges media type includes one or more body parts, each
1259   with its own <x:ref>Content-Type</x:ref> and <x:ref>Content-Range</x:ref>
1260   fields. The required boundary parameter specifies the boundary string used
1261   to separate each body part.
1262</t>
1263<t>
1264  <list style="hanging" x:indent="12em">
1265    <t hangText="Type name:">
1266      multipart
1267    </t>
1268    <t hangText="Subtype name:">
1269      byteranges
1270    </t>
1271    <t hangText="Required parameters:">
1272      boundary
1273    </t>
1274    <t hangText="Optional parameters:">
1275      none
1276    </t>
1277    <t hangText="Encoding considerations:">
1278      only "7bit", "8bit", or "binary" are permitted
1279    </t>
1280    <t hangText="Security considerations:">
1281      none
1282    </t>
1283    <t hangText="Interoperability considerations:">
1284      none
1285    </t>
1286    <t hangText="Published specification:">
1287      This specification (see <xref target="internet.media.type.multipart.byteranges"/>).
1288    </t>
1289    <t hangText="Applications that use this media type:">
1290      HTTP components supporting multiple ranges in a single request.
1291    </t>
1292    <t hangText="Additional information:">
1293      <list style="hanging">
1294        <t hangText="Magic number(s):">none</t>
1295        <t hangText="File extension(s):">none</t>
1296        <t hangText="Macintosh file type code(s):">none</t>
1297      </list>
1298    </t>
1299    <t hangText="Person and email address to contact for further information:">
1300      See Authors Section.
1301    </t>
1302    <t hangText="Intended usage:">
1303      COMMON
1304    </t>
1305    <t hangText="Restrictions on usage:">
1306      none
1307    </t>
1308    <t hangText="Author:">
1309      See Authors Section.
1310    </t>
1311    <t hangText="Change controller:">
1312      IESG
1313    </t>
1314  </list>
1315</t>
1316<t>
1317  Implementation Notes:
1318  <list style="numbers">
1319      <t>Additional CRLFs might precede the first boundary string in the body.</t>
1320
1321      <t>Although <xref target="RFC2046"/> permits the boundary string to be
1322         quoted, some existing implementations handle a quoted boundary
1323         string incorrectly.</t>
1324
1325      <t>A number of clients and servers were coded to an early draft
1326         of the byteranges specification that used a media type of
1327         multipart/x-byteranges<iref item="multipart/x-byteranges Media Type"/><iref item="Media Type" subitem="multipart/x-byteranges"/>,
1328         which is almost (but not quite) compatible with this type.</t>
1329  </list>
1330</t>
1331<t>
1332   Despite the name, the "multipart/byteranges" media type is not limited to
1333   byte ranges. The following example uses an "exampleunit" range unit:
1334</t>
1335<figure><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
1336HTTP/1.1 206 Partial Content
1337Date: Tue, 14 Nov 1995 06:25:24 GMT
1338Last-Modified: Tue, 14 July 04:58:08 GMT
1339Content-Length: 2331785
1340Content-Type: multipart/byteranges; boundary=THIS_STRING_SEPARATES
1341
1342--THIS_STRING_SEPARATES
1343Content-Type: video/example
1344Content-Range: exampleunit 1.2-4.3/25
1345
1346...the first range...
1347--THIS_STRING_SEPARATES
1348Content-Type: video/example
1349Content-Range: exampleunit 11.2-14.3/25
1350
1351...the second range
1352--THIS_STRING_SEPARATES--
1353</artwork>
1354</figure>
1355</section>
1356
1357<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
1358<t>
1359  Servers are given more leeway in how they respond to a range request,
1360  in order to mitigate abuse by malicious (or just greedy) clients.
1361  (<xref target="header.range"/>)
1362</t>
1363<t>
1364  A weak validator cannot be used in a <x:ref>206</x:ref> response.
1365  (<xref target="status.206"/>)
1366</t>
1367<t>
1368  The Content-Range header field only has meaning when the status code
1369  explicitly defines its use.
1370  (<xref target="header.content-range" />)
1371</t>
1372<t>
1373  This specification introduces a Range Unit Registry.
1374  (<xref target="range.unit.registry"/>)
1375</t>
1376<t>
1377  multipart/byteranges can consist of a single part.
1378  (<xref target="internet.media.type.multipart.byteranges"/>)
1379</t>
1380</section>
1381
1382<section title="Imported ABNF" anchor="imported.abnf">
1383  <x:anchor-alias value="ALPHA"/>
1384  <x:anchor-alias value="CHAR"/>
1385  <x:anchor-alias value="CR"/>
1386  <x:anchor-alias value="DIGIT"/>
1387  <x:anchor-alias value="LF"/>
1388  <x:anchor-alias value="OCTET"/>
1389  <x:anchor-alias value="SP"/>
1390  <x:anchor-alias value="VCHAR"/>
1391  <x:anchor-alias value="token"/>
1392  <x:anchor-alias value="OWS"/>
1393  <x:anchor-alias value="HTTP-date"/>
1394  <x:anchor-alias value="entity-tag"/>
1395<t>
1396  The following core rules are included by
1397  reference, as defined in <xref target="RFC5234" x:fmt="of" x:sec="B.1"/>:
1398  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
1399  DIGIT (decimal 0-9), DQUOTE (double quote),
1400  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
1401  OCTET (any 8-bit sequence of data), SP (space), and
1402  VCHAR (any visible US-ASCII character).
1403</t>
1404<t>
1405  Note that all rules derived from <x:ref>token</x:ref> are to
1406  be compared case-insensitively, like <x:ref>range-unit</x:ref> and
1407  <x:ref>acceptable-ranges</x:ref>.
1408</t>
1409<t>
1410  The rules below are defined in <xref target="Part1"/>:
1411</t>
1412<figure><artwork type="abnf2616">
1413  <x:ref>OWS</x:ref>        = &lt;OWS, defined in &whitespace;&gt;
1414  <x:ref>token</x:ref>      = &lt;token, defined in &field-components;&gt;
1415</artwork></figure>
1416<t>
1417  The rules below are defined in other parts:
1418</t>
1419<figure><artwork type="abnf2616">
1420  <x:ref>HTTP-date</x:ref>  = &lt;HTTP-date, defined in &http-date;&gt;
1421  <x:ref>entity-tag</x:ref> = &lt;entity-tag, defined in &entity-tags;&gt;
1422</artwork></figure>
1423</section>
1424
1425<?BEGININC p5-range.abnf-appendix ?>
1426<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
1427<t>
1428  In the collected ABNF below, list rules are expanded as per <xref target="Part1" x:rel="#notation"/>.
1429</t><figure>
1430<artwork type="abnf" name="p5-range.parsed-abnf">
1431<x:ref>Accept-Ranges</x:ref> = acceptable-ranges
1432
1433<x:ref>Content-Range</x:ref> = byte-content-range / other-content-range
1434
1435<x:ref>HTTP-date</x:ref> = &lt;HTTP-date, defined in [Part2], Section 7.1.1.1&gt;
1436
1437<x:ref>If-Range</x:ref> = entity-tag / HTTP-date
1438
1439<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.3&gt;
1440
1441<x:ref>Range</x:ref> = byte-ranges-specifier / other-ranges-specifier
1442
1443<x:ref>acceptable-ranges</x:ref> = ( *( "," OWS ) range-unit *( OWS "," [ OWS
1444 range-unit ] ) ) / "none"
1445
1446<x:ref>byte-content-range</x:ref> = bytes-unit SP ( byte-range-resp /
1447 unsatisfied-range )
1448<x:ref>byte-range</x:ref> = first-byte-pos "-" last-byte-pos
1449<x:ref>byte-range-resp</x:ref> = byte-range "/" ( complete-length / "*" )
1450<x:ref>byte-range-set</x:ref> = *( "," OWS ) ( byte-range-spec /
1451 suffix-byte-range-spec ) *( OWS "," [ OWS ( byte-range-spec /
1452 suffix-byte-range-spec ) ] )
1453<x:ref>byte-range-spec</x:ref> = first-byte-pos "-" [ last-byte-pos ]
1454<x:ref>byte-ranges-specifier</x:ref> = bytes-unit "=" byte-range-set
1455<x:ref>bytes-unit</x:ref> = "bytes"
1456
1457<x:ref>complete-length</x:ref> = 1*DIGIT
1458
1459<x:ref>entity-tag</x:ref> = &lt;entity-tag, defined in [Part4], Section 2.3&gt;
1460
1461<x:ref>first-byte-pos</x:ref> = 1*DIGIT
1462
1463<x:ref>last-byte-pos</x:ref> = 1*DIGIT
1464
1465<x:ref>other-content-range</x:ref> = other-range-unit SP other-range-resp
1466<x:ref>other-range-resp</x:ref> = *CHAR
1467<x:ref>other-range-set</x:ref> = 1*CHAR
1468<x:ref>other-range-unit</x:ref> = token
1469<x:ref>other-ranges-specifier</x:ref> = other-range-unit "=" other-range-set
1470
1471<x:ref>range-unit</x:ref> = bytes-unit / other-range-unit
1472
1473<x:ref>suffix-byte-range-spec</x:ref> = "-" suffix-length
1474<x:ref>suffix-length</x:ref> = 1*DIGIT
1475
1476<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.6&gt;
1477
1478<x:ref>unsatisfied-range</x:ref> = "*/" complete-length
1479</artwork>
1480</figure>
1481</section>
1482<?ENDINC p5-range.abnf-appendix ?>
1483
1484
1485<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
1486<t>
1487  Changes up to the first Working Group Last Call draft are summarized
1488  in <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p5-range-19#appendix-D"/>.
1489</t>
1490
1491<section title="Since draft-ietf-httpbis-p5-range-19" anchor="changes.since.19">
1492<t>
1493  Closed issues:
1494  <list style="symbols">
1495    <t>
1496      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/358"/>:
1497      "ABNF list expansion code problem"
1498    </t>
1499    <t>
1500      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/361"/>:
1501      "ABNF requirements for recipients"
1502    </t>
1503    <t>
1504      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/367"/>:
1505      "reserve 'none' as byte range unit"
1506    </t>
1507    <t>
1508      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/368"/>:
1509      "note introduction of new IANA registries as normative changes"
1510    </t>
1511    <t>
1512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/369"/>:
1513      "range units vs leading zeroes vs size"
1514    </t>
1515  </list>
1516</t>
1517</section>
1518
1519<section title="Since draft-ietf-httpbis-p5-range-20" anchor="changes.since.20">
1520<t>
1521  <list style="symbols">
1522    <t>
1523      Conformance criteria and considerations regarding error handling are
1524      now defined in Part 1.
1525    </t>
1526  </list>
1527</t>
1528</section>
1529
1530<section title="Since draft-ietf-httpbis-p5-range-21" anchor="changes.since.21">
1531<t>
1532  Closed issues:
1533  <list style="symbols">
1534    <t>
1535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/175"/>:
1536      "Security consideration: range flooding"
1537    </t>
1538    <t>
1539      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/223"/>:
1540      "Allowing heuristic caching for new status codes"
1541    </t>
1542    <t>
1543      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/311"/>:
1544      "Add limitations to Range to reduce its use as a denial-of-service tool"
1545    </t>
1546    <t>
1547      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/407"/>:
1548      "416 and multipart/byteranges"
1549    </t>
1550  </list>
1551</t>
1552</section>
1553
1554<section title="Since draft-ietf-httpbis-p5-range-22" anchor="changes.since.22">
1555<t>
1556  Closed issues:
1557  <list style="symbols">
1558    <t>
1559      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/436"/>:
1560      "explain list expansion in ABNF appendices"
1561    </t>
1562    <t>
1563      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/437"/>:
1564      "incorrect example dates"
1565    </t>
1566    <t>
1567      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/438"/>:
1568      "media type registration template issues"
1569    </t>
1570    <t>
1571      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/462"/>:
1572      "Editorial suggestions"
1573    </t>
1574    <t>
1575      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/485"/>:
1576      "MUSTs and other feedback"
1577    </t>
1578  </list>
1579</t>
1580</section>
1581
1582<section title="Since draft-ietf-httpbis-p5-range-23" anchor="changes.since.23">
1583<t>
1584  Closed issues:
1585  <list style="symbols">
1586    <t>
1587      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/489"/>:
1588      "is P5's definition of strong validator consistent with P4?"
1589    </t>
1590    <t>
1591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/490"/>:
1592      "p5 editorial comments"
1593    </t>
1594  </list>
1595</t>
1596</section>
1597</section>
1598
1599</back>
1600</rfc>
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