source: draft-ietf-httpbis/latest/p5-range.xml @ 203

Last change on this file since 203 was 203, checked in by julian.reschke@…, 12 years ago

Add processing instructions for inline comments throughout, and use them for the IANA TBDs.

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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 "February">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY weak-and-strong-validators "<xref target='Part4' x:rel='#weak.and.strong.validators' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19]>
20<?rfc toc="yes" ?>
21<?rfc symrefs="yes" ?>
22<?rfc sortrefs="yes" ?>
23<?rfc compact="yes"?>
24<?rfc subcompact="no" ?>
25<?rfc linkmailto="no" ?>
26<?rfc editing="no" ?>
27<?rfc comments="yes"?>
28<?rfc inline="yes"?>
29<?rfc-ext allow-markup-in-artwork="yes" ?>
30<?rfc-ext include-references-in-index="yes" ?>
31<rfc obsoletes="2616" category="std"
32     ipr="full3978" docName="draft-ietf-httpbis-p5-range-&ID-VERSION;"
33     xmlns:x='http://purl.org/net/xml2rfc/ext'>
34<front>
35
36  <title abbrev="HTTP/1.1, Part 5">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
37
38  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
39    <organization abbrev="Day Software">Day Software</organization>
40    <address>
41      <postal>
42        <street>23 Corporate Plaza DR, Suite 280</street>
43        <city>Newport Beach</city>
44        <region>CA</region>
45        <code>92660</code>
46        <country>USA</country>
47      </postal>
48      <phone>+1-949-706-5300</phone>
49      <facsimile>+1-949-706-5305</facsimile>
50      <email>fielding@gbiv.com</email>
51      <uri>http://roy.gbiv.com/</uri>
52    </address>
53  </author>
54
55  <author initials="J." surname="Gettys" fullname="Jim Gettys">
56    <organization>One Laptop per Child</organization>
57    <address>
58      <postal>
59        <street>21 Oak Knoll Road</street>
60        <city>Carlisle</city>
61        <region>MA</region>
62        <code>01741</code>
63        <country>USA</country>
64      </postal>
65      <email>jg@laptop.org</email>
66      <uri>http://www.laptop.org/</uri>
67    </address>
68  </author>
69 
70  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
71    <organization abbrev="HP">Hewlett-Packard Company</organization>
72    <address>
73      <postal>
74        <street>HP Labs, Large Scale Systems Group</street>
75        <street>1501 Page Mill Road, MS 1177</street>
76        <city>Palo Alto</city>
77        <region>CA</region>
78        <code>94304</code>
79        <country>USA</country>
80      </postal>
81      <email>JeffMogul@acm.org</email>
82    </address>
83  </author>
84
85  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
86    <organization abbrev="Microsoft">Microsoft Corporation</organization>
87    <address>
88      <postal>
89        <street>1 Microsoft Way</street>
90        <city>Redmond</city>
91        <region>WA</region>
92        <code>98052</code>
93        <country>USA</country>
94      </postal>
95      <email>henrikn@microsoft.com</email>
96    </address>
97  </author>
98
99  <author initials="L." surname="Masinter" fullname="Larry Masinter">
100    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
101    <address>
102      <postal>
103        <street>345 Park Ave</street>
104        <city>San Jose</city>
105        <region>CA</region>
106        <code>95110</code>
107        <country>USA</country>
108      </postal>
109      <email>LMM@acm.org</email>
110      <uri>http://larry.masinter.net/</uri>
111    </address>
112  </author>
113 
114  <author initials="P." surname="Leach" fullname="Paul J. Leach">
115    <organization abbrev="Microsoft">Microsoft Corporation</organization>
116    <address>
117      <postal>
118        <street>1 Microsoft Way</street>
119        <city>Redmond</city>
120        <region>WA</region>
121        <code>98052</code>
122      </postal>
123      <email>paulle@microsoft.com</email>
124    </address>
125  </author>
126   
127  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
128    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
129    <address>
130      <postal>
131        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
132        <street>The Stata Center, Building 32</street>
133        <street>32 Vassar Street</street>
134        <city>Cambridge</city>
135        <region>MA</region>
136        <code>02139</code>
137        <country>USA</country>
138      </postal>
139      <email>timbl@w3.org</email>
140      <uri>http://www.w3.org/People/Berners-Lee/</uri>
141    </address>
142  </author>
143
144  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
145    <organization abbrev="W3C">World Wide Web Consortium</organization>
146    <address>
147      <postal>
148        <street>W3C / ERCIM</street>
149        <street>2004, rte des Lucioles</street>
150        <city>Sophia-Antipolis</city>
151        <region>AM</region>
152        <code>06902</code>
153        <country>France</country>
154      </postal>
155      <email>ylafon@w3.org</email>
156      <uri>http://www.raubacapeu.net/people/yves/</uri>
157    </address>
158  </author>
159
160  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
161    <organization abbrev="greenbytes">greenbytes GmbH</organization>
162    <address>
163      <postal>
164        <street>Hafenweg 16</street>
165        <city>Muenster</city><region>NW</region><code>48155</code>
166        <country>Germany</country>
167      </postal>
168      <phone>+49 251 2807760</phone>   
169      <facsimile>+49 251 2807761</facsimile>   
170      <email>julian.reschke@greenbytes.de</email>       
171      <uri>http://greenbytes.de/tech/webdav/</uri>     
172    </address>
173  </author>
174
175  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
176
177<abstract>
178<t>
179   The Hypertext Transfer Protocol (HTTP) is an application-level
180   protocol for distributed, collaborative, hypermedia information
181   systems. HTTP has been in use by the World Wide Web global information
182   initiative since 1990. This document is Part 5 of the seven-part specification
183   that defines the protocol referred to as "HTTP/1.1" and, taken together,
184   obsoletes RFC 2616.  Part 5 defines range-specific requests and
185   the rules for constructing and combining responses to those requests.
186</t>
187</abstract>
188
189<note title="Editorial Note (To be removed by RFC Editor)">
190  <t>
191    Discussion of this draft should take place on the HTTPBIS working group
192    mailing list (ietf-http-wg@w3.org). The current issues list is
193    at <eref target="http://www.tools.ietf.org/wg/httpbis/trac/report/11"/>
194    and related documents (including fancy diffs) can be found at
195    <eref target="http://www.tools.ietf.org/wg/httpbis/"/>.
196  </t>
197  <t>
198    This draft incorporates those issue resolutions that were either
199    collected in the original RFC2616 errata list (<eref target="http://purl.org/NET/http-errata"/>),
200    or which were agreed upon on the mailing list between October 2006 and
201    November 2007 (as published in "draft-lafon-rfc2616bis-03").
202  </t>
203</note>
204</front>
205<middle>
206<section title="Introduction" anchor="introduction">
207<t>
208   HTTP clients often encounter interrupted data transfers as a result
209   of cancelled requests or dropped connections.  When a cache has stored
210   a partial representation, it is desirable to request the remainder
211   of that representation in a subsequent request rather than transfer
212   the entire representation.
213   There are also a number of Web applications that benefit from being
214   able to request only a subset of a larger representation, such as a
215   single page of a very large document or only part of an image to be
216   rendered by a device with limited local storage.
217</t>
218<t>
219   This document defines HTTP/1.1 range requests,
220   partial responses, and the multipart/byteranges media type.
221   The protocol for range requests is an &OPTIONAL; feature of HTTP,
222   designed so resources or recipients that do not implement this feature
223   can respond as if it is a normal GET request without impacting
224   interoperability.  Partial responses are indicated by a distinct status
225   code to not be mistaken for full responses by intermediate caches
226   that might not implement the feature.
227</t>
228<t>
229   Although the HTTP range request mechanism is designed to allow for
230   extensible range types, this specification only defines requests for
231   byte ranges.
232</t>
233
234<section title="Requirements" anchor="intro.requirements">
235<t>
236   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
237   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
238   document are to be interpreted as described in <xref target="RFC2119"/>.
239</t>
240<t>
241   An implementation is not compliant if it fails to satisfy one or more
242   of the &MUST; or &REQUIRED; level requirements for the protocols it
243   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
244   level and all the &SHOULD; level requirements for its protocols is said
245   to be "unconditionally compliant"; one that satisfies all the &MUST;
246   level requirements but not all the &SHOULD; level requirements for its
247   protocols is said to be "conditionally compliant."
248</t>
249</section>
250</section>
251
252<section title="Range Units" anchor="range.units">
253<t>
254   HTTP/1.1 allows a client to request that only part (a range of) the
255   response entity be included within the response. HTTP/1.1 uses range
256   units in the Range (<xref target="header.range"/>) and Content-Range (<xref target="header.content-range"/>)
257   header fields. An entity can be broken down into subranges according
258   to various structural units.
259</t>
260<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="range-unit"/><iref primary="true" item="Grammar" subitem="bytes-unit"/><iref primary="true" item="Grammar" subitem="other-range-unit"/>
261  range-unit       = bytes-unit | other-range-unit
262  bytes-unit       = "bytes"
263  other-range-unit = token
264</artwork></figure>
265<t>
266   The only range unit defined by HTTP/1.1 is "bytes". HTTP/1.1
267   implementations &MAY; ignore ranges specified using other units.
268</t>
269<t>
270   HTTP/1.1 has been designed to allow implementations of applications
271   that do not depend on knowledge of ranges.
272</t>
273</section>
274
275<section title="Status Code Definitions">
276<section title="206 Partial Content" anchor="status.206">
277  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
278  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
279<t>
280   The server has fulfilled the partial GET request for the resource.
281   The request &MUST; have included a Range header field (<xref target="header.range"/>)
282   indicating the desired range, and &MAY; have included an If-Range
283   header field (<xref target="header.if-range"/>) to make the request conditional.
284</t>
285<t>
286   The response &MUST; include the following header fields:
287  <list style="symbols">
288    <t>
289        Either a Content-Range header field (<xref target="header.content-range"/>) indicating
290        the range included with this response, or a multipart/byteranges
291        Content-Type including Content-Range fields for each part. If a
292        Content-Length header field is present in the response, its
293        value &MUST; match the actual number of OCTETs transmitted in the
294        message-body.
295    </t>
296    <t>
297        Date
298    </t>
299    <t>
300        ETag and/or Content-Location, if the header would have been sent
301        in a 200 response to the same request
302    </t>
303    <t>
304        Expires, Cache-Control, and/or Vary, if the field-value might
305        differ from that sent in any previous response for the same
306        variant
307    </t>
308  </list>
309</t>
310<t>
311   If the 206 response is the result of an If-Range request, the response
312   &SHOULD-NOT; include other entity-headers. Otherwise, the response
313   &MUST; include all of the entity-headers that would have been returned
314   with a 200 (OK) response to the same request.
315</t>
316<t>
317   A cache &MUST-NOT; combine a 206 response with other previously cached
318   content if the ETag or Last-Modified headers do not match exactly,
319   see <xref target="combining.byte.ranges"/>.
320</t>
321<t>
322   A cache that does not support the Range and Content-Range headers
323   &MUST-NOT; cache 206 (Partial Content) responses.
324</t>
325</section>
326
327<section title="416 Requested Range Not Satisfiable" anchor="status.416">
328  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
329  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
330<t>
331   A server &SHOULD; return a response with this status code if a request
332   included a Range request-header field (<xref target="header.range"/>), and none of
333   the range-specifier values in this field overlap the current extent
334   of the selected resource, and the request did not include an If-Range
335   request-header field. (For byte-ranges, this means that the first-byte-pos
336   of all of the byte-range-spec values were greater than the
337   current length of the selected resource.)
338</t>
339<t>
340   When this status code is returned for a byte-range request, the
341   response &SHOULD; include a Content-Range entity-header field
342   specifying the current length of the selected resource (see <xref target="header.content-range"/>).
343   This response &MUST-NOT; use the multipart/byteranges content-type.
344</t>
345</section>
346</section>
347
348<section title="Combining Byte Ranges" anchor="combining.byte.ranges">
349<t>
350   A response might transfer only a subrange of the bytes of an entity-body,
351   either because the request included one or more Range
352   specifications, or because a connection was broken prematurely. After
353   several such transfers, a cache might have received several ranges of
354   the same entity-body.
355</t>
356<t>
357   If a cache has a stored non-empty set of subranges for an entity, and
358   an incoming response transfers another subrange, the cache &MAY;
359   combine the new subrange with the existing set if both the following
360   conditions are met:
361  <list style="symbols">
362    <t>Both the incoming response and the cache entry have a cache
363        validator.</t>
364    <t>The two cache validators match using the strong comparison
365        function (see &weak-and-strong-validators;).</t>
366  </list>
367</t>
368<t>
369   If either requirement is not met, the cache &MUST; use only the most
370   recent partial response (based on the Date values transmitted with
371   every response, and using the incoming response if these values are
372   equal or missing), and &MUST; discard the other partial information.
373</t>
374</section>
375
376<section title="Header Field Definitions" anchor="header.fields">
377<t>
378   This section defines the syntax and semantics of HTTP/1.1 header fields
379   related to range requests and partial responses.
380</t>
381<t>
382   For entity-header fields, both sender and recipient refer to either the
383   client or the server, depending on who sends and who receives the entity.
384</t>
385
386<section title="Accept-Ranges" anchor="header.accept-ranges">
387  <iref primary="true" item="Accept-Ranges header" x:for-anchor=""/>
388  <iref primary="true" item="Headers" subitem="Accept-Ranges" x:for-anchor=""/>
389<t>
390      The Accept-Ranges response-header field allows the server to
391      indicate its acceptance of range requests for a resource:
392</t>
393<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Ranges"/><iref primary="true" item="Grammar" subitem="acceptable-ranges"/>
394  Accept-Ranges     = "Accept-Ranges" ":" acceptable-ranges
395  acceptable-ranges = 1#range-unit | "none"
396</artwork></figure>
397<t>
398      Origin servers that accept byte-range requests &MAY; send
399</t>
400<figure><artwork type="example">
401       Accept-Ranges: bytes
402</artwork></figure>
403<t>
404      but are not required to do so. Clients &MAY; generate byte-range
405      requests without having received this header for the resource
406      involved. Range units are defined in <xref target="range.units"/>.
407</t>
408<t>
409      Servers that do not accept any kind of range request for a
410      resource &MAY; send
411</t>
412<figure><artwork type="example">
413       Accept-Ranges: none
414</artwork></figure>
415<t>
416      to advise the client not to attempt a range request.
417</t>
418</section>
419
420<section title="Content-Range" anchor="header.content-range">
421  <iref primary="true" item="Content-Range header" x:for-anchor=""/>
422  <iref primary="true" item="Headers" subitem="Content-Range" x:for-anchor=""/>
423<t>
424   The Content-Range entity-header is sent with a partial entity-body to
425   specify where in the full entity-body the partial body should be
426   applied. Range units are defined in <xref target="range.units"/>.
427</t>
428<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Range"/><iref primary="true" item="Grammar" subitem="content-range-spec"/><iref primary="true" item="Grammar" subitem="byte-content-range-spec"/><iref primary="true" item="Grammar" subitem="byte-range-resp-spec"/><iref primary="true" item="Grammar" subitem="instance-length"/>
429  Content-Range = "Content-Range" ":" content-range-spec
430 
431  content-range-spec      = byte-content-range-spec
432  byte-content-range-spec = bytes-unit SP
433                            byte-range-resp-spec "/"
434                            ( instance-length | "*" )
435 
436  byte-range-resp-spec = (first-byte-pos "-" last-byte-pos)
437                                 | "*"
438  instance-length           = 1*DIGIT
439</artwork></figure>
440<t>
441   The header &SHOULD; indicate the total length of the full entity-body,
442   unless this length is unknown or difficult to determine. The asterisk
443   "*" character means that the instance-length is unknown at the time
444   when the response was generated.
445</t>
446<t>
447   Unlike byte-ranges-specifier values (see <xref target="byte.ranges"/>), a byte-range-resp-spec
448   &MUST; only specify one range, and &MUST; contain
449   absolute byte positions for both the first and last byte of the
450   range.
451</t>
452<t>
453   A byte-content-range-spec with a byte-range-resp-spec whose last-byte-pos
454   value is less than its first-byte-pos value, or whose
455   instance-length value is less than or equal to its last-byte-pos
456   value, is invalid. The recipient of an invalid byte-content-range-spec
457   &MUST; ignore it and any content transferred along with it.
458</t>
459<t>
460   A server sending a response with status code 416 (Requested range not
461   satisfiable) &SHOULD; include a Content-Range field with a byte-range-resp-spec
462   of "*". The instance-length specifies the current length of
463   the selected resource. A response with status code 206 (Partial
464   Content) &MUST-NOT; include a Content-Range field with a byte-range-resp-spec of "*".
465</t>
466<t>
467   Examples of byte-content-range-spec values, assuming that the entity
468   contains a total of 1234 bytes:
469   <list style="symbols">
470      <t>
471        The first 500 bytes:
472<figure><artwork type="text/plain">
473   bytes 0-499/1234
474</artwork></figure>
475      </t>   
476      <t>
477        The second 500 bytes:
478<figure><artwork type="text/plain">
479   bytes 500-999/1234
480</artwork></figure>
481      </t>   
482      <t>
483        All except for the first 500 bytes:
484<figure><artwork type="text/plain">
485   bytes 500-1233/1234
486</artwork></figure>
487      </t>   
488      <t>
489        The last 500 bytes:
490<figure><artwork type="text/plain">
491   bytes 734-1233/1234
492</artwork></figure>
493      </t>   
494   </list>
495</t>
496<t>
497   When an HTTP message includes the content of a single range (for
498   example, a response to a request for a single range, or to a request
499   for a set of ranges that overlap without any holes), this content is
500   transmitted with a Content-Range header, and a Content-Length header
501   showing the number of bytes actually transferred. For example,
502</t>
503<figure><artwork type="example">
504    HTTP/1.1 206 Partial Content
505    Date: Wed, 15 Nov 1995 06:25:24 GMT
506    Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
507    Content-Range: bytes 21010-47021/47022
508    Content-Length: 26012
509    Content-Type: image/gif
510</artwork></figure>
511<t>
512   When an HTTP message includes the content of multiple ranges (for
513   example, a response to a request for multiple non-overlapping
514   ranges), these are transmitted as a multipart message. The multipart
515   media type used for this purpose is "multipart/byteranges" as defined
516   in <xref target="internet.media.type.multipart.byteranges"/>. See <xref target="changes.from.rfc.2068"/> for a compatibility issue.
517</t>
518<t>
519   A response to a request for a single range &MUST-NOT; be sent using the
520   multipart/byteranges media type.  A response to a request for
521   multiple ranges, whose result is a single range, &MAY; be sent as a
522   multipart/byteranges media type with one part. A client that cannot
523   decode a multipart/byteranges message &MUST-NOT; ask for multiple
524   byte-ranges in a single request.
525</t>
526<t>
527   When a client requests multiple byte-ranges in one request, the
528   server &SHOULD; return them in the order that they appeared in the
529   request.
530</t>
531<t>
532   If the server ignores a byte-range-spec because it is syntactically
533   invalid, the server &SHOULD; treat the request as if the invalid Range
534   header field did not exist. (Normally, this means return a 200
535   response containing the full entity).
536</t>
537<t>
538   If the server receives a request (other than one including an If-Range
539   request-header field) with an unsatisfiable Range request-header
540   field (that is, all of whose byte-range-spec values have a
541   first-byte-pos value greater than the current length of the selected
542   resource), it &SHOULD; return a response code of 416 (Requested range
543   not satisfiable) (<xref target="status.416"/>).
544  <list><t>
545      <x:h>Note:</x:h> clients cannot depend on servers to send a 416 (Requested
546      range not satisfiable) response instead of a 200 (OK) response for
547      an unsatisfiable Range request-header, since not all servers
548      implement this request-header.
549  </t></list>
550</t>
551</section>
552
553<section title="If-Range" anchor="header.if-range">
554  <iref primary="true" item="If-Range header" x:for-anchor=""/>
555  <iref primary="true" item="Headers" subitem="If-Range" x:for-anchor=""/>
556<t>
557   If a client has a partial copy of an entity in its cache, and wishes
558   to have an up-to-date copy of the entire entity in its cache, it
559   could use the Range request-header with a conditional GET (using
560   either or both of If-Unmodified-Since and If-Match.) However, if the
561   condition fails because the entity has been modified, the client
562   would then have to make a second request to obtain the entire current
563   entity-body.
564</t>
565<t>
566   The If-Range header allows a client to "short-circuit" the second
567   request. Informally, its meaning is `if the entity is unchanged, send
568   me the part(s) that I am missing; otherwise, send me the entire new
569   entity'.
570</t>
571<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-Range"/>
572  If-Range = "If-Range" ":" ( entity-tag | HTTP-date )
573</artwork></figure>
574<t>
575   If the client has no entity tag for an entity, but does have a Last-Modified
576   date, it &MAY; use that date in an If-Range header. (The
577   server can distinguish between a valid HTTP-date and any form of
578   entity-tag by examining no more than two characters.) The If-Range
579   header &SHOULD; only be used together with a Range header, and &MUST; be
580   ignored if the request does not include a Range header, or if the
581   server does not support the sub-range operation.
582</t>
583<t>
584   If the entity tag given in the If-Range header matches the current
585   entity tag for the entity, then the server &SHOULD; provide the
586   specified sub-range of the entity using a 206 (Partial Content)
587   response. If the entity tag does not match, then the server &SHOULD;
588   return the entire entity using a 200 (OK) response.
589</t>
590</section>
591
592<section title="Range" anchor="header.range">
593  <iref primary="true" item="Range header" x:for-anchor=""/>
594  <iref primary="true" item="Headers" subitem="Range" x:for-anchor=""/>
595
596<section title="Byte Ranges" anchor="byte.ranges">
597<t>
598   Since all HTTP entities are represented in HTTP messages as sequences
599   of bytes, the concept of a byte range is meaningful for any HTTP
600   entity. (However, not all clients and servers need to support byte-range
601   operations.)
602</t>
603<t>
604   Byte range specifications in HTTP apply to the sequence of bytes in
605   the entity-body (not necessarily the same as the message-body).
606</t>
607<t>
608   A byte range operation &MAY; specify a single range of bytes, or a set
609   of ranges within a single entity.
610</t>
611<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"/>
612  ranges-specifier = byte-ranges-specifier
613  byte-ranges-specifier = bytes-unit "=" byte-range-set
614  byte-range-set  = 1#( byte-range-spec | suffix-byte-range-spec )
615  byte-range-spec = first-byte-pos "-" [last-byte-pos]
616  first-byte-pos  = 1*DIGIT
617  last-byte-pos   = 1*DIGIT
618</artwork></figure>
619<t>
620   The first-byte-pos value in a byte-range-spec gives the byte-offset
621   of the first byte in a range. The last-byte-pos value gives the
622   byte-offset of the last byte in the range; that is, the byte
623   positions specified are inclusive. Byte offsets start at zero.
624</t>
625<t>
626   If the last-byte-pos value is present, it &MUST; be greater than or
627   equal to the first-byte-pos in that byte-range-spec, or the byte-range-spec
628   is syntactically invalid. The recipient of a byte-range-set
629   that includes one or more syntactically invalid byte-range-spec
630   values &MUST; ignore the header field that includes that byte-range-set.
631</t>
632<t>
633   If the last-byte-pos value is absent, or if the value is greater than
634   or equal to the current length of the entity-body, last-byte-pos is
635   taken to be equal to one less than the current length of the entity-body
636   in bytes.
637</t>
638<t>
639   By its choice of last-byte-pos, a client can limit the number of
640   bytes retrieved without knowing the size of the entity.
641</t>
642<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="suffix-byte-range-spec"/><iref primary="true" item="Grammar" subitem="suffix-length"/>
643  suffix-byte-range-spec = "-" suffix-length
644  suffix-length = 1*DIGIT
645</artwork></figure>
646<t>
647   A suffix-byte-range-spec is used to specify the suffix of the
648   entity-body, of a length given by the suffix-length value. (That is,
649   this form specifies the last N bytes of an entity-body.) If the
650   entity is shorter than the specified suffix-length, the entire
651   entity-body is used.
652</t>
653<t>
654   If a syntactically valid byte-range-set includes at least one byte-range-spec
655   whose first-byte-pos is less than the current length of
656   the entity-body, or at least one suffix-byte-range-spec with a non-zero
657   suffix-length, then the byte-range-set is satisfiable.
658   Otherwise, the byte-range-set is unsatisfiable. If the byte-range-set
659   is unsatisfiable, the server &SHOULD; return a response with a status
660   of 416 (Requested range not satisfiable). Otherwise, the server
661   &SHOULD; return a response with a status of 206 (Partial Content)
662   containing the satisfiable ranges of the entity-body.
663</t>
664<t>
665   Examples of byte-ranges-specifier values (assuming an entity-body of
666   length 10000):
667  <list style="symbols">
668     <t>The first 500 bytes (byte offsets 0-499, inclusive):  bytes=0-499</t>
669
670     <t>The second 500 bytes (byte offsets 500-999, inclusive):
671        bytes=500-999</t>
672
673     <t>The final 500 bytes (byte offsets 9500-9999, inclusive):
674        bytes=-500</t>
675
676     <t>Or bytes=9500-</t>
677
678     <t>The first and last bytes only (bytes 0 and 9999):  bytes=0-0,-1</t>
679
680     <t>Several legal but not canonical specifications of the second 500
681        bytes (byte offsets 500-999, inclusive):
682        <vspace/>
683         bytes=500-600,601-999<vspace/>
684         bytes=500-700,601-999</t>
685  </list>
686</t>
687</section>
688
689<section title="Range Retrieval Requests" anchor="range.retrieval.requests">
690<t>
691   HTTP retrieval requests using conditional or unconditional GET
692   methods &MAY; request one or more sub-ranges of the entity, instead of
693   the entire entity, using the Range request header, which applies to
694   the entity returned as the result of the request:
695</t>
696<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Range"/>
697  Range = "Range" ":" ranges-specifier
698</artwork></figure>
699<t>
700   A server &MAY; ignore the Range header. However, HTTP/1.1 origin
701   servers and intermediate caches ought to support byte ranges when
702   possible, since Range supports efficient recovery from partially
703   failed transfers, and supports efficient partial retrieval of large
704   entities.
705</t>
706<t>
707   If the server supports the Range header and the specified range or
708   ranges are appropriate for the entity:
709  <list style="symbols">
710     <t>The presence of a Range header in an unconditional GET modifies
711        what is returned if the GET is otherwise successful. In other
712        words, the response carries a status code of 206 (Partial
713        Content) instead of 200 (OK).</t>
714
715     <t>The presence of a Range header in a conditional GET (a request
716        using one or both of If-Modified-Since and If-None-Match, or
717        one or both of If-Unmodified-Since and If-Match) modifies what
718        is returned if the GET is otherwise successful and the
719        condition is true. It does not affect the 304 (Not Modified)
720        response returned if the conditional is false.</t>
721  </list>
722</t>
723<t>
724   In some cases, it might be more appropriate to use the If-Range
725   header (see <xref target="header.if-range"/>) in addition to the Range header.
726</t>
727<t>
728   If a proxy that supports ranges receives a Range request, forwards
729   the request to an inbound server, and receives an entire entity in
730   reply, it &SHOULD; only return the requested range to its client. It
731   &SHOULD; store the entire received response in its cache if that is
732   consistent with its cache allocation policies.
733</t>
734</section>
735</section>
736</section>
737
738<section title="IANA Considerations" anchor="IANA.considerations">
739<t>
740   <cref>TBD.</cref>
741</t>
742</section>
743
744<section title="Security Considerations" anchor="security.considerations">
745<t>
746   No additional security considerations have been identified beyond
747   those applicable to HTTP in general &messaging;.
748</t>
749</section>
750
751<section title="Acknowledgments" anchor="ack">
752<t>
753   Most of the specification of ranges is based on work originally done
754   by Ari Luotonen and John Franks, with additional input from Steve
755   Zilles, Daniel W. Connolly, Roy T. Fielding, Jim Gettys, Martin Hamilton,
756   Koen Holtman, Shel Kaplan, Paul Leach, Alex Lopez-Ortiz, Larry Masinter,
757   Jeff Mogul, Lou Montulli, David W. Morris, Luigi Rizzo, and Bill Weihl.
758</t>
759</section>
760</middle>
761<back>
762
763<references title="Normative References">
764
765<reference anchor="Part1">
766  <front>
767    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
768    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
769      <organization abbrev="Day Software">Day Software</organization>
770      <address><email>fielding@gbiv.com</email></address>
771    </author>
772    <author initials="J." surname="Gettys" fullname="Jim Gettys">
773      <organization>One Laptop per Child</organization>
774      <address><email>jg@laptop.org</email></address>
775    </author>
776    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
777      <organization abbrev="HP">Hewlett-Packard Company</organization>
778      <address><email>JeffMogul@acm.org</email></address>
779    </author>
780    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
781      <organization abbrev="Microsoft">Microsoft Corporation</organization>
782      <address><email>henrikn@microsoft.com</email></address>
783    </author>
784    <author initials="L." surname="Masinter" fullname="Larry Masinter">
785      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
786      <address><email>LMM@acm.org</email></address>
787    </author>
788    <author initials="P." surname="Leach" fullname="Paul J. Leach">
789      <organization abbrev="Microsoft">Microsoft Corporation</organization>
790      <address><email>paulle@microsoft.com</email></address>
791    </author>
792    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
793      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
794      <address><email>timbl@w3.org</email></address>
795    </author>
796    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
797      <organization abbrev="W3C">World Wide Web Consortium</organization>
798      <address><email>ylafon@w3.org</email></address>
799    </author>
800    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
801      <organization abbrev="greenbytes">greenbytes GmbH</organization>
802      <address><email>julian.reschke@greenbytes.de</email></address>
803    </author>
804    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
805  </front>
806  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
807  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
808</reference>
809
810<reference anchor="Part3">
811  <front>
812    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
813    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
814      <organization abbrev="Day Software">Day Software</organization>
815      <address><email>fielding@gbiv.com</email></address>
816    </author>
817    <author initials="J." surname="Gettys" fullname="Jim Gettys">
818      <organization>One Laptop per Child</organization>
819      <address><email>jg@laptop.org</email></address>
820    </author>
821    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
822      <organization abbrev="HP">Hewlett-Packard Company</organization>
823      <address><email>JeffMogul@acm.org</email></address>
824    </author>
825    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
826      <organization abbrev="Microsoft">Microsoft Corporation</organization>
827      <address><email>henrikn@microsoft.com</email></address>
828    </author>
829    <author initials="L." surname="Masinter" fullname="Larry Masinter">
830      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
831      <address><email>LMM@acm.org</email></address>
832    </author>
833    <author initials="P." surname="Leach" fullname="Paul J. Leach">
834      <organization abbrev="Microsoft">Microsoft Corporation</organization>
835      <address><email>paulle@microsoft.com</email></address>
836    </author>
837    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
838      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
839      <address><email>timbl@w3.org</email></address>
840    </author>
841    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
842      <organization abbrev="W3C">World Wide Web Consortium</organization>
843      <address><email>ylafon@w3.org</email></address>
844    </author>
845    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
846      <organization abbrev="greenbytes">greenbytes GmbH</organization>
847      <address><email>julian.reschke@greenbytes.de</email></address>
848    </author>
849    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
850  </front>
851  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
852  <x:source href="p3-payload.xml" basename="p3-payload"/>
853</reference>
854
855<reference anchor="Part4">
856  <front>
857    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
858    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
859      <organization abbrev="Day Software">Day Software</organization>
860      <address><email>fielding@gbiv.com</email></address>
861    </author>
862    <author initials="J." surname="Gettys" fullname="Jim Gettys">
863      <organization>One Laptop per Child</organization>
864      <address><email>jg@laptop.org</email></address>
865    </author>
866    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
867      <organization abbrev="HP">Hewlett-Packard Company</organization>
868      <address><email>JeffMogul@acm.org</email></address>
869    </author>
870    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
871      <organization abbrev="Microsoft">Microsoft Corporation</organization>
872      <address><email>henrikn@microsoft.com</email></address>
873    </author>
874    <author initials="L." surname="Masinter" fullname="Larry Masinter">
875      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
876      <address><email>LMM@acm.org</email></address>
877    </author>
878    <author initials="P." surname="Leach" fullname="Paul J. Leach">
879      <organization abbrev="Microsoft">Microsoft Corporation</organization>
880      <address><email>paulle@microsoft.com</email></address>
881    </author>
882    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
883      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
884      <address><email>timbl@w3.org</email></address>
885    </author>
886    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
887      <organization abbrev="W3C">World Wide Web Consortium</organization>
888      <address><email>ylafon@w3.org</email></address>
889    </author>
890    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
891      <organization abbrev="greenbytes">greenbytes GmbH</organization>
892      <address><email>julian.reschke@greenbytes.de</email></address>
893    </author>
894    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
895  </front>
896  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
897  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
898</reference>
899
900<reference anchor="Part6">
901  <front>
902    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
903    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
904      <organization abbrev="Day Software">Day Software</organization>
905      <address><email>fielding@gbiv.com</email></address>
906    </author>
907    <author initials="J." surname="Gettys" fullname="Jim Gettys">
908      <organization>One Laptop per Child</organization>
909      <address><email>jg@laptop.org</email></address>
910    </author>
911    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
912      <organization abbrev="HP">Hewlett-Packard Company</organization>
913      <address><email>JeffMogul@acm.org</email></address>
914    </author>
915    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
916      <organization abbrev="Microsoft">Microsoft Corporation</organization>
917      <address><email>henrikn@microsoft.com</email></address>
918    </author>
919    <author initials="L." surname="Masinter" fullname="Larry Masinter">
920      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
921      <address><email>LMM@acm.org</email></address>
922    </author>
923    <author initials="P." surname="Leach" fullname="Paul J. Leach">
924      <organization abbrev="Microsoft">Microsoft Corporation</organization>
925      <address><email>paulle@microsoft.com</email></address>
926    </author>
927    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
928      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
929      <address><email>timbl@w3.org</email></address>
930    </author>
931    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
932      <organization abbrev="W3C">World Wide Web Consortium</organization>
933      <address><email>ylafon@w3.org</email></address>
934    </author>
935    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
936      <organization abbrev="greenbytes">greenbytes GmbH</organization>
937      <address><email>julian.reschke@greenbytes.de</email></address>
938    </author>
939    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
940  </front>
941  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
942  <x:source href="p6-cache.xml" basename="p6-cache"/>
943</reference>
944
945<reference anchor="RFC2046">
946  <front>
947    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
948    <author initials="N." surname="Freed" fullname="Ned Freed">
949      <organization>Innosoft International, Inc.</organization>
950      <address><email>ned@innosoft.com</email></address>
951    </author>
952    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
953      <organization>First Virtual Holdings</organization>
954      <address><email>nsb@nsb.fv.com</email></address>
955    </author>
956    <date month="November" year="1996"/>
957  </front>
958  <seriesInfo name="RFC" value="2046"/>
959</reference>
960
961<reference anchor="RFC2119">
962  <front>
963    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
964    <author initials="S." surname="Bradner" fullname="Scott Bradner">
965      <organization>Harvard University</organization>
966      <address><email>sob@harvard.edu</email></address>
967    </author>
968    <date month="March" year="1997"/>
969  </front>
970  <seriesInfo name="BCP" value="14"/>
971  <seriesInfo name="RFC" value="2119"/>
972</reference>
973
974</references>
975
976<references title="Informative References">
977
978<reference anchor="RFC2616">
979  <front>
980    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
981    <author initials="R." surname="Fielding" fullname="R. Fielding">
982      <organization>University of California, Irvine</organization>
983      <address><email>fielding@ics.uci.edu</email></address>
984    </author>
985    <author initials="J." surname="Gettys" fullname="J. Gettys">
986      <organization>W3C</organization>
987      <address><email>jg@w3.org</email></address>
988    </author>
989    <author initials="J." surname="Mogul" fullname="J. Mogul">
990      <organization>Compaq Computer Corporation</organization>
991      <address><email>mogul@wrl.dec.com</email></address>
992    </author>
993    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
994      <organization>MIT Laboratory for Computer Science</organization>
995      <address><email>frystyk@w3.org</email></address>
996    </author>
997    <author initials="L." surname="Masinter" fullname="L. Masinter">
998      <organization>Xerox Corporation</organization>
999      <address><email>masinter@parc.xerox.com</email></address>
1000    </author>
1001    <author initials="P." surname="Leach" fullname="P. Leach">
1002      <organization>Microsoft Corporation</organization>
1003      <address><email>paulle@microsoft.com</email></address>
1004    </author>
1005    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
1006      <organization>W3C</organization>
1007      <address><email>timbl@w3.org</email></address>
1008    </author>
1009    <date month="June" year="1999"/>
1010  </front>
1011  <seriesInfo name="RFC" value="2616"/>
1012</reference>
1013
1014<reference anchor="RFC4288">
1015  <front>
1016    <title>Media Type Specifications and Registration Procedures</title>
1017    <author initials="N." surname="Freed" fullname="N. Freed">
1018      <organization>Sun Microsystems</organization>
1019      <address>
1020        <email>ned.freed@mrochek.com</email>
1021      </address>
1022    </author>
1023    <author initials="J." surname="Klensin" fullname="J. Klensin">
1024      <organization/>
1025      <address>
1026        <email>klensin+ietf@jck.com</email>
1027      </address>
1028    </author>
1029    <date year="2005" month="December"/>
1030  </front>
1031  <seriesInfo name="BCP" value="13"/>
1032  <seriesInfo name="RFC" value="4288"/>
1033</reference>
1034
1035</references>
1036
1037<section title="Internet Media Type multipart/byteranges" anchor="internet.media.type.multipart.byteranges">
1038<iref item="Media Type" subitem="multipart/byteranges" primary="true"/>
1039<iref item="multipart/byteranges Media Type" primary="true"/>
1040<t>
1041   When an HTTP 206 (Partial Content) response message includes the
1042   content of multiple ranges (a response to a request for multiple
1043   non-overlapping ranges), these are transmitted as a multipart
1044   message-body <xref target="RFC2046"/>. The media type for this purpose is called
1045   "multipart/byteranges".  The following is to be registered with IANA <xref target="RFC4288"/>.
1046</t><t>
1047   The multipart/byteranges media type includes two or more parts, each
1048   with its own Content-Type and Content-Range fields. The required
1049   boundary parameter specifies the boundary string used to separate
1050   each body-part.
1051</t>
1052<t>
1053  <list style="hanging" x:indent="12em">
1054    <t hangText="Type name:">
1055      multipart
1056    </t>
1057    <t hangText="Subtype name:">
1058      byteranges
1059    </t>
1060    <t hangText="Required parameters:">
1061      boundary
1062    </t>
1063    <t hangText="Optional parameters:">
1064      none
1065    </t>
1066    <t hangText="Encoding considerations:">
1067      only "7bit", "8bit", or "binary" are permitted
1068    </t>
1069    <t hangText="Security considerations:">
1070      none
1071    </t>
1072    <t hangText="Interoperability considerations:">
1073      none
1074    </t>
1075    <t hangText="Published specification:">
1076      This specification (see <xref target="internet.media.type.multipart.byteranges"/>).
1077    </t>
1078    <t hangText="Applications that use this media type:">
1079    </t>
1080    <t hangText="Additional information:">
1081      <list style="hanging">
1082        <t hangText="Magic number(s):">none</t>
1083        <t hangText="File extension(s):">none</t>
1084        <t hangText="Macintosh file type code(s):">none</t>
1085      </list>
1086    </t>
1087    <t hangText="Person and email address to contact for further information:">
1088      See Authors Section.
1089    </t>
1090                <t hangText="Intended usage:">
1091                  COMMON
1092    </t>
1093                <t hangText="Restrictions on usage:">
1094                  none
1095    </t>
1096    <t hangText="Author/Change controller:">
1097      IESG
1098    </t>
1099  </list>
1100</t>
1101<figure><preamble>
1102   For example:
1103</preamble><artwork type="example">
1104   HTTP/1.1 206 Partial Content
1105   Date: Wed, 15 Nov 1995 06:25:24 GMT
1106   Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
1107   Content-type: multipart/byteranges; boundary=THIS_STRING_SEPARATES
1108
1109   --THIS_STRING_SEPARATES
1110   Content-type: application/pdf
1111   Content-range: bytes 500-999/8000
1112
1113   ...the first range...
1114   --THIS_STRING_SEPARATES
1115   Content-type: application/pdf
1116   Content-range: bytes 7000-7999/8000
1117
1118   ...the second range
1119   --THIS_STRING_SEPARATES--
1120</artwork></figure>
1121<t>
1122      Notes:
1123  <list style="numbers">
1124      <t>Additional CRLFs may precede the first boundary string in the
1125         entity.</t>
1126
1127      <t>Although <xref target="RFC2046"/> permits the boundary string to be
1128         quoted, some existing implementations handle a quoted boundary
1129         string incorrectly.</t>
1130
1131      <t>A number of browsers and servers were coded to an early draft
1132         of the byteranges specification to use a media type of
1133         multipart/x-byteranges<iref item="multipart/x-byteranges Media Type"/><iref item="Media Type" subitem="multipart/x-byteranges"/>, which is almost, but not quite
1134         compatible with the version documented in HTTP/1.1.</t>
1135  </list>
1136</t>
1137</section>
1138
1139<section title="Compatibility with Previous Versions" anchor="compatibility">
1140<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
1141<t>
1142   Transfer-coding and message lengths all interact in ways that
1143   required fixing exactly when chunked encoding is used (to allow for
1144   transfer encoding that may not be self delimiting); it was important
1145   to straighten out exactly how message lengths are computed.
1146   (<xref target="header.content-range"/>,
1147   see also <xref target="Part1"/>, <xref target="Part3"/> and <xref target="Part6"/>)
1148</t>
1149<t>
1150   There are situations where a server (especially a proxy) does not
1151   know the full length of a response but is capable of serving a
1152   byterange request. We therefore need a mechanism to allow byteranges
1153   with a content-range not indicating the full length of the message.
1154   (<xref target="header.content-range"/>)
1155</t>
1156<t>
1157   Range request responses would become very verbose if all meta-data
1158   were always returned; by allowing the server to only send needed
1159   headers in a 206 response, this problem can be avoided.
1160   (Section <xref target="status.206" format="counter"/>
1161   and <xref target="header.if-range" format="counter"/>)
1162</t>
1163<t>
1164   Fix problem with unsatisfiable range requests; there are two cases:
1165   syntactic problems, and range doesn't exist in the document. The 416
1166   status code was needed to resolve this ambiguity needed to indicate
1167   an error for a byte range request that falls outside of the actual
1168   contents of a document. (Section <xref target="status.416" format="counter"/>, <xref target="header.content-range" format="counter"/>)
1169</t>
1170</section>
1171
1172<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
1173<t>
1174  Clarify that it is not ok to use a weak cache validator in a 206 response.
1175  (<xref target="status.206"/>)
1176</t>
1177</section>
1178
1179</section>
1180
1181<section title="Change Log (to be removed by RFC Editor before publication)">
1182
1183<section title="Since RFC2616">
1184<t>
1185  Extracted relevant partitions from <xref target="RFC2616"/>.
1186</t>
1187</section>
1188
1189<section title="Since draft-ietf-httpbis-p5-range-00">
1190<t>
1191  Closed issues:
1192  <list style="symbols"> 
1193    <t>
1194      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/18"/>:
1195      "Cache validators in 206 responses"
1196      (<eref target="http://purl.org/NET/http-errata#ifrange206"/>)
1197    </t>
1198    <t>
1199      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
1200      "Normative and Informative references"
1201    </t>
1202    <t>
1203      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
1204      "Normative up-to-date references"
1205    </t>
1206  </list>
1207</t>
1208</section>
1209
1210<section title="Since draft-ietf-httpbis-p5-range-01">
1211<t>
1212  Closed issues:
1213  <list style="symbols"> 
1214    <t>
1215      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
1216      "Updating to RFC4288"
1217    </t>
1218  </list>
1219</t>
1220</section>
1221
1222</section>
1223
1224</back>
1225</rfc>
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