source: draft-ietf-httpbis/latest/p5-range.xml @ 91

Last change on this file since 91 was 79, checked in by fielding@…, 12 years ago

Resolve #18: Cache validators in 206 responses

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1<?xml version="1.0" encoding="utf-8"?>
2<!DOCTYPE rfc [
3  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
4  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
5  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
6  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
7  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
8  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
9  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
10  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
11  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
12  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
13  <!ENTITY ID-VERSION "latest">
14  <!ENTITY ID-MONTH "December">
15  <!ENTITY ID-YEAR "2007">
16  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
17  <!ENTITY weak-and-strong-validators "<xref target='Part4' x:rel='#weak.and.strong.validators' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18]>
19<?rfc toc="yes" ?>
20<?rfc symrefs="yes" ?>
21<?rfc sortrefs="yes" ?>
22<?rfc compact="yes"?>
23<?rfc subcompact="no" ?>
24<?rfc linkmailto="no" ?>
25<?rfc editing="no" ?>
26<?rfc-ext allow-markup-in-artwork="yes" ?>
27<?rfc-ext include-references-in-index="yes" ?>
28<rfc obsoletes="2068, 2616" category="std"
29     ipr="full3978" docName="draft-ietf-httpbis-p5-range-&ID-VERSION;"
30     xmlns:x='http://purl.org/net/xml2rfc/ext' xmlns:ed="http://greenbytes.de/2002/rfcedit">
31<front>
32
33  <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
34
35  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
36    <organization abbrev="Day Software">Day Software</organization>
37    <address>
38      <postal>
39        <street>23 Corporate Plaza DR, Suite 280</street>
40        <city>Newport Beach</city>
41        <region>CA</region>
42        <code>92660</code>
43        <country>USA</country>
44      </postal>
45      <phone>+1-949-706-5300</phone>
46      <facsimile>+1-949-706-5305</facsimile>
47      <email>fielding@gbiv.com</email>
48      <uri>http://roy.gbiv.com/</uri>
49    </address>
50  </author>
51
52  <author initials="J." surname="Gettys" fullname="Jim Gettys">
53    <organization>One Laptop per Child</organization>
54    <address>
55      <postal>
56        <street>21 Oak Knoll Road</street>
57        <city>Carlisle</city>
58        <region>MA</region>
59        <code>01741</code>
60        <country>USA</country>
61      </postal>
62      <email>jg@laptop.org</email>
63      <uri>http://www.laptop.org/</uri>
64    </address>
65  </author>
66 
67  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
68    <organization abbrev="HP">Hewlett-Packard Company</organization>
69    <address>
70      <postal>
71        <street>HP Labs, Large Scale Systems Group</street>
72        <street>1501 Page Mill Road, MS 1177</street>
73        <city>Palo Alto</city>
74        <region>CA</region>
75        <code>94304</code>
76        <country>USA</country>
77      </postal>
78      <email>JeffMogul@acm.org</email>
79    </address>
80  </author>
81
82  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
83    <organization abbrev="Microsoft">Microsoft Corporation</organization>
84    <address>
85      <postal>
86        <street>1 Microsoft Way</street>
87        <city>Redmond</city>
88        <region>WA</region>
89        <code>98052</code>
90        <country>USA</country>
91      </postal>
92      <email>henrikn@microsoft.com</email>
93    </address>
94  </author>
95
96  <author initials="L." surname="Masinter" fullname="Larry Masinter">
97    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
98    <address>
99      <postal>
100        <street>345 Park Ave</street>
101        <city>San Jose</city>
102        <region>CA</region>
103        <code>95110</code>
104        <country>USA</country>
105      </postal>
106      <email>LMM@acm.org</email>
107      <uri>http://larry.masinter.net/</uri>
108    </address>
109  </author>
110 
111  <author initials="P." surname="Leach" fullname="Paul J. Leach">
112    <organization abbrev="Microsoft">Microsoft Corporation</organization>
113    <address>
114      <postal>
115        <street>1 Microsoft Way</street>
116        <city>Redmond</city>
117        <region>WA</region>
118        <code>98052</code>
119      </postal>
120      <email>paulle@microsoft.com</email>
121    </address>
122  </author>
123   
124  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
125    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
126    <address>
127      <postal>
128        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
129        <street>The Stata Center, Building 32</street>
130        <street>32 Vassar Street</street>
131        <city>Cambridge</city>
132        <region>MA</region>
133        <code>02139</code>
134        <country>USA</country>
135      </postal>
136      <email>timbl@w3.org</email>
137      <uri>http://www.w3.org/People/Berners-Lee/</uri>
138    </address>
139  </author>
140
141  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
142
143<abstract>
144<t>
145   The Hypertext Transfer Protocol (HTTP) is an application-level
146   protocol for distributed, collaborative, hypermedia information
147   systems. HTTP has been in use by the World Wide Web global information
148   initiative since 1990. This document is Part 5 of the seven-part specification
149   that defines the protocol referred to as "HTTP/1.1" and, taken together,
150   obsoletes RFC 2616.  Part 5 defines range-specific requests and
151   the rules for constructing and combining responses to those requests.
152</t>
153</abstract>
154
155<note title="Editorial Note (To be removed by RFC Editor)">
156  <t>
157    This version of the HTTP specification contains only minimal editorial
158    changes from <xref target="RFC2616"/> (abstract, introductory paragraph,
159    and authors' addresses).  All other changes are due to partitioning the
160    original into seven mostly independent parts.  The intent is for readers
161    of future drafts to able to use draft 00 as the basis for comparison
162    when the WG makes later changes to the specification text.  This draft
163    will shortly be followed by draft 01 (containing the first round of changes
164    that have already been agreed to on the mailing list). There is no point in
165    reviewing this draft other than to verify that the partitioning has been
166    done correctly.  Roy T. Fielding, Yves Lafon, and Julian Reschke
167    will be the editors after draft 00 is submitted.
168  </t>
169  <t>
170    Discussion of this draft should take place on the HTTPBIS working group
171    mailing list (ietf-http-wg@w3.org). The current issues list is
172    at <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/report/11"/>
173    and related documents (including fancy diffs) can be found at
174    <eref target="http://www3.tools.ietf.org/wg/httpbis/"/>.
175  </t>
176</note>
177</front>
178<middle>
179<section title="Introduction" anchor="introduction">
180<t>
181   This document will define aspects of HTTP related to range requests,
182   partial responses, and the multipart/byteranges media type.  Right now
183   it only includes the extracted relevant sections of
184   <xref target="RFC2616">RFC 2616</xref> without edit.
185</t>
186</section>
187
188<section title="Range Units" anchor="range.units">
189<t>
190   HTTP/1.1 allows a client to request that only part (a range of) the
191   response entity be included within the response. HTTP/1.1 uses range
192   units in the Range (<xref target="header.range"/>) and Content-Range (<xref target="header.content-range"/>)
193   header fields. An entity can be broken down into subranges according
194   to various structural units.
195</t>
196<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"/>
197   range-unit       = bytes-unit | other-range-unit
198   bytes-unit       = "bytes"
199   other-range-unit = token
200</artwork></figure>
201<t>
202   The only range unit defined by HTTP/1.1 is "bytes". HTTP/1.1
203   implementations &MAY; ignore ranges specified using other units.
204</t>
205<t>
206   HTTP/1.1 has been designed to allow implementations of applications
207   that do not depend on knowledge of ranges.
208</t>
209</section>
210
211<section title="Status Code Definitions">
212<section title="206 Partial Content" anchor="status.206">
213  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
214  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
215<t>
216   The server has fulfilled the partial GET request for the resource.
217   The request &MUST; have included a Range header field (<xref target="header.range"/>)
218   indicating the desired range, and &MAY; have included an If-Range
219   header field (<xref target="header.if-range"/>) to make the request conditional.
220</t>
221<t>
222   The response &MUST; include the following header fields:
223  <list style="symbols">
224    <t>
225        Either a Content-Range header field (<xref target="header.content-range"/>) indicating
226        the range included with this response, or a multipart/byteranges
227        Content-Type including Content-Range fields for each part. If a
228        Content-Length header field is present in the response, its
229        value &MUST; match the actual number of OCTETs transmitted in the
230        message-body.
231    </t>
232    <t>
233        Date
234    </t>
235    <t>
236        ETag and/or Content-Location, if the header would have been sent
237        in a 200 response to the same request
238    </t>
239    <t>
240        Expires, Cache-Control, and/or Vary, if the field-value might
241        differ from that sent in any previous response for the same
242        variant
243    </t>
244  </list>
245</t>
246<t>
247   If the 206 response is the result of an If-Range request, the response
248   &SHOULD-NOT; include other entity-headers. Otherwise, the response
249   &MUST; include all of the entity-headers that would have been returned
250   with a 200 (OK) response to the same request.
251</t>
252<t>
253   A cache &MUST-NOT; combine a 206 response with other previously cached
254   content if the ETag or Last-Modified headers do not match exactly,
255   see <xref target="combining.byte.ranges" format="counter"/>.
256</t>
257<t>
258   A cache that does not support the Range and Content-Range headers
259   &MUST-NOT; cache 206 (Partial) responses.
260</t>
261</section>
262
263<section title="416 Requested Range Not Satisfiable" anchor="status.416">
264  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
265  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
266<t>
267   A server &SHOULD; return a response with this status code if a request
268   included a Range request-header field (<xref target="header.range"/>), and none of
269   the range-specifier values in this field overlap the current extent
270   of the selected resource, and the request did not include an If-Range
271   request-header field. (For byte-ranges, this means that the first-byte-pos
272   of all of the byte-range-spec values were greater than the
273   current length of the selected resource.)
274</t>
275<t>
276   When this status code is returned for a byte-range request, the
277   response &SHOULD; include a Content-Range entity-header field
278   specifying the current length of the selected resource (see <xref target="header.content-range"/>).
279   This response &MUST-NOT; use the multipart/byteranges content-type.
280</t>
281</section>
282</section>
283
284<section title="Combining Byte Ranges" anchor="combining.byte.ranges">
285<t>
286   A response might transfer only a subrange of the bytes of an entity-body,
287   either because the request included one or more Range
288   specifications, or because a connection was broken prematurely. After
289   several such transfers, a cache might have received several ranges of
290   the same entity-body.
291</t>
292<t>
293   If a cache has a stored non-empty set of subranges for an entity, and
294   an incoming response transfers another subrange, the cache &MAY;
295   combine the new subrange with the existing set if both the following
296   conditions are met:
297  <list style="symbols">
298    <t>Both the incoming response and the cache entry have a cache
299        validator.</t>
300    <t>The two cache validators match using the strong comparison
301        function (see &weak-and-strong-validators;).</t>
302  </list>
303</t>
304<t>
305   If either requirement is not met, the cache &MUST; use only the most
306   recent partial response (based on the Date values transmitted with
307   every response, and using the incoming response if these values are
308   equal or missing), and &MUST; discard the other partial information.
309</t>
310</section>
311
312<section title="Header Field Definitions" anchor="header.fields">
313<t>
314   This section defines the syntax and semantics of all standard
315   HTTP/1.1 header fields. For entity-header fields, both sender and
316   recipient refer to either the client or the server, depending on who
317   sends and who receives the entity.
318</t>
319<section title="Accept-Ranges" anchor="header.accept-ranges">
320  <iref primary="true" item="Accept-Ranges header" x:for-anchor=""/>
321  <iref primary="true" item="Headers" subitem="Accept-Ranges" x:for-anchor=""/>
322<t>
323      The Accept-Ranges response-header field allows the server to
324      indicate its acceptance of range requests for a resource:
325</t>
326<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Ranges"/><iref primary="true" item="Grammar" subitem="acceptable-ranges"/>
327       Accept-Ranges     = "Accept-Ranges" ":" acceptable-ranges
328       acceptable-ranges = 1#range-unit | "none"
329</artwork></figure>
330<t>
331      Origin servers that accept byte-range requests &MAY; send
332</t>
333<figure><artwork type="example">
334       Accept-Ranges: bytes
335</artwork></figure>
336<t>
337      but are not required to do so. Clients &MAY; generate byte-range
338      requests without having received this header for the resource
339      involved. Range units are defined in <xref target="range.units"/>.
340</t>
341<t>
342      Servers that do not accept any kind of range request for a
343      resource &MAY; send
344</t>
345<figure><artwork type="example">
346       Accept-Ranges: none
347</artwork></figure>
348<t>
349      to advise the client not to attempt a range request.
350</t>
351</section>
352
353<section title="Content-Range" anchor="header.content-range">
354  <iref primary="true" item="Content-Range header" x:for-anchor=""/>
355  <iref primary="true" item="Headers" subitem="Content-Range" x:for-anchor=""/>
356<t>
357   The Content-Range entity-header is sent with a partial entity-body to
358   specify where in the full entity-body the partial body should be
359   applied. Range units are defined in <xref target="range.units"/>.
360</t>
361<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"/>
362    Content-Range = "Content-Range" ":" content-range-spec
363
364    content-range-spec      = byte-content-range-spec
365    byte-content-range-spec = bytes-unit SP
366                              byte-range-resp-spec "/"
367                              ( instance-length | "*" )
368
369    byte-range-resp-spec = (first-byte-pos "-" last-byte-pos)
370                                   | "*"
371    instance-length           = 1*DIGIT
372</artwork></figure>
373<t>
374   The header &SHOULD; indicate the total length of the full entity-body,
375   unless this length is unknown or difficult to determine. The asterisk
376   "*" character means that the instance-length is unknown at the time
377   when the response was generated.
378</t>
379<t>
380   Unlike byte-ranges-specifier values (see <xref target="byte.ranges"/>), a byte-range-resp-spec
381   &MUST; only specify one range, and &MUST; contain
382   absolute byte positions for both the first and last byte of the
383   range.
384</t>
385<t>
386   A byte-content-range-spec with a byte-range-resp-spec whose last-byte-pos
387   value is less than its first-byte-pos value, or whose
388   instance-length value is less than or equal to its last-byte-pos
389   value, is invalid. The recipient of an invalid byte-content-range-spec
390   &MUST; ignore it and any content transferred along with it.
391</t>
392<t>
393   A server sending a response with status code 416 (Requested range not
394   satisfiable) &SHOULD; include a Content-Range field with a byte-range-resp-spec
395   of "*". The instance-length specifies the current length of
396   the selected resource. A response with status code 206 (Partial
397   Content) &MUST-NOT; include a Content-Range field with a byte-range-resp-spec of "*".
398</t>
399<t>
400   Examples of byte-content-range-spec values, assuming that the entity
401   contains a total of 1234 bytes:
402   <list style="symbols">
403      <t>
404        The first 500 bytes:
405<figure><artwork type="text/plain">
406   bytes 0-499/1234
407</artwork></figure>
408      </t>   
409      <t>
410        The second 500 bytes:
411<figure><artwork type="text/plain">
412   bytes 500-999/1234
413</artwork></figure>
414      </t>   
415      <t>
416        All except for the first 500 bytes:
417<figure><artwork type="text/plain">
418   bytes 500-1233/1234
419</artwork></figure>
420      </t>   
421      <t>
422        The last 500 bytes:
423<figure><artwork type="text/plain">
424   bytes 734-1233/1234
425</artwork></figure>
426      </t>   
427   </list>
428</t>
429<t>
430   When an HTTP message includes the content of a single range (for
431   example, a response to a request for a single range, or to a request
432   for a set of ranges that overlap without any holes), this content is
433   transmitted with a Content-Range header, and a Content-Length header
434   showing the number of bytes actually transferred. For example,
435</t>
436<figure><artwork type="example">
437    HTTP/1.1 206 Partial content
438    Date: Wed, 15 Nov 1995 06:25:24 GMT
439    Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
440    Content-Range: bytes 21010-47021/47022
441    Content-Length: 26012
442    Content-Type: image/gif
443</artwork></figure>
444<t>
445   When an HTTP message includes the content of multiple ranges (for
446   example, a response to a request for multiple non-overlapping
447   ranges), these are transmitted as a multipart message. The multipart
448   media type used for this purpose is "multipart/byteranges" as defined
449   in <xref target="internet.media.type.multipart.byteranges"/>. See <xref target="changes.from.rfc.2068"/> for a compatibility issue.
450</t>
451<t>
452   A response to a request for a single range &MUST-NOT; be sent using the
453   multipart/byteranges media type.  A response to a request for
454   multiple ranges, whose result is a single range, &MAY; be sent as a
455   multipart/byteranges media type with one part. A client that cannot
456   decode a multipart/byteranges message &MUST-NOT; ask for multiple
457   byte-ranges in a single request.
458</t>
459<t>
460   When a client requests multiple byte-ranges in one request, the
461   server &SHOULD; return them in the order that they appeared in the
462   request.
463</t>
464<t>
465   If the server ignores a byte-range-spec because it is syntactically
466   invalid, the server &SHOULD; treat the request as if the invalid Range
467   header field did not exist. (Normally, this means return a 200
468   response containing the full entity).
469</t>
470<t>
471   If the server receives a request (other than one including an If-Range
472   request-header field) with an unsatisfiable Range request-header
473   field (that is, all of whose byte-range-spec values have a
474   first-byte-pos value greater than the current length of the selected
475   resource), it &SHOULD; return a response code of 416 (Requested range
476   not satisfiable) (<xref target="status.416"/>).
477  <list><t>
478      <x:h>Note:</x:h> clients cannot depend on servers to send a 416 (Requested
479      range not satisfiable) response instead of a 200 (OK) response for
480      an unsatisfiable Range request-header, since not all servers
481      implement this request-header.
482  </t></list>
483</t>
484</section>
485
486<section title="If-Range" anchor="header.if-range">
487  <iref primary="true" item="If-Range header" x:for-anchor=""/>
488  <iref primary="true" item="Headers" subitem="If-Range" x:for-anchor=""/>
489<t>
490   If a client has a partial copy of an entity in its cache, and wishes
491   to have an up-to-date copy of the entire entity in its cache, it
492   could use the Range request-header with a conditional GET (using
493   either or both of If-Unmodified-Since and If-Match.) However, if the
494   condition fails because the entity has been modified, the client
495   would then have to make a second request to obtain the entire current
496   entity-body.
497</t>
498<t>
499   The If-Range header allows a client to "short-circuit" the second
500   request. Informally, its meaning is `if the entity is unchanged, send
501   me the part(s) that I am missing; otherwise, send me the entire new
502   entity'.
503</t>
504<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-Range"/>
505     If-Range = "If-Range" ":" ( entity-tag | HTTP-date )
506</artwork></figure>
507<t>
508   If the client has no entity tag for an entity, but does have a Last-Modified
509   date, it &MAY; use that date in an If-Range header. (The
510   server can distinguish between a valid HTTP-date and any form of
511   entity-tag by examining no more than two characters.) The If-Range
512   header &SHOULD; only be used together with a Range header, and &MUST; be
513   ignored if the request does not include a Range header, or if the
514   server does not support the sub-range operation.
515</t>
516<t>
517   If the entity tag given in the If-Range header matches the current
518   entity tag for the entity, then the server &SHOULD; provide the
519   specified sub-range of the entity using a 206 (Partial content)
520   response. If the entity tag does not match, then the server &SHOULD;
521   return the entire entity using a 200 (OK) response.
522</t>
523</section>
524
525<section title="Range" anchor="header.range">
526  <iref primary="true" item="Range header" x:for-anchor=""/>
527  <iref primary="true" item="Headers" subitem="Range" x:for-anchor=""/>
528
529<section title="Byte Ranges" anchor="byte.ranges">
530<t>
531   Since all HTTP entities are represented in HTTP messages as sequences
532   of bytes, the concept of a byte range is meaningful for any HTTP
533   entity. (However, not all clients and servers need to support byte-range
534   operations.)
535</t>
536<t>
537   Byte range specifications in HTTP apply to the sequence of bytes in
538   the entity-body (not necessarily the same as the message-body).
539</t>
540<t>
541   A byte range operation &MAY; specify a single range of bytes, or a set
542   of ranges within a single entity.
543</t>
544<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"/>
545    ranges-specifier = byte-ranges-specifier
546    byte-ranges-specifier = bytes-unit "=" byte-range-set
547    byte-range-set  = 1#( byte-range-spec | suffix-byte-range-spec )
548    byte-range-spec = first-byte-pos "-" [last-byte-pos]
549    first-byte-pos  = 1*DIGIT
550    last-byte-pos   = 1*DIGIT
551</artwork></figure>
552<t>
553   The first-byte-pos value in a byte-range-spec gives the byte-offset
554   of the first byte in a range. The last-byte-pos value gives the
555   byte-offset of the last byte in the range; that is, the byte
556   positions specified are inclusive. Byte offsets start at zero.
557</t>
558<t>
559   If the last-byte-pos value is present, it &MUST; be greater than or
560   equal to the first-byte-pos in that byte-range-spec, or the byte-range-spec
561   is syntactically invalid. The recipient of a byte-range-set
562   that includes one or more syntactically invalid byte-range-spec
563   values &MUST; ignore the header field that includes that byte-range-set.
564</t>
565<t>
566   If the last-byte-pos value is absent, or if the value is greater than
567   or equal to the current length of the entity-body, last-byte-pos is
568   taken to be equal to one less than the current length of the entity-body
569   in bytes.
570</t>
571<t>
572   By its choice of last-byte-pos, a client can limit the number of
573   bytes retrieved without knowing the size of the entity.
574</t>
575<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="suffix-byte-range-spec"/><iref primary="true" item="Grammar" subitem="suffix-length"/>
576    suffix-byte-range-spec = "-" suffix-length
577    suffix-length = 1*DIGIT
578</artwork></figure>
579<t>
580   A suffix-byte-range-spec is used to specify the suffix of the
581   entity-body, of a length given by the suffix-length value. (That is,
582   this form specifies the last N bytes of an entity-body.) If the
583   entity is shorter than the specified suffix-length, the entire
584   entity-body is used.
585</t>
586<t>
587   If a syntactically valid byte-range-set includes at least one byte-range-spec
588   whose first-byte-pos is less than the current length of
589   the entity-body, or at least one suffix-byte-range-spec with a non-zero
590   suffix-length, then the byte-range-set is satisfiable.
591   Otherwise, the byte-range-set is unsatisfiable. If the byte-range-set
592   is unsatisfiable, the server &SHOULD; return a response with a status
593   of 416 (Requested range not satisfiable). Otherwise, the server
594   &SHOULD; return a response with a status of 206 (Partial Content)
595   containing the satisfiable ranges of the entity-body.
596</t>
597<t>
598   Examples of byte-ranges-specifier values (assuming an entity-body of
599   length 10000):
600  <list style="symbols">
601     <t>The first 500 bytes (byte offsets 0-499, inclusive):  bytes=0-499</t>
602
603     <t>The second 500 bytes (byte offsets 500-999, inclusive):
604        bytes=500-999</t>
605
606     <t>The final 500 bytes (byte offsets 9500-9999, inclusive):
607        bytes=-500</t>
608
609     <t>Or bytes=9500-</t>
610
611     <t>The first and last bytes only (bytes 0 and 9999):  bytes=0-0,-1</t>
612
613     <t>Several legal but not canonical specifications of the second 500
614        bytes (byte offsets 500-999, inclusive):
615        <vspace/>
616         bytes=500-600,601-999<vspace/>
617         bytes=500-700,601-999</t>
618  </list>
619</t>
620</section>
621
622<section title="Range Retrieval Requests" anchor="range.retrieval.requests">
623<t>
624   HTTP retrieval requests using conditional or unconditional GET
625   methods &MAY; request one or more sub-ranges of the entity, instead of
626   the entire entity, using the Range request header, which applies to
627   the entity returned as the result of the request:
628</t>
629<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Range"/>
630   Range = "Range" ":" ranges-specifier
631</artwork></figure>
632<t>
633   A server &MAY; ignore the Range header. However, HTTP/1.1 origin
634   servers and intermediate caches ought to support byte ranges when
635   possible, since Range supports efficient recovery from partially
636   failed transfers, and supports efficient partial retrieval of large
637   entities.
638</t>
639<t>
640   If the server supports the Range header and the specified range or
641   ranges are appropriate for the entity:
642  <list style="symbols">
643     <t>The presence of a Range header in an unconditional GET modifies
644        what is returned if the GET is otherwise successful. In other
645        words, the response carries a status code of 206 (Partial
646        Content) instead of 200 (OK).</t>
647
648     <t>The presence of a Range header in a conditional GET (a request
649        using one or both of If-Modified-Since and If-None-Match, or
650        one or both of If-Unmodified-Since and If-Match) modifies what
651        is returned if the GET is otherwise successful and the
652        condition is true. It does not affect the 304 (Not Modified)
653        response returned if the conditional is false.</t>
654  </list>
655</t>
656<t>
657   In some cases, it might be more appropriate to use the If-Range
658   header (see <xref target="header.if-range"/>) in addition to the Range header.
659</t>
660<t>
661   If a proxy that supports ranges receives a Range request, forwards
662   the request to an inbound server, and receives an entire entity in
663   reply, it &SHOULD; only return the requested range to its client. It
664   &SHOULD; store the entire received response in its cache if that is
665   consistent with its cache allocation policies.
666</t>
667</section>
668</section>
669</section>
670
671<section title="IANA Considerations" anchor="IANA.considerations">
672<t>
673   TBD.
674</t>
675</section>
676
677<section title="Security Considerations" anchor="security.considerations">
678<t>
679   No additional security considerations have been identified beyond
680   those applicable to HTTP in general &messaging;.
681</t>
682</section>
683
684<section title="Acknowledgments" anchor="ack">
685<t>
686   Most of the specification of ranges is based on work originally done
687   by Ari Luotonen and John Franks, with additional input from Steve
688   Zilles.
689</t>
690<t>
691   Based on an XML translation of RFC 2616 by Julian Reschke.
692</t>
693</section>
694</middle>
695<back>
696<references>
697
698<reference anchor="Part1">
699   <front>
700      <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
701      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
702         <organization abbrev="Day Software">Day Software</organization>
703         <address><email>fielding@gbiv.com</email></address>
704      </author>
705      <author initials="J." surname="Gettys" fullname="Jim Gettys">
706         <organization>One Laptop per Child</organization>
707         <address><email>jg@laptop.org</email></address>
708      </author>
709      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
710         <organization abbrev="HP">Hewlett-Packard Company</organization>
711         <address><email>JeffMogul@acm.org</email></address>
712      </author>
713      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
714         <organization abbrev="Microsoft">Microsoft Corporation</organization>
715         <address><email>henrikn@microsoft.com</email></address>
716      </author>
717      <author initials="L." surname="Masinter" fullname="Larry Masinter">
718         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
719         <address><email>LMM@acm.org</email></address>
720      </author>
721      <author initials="P." surname="Leach" fullname="Paul J. Leach">
722         <organization abbrev="Microsoft">Microsoft Corporation</organization>
723         <address><email>paulle@microsoft.com</email></address>
724      </author>
725      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
726         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
727         <address><email>timbl@w3.org</email></address>
728      </author>
729      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
730   </front>
731   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
732   <x:source href="p1-messaging.xml" basename="p1-messaging"/>
733</reference>
734
735<reference anchor="Part4">
736   <front>
737      <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
738      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
739         <organization abbrev="Day Software">Day Software</organization>
740         <address><email>fielding@gbiv.com</email></address>
741      </author>
742      <author initials="J." surname="Gettys" fullname="Jim Gettys">
743         <organization>One Laptop per Child</organization>
744         <address><email>jg@laptop.org</email></address>
745      </author>
746      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
747         <organization abbrev="HP">Hewlett-Packard Company</organization>
748         <address><email>JeffMogul@acm.org</email></address>
749      </author>
750      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
751         <organization abbrev="Microsoft">Microsoft Corporation</organization>
752         <address><email>henrikn@microsoft.com</email></address>
753      </author>
754      <author initials="L." surname="Masinter" fullname="Larry Masinter">
755         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
756         <address><email>LMM@acm.org</email></address>
757      </author>
758      <author initials="P." surname="Leach" fullname="Paul J. Leach">
759         <organization abbrev="Microsoft">Microsoft Corporation</organization>
760         <address><email>paulle@microsoft.com</email></address>
761      </author>
762      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
763         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
764         <address><email>timbl@w3.org</email></address>
765      </author>
766      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
767   </front>
768   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
769   <x:source href="p4-conditional.xml" basename="p4-conditional"/>
770</reference>
771
772<reference anchor="RFC2616">
773   <front>
774      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
775      <author initials="R." surname="Fielding" fullname="R. Fielding">
776         <organization>University of California, Irvine</organization>
777         <address><email>fielding@ics.uci.edu</email></address>
778      </author>
779      <author initials="J." surname="Gettys" fullname="J. Gettys">
780         <organization>W3C</organization>
781         <address><email>jg@w3.org</email></address>
782      </author>
783      <author initials="J." surname="Mogul" fullname="J. Mogul">
784         <organization>Compaq Computer Corporation</organization>
785         <address><email>mogul@wrl.dec.com</email></address>
786      </author>
787      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
788         <organization>MIT Laboratory for Computer Science</organization>
789         <address><email>frystyk@w3.org</email></address>
790      </author>
791      <author initials="L." surname="Masinter" fullname="L. Masinter">
792         <organization>Xerox Corporation</organization>
793         <address><email>masinter@parc.xerox.com</email></address>
794      </author>
795      <author initials="P." surname="Leach" fullname="P. Leach">
796         <organization>Microsoft Corporation</organization>
797         <address><email>paulle@microsoft.com</email></address>
798      </author>
799      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
800         <organization>W3C</organization>
801         <address><email>timbl@w3.org</email></address>
802      </author>
803      <date month="June" year="1999"/>
804   </front>
805   <seriesInfo name="RFC" value="2616"/>
806</reference>
807
808<reference anchor="RFC2046">
809<front>
810<title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
811<author initials="N." surname="Freed" fullname="Ned Freed">
812<organization>Innosoft International, Inc.</organization>
813<address>
814<postal>
815<street>1050 East Garvey Avenue South</street>
816<city>West Covina</city>
817<region>CA</region>
818<code>91790</code>
819<country>US</country></postal>
820<phone>+1 818 919 3600</phone>
821<facsimile>+1 818 919 3614</facsimile>
822<email>ned@innosoft.com</email></address></author>
823<author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
824<organization>First Virtual Holdings</organization>
825<address>
826<postal>
827<street>25 Washington Avenue</street>
828<city>Morristown</city>
829<region>NJ</region>
830<code>07960</code>
831<country>US</country></postal>
832<phone>+1 201 540 8967</phone>
833<facsimile>+1 201 993 3032</facsimile>
834<email>nsb@nsb.fv.com</email></address></author>
835<date month="November" year="1996"/>
836</front>
837<seriesInfo name="RFC" value="2046"/>
838</reference>
839
840</references>
841
842<section title="Internet Media Type multipart/byteranges" anchor="internet.media.type.multipart.byteranges">
843<iref item="Media Type" subitem="multipart/byteranges" primary="true"/>
844<iref item="multipart/byteranges Media Type" primary="true"/>
845<t>
846   When an HTTP 206 (Partial Content) response message includes the
847   content of multiple ranges (a response to a request for multiple
848   non-overlapping ranges), these are transmitted as a multipart
849   message-body. The media type for this purpose is called
850   "multipart/byteranges".
851</t><t>
852   The multipart/byteranges media type includes two or more parts, each
853   with its own Content-Type and Content-Range fields. The required
854   boundary parameter specifies the boundary string used to separate
855   each body-part.
856</t>
857<t>
858  <list style="hanging" x:indent="12em">
859    <t hangText="Media Type name:">
860      multipart
861    </t>
862    <t hangText="Media subtype name:">
863      byteranges
864    </t>
865    <t hangText="Required parameters:">
866      boundary
867    </t>
868    <t hangText="Optional parameters:">
869      none
870    </t>
871    <t hangText="Encoding considerations:">
872      only "7bit", "8bit", or "binary" are permitted
873    </t>
874    <t hangText="Security considerations:">
875      none
876    </t>
877  </list>
878</t>
879<figure><preamble>
880   For example:
881</preamble><artwork type="example">
882   HTTP/1.1 206 Partial Content
883   Date: Wed, 15 Nov 1995 06:25:24 GMT
884   Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
885   Content-type: multipart/byteranges; boundary=THIS_STRING_SEPARATES
886
887   --THIS_STRING_SEPARATES
888   Content-type: application/pdf
889   Content-range: bytes 500-999/8000
890
891   ...the first range...
892   --THIS_STRING_SEPARATES
893   Content-type: application/pdf
894   Content-range: bytes 7000-7999/8000
895
896   ...the second range
897   --THIS_STRING_SEPARATES--
898</artwork></figure>
899<t>
900      Notes:
901  <list style="numbers">
902      <t>Additional CRLFs may precede the first boundary string in the
903         entity.</t>
904
905      <t>Although RFC 2046 <xref target="RFC2046"/> permits the boundary string to be
906         quoted, some existing implementations handle a quoted boundary
907         string incorrectly.</t>
908
909      <t>A number of browsers and servers were coded to an early draft
910         of the byteranges specification to use a media type of
911         multipart/x-byteranges<iref item="multipart/x-byteranges Media Type"/><iref item="Media Type" subitem="multipart/x-byteranges"/>, which is almost, but not quite
912         compatible with the version documented in HTTP/1.1.</t>
913  </list>
914</t>
915</section>
916
917<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
918<t>
919   There are situations where a server (especially a proxy) does not
920   know the full length of a response but is capable of serving a
921   byterange request. We therefore need a mechanism to allow byteranges
922   with a content-range not indicating the full length of the message.
923   (<xref target="header.content-range"/>)
924</t>
925<t>
926   Range request responses would become very verbose if all meta-data
927   were always returned; by allowing the server to only send needed
928   headers in a 206 response, this problem can be avoided.
929</t>
930<t>
931   Fix problem with unsatisfiable range requests; there are two cases:
932   syntactic problems, and range doesn't exist in the document. The 416
933   status code was needed to resolve this ambiguity needed to indicate
934   an error for a byte range request that falls outside of the actual
935   contents of a document. (Section <xref target="status.416" format="counter"/>, <xref target="header.content-range" format="counter"/>)
936</t>
937</section>
938
939</back>
940</rfc>
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