source: draft-ietf-httpbis/latest/p5-range.xml @ 36

Last change on this file since 36 was 36, checked in by fielding@…, 12 years ago

Add an editorial note about status and list.
Streamline the new references and place them up front.

  • Property svn:eol-style set to native
File size: 38.7 KB
Line 
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, 2617" 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 and RFC 2617.  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://www.w3.org/Protocols/HTTP/1.1/rfc2616bis/issues/"/>
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="206 Partial Content" anchor="status.206">
212  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
213  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
214<t>
215   The server has fulfilled the partial GET request for the resource.
216   The request &MUST; have included a Range header field (<xref target="header.range"/>)
217   indicating the desired range, and &MAY; have included an If-Range
218   header field (<xref target="header.if-range"/>) to make the request conditional.
219</t>
220<t>
221   The response &MUST; include the following header fields:
222  <list style="symbols">
223    <t>
224        Either a Content-Range header field (<xref target="header.content-range"/>) indicating
225        the range included with this response, or a multipart/byteranges
226        Content-Type including Content-Range fields for each part. If a
227        Content-Length header field is present in the response, its
228        value &MUST; match the actual number of OCTETs transmitted in the
229        message-body.
230    </t>
231    <t>
232        Date
233    </t>
234    <t>
235        ETag and/or Content-Location, if the header would have been sent
236        in a 200 response to the same request
237    </t>
238    <t>
239        Expires, Cache-Control, and/or Vary, if the field-value might
240        differ from that sent in any previous response for the same
241        variant
242    </t>
243  </list>
244</t>
245<t>
246   If the 206 response is the result of an If-Range request that used a
247   strong cache validator (see &weak-and-strong-validators;), the response &SHOULD-NOT; 
248   include other entity-headers. If the response is the result of an
249   If-Range request that used a weak validator, the response &MUST-NOT;
250   include other entity-headers; this prevents inconsistencies between
251   cached entity-bodies and updated headers. Otherwise, the response
252   &MUST; include all of the entity-headers that would have been returned
253   with a 200 (OK) response to the same request.
254</t>
255<t>
256   A cache &MUST-NOT; combine a 206 response with other previously cached
257   content if the ETag or Last-Modified headers do not match exactly,
258   see <xref target="combining.byte.ranges" format="counter"/>.
259</t>
260<t>
261   A cache that does not support the Range and Content-Range headers
262   &MUST-NOT; cache 206 (Partial) responses.
263</t>
264</section>
265
266<section title="416 Requested Range Not Satisfiable" anchor="status.416">
267  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
268  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
269<t>
270   A server &SHOULD; return a response with this status code if a request
271   included a Range request-header field (<xref target="header.range"/>), and none of
272   the range-specifier values in this field overlap the current extent
273   of the selected resource, and the request did not include an If-Range
274   request-header field. (For byte-ranges, this means that the first-byte-pos
275   of all of the byte-range-spec values were greater than the
276   current length of the selected resource.)
277</t>
278<t>
279   When this status code is returned for a byte-range request, the
280   response &SHOULD; include a Content-Range entity-header field
281   specifying the current length of the selected resource (see <xref target="header.content-range"/>).
282   This response &MUST-NOT; use the multipart/byteranges content-type.
283</t>
284</section>
285
286<section title="Combining Byte Ranges" anchor="combining.byte.ranges">
287<t>
288   A response might transfer only a subrange of the bytes of an entity-body,
289   either because the request included one or more Range
290   specifications, or because a connection was broken prematurely. After
291   several such transfers, a cache might have received several ranges of
292   the same entity-body.
293</t>
294<t>
295   If a cache has a stored non-empty set of subranges for an entity, and
296   an incoming response transfers another subrange, the cache &MAY;
297   combine the new subrange with the existing set if both the following
298   conditions are met:
299  <list style="symbols">
300    <t>Both the incoming response and the cache entry have a cache
301        validator.</t>
302    <t>The two cache validators match using the strong comparison
303        function (see &weak-and-strong-validators;).</t>
304  </list>
305</t>
306<t>
307   If either requirement is not met, the cache &MUST; use only the most
308   recent partial response (based on the Date values transmitted with
309   every response, and using the incoming response if these values are
310   equal or missing), and &MUST; discard the other partial information.
311</t>
312</section>
313
314<section title="Header Field Definitions" anchor="header.fields">
315<t>
316   This section defines the syntax and semantics of all standard
317   HTTP/1.1 header fields. For entity-header fields, both sender and
318   recipient refer to either the client or the server, depending on who
319   sends and who receives the entity.
320</t>
321<section title="Accept-Ranges" anchor="header.accept-ranges">
322  <iref primary="true" item="Accept-Ranges header" x:for-anchor=""/>
323  <iref primary="true" item="Headers" subitem="Accept-Ranges" x:for-anchor=""/>
324<t>
325      The Accept-Ranges response-header field allows the server to
326      indicate its acceptance of range requests for a resource:
327</t>
328<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Ranges"/><iref primary="true" item="Grammar" subitem="acceptable-ranges"/>
329       Accept-Ranges     = "Accept-Ranges" ":" acceptable-ranges
330       acceptable-ranges = 1#range-unit | "none"
331</artwork></figure>
332<t>
333      Origin servers that accept byte-range requests &MAY; send
334</t>
335<figure><artwork type="example">
336       Accept-Ranges: bytes
337</artwork></figure>
338<t>
339      but are not required to do so. Clients &MAY; generate byte-range
340      requests without having received this header for the resource
341      involved. Range units are defined in <xref target="range.units"/>.
342</t>
343<t>
344      Servers that do not accept any kind of range request for a
345      resource &MAY; send
346</t>
347<figure><artwork type="example">
348       Accept-Ranges: none
349</artwork></figure>
350<t>
351      to advise the client not to attempt a range request.
352</t>
353</section>
354
355<section title="Content-Range" anchor="header.content-range">
356  <iref primary="true" item="Content-Range header" x:for-anchor=""/>
357  <iref primary="true" item="Headers" subitem="Content-Range" x:for-anchor=""/>
358<t>
359   The Content-Range entity-header is sent with a partial entity-body to
360   specify where in the full entity-body the partial body should be
361   applied. Range units are defined in <xref target="range.units"/>.
362</t>
363<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"/>
364    Content-Range = "Content-Range" ":" content-range-spec
365
366    content-range-spec      = byte-content-range-spec
367    byte-content-range-spec = bytes-unit SP
368                              byte-range-resp-spec "/"
369                              ( instance-length | "*" )
370
371    byte-range-resp-spec = (first-byte-pos "-" last-byte-pos)
372                                   | "*"
373    instance-length           = 1*DIGIT
374</artwork></figure>
375<t>
376   The header &SHOULD; indicate the total length of the full entity-body,
377   unless this length is unknown or difficult to determine. The asterisk
378   "*" character means that the instance-length is unknown at the time
379   when the response was generated.
380</t>
381<t>
382   Unlike byte-ranges-specifier values (see <xref target="byte.ranges"/>), a byte-range-resp-spec
383   &MUST; only specify one range, and &MUST; contain
384   absolute byte positions for both the first and last byte of the
385   range.
386</t>
387<t>
388   A byte-content-range-spec with a byte-range-resp-spec whose last-byte-pos
389   value is less than its first-byte-pos value, or whose
390   instance-length value is less than or equal to its last-byte-pos
391   value, is invalid. The recipient of an invalid byte-content-range-spec
392   &MUST; ignore it and any content transferred along with it.
393</t>
394<t>
395   A server sending a response with status code 416 (Requested range not
396   satisfiable) &SHOULD; include a Content-Range field with a byte-range-resp-spec
397   of "*". The instance-length specifies the current length of
398   the selected resource. A response with status code 206 (Partial
399   Content) &MUST-NOT; include a Content-Range field with a byte-range-resp-spec of "*".
400</t>
401<t>
402   Examples of byte-content-range-spec values, assuming that the entity
403   contains a total of 1234 bytes:
404   <list style="symbols">
405      <t>
406        The first 500 bytes:
407<figure><artwork type="text/plain">
408   bytes 0-499/1234
409</artwork></figure>
410      </t>   
411      <t>
412        The second 500 bytes:
413<figure><artwork type="text/plain">
414   bytes 500-999/1234
415</artwork></figure>
416      </t>   
417      <t>
418        All except for the first 500 bytes:
419<figure><artwork type="text/plain">
420   bytes 500-1233/1234
421</artwork></figure>
422      </t>   
423      <t>
424        The last 500 bytes:
425<figure><artwork type="text/plain">
426   bytes 734-1233/1234
427</artwork></figure>
428      </t>   
429   </list>
430</t>
431<t>
432   When an HTTP message includes the content of a single range (for
433   example, a response to a request for a single range, or to a request
434   for a set of ranges that overlap without any holes), this content is
435   transmitted with a Content-Range header, and a Content-Length header
436   showing the number of bytes actually transferred. For example,
437</t>
438<figure><artwork type="example">
439    HTTP/1.1 206 Partial content
440    Date: Wed, 15 Nov 1995 06:25:24 GMT
441    Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
442    Content-Range: bytes 21010-47021/47022
443    Content-Length: 26012
444    Content-Type: image/gif
445</artwork></figure>
446<t>
447   When an HTTP message includes the content of multiple ranges (for
448   example, a response to a request for multiple non-overlapping
449   ranges), these are transmitted as a multipart message. The multipart
450   media type used for this purpose is "multipart/byteranges" as defined
451   in <xref target="internet.media.type.multipart.byteranges"/>. See <xref target="changes.from.rfc.2068"/> for a compatibility issue.
452</t>
453<t>
454   A response to a request for a single range &MUST-NOT; be sent using the
455   multipart/byteranges media type.  A response to a request for
456   multiple ranges, whose result is a single range, &MAY; be sent as a
457   multipart/byteranges media type with one part. A client that cannot
458   decode a multipart/byteranges message &MUST-NOT; ask for multiple
459   byte-ranges in a single request.
460</t>
461<t>
462   When a client requests multiple byte-ranges in one request, the
463   server &SHOULD; return them in the order that they appeared in the
464   request.
465</t>
466<t>
467   If the server ignores a byte-range-spec because it is syntactically
468   invalid, the server &SHOULD; treat the request as if the invalid Range
469   header field did not exist. (Normally, this means return a 200
470   response containing the full entity).
471</t>
472<t>
473   If the server receives a request (other than one including an If-Range
474   request-header field) with an unsatisfiable Range request-header
475   field (that is, all of whose byte-range-spec values have a
476   first-byte-pos value greater than the current length of the selected
477   resource), it &SHOULD; return a response code of 416 (Requested range
478   not satisfiable) (<xref target="status.416"/>).
479  <list><t>
480      <x:h>Note:</x:h> clients cannot depend on servers to send a 416 (Requested
481      range not satisfiable) response instead of a 200 (OK) response for
482      an unsatisfiable Range request-header, since not all servers
483      implement this request-header.
484  </t></list>
485</t>
486</section>
487
488<section title="If-Range" anchor="header.if-range">
489  <iref primary="true" item="If-Range header" x:for-anchor=""/>
490  <iref primary="true" item="Headers" subitem="If-Range" x:for-anchor=""/>
491<t>
492   If a client has a partial copy of an entity in its cache, and wishes
493   to have an up-to-date copy of the entire entity in its cache, it
494   could use the Range request-header with a conditional GET (using
495   either or both of If-Unmodified-Since and If-Match.) However, if the
496   condition fails because the entity has been modified, the client
497   would then have to make a second request to obtain the entire current
498   entity-body.
499</t>
500<t>
501   The If-Range header allows a client to "short-circuit" the second
502   request. Informally, its meaning is `if the entity is unchanged, send
503   me the part(s) that I am missing; otherwise, send me the entire new
504   entity'.
505</t>
506<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-Range"/>
507     If-Range = "If-Range" ":" ( entity-tag | HTTP-date )
508</artwork></figure>
509<t>
510   If the client has no entity tag for an entity, but does have a Last-Modified
511   date, it &MAY; use that date in an If-Range header. (The
512   server can distinguish between a valid HTTP-date and any form of
513   entity-tag by examining no more than two characters.) The If-Range
514   header &SHOULD; only be used together with a Range header, and &MUST; be
515   ignored if the request does not include a Range header, or if the
516   server does not support the sub-range operation.
517</t>
518<t>
519   If the entity tag given in the If-Range header matches the current
520   entity tag for the entity, then the server &SHOULD; provide the
521   specified sub-range of the entity using a 206 (Partial content)
522   response. If the entity tag does not match, then the server &SHOULD;
523   return the entire entity using a 200 (OK) response.
524</t>
525</section>
526
527<section title="Range" anchor="header.range">
528  <iref primary="true" item="Range header" x:for-anchor=""/>
529  <iref primary="true" item="Headers" subitem="Range" x:for-anchor=""/>
530
531<section title="Byte Ranges" anchor="byte.ranges">
532<t>
533   Since all HTTP entities are represented in HTTP messages as sequences
534   of bytes, the concept of a byte range is meaningful for any HTTP
535   entity. (However, not all clients and servers need to support byte-range
536   operations.)
537</t>
538<t>
539   Byte range specifications in HTTP apply to the sequence of bytes in
540   the entity-body (not necessarily the same as the message-body).
541</t>
542<t>
543   A byte range operation &MAY; specify a single range of bytes, or a set
544   of ranges within a single entity.
545</t>
546<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"/>
547    ranges-specifier = byte-ranges-specifier
548    byte-ranges-specifier = bytes-unit "=" byte-range-set
549    byte-range-set  = 1#( byte-range-spec | suffix-byte-range-spec )
550    byte-range-spec = first-byte-pos "-" [last-byte-pos]
551    first-byte-pos  = 1*DIGIT
552    last-byte-pos   = 1*DIGIT
553</artwork></figure>
554<t>
555   The first-byte-pos value in a byte-range-spec gives the byte-offset
556   of the first byte in a range. The last-byte-pos value gives the
557   byte-offset of the last byte in the range; that is, the byte
558   positions specified are inclusive. Byte offsets start at zero.
559</t>
560<t>
561   If the last-byte-pos value is present, it &MUST; be greater than or
562   equal to the first-byte-pos in that byte-range-spec, or the byte-range-spec
563   is syntactically invalid. The recipient of a byte-range-set
564   that includes one or more syntactically invalid byte-range-spec
565   values &MUST; ignore the header field that includes that byte-range-set.
566</t>
567<t>
568   If the last-byte-pos value is absent, or if the value is greater than
569   or equal to the current length of the entity-body, last-byte-pos is
570   taken to be equal to one less than the current length of the entity-body
571   in bytes.
572</t>
573<t>
574   By its choice of last-byte-pos, a client can limit the number of
575   bytes retrieved without knowing the size of the entity.
576</t>
577<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="suffix-byte-range-spec"/><iref primary="true" item="Grammar" subitem="suffix-length"/>
578    suffix-byte-range-spec = "-" suffix-length
579    suffix-length = 1*DIGIT
580</artwork></figure>
581<t>
582   A suffix-byte-range-spec is used to specify the suffix of the
583   entity-body, of a length given by the suffix-length value. (That is,
584   this form specifies the last N bytes of an entity-body.) If the
585   entity is shorter than the specified suffix-length, the entire
586   entity-body is used.
587</t>
588<t>
589   If a syntactically valid byte-range-set includes at least one byte-range-spec
590   whose first-byte-pos is less than the current length of
591   the entity-body, or at least one suffix-byte-range-spec with a non-zero
592   suffix-length, then the byte-range-set is satisfiable.
593   Otherwise, the byte-range-set is unsatisfiable. If the byte-range-set
594   is unsatisfiable, the server &SHOULD; return a response with a status
595   of 416 (Requested range not satisfiable). Otherwise, the server
596   &SHOULD; return a response with a status of 206 (Partial Content)
597   containing the satisfiable ranges of the entity-body.
598</t>
599<t>
600   Examples of byte-ranges-specifier values (assuming an entity-body of
601   length 10000):
602  <list style="symbols">
603     <t>The first 500 bytes (byte offsets 0-499, inclusive):  bytes=0-499</t>
604
605     <t>The second 500 bytes (byte offsets 500-999, inclusive):
606        bytes=500-999</t>
607
608     <t>The final 500 bytes (byte offsets 9500-9999, inclusive):
609        bytes=-500</t>
610
611     <t>Or bytes=9500-</t>
612
613     <t>The first and last bytes only (bytes 0 and 9999):  bytes=0-0,-1</t>
614
615     <t>Several legal but not canonical specifications of the second 500
616        bytes (byte offsets 500-999, inclusive):
617        <vspace/>
618         bytes=500-600,601-999<vspace/>
619         bytes=500-700,601-999</t>
620  </list>
621</t>
622</section>
623
624<section title="Range Retrieval Requests" anchor="range.retrieval.requests">
625<t>
626   HTTP retrieval requests using conditional or unconditional GET
627   methods &MAY; request one or more sub-ranges of the entity, instead of
628   the entire entity, using the Range request header, which applies to
629   the entity returned as the result of the request:
630</t>
631<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Range"/>
632   Range = "Range" ":" ranges-specifier
633</artwork></figure>
634<t>
635   A server &MAY; ignore the Range header. However, HTTP/1.1 origin
636   servers and intermediate caches ought to support byte ranges when
637   possible, since Range supports efficient recovery from partially
638   failed transfers, and supports efficient partial retrieval of large
639   entities.
640</t>
641<t>
642   If the server supports the Range header and the specified range or
643   ranges are appropriate for the entity:
644  <list style="symbols">
645     <t>The presence of a Range header in an unconditional GET modifies
646        what is returned if the GET is otherwise successful. In other
647        words, the response carries a status code of 206 (Partial
648        Content) instead of 200 (OK).</t>
649
650     <t>The presence of a Range header in a conditional GET (a request
651        using one or both of If-Modified-Since and If-None-Match, or
652        one or both of If-Unmodified-Since and If-Match) modifies what
653        is returned if the GET is otherwise successful and the
654        condition is true. It does not affect the 304 (Not Modified)
655        response returned if the conditional is false.</t>
656  </list>
657</t>
658<t>
659   In some cases, it might be more appropriate to use the If-Range
660   header (see <xref target="header.if-range"/>) in addition to the Range header.
661</t>
662<t>
663   If a proxy that supports ranges receives a Range request, forwards
664   the request to an inbound server, and receives an entire entity in
665   reply, it &SHOULD; only return the requested range to its client. It
666   &SHOULD; store the entire received response in its cache if that is
667   consistent with its cache allocation policies.
668</t>
669</section>
670</section>
671</section>
672
673<section title="IANA Considerations" anchor="IANA.considerations">
674<t>
675   TBD.
676</t>
677</section>
678
679<section title="Security Considerations" anchor="security.considerations">
680<t>
681   No additional security considerations have been identified beyond
682   those applicable to HTTP in general &messaging;.
683</t>
684</section>
685
686<section title="Acknowledgments" anchor="ack">
687<t>
688   Most of the specification of ranges is based on work originally done
689   by Ari Luotonen and John Franks, with additional input from Steve
690   Zilles.
691</t>
692<t>
693   Based on an XML translation of RFC 2616 by Julian Reschke.
694</t>
695</section>
696</middle>
697<back>
698<references>
699
700<reference anchor="Part1">
701   <front>
702      <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
703      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
704         <organization abbrev="Day Software">Day Software</organization>
705         <address><email>fielding@gbiv.com</email></address>
706      </author>
707      <author initials="J." surname="Gettys" fullname="Jim Gettys">
708         <organization>One Laptop per Child</organization>
709         <address><email>jg@laptop.org</email></address>
710      </author>
711      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
712         <organization abbrev="HP">Hewlett-Packard Company</organization>
713         <address><email>JeffMogul@acm.org</email></address>
714      </author>
715      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
716         <organization abbrev="Microsoft">Microsoft Corporation</organization>
717         <address><email>henrikn@microsoft.com</email></address>
718      </author>
719      <author initials="L." surname="Masinter" fullname="Larry Masinter">
720         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
721         <address><email>LMM@acm.org</email></address>
722      </author>
723      <author initials="P." surname="Leach" fullname="Paul J. Leach">
724         <organization abbrev="Microsoft">Microsoft Corporation</organization>
725         <address><email>paulle@microsoft.com</email></address>
726      </author>
727      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
728         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
729         <address><email>timbl@w3.org</email></address>
730      </author>
731      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
732   </front>
733   <seriesInfo name="Internet-Draft" value="draft-fielding-p1-messaging-&ID-VERSION;"/>
734   <x:source href="p1-messaging.xml" basename="p1-messaging"/>
735</reference>
736
737<reference anchor="Part4">
738   <front>
739      <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
740      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
741         <organization abbrev="Day Software">Day Software</organization>
742         <address><email>fielding@gbiv.com</email></address>
743      </author>
744      <author initials="J." surname="Gettys" fullname="Jim Gettys">
745         <organization>One Laptop per Child</organization>
746         <address><email>jg@laptop.org</email></address>
747      </author>
748      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
749         <organization abbrev="HP">Hewlett-Packard Company</organization>
750         <address><email>JeffMogul@acm.org</email></address>
751      </author>
752      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
753         <organization abbrev="Microsoft">Microsoft Corporation</organization>
754         <address><email>henrikn@microsoft.com</email></address>
755      </author>
756      <author initials="L." surname="Masinter" fullname="Larry Masinter">
757         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
758         <address><email>LMM@acm.org</email></address>
759      </author>
760      <author initials="P." surname="Leach" fullname="Paul J. Leach">
761         <organization abbrev="Microsoft">Microsoft Corporation</organization>
762         <address><email>paulle@microsoft.com</email></address>
763      </author>
764      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
765         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
766         <address><email>timbl@w3.org</email></address>
767      </author>
768      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
769   </front>
770   <seriesInfo name="Internet-Draft" value="draft-fielding-p4-conditional-&ID-VERSION;"/>
771   <x:source href="p4-conditional.xml" basename="p4-conditional"/>
772</reference>
773
774<reference anchor="RFC2616">
775   <front>
776      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
777      <author initials="R." surname="Fielding" fullname="R. Fielding">
778         <organization>University of California, Irvine</organization>
779         <address><email>fielding@ics.uci.edu</email></address>
780      </author>
781      <author initials="J." surname="Gettys" fullname="J. Gettys">
782         <organization>W3C</organization>
783         <address><email>jg@w3.org</email></address>
784      </author>
785      <author initials="J." surname="Mogul" fullname="J. Mogul">
786         <organization>Compaq Computer Corporation</organization>
787         <address><email>mogul@wrl.dec.com</email></address>
788      </author>
789      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
790         <organization>MIT Laboratory for Computer Science</organization>
791         <address><email>frystyk@w3.org</email></address>
792      </author>
793      <author initials="L." surname="Masinter" fullname="L. Masinter">
794         <organization>Xerox Corporation</organization>
795         <address><email>masinter@parc.xerox.com</email></address>
796      </author>
797      <author initials="P." surname="Leach" fullname="P. Leach">
798         <organization>Microsoft Corporation</organization>
799         <address><email>paulle@microsoft.com</email></address>
800      </author>
801      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
802         <organization>W3C</organization>
803         <address><email>timbl@w3.org</email></address>
804      </author>
805      <date month="June" year="1999"/>
806   </front>
807   <seriesInfo name="RFC" value="2616"/>
808</reference>
809
810<reference anchor="RFC2046">
811<front>
812<title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
813<author initials="N." surname="Freed" fullname="Ned Freed">
814<organization>Innosoft International, Inc.</organization>
815<address>
816<postal>
817<street>1050 East Garvey Avenue South</street>
818<city>West Covina</city>
819<region>CA</region>
820<code>91790</code>
821<country>US</country></postal>
822<phone>+1 818 919 3600</phone>
823<facsimile>+1 818 919 3614</facsimile>
824<email>ned@innosoft.com</email></address></author>
825<author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
826<organization>First Virtual Holdings</organization>
827<address>
828<postal>
829<street>25 Washington Avenue</street>
830<city>Morristown</city>
831<region>NJ</region>
832<code>07960</code>
833<country>US</country></postal>
834<phone>+1 201 540 8967</phone>
835<facsimile>+1 201 993 3032</facsimile>
836<email>nsb@nsb.fv.com</email></address></author>
837<date month="November" year="1996"/>
838</front>
839<seriesInfo name="RFC" value="2046"/>
840</reference>
841
842</references>
843
844<section title="Internet Media Type multipart/byteranges" anchor="internet.media.type.multipart.byteranges">
845<iref item="Media Type" subitem="multipart/byteranges" primary="true"/>
846<iref item="multipart/byteranges Media Type" primary="true"/>
847<t>
848   When an HTTP 206 (Partial Content) response message includes the
849   content of multiple ranges (a response to a request for multiple
850   non-overlapping ranges), these are transmitted as a multipart
851   message-body. The media type for this purpose is called
852   "multipart/byteranges".
853</t><t>
854   The multipart/byteranges media type includes two or more parts, each
855   with its own Content-Type and Content-Range fields. The required
856   boundary parameter specifies the boundary string used to separate
857   each body-part.
858</t>
859<t>
860  <list style="hanging" x:indent="12em">
861    <t hangText="Media Type name:">
862      multipart
863    </t>
864    <t hangText="Media subtype name:">
865      byteranges
866    </t>
867    <t hangText="Required parameters:">
868      boundary
869    </t>
870    <t hangText="Optional parameters:">
871      none
872    </t>
873    <t hangText="Encoding considerations:">
874      only "7bit", "8bit", or "binary" are permitted
875    </t>
876    <t hangText="Security considerations:">
877      none
878    </t>
879  </list>
880</t>
881<figure><preamble>
882   For example:
883</preamble><artwork type="example">
884   HTTP/1.1 206 Partial Content
885   Date: Wed, 15 Nov 1995 06:25:24 GMT
886   Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
887   Content-type: multipart/byteranges; boundary=THIS_STRING_SEPARATES
888
889   --THIS_STRING_SEPARATES
890   Content-type: application/pdf
891   Content-range: bytes 500-999/8000
892
893   ...the first range...
894   --THIS_STRING_SEPARATES
895   Content-type: application/pdf
896   Content-range: bytes 7000-7999/8000
897
898   ...the second range
899   --THIS_STRING_SEPARATES--
900</artwork></figure>
901<t>
902      Notes:
903  <list style="numbers">
904      <t>Additional CRLFs may precede the first boundary string in the
905         entity.</t>
906
907      <t>Although RFC 2046 <xref target="RFC2046"/> permits the boundary string to be
908         quoted, some existing implementations handle a quoted boundary
909         string incorrectly.</t>
910
911      <t>A number of browsers and servers were coded to an early draft
912         of the byteranges specification to use a media type of
913         multipart/x-byteranges<iref item="multipart/x-byteranges Media Type"/><iref item="Media Type" subitem="multipart/x-byteranges"/>, which is almost, but not quite
914         compatible with the version documented in HTTP/1.1.</t>
915  </list>
916</t>
917</section>
918
919<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
920<t>
921   There are situations where a server (especially a proxy) does not
922   know the full length of a response but is capable of serving a
923   byterange request. We therefore need a mechanism to allow byteranges
924   with a content-range not indicating the full length of the message.
925   (<xref target="header.content-range"/>)
926</t>
927<t>
928   Range request responses would become very verbose if all meta-data
929   were always returned; by allowing the server to only send needed
930   headers in a 206 response, this problem can be avoided.
931</t>
932<t>
933   Fix problem with unsatisfiable range requests; there are two cases:
934   syntactic problems, and range doesn't exist in the document. The 416
935   status code was needed to resolve this ambiguity needed to indicate
936   an error for a byte range request that falls outside of the actual
937   contents of a document. (Section <xref target="status.416" format="counter"/>, <xref target="header.content-range" format="counter"/>)
938</t>
939</section>
940
941</back>
942</rfc>
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