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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 "December">
16  <!ENTITY ID-YEAR "2007">
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-ext allow-markup-in-artwork="yes" ?>
28<?rfc-ext include-references-in-index="yes" ?>
29<rfc obsoletes="2068, 2616" category="std"
30     ipr="full3978" docName="draft-ietf-httpbis-p5-range-&ID-VERSION;"
31     xmlns:x='http://purl.org/net/xml2rfc/ext' xmlns:ed="http://greenbytes.de/2002/rfcedit">
32<front>
33
34  <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
35
36  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
37    <organization abbrev="Day Software">Day Software</organization>
38    <address>
39      <postal>
40        <street>23 Corporate Plaza DR, Suite 280</street>
41        <city>Newport Beach</city>
42        <region>CA</region>
43        <code>92660</code>
44        <country>USA</country>
45      </postal>
46      <phone>+1-949-706-5300</phone>
47      <facsimile>+1-949-706-5305</facsimile>
48      <email>fielding@gbiv.com</email>
49      <uri>http://roy.gbiv.com/</uri>
50    </address>
51  </author>
52
53  <author initials="J." surname="Gettys" fullname="Jim Gettys">
54    <organization>One Laptop per Child</organization>
55    <address>
56      <postal>
57        <street>21 Oak Knoll Road</street>
58        <city>Carlisle</city>
59        <region>MA</region>
60        <code>01741</code>
61        <country>USA</country>
62      </postal>
63      <email>jg@laptop.org</email>
64      <uri>http://www.laptop.org/</uri>
65    </address>
66  </author>
67 
68  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
69    <organization abbrev="HP">Hewlett-Packard Company</organization>
70    <address>
71      <postal>
72        <street>HP Labs, Large Scale Systems Group</street>
73        <street>1501 Page Mill Road, MS 1177</street>
74        <city>Palo Alto</city>
75        <region>CA</region>
76        <code>94304</code>
77        <country>USA</country>
78      </postal>
79      <email>JeffMogul@acm.org</email>
80    </address>
81  </author>
82
83  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
84    <organization abbrev="Microsoft">Microsoft Corporation</organization>
85    <address>
86      <postal>
87        <street>1 Microsoft Way</street>
88        <city>Redmond</city>
89        <region>WA</region>
90        <code>98052</code>
91        <country>USA</country>
92      </postal>
93      <email>henrikn@microsoft.com</email>
94    </address>
95  </author>
96
97  <author initials="L." surname="Masinter" fullname="Larry Masinter">
98    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
99    <address>
100      <postal>
101        <street>345 Park Ave</street>
102        <city>San Jose</city>
103        <region>CA</region>
104        <code>95110</code>
105        <country>USA</country>
106      </postal>
107      <email>LMM@acm.org</email>
108      <uri>http://larry.masinter.net/</uri>
109    </address>
110  </author>
111 
112  <author initials="P." surname="Leach" fullname="Paul J. Leach">
113    <organization abbrev="Microsoft">Microsoft Corporation</organization>
114    <address>
115      <postal>
116        <street>1 Microsoft Way</street>
117        <city>Redmond</city>
118        <region>WA</region>
119        <code>98052</code>
120      </postal>
121      <email>paulle@microsoft.com</email>
122    </address>
123  </author>
124   
125  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
126    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
127    <address>
128      <postal>
129        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
130        <street>The Stata Center, Building 32</street>
131        <street>32 Vassar Street</street>
132        <city>Cambridge</city>
133        <region>MA</region>
134        <code>02139</code>
135        <country>USA</country>
136      </postal>
137      <email>timbl@w3.org</email>
138      <uri>http://www.w3.org/People/Berners-Lee/</uri>
139    </address>
140  </author>
141
142  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
143    <organization abbrev="W3C">World Wide Web Consortium</organization>
144    <address>
145      <postal>
146        <street>W3C / ERCIM</street>
147        <street>2004, rte des Lucioles</street>
148        <city>Sophia-Antipolis</city>
149        <region>AM</region>
150        <code>06902</code>
151        <country>France</country>
152      </postal>
153      <email>ylafon@w3.org</email>
154      <uri>http://www.raubacapeu.net/people/yves/</uri>
155    </address>
156  </author>
157
158  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
159    <organization abbrev="greenbytes">greenbytes GmbH</organization>
160    <address>
161      <postal>
162        <street>Hafenweg 16</street>
163        <city>Muenster</city><region>NW</region><code>48155</code>
164        <country>Germany</country>
165      </postal>
166      <phone>+49 251 2807760</phone>   
167      <facsimile>+49 251 2807761</facsimile>   
168      <email>julian.reschke@greenbytes.de</email>       
169      <uri>http://greenbytes.de/tech/webdav/</uri>     
170    </address>
171  </author>
172
173  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
174
175<abstract>
176<t>
177   The Hypertext Transfer Protocol (HTTP) is an application-level
178   protocol for distributed, collaborative, hypermedia information
179   systems. HTTP has been in use by the World Wide Web global information
180   initiative since 1990. This document is Part 5 of the seven-part specification
181   that defines the protocol referred to as "HTTP/1.1" and, taken together,
182   obsoletes RFC 2616.  Part 5 defines range-specific requests and
183   the rules for constructing and combining responses to those requests.
184</t>
185</abstract>
186
187<note title="Editorial Note (To be removed by RFC Editor)">
188  <t>
189    Discussion of this draft should take place on the HTTPBIS working group
190    mailing list (ietf-http-wg@w3.org). The current issues list is
191    at <eref target="http://www.tools.ietf.org/wg/httpbis/trac/report/11"/>
192    and related documents (including fancy diffs) can be found at
193    <eref target="http://www.tools.ietf.org/wg/httpbis/"/>.
194  </t>
195</note>
196</front>
197<middle>
198<section title="Introduction" anchor="introduction">
199<t>
200   This document will define aspects of HTTP related to range requests,
201   partial responses, and the multipart/byteranges media type.  Right now
202   it only includes the extracted relevant sections of
203   <xref target="RFC2616">RFC 2616</xref> without edit.
204</t>
205
206<section title="Requirements" anchor="intro.requirements">
207<t>
208   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
209   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
210   document are to be interpreted as described in <xref target="RFC2119"/>.
211</t>
212<t>
213   An implementation is not compliant if it fails to satisfy one or more
214   of the &MUST; or &REQUIRED; level requirements for the protocols it
215   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
216   level and all the &SHOULD; level requirements for its protocols is said
217   to be "unconditionally compliant"; one that satisfies all the &MUST;
218   level requirements but not all the &SHOULD; level requirements for its
219   protocols is said to be "conditionally compliant."
220</t>
221</section>
222</section>
223
224<section title="Range Units" anchor="range.units">
225<t>
226   HTTP/1.1 allows a client to request that only part (a range of) the
227   response entity be included within the response. HTTP/1.1 uses range
228   units in the Range (<xref target="header.range"/>) and Content-Range (<xref target="header.content-range"/>)
229   header fields. An entity can be broken down into subranges according
230   to various structural units.
231</t>
232<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"/>
233   range-unit       = bytes-unit | other-range-unit
234   bytes-unit       = "bytes"
235   other-range-unit = token
236</artwork></figure>
237<t>
238   The only range unit defined by HTTP/1.1 is "bytes". HTTP/1.1
239   implementations &MAY; ignore ranges specified using other units.
240</t>
241<t>
242   HTTP/1.1 has been designed to allow implementations of applications
243   that do not depend on knowledge of ranges.
244</t>
245</section>
246
247<section title="Status Code Definitions">
248<section title="206 Partial Content" anchor="status.206">
249  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
250  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
251<t>
252   The server has fulfilled the partial GET request for the resource.
253   The request &MUST; have included a Range header field (<xref target="header.range"/>)
254   indicating the desired range, and &MAY; have included an If-Range
255   header field (<xref target="header.if-range"/>) to make the request conditional.
256</t>
257<t>
258   The response &MUST; include the following header fields:
259  <list style="symbols">
260    <t>
261        Either a Content-Range header field (<xref target="header.content-range"/>) indicating
262        the range included with this response, or a multipart/byteranges
263        Content-Type including Content-Range fields for each part. If a
264        Content-Length header field is present in the response, its
265        value &MUST; match the actual number of OCTETs transmitted in the
266        message-body.
267    </t>
268    <t>
269        Date
270    </t>
271    <t>
272        ETag and/or Content-Location, if the header would have been sent
273        in a 200 response to the same request
274    </t>
275    <t>
276        Expires, Cache-Control, and/or Vary, if the field-value might
277        differ from that sent in any previous response for the same
278        variant
279    </t>
280  </list>
281</t>
282<t>
283   If the 206 response is the result of an If-Range request, the response
284   &SHOULD-NOT; include other entity-headers. Otherwise, the response
285   &MUST; include all of the entity-headers that would have been returned
286   with a 200 (OK) response to the same request.
287</t>
288<t>
289   A cache &MUST-NOT; combine a 206 response with other previously cached
290   content if the ETag or Last-Modified headers do not match exactly,
291   see <xref target="combining.byte.ranges" format="counter"/>.
292</t>
293<t>
294   A cache that does not support the Range and Content-Range headers
295   &MUST-NOT; cache 206 (Partial) responses.
296</t>
297</section>
298
299<section title="416 Requested Range Not Satisfiable" anchor="status.416">
300  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
301  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
302<t>
303   A server &SHOULD; return a response with this status code if a request
304   included a Range request-header field (<xref target="header.range"/>), and none of
305   the range-specifier values in this field overlap the current extent
306   of the selected resource, and the request did not include an If-Range
307   request-header field. (For byte-ranges, this means that the first-byte-pos
308   of all of the byte-range-spec values were greater than the
309   current length of the selected resource.)
310</t>
311<t>
312   When this status code is returned for a byte-range request, the
313   response &SHOULD; include a Content-Range entity-header field
314   specifying the current length of the selected resource (see <xref target="header.content-range"/>).
315   This response &MUST-NOT; use the multipart/byteranges content-type.
316</t>
317</section>
318</section>
319
320<section title="Combining Byte Ranges" anchor="combining.byte.ranges">
321<t>
322   A response might transfer only a subrange of the bytes of an entity-body,
323   either because the request included one or more Range
324   specifications, or because a connection was broken prematurely. After
325   several such transfers, a cache might have received several ranges of
326   the same entity-body.
327</t>
328<t>
329   If a cache has a stored non-empty set of subranges for an entity, and
330   an incoming response transfers another subrange, the cache &MAY;
331   combine the new subrange with the existing set if both the following
332   conditions are met:
333  <list style="symbols">
334    <t>Both the incoming response and the cache entry have a cache
335        validator.</t>
336    <t>The two cache validators match using the strong comparison
337        function (see &weak-and-strong-validators;).</t>
338  </list>
339</t>
340<t>
341   If either requirement is not met, the cache &MUST; use only the most
342   recent partial response (based on the Date values transmitted with
343   every response, and using the incoming response if these values are
344   equal or missing), and &MUST; discard the other partial information.
345</t>
346</section>
347
348<section title="Header Field Definitions" anchor="header.fields">
349<t>
350   This section defines the syntax and semantics of all standard
351   HTTP/1.1 header fields. For entity-header fields, both sender and
352   recipient refer to either the client or the server, depending on who
353   sends and who receives the entity.
354</t>
355<section title="Accept-Ranges" anchor="header.accept-ranges">
356  <iref primary="true" item="Accept-Ranges header" x:for-anchor=""/>
357  <iref primary="true" item="Headers" subitem="Accept-Ranges" x:for-anchor=""/>
358<t>
359      The Accept-Ranges response-header field allows the server to
360      indicate its acceptance of range requests for a resource:
361</t>
362<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Ranges"/><iref primary="true" item="Grammar" subitem="acceptable-ranges"/>
363       Accept-Ranges     = "Accept-Ranges" ":" acceptable-ranges
364       acceptable-ranges = 1#range-unit | "none"
365</artwork></figure>
366<t>
367      Origin servers that accept byte-range requests &MAY; send
368</t>
369<figure><artwork type="example">
370       Accept-Ranges: bytes
371</artwork></figure>
372<t>
373      but are not required to do so. Clients &MAY; generate byte-range
374      requests without having received this header for the resource
375      involved. Range units are defined in <xref target="range.units"/>.
376</t>
377<t>
378      Servers that do not accept any kind of range request for a
379      resource &MAY; send
380</t>
381<figure><artwork type="example">
382       Accept-Ranges: none
383</artwork></figure>
384<t>
385      to advise the client not to attempt a range request.
386</t>
387</section>
388
389<section title="Content-Range" anchor="header.content-range">
390  <iref primary="true" item="Content-Range header" x:for-anchor=""/>
391  <iref primary="true" item="Headers" subitem="Content-Range" x:for-anchor=""/>
392<t>
393   The Content-Range entity-header is sent with a partial entity-body to
394   specify where in the full entity-body the partial body should be
395   applied. Range units are defined in <xref target="range.units"/>.
396</t>
397<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"/>
398    Content-Range = "Content-Range" ":" content-range-spec
399
400    content-range-spec      = byte-content-range-spec
401    byte-content-range-spec = bytes-unit SP
402                              byte-range-resp-spec "/"
403                              ( instance-length | "*" )
404
405    byte-range-resp-spec = (first-byte-pos "-" last-byte-pos)
406                                   | "*"
407    instance-length           = 1*DIGIT
408</artwork></figure>
409<t>
410   The header &SHOULD; indicate the total length of the full entity-body,
411   unless this length is unknown or difficult to determine. The asterisk
412   "*" character means that the instance-length is unknown at the time
413   when the response was generated.
414</t>
415<t>
416   Unlike byte-ranges-specifier values (see <xref target="byte.ranges"/>), a byte-range-resp-spec
417   &MUST; only specify one range, and &MUST; contain
418   absolute byte positions for both the first and last byte of the
419   range.
420</t>
421<t>
422   A byte-content-range-spec with a byte-range-resp-spec whose last-byte-pos
423   value is less than its first-byte-pos value, or whose
424   instance-length value is less than or equal to its last-byte-pos
425   value, is invalid. The recipient of an invalid byte-content-range-spec
426   &MUST; ignore it and any content transferred along with it.
427</t>
428<t>
429   A server sending a response with status code 416 (Requested range not
430   satisfiable) &SHOULD; include a Content-Range field with a byte-range-resp-spec
431   of "*". The instance-length specifies the current length of
432   the selected resource. A response with status code 206 (Partial
433   Content) &MUST-NOT; include a Content-Range field with a byte-range-resp-spec of "*".
434</t>
435<t>
436   Examples of byte-content-range-spec values, assuming that the entity
437   contains a total of 1234 bytes:
438   <list style="symbols">
439      <t>
440        The first 500 bytes:
441<figure><artwork type="text/plain">
442   bytes 0-499/1234
443</artwork></figure>
444      </t>   
445      <t>
446        The second 500 bytes:
447<figure><artwork type="text/plain">
448   bytes 500-999/1234
449</artwork></figure>
450      </t>   
451      <t>
452        All except for the first 500 bytes:
453<figure><artwork type="text/plain">
454   bytes 500-1233/1234
455</artwork></figure>
456      </t>   
457      <t>
458        The last 500 bytes:
459<figure><artwork type="text/plain">
460   bytes 734-1233/1234
461</artwork></figure>
462      </t>   
463   </list>
464</t>
465<t>
466   When an HTTP message includes the content of a single range (for
467   example, a response to a request for a single range, or to a request
468   for a set of ranges that overlap without any holes), this content is
469   transmitted with a Content-Range header, and a Content-Length header
470   showing the number of bytes actually transferred. For example,
471</t>
472<figure><artwork type="example">
473    HTTP/1.1 206 Partial content
474    Date: Wed, 15 Nov 1995 06:25:24 GMT
475    Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
476    Content-Range: bytes 21010-47021/47022
477    Content-Length: 26012
478    Content-Type: image/gif
479</artwork></figure>
480<t>
481   When an HTTP message includes the content of multiple ranges (for
482   example, a response to a request for multiple non-overlapping
483   ranges), these are transmitted as a multipart message. The multipart
484   media type used for this purpose is "multipart/byteranges" as defined
485   in <xref target="internet.media.type.multipart.byteranges"/>. See <xref target="changes.from.rfc.2068"/> for a compatibility issue.
486</t>
487<t>
488   A response to a request for a single range &MUST-NOT; be sent using the
489   multipart/byteranges media type.  A response to a request for
490   multiple ranges, whose result is a single range, &MAY; be sent as a
491   multipart/byteranges media type with one part. A client that cannot
492   decode a multipart/byteranges message &MUST-NOT; ask for multiple
493   byte-ranges in a single request.
494</t>
495<t>
496   When a client requests multiple byte-ranges in one request, the
497   server &SHOULD; return them in the order that they appeared in the
498   request.
499</t>
500<t>
501   If the server ignores a byte-range-spec because it is syntactically
502   invalid, the server &SHOULD; treat the request as if the invalid Range
503   header field did not exist. (Normally, this means return a 200
504   response containing the full entity).
505</t>
506<t>
507   If the server receives a request (other than one including an If-Range
508   request-header field) with an unsatisfiable Range request-header
509   field (that is, all of whose byte-range-spec values have a
510   first-byte-pos value greater than the current length of the selected
511   resource), it &SHOULD; return a response code of 416 (Requested range
512   not satisfiable) (<xref target="status.416"/>).
513  <list><t>
514      <x:h>Note:</x:h> clients cannot depend on servers to send a 416 (Requested
515      range not satisfiable) response instead of a 200 (OK) response for
516      an unsatisfiable Range request-header, since not all servers
517      implement this request-header.
518  </t></list>
519</t>
520</section>
521
522<section title="If-Range" anchor="header.if-range">
523  <iref primary="true" item="If-Range header" x:for-anchor=""/>
524  <iref primary="true" item="Headers" subitem="If-Range" x:for-anchor=""/>
525<t>
526   If a client has a partial copy of an entity in its cache, and wishes
527   to have an up-to-date copy of the entire entity in its cache, it
528   could use the Range request-header with a conditional GET (using
529   either or both of If-Unmodified-Since and If-Match.) However, if the
530   condition fails because the entity has been modified, the client
531   would then have to make a second request to obtain the entire current
532   entity-body.
533</t>
534<t>
535   The If-Range header allows a client to "short-circuit" the second
536   request. Informally, its meaning is `if the entity is unchanged, send
537   me the part(s) that I am missing; otherwise, send me the entire new
538   entity'.
539</t>
540<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-Range"/>
541     If-Range = "If-Range" ":" ( entity-tag | HTTP-date )
542</artwork></figure>
543<t>
544   If the client has no entity tag for an entity, but does have a Last-Modified
545   date, it &MAY; use that date in an If-Range header. (The
546   server can distinguish between a valid HTTP-date and any form of
547   entity-tag by examining no more than two characters.) The If-Range
548   header &SHOULD; only be used together with a Range header, and &MUST; be
549   ignored if the request does not include a Range header, or if the
550   server does not support the sub-range operation.
551</t>
552<t>
553   If the entity tag given in the If-Range header matches the current
554   entity tag for the entity, then the server &SHOULD; provide the
555   specified sub-range of the entity using a 206 (Partial content)
556   response. If the entity tag does not match, then the server &SHOULD;
557   return the entire entity using a 200 (OK) response.
558</t>
559</section>
560
561<section title="Range" anchor="header.range">
562  <iref primary="true" item="Range header" x:for-anchor=""/>
563  <iref primary="true" item="Headers" subitem="Range" x:for-anchor=""/>
564
565<section title="Byte Ranges" anchor="byte.ranges">
566<t>
567   Since all HTTP entities are represented in HTTP messages as sequences
568   of bytes, the concept of a byte range is meaningful for any HTTP
569   entity. (However, not all clients and servers need to support byte-range
570   operations.)
571</t>
572<t>
573   Byte range specifications in HTTP apply to the sequence of bytes in
574   the entity-body (not necessarily the same as the message-body).
575</t>
576<t>
577   A byte range operation &MAY; specify a single range of bytes, or a set
578   of ranges within a single entity.
579</t>
580<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"/>
581    ranges-specifier = byte-ranges-specifier
582    byte-ranges-specifier = bytes-unit "=" byte-range-set
583    byte-range-set  = 1#( byte-range-spec | suffix-byte-range-spec )
584    byte-range-spec = first-byte-pos "-" [last-byte-pos]
585    first-byte-pos  = 1*DIGIT
586    last-byte-pos   = 1*DIGIT
587</artwork></figure>
588<t>
589   The first-byte-pos value in a byte-range-spec gives the byte-offset
590   of the first byte in a range. The last-byte-pos value gives the
591   byte-offset of the last byte in the range; that is, the byte
592   positions specified are inclusive. Byte offsets start at zero.
593</t>
594<t>
595   If the last-byte-pos value is present, it &MUST; be greater than or
596   equal to the first-byte-pos in that byte-range-spec, or the byte-range-spec
597   is syntactically invalid. The recipient of a byte-range-set
598   that includes one or more syntactically invalid byte-range-spec
599   values &MUST; ignore the header field that includes that byte-range-set.
600</t>
601<t>
602   If the last-byte-pos value is absent, or if the value is greater than
603   or equal to the current length of the entity-body, last-byte-pos is
604   taken to be equal to one less than the current length of the entity-body
605   in bytes.
606</t>
607<t>
608   By its choice of last-byte-pos, a client can limit the number of
609   bytes retrieved without knowing the size of the entity.
610</t>
611<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="suffix-byte-range-spec"/><iref primary="true" item="Grammar" subitem="suffix-length"/>
612    suffix-byte-range-spec = "-" suffix-length
613    suffix-length = 1*DIGIT
614</artwork></figure>
615<t>
616   A suffix-byte-range-spec is used to specify the suffix of the
617   entity-body, of a length given by the suffix-length value. (That is,
618   this form specifies the last N bytes of an entity-body.) If the
619   entity is shorter than the specified suffix-length, the entire
620   entity-body is used.
621</t>
622<t>
623   If a syntactically valid byte-range-set includes at least one byte-range-spec
624   whose first-byte-pos is less than the current length of
625   the entity-body, or at least one suffix-byte-range-spec with a non-zero
626   suffix-length, then the byte-range-set is satisfiable.
627   Otherwise, the byte-range-set is unsatisfiable. If the byte-range-set
628   is unsatisfiable, the server &SHOULD; return a response with a status
629   of 416 (Requested range not satisfiable). Otherwise, the server
630   &SHOULD; return a response with a status of 206 (Partial Content)
631   containing the satisfiable ranges of the entity-body.
632</t>
633<t>
634   Examples of byte-ranges-specifier values (assuming an entity-body of
635   length 10000):
636  <list style="symbols">
637     <t>The first 500 bytes (byte offsets 0-499, inclusive):  bytes=0-499</t>
638
639     <t>The second 500 bytes (byte offsets 500-999, inclusive):
640        bytes=500-999</t>
641
642     <t>The final 500 bytes (byte offsets 9500-9999, inclusive):
643        bytes=-500</t>
644
645     <t>Or bytes=9500-</t>
646
647     <t>The first and last bytes only (bytes 0 and 9999):  bytes=0-0,-1</t>
648
649     <t>Several legal but not canonical specifications of the second 500
650        bytes (byte offsets 500-999, inclusive):
651        <vspace/>
652         bytes=500-600,601-999<vspace/>
653         bytes=500-700,601-999</t>
654  </list>
655</t>
656</section>
657
658<section title="Range Retrieval Requests" anchor="range.retrieval.requests">
659<t>
660   HTTP retrieval requests using conditional or unconditional GET
661   methods &MAY; request one or more sub-ranges of the entity, instead of
662   the entire entity, using the Range request header, which applies to
663   the entity returned as the result of the request:
664</t>
665<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Range"/>
666   Range = "Range" ":" ranges-specifier
667</artwork></figure>
668<t>
669   A server &MAY; ignore the Range header. However, HTTP/1.1 origin
670   servers and intermediate caches ought to support byte ranges when
671   possible, since Range supports efficient recovery from partially
672   failed transfers, and supports efficient partial retrieval of large
673   entities.
674</t>
675<t>
676   If the server supports the Range header and the specified range or
677   ranges are appropriate for the entity:
678  <list style="symbols">
679     <t>The presence of a Range header in an unconditional GET modifies
680        what is returned if the GET is otherwise successful. In other
681        words, the response carries a status code of 206 (Partial
682        Content) instead of 200 (OK).</t>
683
684     <t>The presence of a Range header in a conditional GET (a request
685        using one or both of If-Modified-Since and If-None-Match, or
686        one or both of If-Unmodified-Since and If-Match) modifies what
687        is returned if the GET is otherwise successful and the
688        condition is true. It does not affect the 304 (Not Modified)
689        response returned if the conditional is false.</t>
690  </list>
691</t>
692<t>
693   In some cases, it might be more appropriate to use the If-Range
694   header (see <xref target="header.if-range"/>) in addition to the Range header.
695</t>
696<t>
697   If a proxy that supports ranges receives a Range request, forwards
698   the request to an inbound server, and receives an entire entity in
699   reply, it &SHOULD; only return the requested range to its client. It
700   &SHOULD; store the entire received response in its cache if that is
701   consistent with its cache allocation policies.
702</t>
703</section>
704</section>
705</section>
706
707<section title="IANA Considerations" anchor="IANA.considerations">
708<t>
709   TBD.
710</t>
711</section>
712
713<section title="Security Considerations" anchor="security.considerations">
714<t>
715   No additional security considerations have been identified beyond
716   those applicable to HTTP in general &messaging;.
717</t>
718</section>
719
720<section title="Acknowledgments" anchor="ack">
721<t>
722   Most of the specification of ranges is based on work originally done
723   by Ari Luotonen and John Franks, with additional input from Steve
724   Zilles.
725</t>
726</section>
727</middle>
728<back>
729<references>
730
731<reference anchor="Part1">
732   <front>
733      <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
734      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
735         <organization abbrev="Day Software">Day Software</organization>
736         <address><email>fielding@gbiv.com</email></address>
737      </author>
738      <author initials="J." surname="Gettys" fullname="Jim Gettys">
739         <organization>One Laptop per Child</organization>
740         <address><email>jg@laptop.org</email></address>
741      </author>
742      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
743         <organization abbrev="HP">Hewlett-Packard Company</organization>
744         <address><email>JeffMogul@acm.org</email></address>
745      </author>
746      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
747         <organization abbrev="Microsoft">Microsoft Corporation</organization>
748         <address><email>henrikn@microsoft.com</email></address>
749      </author>
750      <author initials="L." surname="Masinter" fullname="Larry Masinter">
751         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
752         <address><email>LMM@acm.org</email></address>
753      </author>
754      <author initials="P." surname="Leach" fullname="Paul J. Leach">
755         <organization abbrev="Microsoft">Microsoft Corporation</organization>
756         <address><email>paulle@microsoft.com</email></address>
757      </author>
758      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
759         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
760         <address><email>timbl@w3.org</email></address>
761      </author>
762      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
763         <organization abbrev="W3C">World Wide Web Consortium</organization>
764         <address><email>ylafon@w3.org</email></address>
765      </author>
766      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
767         <organization abbrev="greenbytes">greenbytes GmbH</organization>
768         <address><email>julian.reschke@greenbytes.de</email></address>
769      </author>
770      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
771   </front>
772   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
773   <x:source href="p1-messaging.xml" basename="p1-messaging"/>
774</reference>
775
776<reference anchor="Part4">
777   <front>
778      <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
779      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
780         <organization abbrev="Day Software">Day Software</organization>
781         <address><email>fielding@gbiv.com</email></address>
782      </author>
783      <author initials="J." surname="Gettys" fullname="Jim Gettys">
784         <organization>One Laptop per Child</organization>
785         <address><email>jg@laptop.org</email></address>
786      </author>
787      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
788         <organization abbrev="HP">Hewlett-Packard Company</organization>
789         <address><email>JeffMogul@acm.org</email></address>
790      </author>
791      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
792         <organization abbrev="Microsoft">Microsoft Corporation</organization>
793         <address><email>henrikn@microsoft.com</email></address>
794      </author>
795      <author initials="L." surname="Masinter" fullname="Larry Masinter">
796         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
797         <address><email>LMM@acm.org</email></address>
798      </author>
799      <author initials="P." surname="Leach" fullname="Paul J. Leach">
800         <organization abbrev="Microsoft">Microsoft Corporation</organization>
801         <address><email>paulle@microsoft.com</email></address>
802      </author>
803      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
804         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
805         <address><email>timbl@w3.org</email></address>
806      </author>
807      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
808         <organization abbrev="W3C">World Wide Web Consortium</organization>
809         <address><email>ylafon@w3.org</email></address>
810      </author>
811      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
812         <organization abbrev="greenbytes">greenbytes GmbH</organization>
813         <address><email>julian.reschke@greenbytes.de</email></address>
814      </author>
815      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
816   </front>
817   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
818   <x:source href="p4-conditional.xml" basename="p4-conditional"/>
819</reference>
820
821<reference anchor="RFC2616">
822   <front>
823      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
824      <author initials="R." surname="Fielding" fullname="R. Fielding">
825         <organization>University of California, Irvine</organization>
826         <address><email>fielding@ics.uci.edu</email></address>
827      </author>
828      <author initials="J." surname="Gettys" fullname="J. Gettys">
829         <organization>W3C</organization>
830         <address><email>jg@w3.org</email></address>
831      </author>
832      <author initials="J." surname="Mogul" fullname="J. Mogul">
833         <organization>Compaq Computer Corporation</organization>
834         <address><email>mogul@wrl.dec.com</email></address>
835      </author>
836      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
837         <organization>MIT Laboratory for Computer Science</organization>
838         <address><email>frystyk@w3.org</email></address>
839      </author>
840      <author initials="L." surname="Masinter" fullname="L. Masinter">
841         <organization>Xerox Corporation</organization>
842         <address><email>masinter@parc.xerox.com</email></address>
843      </author>
844      <author initials="P." surname="Leach" fullname="P. Leach">
845         <organization>Microsoft Corporation</organization>
846         <address><email>paulle@microsoft.com</email></address>
847      </author>
848      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
849         <organization>W3C</organization>
850         <address><email>timbl@w3.org</email></address>
851      </author>
852      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
853         <organization abbrev="W3C">World Wide Web Consortium</organization>
854         <address><email>ylafon@w3.org</email></address>
855      </author>
856      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
857         <organization abbrev="greenbytes">greenbytes GmbH</organization>
858         <address><email>julian.reschke@greenbytes.de</email></address>
859      </author>
860      <date month="June" year="1999"/>
861   </front>
862   <seriesInfo name="RFC" value="2616"/>
863</reference>
864
865<reference anchor="RFC2046">
866  <front>
867    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
868    <author initials="N." surname="Freed" fullname="Ned Freed">
869      <organization>Innosoft International, Inc.</organization>
870      <address><email>ned@innosoft.com</email></address>
871    </author>
872    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
873      <organization>First Virtual Holdings</organization>
874      <address><email>nsb@nsb.fv.com</email></address>
875    </author>
876    <date month="November" year="1996"/>
877  </front>
878  <seriesInfo name="RFC" value="2046"/>
879</reference>
880
881<reference anchor="RFC2119">
882  <front>
883    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
884    <author initials="S." surname="Bradner" fullname="Scott Bradner">
885      <organization>Harvard University</organization>
886      <address><email>sob@harvard.edu</email></address>
887    </author>
888    <date month="March" year="1997"/>
889  </front>
890  <seriesInfo name="BCP" value="14"/>
891  <seriesInfo name="RFC" value="2119"/>
892</reference>
893
894</references>
895
896<section title="Internet Media Type multipart/byteranges" anchor="internet.media.type.multipart.byteranges">
897<iref item="Media Type" subitem="multipart/byteranges" primary="true"/>
898<iref item="multipart/byteranges Media Type" primary="true"/>
899<t>
900   When an HTTP 206 (Partial Content) response message includes the
901   content of multiple ranges (a response to a request for multiple
902   non-overlapping ranges), these are transmitted as a multipart
903   message-body. The media type for this purpose is called
904   "multipart/byteranges".
905</t><t>
906   The multipart/byteranges media type includes two or more parts, each
907   with its own Content-Type and Content-Range fields. The required
908   boundary parameter specifies the boundary string used to separate
909   each body-part.
910</t>
911<t>
912  <list style="hanging" x:indent="12em">
913    <t hangText="Media Type name:">
914      multipart
915    </t>
916    <t hangText="Media subtype name:">
917      byteranges
918    </t>
919    <t hangText="Required parameters:">
920      boundary
921    </t>
922    <t hangText="Optional parameters:">
923      none
924    </t>
925    <t hangText="Encoding considerations:">
926      only "7bit", "8bit", or "binary" are permitted
927    </t>
928    <t hangText="Security considerations:">
929      none
930    </t>
931  </list>
932</t>
933<figure><preamble>
934   For example:
935</preamble><artwork type="example">
936   HTTP/1.1 206 Partial Content
937   Date: Wed, 15 Nov 1995 06:25:24 GMT
938   Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
939   Content-type: multipart/byteranges; boundary=THIS_STRING_SEPARATES
940
941   --THIS_STRING_SEPARATES
942   Content-type: application/pdf
943   Content-range: bytes 500-999/8000
944
945   ...the first range...
946   --THIS_STRING_SEPARATES
947   Content-type: application/pdf
948   Content-range: bytes 7000-7999/8000
949
950   ...the second range
951   --THIS_STRING_SEPARATES--
952</artwork></figure>
953<t>
954      Notes:
955  <list style="numbers">
956      <t>Additional CRLFs may precede the first boundary string in the
957         entity.</t>
958
959      <t>Although <xref target="RFC2046"/> permits the boundary string to be
960         quoted, some existing implementations handle a quoted boundary
961         string incorrectly.</t>
962
963      <t>A number of browsers and servers were coded to an early draft
964         of the byteranges specification to use a media type of
965         multipart/x-byteranges<iref item="multipart/x-byteranges Media Type"/><iref item="Media Type" subitem="multipart/x-byteranges"/>, which is almost, but not quite
966         compatible with the version documented in HTTP/1.1.</t>
967  </list>
968</t>
969</section>
970
971<section title="Compatibility with Previous Versions" anchor="compatibility">
972<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
973<t>
974   There are situations where a server (especially a proxy) does not
975   know the full length of a response but is capable of serving a
976   byterange request. We therefore need a mechanism to allow byteranges
977   with a content-range not indicating the full length of the message.
978   (<xref target="header.content-range"/>)
979</t>
980<t>
981   Range request responses would become very verbose if all meta-data
982   were always returned; by allowing the server to only send needed
983   headers in a 206 response, this problem can be avoided.
984</t>
985<t>
986   Fix problem with unsatisfiable range requests; there are two cases:
987   syntactic problems, and range doesn't exist in the document. The 416
988   status code was needed to resolve this ambiguity needed to indicate
989   an error for a byte range request that falls outside of the actual
990   contents of a document. (Section <xref target="status.416" format="counter"/>, <xref target="header.content-range" format="counter"/>)
991</t>
992</section>
993
994<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
995<t>
996  Clarify that it is not ok to use a weak cache validator in a 206 response.
997  (<xref target="status.206"/>)
998</t>
999</section>
1000
1001</section>
1002
1003<section title="Change Log (to be removed by RFC Editor before publication)">
1004
1005<section title="Since RFC2616">
1006<t>
1007  Extracted relevant partitions from <xref target="RFC2616"/>.
1008</t>
1009</section>
1010
1011<section title="Since draft-ietf-httpbis-p5-range-00">
1012<t>
1013  Closed issues:
1014  <list style="symbols"> 
1015    <t>
1016      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/18"/>:
1017      "Cache validators in 206 responses"
1018      (<eref target="http://purl.org/NET/http-errata#ifrange206"/>)
1019    </t>
1020  </list>
1021</t>
1022</section>
1023
1024</section>
1025
1026</back>
1027</rfc>
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