source: draft-ietf-httpbis/latest/p5-range.xml @ 94

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added Yves Lafon in authors section

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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  <author initials="Y." surname="Lafon" fullname="Yves Lafon">
142    <organization abbrev="W3C">World Wide Web Consortium</organization>
143    <address>
144      <postal>
145        <street>W3C / ERCIM</street>
146        <street>2004, rte des Lucioles</street>
147        <city>Sophia-Antipolis</city>
148        <region>AM</region>
149        <code>06902</code>
150        <country>France</country>
151      </postal>
152      <email>ylafon@w3.org</email>
153      <uri>http://www.raubacapeu.net/people/yves/</uri>
154    </address>
155  </author>
156
157  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
158
159<abstract>
160<t>
161   The Hypertext Transfer Protocol (HTTP) is an application-level
162   protocol for distributed, collaborative, hypermedia information
163   systems. HTTP has been in use by the World Wide Web global information
164   initiative since 1990. This document is Part 5 of the seven-part specification
165   that defines the protocol referred to as "HTTP/1.1" and, taken together,
166   obsoletes RFC 2616.  Part 5 defines range-specific requests and
167   the rules for constructing and combining responses to those requests.
168</t>
169</abstract>
170
171<note title="Editorial Note (To be removed by RFC Editor)">
172  <t>
173    This version of the HTTP specification contains only minimal editorial
174    changes from <xref target="RFC2616"/> (abstract, introductory paragraph,
175    and authors' addresses).  All other changes are due to partitioning the
176    original into seven mostly independent parts.  The intent is for readers
177    of future drafts to able to use draft 00 as the basis for comparison
178    when the WG makes later changes to the specification text.  This draft
179    will shortly be followed by draft 01 (containing the first round of changes
180    that have already been agreed to on the mailing list). There is no point in
181    reviewing this draft other than to verify that the partitioning has been
182    done correctly.  Roy T. Fielding, Yves Lafon, and Julian Reschke
183    will be the editors after draft 00 is submitted.
184  </t>
185  <t>
186    Discussion of this draft should take place on the HTTPBIS working group
187    mailing list (ietf-http-wg@w3.org). The current issues list is
188    at <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/report/11"/>
189    and related documents (including fancy diffs) can be found at
190    <eref target="http://www3.tools.ietf.org/wg/httpbis/"/>.
191  </t>
192</note>
193</front>
194<middle>
195<section title="Introduction" anchor="introduction">
196<t>
197   This document will define aspects of HTTP related to range requests,
198   partial responses, and the multipart/byteranges media type.  Right now
199   it only includes the extracted relevant sections of
200   <xref target="RFC2616">RFC 2616</xref> without edit.
201</t>
202</section>
203
204<section title="Range Units" anchor="range.units">
205<t>
206   HTTP/1.1 allows a client to request that only part (a range of) the
207   response entity be included within the response. HTTP/1.1 uses range
208   units in the Range (<xref target="header.range"/>) and Content-Range (<xref target="header.content-range"/>)
209   header fields. An entity can be broken down into subranges according
210   to various structural units.
211</t>
212<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"/>
213   range-unit       = bytes-unit | other-range-unit
214   bytes-unit       = "bytes"
215   other-range-unit = token
216</artwork></figure>
217<t>
218   The only range unit defined by HTTP/1.1 is "bytes". HTTP/1.1
219   implementations &MAY; ignore ranges specified using other units.
220</t>
221<t>
222   HTTP/1.1 has been designed to allow implementations of applications
223   that do not depend on knowledge of ranges.
224</t>
225</section>
226
227<section title="Status Code Definitions">
228<section title="206 Partial Content" anchor="status.206">
229  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
230  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
231<t>
232   The server has fulfilled the partial GET request for the resource.
233   The request &MUST; have included a Range header field (<xref target="header.range"/>)
234   indicating the desired range, and &MAY; have included an If-Range
235   header field (<xref target="header.if-range"/>) to make the request conditional.
236</t>
237<t>
238   The response &MUST; include the following header fields:
239  <list style="symbols">
240    <t>
241        Either a Content-Range header field (<xref target="header.content-range"/>) indicating
242        the range included with this response, or a multipart/byteranges
243        Content-Type including Content-Range fields for each part. If a
244        Content-Length header field is present in the response, its
245        value &MUST; match the actual number of OCTETs transmitted in the
246        message-body.
247    </t>
248    <t>
249        Date
250    </t>
251    <t>
252        ETag and/or Content-Location, if the header would have been sent
253        in a 200 response to the same request
254    </t>
255    <t>
256        Expires, Cache-Control, and/or Vary, if the field-value might
257        differ from that sent in any previous response for the same
258        variant
259    </t>
260  </list>
261</t>
262<t>
263   If the 206 response is the result of an If-Range request, the response
264   &SHOULD-NOT; include other entity-headers. Otherwise, the response
265   &MUST; include all of the entity-headers that would have been returned
266   with a 200 (OK) response to the same request.
267</t>
268<t>
269   A cache &MUST-NOT; combine a 206 response with other previously cached
270   content if the ETag or Last-Modified headers do not match exactly,
271   see <xref target="combining.byte.ranges" format="counter"/>.
272</t>
273<t>
274   A cache that does not support the Range and Content-Range headers
275   &MUST-NOT; cache 206 (Partial) responses.
276</t>
277</section>
278
279<section title="416 Requested Range Not Satisfiable" anchor="status.416">
280  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
281  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
282<t>
283   A server &SHOULD; return a response with this status code if a request
284   included a Range request-header field (<xref target="header.range"/>), and none of
285   the range-specifier values in this field overlap the current extent
286   of the selected resource, and the request did not include an If-Range
287   request-header field. (For byte-ranges, this means that the first-byte-pos
288   of all of the byte-range-spec values were greater than the
289   current length of the selected resource.)
290</t>
291<t>
292   When this status code is returned for a byte-range request, the
293   response &SHOULD; include a Content-Range entity-header field
294   specifying the current length of the selected resource (see <xref target="header.content-range"/>).
295   This response &MUST-NOT; use the multipart/byteranges content-type.
296</t>
297</section>
298</section>
299
300<section title="Combining Byte Ranges" anchor="combining.byte.ranges">
301<t>
302   A response might transfer only a subrange of the bytes of an entity-body,
303   either because the request included one or more Range
304   specifications, or because a connection was broken prematurely. After
305   several such transfers, a cache might have received several ranges of
306   the same entity-body.
307</t>
308<t>
309   If a cache has a stored non-empty set of subranges for an entity, and
310   an incoming response transfers another subrange, the cache &MAY;
311   combine the new subrange with the existing set if both the following
312   conditions are met:
313  <list style="symbols">
314    <t>Both the incoming response and the cache entry have a cache
315        validator.</t>
316    <t>The two cache validators match using the strong comparison
317        function (see &weak-and-strong-validators;).</t>
318  </list>
319</t>
320<t>
321   If either requirement is not met, the cache &MUST; use only the most
322   recent partial response (based on the Date values transmitted with
323   every response, and using the incoming response if these values are
324   equal or missing), and &MUST; discard the other partial information.
325</t>
326</section>
327
328<section title="Header Field Definitions" anchor="header.fields">
329<t>
330   This section defines the syntax and semantics of all standard
331   HTTP/1.1 header fields. For entity-header fields, both sender and
332   recipient refer to either the client or the server, depending on who
333   sends and who receives the entity.
334</t>
335<section title="Accept-Ranges" anchor="header.accept-ranges">
336  <iref primary="true" item="Accept-Ranges header" x:for-anchor=""/>
337  <iref primary="true" item="Headers" subitem="Accept-Ranges" x:for-anchor=""/>
338<t>
339      The Accept-Ranges response-header field allows the server to
340      indicate its acceptance of range requests for a resource:
341</t>
342<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Ranges"/><iref primary="true" item="Grammar" subitem="acceptable-ranges"/>
343       Accept-Ranges     = "Accept-Ranges" ":" acceptable-ranges
344       acceptable-ranges = 1#range-unit | "none"
345</artwork></figure>
346<t>
347      Origin servers that accept byte-range requests &MAY; send
348</t>
349<figure><artwork type="example">
350       Accept-Ranges: bytes
351</artwork></figure>
352<t>
353      but are not required to do so. Clients &MAY; generate byte-range
354      requests without having received this header for the resource
355      involved. Range units are defined in <xref target="range.units"/>.
356</t>
357<t>
358      Servers that do not accept any kind of range request for a
359      resource &MAY; send
360</t>
361<figure><artwork type="example">
362       Accept-Ranges: none
363</artwork></figure>
364<t>
365      to advise the client not to attempt a range request.
366</t>
367</section>
368
369<section title="Content-Range" anchor="header.content-range">
370  <iref primary="true" item="Content-Range header" x:for-anchor=""/>
371  <iref primary="true" item="Headers" subitem="Content-Range" x:for-anchor=""/>
372<t>
373   The Content-Range entity-header is sent with a partial entity-body to
374   specify where in the full entity-body the partial body should be
375   applied. Range units are defined in <xref target="range.units"/>.
376</t>
377<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"/>
378    Content-Range = "Content-Range" ":" content-range-spec
379
380    content-range-spec      = byte-content-range-spec
381    byte-content-range-spec = bytes-unit SP
382                              byte-range-resp-spec "/"
383                              ( instance-length | "*" )
384
385    byte-range-resp-spec = (first-byte-pos "-" last-byte-pos)
386                                   | "*"
387    instance-length           = 1*DIGIT
388</artwork></figure>
389<t>
390   The header &SHOULD; indicate the total length of the full entity-body,
391   unless this length is unknown or difficult to determine. The asterisk
392   "*" character means that the instance-length is unknown at the time
393   when the response was generated.
394</t>
395<t>
396   Unlike byte-ranges-specifier values (see <xref target="byte.ranges"/>), a byte-range-resp-spec
397   &MUST; only specify one range, and &MUST; contain
398   absolute byte positions for both the first and last byte of the
399   range.
400</t>
401<t>
402   A byte-content-range-spec with a byte-range-resp-spec whose last-byte-pos
403   value is less than its first-byte-pos value, or whose
404   instance-length value is less than or equal to its last-byte-pos
405   value, is invalid. The recipient of an invalid byte-content-range-spec
406   &MUST; ignore it and any content transferred along with it.
407</t>
408<t>
409   A server sending a response with status code 416 (Requested range not
410   satisfiable) &SHOULD; include a Content-Range field with a byte-range-resp-spec
411   of "*". The instance-length specifies the current length of
412   the selected resource. A response with status code 206 (Partial
413   Content) &MUST-NOT; include a Content-Range field with a byte-range-resp-spec of "*".
414</t>
415<t>
416   Examples of byte-content-range-spec values, assuming that the entity
417   contains a total of 1234 bytes:
418   <list style="symbols">
419      <t>
420        The first 500 bytes:
421<figure><artwork type="text/plain">
422   bytes 0-499/1234
423</artwork></figure>
424      </t>   
425      <t>
426        The second 500 bytes:
427<figure><artwork type="text/plain">
428   bytes 500-999/1234
429</artwork></figure>
430      </t>   
431      <t>
432        All except for the first 500 bytes:
433<figure><artwork type="text/plain">
434   bytes 500-1233/1234
435</artwork></figure>
436      </t>   
437      <t>
438        The last 500 bytes:
439<figure><artwork type="text/plain">
440   bytes 734-1233/1234
441</artwork></figure>
442      </t>   
443   </list>
444</t>
445<t>
446   When an HTTP message includes the content of a single range (for
447   example, a response to a request for a single range, or to a request
448   for a set of ranges that overlap without any holes), this content is
449   transmitted with a Content-Range header, and a Content-Length header
450   showing the number of bytes actually transferred. For example,
451</t>
452<figure><artwork type="example">
453    HTTP/1.1 206 Partial content
454    Date: Wed, 15 Nov 1995 06:25:24 GMT
455    Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
456    Content-Range: bytes 21010-47021/47022
457    Content-Length: 26012
458    Content-Type: image/gif
459</artwork></figure>
460<t>
461   When an HTTP message includes the content of multiple ranges (for
462   example, a response to a request for multiple non-overlapping
463   ranges), these are transmitted as a multipart message. The multipart
464   media type used for this purpose is "multipart/byteranges" as defined
465   in <xref target="internet.media.type.multipart.byteranges"/>. See <xref target="changes.from.rfc.2068"/> for a compatibility issue.
466</t>
467<t>
468   A response to a request for a single range &MUST-NOT; be sent using the
469   multipart/byteranges media type.  A response to a request for
470   multiple ranges, whose result is a single range, &MAY; be sent as a
471   multipart/byteranges media type with one part. A client that cannot
472   decode a multipart/byteranges message &MUST-NOT; ask for multiple
473   byte-ranges in a single request.
474</t>
475<t>
476   When a client requests multiple byte-ranges in one request, the
477   server &SHOULD; return them in the order that they appeared in the
478   request.
479</t>
480<t>
481   If the server ignores a byte-range-spec because it is syntactically
482   invalid, the server &SHOULD; treat the request as if the invalid Range
483   header field did not exist. (Normally, this means return a 200
484   response containing the full entity).
485</t>
486<t>
487   If the server receives a request (other than one including an If-Range
488   request-header field) with an unsatisfiable Range request-header
489   field (that is, all of whose byte-range-spec values have a
490   first-byte-pos value greater than the current length of the selected
491   resource), it &SHOULD; return a response code of 416 (Requested range
492   not satisfiable) (<xref target="status.416"/>).
493  <list><t>
494      <x:h>Note:</x:h> clients cannot depend on servers to send a 416 (Requested
495      range not satisfiable) response instead of a 200 (OK) response for
496      an unsatisfiable Range request-header, since not all servers
497      implement this request-header.
498  </t></list>
499</t>
500</section>
501
502<section title="If-Range" anchor="header.if-range">
503  <iref primary="true" item="If-Range header" x:for-anchor=""/>
504  <iref primary="true" item="Headers" subitem="If-Range" x:for-anchor=""/>
505<t>
506   If a client has a partial copy of an entity in its cache, and wishes
507   to have an up-to-date copy of the entire entity in its cache, it
508   could use the Range request-header with a conditional GET (using
509   either or both of If-Unmodified-Since and If-Match.) However, if the
510   condition fails because the entity has been modified, the client
511   would then have to make a second request to obtain the entire current
512   entity-body.
513</t>
514<t>
515   The If-Range header allows a client to "short-circuit" the second
516   request. Informally, its meaning is `if the entity is unchanged, send
517   me the part(s) that I am missing; otherwise, send me the entire new
518   entity'.
519</t>
520<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-Range"/>
521     If-Range = "If-Range" ":" ( entity-tag | HTTP-date )
522</artwork></figure>
523<t>
524   If the client has no entity tag for an entity, but does have a Last-Modified
525   date, it &MAY; use that date in an If-Range header. (The
526   server can distinguish between a valid HTTP-date and any form of
527   entity-tag by examining no more than two characters.) The If-Range
528   header &SHOULD; only be used together with a Range header, and &MUST; be
529   ignored if the request does not include a Range header, or if the
530   server does not support the sub-range operation.
531</t>
532<t>
533   If the entity tag given in the If-Range header matches the current
534   entity tag for the entity, then the server &SHOULD; provide the
535   specified sub-range of the entity using a 206 (Partial content)
536   response. If the entity tag does not match, then the server &SHOULD;
537   return the entire entity using a 200 (OK) response.
538</t>
539</section>
540
541<section title="Range" anchor="header.range">
542  <iref primary="true" item="Range header" x:for-anchor=""/>
543  <iref primary="true" item="Headers" subitem="Range" x:for-anchor=""/>
544
545<section title="Byte Ranges" anchor="byte.ranges">
546<t>
547   Since all HTTP entities are represented in HTTP messages as sequences
548   of bytes, the concept of a byte range is meaningful for any HTTP
549   entity. (However, not all clients and servers need to support byte-range
550   operations.)
551</t>
552<t>
553   Byte range specifications in HTTP apply to the sequence of bytes in
554   the entity-body (not necessarily the same as the message-body).
555</t>
556<t>
557   A byte range operation &MAY; specify a single range of bytes, or a set
558   of ranges within a single entity.
559</t>
560<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"/>
561    ranges-specifier = byte-ranges-specifier
562    byte-ranges-specifier = bytes-unit "=" byte-range-set
563    byte-range-set  = 1#( byte-range-spec | suffix-byte-range-spec )
564    byte-range-spec = first-byte-pos "-" [last-byte-pos]
565    first-byte-pos  = 1*DIGIT
566    last-byte-pos   = 1*DIGIT
567</artwork></figure>
568<t>
569   The first-byte-pos value in a byte-range-spec gives the byte-offset
570   of the first byte in a range. The last-byte-pos value gives the
571   byte-offset of the last byte in the range; that is, the byte
572   positions specified are inclusive. Byte offsets start at zero.
573</t>
574<t>
575   If the last-byte-pos value is present, it &MUST; be greater than or
576   equal to the first-byte-pos in that byte-range-spec, or the byte-range-spec
577   is syntactically invalid. The recipient of a byte-range-set
578   that includes one or more syntactically invalid byte-range-spec
579   values &MUST; ignore the header field that includes that byte-range-set.
580</t>
581<t>
582   If the last-byte-pos value is absent, or if the value is greater than
583   or equal to the current length of the entity-body, last-byte-pos is
584   taken to be equal to one less than the current length of the entity-body
585   in bytes.
586</t>
587<t>
588   By its choice of last-byte-pos, a client can limit the number of
589   bytes retrieved without knowing the size of the entity.
590</t>
591<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="suffix-byte-range-spec"/><iref primary="true" item="Grammar" subitem="suffix-length"/>
592    suffix-byte-range-spec = "-" suffix-length
593    suffix-length = 1*DIGIT
594</artwork></figure>
595<t>
596   A suffix-byte-range-spec is used to specify the suffix of the
597   entity-body, of a length given by the suffix-length value. (That is,
598   this form specifies the last N bytes of an entity-body.) If the
599   entity is shorter than the specified suffix-length, the entire
600   entity-body is used.
601</t>
602<t>
603   If a syntactically valid byte-range-set includes at least one byte-range-spec
604   whose first-byte-pos is less than the current length of
605   the entity-body, or at least one suffix-byte-range-spec with a non-zero
606   suffix-length, then the byte-range-set is satisfiable.
607   Otherwise, the byte-range-set is unsatisfiable. If the byte-range-set
608   is unsatisfiable, the server &SHOULD; return a response with a status
609   of 416 (Requested range not satisfiable). Otherwise, the server
610   &SHOULD; return a response with a status of 206 (Partial Content)
611   containing the satisfiable ranges of the entity-body.
612</t>
613<t>
614   Examples of byte-ranges-specifier values (assuming an entity-body of
615   length 10000):
616  <list style="symbols">
617     <t>The first 500 bytes (byte offsets 0-499, inclusive):  bytes=0-499</t>
618
619     <t>The second 500 bytes (byte offsets 500-999, inclusive):
620        bytes=500-999</t>
621
622     <t>The final 500 bytes (byte offsets 9500-9999, inclusive):
623        bytes=-500</t>
624
625     <t>Or bytes=9500-</t>
626
627     <t>The first and last bytes only (bytes 0 and 9999):  bytes=0-0,-1</t>
628
629     <t>Several legal but not canonical specifications of the second 500
630        bytes (byte offsets 500-999, inclusive):
631        <vspace/>
632         bytes=500-600,601-999<vspace/>
633         bytes=500-700,601-999</t>
634  </list>
635</t>
636</section>
637
638<section title="Range Retrieval Requests" anchor="range.retrieval.requests">
639<t>
640   HTTP retrieval requests using conditional or unconditional GET
641   methods &MAY; request one or more sub-ranges of the entity, instead of
642   the entire entity, using the Range request header, which applies to
643   the entity returned as the result of the request:
644</t>
645<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Range"/>
646   Range = "Range" ":" ranges-specifier
647</artwork></figure>
648<t>
649   A server &MAY; ignore the Range header. However, HTTP/1.1 origin
650   servers and intermediate caches ought to support byte ranges when
651   possible, since Range supports efficient recovery from partially
652   failed transfers, and supports efficient partial retrieval of large
653   entities.
654</t>
655<t>
656   If the server supports the Range header and the specified range or
657   ranges are appropriate for the entity:
658  <list style="symbols">
659     <t>The presence of a Range header in an unconditional GET modifies
660        what is returned if the GET is otherwise successful. In other
661        words, the response carries a status code of 206 (Partial
662        Content) instead of 200 (OK).</t>
663
664     <t>The presence of a Range header in a conditional GET (a request
665        using one or both of If-Modified-Since and If-None-Match, or
666        one or both of If-Unmodified-Since and If-Match) modifies what
667        is returned if the GET is otherwise successful and the
668        condition is true. It does not affect the 304 (Not Modified)
669        response returned if the conditional is false.</t>
670  </list>
671</t>
672<t>
673   In some cases, it might be more appropriate to use the If-Range
674   header (see <xref target="header.if-range"/>) in addition to the Range header.
675</t>
676<t>
677   If a proxy that supports ranges receives a Range request, forwards
678   the request to an inbound server, and receives an entire entity in
679   reply, it &SHOULD; only return the requested range to its client. It
680   &SHOULD; store the entire received response in its cache if that is
681   consistent with its cache allocation policies.
682</t>
683</section>
684</section>
685</section>
686
687<section title="IANA Considerations" anchor="IANA.considerations">
688<t>
689   TBD.
690</t>
691</section>
692
693<section title="Security Considerations" anchor="security.considerations">
694<t>
695   No additional security considerations have been identified beyond
696   those applicable to HTTP in general &messaging;.
697</t>
698</section>
699
700<section title="Acknowledgments" anchor="ack">
701<t>
702   Most of the specification of ranges is based on work originally done
703   by Ari Luotonen and John Franks, with additional input from Steve
704   Zilles.
705</t>
706<t>
707   Based on an XML translation of RFC 2616 by Julian Reschke.
708</t>
709</section>
710</middle>
711<back>
712<references>
713
714<reference anchor="Part1">
715   <front>
716      <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
717      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
718         <organization abbrev="Day Software">Day Software</organization>
719         <address><email>fielding@gbiv.com</email></address>
720      </author>
721      <author initials="J." surname="Gettys" fullname="Jim Gettys">
722         <organization>One Laptop per Child</organization>
723         <address><email>jg@laptop.org</email></address>
724      </author>
725      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
726         <organization abbrev="HP">Hewlett-Packard Company</organization>
727         <address><email>JeffMogul@acm.org</email></address>
728      </author>
729      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
730         <organization abbrev="Microsoft">Microsoft Corporation</organization>
731         <address><email>henrikn@microsoft.com</email></address>
732      </author>
733      <author initials="L." surname="Masinter" fullname="Larry Masinter">
734         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
735         <address><email>LMM@acm.org</email></address>
736      </author>
737      <author initials="P." surname="Leach" fullname="Paul J. Leach">
738         <organization abbrev="Microsoft">Microsoft Corporation</organization>
739         <address><email>paulle@microsoft.com</email></address>
740      </author>
741      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
742         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
743         <address><email>timbl@w3.org</email></address>
744      </author>
745      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
746   </front>
747   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
748   <x:source href="p1-messaging.xml" basename="p1-messaging"/>
749</reference>
750
751<reference anchor="Part4">
752   <front>
753      <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
754      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
755         <organization abbrev="Day Software">Day Software</organization>
756         <address><email>fielding@gbiv.com</email></address>
757      </author>
758      <author initials="J." surname="Gettys" fullname="Jim Gettys">
759         <organization>One Laptop per Child</organization>
760         <address><email>jg@laptop.org</email></address>
761      </author>
762      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
763         <organization abbrev="HP">Hewlett-Packard Company</organization>
764         <address><email>JeffMogul@acm.org</email></address>
765      </author>
766      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
767         <organization abbrev="Microsoft">Microsoft Corporation</organization>
768         <address><email>henrikn@microsoft.com</email></address>
769      </author>
770      <author initials="L." surname="Masinter" fullname="Larry Masinter">
771         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
772         <address><email>LMM@acm.org</email></address>
773      </author>
774      <author initials="P." surname="Leach" fullname="Paul J. Leach">
775         <organization abbrev="Microsoft">Microsoft Corporation</organization>
776         <address><email>paulle@microsoft.com</email></address>
777      </author>
778      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
779         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
780         <address><email>timbl@w3.org</email></address>
781      </author>
782      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
783   </front>
784   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
785   <x:source href="p4-conditional.xml" basename="p4-conditional"/>
786</reference>
787
788<reference anchor="RFC2616">
789   <front>
790      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
791      <author initials="R." surname="Fielding" fullname="R. Fielding">
792         <organization>University of California, Irvine</organization>
793         <address><email>fielding@ics.uci.edu</email></address>
794      </author>
795      <author initials="J." surname="Gettys" fullname="J. Gettys">
796         <organization>W3C</organization>
797         <address><email>jg@w3.org</email></address>
798      </author>
799      <author initials="J." surname="Mogul" fullname="J. Mogul">
800         <organization>Compaq Computer Corporation</organization>
801         <address><email>mogul@wrl.dec.com</email></address>
802      </author>
803      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
804         <organization>MIT Laboratory for Computer Science</organization>
805         <address><email>frystyk@w3.org</email></address>
806      </author>
807      <author initials="L." surname="Masinter" fullname="L. Masinter">
808         <organization>Xerox Corporation</organization>
809         <address><email>masinter@parc.xerox.com</email></address>
810      </author>
811      <author initials="P." surname="Leach" fullname="P. Leach">
812         <organization>Microsoft Corporation</organization>
813         <address><email>paulle@microsoft.com</email></address>
814      </author>
815      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
816         <organization>W3C</organization>
817         <address><email>timbl@w3.org</email></address>
818      </author>
819      <date month="June" year="1999"/>
820   </front>
821   <seriesInfo name="RFC" value="2616"/>
822</reference>
823
824<reference anchor="RFC2046">
825<front>
826<title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
827<author initials="N." surname="Freed" fullname="Ned Freed">
828<organization>Innosoft International, Inc.</organization>
829<address>
830<postal>
831<street>1050 East Garvey Avenue South</street>
832<city>West Covina</city>
833<region>CA</region>
834<code>91790</code>
835<country>US</country></postal>
836<phone>+1 818 919 3600</phone>
837<facsimile>+1 818 919 3614</facsimile>
838<email>ned@innosoft.com</email></address></author>
839<author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
840<organization>First Virtual Holdings</organization>
841<address>
842<postal>
843<street>25 Washington Avenue</street>
844<city>Morristown</city>
845<region>NJ</region>
846<code>07960</code>
847<country>US</country></postal>
848<phone>+1 201 540 8967</phone>
849<facsimile>+1 201 993 3032</facsimile>
850<email>nsb@nsb.fv.com</email></address></author>
851<date month="November" year="1996"/>
852</front>
853<seriesInfo name="RFC" value="2046"/>
854</reference>
855
856</references>
857
858<section title="Internet Media Type multipart/byteranges" anchor="internet.media.type.multipart.byteranges">
859<iref item="Media Type" subitem="multipart/byteranges" primary="true"/>
860<iref item="multipart/byteranges Media Type" primary="true"/>
861<t>
862   When an HTTP 206 (Partial Content) response message includes the
863   content of multiple ranges (a response to a request for multiple
864   non-overlapping ranges), these are transmitted as a multipart
865   message-body. The media type for this purpose is called
866   "multipart/byteranges".
867</t><t>
868   The multipart/byteranges media type includes two or more parts, each
869   with its own Content-Type and Content-Range fields. The required
870   boundary parameter specifies the boundary string used to separate
871   each body-part.
872</t>
873<t>
874  <list style="hanging" x:indent="12em">
875    <t hangText="Media Type name:">
876      multipart
877    </t>
878    <t hangText="Media subtype name:">
879      byteranges
880    </t>
881    <t hangText="Required parameters:">
882      boundary
883    </t>
884    <t hangText="Optional parameters:">
885      none
886    </t>
887    <t hangText="Encoding considerations:">
888      only "7bit", "8bit", or "binary" are permitted
889    </t>
890    <t hangText="Security considerations:">
891      none
892    </t>
893  </list>
894</t>
895<figure><preamble>
896   For example:
897</preamble><artwork type="example">
898   HTTP/1.1 206 Partial Content
899   Date: Wed, 15 Nov 1995 06:25:24 GMT
900   Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
901   Content-type: multipart/byteranges; boundary=THIS_STRING_SEPARATES
902
903   --THIS_STRING_SEPARATES
904   Content-type: application/pdf
905   Content-range: bytes 500-999/8000
906
907   ...the first range...
908   --THIS_STRING_SEPARATES
909   Content-type: application/pdf
910   Content-range: bytes 7000-7999/8000
911
912   ...the second range
913   --THIS_STRING_SEPARATES--
914</artwork></figure>
915<t>
916      Notes:
917  <list style="numbers">
918      <t>Additional CRLFs may precede the first boundary string in the
919         entity.</t>
920
921      <t>Although RFC 2046 <xref target="RFC2046"/> permits the boundary string to be
922         quoted, some existing implementations handle a quoted boundary
923         string incorrectly.</t>
924
925      <t>A number of browsers and servers were coded to an early draft
926         of the byteranges specification to use a media type of
927         multipart/x-byteranges<iref item="multipart/x-byteranges Media Type"/><iref item="Media Type" subitem="multipart/x-byteranges"/>, which is almost, but not quite
928         compatible with the version documented in HTTP/1.1.</t>
929  </list>
930</t>
931</section>
932
933<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
934<t>
935   There are situations where a server (especially a proxy) does not
936   know the full length of a response but is capable of serving a
937   byterange request. We therefore need a mechanism to allow byteranges
938   with a content-range not indicating the full length of the message.
939   (<xref target="header.content-range"/>)
940</t>
941<t>
942   Range request responses would become very verbose if all meta-data
943   were always returned; by allowing the server to only send needed
944   headers in a 206 response, this problem can be avoided.
945</t>
946<t>
947   Fix problem with unsatisfiable range requests; there are two cases:
948   syntactic problems, and range doesn't exist in the document. The 416
949   status code was needed to resolve this ambiguity needed to indicate
950   an error for a byte range request that falls outside of the actual
951   contents of a document. (Section <xref target="status.416" format="counter"/>, <xref target="header.content-range" format="counter"/>)
952</t>
953</section>
954
955</back>
956</rfc>
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