source: draft-ietf-httpbis/latest/p5-range.xml @ 113

Last change on this file since 113 was 113, checked in by julian.reschke@…, 12 years ago

Use canonical URLs for links to tools.ietf.org.

  • Property svn:eol-style set to native
File size: 42.0 KB
Line 
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    This version of the HTTP specification contains only minimal editorial
190    changes from <xref target="RFC2616"/> (abstract, introductory paragraph,
191    and authors' addresses).  All other changes are due to partitioning the
192    original into seven mostly independent parts.  The intent is for readers
193    of future drafts to able to use draft 00 as the basis for comparison
194    when the WG makes later changes to the specification text.  This draft
195    will shortly be followed by draft 01 (containing the first round of changes
196    that have already been agreed to on the mailing list). There is no point in
197    reviewing this draft other than to verify that the partitioning has been
198    done correctly.  Roy T. Fielding, Yves Lafon, and Julian Reschke
199    will be the editors after draft 00 is submitted.
200  </t>
201  <t>
202    Discussion of this draft should take place on the HTTPBIS working group
203    mailing list (ietf-http-wg@w3.org). The current issues list is
204    at <eref target="http://www.tools.ietf.org/wg/httpbis/trac/report/11"/>
205    and related documents (including fancy diffs) can be found at
206    <eref target="http://www.tools.ietf.org/wg/httpbis/"/>.
207  </t>
208</note>
209</front>
210<middle>
211<section title="Introduction" anchor="introduction">
212<t>
213   This document will define aspects of HTTP related to range requests,
214   partial responses, and the multipart/byteranges media type.  Right now
215   it only includes the extracted relevant sections of
216   <xref target="RFC2616">RFC 2616</xref> without edit.
217</t>
218
219<section title="Requirements" anchor="intro.requirements">
220<t>
221   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
222   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
223   document are to be interpreted as described in <xref target="RFC2119"/>.
224</t>
225<t>
226   An implementation is not compliant if it fails to satisfy one or more
227   of the &MUST; or &REQUIRED; level requirements for the protocols it
228   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
229   level and all the &SHOULD; level requirements for its protocols is said
230   to be "unconditionally compliant"; one that satisfies all the &MUST;
231   level requirements but not all the &SHOULD; level requirements for its
232   protocols is said to be "conditionally compliant."
233</t>
234</section>
235</section>
236
237<section title="Range Units" anchor="range.units">
238<t>
239   HTTP/1.1 allows a client to request that only part (a range of) the
240   response entity be included within the response. HTTP/1.1 uses range
241   units in the Range (<xref target="header.range"/>) and Content-Range (<xref target="header.content-range"/>)
242   header fields. An entity can be broken down into subranges according
243   to various structural units.
244</t>
245<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"/>
246   range-unit       = bytes-unit | other-range-unit
247   bytes-unit       = "bytes"
248   other-range-unit = token
249</artwork></figure>
250<t>
251   The only range unit defined by HTTP/1.1 is "bytes". HTTP/1.1
252   implementations &MAY; ignore ranges specified using other units.
253</t>
254<t>
255   HTTP/1.1 has been designed to allow implementations of applications
256   that do not depend on knowledge of ranges.
257</t>
258</section>
259
260<section title="Status Code Definitions">
261<section title="206 Partial Content" anchor="status.206">
262  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
263  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
264<t>
265   The server has fulfilled the partial GET request for the resource.
266   The request &MUST; have included a Range header field (<xref target="header.range"/>)
267   indicating the desired range, and &MAY; have included an If-Range
268   header field (<xref target="header.if-range"/>) to make the request conditional.
269</t>
270<t>
271   The response &MUST; include the following header fields:
272  <list style="symbols">
273    <t>
274        Either a Content-Range header field (<xref target="header.content-range"/>) indicating
275        the range included with this response, or a multipart/byteranges
276        Content-Type including Content-Range fields for each part. If a
277        Content-Length header field is present in the response, its
278        value &MUST; match the actual number of OCTETs transmitted in the
279        message-body.
280    </t>
281    <t>
282        Date
283    </t>
284    <t>
285        ETag and/or Content-Location, if the header would have been sent
286        in a 200 response to the same request
287    </t>
288    <t>
289        Expires, Cache-Control, and/or Vary, if the field-value might
290        differ from that sent in any previous response for the same
291        variant
292    </t>
293  </list>
294</t>
295<t>
296   If the 206 response is the result of an If-Range request, the response
297   &SHOULD-NOT; include other entity-headers. Otherwise, the response
298   &MUST; include all of the entity-headers that would have been returned
299   with a 200 (OK) response to the same request.
300</t>
301<t>
302   A cache &MUST-NOT; combine a 206 response with other previously cached
303   content if the ETag or Last-Modified headers do not match exactly,
304   see <xref target="combining.byte.ranges" format="counter"/>.
305</t>
306<t>
307   A cache that does not support the Range and Content-Range headers
308   &MUST-NOT; cache 206 (Partial) responses.
309</t>
310</section>
311
312<section title="416 Requested Range Not Satisfiable" anchor="status.416">
313  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
314  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
315<t>
316   A server &SHOULD; return a response with this status code if a request
317   included a Range request-header field (<xref target="header.range"/>), and none of
318   the range-specifier values in this field overlap the current extent
319   of the selected resource, and the request did not include an If-Range
320   request-header field. (For byte-ranges, this means that the first-byte-pos
321   of all of the byte-range-spec values were greater than the
322   current length of the selected resource.)
323</t>
324<t>
325   When this status code is returned for a byte-range request, the
326   response &SHOULD; include a Content-Range entity-header field
327   specifying the current length of the selected resource (see <xref target="header.content-range"/>).
328   This response &MUST-NOT; use the multipart/byteranges content-type.
329</t>
330</section>
331</section>
332
333<section title="Combining Byte Ranges" anchor="combining.byte.ranges">
334<t>
335   A response might transfer only a subrange of the bytes of an entity-body,
336   either because the request included one or more Range
337   specifications, or because a connection was broken prematurely. After
338   several such transfers, a cache might have received several ranges of
339   the same entity-body.
340</t>
341<t>
342   If a cache has a stored non-empty set of subranges for an entity, and
343   an incoming response transfers another subrange, the cache &MAY;
344   combine the new subrange with the existing set if both the following
345   conditions are met:
346  <list style="symbols">
347    <t>Both the incoming response and the cache entry have a cache
348        validator.</t>
349    <t>The two cache validators match using the strong comparison
350        function (see &weak-and-strong-validators;).</t>
351  </list>
352</t>
353<t>
354   If either requirement is not met, the cache &MUST; use only the most
355   recent partial response (based on the Date values transmitted with
356   every response, and using the incoming response if these values are
357   equal or missing), and &MUST; discard the other partial information.
358</t>
359</section>
360
361<section title="Header Field Definitions" anchor="header.fields">
362<t>
363   This section defines the syntax and semantics of all standard
364   HTTP/1.1 header fields. For entity-header fields, both sender and
365   recipient refer to either the client or the server, depending on who
366   sends and who receives the entity.
367</t>
368<section title="Accept-Ranges" anchor="header.accept-ranges">
369  <iref primary="true" item="Accept-Ranges header" x:for-anchor=""/>
370  <iref primary="true" item="Headers" subitem="Accept-Ranges" x:for-anchor=""/>
371<t>
372      The Accept-Ranges response-header field allows the server to
373      indicate its acceptance of range requests for a resource:
374</t>
375<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Ranges"/><iref primary="true" item="Grammar" subitem="acceptable-ranges"/>
376       Accept-Ranges     = "Accept-Ranges" ":" acceptable-ranges
377       acceptable-ranges = 1#range-unit | "none"
378</artwork></figure>
379<t>
380      Origin servers that accept byte-range requests &MAY; send
381</t>
382<figure><artwork type="example">
383       Accept-Ranges: bytes
384</artwork></figure>
385<t>
386      but are not required to do so. Clients &MAY; generate byte-range
387      requests without having received this header for the resource
388      involved. Range units are defined in <xref target="range.units"/>.
389</t>
390<t>
391      Servers that do not accept any kind of range request for a
392      resource &MAY; send
393</t>
394<figure><artwork type="example">
395       Accept-Ranges: none
396</artwork></figure>
397<t>
398      to advise the client not to attempt a range request.
399</t>
400</section>
401
402<section title="Content-Range" anchor="header.content-range">
403  <iref primary="true" item="Content-Range header" x:for-anchor=""/>
404  <iref primary="true" item="Headers" subitem="Content-Range" x:for-anchor=""/>
405<t>
406   The Content-Range entity-header is sent with a partial entity-body to
407   specify where in the full entity-body the partial body should be
408   applied. Range units are defined in <xref target="range.units"/>.
409</t>
410<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"/>
411    Content-Range = "Content-Range" ":" content-range-spec
412
413    content-range-spec      = byte-content-range-spec
414    byte-content-range-spec = bytes-unit SP
415                              byte-range-resp-spec "/"
416                              ( instance-length | "*" )
417
418    byte-range-resp-spec = (first-byte-pos "-" last-byte-pos)
419                                   | "*"
420    instance-length           = 1*DIGIT
421</artwork></figure>
422<t>
423   The header &SHOULD; indicate the total length of the full entity-body,
424   unless this length is unknown or difficult to determine. The asterisk
425   "*" character means that the instance-length is unknown at the time
426   when the response was generated.
427</t>
428<t>
429   Unlike byte-ranges-specifier values (see <xref target="byte.ranges"/>), a byte-range-resp-spec
430   &MUST; only specify one range, and &MUST; contain
431   absolute byte positions for both the first and last byte of the
432   range.
433</t>
434<t>
435   A byte-content-range-spec with a byte-range-resp-spec whose last-byte-pos
436   value is less than its first-byte-pos value, or whose
437   instance-length value is less than or equal to its last-byte-pos
438   value, is invalid. The recipient of an invalid byte-content-range-spec
439   &MUST; ignore it and any content transferred along with it.
440</t>
441<t>
442   A server sending a response with status code 416 (Requested range not
443   satisfiable) &SHOULD; include a Content-Range field with a byte-range-resp-spec
444   of "*". The instance-length specifies the current length of
445   the selected resource. A response with status code 206 (Partial
446   Content) &MUST-NOT; include a Content-Range field with a byte-range-resp-spec of "*".
447</t>
448<t>
449   Examples of byte-content-range-spec values, assuming that the entity
450   contains a total of 1234 bytes:
451   <list style="symbols">
452      <t>
453        The first 500 bytes:
454<figure><artwork type="text/plain">
455   bytes 0-499/1234
456</artwork></figure>
457      </t>   
458      <t>
459        The second 500 bytes:
460<figure><artwork type="text/plain">
461   bytes 500-999/1234
462</artwork></figure>
463      </t>   
464      <t>
465        All except for the first 500 bytes:
466<figure><artwork type="text/plain">
467   bytes 500-1233/1234
468</artwork></figure>
469      </t>   
470      <t>
471        The last 500 bytes:
472<figure><artwork type="text/plain">
473   bytes 734-1233/1234
474</artwork></figure>
475      </t>   
476   </list>
477</t>
478<t>
479   When an HTTP message includes the content of a single range (for
480   example, a response to a request for a single range, or to a request
481   for a set of ranges that overlap without any holes), this content is
482   transmitted with a Content-Range header, and a Content-Length header
483   showing the number of bytes actually transferred. For example,
484</t>
485<figure><artwork type="example">
486    HTTP/1.1 206 Partial content
487    Date: Wed, 15 Nov 1995 06:25:24 GMT
488    Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
489    Content-Range: bytes 21010-47021/47022
490    Content-Length: 26012
491    Content-Type: image/gif
492</artwork></figure>
493<t>
494   When an HTTP message includes the content of multiple ranges (for
495   example, a response to a request for multiple non-overlapping
496   ranges), these are transmitted as a multipart message. The multipart
497   media type used for this purpose is "multipart/byteranges" as defined
498   in <xref target="internet.media.type.multipart.byteranges"/>. See <xref target="changes.from.rfc.2068"/> for a compatibility issue.
499</t>
500<t>
501   A response to a request for a single range &MUST-NOT; be sent using the
502   multipart/byteranges media type.  A response to a request for
503   multiple ranges, whose result is a single range, &MAY; be sent as a
504   multipart/byteranges media type with one part. A client that cannot
505   decode a multipart/byteranges message &MUST-NOT; ask for multiple
506   byte-ranges in a single request.
507</t>
508<t>
509   When a client requests multiple byte-ranges in one request, the
510   server &SHOULD; return them in the order that they appeared in the
511   request.
512</t>
513<t>
514   If the server ignores a byte-range-spec because it is syntactically
515   invalid, the server &SHOULD; treat the request as if the invalid Range
516   header field did not exist. (Normally, this means return a 200
517   response containing the full entity).
518</t>
519<t>
520   If the server receives a request (other than one including an If-Range
521   request-header field) with an unsatisfiable Range request-header
522   field (that is, all of whose byte-range-spec values have a
523   first-byte-pos value greater than the current length of the selected
524   resource), it &SHOULD; return a response code of 416 (Requested range
525   not satisfiable) (<xref target="status.416"/>).
526  <list><t>
527      <x:h>Note:</x:h> clients cannot depend on servers to send a 416 (Requested
528      range not satisfiable) response instead of a 200 (OK) response for
529      an unsatisfiable Range request-header, since not all servers
530      implement this request-header.
531  </t></list>
532</t>
533</section>
534
535<section title="If-Range" anchor="header.if-range">
536  <iref primary="true" item="If-Range header" x:for-anchor=""/>
537  <iref primary="true" item="Headers" subitem="If-Range" x:for-anchor=""/>
538<t>
539   If a client has a partial copy of an entity in its cache, and wishes
540   to have an up-to-date copy of the entire entity in its cache, it
541   could use the Range request-header with a conditional GET (using
542   either or both of If-Unmodified-Since and If-Match.) However, if the
543   condition fails because the entity has been modified, the client
544   would then have to make a second request to obtain the entire current
545   entity-body.
546</t>
547<t>
548   The If-Range header allows a client to "short-circuit" the second
549   request. Informally, its meaning is `if the entity is unchanged, send
550   me the part(s) that I am missing; otherwise, send me the entire new
551   entity'.
552</t>
553<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-Range"/>
554     If-Range = "If-Range" ":" ( entity-tag | HTTP-date )
555</artwork></figure>
556<t>
557   If the client has no entity tag for an entity, but does have a Last-Modified
558   date, it &MAY; use that date in an If-Range header. (The
559   server can distinguish between a valid HTTP-date and any form of
560   entity-tag by examining no more than two characters.) The If-Range
561   header &SHOULD; only be used together with a Range header, and &MUST; be
562   ignored if the request does not include a Range header, or if the
563   server does not support the sub-range operation.
564</t>
565<t>
566   If the entity tag given in the If-Range header matches the current
567   entity tag for the entity, then the server &SHOULD; provide the
568   specified sub-range of the entity using a 206 (Partial content)
569   response. If the entity tag does not match, then the server &SHOULD;
570   return the entire entity using a 200 (OK) response.
571</t>
572</section>
573
574<section title="Range" anchor="header.range">
575  <iref primary="true" item="Range header" x:for-anchor=""/>
576  <iref primary="true" item="Headers" subitem="Range" x:for-anchor=""/>
577
578<section title="Byte Ranges" anchor="byte.ranges">
579<t>
580   Since all HTTP entities are represented in HTTP messages as sequences
581   of bytes, the concept of a byte range is meaningful for any HTTP
582   entity. (However, not all clients and servers need to support byte-range
583   operations.)
584</t>
585<t>
586   Byte range specifications in HTTP apply to the sequence of bytes in
587   the entity-body (not necessarily the same as the message-body).
588</t>
589<t>
590   A byte range operation &MAY; specify a single range of bytes, or a set
591   of ranges within a single entity.
592</t>
593<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"/>
594    ranges-specifier = byte-ranges-specifier
595    byte-ranges-specifier = bytes-unit "=" byte-range-set
596    byte-range-set  = 1#( byte-range-spec | suffix-byte-range-spec )
597    byte-range-spec = first-byte-pos "-" [last-byte-pos]
598    first-byte-pos  = 1*DIGIT
599    last-byte-pos   = 1*DIGIT
600</artwork></figure>
601<t>
602   The first-byte-pos value in a byte-range-spec gives the byte-offset
603   of the first byte in a range. The last-byte-pos value gives the
604   byte-offset of the last byte in the range; that is, the byte
605   positions specified are inclusive. Byte offsets start at zero.
606</t>
607<t>
608   If the last-byte-pos value is present, it &MUST; be greater than or
609   equal to the first-byte-pos in that byte-range-spec, or the byte-range-spec
610   is syntactically invalid. The recipient of a byte-range-set
611   that includes one or more syntactically invalid byte-range-spec
612   values &MUST; ignore the header field that includes that byte-range-set.
613</t>
614<t>
615   If the last-byte-pos value is absent, or if the value is greater than
616   or equal to the current length of the entity-body, last-byte-pos is
617   taken to be equal to one less than the current length of the entity-body
618   in bytes.
619</t>
620<t>
621   By its choice of last-byte-pos, a client can limit the number of
622   bytes retrieved without knowing the size of the entity.
623</t>
624<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="suffix-byte-range-spec"/><iref primary="true" item="Grammar" subitem="suffix-length"/>
625    suffix-byte-range-spec = "-" suffix-length
626    suffix-length = 1*DIGIT
627</artwork></figure>
628<t>
629   A suffix-byte-range-spec is used to specify the suffix of the
630   entity-body, of a length given by the suffix-length value. (That is,
631   this form specifies the last N bytes of an entity-body.) If the
632   entity is shorter than the specified suffix-length, the entire
633   entity-body is used.
634</t>
635<t>
636   If a syntactically valid byte-range-set includes at least one byte-range-spec
637   whose first-byte-pos is less than the current length of
638   the entity-body, or at least one suffix-byte-range-spec with a non-zero
639   suffix-length, then the byte-range-set is satisfiable.
640   Otherwise, the byte-range-set is unsatisfiable. If the byte-range-set
641   is unsatisfiable, the server &SHOULD; return a response with a status
642   of 416 (Requested range not satisfiable). Otherwise, the server
643   &SHOULD; return a response with a status of 206 (Partial Content)
644   containing the satisfiable ranges of the entity-body.
645</t>
646<t>
647   Examples of byte-ranges-specifier values (assuming an entity-body of
648   length 10000):
649  <list style="symbols">
650     <t>The first 500 bytes (byte offsets 0-499, inclusive):  bytes=0-499</t>
651
652     <t>The second 500 bytes (byte offsets 500-999, inclusive):
653        bytes=500-999</t>
654
655     <t>The final 500 bytes (byte offsets 9500-9999, inclusive):
656        bytes=-500</t>
657
658     <t>Or bytes=9500-</t>
659
660     <t>The first and last bytes only (bytes 0 and 9999):  bytes=0-0,-1</t>
661
662     <t>Several legal but not canonical specifications of the second 500
663        bytes (byte offsets 500-999, inclusive):
664        <vspace/>
665         bytes=500-600,601-999<vspace/>
666         bytes=500-700,601-999</t>
667  </list>
668</t>
669</section>
670
671<section title="Range Retrieval Requests" anchor="range.retrieval.requests">
672<t>
673   HTTP retrieval requests using conditional or unconditional GET
674   methods &MAY; request one or more sub-ranges of the entity, instead of
675   the entire entity, using the Range request header, which applies to
676   the entity returned as the result of the request:
677</t>
678<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Range"/>
679   Range = "Range" ":" ranges-specifier
680</artwork></figure>
681<t>
682   A server &MAY; ignore the Range header. However, HTTP/1.1 origin
683   servers and intermediate caches ought to support byte ranges when
684   possible, since Range supports efficient recovery from partially
685   failed transfers, and supports efficient partial retrieval of large
686   entities.
687</t>
688<t>
689   If the server supports the Range header and the specified range or
690   ranges are appropriate for the entity:
691  <list style="symbols">
692     <t>The presence of a Range header in an unconditional GET modifies
693        what is returned if the GET is otherwise successful. In other
694        words, the response carries a status code of 206 (Partial
695        Content) instead of 200 (OK).</t>
696
697     <t>The presence of a Range header in a conditional GET (a request
698        using one or both of If-Modified-Since and If-None-Match, or
699        one or both of If-Unmodified-Since and If-Match) modifies what
700        is returned if the GET is otherwise successful and the
701        condition is true. It does not affect the 304 (Not Modified)
702        response returned if the conditional is false.</t>
703  </list>
704</t>
705<t>
706   In some cases, it might be more appropriate to use the If-Range
707   header (see <xref target="header.if-range"/>) in addition to the Range header.
708</t>
709<t>
710   If a proxy that supports ranges receives a Range request, forwards
711   the request to an inbound server, and receives an entire entity in
712   reply, it &SHOULD; only return the requested range to its client. It
713   &SHOULD; store the entire received response in its cache if that is
714   consistent with its cache allocation policies.
715</t>
716</section>
717</section>
718</section>
719
720<section title="IANA Considerations" anchor="IANA.considerations">
721<t>
722   TBD.
723</t>
724</section>
725
726<section title="Security Considerations" anchor="security.considerations">
727<t>
728   No additional security considerations have been identified beyond
729   those applicable to HTTP in general &messaging;.
730</t>
731</section>
732
733<section title="Acknowledgments" anchor="ack">
734<t>
735   Most of the specification of ranges is based on work originally done
736   by Ari Luotonen and John Franks, with additional input from Steve
737   Zilles.
738</t>
739</section>
740</middle>
741<back>
742<references>
743
744<reference anchor="Part1">
745   <front>
746      <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
747      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
748         <organization abbrev="Day Software">Day Software</organization>
749         <address><email>fielding@gbiv.com</email></address>
750      </author>
751      <author initials="J." surname="Gettys" fullname="Jim Gettys">
752         <organization>One Laptop per Child</organization>
753         <address><email>jg@laptop.org</email></address>
754      </author>
755      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
756         <organization abbrev="HP">Hewlett-Packard Company</organization>
757         <address><email>JeffMogul@acm.org</email></address>
758      </author>
759      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
760         <organization abbrev="Microsoft">Microsoft Corporation</organization>
761         <address><email>henrikn@microsoft.com</email></address>
762      </author>
763      <author initials="L." surname="Masinter" fullname="Larry Masinter">
764         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
765         <address><email>LMM@acm.org</email></address>
766      </author>
767      <author initials="P." surname="Leach" fullname="Paul J. Leach">
768         <organization abbrev="Microsoft">Microsoft Corporation</organization>
769         <address><email>paulle@microsoft.com</email></address>
770      </author>
771      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
772         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
773         <address><email>timbl@w3.org</email></address>
774      </author>
775      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
776         <organization abbrev="W3C">World Wide Web Consortium</organization>
777         <address><email>ylafon@w3.org</email></address>
778      </author>
779      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
780         <organization abbrev="greenbytes">greenbytes GmbH</organization>
781         <address><email>julian.reschke@greenbytes.de</email></address>
782      </author>
783      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
784   </front>
785   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
786   <x:source href="p1-messaging.xml" basename="p1-messaging"/>
787</reference>
788
789<reference anchor="Part4">
790   <front>
791      <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
792      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
793         <organization abbrev="Day Software">Day Software</organization>
794         <address><email>fielding@gbiv.com</email></address>
795      </author>
796      <author initials="J." surname="Gettys" fullname="Jim Gettys">
797         <organization>One Laptop per Child</organization>
798         <address><email>jg@laptop.org</email></address>
799      </author>
800      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
801         <organization abbrev="HP">Hewlett-Packard Company</organization>
802         <address><email>JeffMogul@acm.org</email></address>
803      </author>
804      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
805         <organization abbrev="Microsoft">Microsoft Corporation</organization>
806         <address><email>henrikn@microsoft.com</email></address>
807      </author>
808      <author initials="L." surname="Masinter" fullname="Larry Masinter">
809         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
810         <address><email>LMM@acm.org</email></address>
811      </author>
812      <author initials="P." surname="Leach" fullname="Paul J. Leach">
813         <organization abbrev="Microsoft">Microsoft Corporation</organization>
814         <address><email>paulle@microsoft.com</email></address>
815      </author>
816      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
817         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
818         <address><email>timbl@w3.org</email></address>
819      </author>
820      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
821         <organization abbrev="W3C">World Wide Web Consortium</organization>
822         <address><email>ylafon@w3.org</email></address>
823      </author>
824      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
825         <organization abbrev="greenbytes">greenbytes GmbH</organization>
826         <address><email>julian.reschke@greenbytes.de</email></address>
827      </author>
828      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
829   </front>
830   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
831   <x:source href="p4-conditional.xml" basename="p4-conditional"/>
832</reference>
833
834<reference anchor="RFC2616">
835   <front>
836      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
837      <author initials="R." surname="Fielding" fullname="R. Fielding">
838         <organization>University of California, Irvine</organization>
839         <address><email>fielding@ics.uci.edu</email></address>
840      </author>
841      <author initials="J." surname="Gettys" fullname="J. Gettys">
842         <organization>W3C</organization>
843         <address><email>jg@w3.org</email></address>
844      </author>
845      <author initials="J." surname="Mogul" fullname="J. Mogul">
846         <organization>Compaq Computer Corporation</organization>
847         <address><email>mogul@wrl.dec.com</email></address>
848      </author>
849      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
850         <organization>MIT Laboratory for Computer Science</organization>
851         <address><email>frystyk@w3.org</email></address>
852      </author>
853      <author initials="L." surname="Masinter" fullname="L. Masinter">
854         <organization>Xerox Corporation</organization>
855         <address><email>masinter@parc.xerox.com</email></address>
856      </author>
857      <author initials="P." surname="Leach" fullname="P. Leach">
858         <organization>Microsoft Corporation</organization>
859         <address><email>paulle@microsoft.com</email></address>
860      </author>
861      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
862         <organization>W3C</organization>
863         <address><email>timbl@w3.org</email></address>
864      </author>
865      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
866         <organization abbrev="W3C">World Wide Web Consortium</organization>
867         <address><email>ylafon@w3.org</email></address>
868      </author>
869      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
870         <organization abbrev="greenbytes">greenbytes GmbH</organization>
871         <address><email>julian.reschke@greenbytes.de</email></address>
872      </author>
873      <date month="June" year="1999"/>
874   </front>
875   <seriesInfo name="RFC" value="2616"/>
876</reference>
877
878<reference anchor="RFC2046">
879  <front>
880    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
881    <author initials="N." surname="Freed" fullname="Ned Freed">
882      <organization>Innosoft International, Inc.</organization>
883      <address><email>ned@innosoft.com</email></address>
884    </author>
885    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
886      <organization>First Virtual Holdings</organization>
887      <address><email>nsb@nsb.fv.com</email></address>
888    </author>
889    <date month="November" year="1996"/>
890  </front>
891  <seriesInfo name="RFC" value="2046"/>
892</reference>
893
894<reference anchor="RFC2119">
895  <front>
896    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
897    <author initials="S." surname="Bradner" fullname="Scott Bradner">
898      <organization>Harvard University</organization>
899      <address><email>sob@harvard.edu</email></address>
900    </author>
901    <date month="March" year="1997"/>
902  </front>
903  <seriesInfo name="BCP" value="14"/>
904  <seriesInfo name="RFC" value="2119"/>
905</reference>
906
907</references>
908
909<section title="Internet Media Type multipart/byteranges" anchor="internet.media.type.multipart.byteranges">
910<iref item="Media Type" subitem="multipart/byteranges" primary="true"/>
911<iref item="multipart/byteranges Media Type" primary="true"/>
912<t>
913   When an HTTP 206 (Partial Content) response message includes the
914   content of multiple ranges (a response to a request for multiple
915   non-overlapping ranges), these are transmitted as a multipart
916   message-body. The media type for this purpose is called
917   "multipart/byteranges".
918</t><t>
919   The multipart/byteranges media type includes two or more parts, each
920   with its own Content-Type and Content-Range fields. The required
921   boundary parameter specifies the boundary string used to separate
922   each body-part.
923</t>
924<t>
925  <list style="hanging" x:indent="12em">
926    <t hangText="Media Type name:">
927      multipart
928    </t>
929    <t hangText="Media subtype name:">
930      byteranges
931    </t>
932    <t hangText="Required parameters:">
933      boundary
934    </t>
935    <t hangText="Optional parameters:">
936      none
937    </t>
938    <t hangText="Encoding considerations:">
939      only "7bit", "8bit", or "binary" are permitted
940    </t>
941    <t hangText="Security considerations:">
942      none
943    </t>
944  </list>
945</t>
946<figure><preamble>
947   For example:
948</preamble><artwork type="example">
949   HTTP/1.1 206 Partial Content
950   Date: Wed, 15 Nov 1995 06:25:24 GMT
951   Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
952   Content-type: multipart/byteranges; boundary=THIS_STRING_SEPARATES
953
954   --THIS_STRING_SEPARATES
955   Content-type: application/pdf
956   Content-range: bytes 500-999/8000
957
958   ...the first range...
959   --THIS_STRING_SEPARATES
960   Content-type: application/pdf
961   Content-range: bytes 7000-7999/8000
962
963   ...the second range
964   --THIS_STRING_SEPARATES--
965</artwork></figure>
966<t>
967      Notes:
968  <list style="numbers">
969      <t>Additional CRLFs may precede the first boundary string in the
970         entity.</t>
971
972      <t>Although <xref target="RFC2046"/> permits the boundary string to be
973         quoted, some existing implementations handle a quoted boundary
974         string incorrectly.</t>
975
976      <t>A number of browsers and servers were coded to an early draft
977         of the byteranges specification to use a media type of
978         multipart/x-byteranges<iref item="multipart/x-byteranges Media Type"/><iref item="Media Type" subitem="multipart/x-byteranges"/>, which is almost, but not quite
979         compatible with the version documented in HTTP/1.1.</t>
980  </list>
981</t>
982</section>
983
984<section title="Compatibility with Previous Versions" anchor="compatibility">
985<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
986<t>
987   There are situations where a server (especially a proxy) does not
988   know the full length of a response but is capable of serving a
989   byterange request. We therefore need a mechanism to allow byteranges
990   with a content-range not indicating the full length of the message.
991   (<xref target="header.content-range"/>)
992</t>
993<t>
994   Range request responses would become very verbose if all meta-data
995   were always returned; by allowing the server to only send needed
996   headers in a 206 response, this problem can be avoided.
997</t>
998<t>
999   Fix problem with unsatisfiable range requests; there are two cases:
1000   syntactic problems, and range doesn't exist in the document. The 416
1001   status code was needed to resolve this ambiguity needed to indicate
1002   an error for a byte range request that falls outside of the actual
1003   contents of a document. (Section <xref target="status.416" format="counter"/>, <xref target="header.content-range" format="counter"/>)
1004</t>
1005</section>
1006
1007<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
1008<t>
1009  Clarify that it is not ok to use a weak cache validator in a 206 response.
1010  (<xref target="status.206"/>)
1011</t>
1012</section>
1013
1014</section>
1015
1016
1017</back>
1018</rfc>
Note: See TracBrowser for help on using the repository browser.