| HTTPbis Working Group | R. Fielding, Ed. |
| Internet-Draft | Adobe |
| Obsoletes: 2616 (if approved) | J. Gettys |
| Intended status: Standards Track | Alcatel-Lucent |
| Expires: October 20, 2011 | J. Mogul |
| HP | |
| H. Frystyk | |
| Microsoft | |
| L. Masinter | |
| Adobe | |
| P. Leach | |
| Microsoft | |
| T. Berners-Lee | |
| W3C/MIT | |
| Y. Lafon, Ed. | |
| W3C | |
| J. F. Reschke, Ed. | |
| greenbytes | |
| April 18, 2011 |
HTTP/1.1, part 5: Range Requests and Partial Responses
draft-ietf-httpbis-p5-range-14
The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 5 of the seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 5 defines range-specific requests and the rules for constructing and combining responses to those requests.
Discussion of this draft should take place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org), which is archived at http://lists.w3.org/Archives/Public/ietf-http-wg/.
The current issues list is at http://tools.ietf.org/wg/httpbis/trac/report/3 and related documents (including fancy diffs) can be found at http://tools.ietf.org/wg/httpbis/.
The changes in this draft are summarized in Appendix Appendix D.15.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 20, 2011.
Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English.
HTTP clients often encounter interrupted data transfers as a result of cancelled requests or dropped connections. When a cache has stored a partial representation, it is desirable to request the remainder of that representation in a subsequent request rather than transfer the entire representation. There are also a number of Web applications that benefit from being able to request only a subset of a larger representation, such as a single page of a very large document or only part of an image to be rendered by a device with limited local storage.
This document defines HTTP/1.1 range requests, partial responses, and the multipart/byteranges media type. The protocol for range requests is an OPTIONAL feature of HTTP, designed so resources or recipients that do not implement this feature can respond as if it is a normal GET request without impacting interoperability. Partial responses are indicated by a distinct status code to not be mistaken for full responses by intermediate caches that might not implement the feature.
Although the HTTP range request mechanism is designed to allow for extensible range types, this specification only defines requests for byte ranges.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
An implementation is not compliant if it fails to satisfy one or more of the "MUST" or "REQUIRED" level requirements for the protocols it implements. An implementation that satisfies all the "MUST" or "REQUIRED" level and all the "SHOULD" level requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the "MUST" level requirements but not all the "SHOULD" level requirements for its protocols is said to be "conditionally compliant".
This specification uses the ABNF syntax defined in Section 1.2 of [Part1] (which extends the syntax defined in [RFC5234] with a list rule). Appendix Appendix C shows the collected ABNF, with the list rule expanded.
The following core rules are included by reference, as defined in [RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit sequence of data), SP (space), VCHAR (any visible USASCII character), and WSP (whitespace).
The core rules below are defined in Section 1.2.2 of [Part1]:
token = <token, defined in [Part1], Section 1.2.2> OWS = <OWS, defined in [Part1], Section 1.2.2>
The ABNF rules below are defined in other parts:
HTTP-date = <HTTP-date, defined in [Part1], Section 6.1>
entity-tag = <entity-tag, defined in [Part4], Section 2.2>
HTTP/1.1 allows a client to request that only part (a range) of the representation be included within the response. HTTP/1.1 uses range units in the Range (Section 5.4) and Content-Range (Section 5.2) header fields. A representation can be broken down into subranges according to various structural units.
range-unit = bytes-unit / other-range-unit bytes-unit = "bytes" other-range-unit = token
HTTP/1.1 has been designed to allow implementations of applications that do not depend on knowledge of ranges. The only range unit defined by HTTP/1.1 is "bytes". Additional specifiers can be defined as described in Section 2.1.
If a range unit is not understood in a request, a server MUST ignore the whole Range header field (Section 5.4). If a range unit is not understood in a response, an intermediary SHOULD pass the response to the client; a client MUST fail.
The HTTP Range Specifier Registry defines the name space for the range specifier names.
Registrations MUST include the following fields:
Values to be added to this name space are subject to IETF review ([RFC5226], Section 4.1).
The registry itself is maintained at http://www.iana.org/assignments/http-range-specifiers.
The server has fulfilled the partial GET request for the resource. The request MUST have included a Range header field (Section 5.4) indicating the desired range, and MAY have included an If-Range header field (Section 5.3) to make the request conditional.
The response MUST include the following header fields:
If the 206 response is the result of an If-Range request, the response SHOULD NOT include other representation header fields. Otherwise, the response MUST include all of the representation header fields that would have been returned with a 200 (OK) response to the same request.
A cache MUST NOT combine a 206 response with other previously cached content if the ETag or Last-Modified header fields do not match exactly, see Section 4.
A cache that does not support the Range and Content-Range header fields MUST NOT cache 206 (Partial Content) responses. Furthermore, if a response uses a range unit that is not understood by the cache, then it MUST NOT be cached either.
A server SHOULD return a response with this status code if a request included a Range header field (Section 5.4), and none of the ranges-specifier values in this field overlap the current extent of the selected resource, and the request did not include an If-Range header field (Section 5.3). (For byte-ranges, this means that the first-byte-pos of all of the byte-range-spec values were greater than the current length of the selected resource.)
When this status code is returned for a byte-range request, the response SHOULD include a Content-Range header field specifying the current length of the representation (see Section 5.2). This response MUST NOT use the multipart/byteranges content-type.
A response might transfer only a subrange of a representation, either because the request included one or more Range specifications, or because a connection closed prematurely. After several such transfers, a cache might have received several ranges of the same representation.
If a cache has a stored non-empty set of subranges for a representation, and an incoming response transfers another subrange, the cache MAY combine the new subrange with the existing set if both the following conditions are met:
If either requirement is not met, the cache MUST use only the most recent partial response (based on the Date values transmitted with every response, and using the incoming response if these values are equal or missing), and MUST discard the other partial information.
This section defines the syntax and semantics of HTTP/1.1 header fields related to range requests and partial responses.
The "Accept-Ranges" header field allows a resource to indicate its acceptance of range requests.
Accept-Ranges = acceptable-ranges acceptable-ranges = 1#range-unit / "none"
Origin servers that accept byte-range requests MAY send
Accept-Ranges: bytes
but are not required to do so. Clients MAY generate range requests without having received this header field for the resource involved. Range units are defined in Section 2.
Servers that do not accept any kind of range request for a resource MAY send
Accept-Ranges: none
to advise the client not to attempt a range request.
The "Content-Range" header field is sent with a partial representation to specify where in the full representation the payload body is intended to be applied.
Range units are defined in Section 2.
Content-Range = content-range-spec
content-range-spec = byte-content-range-spec
/ other-content-range-spec
byte-content-range-spec = bytes-unit SP
byte-range-resp-spec "/"
( instance-length / "*" )
byte-range-resp-spec = (first-byte-pos "-" last-byte-pos)
/ "*"
instance-length = 1*DIGIT
other-content-range-spec = other-range-unit SP
other-range-resp-spec
other-range-resp-spec = *CHAR
The header field SHOULD indicate the total length of the full representation, unless this length is unknown or difficult to determine. The asterisk "*" character means that the instance-length is unknown at the time when the response was generated.
Unlike byte-ranges-specifier values (see Section 5.4.1), a byte-range-resp-spec MUST only specify one range, and MUST contain absolute byte positions for both the first and last byte of the range.
A byte-content-range-spec with a byte-range-resp-spec whose last-byte-pos value is less than its first-byte-pos value, or whose instance-length value is less than or equal to its last-byte-pos value, is invalid. The recipient of an invalid byte-content-range-spec MUST ignore it and any content transferred along with it.
In the case of a byte range request: A server sending a response with status code 416 (Requested range not satisfiable) SHOULD include a Content-Range field with a byte-range-resp-spec of "*". The instance-length specifies the current length of the selected resource. A response with status code 206 (Partial Content) MUST NOT include a Content-Range field with a byte-range-resp-spec of "*".
bytes 0-499/1234
bytes 500-999/1234
bytes 500-1233/1234
bytes 734-1233/1234
Examples of byte-content-range-spec values, assuming that the representation contains a total of 1234 bytes:
When an HTTP message includes the content of a single range (for example, a response to a request for a single range, or to a request for a set of ranges that overlap without any holes), this content is transmitted with a Content-Range header field, and a Content-Length header field showing the number of bytes actually transferred. For example,
HTTP/1.1 206 Partial Content Date: Wed, 15 Nov 1995 06:25:24 GMT Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT Content-Range: bytes 21010-47021/47022 Content-Length: 26012 Content-Type: image/gif
When an HTTP message includes the content of multiple ranges (for example, a response to a request for multiple non-overlapping ranges), these are transmitted as a multipart message. The multipart media type used for this purpose is "multipart/byteranges" as defined in Appendix Appendix A.
A response to a request for a single range MUST NOT be sent using the multipart/byteranges media type. A response to a request for multiple ranges, whose result is a single range, MAY be sent as a multipart/byteranges media type with one part. A client that cannot decode a multipart/byteranges message MUST NOT ask for multiple ranges in a single request.
When a client requests multiple ranges in one request, the server SHOULD return them in the order that they appeared in the request.
If the server ignores a byte-range-spec because it is syntactically invalid, the server SHOULD treat the request as if the invalid Range header field did not exist. (Normally, this means return a 200 response containing the full representation).
If the server receives a request (other than one including an If-Range header field) with an unsatisfiable Range header field (that is, all of whose byte-range-spec values have a first-byte-pos value greater than the current length of the selected resource), it SHOULD return a response code of 416 (Requested range not satisfiable) (Section 3.2).
If a client has a partial copy of a representation in its cache, and wishes to have an up-to-date copy of the entire representation in its cache, it could use the Range header field with a conditional GET (using either or both of If-Unmodified-Since and If-Match.) However, if the condition fails because the representation has been modified, the client would then have to make a second request to obtain the entire current representation.
The "If-Range" header field allows a client to "short-circuit" the second request. Informally, its meaning is "if the representation is unchanged, send me the part(s) that I am missing; otherwise, send me the entire new representation".
If-Range = entity-tag / HTTP-date
Only a strong validator (Section 2.2.2 of [Part4]) is usable for range retrieval, since otherwise the client might end up with an internally inconsistent representation. Clients MUST NOT use weak validators in range requests. A cache or origin server receiving a conditional range request MUST use the strong comparison function to evaluate the condition.
If the client has no entity-tag for a representation, but does have a Last-Modified date, it MAY use that date in an If-Range header field. (The server can distinguish between a valid HTTP-date and any form of entity-tag by examining no more than two characters.) The If-Range header field SHOULD only be used together with a Range header field, and MUST be ignored if the request does not include a Range header field, or if the server does not support the sub-range operation.
If a client wishes to perform a sub-range retrieval on a value for which it has only a Last-Modified time and no opaque validator, it MAY do this only if the Last-Modified time is strong in the sense described in Section 2.1.2 of [Part4].
If the entity-tag given in the If-Range header field matches the current cache validator for the representation, then the server SHOULD provide the specified sub-range of the representation using a 206 (Partial Content) response. If the cache validator does not match, then the server SHOULD return the entire representation using a 200 (OK) response.
Since all HTTP representations are transferred as sequences of bytes, the concept of a byte range is meaningful for any HTTP representation. (However, not all clients and servers need to support byte-range operations.)
Byte range specifications in HTTP apply to the sequence of bytes in the representation body (not necessarily the same as the message-body).
A byte range operation MAY specify a single range of bytes, or a set of ranges within a single representation.
byte-ranges-specifier = bytes-unit "=" byte-range-set byte-range-set = 1#( byte-range-spec / suffix-byte-range-spec ) byte-range-spec = first-byte-pos "-" [ last-byte-pos ] first-byte-pos = 1*DIGIT last-byte-pos = 1*DIGIT
The first-byte-pos value in a byte-range-spec gives the byte-offset of the first byte in a range. The last-byte-pos value gives the byte-offset of the last byte in the range; that is, the byte positions specified are inclusive. Byte offsets start at zero.
If the last-byte-pos value is present, it MUST be greater than or equal to the first-byte-pos in that byte-range-spec, or the byte-range-spec is syntactically invalid. The recipient of a byte-range-set that includes one or more syntactically invalid byte-range-spec values MUST ignore the header field that includes that byte-range-set.
If the last-byte-pos value is absent, or if the value is greater than or equal to the current length of the representation body, last-byte-pos is taken to be equal to one less than the current length of the representation in bytes.
By its choice of last-byte-pos, a client can limit the number of bytes retrieved without knowing the size of the representation.
suffix-byte-range-spec = "-" suffix-length suffix-length = 1*DIGIT
A suffix-byte-range-spec is used to specify the suffix of the representation body, of a length given by the suffix-length value. (That is, this form specifies the last N bytes of a representation.) If the representation is shorter than the specified suffix-length, the entire representation is used.
If a syntactically valid byte-range-set includes at least one byte-range-spec whose first-byte-pos is less than the current length of the representation, or at least one suffix-byte-range-spec with a non-zero suffix-length, then the byte-range-set is satisfiable. Otherwise, the byte-range-set is unsatisfiable. If the byte-range-set is unsatisfiable, the server SHOULD return a response with a 416 (Requested range not satisfiable) status code. Otherwise, the server SHOULD return a response with a 206 (Partial Content) status code containing the satisfiable ranges of the representation.
bytes=0-499
bytes=500-999
bytes=-500
bytes=9500-
bytes=0-0,-1
bytes=500-600,601-999
bytes=500-700,601-999
Examples of byte-ranges-specifier values (assuming a representation of length 10000):
The "Range" header field defines the GET method (conditional or not) to request one or more sub-ranges of the response representation body, instead of the entire representation body.
Range = byte-ranges-specifier / other-ranges-specifier other-ranges-specifier = other-range-unit "=" other-range-set other-range-set = 1*CHAR
A server MAY ignore the Range header field. However, HTTP/1.1 origin servers and intermediate caches ought to support byte ranges when possible, since Range supports efficient recovery from partially failed transfers, and supports efficient partial retrieval of large representations.
If the server supports the Range header field and the specified range or ranges are appropriate for the representation:
In some cases, it might be more appropriate to use the If-Range header field (see Section 5.3) in addition to the Range header field.
If a proxy that supports ranges receives a Range request, forwards the request to an inbound server, and receives an entire representation in reply, it MAY only return the requested range to its client.
The HTTP Status Code Registry located at http://www.iana.org/assignments/http-status-codes shall be updated with the registrations below:
| Value | Description | Reference |
|---|---|---|
| 206 | Partial Content | Section 3.1 |
| 416 | Requested Range Not Satisfiable | Section 3.2 |
The Message Header Field Registry located at http://www.iana.org/assignments/message-headers/message-header-index.html shall be updated with the permanent registrations below (see [RFC3864]):
| Header Field Name | Protocol | Status | Reference |
|---|---|---|---|
| Accept-Ranges | http | standard | Section 5.1 |
| Content-Range | http | standard | Section 5.2 |
| If-Range | http | standard | Section 5.3 |
| Range | http | standard | Section 5.4 |
The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
The registration procedure for HTTP Range Specifiers is defined by Section 2.1 of this document.
The HTTP Range Specifier Registry shall be created at http://www.iana.org/assignments/http-range-specifiers and be populated with the registrations below:
| Range Specifier Name | Description | Reference |
|---|---|---|
| bytes | a range of octets | (this specification) |
The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
No additional security considerations have been identified beyond those applicable to HTTP in general [Part1].
Most of the specification of ranges is based on work originally done by Ari Luotonen and John Franks, with additional input from Steve Zilles, Daniel W. Connolly, Roy T. Fielding, Jim Gettys, Martin Hamilton, Koen Holtman, Shel Kaplan, Paul Leach, Alex Lopez-Ortiz, Larry Masinter, Jeff Mogul, Lou Montulli, David W. Morris, Luigi Rizzo, and Bill Weihl.
| [Part1] | Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y. and J. F. Reschke, "HTTP/1.1, part 1: URIs, Connections, and Message Parsing", Internet-Draft draft-ietf-httpbis-p1-messaging-14, April 2011. |
| [Part4] | Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y. and J. F. Reschke, "HTTP/1.1, part 4: Conditional Requests", Internet-Draft draft-ietf-httpbis-p4-conditional-14, April 2011. |
| [RFC2046] | Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC5234] | Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. |
| [RFC2616] | Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. |
| [RFC3864] | Klyne, G., Nottingham, M. and J. Mogul, "Registration Procedures for Message Header Fields", BCP 90, RFC 3864, September 2004. |
| [RFC4288] | Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", BCP 13, RFC 4288, December 2005. |
| [RFC5226] | Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. |
When an HTTP 206 (Partial Content) response message includes the content of multiple ranges (a response to a request for multiple non-overlapping ranges), these are transmitted as a multipart message-body ([RFC2046], Section 5.1). The media type for this purpose is called "multipart/byteranges". The following is to be registered with IANA [RFC4288].
The multipart/byteranges media type includes one or more parts, each with its own Content-Type and Content-Range fields. The required boundary parameter specifies the boundary string used to separate each body-part.
For example:
HTTP/1.1 206 Partial Content Date: Wed, 15 Nov 1995 06:25:24 GMT Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT Content-type: multipart/byteranges; boundary=THIS_STRING_SEPARATES --THIS_STRING_SEPARATES Content-type: application/pdf Content-range: bytes 500-999/8000 ...the first range... --THIS_STRING_SEPARATES Content-type: application/pdf Content-range: bytes 7000-7999/8000 ...the second range --THIS_STRING_SEPARATES--
Other example:
HTTP/1.1 206 Partial Content Date: Tue, 14 Nov 1995 06:25:24 GMT Last-Modified: Tue, 14 July 04:58:08 GMT Content-type: multipart/byteranges; boundary=THIS_STRING_SEPARATES --THIS_STRING_SEPARATES Content-type: video/example Content-range: exampleunit 1.2-4.3/25 ...the first range... --THIS_STRING_SEPARATES Content-type: video/example Content-range: exampleunit 11.2-14.3/25 ...the second range --THIS_STRING_SEPARATES--
Notes:
Clarify that it is not ok to use a weak cache validator in a 206 response. (Section 3.1)
Change ABNF productions for header fields to only define the field value. (Section 5)
Clarify that multipart/byteranges can consist of a single part. (Appendix Appendix A)
Accept-Ranges = acceptable-ranges Content-Range = content-range-spec HTTP-date = <HTTP-date, defined in [Part1], Section 6.1> If-Range = entity-tag / HTTP-date OWS = <OWS, defined in [Part1], Section 1.2.2> Range = byte-ranges-specifier / other-ranges-specifier acceptable-ranges = ( *( "," OWS ) range-unit *( OWS "," [ OWS range-unit ] ) ) / "none" byte-content-range-spec = bytes-unit SP byte-range-resp-spec "/" ( instance-length / "*" ) byte-range-resp-spec = ( first-byte-pos "-" last-byte-pos ) / "*" byte-range-set = ( *( "," OWS ) byte-range-spec ) / ( suffix-byte-range-spec *( OWS "," [ ( OWS byte-range-spec ) / suffix-byte-range-spec ] ) ) byte-range-spec = first-byte-pos "-" [ last-byte-pos ] byte-ranges-specifier = bytes-unit "=" byte-range-set bytes-unit = "bytes" content-range-spec = byte-content-range-spec / other-content-range-spec entity-tag = <entity-tag, defined in [Part4], Section 2.2> first-byte-pos = 1*DIGIT instance-length = 1*DIGIT last-byte-pos = 1*DIGIT other-content-range-spec = other-range-unit SP other-range-resp-spec other-range-resp-spec = *CHAR other-range-set = 1*CHAR other-range-unit = token other-ranges-specifier = other-range-unit "=" other-range-set range-unit = bytes-unit / other-range-unit suffix-byte-range-spec = "-" suffix-length suffix-length = 1*DIGIT token = <token, defined in [Part1], Section 1.2.2>
ABNF diagnostics:
; Accept-Ranges defined but not used ; Content-Range defined but not used ; If-Range defined but not used ; Range defined but not used
Extracted relevant partitions from [RFC2616].
Closed issues:
Closed issues:
Ongoing work on ABNF conversion (http://tools.ietf.org/wg/httpbis/trac/ticket/36):
Ongoing work on IANA Message Header Field Registration (http://tools.ietf.org/wg/httpbis/trac/ticket/40):
None.
Closed issues:
Ongoing work on ABNF conversion (http://tools.ietf.org/wg/httpbis/trac/ticket/36):
Closed issues:
Ongoing work on Custom Ranges (http://tools.ietf.org/wg/httpbis/trac/ticket/85):
Final work on ABNF conversion (http://tools.ietf.org/wg/httpbis/trac/ticket/36):
Closed issues:
Closed issues:
No significant changes.
No significant changes.
Closed issues:
Ongoing work on Custom Ranges (http://tools.ietf.org/wg/httpbis/trac/ticket/85):
Closed issues:
Closed issues:
Closed issues:
| M | |
| Media Type | |
| multipart/x-byteranges | |
| multipart/x-byteranges Media Type |