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MAY“> MUST“> MUST NOT“> OPTIONAL“> RECOMMENDED“> REQUIRED“> SHALL“> SHALL NOT“> SHOULD“> SHOULD NOT“> Note:“> “> “> “> “> “> “> “> “> “> “> “> “> “> ]> Adobe Systems Incorporated

345 Park Ave San Jose CA 95110 USA fielding@gbiv.com http://roy.gbiv.com/

World Wide Web Consortium

W3C / ERCIM 2004, rte des Lucioles Sophia-Antipolis AM 06902 France ylafon@w3.org http://www.raubacapeu.net/people/yves/

greenbytes GmbH

Hafenweg 16 MuensterNW48155 Germany julian.reschke@greenbytes.de http://greenbytes.de/tech/webdav/

HTTPbis Working Group The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information systems. This document defines range requests and the rules for constructing and combining responses to those requests. Discussion of this draft takes place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org), which is archived at . The current issues list is at and related documents (including fancy diffs) can be found at . The changes in this draft are summarized in .

HTTP clients often encounter interrupted data transfers as a result of canceled requests or dropped connections. When a client 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 . Conformance criteria and considerations regarding error handling are defined in &conformance;.

This specification uses the Augmented Backus-Naur Form (ABNF) notation of with the list rule extension defined in ¬ation;. describes rules imported from other documents. shows the collected ABNF with the list rule expanded.

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 () and Content-Range () 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 . If a range unit is not understood in a request, a server &MUST; ignore the whole Range header field (). 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: Name Description Pointer to specification text Values to be added to this name space require IETF Review (see ). The registry itself is maintained at .

The server has fulfilled the partial GET request for the resource. The request &MUST; have included a Range header field () indicating the desired range, and &MAY; have included an If-Range header field () to make the request conditional. The response &MUST; include the following header fields: Either a Content-Range header field () indicating the range included with this response, or a multipart/byteranges Content-Type including Content-Range fields for each part. If a Content-Length header field is present in the response, its value &MUST; match the actual number of octets transmitted in the message body. Date Cache-Control, ETag, Expires, Content-Location and/or Vary, if the header field would have been sent in a 200 (OK) response to the same request If a 206 is sent in response to a request with an If-Range header field, it &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. Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness for 206 responses.

A server &SHOULD; return a response with this status code if a request included a Range header field (), 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 (). (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 ). This response &MUST-NOT; use the multipart/byteranges content-type. For example,

HTTP/1.1 416 Requested Range Not Satisfiable Date: Mon, 20 Jan 2012 15:41:54 GMT Content-Range: bytes */47022 Content-Type: image/gif

&Note; Clients cannot depend on servers to send a 416 (Requested Range Not Satisfiable) response instead of a 200 (OK) response for an unsatisfiable Range header field, since not all servers implement this header field.

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 . A server &MAY; combine requested ranges when those ranges are overlapping (see ). 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 asks for multiple ranges in one request, the server &SHOULD; return them in the order that they appeared in the request.

A response might transfer only a subrange of a representation if the connection closed prematurely or if the request used one or more Range specifications. After several such transfers, a client might have received several ranges of the same representation. These ranges can only be safely combined if they all have in common the same strong validator, where “strong validator” is defined to be either an entity-tag that is not marked as weak (&entity-tags;) or, if no entity-tag is provided, a Last-Modified value that is strong in the sense defined by &lastmod-comparison;. When a client receives an incomplete 200 (OK) or 206 (Partial Content) response and already has one or more stored responses for the same method and effective request URI, all of the stored responses with the same strong validator &MAY; be combined with the partial content in this new response. If none of the stored responses contain the same strong validator, then this new response corresponds to a new representation and &MUST-NOT; be combined with the existing stored responses. If the new response is an incomplete 200 (OK) response, then the header fields of that new response are used for any combined response and replace those of the matching stored responses. If the new response is a 206 (Partial Content) response and at least one of the matching stored responses is a 200 (OK), then the combined response header fields consist of the most recent 200 response’s header fields. If all of the matching stored responses are 206 responses, then the stored response with the most header fields is used as the source of header fields for the combined response, except that the client &MUST; use other header fields provided in the new response, aside from Content-Range, to replace all instances of the corresponding header fields in the stored response. The combined response message body consists of the union of partial content ranges in the new response and each of the selected responses. If the union consists of the entire range of the representation, then the combined response &MUST; be recorded as a complete 200 (OK) response with a Content-Length header field that reflects the complete length. Otherwise, the combined response(s) &MUST; include a Content-Range header field describing the included range(s) and be recorded as incomplete. If the union consists of a discontinuous range of the representation, then the client &MAY; store it as either a multipart range response or as multiple 206 responses with one continuous range each.

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 . 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 .

Content-Range = 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 ), 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 “*”. The “Content-Range” header field has no meaning for status codes that do not explicitly describe its semantic. Currently, only status codes 206 (Partial Content) and 416 (Requested Range Not Satisfiable) describe the meaning of this header field. Examples of byte-content-range-spec values, assuming that the representation contains a total of 1234 bytes: The first 500 bytes:

bytes 0-499/1234

The second 500 bytes:

bytes 500-999/1234

All except for the first 500 bytes:

bytes 500-1233/1234

The last 500 bytes:

bytes 734-1233/1234

If the server ignores a byte-range-spec (for example if it is syntactically invalid, or if it might be seen as a denial-of-service attack), the server &SHOULD; treat the request as if the invalid Range header field did not exist. (Normally, this means return a 200 (OK) response containing the full representation).

If a client has a partial copy of a representation and wishes to have an up-to-date copy of the entire representation, 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

Clients &MUST-NOT; use an entity-tag marked as weak in an If-Range field value and &MUST-NOT; use a Last-Modified date in an If-Range field value unless it has no entity-tag for the representation and the Last-Modified date it does have for the representation is strong in the sense defined by &lastmod-comparison;. A server that evaluates a conditional range request that is applicable to one of its representations &MUST; evaluate the condition as false if the entity-tag used as a validator is marked as weak or, when an HTTP-date is used as the validator, if the date value is not strong in the sense defined by &lastmod-comparison;. (A server can distinguish between a valid HTTP-date and any form of entity-tag by examining the first two characters.) The If-Range header field &SHOULD; only be sent by clients together with a Range header field. The If-Range header field &MUST; be ignored if it is received in a request that does not include a Range header field. The If-Range header field &MUST; be ignored by a server that does not support the sub-range operation. If the validator given in the If-Range header field matches the current validator for the selected representation of the target resource, then the server &SHOULD; send the specified sub-range of the representation using a 206 (Partial Content) response. If the validator does not match, then the server &SHOULD; send 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 data (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 data, 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 data, 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. In the byte range syntax, first-byte-pos, last-byte-pos, and suffix-length are expressed as decimal number of octets. Since there is no predefined limit to the length of an HTTP payload, recipients &SHOULD; anticipate potentially large decimal numerals and prevent parsing errors due to integer conversion overflows. Examples of byte-ranges-specifier values (assuming a representation of length 10000): The first 500 bytes (byte offsets 0-499, inclusive):

bytes=0-499

The second 500 bytes (byte offsets 500-999, inclusive):

bytes=500-999

The final 500 bytes (byte offsets 9500-9999, inclusive):

bytes=-500

Or:

bytes=9500-

The first and last bytes only (bytes 0 and 9999):

bytes=0-0,-1

Several legal but not canonical specifications of the second 500 bytes (byte offsets 500-999, inclusive):

bytes=500-600,601-999 bytes=500-700,601-999

The “Range” header field defines the GET method (conditional or not) to request one or more sub-ranges of the response representation data, instead of the entire representation data.

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, 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: The presence of a Range header field in an unconditional GET modifies what is returned if the GET is otherwise successful. In other words, the response carries a status code of 206 (Partial Content) instead of 200 (OK). The presence of a Range header field in a conditional GET (a request using one or both of If-Modified-Since and If-None-Match, or one or both of If-Unmodified-Since and If-Match) modifies what is returned if the GET is otherwise successful and the condition is true. It does not affect the 304 (Not Modified) response returned if the conditional is false. In some cases, it might be more appropriate to use the If-Range header field (see ) 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 shall be updated with the registrations below: Value Description Reference 206 Partial Content 416 Requested Range Not Satisfiable

The Message Header Field Registry located at shall be updated with the permanent registrations below (see ): Header Field Name Protocol Status Reference Accept-Ranges http standard Content-Range http standard If-Range http standard Range http standard The change controller is: “IETF (iesg@ietf.org) – Internet Engineering Task Force”.

The registration procedure for HTTP Range Specifiers is defined by of this document. The HTTP Range Specifier Registry shall be created at and be populated with the registrations below: Range Specifier Name Description Reference bytes a range of octets none reserved as keyword, indicating no ranges are supported The change controller is: “IETF (iesg@ietf.org) – Internet Engineering Task Force”.

This section is meant to inform application developers, information providers, and users of the security limitations in HTTP/1.1 as described by this document. The discussion does not include definitive solutions to the problems revealed, though it does make some suggestions for reducing security risks.

Range requests containing overlapping ranges can lead to the situation where a server is sending far more data than the size of the complete resource representation.

See &acks;.

Adobe Systems Incorporated

fielding@gbiv.com

greenbytes GmbH

julian.reschke@greenbytes.de

Content-Length Adobe Systems Incorporated

fielding@gbiv.com

greenbytes GmbH

julian.reschke@greenbytes.de

200 (OK) 410 (Gone) Content-Location Content-Type Location Vary Adobe Systems Incorporated

fielding@gbiv.com

greenbytes GmbH

julian.reschke@greenbytes.de

304 (Not Modified) ETag If-Match If-Modified-Since If-None-Match If-Unmodified-Since Last-Modified Adobe Systems Incorporated

fielding@gbiv.com

Akamai

mnot@mnot.net

greenbytes GmbH

julian.reschke@greenbytes.de

Cache-Control Expires Innosoft International, Inc.

ned@innosoft.com

First Virtual Holdings

nsb@nsb.fv.com

Harvard University

sob@harvard.edu

Brandenburg InternetWorking

dcrocker@bbiw.net

THUS plc.

paul.overell@thus.net

University of California, Irvine

fielding@ics.uci.edu

W3C

jg@w3.org

Compaq Computer Corporation

mogul@wrl.dec.com

MIT Laboratory for Computer Science

frystyk@w3.org

Xerox Corporation

masinter@parc.xerox.com

Microsoft Corporation

paulle@microsoft.com

W3C

timbl@w3.org

Nine by Nine

GK-IETF@ninebynine.org

BEA Systems

mnot@pobox.com

HP Labs

JeffMogul@acm.org

Sun Microsystems

ned.freed@mrochek.com

klensin+ietf@jck.com

IBM

narten@us.ibm.com

Google

Harald@Alvestrand.no

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 (). The media type for this purpose is called “multipart/byteranges”. The following is to be registered with IANA . 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. multipart byteranges boundary none only “7bit”, “8bit”, or “binary” are permitted none none This specification (see ). HTTP components supporting multiple ranges in a single request. none none none See Authors Section. COMMON none IESG &Note; Despite the name “multipart/byteranges” is not limited to the byte ranges only.

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–

Another example, using the “exampleunit” range unit: 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: Additional CRLFs &MAY; precede the first boundary string in the body. Although permits the boundary string to be quoted, some existing implementations handle a quoted boundary string incorrectly. A number of clients and servers were coded to an early draft of the byteranges specification to use a media type of multipart/x-byteranges, which is almost, but not quite compatible with the version documented in HTTP/1.1.

Introduce Range Specifier Registry. () Clarify that it is not ok to use a weak validator in a 206 response. () Clarify that multipart/byteranges can consist of a single part. ()

The following core rules are included by reference, as defined in : 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), and VCHAR (any visible US-ASCII character). Note that all rules derived from token are to be compared case-insensitively, like range-unit and acceptable-ranges. The rules below are defined in :

OWS = <OWS, defined in &whitespace;> token = <token, defined in &field-components;>

The rules below are defined in other parts:

HTTP-date = <HTTP-date, defined in &http-date;> entity-tag = <entity-tag, defined in &entity-tags;>

Accept-Ranges = acceptable-ranges Content-Range = byte-content-range-spec / other-content-range-spec HTTP-date = <HTTP-date, defined in [Part2], Section 8.1.1.1> If-Range = entity-tag / HTTP-date OWS = <OWS, defined in [Part1], Section 3.2.1> 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” entity-tag = <entity-tag, defined in [Part4], Section 2.3> 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 3.2.4>

Changes up to the first Working Group Last Call draft are summarized in .

Closed issues: : “ABNF list expansion code problem” : “ABNF requirements for recipients” : “reserve ‘none’ as byte range unit” : “note introduction of new IANA registries as normative changes” : “range units vs leading zeroes vs size”

Conformance criteria and considerations regarding error handling are now defined in Part 1.