Internet Engineering Task Force (IETF) R. Fielding, Ed.

Internet Engineering Task Force (IETF) R. Fielding, Ed.
Request for Comments: 7233 Adobe
Obsoletes: 2616 Y. Lafon, Ed.
Category: Standards Track W3C
ISSN: 2070-1721 J. Reschke, Ed.
greenbytes
June 2014

Hypertext Transfer Protocol (HTTP/1.1): Range Requests

Abstract

The Hypertext Transfer Protocol (HTTP) is a stateless 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.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7233.

Fielding, et al. Standards Track [Page 1]

RFC 7233 HTTP/1.1 Range Requests June 2014

Copyright Notice

Copyright (c) 2014 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
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publication of this document. Please review these documents
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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.

Fielding, et al. Standards Track [Page 2]

RFC 7233 HTTP/1.1 Range Requests June 2014

Table of Contents

1. Introduction ....................................................4
1.1. Conformance and Error Handling .............................4
1.2. Syntax Notation ............................................4
2. Range Units .....................................................5
2.1. Byte Ranges ................................................5
2.2. Other Range Units ..........................................7
2.3. Accept-Ranges ..............................................7
3. Range Requests ..................................................8
3.1. Range ......................................................8
3.2. If-Range ...................................................9
4. Responses to a Range Request ...................................10
4.1. 206 Partial Content .......................................10
4.2. Content-Range .............................................12
4.3. Combining Ranges ..........................................14
4.4. 416 Range Not Satisfiable .................................15
5. IANA Considerations ............................................16
5.1. Range Unit Registry .......................................16
5.1.1. Procedure ..........................................16
5.1.2. Registrations ......................................16
5.2. Status Code Registration ..................................17
5.3. Header Field Registration .................................17
5.4. Internet Media Type Registration ..........................17
5.4.1. Internet Media Type multipart/byteranges ...........18
6. Security Considerations ........................................19
6.1. Denial-of-Service Attacks Using Range .....................19
7. Acknowledgments ................................................19
8. References .....................................................20
8.1. Normative References ......................................20
8.2. Informative References ....................................20
Appendix A. Internet Media Type multipart/byteranges ..............21
Appendix B. Changes from RFC 2616 .................................22
Appendix C. Imported ABNF .........................................22
Appendix D. Collected ABNF ........................................23
Index .............................................................24

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1. Introduction

Hypertext Transfer Protocol (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. Likewise, devices with limited local storage
might benefit from being able to request only a subset of a larger
representation, such as a single page of a very large document, or
the dimensions of an embedded image.

This document defines HTTP/1.1 range requests, partial responses, and
the multipart/byteranges media type. Range requests are an OPTIONAL
feature of HTTP, designed so that recipients not implementing this
feature (or not supporting it for the target resource) 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 caches that might not implement the
feature.

Although the range request mechanism is designed to allow for
extensible range types, this specification only defines requests for
byte ranges.

1.1. Conformance and Error Handling

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].

Conformance criteria and considerations regarding error handling are
defined in Section 2.5 of [RFC7230].

1.2. Syntax Notation

This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234] with a list extension, defined in Section 7 of
[RFC7230], that allows for compact definition of comma-separated
lists using a '#' operator (similar to how the '*' operator indicates
repetition). Appendix C describes rules imported from other
documents. Appendix D shows the collected grammar with all list
operators expanded to standard ABNF notation.

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RFC 7233 HTTP/1.1 Range Requests June 2014

2. Range Units

A representation can be partitioned into subranges according to
various structural units, depending on the structure inherent in the
representation's media type. This "range unit" is used in the
Accept-Ranges (Section 2.3) response header field to advertise
support for range requests, the Range (Section 3.1) request header
field to delineate the parts of a representation that are requested,
and the Content-Range (Section 4.2) payload header field to describe
which part of a representation is being transferred.

range-unit = bytes-unit / other-range-unit

2.1. Byte Ranges

Since representation data is transferred in payloads as a sequence of
octets, a byte range is a meaningful substructure for any
representation transferable over HTTP (Section 3 of [RFC7231]). The
"bytes" range unit is defined for expressing subranges of the data's
octet sequence.

bytes-unit = "bytes"

A byte-range request can 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.

Examples of byte-ranges-specifier values:

o The first 500 bytes (byte offsets 0-499, inclusive):

bytes=0-499

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

bytes=500-999

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A byte-range-spec is invalid if the last-byte-pos value is present
and less than the first-byte-pos.

A client can limit the number of bytes requested without knowing the
size of the selected representation. 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, the byte range is interpreted as
the remainder of the representation (i.e., the server replaces the
value of last-byte-pos with a value that is one less than the current
length of the selected representation).

A client can request the last N bytes of the selected representation
using a suffix-byte-range-spec.

suffix-byte-range-spec = "-" suffix-length
suffix-length = 1*DIGIT

If the selected representation is shorter than the specified
suffix-length, the entire representation is used.

Additional examples, assuming a representation of length 10000:

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

bytes=-500

Or:

bytes=9500-

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

bytes=0-0,-1

o Other valid (but not canonical) specifications of the second 500
bytes (byte offsets 500-999, inclusive):

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

If a valid byte-range-set includes at least one byte-range-spec with
a first-byte-pos that 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.

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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 a payload, recipients MUST
anticipate potentially large decimal numerals and prevent parsing
errors due to integer conversion overflows.

2.2. Other Range Units

Range units are intended to be extensible. New range units ought to
be registered with IANA, as defined in Section 5.1.

other-range-unit = token

2.3. Accept-Ranges

The "Accept-Ranges" header field allows a server to indicate that it
supports range requests for the target resource.

Accept-Ranges = acceptable-ranges
acceptable-ranges = 1#range-unit / "none"

An origin server that supports byte-range requests for a given target
resource MAY send

Accept-Ranges: bytes

to indicate what range units are supported. A client MAY generate
range requests without having received this header field for the
resource involved. Range units are defined in Section 2.

A server that does not support any kind of range request for the
target resource MAY send

Accept-Ranges: none

to advise the client not to attempt a range request.

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3. Range Requests

3.1. Range

The "Range" header field on a GET request modifies the method
semantics to request transfer of only one or more subranges of the
selected representation data, rather than the entire selected
representation data.

Range = byte-ranges-specifier / other-ranges-specifier
other-ranges-specifier = other-range-unit "=" other-range-set
other-range-set = 1*VCHAR

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 partial retrieval of large representations. A server
MUST ignore a Range header field received with a request method other
than GET.

An origin server MUST ignore a Range header field that contains a
range unit it does not understand. A proxy MAY discard a Range
header field that contains a range unit it does not understand.

A server that supports range requests MAY ignore or reject a Range
header field that consists of more than two overlapping ranges, or a
set of many small ranges that are not listed in ascending order,
since both are indications of either a broken client or a deliberate
denial-of-service attack (Section 6.1). A client SHOULD NOT request
multiple ranges that are inherently less efficient to process and
transfer than a single range that encompasses the same data.

A client that is requesting multiple ranges SHOULD list those ranges
in ascending order (the order in which they would typically be
received in a complete representation) unless there is a specific
need to request a later part earlier. For example, a user agent
processing a large representation with an internal catalog of parts
might need to request later parts first, particularly if the
representation consists of pages stored in reverse order and the user
agent wishes to transfer one page at a time.

The Range header field is evaluated after evaluating the precondition
header fields defined in [RFC7232], and only if the result in absence
of the Range header field would be a 200 (OK) response. In other
words, Range is ignored when a conditional GET would result in a 304
(Not Modified) response.

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The If-Range header field (Section 3.2) can be used as a precondition
to applying the Range header field.

If all of the preconditions are true, the server supports the Range
header field for the target resource, and the specified range(s) are
valid and satisfiable (as defined in Section 2.1), the server SHOULD
send a 206 (Partial Content) response with a payload containing one
or more partial representations that correspond to the satisfiable
ranges requested, as defined in Section 4.

If all of the preconditions are true, the server supports the Range
header field for the target resource, and the specified range(s) are
invalid or unsatisfiable, the server SHOULD send a 416 (Range Not
Satisfiable) response.

3.2. If-Range

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 precondition
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 as follows: if the
representation is unchanged, send me the part(s) that I am requesting
in Range; otherwise, send me the entire representation.

If-Range = entity-tag / HTTP-date

A client MUST NOT generate an If-Range header field in a request that
does not contain a Range header field. A server MUST ignore an
If-Range header field received in a request that does not contain a
Range header field. An origin server MUST ignore an If-Range header
field received in a request for a target resource that does not
support Range requests.

A client MUST NOT generate an If-Range header field containing an
entity-tag that is marked as weak. A client MUST NOT generate an
If-Range header field containing an HTTP-date unless the client has
no entity-tag for the corresponding representation and the date is a
strong validator in the sense defined by Section 2.2.2 of [RFC7232].

A server that evaluates an If-Range precondition MUST use the strong
comparison function when comparing entity-tags (Section 2.3.2 of
[RFC7232]) and MUST evaluate the condition as false if an HTTP-date

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validator is provided that is not a strong validator in the sense
defined by Section 2.2.2 of [RFC7232]. A valid entity-tag can be
distinguished from a valid HTTP-date by examining the first two
characters for a DQUOTE.

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 process the Range header field as
requested. If the validator does not match, the server MUST ignore
the Range header field. Note that this comparison by exact match,
including when the validator is an HTTP-date, differs from the
"earlier than or equal to" comparison used when evaluating an
If-Unmodified-Since conditional.

4. Responses to a Range Request

4.1. 206 Partial Content

The 206 (Partial Content) status code indicates that the server is
successfully fulfilling a range request for the target resource by
transferring one or more parts of the selected representation that
correspond to the satisfiable ranges found in the request's Range
header field (Section 3.1).

If a single part is being transferred, the server generating the 206
response MUST generate a Content-Range header field, describing what
range of the selected representation is enclosed, and a payload
consisting of the range. 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

... 26012 bytes of partial image data ...

If multiple parts are being transferred, the server generating the
206 response MUST generate a "multipart/byteranges" payload, as
defined in Appendix A, and a Content-Type header field containing the
multipart/byteranges media type and its required boundary parameter.
To avoid confusion with single-part responses, a server MUST NOT
generate a Content-Range header field in the HTTP header section of a
multiple part response (this field will be sent in each part
instead).

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Within the header area of each body part in the multipart payload,
the server MUST generate a Content-Range header field corresponding
to the range being enclosed in that body part. If the selected
representation would have had a Content-Type header field in a 200
(OK) response, the server SHOULD generate that same Content-Type
field in the header area of 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-Length: 1741
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--

When multiple ranges are requested, a server MAY coalesce any of the
ranges that overlap, or that are separated by a gap that is smaller
than the overhead of sending multiple parts, regardless of the order
in which the corresponding byte-range-spec appeared in the received
Range header field. Since the typical overhead between parts of a
multipart/byteranges payload is around 80 bytes, depending on the
selected representation's media type and the chosen boundary
parameter length, it can be less efficient to transfer many small
disjoint parts than it is to transfer the entire selected
representation.

A server MUST NOT generate a multipart response to a request for a
single range, since a client that does not request multiple parts
might not support multipart responses. However, a server MAY
generate a multipart/byteranges payload with only a single body part
if multiple ranges were requested and only one range was found to be
satisfiable or only one range remained after coalescing. A client
that cannot process a multipart/byteranges response MUST NOT generate
a request that asks for multiple ranges.

When a multipart response payload is generated, the server SHOULD
send the parts in the same order that the corresponding
byte-range-spec appeared in the received Range header field,

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excluding those ranges that were deemed unsatisfiable or that were
coalesced into other ranges. A client that receives a multipart
response MUST inspect the Content-Range header field present in each
body part in order to determine which range is contained in that body
part; a client cannot rely on receiving the same ranges that it
requested, nor the same order that it requested.

When a 206 response is generated, the server MUST generate the
following header fields, in addition to those required above, if the
field would have been sent in a 200 (OK) response to the same
request: Date, Cache-Control, ETag, Expires, Content-Location, and
Vary.

If a 206 is generated in response to a request with an If-Range
header field, the sender SHOULD NOT generate other representation
header fields beyond those required above, because the client is
understood to already have a prior response containing those header
fields. Otherwise, the sender MUST generate all of the
representation header fields that would have been sent in a 200 (OK)
response to the same request.

A 206 response is cacheable by default; i.e., unless otherwise
indicated by explicit cache controls (see Section 4.2.2 of
[RFC7234]).

4.2. Content-Range

The "Content-Range" header field is sent in a single part 206
(Partial Content) response to indicate the partial range of the
selected representation enclosed as the message payload, sent in each
part of a multipart 206 response to indicate the range enclosed
within each body part, and sent in 416 (Range Not Satisfiable)
responses to provide information about the selected representation.

Content-Range = byte-content-range
/ other-content-range

byte-content-range = bytes-unit SP
( byte-range-resp / unsatisfied-range )

byte-range-resp = byte-range "/" ( complete-length / "*" )
byte-range = first-byte-pos "-" last-byte-pos
unsatisfied-range = "*/" complete-length

complete-length = 1*DIGIT

other-content-range = other-range-unit SP other-range-resp
other-range-resp = *CHAR

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If a 206 (Partial Content) response contains a Content-Range header
field with a range unit (Section 2) that the recipient does not
understand, the recipient MUST NOT attempt to recombine it with a
stored representation. A proxy that receives such a message SHOULD
forward it downstream.

For byte ranges, a sender SHOULD indicate the complete length of the
representation from which the range has been extracted, unless the
complete length is unknown or difficult to determine. An asterisk
character ("*") in place of the complete-length indicates that the
representation length was unknown when the header field was
generated.

The following example illustrates when the complete length of the
selected representation is known by the sender to be 1234 bytes:

Content-Range: bytes 42-1233/1234

and this second example illustrates when the complete length is
unknown:

Content-Range: bytes 42-1233/*

A Content-Range field value is invalid if it contains a
byte-range-resp that has a last-byte-pos value less than its
first-byte-pos value, or a complete-length value less than or equal
to its last-byte-pos value. The recipient of an invalid
Content-Range MUST NOT attempt to recombine the received content with
a stored representation.

A server generating a 416 (Range Not Satisfiable) response to a
byte-range request SHOULD send a Content-Range header field with an
unsatisfied-range value, as in the following example:

Content-Range: bytes */1234

The complete-length in a 416 response indicates the current length of
the selected representation.

The Content-Range header field has no meaning for status codes that
do not explicitly describe its semantic. For this specification,
only the 206 (Partial Content) and 416 (Range Not Satisfiable) status
codes describe a meaning for Content-Range.

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The following are examples of Content-Range values in which the
selected representation contains a total of 1234 bytes:

o The first 500 bytes:

Content-Range: bytes 0-499/1234

o The second 500 bytes:

Content-Range: bytes 500-999/1234

o All except for the first 500 bytes:

Content-Range: bytes 500-1233/1234

o The last 500 bytes:

Content-Range: bytes 734-1233/1234

4.3. Combining Ranges

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 (Section 2.1 of [RFC7232]).

A client that has received multiple partial responses to GET requests
on a target resource MAY combine those responses into a larger
continuous range if they share the same strong validator.

If the most recent response is an incomplete 200 (OK) response, then
the header fields of that response are used for any combined response
and replace those of the matching stored responses.

If the most recent 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 recent
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.

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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 client MUST process the combined response as
if it were a complete 200 (OK) response, including a Content-Length
header field that reflects the complete length. Otherwise, the
client MUST process the set of continuous ranges as one of the
following: an incomplete 200 (OK) response if the combined response
is a prefix of the representation, a single 206 (Partial Content)
response containing a multipart/byteranges body, or multiple 206
(Partial Content) responses, each with one continuous range that is
indicated by a Content-Range header field.

4.4. 416 Range Not Satisfiable

The 416 (Range Not Satisfiable) status code indicates that none of
the ranges in the request's Range header field (Section 3.1) overlap
the current extent of the selected resource or that the set of ranges
requested has been rejected due to invalid ranges or an excessive
request of small or overlapping ranges.

For byte ranges, failing to overlap the current extent means that the
first-byte-pos of all of the byte-range-spec values were greater than
the current length of the selected representation. When this status
code is generated in response to a byte-range request, the sender
SHOULD generate a Content-Range header field specifying the current
length of the selected representation (Section 4.2).

For example:

HTTP/1.1 416 Range Not Satisfiable
Date: Fri, 20 Jan 2012 15:41:54 GMT
Content-Range: bytes */47022

Note: Because servers are free to ignore Range, many
implementations will simply respond with the entire selected
representation in a 200 (OK) response. That is partly because
most clients are prepared to receive a 200 (OK) to complete the
task (albeit less efficiently) and partly because clients might
not stop making an invalid partial request until they have
received a complete representation. Thus, clients cannot depend
on receiving a 416 (Range Not Satisfiable) response even when it
is most appropriate.

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5. IANA Considerations

5.1. Range Unit Registry

The "HTTP Range Unit Registry" defines the namespace for the range
unit names and refers to their corresponding specifications. The
registry has been created and is now maintained at
<http://www.iana.org/assignments/http-parameters>.

5.1.1. Procedure

Registration of an HTTP Range Unit MUST include the following fields:

o Name

o Description

o Pointer to specification text

Values to be added to this namespace require IETF Review (see
[RFC5226], Section 4.1).

5.1.2. Registrations

The initial range unit registry contains the registrations below:

+-------------+---------------------------------------+-------------+
| Range Unit | Description | Reference |
| Name | | |
+-------------+---------------------------------------+-------------+
| bytes | a range of octets | Section 2.1 |
| none | reserved as keyword, indicating no | Section 2.3 |
| | ranges are supported | |
+-------------+---------------------------------------+-------------+

The change controller is: "IETF ([email protected]) - Internet
Engineering Task Force".

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5.2. Status Code Registration

The "Hypertext Transfer Protocol (HTTP) Status Code Registry" located
at <http://www.iana.org/assignments/http-status-codes> has been
updated to include the registrations below:

+-------+-----------------------+-------------+
| Value | Description | Reference |
+-------+-----------------------+-------------+
| 206 | Partial Content | Section 4.1 |
| 416 | Range Not Satisfiable | Section 4.4 |
+-------+-----------------------+-------------+

5.3. Header Field Registration

HTTP header fields are registered within the "Message Headers"
registry maintained at
<http://www.iana.org/assignments/message-headers/>.

This document defines the following HTTP header fields, so their
associated registry entries have been updated according to the
permanent registrations below (see [BCP90]):

+-------------------+----------+----------+-------------+
| Header Field Name | Protocol | Status | Reference |
+-------------------+----------+----------+-------------+
| Accept-Ranges | http | standard | Section 2.3 |
| Content-Range | http | standard | Section 4.2 |
| If-Range | http | standard | Section 3.2 |
| Range | http | standard | Section 3.1 |
+-------------------+----------+----------+-------------+

The change controller is: "IETF ([email protected]) - Internet
Engineering Task Force".

5.4. Internet Media Type Registration

IANA maintains the registry of Internet media types [BCP13] at
<http://www.iana.org/assignments/media-types>.

This document serves as the specification for the Internet media type
"multipart/byteranges". The following has been registered with IANA.

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RFC 7233 HTTP/1.1 Range Requests June 2014

5.4.1. Internet Media Type multipart/byteranges

Type name: multipart

Subtype name: byteranges

Required parameters: boundary

Optional parameters: N/A

Encoding considerations: only "7bit", "8bit", or "binary" are
permitted

Security considerations: see Section 6

Interoperability considerations: N/A

Published specification: This specification (see Appendix A).

Applications that use this media type: HTTP components supporting
multiple ranges in a single request.

Fragment identifier considerations: N/A

Additional information:

Deprecated alias names for this type: N/A

Magic number(s): N/A

File extension(s): N/A

Macintosh file type code(s): N/A

Person and email address to contact for further information: See
Authors' Addresses section.

Intended usage: COMMON

Restrictions on usage: N/A

Author: See Authors' Addresses section.

Change controller: IESG

Fielding, et al. Standards Track [Page 18]

RFC 7233 HTTP/1.1 Range Requests June 2014

6. Security Considerations

This section is meant to inform developers, information providers,
and users of known security concerns specific to the HTTP range
request mechanisms. More general security considerations are
addressed in HTTP messaging [RFC7230] and semantics [RFC7231].

6.1. Denial-of-Service Attacks Using Range

Unconstrained multiple range requests are susceptible to denial-of-
service attacks because the effort required to request many
overlapping ranges of the same data is tiny compared to the time,
memory, and bandwidth consumed by attempting to serve the requested
data in many parts. Servers ought to ignore, coalesce, or reject
egregious range requests, such as requests for more than two
overlapping ranges or for many small ranges in a single set,
particularly when the ranges are requested out of order for no
apparent reason. Multipart range requests are not designed to
support random access.

7. Acknowledgments

See Section 10 of [RFC7230].

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RFC 7233 HTTP/1.1 Range Requests June 2014

8. References

8.1. Normative References

[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., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.

[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, June 2014.

[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
June 2014.

[RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Conditional Requests", RFC 7232,
June 2014.

[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, June 2014.

8.2. Informative References

[BCP13] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, January 2013.

[BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.

[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.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.

Fielding, et al. Standards Track [Page 20]

RFC 7233 HTTP/1.1 Range Requests June 2014

Appendix A. Internet Media Type multipart/byteranges

When a 206 (Partial Content) response message includes the content of
multiple ranges, they are transmitted as body parts in a multipart
message body ([RFC2046], Section 5.1) with the media type of
"multipart/byteranges".

The multipart/byteranges media type includes one or more body 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.

Implementation Notes:

1. Additional CRLFs might precede the first boundary string in the
body.

2. Although [RFC2046] permits the boundary string to be quoted, some
existing implementations handle a quoted boundary string
incorrectly.

3. A number of clients and servers were coded to an early draft of
the byteranges specification that used a media type of multipart/
x-byteranges, which is almost (but not quite) compatible with
this type.

Despite the name, the "multipart/byteranges" media type is not
limited to byte ranges. The following example uses an "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-Length: 2331785
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--

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RFC 7233 HTTP/1.1 Range Requests June 2014

Appendix B. Changes from RFC 2616

Servers are given more leeway in how they respond to a range request,
in order to mitigate abuse by malicious (or just greedy) clients.
(Section 3.1)

A weak validator cannot be used in a 206 response. (Section 4.1)

The Content-Range header field only has meaning when the status code
explicitly defines its use. (Section 4.2)

This specification introduces a Range Unit Registry. (Section 5.1)

multipart/byteranges can consist of a single part. (Appendix A)

Appendix C. Imported ABNF

The following core rules are included by reference, as defined in
Appendix B.1 of [RFC5234]: 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 [RFC7230]:

OWS = <OWS, see [RFC7230], Section 3.2.3>
token = <token, see [RFC7230], Section 3.2.6>

The rules below are defined in other parts:

HTTP-date = <HTTP-date, see [RFC7231], Section 7.1.1.1>
entity-tag = <entity-tag, see [RFC7232], Section 2.3>

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RFC 7233 HTTP/1.1 Range Requests June 2014

Appendix D. Collected ABNF

In the collected ABNF below, list rules are expanded as per Section
1.2 of [RFC7230].

Accept-Ranges = acceptable-ranges

Content-Range = byte-content-range / other-content-range

HTTP-date = <HTTP-date, see [RFC7231], Section 7.1.1.1>

If-Range = entity-tag / HTTP-date

OWS = <OWS, see [RFC7230], Section 3.2.3>

Range = byte-ranges-specifier / other-ranges-specifier

acceptable-ranges = ( *( "," OWS ) range-unit *( OWS "," [ OWS
range-unit ] ) ) / "none"

byte-content-range = bytes-unit SP ( byte-range-resp /
unsatisfied-range )
byte-range = first-byte-pos "-" last-byte-pos
byte-range-resp = byte-range "/" ( complete-length / "*" )
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"

complete-length = 1*DIGIT

entity-tag = <entity-tag, see [RFC7232], Section 2.3>

first-byte-pos = 1*DIGIT

last-byte-pos = 1*DIGIT

other-content-range = other-range-unit SP other-range-resp
other-range-resp = *CHAR
other-range-set = 1*VCHAR
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

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RFC 7233 HTTP/1.1 Range Requests June 2014

suffix-length = 1*DIGIT

token = <token, see [RFC7230], Section 3.2.6>

unsatisfied-range = "*/" complete-length

Index

2
206 Partial Content (status code) 10

4
416 Range Not Satisfiable (status code) 15

A
Accept-Ranges header field 7

C
Content-Range header field 12

G
Grammar
Accept-Ranges 7
acceptable-ranges 7
byte-content-range 12
byte-range 12
byte-range-resp 12
byte-range-set 5
byte-range-spec 5
byte-ranges-specifier 5
bytes-unit 5
complete-length 12
Content-Range 12
first-byte-pos 5
If-Range 9
last-byte-pos 5
other-content-range 12
other-range-resp 12
other-range-unit 5, 7
Range 8
range-unit 5
ranges-specifier 5
suffix-byte-range-spec 6
suffix-length 6
unsatisfied-range 12

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RFC 7233 HTTP/1.1 Range Requests June 2014

I
If-Range header field 9

M
Media Type
multipart/byteranges 18, 21
multipart/x-byteranges 19
multipart/byteranges Media Type 18, 21
multipart/x-byteranges Media Type 21

R
Range header field 8

Authors' Addresses

Roy T. Fielding (editor)
Adobe Systems Incorporated
345 Park Ave
San Jose, CA 95110
USA

EMail: [email protected]
URI: http://roy.gbiv.com/

Yves Lafon (editor)
World Wide Web Consortium
W3C / ERCIM
2004, rte des Lucioles
Sophia-Antipolis, AM 06902
France

EMail: [email protected]
URI: http://www.raubacapeu.net/people/yves/

Julian F. Reschke (editor)
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany

EMail: [email protected]
URI: http://greenbytes.de/tech/webdav/

Fielding, et al. Standards Track [Page 25]