Internet DRAFT - draft-ietf-httpbis-p5-range
draft-ietf-httpbis-p5-range
HTTPbis Working Group R. Fielding, Ed.
Internet-Draft Adobe
Obsoletes: 2616 (if approved) Y. Lafon, Ed.
Intended status: Standards Track W3C
Expires: August 10, 2014 J. Reschke, Ed.
greenbytes
February 6, 2014
Hypertext Transfer Protocol (HTTP/1.1): Range Requests
draft-ietf-httpbis-p5-range-26
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.
Editorial Note (To be removed by RFC Editor)
Discussion of this draft takes 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 E.2.
Status of This Memo
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
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This Internet-Draft will expire on August 10, 2014.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Conformance and Error Handling . . . . . . . . . . . . . . 4
1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 4
2. Range Units . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Byte Ranges . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Other Range Units . . . . . . . . . . . . . . . . . . . . 7
2.3. Accept-Ranges . . . . . . . . . . . . . . . . . . . . . . 7
3. Range Requests . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Range . . . . . . . . . . . . . . . . . . . . . . . . . . 7
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 . . . . . . . . . . . . . . . . . . . . . 15
5.1. Range Unit Registry . . . . . . . . . . . . . . . . . . . 15
5.1.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 15
5.1.2. Registrations . . . . . . . . . . . . . . . . . . . . 16
5.2. Status Code Registration . . . . . . . . . . . . . . . . . 16
5.3. Header Field Registration . . . . . . . . . . . . . . . . 16
5.4. Internet Media Type Registration . . . . . . . . . . . . . 17
5.4.1. Internet Media Type multipart/byteranges . . . . . . . 17
6. Security Considerations . . . . . . . . . . . . . . . . . . . 18
6.1. Denial of Service Attacks using Range . . . . . . . . . . 18
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1. Normative References . . . . . . . . . . . . . . . . . . . 19
8.2. Informative References . . . . . . . . . . . . . . . . . . 19
Appendix A. Internet Media Type multipart/byteranges . . . . . . 20
Appendix B. Changes from RFC 2616 . . . . . . . . . . . . . . . . 21
Appendix C. Imported ABNF . . . . . . . . . . . . . . . . . . . . 21
Appendix D. Collected ABNF . . . . . . . . . . . . . . . . . . . 21
Appendix E. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 23
E.1. Since draft-ietf-httpbis-p5-range-24 . . . . . . . . . . . 23
E.2. Since draft-ietf-httpbis-p5-range-25 . . . . . . . . . . . 23
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
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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 [Part1].
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
[Part1], 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.
2. Range Units
A representation can be partitioned into subranges according to
various structural units, depending on the structure inherent in the
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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 [Part2]). 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
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
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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.
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.
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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.
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
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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 [Part4], 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.
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.
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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: 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 [Part4].
A server that evaluates an If-Range precondition MUST use the strong
comparison function when comparing entity-tags (Section 2.3.2 of
[Part4]) and MUST evaluate the condition as false if an HTTP-date
validator is provided that is not a strong validator in the sense
defined by Section 2.2.2 of [Part4]. 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.
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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).
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:
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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, 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.
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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 [Part6]).
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
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
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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.
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
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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 [Part4]).
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.
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.
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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.
5. IANA Considerations
5.1. Range Unit Registry
The HTTP Range Unit Registry defines the name space for the range
unit names and refers to their corresponding specifications. The
registry will be created and maintained at (the suggested URI)
<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
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o Pointer to specification text
Values to be added to this name space require IETF Review (see
[RFC5226], Section 4.1).
5.1.2. Registrations
The initial HTTP Range Unit Registry shall contain 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 (iesg@ietf.org) - Internet
Engineering Task Force".
5.2. Status Code Registration
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 4.1 |
| 416 | Range Not Satisfiable | Section 4.4 |
+-------+-----------------------+-------------+
5.3. Header Field Registration
HTTP header fields are registered within the Message Header Field
Registry maintained at <http://www.iana.org/assignments/
message-headers/message-header-index.html>.
This document defines the following HTTP header fields, so their
associated registry entries shall be updated according to the
permanent registrations below (see [BCP90]):
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+-------------------+----------+----------+-------------+
| 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 (iesg@ietf.org) - 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 is to be registered with IANA.
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:
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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 Section.
Intended usage: COMMON
Restrictions on usage: N/A
Author: See Authors Section.
Change controller: IESG
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 [Part1] and semantics [Part2].
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 [Part1].
8. References
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8.1. Normative References
[Part1] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
draft-ietf-httpbis-p1-messaging-26 (work in progress),
February 2014.
[Part2] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content",
draft-ietf-httpbis-p2-semantics-26 (work in progress),
February 2014.
[Part4] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Conditional Requests",
draft-ietf-httpbis-p4-conditional-26 (work in progress),
February 2014.
[Part6] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
draft-ietf-httpbis-p6-cache-26 (work in progress),
February 2014.
[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.
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,
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May 2008.
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
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--THIS_STRING_SEPARATES--
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 [Part1]:
OWS = <OWS, defined in [Part1], Section 3.2.3>
token = <token, defined in [Part1], Section 3.2.6>
The rules below are defined in other parts:
HTTP-date = <HTTP-date, defined in [Part2], Section 7.1.1.1>
entity-tag = <entity-tag, defined in [Part4], Section 2.3>
Appendix D. Collected ABNF
In the collected ABNF below, list rules are expanded as per Section
1.2 of [Part1].
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Accept-Ranges = acceptable-ranges
Content-Range = byte-content-range / other-content-range
HTTP-date = <HTTP-date, defined in [Part2], Section 7.1.1.1>
If-Range = entity-tag / HTTP-date
OWS = <OWS, defined in [Part1], 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, defined in [Part4], 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
suffix-length = 1*DIGIT
token = <token, defined in [Part1], Section 3.2.6>
unsatisfied-range = "*/" complete-length
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Appendix E. Change Log (to be removed by RFC Editor before publication)
Changes up to the IETF Last Call draft are summarized in <http://
tools.ietf.org/html/draft-ietf-httpbis-p5-range-24#appendix-E>.
E.1. Since draft-ietf-httpbis-p5-range-24
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/506>: "APPSDIR
review of draft-ietf-httpbis-p5-range-24"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/507>: "integer value
parsing"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/508>: "broken
sentence in description of 206"
E.2. Since draft-ietf-httpbis-p5-range-25
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/526>: "check media
type registration templates"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/527>: "use of CHAR
for other-range-set"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/538>: "add
'stateless' to Abstract"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/542>: "improve
introduction of list rule"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/549>: "augment
security considerations with pointers to current research"
Index
2
206 Partial Content (status code) 10
4
416 Range Not Satisfiable (status code) 15
A
Accept-Ranges header field 7
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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 7
range-unit 5
ranges-specifier 5
suffix-byte-range-spec 6
suffix-length 6
unsatisfied-range 12
I
If-Range header field 9
M
Media Type
multipart/byteranges 17, 20
multipart/x-byteranges 20
multipart/byteranges Media Type 17, 20
multipart/x-byteranges Media Type 20
R
Range header field 7
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Authors' Addresses
Roy T. Fielding (editor)
Adobe Systems Incorporated
345 Park Ave
San Jose, CA 95110
USA
EMail: fielding@gbiv.com
URI: http://roy.gbiv.com/
Yves Lafon (editor)
World Wide Web Consortium
W3C / ERCIM
2004, rte des Lucioles
Sophia-Antipolis, AM 06902
France
EMail: ylafon@w3.org
URI: http://www.raubacapeu.net/people/yves/
Julian F. Reschke (editor)
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/
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