draft-ietf-httpbis-rand-access-live-01.txt   draft-ietf-httpbis-rand-access-live-02.txt 
HTTP Working Group C. Pratt HTTP Working Group C. Pratt
Internet-Draft CableLabs Internet-Draft CableLabs
Intended status: Experimental B. Stark Intended status: Experimental B. Stark
Expires: March 8, 2018 AT&T Expires: May 18, 2018 AT&T
D. Thakore D. Thakore
CableLabs CableLabs
September 4, 2017 November 14, 2017
HTTP Random Access and Live Content HTTP Random Access and Live Content
draft-ietf-httpbis-rand-access-live-01 draft-ietf-httpbis-rand-access-live-02
Abstract Abstract
To accommodate byte range requests for content that has data appended To accommodate byte range requests for content that has data appended
over time, this document defines semantics that allow a HTTP client over time, this document defines semantics that allow a HTTP client
and server to perform byte-range GET and HEAD requests that start at and server to perform byte-range GET and HEAD requests that start at
an arbitrary byte offset within the representation and ends at an an arbitrary byte offset within the representation and ends at an
indeterminate offset. indeterminate offset.
Editorial Note (To be removed by RFC Editor before publication) Editorial Note (To be removed by RFC Editor before publication)
skipping to change at page 1, line 40 skipping to change at page 1, line 40
<https://github.com/httpwg/http-extensions/labels/rand-access-live>. <https://github.com/httpwg/http-extensions/labels/rand-access-live>.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 8, 2018. This Internet-Draft will expire on May 18, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Performing Range requests on Random-Access Aggregating 2. Performing Range requests on Random-Access Aggregating
("live") Content . . . . . . . . . . . . . . . . . . . . . . 3 ("live") Content . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Establishing the Randomly Accessible Byte Range . . . . . 4 2.1. Establishing the Randomly Accessible Byte Range . . . . . 4
2.2. Byte-Range Requests Beyond the Randomly Accessible Byte 2.2. Byte-Range Requests Beyond the Randomly Accessible Byte
Range . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Byte-Range Responses Beyond the Randomly Accessible Byte
Range . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Range . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Other Applications of Random-Access Aggregating Content . . . 6 3. Other Applications of Random-Access Aggregating Content . . . 7
3.1. Requests Starting at the Aggregation ("Live") Point . . . 6 3.1. Requests Starting at the Aggregation ("Live") Point . . . 7
3.2. Shift Buffer Representations . . . . . . . . . . . . . . 7 3.2. Shift Buffer Representations . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8 4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Normative References . . . . . . . . . . . . . . . . . . 8 5.1. Normative References . . . . . . . . . . . . . . . . . . 9
5.2. Informative References . . . . . . . . . . . . . . . . . 8 5.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
Some Hypertext Transfer Protocol (HTTP) Clients use byte-range Some Hypertext Transfer Protocol (HTTP) clients use byte-range
requests (Range requests using the "bytes" Range Unit) to transfer requests (Range requests using the "bytes" Range Unit) to transfer
select portions of large representations. And in some cases large select portions of large representations. And in some cases large
representations require content to be continuously or periodically representations require content to be continuously or periodically
appended - such as representations consisting of live audio or video appended - such as representations consisting of live audio or video
sources, blockchain databases, and log files. Clients cannot access sources, blockchain databases, and log files. Clients cannot access
the appended/live content using a Range request with the bytes range the appended/live content using a Range request with the bytes range
unit using the currently defined byte-range semantics without unit using the currently defined byte-range semantics without
accepting performance or behavior sacrifices which are not acceptable accepting performance or behavior sacrifices which are not acceptable
for many applications. for many applications.
For instance, HTTP Clients have the ability to access appended For instance, HTTP clients have the ability to access appended
content by simply transferring the entire accessible portion of the content on an indeterminate-length resource by transferring the
representation from the beginning and continuing to read the appended entire representation from the beginning and continuing to read the
content as it's made available. Obviously, this is highly appended content as it's made available. Obviously, this is highly
inefficient for cases where the representation is large and only a inefficient for cases where the representation is large and only the
portion of the randomly-accessible content is needed by the Client. most recently appended content is needed by the client.
And when bandwidth is limited, the Client may never be able to
transfer all of the currently accessible potion and "catch up" with
the appending content.
Alternatively, Clients can also access appended content by sending Alternatively, clients can also access appended content by sending
periodic open-ended bytes Range requests using the last-known end periodic open-ended bytes Range requests using the last-known end
byte position as the range start. Performing low-frequency periodic byte position as the range start. Performing low-frequency periodic
bytes Range requests in this fashion (polling) introduces latency bytes Range requests in this fashion (polling) introduces latency
since the Client will necessarily be somewhat behind the aggregated since the client will necessarily be somewhat behind the aggregated
content - mimicking the behavior (and latency) of segmented content content - mimicking the behavior (and latency) of segmented content
representations such as HLS or MPEG-DASH. And performing these Range representations such as HLS or MPEG-DASH. And while performing these
requests at higher frequency incurs more processing overhead and HTTP Range requests at higher frequency can reduce this latency, it also
exchanges as the requests will often return no content - since incurs more processing overhead and HTTP exchanges as many of the
content is usually aggregated in groups of bytes (e.g. a video frame, requests will return no content - since content is usually aggregated
audio sample, block, or log entry). in groups of bytes (e.g. a video frame, audio sample, block, or log
entry).
To accommodate byte-range requests on large representations which This document describes a usage model for range requests which
have data appended over time efficiently and with low latency, this enables efficient retrieval of representations that are appended to
recommendation defines semantics whereby the HTTP Client performs over time by using large values and associated semantics for
byte-range requests using a combination of open-ended byte-range HEAD communicating range end positions. This model allows representations
requests and GET requests using "Large Value" last-byte-pos values. to be progressively delivered by servers as new content is added. It
also ensures compatibility with servers and intermediaries that don't
support this technique.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Performing Range requests on Random-Access Aggregating ("live") 2. Performing Range requests on Random-Access Aggregating ("live")
Content Content
There are two critical operations for accessing randomly accessing This document recommends a two-step process for accessing resources
live/aggregating representations: that have indeterminate length representations. Two steps are
necessary because of limitations with the Range request header and
o Establishing the randomly-accessible range of the representation, the Content-Range response header fields. A server cannot know from
and a range request that a client wishes to receive a response that does
not have a definite end. More critically, the header fields do not
o Performing range requests that continue beyond the randomly- allow the server to signal that a resource has indeterminate length
accessible range. without also providing a fixed portion of the resource. A client
first learns that the resource has a representation of indeterminate
length by requesting a range of the resource. The server responds
with the range that is available, but indicates that the length of
the representation is unknown using the existing Content-Range
syntax. See Section 2.1 for details and examples. Once the client
knows the resource has indeterminate length, it can request a range
with a very large end position from the resource. The client chooses
an explicit end value larger than can be transferred in the
foreseeable term. A server which supports range requests of
indeterminate length signals its understanding of the client's
indeterminate range request by indicating that the range it is
providing has a range end that exactly matches the client's requested
range end rather than a range that is bounded by what is currently
available. See Section 2.2 for details.
2.1. Establishing the Randomly Accessible Byte Range 2.1. Establishing the Randomly Accessible Byte Range
Establishing if a representation is continuously aggregating ("live") Establishing if a representation is continuously aggregating ("live")
and determining the randomly-accessible byte range can both be and determining the randomly-accessible byte range can both be
determined using the existing definition for an open-ended byte-range determined using the existing definition for an open-ended byte-range
request. Specifically, [RFC7233] defines a byte-range request of the request. Specifically, [RFC7233] defines a byte-range request of the
form: form:
byte-range-spec = first-byte-pos "-" [ last-byte-pos ] byte-range-spec = first-byte-pos "-" [ last-byte-pos ]
which allows a Client to send a HEAD request with a first-byte-pos which allows a client to send a HEAD request with a first-byte-pos
and leave last-byte-pos absent. A Server that receives a satisfiable and leave last-byte-pos absent. A server that receives a satisfiable
byte-range request (with first-byte-pos smaller than the current byte-range request (with first-byte-pos smaller than the current
representation length) must respond with a 206 status code (Partial representation length) may respond with a 206 status code (Partial
Content) with a Content-Range header indicating the currently Content) with a Content-Range header indicating the currently
satisfiable byte range. For example, a Client-issued HEAD request satisfiable byte range. For example:
performed against a continuously aggregating representation hosted on
a Server could contain a byte-range header of the form:
Range: bytes=0- HEAD /resource HTTP/1.1
Range: bytes=0-
could return the header returns a response of the form:
Content-Range: bytes 0-1234567/* HTTP/1.1 206 Partial Content
Content-Range: bytes 0-1234567/*
from the Server indicating that (1) the complete representation from the server indicating that (1) the complete representation
length is unknown (via the "*" in place of the complete-length field) length is unknown (via the "*" in place of the complete-length field)
and (2) that only bytes 0-1234567 were accessable at the time the and (2) that only bytes 0-1234567 were accessable at the time the
request was processed by the Server. The Client can infer from this request was processed by the server. The client can infer from this
response that bytes 0-1234567 of the representation can be requested response that bytes 0-1234567 of the representation can be requested
and returned in a timely fashion (the bytes are immediately and returned in a timely fashion (the bytes are immediately
available). available).
2.2. Byte-Range Requests Beyond the Randomly Accessible Byte Range 2.2. Byte-Range Requests Beyond the Randomly Accessible Byte Range
Once a Client has determined that a representation has an Once a client has determined that a representation has an
indeterminate length and established the byte range that can be indeterminate length and established the byte range that can be
accessed, it may want to perform a request with a start position accessed, it may want to perform a request with a start position
within the randomly-accessible content range and an end position at within the randomly-accessible content range and an end position at
an indefinite "live" point - a point where the byte-range GET request an indefinite "live" point - a point where the byte-range GET request
is fulfilled on-demand as the content is aggregated. is fulfilled on-demand as the content is aggregated.
For example, for a large video asset, a client may wish to start a For example, for a large video asset, a client may wish to start a
content transfer from the video "key" frame immediately before the content transfer from the video "key" frame immediately before the
point of aggregation and continue the content transfer indefinitely point of aggregation and continue the content transfer indefinitely
as content is aggregated - in order to support low-latency startup of as content is aggregated - in order to support low-latency startup of
skipping to change at page 5, line 19 skipping to change at page 5, line 34
( byte-range-resp / unsatisfied-range ) ( byte-range-resp / unsatisfied-range )
byte-range-resp = byte-range "/" ( complete-length / "*" ) byte-range-resp = byte-range "/" ( complete-length / "*" )
byte-range = first-byte-pos "-" last-byte-pos byte-range = first-byte-pos "-" last-byte-pos
unsatisfied-range = "*/" complete-length unsatisfied-range = "*/" complete-length
complete-length = 1*DIGIT complete-length = 1*DIGIT
Specifically, last-byte-pos is required in byte-range. So in order Specifically, last-byte-pos is required in byte-range. So in order
to preserve interoperability with existing HTTP clients, servers, to preserve interoperability with existing HTTP clients, servers,
proxies, and caches, this document proposes a mechanism for a Client proxies, and caches, this document proposes a mechanism for a client
to indicate support for handling an indeterminate-length byte-range to indicate support for handling an indeterminate-length byte-range
response, and a mechanism for a Server to indicate if/when it's response, and a mechanism for a server to indicate if/when it's
providing a indeterminate-length response. providing a indeterminate-length response.
A Client can indicate support for handling indeterminate-length byte- A client can indicate support for handling indeterminate-length byte-
range responses by providing a Very Large Value for the last-byte-pos range responses by providing a Very Large Value for the last-byte-pos
in the byte-range request. For example, a Client can perform a byte- in the byte-range request. For example, a client can perform a byte-
range GET request of the form: range GET request of the form:
Range: bytes=1230000-999999999999 GET /resource HTTP/1.1
Range: bytes=1230000-999999999999
where the last-byte-pos in the Request is much larger than the last- where the last-byte-pos in the Request is much larger than the last-
byte-pos returned in response to an open-ended byte-range HEAD byte-pos returned in response to an open-ended byte-range HEAD
request, as described above. request, as described above.
2.3. Byte-Range Responses Beyond the Randomly Accessible Byte Range In response, a server may indicate that it is supplying a
continuously aggregating ("live") response by supplying the client
A Server may indicate that it is supplying a continuously aggregating request's last-byte-pos in the Content-Range response header.
("live") response by supplying the Client request's last-byte-pos in
the Content-Range response header.
For example: For example:
Range: bytes=1230000-999999999999 GET /resource HTTP/1.1
Range: bytes=1230000-999999999999
could return returns
Content-Range: bytes 1230000-999999999999/* HTTP/1.1 206 Partial Content
Content-Range: bytes 1230000-999999999999/*
from the Server to indicate that the response will start at byte from the server to indicate that the response will start at byte
1230000 and continues indefinitely to include all aggregated content, 1230000 and continues indefinitely to include all aggregated content,
as it becomes available. as it becomes available.
A Server that doesn't support or supply a continuously aggregating A server that doesn't support or supply a continuously aggregating
("live") response should supply the currently satisfiable byte range, ("live") response will supply the currently satisfiable byte range,
as it would with an open-ended byte request. as it would with an open-ended byte request.
For example: For example:
Range: bytes=1230000-999999999999 GET /resource HTTP/1.1
Range: bytes=1230000-999999999999
could return will return
Content-Range: bytes 1230000-1234567/* HTTP/1.1 206 Partial Content
Content-Range: bytes 1230000-1234567/*
from the Server to indicate that the response will start at byte from the server to indicate that the response will start at byte
1230000 and end at byte 1234567 and will not include any aggregated 1230000 and end at byte 1234567 and will not include any aggregated
content. This is the response expected from a typical HTTP Server - content. This is the response expected from a typical HTTP server -
one that doesn't support byte-range requests on aggregating content. one that doesn't support byte-range requests on aggregating content.
A Client that doesn't receive a response indicating it is A client that doesn't receive a response indicating it is
continuously aggregating must use other means to access aggregated continuously aggregating must use other means to access aggregated
content (e.g. periodic byte-range polling). content (e.g. periodic byte-range polling).
A Server that does return a continuously aggregating ("live") A server that does return a continuously aggregating ("live")
response should return data using chunked transfer coding and not response should return data using chunked transfer coding and not
provide a Content-Length header. A 0-length chunk indicates that provide a Content-Length header. A 0-length chunk indicates the end
aggregation of the transferring resource is permanently discontinued, of the transfer, per section 4.1 of [RFC7230].
per section 4.1 of [RFC7233].
3. Other Applications of Random-Access Aggregating Content 3. Other Applications of Random-Access Aggregating Content
3.1. Requests Starting at the Aggregation ("Live") Point 3.1. Requests Starting at the Aggregation ("Live") Point
If a Client would like to start the content transfer at the A client that wishes to only receive newly-aggregated portions of a
Aggregation ("live") point without including any randomly-accessible resource (i.e., start at the "live" point), can use a HEAD request to
portion of the representation, then it should supply the last-byte- learn what range the server has currently available and initiate an
pos from the most-recently received byte-range-spec and a Very Large indeterminate-length transfer. For example:
Value for the last-byte-pos in the byte-range request.
For example a HEAD request containing:
Range: bytes=0-
could return HEAD /resource HTTP/1.1
Range: bytes=0-
Content-Range: bytes 0-1234567/* With the Content-Range response header indicating the (or ranges)
available. For example:
and a GET request containing 206 Partial Content
Content-Range: bytes 0-1234567/*
Range: bytes=1234567-999999999999 The client can then issue a request for a range starting at the end
value (using a very large value for the end of a range) and receive
only new content.
could return GET /resource HTTP/1.1
Range: bytes=1234567-999999999999
Content-Range: bytes 1234567-999999999999/* with a server returning a Content-Range response indicating that an
indeterminate-length response body will be provided
with the response body starting with continuously aggregating 206 Partial Content
("live") data and continuing indefinitely. Content-Range: bytes 1234567-999999999999/*
3.2. Shift Buffer Representations 3.2. Shift Buffer Representations
Some representations lend themselves to front-end content deletion in Some representations lend themselves to front-end content deletion in
addition to aggregation. While still supporting random access, addition to aggregation. While still supporting random access,
representations of this type have a portion at the beginning (the "0" representations of this type have a portion at the beginning (the "0"
end) of the randomly-accessible region that become inaccessible over end) of the randomly-accessible region that become inaccessible over
time. Examples of this kind of representation would be an audio- time. Examples of this kind of representation would be an audio-
video time-shift buffer or a rolling log file. video time-shift buffer or a rolling log file.
For example a HEAD Range request containing: For example a Range request containing:
Range: bytes=0-
could return HEAD /resource HTTP/1.1
Range: bytes=0-
Content-Range: bytes 1000000-1234567/* returns
206 Partial Content
Content-Range: bytes 1000000-1234567/*
indicating that the first 1000000 bytes were not accessible at the indicating that the first 1000000 bytes were not accessible at the
time the HEAD request was processed. Subsequent HEAD requests could time the HEAD request was processed. Subsequent HEAD requests could
return: return:
Content-Range: bytes 1000000-1234567/* Content-Range: bytes 1000000-1234567/*
Content-Range: bytes 1010000-1244567/* Content-Range: bytes 1010000-1244567/*
Content-Range: bytes 1020000-1254567/* Content-Range: bytes 1020000-1254567/*
Note though that the difference between the first-byte-pos and last- Note though that the difference between the first-byte-pos and last-
byte-pos need not be constant. byte-pos need not be constant.
The Client could then follow-up with a GET Range request containing The client could then follow-up with a GET Range request containing
Range: bytes=1020000-999999999999 GET /resource HTTP/1.1
Range: bytes=1020000-999999999999
with the Server returning with the server returning
Content-Range: bytes 1020000-999999999999/* 206 Partial Content
Content-Range: bytes 1020000-999999999999/*
with the response body returning bytes 1020000-1254567 immediately with the response body returning bytes 1020000-1254567 immediately
and aggregated ("live") data being returned as the content is and aggregated ("live") data being returned as the content is
aggregated. aggregated.
4. Security Considerations 4. Security Considerations
One potential issue with this recommendation is related to the use of One potential issue with this recommendation is related to the use of
very-large last-byte-pos values. Some Client and Server very-large last-byte-pos values. Some client and server
implementations may not be prepared to deal with byte position values implementations may not be prepared to deal with byte position values
of 2^^63 and beyond. So in applications where there's no expectation of 2^^63 and beyond. So in applications where there's no expectation
that the representation will ever exceed 2^^63, a value smaller than that the representation will ever exceed 2^^63, a value smaller than
this value should be used as the Very Large last-byte-pos in a byte- this value should be used as the Very Large last-byte-pos in a byte-
seek request or content-range response. seek request or content-range response. Also, some implementations
(e.g. JavaScript-based clients and servers) are not able to
represent all values beyond 2^^53. So similarly, if there's no
expectation that a representation will ever exceed 2^^53 bytes,
values smaller than this limit should be used for the last-byte-pos
in byte-range requests.
5. References 5. References
5.1. Normative References 5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997,
editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014, RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>. <https://www.rfc-editor.org/info/rfc7230>.
[RFC7233] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed., [RFC7233] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
"Hypertext Transfer Protocol (HTTP/1.1): Range Requests", "Hypertext Transfer Protocol (HTTP/1.1): Range Requests",
RFC 7233, DOI 10.17487/RFC7233, June 2014, RFC 7233, DOI 10.17487/RFC7233, June 2014,
<https://www.rfc-editor.org/info/rfc7233>. <https://www.rfc-editor.org/info/rfc7233>.
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