draft-ietf-httpbis-rand-access-live-04.txt		draft-ietf-httpbis-rand-access-live-latest.txt
	HTTP Working Group C. Pratt		HTTP Working Group C. Pratt
	Internet-Draft		Internet-Draft
	Intended status: Experimental D. Thakore		Intended status: Experimental D. Thakore
	Expires: September 7, 2019 CableLabs		Expires: January 7, 2025 CableLabs
	B. Stark		B. Stark
	AT&T		AT&T
	March 6, 2019		July 6, 2024
	HTTP Random Access and Live Content		HTTP Random Access and Live Content
	draft-ietf-httpbis-rand-access-live-04		draft-ietf-httpbis-rand-access-live-latest
	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 an HTTP client
	and server to perform byte-range GET and HEAD requests that start at		and a server to perform byte-range GET and HEAD requests that start
	an arbitrary byte offset within the representation and ends at an		at an arbitrary byte offset within the representation and end 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)
	Discussion of this draft takes place on the HTTPBIS working group		Discussion of this draft takes place on the HTTPBIS working group
	mailing list (ietf-http-wg@w3.org), which is archived at		mailing list (ietf-http-wg@w3.org), which is archived at
	<https://lists.w3.org/Archives/Public/ietf-http-wg/>.		<https://lists.w3.org/Archives/Public/ietf-http-wg/>.
	Working Group information can be found at <http://httpwg.github.io/>;		Working Group information can be found at <http://httpwg.github.io/>;
	source code and issues list for this draft can be found at		source code and issues list for this draft can be found at
	skipping to change at page 1, line 47 ¶		skipping to change at page 1, line 47 ¶
	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 https://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 September 7, 2019.		This Internet-Draft will expire on January 7, 2025.
	Copyright Notice		Copyright Notice
	Copyright (c) 2019 IETF Trust and the persons identified as the		Copyright (c) 2024 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3		1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
	1.2. Notational Conventions . . . . . . . . . . . . . . . . . 3		2. Performing Range Requests on Random-Access Aggregating (Live)
	2. Performing Range requests on Random-Access Aggregating		Content . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	("live") Content . . . . . . . . . . . . . . . . . . . . . . 4
	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 . . . . . . . . . . . . . . . . . . . . . . . . . . 5		Range . . . . . . . . . . . . . . . . . . . . . . . . . . 5
	3. Other Applications of Random-Access Aggregating Content . . . 7		3. Other Applications of Random-Access Aggregating Content . . . 7
	3.1. Requests Starting at the Aggregation ("Live") Point . . . 7		3.1. Requests Starting at the Aggregation/Live Point . . . . . 7
	3.2. Shift Buffer Representations . . . . . . . . . . . . . . 8		3.2. Shift-Buffer Representations . . . . . . . . . . . . . . 8
	4. Recommendations for Very Large Values . . . . . . . . . . . . 10		4. Recommendations for Byte-Range Request last-byte-pos Values . 9
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10		5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 10		6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
	7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11		7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
	7.1. Normative References . . . . . . . . . . . . . . . . . . 11		7.1. Normative References . . . . . . . . . . . . . . . . . . 10
	7.2. Informative References . . . . . . . . . . . . . . . . . 11		7.2. Informative References . . . . . . . . . . . . . . . . . 11
	Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11		Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
	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 ([RFC7233]). And in some		select portions of large representations [RFC7233]. In some cases,
	cases large representations require content to be continuously or		large representations require content to be continuously or
	periodically appended - such as representations consisting of live		periodically appended, such as representations consisting of live
	audio or video sources, blockchain databases, and log files. Clients		audio or video sources, blockchain databases, and log files. Clients
	cannot access the appended/live content using a Range request with		cannot access the appended/live content using a range request with
	the bytes range unit using the currently defined byte-range semantics		the "bytes" range unit using the currently defined byte-range
	without accepting performance or behavior sacrifices which are not		semantics without accepting performance or behavior sacrifices that
	acceptable for many applications.		are not acceptable for many applications.
	For instance, HTTP clients have the ability to access appended		For instance, HTTP clients have the ability to access appended
	content on an indeterminate-length resource by transferring the		content on an indeterminate-length resource by transferring the
	entire representation from the beginning and continuing to read the		entire representation from the beginning and continuing to read the
	appended 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 the		inefficient for cases where the representation is large and only the
	most recently appended content is needed by the client.		most recently appended content is needed by the client.
	Alternatively, clients can also access appended content by sending		Alternatively, clients can access appended content by sending
	periodic open-ended bytes Range requests using the last-known end		periodic, open-ended byte-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		byte-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 in transferring
	content - mimicking the behavior (and latency) of segmented content		the aggregated content, effectively resulting in the same kind of
	representations such as "HTTP Live Streaming" (HLS, [RFC8216]) or		latency issues with the segmented content transfer mechanisms in
	"Dynamic Adaptive Streaming over HTTP" (MPEG-DASH, [DASH]). And		"HTTP Live Streaming" (HLS) [RFC8216] and "Dynamic Adaptive Streaming
	while performing these Range requests at higher frequency can reduce		over HTTP" [MPEG-DASH]. While performing these range requests at
	this latency, it also incurs more processing overhead and HTTP		higher frequency can reduce this latency, it also incurs more
	exchanges as many of the requests will return no content - since		processing overhead and HTTP exchanges as many of the requests will
	content is usually aggregated in groups of bytes (e.g. a video frame,		return no content, since content is usually aggregated in groups of
	audio sample, block, or log entry).		bytes (e.g., a video frame, audio sample, block, or log entry).
	This document describes a usage model for range requests which		This document describes a usage model for range requests that enables
	enables efficient retrieval of representations that are appended to		efficient retrieval of representations that are appended to over time
	over time by using large values and associated semantics for		by using large values and associated semantics for communicating
	communicating range end positions. This model allows representations		range end positions. This model allows representations to be
	to be progressively delivered by servers as new content is added. It		progressively delivered by servers as new content is added. It also
	also ensures compatibility with servers and intermediaries that don't		ensures compatibility with servers and intermediaries that don't
	support this technique.		support this technique.
	1.1. Requirements Language		1.1. Notational Conventions
	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 RFC 2119 [RFC2119].
	1.2. Notational Conventions
	This document cites productions in Augmented Backus-Naur Form (ABNF)		This document cites Augmented Backus-Naur Form (ABNF) productions
	productions from [RFC7233], using the notation defined in [RFC5234].		from [RFC7233], using the notation defined in [RFC5234].
	2. Performing Range requests on Random-Access Aggregating ("live")		2. Performing Range Requests on Random-Access Aggregating (Live)
	Content		Content
	This document recommends a two-step process for accessing resources		This document recommends a two-step process for accessing resources
	that have indeterminate length representations.		that have indeterminate-length representations.
	Two steps are necessary because of limitations with the Range request		Two steps are necessary because of limitations with the range request
	header fields and the Content-Range response header fields. A server		header fields and the Content-Range response header fields. A server
	cannot know from a range request that a client wishes to receive a		cannot know from a range request that a client wishes to receive a
	response that does not have a definite end. More critically, the		response that does not have a definite end. More critically, the
	header fields do not allow the server to signal that a resource has		header fields do not allow the server to signal that a resource has
	indeterminate length without also providing a fixed portion of the		indeterminate length without also providing a fixed portion of the
	resource.		resource.
	A client first learns that the resource has a representation of		A client first learns that the resource has a representation of
	indeterminate length by requesting a range of the resource. The		indeterminate length by requesting a range of the resource. The
	server responds with the range that is available, but indicates that		server responds with the range that is available but indicates that
	the length of the representation is unknown using the existing		the length of the representation is unknown using the existing
	Content-Range syntax. See Section 2.1 for details and examples.		Content-Range syntax. See Section 2.1 for details and examples.
	Once the client knows the resource has indeterminate length, it can		Once the client knows the resource has indeterminate length, it can
	request a range with a very large end position from the resource.		request a range with a very large end position from the resource.
	The client chooses an explicit end value larger than can be		The client chooses an explicit end value larger than can be
	transferred in the foreseeable term. A server which supports range		transferred in the foreseeable term. A server that supports range
	requests of indeterminate length signals its understanding of the		requests of indeterminate length signals its understanding of the
	client's indeterminate range request by indicating that the range it		client's indeterminate range request by indicating that the range it
	is providing has a range end that exactly matches the client's		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		requested range end rather than a range that is bounded by what is
	currently available. See Section 2.2 for details.		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")		Determining 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		performed using the existing definition for an open-ended byte-range
	request. Specifically, Section 2.1 of [RFC7233] defines a byte-range		request. Specifically, Section 2.1 of [RFC7233] defines a byte-range
	request of the form:		request of the 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) may respond with a 206 status code (Partial		representation length) may respond with a 206 status code (Partial
	Content) with a Content-Range header field indicating the currently		Content) with a Content-Range header field indicating the currently
	satisfiable byte range. For example:		satisfiable byte range. For example:
	HEAD /resource HTTP/1.1		HEAD /resource HTTP/1.1
	Host: example.com		Host: example.com
	Range: bytes=0-		Range: bytes=0-
	returns a response of the form:		returns a response of the form:
	HTTP/1.1 206 Partial Content		HTTP/1.1 206 Partial Content
	Content-Range: bytes 0-1234567/*		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 accessible at the time the		and (2) only bytes 0-1234567 were accessible at the time the request
	request was processed by the server. The client can infer from this		was processed by the server. The client can infer from this response
	response that bytes 0-1234567 of the representation can be requested		that bytes 0-1234567 of the representation can be requested and
	and returned in a timely fashion (the bytes are immediately		transfer can be performed immediately.
	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
	a live video stream.		a live video stream.
	Unlike a byte-range Range request, a byte-range Content-Range		Unlike a byte-range request header field, a byte-content-range
	response header field cannot be "open ended", per Section 4.2 of		response header field cannot be "open-ended", per Section 4.2 of
	[RFC7233]:		[RFC7233]:
	byte-content-range = bytes-unit SP		byte-content-range = bytes-unit SP
	( 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 an indeterminate-length response.		providing an 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:
	GET /resource HTTP/1.1		GET /resource HTTP/1.1
	Host: example.com		Host: example.com
	Range: bytes=1230000-999999999999		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, and much larger than the expected		request, as described above, and much larger than the expected
	maximum size of the representation. See Section 6 for range value		maximum size of the representation. See Section 6 for range value
	considerations.		considerations.
	In response, a server may indicate that it is supplying a		In response, a server may indicate that it is supplying a
	continuously aggregating ("live") response by supplying the client		continuously aggregating/live response by supplying the client
	request's last-byte-pos in the Content-Range response header field.		request's last-byte-pos in the Content-Range response header field.
	For example:		For example:
	GET /resource HTTP/1.1		GET /resource HTTP/1.1
	Host: example.com		Host: example.com
	Range: bytes=1230000-999999999999		Range: bytes=1230000-999999999999
	returns		returns
	HTTP/1.1 206 Partial Content		HTTP/1.1 206 Partial Content
	Content-Range: bytes 1230000-999999999999/*		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 continue 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 will supply the currently satisfiable byte range,		live response will supply the currently satisfiable byte range, as it
	as it would with an open-ended byte request.		would with an open-ended byte request.
	For example:		For example:
	GET /resource HTTP/1.1		GET /resource HTTP/1.1
	Host: example.com		Host: example.com
	Range: bytes=1230000-999999999999		Range: bytes=1230000-999999999999
	will return		returns
	HTTP/1.1 206 Partial Content		HTTP/1.1 206 Partial Content
	Content-Range: bytes 1230000-1234567/*		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, end at byte 1234567, and not include any aggregated content.
	content. This is the response expected from a typical HTTP server -		This is the response expected from a typical HTTP server -- one that
	one that doesn't support byte-range requests on aggregating content.		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
	response should return data using chunked transfer coding and not		should return data using chunked transfer coding and not provide a
	provide a Content-Length header field. A 0-length chunk indicates		Content-Length header field. A 0-length chunk indicates the end of
	the end of the transfer, per Section 4.1 of [RFC7230].		the transfer, per Section 4.1 of [RFC7230].
	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
	A client that wishes to only receive newly-aggregated portions of a		A client that wishes to only receive newly aggregated portions of a
	resource (i.e., start at the "live" point), can use a HEAD request to		resource (i.e., start at the live point) can use a HEAD request to
	learn what range the server has currently available and initiate an		learn what range the server has currently available and initiate an
	indeterminate-length transfer. For example:		indeterminate-length transfer. For example:
	HEAD /resource HTTP/1.1		HEAD /resource HTTP/1.1
	Host: example.com		Host: example.com
	Range: bytes=0-		Range: bytes=0-
	With the Content-Range response header field indicating the range (or		with the Content-Range response header field indicating the range (or
	ranges) available. For example:		ranges) available. For example:
	206 Partial Content		206 Partial Content
	Content-Range: bytes 0-1234567/*		Content-Range: bytes 0-1234567/*
	The client can then issue a request for a range starting at the end		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		value (using a very large value for the end of a range) and receive
	only new content.		only new content.
	GET /resource HTTP/1.1		For example:
	Host: example.com
	Range: bytes=1234567-999999999999		GET /resource HTTP/1.1
			Host: example.com
			Range: bytes=1234567-999999999999
	with a server returning a Content-Range response indicating that an		with a server returning a Content-Range response indicating that an
	indeterminate-length response body will be provided		indeterminate-length response body will be provided:
	206 Partial Content		206 Partial Content
	Content-Range: bytes 1234567-999999999999/*		Content-Range: bytes 1234567-999999999999/*
	3.2. Shift Buffer Representations		3.2. Shift-Buffer Representations
	Some representations lend themselves to front-end content removal in		Some representations lend themselves to front-end content removal 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 becomes 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 Range request containing:		For example, a range request containing:
	HEAD /resource HTTP/1.1		HEAD /resource HTTP/1.1
	Host: example.com		Host: example.com
	Range: bytes=0-		Range: bytes=0-
	returns		returns
	206 Partial Content		206 Partial Content
	Content-Range: bytes 1000000-1234567/*		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:
	GET /resource HTTP/1.1
	Host: example.com		GET /resource HTTP/1.1
	Range: bytes=1020000-999999999999		Host: example.com
			Range: bytes=1020000-999999999999
	with the server returning		with the server returning
	206 Partial Content		206 Partial Content
	Content-Range: bytes 1020000-999999999999/*		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.
	A server that doesn't support or supply a continuously aggregating
	("live") response will supply the currently satisfiable byte range,
	as it would with an open-ended byte request.
	For example:		A server that doesn't support or supply a continuously aggregating/
			live response will supply the currently satisfiable byte range, as it
			would with an open-ended byte request. For example:
	GET /resource HTTP/1.1		GET /resource HTTP/1.1
	Host: example.com		Host: example.com
	Range: bytes=0-999999999999		Range: bytes=0-999999999999
	will return		returns
	HTTP/1.1 206 Partial Content		HTTP/1.1 206 Partial Content
	Content-Range: bytes 1020000-1254567/*		Content-Range: bytes 1020000-1254567/*
	from the server to indicate that the response will start at byte		from the server to indicate that the response will start at byte
	1020000, end at byte 1254567, and will not include any aggregated		1020000, end at byte 1254567, and not include any aggregated content.
	content. This is the response expected from a typical HTTP server -		This is the response expected from a typical HTTP server -- one that
	one that doesn't support byte-range requests on aggregating content.		doesn't support byte-range requests on aggregating content.
	Note that responses to GET requests against shift-buffer		Note that responses to GET requests performed on shift-buffer
	representations using Range can be cached by intermediaries, since		representations using Range headers can be cached by intermediaries,
	the Content-Range response header indicates which portion of the		since the Content-Range response header indicates which portion of
	representation is being returned in the response body. However GET		the representation is being returned in the response body. However,
	requests without a Range header cannot be cached since the first byte		GET requests without a Range header cannot be cached since the first
	of the response body can vary from request to request. To ensure		byte of the response body can vary from request to request. To
	Range-less GET requests against shift-buffer representations are not		ensure GET requests without Range headers on shift-buffer
	cached, servers hosting a shift-buffer representation should either		representations are not cached, servers hosting a shift-buffer
	not return a 200-level response (e.g. sending a 300-level redirect		representation should either not return a 200-level response (e.g.,
	response with a URI that represents the current start of the shift-		send a 300-level redirect response with a URI that represents the
	buffer) or indicate the response is non-cacheable. See HTTP Caching		current start of the shift buffer) or indicate the response is non-
	([RFC7234]) for details on HTTP cache control.		cacheable. See [RFC7234] for details on HTTP cache control.
	4. Recommendations for Very Large Values		4. Recommendations for Byte-Range Request last-byte-pos Values
	While it would be ideal to define a single numerical Very Large		While it would be ideal to define a single large last-byte-pos value
	Value, there's no single value that would work for all applications		for byte-range requests, there's no single value that would work for
	and platforms. e.g. JavaScript numbers cannot represent all integer		all applications and platforms. For example, JavaScript numbers
	values above 2^^53, so a JavaScript application may want to use		cannot represent all integer values above 2^^53, so a JavaScript
	2^^53-1 for a Very Large Value. This value, however, would not be		application may want to use 2^^53-1 for last-byte-pos. This value,
	sufficient for all applications, such as continuously-streaming high-		however, would not be sufficient for all applications, such as long-
	bitrate streams. So the value 2^^53-1 (9007199254740991) is		duration high-bitrate streams. So 2^^53-1 (9007199254740991) is
	recommended as a Very Large Value unless an application has a good		recommended as a last-byte-pos unless an application has a good
	justification to use a smaller or larger value. e.g. If it's always		justification to use a smaller or larger value. For example, if it
	known that the resource won't exceed a value smaller than the		is always known that the resource won't exceed a value smaller than
	recommended Very Large Value for an application, a smaller value can		the recommended last-byte-pos for an application, a smaller value can
	be used. And if it's likely that an application will utilize		be used. If it's likely that an application will utilize resources
	resources larger than the recommended Very Large Value - such as a		larger than the recommended last-byte-pos (such as a continuously
	continuously aggregating high-bitrate media stream - a larger value		aggregating high-bitrate media stream), a larger value should be
	should be used.		used.
	Note that, in accordance with the semantics defined above, servers		Note that, in accordance with the semantics defined above, servers
	that support random-access live content will need to return the last-		that support random-access live content will need to return the last-
	byte-pos provided in the Range request in some cases - even if the		byte-pos provided in the byte-range request in some cases -- even if
	last-byte-pos cannot be represented as a numerical value internally		the last-byte-pos cannot be represented as a numerical value
	by the server. As is the case with any live/continuously aggregating		internally by the server. As is the case with any continuously
	resource, the server should terminate the content transfer when the		aggregating/live resource, the server should terminate the content
	end of the resource is reached - whether the end is due to		transfer when the end of the resource is reached -- whether the end
	termination of the content source or the content length exceeds the		is due to termination of the content source or the content length
	server's maximum representation length.		exceeds the server's maximum representation length.
	5. IANA Considerations		5. IANA Considerations
	This document has no actions for IANA.		This document has no IANA actions.
	6. Security Considerations		6. Security Considerations
	As described above, servers need to be prepared to receive last-byte-		As described above, servers need to be prepared to receive last-byte-
	pos values in Range requests that are numerically larger than the		pos values in range requests that are numerically larger than the
	server implementation supports - and return these values in Content-		server implementation supports and return these values in Content-
	Range response header fields. Servers should check the last-byte-pos		Range response header fields. Servers should check the last-byte-pos
	value before converting and storing them into numeric form to ensure		value before converting and storing them into numeric form to ensure
	the value doesn't cause an overflow or index incorrect data. The		the value doesn't cause an overflow or index incorrect data. The
	simplest way to satisfy the live-range semantics defined in this		simplest way to satisfy the live-range semantics defined in this
	document without potential overflow issues is to store the last-byte-		document without potential overflow issues is to store the last-byte-
	pos as a string value and return it in the byte-range Content-Range		pos as a string value and return it in the byte-range Content-Range
	response header's last-byte-pos field.		response header's last-byte-pos field.
	7. References		7. References
	7.1. Normative References		7.1. Normative References
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
	Requirement Levels", BCP 14, RFC 2119,		Specifications: ABNF", STD 68, RFC 5234,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC5234, January 2008,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc5234>.
	[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>.
	[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,		[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
	Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",		Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
	RFC 7234, DOI 10.17487/RFC7234, June 2014,		RFC 7234, DOI 10.17487/RFC7234, June 2014,
	<https://www.rfc-editor.org/info/rfc7234>.		<https://www.rfc-editor.org/info/rfc7234>.
	7.2. Informative References		7.2. Informative References
	[DASH] ISO, "Information technology -- Dynamic adaptive streaming		[MPEG-DASH]
			ISO, "Information technology -- Dynamic adaptive streaming
	over HTTP (DASH) -- Part 1: Media presentation description		over HTTP (DASH) -- Part 1: Media presentation description
	and segment formats", ISO/IEC 23009-1:2014, May 2014,		and segment formats", ISO/IEC 23009-1, August 2019,
	<http://standards.iso.org/ittf/PubliclyAvailableStandards/		<https://www.iso.org/standard/75485.html>.
	c065274_ISO_IEC_23009-1_2014.zip>.
	[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
	Specifications: ABNF", STD 68, RFC 5234,
	DOI 10.17487/RFC5234, January 2008,
	<https://www.rfc-editor.org/info/rfc5234>.
	[RFC8216] Pantos, R., Ed. and W. May, "HTTP Live Streaming",		[RFC8216] Pantos, R., Ed. and W. May, "HTTP Live Streaming",
	RFC 8216, DOI 10.17487/RFC8216, August 2017,		RFC 8216, DOI 10.17487/RFC8216, August 2017,
	<https://www.rfc-editor.org/info/rfc8216>.		<https://www.rfc-editor.org/info/rfc8216>.
	Acknowledgements		Acknowledgements
	Mark Nottingham, Patrick McManus, Julian Reschke, Remy Lebeau, Rodger		The authors would like to thank Mark Nottingham, Patrick McManus,
	Combs, Thorsten Lohmar, Martin Thompson, Adrien de Croy, K. Morgan,		Julian Reschke, Remy Lebeau, Rodger Combs, Thorsten Lohmar, Martin
	Roy T. Fielding, Jeremy Poulter.		Thompson, Adrien de Croy, K. Morgan, Roy T. Fielding, and Jeremy
			Poulter.
	Authors' Addresses		Authors' Addresses
	Craig Pratt		Craig Pratt
	Portland, OR 97229		Portland, OR 97229
	US		United States of America
	Email: pratt@acm.org		Email: pratt@acm.org
	Darshak Thakore		Darshak Thakore
	CableLabs		CableLabs
	858 Coal Creek Circle		858 Coal Creek Circle
	Louisville, CO 80027		Louisville, CO 80027
	US		United States of America
	Email: d.thakore@cablelabs.com		Email: d.thakore@cablelabs.com
	Barbara Stark		Barbara Stark
	AT&T		AT&T
	Atlanta, GA		Atlanta, GA
	US		United States of America
	Email: barbara.stark@att.com		Email: barbara.stark@att.com
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