From 7081a4657ccc2f9b85c7d51f7f0e7490c99b2f5b Mon Sep 17 00:00:00 2001 From: Craig Pratt Date: Wed, 28 Mar 2018 13:39:27 -0400 Subject: [PATCH 1/2] Incorporated Darshak's edits minus whitespace This should match what was submitted for draft -03 - without (inconsequential) whitespace changes that were introduced by his editor. --- draft-ietf-httpbis-rand-access-live.xml | 39 +++++++++++++------------ 1 file changed, 20 insertions(+), 19 deletions(-) diff --git a/draft-ietf-httpbis-rand-access-live.xml b/draft-ietf-httpbis-rand-access-live.xml index f515d54d6..5cae1bb35 100644 --- a/draft-ietf-httpbis-rand-access-live.xml +++ b/draft-ietf-httpbis-rand-access-live.xml @@ -70,10 +70,8 @@ fullname="Craig Pratt" initials="C." surname="Pratt"> -
- Portland OR 97229 @@ -83,22 +81,6 @@
- - AT&T -
- - - Atlanta - GA - - US - - barbara.stark@att.com -
- - @@ -109,12 +91,27 @@ Louisville CO 80027 + US d.thakore@cablelabs.com - + + AT&T +
+ + Atlanta + GA + US + + barbara.stark@att.com +
+ + + @@ -481,6 +478,10 @@ Content-Range: bytes 1020000-1254567/* +
+ This document has no actions for IANA. +
+
One potential issue with this recommendation is related to the use of very-large last-byte-pos values. Some client and server implementations may not be prepared to deal with byte position values 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 this value should be used as the Very Large last-byte-pos in a byte-seek request or content-range response. From 61eed494466c2adafab145adc664ec49f2e87d14 Mon Sep 17 00:00:00 2001 From: Craig Pratt Date: Wed, 28 Mar 2018 13:50:18 -0400 Subject: [PATCH 2/2] Whitespace cleanup --- draft-ietf-httpbis-rand-access-live.xml | 120 ++++++++++++------------ 1 file changed, 60 insertions(+), 60 deletions(-) diff --git a/draft-ietf-httpbis-rand-access-live.xml b/draft-ietf-httpbis-rand-access-live.xml index 5cae1bb35..0c7be58f9 100644 --- a/draft-ietf-httpbis-rand-access-live.xml +++ b/draft-ietf-httpbis-rand-access-live.xml @@ -14,10 +14,10 @@ - - + - + @@ -36,27 +36,27 @@ - - + - + - + The tags used are the anchor attributes of the references. --> - @@ -67,8 +67,8 @@ HTTP Random Access and Live Content
@@ -80,9 +80,9 @@ pratt@acm.org
- + CableLabs
@@ -96,7 +96,7 @@ d.thakore@cablelabs.com
- + @@ -112,9 +112,9 @@ - + - + Applications and Real-Time @@ -124,21 +124,21 @@ omit this element in which case in defaults to "Network Working Group" - a hangover from the ancient history of the IETF! --> HTTP - + http range unit live aggregation - + - - + + - To accommodate byte range requests for content that has - data appended over time, this document defines semantics + To accommodate byte range requests for content that has + data appended over time, this document defines semantics that allow a HTTP client and server to perform byte-range - GET and HEAD requests that start at an arbitrary byte offset + GET and HEAD requests that start at an arbitrary byte offset within the representation and ends at an indeterminate offset. @@ -161,13 +161,13 @@ - +
Some Hypertext Transfer Protocol (HTTP) clients use byte-range requests (Range requests using the "bytes" Range Unit) to transfer select portions of large representations (). And in some cases large representations require content to be continuously or periodically appended - such as representations consisting of live audio or video sources, blockchain databases, and log files. Clients cannot access the appended/live content using a Range request with the bytes range unit using the currently defined byte-range semantics without accepting performance or behavior sacrifices which are not acceptable for many applications. - For instance, HTTP clients have the ability to access appended content on an indeterminate-length resource by transferring the entire representation from the beginning and continuing to read the appended content as it's made available. Obviously, this is highly inefficient for cases where the representation is large and only the most recently appended content is needed by the client. + For instance, HTTP clients have the ability to access appended content on an indeterminate-length resource by transferring the entire representation from the beginning and continuing to read the appended content as it's made available. Obviously, this is highly inefficient for cases where the representation is large and only the most recently appended content is needed by the client. Alternatively, clients can also access appended content by sending periodic open-ended bytes Range requests using the last-known end byte position as the range start. Performing low-frequency periodic bytes Range requests in this fashion (polling) introduces latency since the client will necessarily be somewhat behind the aggregated content - mimicking the behavior (and latency) of segmented content representations such as "HTTP Live Streaming" (HLS, ) or "Dynamic Adaptive Streaming over HTTP" (MPEG-DASH, ). And while performing these Range requests at higher frequency can reduce this latency, it also incurs more processing overhead and HTTP exchanges as many of the requests will return no content - since content is usually aggregated in groups of bytes (e.g. a video frame, audio sample, block, or log entry). @@ -197,12 +197,12 @@
- +
This document recommends a two-step process for accessing resources that have indeterminate length representations. - + Two steps are necessary because of limitations with the Range request header fields and the Content-Range response header fields. A server cannot know from a range request that a client wishes to receive a response @@ -214,7 +214,7 @@ 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 + Content-Range syntax. See for details and examples. Once the client knows the resource has indeterminate length, it can @@ -227,8 +227,8 @@ range end rather than a range that is bounded by what is currently available. See for details. - -
+ +
Establishing if a representation is continuously aggregating ("live") and determining the randomly-accessible byte range can both be determined using the existing definition for an open-ended byte-range request. Specifically, defines a byte-range request of the form: @@ -247,9 +247,9 @@ Host: example.com Range: bytes=0- - + returns a response of the form: - +
HTTP/1.1 206 Partial Content Content-Range: bytes 0-1234567/* @@ -260,11 +260,11 @@ Content-Range: bytes 0-1234567/*
- Once a client has determined that a representation has an indeterminate length and established the byte range that can be accessed, it may want to perform a request with a start position within the randomly-accessible content range and an end position at an indefinite "live" point - a point where the byte-range GET request is fulfilled on-demand as the content is aggregated. + Once a client has determined that a representation has an indeterminate length and established the byte range that can be accessed, it may want to perform a request with a start position within the randomly-accessible content range and an end position at an indefinite "live" point - a point where the byte-range GET request is fulfilled on-demand as the content is aggregated. For example, for a large video asset, a client may wish to start a content transfer from the video "key" frame immediately before the point of aggregation and continue the content transfer indefinitely as content is aggregated - in order to support low-latency startup of a live video stream. - + Unlike a byte-range Range request, a byte-range Content-Range response header field cannot be "open ended", per : @@ -275,11 +275,11 @@ Content-Range: bytes 0-1234567/* byte-range-resp = byte-range "/" ( complete-length / "*" ) byte-range = first-byte-pos "-" last-byte-pos unsatisfied-range = "*/" complete-length - + complete-length = 1*DIGIT - Specifically, last-byte-pos is required in byte-range. So in order to preserve interoperability with existing HTTP clients, servers, proxies, and caches, this document proposes a mechanism for a client to indicate support for handling an indeterminate-length byte-range response, and a mechanism for a server to indicate if/when it's providing a indeterminate-length response. + Specifically, last-byte-pos is required in byte-range. So in order to preserve interoperability with existing HTTP clients, servers, proxies, and caches, this document proposes a mechanism for a client to indicate support for handling an indeterminate-length byte-range response, and a mechanism for a server to indicate if/when it's providing a indeterminate-length response. A client can indicate support for handling indeterminate-length byte-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-range GET request of the form: @@ -290,11 +290,11 @@ Host: example.com Range: bytes=1230000-999999999999 - + 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 request, as described above. - In response, a server may indicate that it is supplying a continuously aggregating ("live") response by supplying the client request's last-byte-pos in the Content-Range response header field. + In response, a server may indicate that it is supplying a continuously aggregating ("live") response by supplying the client request's last-byte-pos in the Content-Range response header field. For example: @@ -307,12 +307,12 @@ Range: bytes=1230000-999999999999 returns - +
HTTP/1.1 206 Partial Content Content-Range: bytes 1230000-999999999999/*
- + from the server to indicate that the response will start at byte 1230000 and continues indefinitely to include all aggregated content, as it becomes available. @@ -334,7 +334,7 @@ Range: bytes=1230000-999999999999 HTTP/1.1 206 Partial Content Content-Range: bytes 1230000-1234567/* - + from the server to indicate that the response will start at byte 1230000 and end at byte 1234567 and will not include any aggregated content. This is the response expected from a typical HTTP server - one that doesn't support byte-range requests on aggregating content. @@ -345,7 +345,7 @@ Content-Range: bytes 1230000-1234567/*
-
+
A client that wishes to only receive newly-aggregated portions of a @@ -431,7 +431,7 @@ Range: bytes=1020000-999999999999 with the server returning - +
206 Partial Content Content-Range: bytes 1020000-999999999999/* @@ -462,15 +462,15 @@ Content-Range: bytes 1020000-1254567/* from the server to indicate that the response will start at byte 1020000, end at byte 1254567, and will not include any aggregated content. This is the response expected from a typical HTTP server - one that doesn't support byte-range requests on aggregating content. - Note that responses to GET requests against shift-buffer representations using Range - can be cached by intermediaries, since the Content-Range response header indicates - which portion of the representation is being returned in the response body. However - GET requests without a Range header cannot be cached since the first byte of the response - body can vary from request to request. To ensure Range-less GET requests against - shift-buffer representations are not cached, servers hosting a shift-buffer - representation should either not return a 200-level response (e.g. sending a - 300-level redirect response with a URI that represents the current start of the - shift-buffer) or indicate the response is non-cacheable. See HTTP Caching + Note that responses to GET requests against shift-buffer representations using Range + can be cached by intermediaries, since the Content-Range response header indicates + which portion of the representation is being returned in the response body. However + GET requests without a Range header cannot be cached since the first byte of the response + body can vary from request to request. To ensure Range-less GET requests against + shift-buffer representations are not cached, servers hosting a shift-buffer + representation should either not return a 200-level response (e.g. sending a + 300-level redirect response with a URI that represents the current start of the + shift-buffer) or indicate the response is non-cacheable. See HTTP Caching () for details on HTTP cache control.
@@ -485,7 +485,7 @@ Content-Range: bytes 1020000-1254567/*
One potential issue with this recommendation is related to the use of very-large last-byte-pos values. Some client and server implementations may not be prepared to deal with byte position values 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 this value should be used as the Very Large last-byte-pos in a byte-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.
@@ -514,13 +514,13 @@ Content-Range: bytes 1020000-1254567/* - +
Mark Nottingham, Patrick McManus, Julian Reschke, Remy Lebeau, Rodger Combs, Thorsten Lohmar, Martin Thompson, Adrien de Croy, K. Morgan, Roy T. Fielding, Jeremy Poulter.
- +