HTTP Random Access and Live Content
RFC 8673

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Internet Engineering Task Force (IETF)                          C. Pratt
Request for Comments: 8673                                              
Category: Experimental                                        D. Thakore
ISSN: 2070-1721                                                CableLabs
                                                                B. Stark
                                                                    AT&T
                                                           November 2019

                  HTTP Random Access and Live Content

Abstract

   To accommodate byte-range requests for content that has data appended
   over time, this document defines semantics that allow an HTTP client
   and a server to perform byte-range GET and HEAD requests that start
   at an arbitrary byte offset within the representation and end at an
   indeterminate offset.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Engineering
   Task Force (IETF).  It represents the consensus of the IETF
   community.  It has received public review and has been approved for
   publication by the Internet Engineering Steering Group (IESG).  Not
   all documents approved by the IESG are candidates for any level of
   Internet Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8673.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
     1.1.  Notational Conventions
   2.  Performing Range Requests on Random-Access Aggregating (Live)
           Content
     2.1.  Establishing the Randomly Accessible Byte Range
     2.2.  Byte-Range Requests beyond the Randomly Accessible Byte
           Range
   3.  Other Applications of Random-Access Aggregating Content
     3.1.  Requests Starting at the Aggregation/Live Point
     3.2.  Shift-Buffer Representations
   4.  Recommendations for Byte-Range Request last-byte-pos Values
   5.  IANA Considerations
   6.  Security Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   Some Hypertext Transfer Protocol (HTTP) clients use byte-range
   requests (range requests using the "bytes" range unit) to transfer
   select portions of large representations [RFC7233].  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 that
   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.

   Alternatively, clients can access appended content by sending
   periodic, open-ended byte-range requests using the last known end
   byte position as the range start.  Performing low-frequency periodic
   byte-range requests in this fashion (polling) introduces latency
   since the client will necessarily be somewhat behind in transferring
   the aggregated content, effectively resulting in the same kind of
   latency issues with the segmented content transfer mechanisms in
   "HTTP Live Streaming" (HLS) [RFC8216] and "Dynamic Adaptive Streaming
   over HTTP" [MPEG-DASH].  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