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Network Working Group                                            de Croy
Internet-Draft                                                      QBIK
Intended status: Standards Track                           July 23, 2008
Expires: January 23, 2009


                      Progress notifications for HTTP
                       draft-decroy-http-progress-04

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Copyright Notice

   Copyright (C) The IETF Trust (2008).
















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Abstract

   This document specifies an extension to HTTP to allow the sending of
   progress messages to user-agents during lengthy processing which
   could otherwise cause users or user-agents to abandon requests.


Table of Contents

   1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction and motivation  . . . . . . . . . . . . . . . . .  4
     2.1 The need for progress information. . . . . . . . . . . . . .  4
     2.2 Aim of this document . . . . . . . . . . . . . . . . . . . .  4
   3.  Header Field Definitions . . . . . . . . . . . . . . . . . . .  5
     3.1 Progress . . . . . . . . . . . . . . . . . . . . . . . . . .  5
       3.1.1 Client request . . . . . . . . . . . . . . . . . . . . .  5
       3.1.2 1xx Responses. . . . . . . . . . . . . . . . . . . . . .  6
   4.  Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     4.1 Progress Intervals . . . . . . . . . . . . . . . . . . . . .  7
   5.  Example. . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Compatibilty issues. . . . . . . . . . . . . . . . . . . . . .  9
   7.  Implementation Notes . . . . . . . . . . . . . . . . . . . . . 10
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   9.  Notes & TODO . . . . . . . . . . . . . . . . . . . . . . . . . 12
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 14
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
   Intellectual Property and Copyright Statements . . . . . . . . . . 16






















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1.  Terminology

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT"
   and "MAY" that appear in this document are to be interpreted as
   described in [RFC2119]














































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2.  Introduction and motivation

2.1 The need for progress information

   Resource transfers using HTTP are increasingly subject to ever-
   more complex processing, particularly by proxy servers.  Processing
   such as scanning resources for virii at an HTTP proxy creates
   special problems that cannot be resolved cleanly with the current
   specification of HTTP.

   Many types of processing require access to an entire message body.
   This can take considerable time to accumulate depending on upstream
   link bandwidth and/or other factors.  It may not be safe to send
   any part of the resource to the client until processing is complete.

   Frequently problems occur where human users of client agents give up
   waiting for visible progress, typically resulting in retries wasting
   time, network and other resources.

   Furthermore, some automated clients will give up waiting when no
   resource data is received within a certain timeframe.

   There is a clear need for upstream agents to be able to provide
   timely progress notifications to downstream agents to enable them to
   make proper decisions about whether it is appropriate to keep
   waiting.


2.3 Aim of this document

   This document aims to solve this problem by providing a defined
   mechanism whereby intermediaries or server agents can provide
   progress notifications back to the client agent (and the human user),
   thereby avoiding inappropriate timeouts, and retries.

















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3 Header field definitions

   This document defines a new header field to indicate progress.
   This field allows optional textual state indication as well as
   requiring numeric indication of completeness.

3.1 Progress

   The Progress field MAY appear in any request message sent by a client
   or in any server or proxy-generated 1xx series of response messages.
   The Progress field MUST not appear in any other series of response
   messages.

   A server that complies with this document upon receiving a request
   containing a Progress field MUST provide an interim response message
   (1XX) within a reasonable time period AND provide further periodic
   updates until the final response to the request is sent.

   A proxy that complies with this document upon receiving a request
   containing a Progress field MUST forward the tag unchanged to any
   upstream agent.  The proxy however is responsible for providing
   progress messages to the client, and in the event that no upstream
   notifications are available, it MUST satisfy the client progress
   notifications whilst it is still prepared to process the request.

   The proxy SHOULD pass any 1XX messages back through to the
   client unchanged.

   Progress indication is worthless if it is not timely.  A discussion
   of timing is in section 4


   The form of the field is defined below

3.1.1 Client request

   Progress = "Progress" ":" interval

   interval = 1*4DIGIT
              ; the time (s) within which the client expects a response

   Example:

   Progress: 10







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3.1.2 1xx Responses

   Progress         = "Progress" ":" prog-num [SP prog-text]

   prog-text        = quoted-string

   prog-num         = percent | (bytes-processed "/" bytes-total)

   percent          = "%" %d0-100
                      ; integer percentage complete, 0 - 100

   bytes-processed  = number

   bytes-total      = number | "UNKNOWN"

   The textual information is intended to be displayed verbatim to a
   user in an area usually associated with progress indication.  The
   numeric-progress field can be used to display a progress bar and/or
   show how much data has been received by an upstream proxy.

   The prog-text SHOULD be in a natural language and character set that
   is most likely to be intelligible to the human user receiving the
   response. This decision MAY be based on any available knowledge. The
   default language is English and the default character set is
   ISO-8859-1. If a character set other than ISO-8859-1 is used, it MUST
   be encoded in the prog-text using the method described in [RFC2047].

   Examples:

      Progress: 20480/UNKNOWN "Generating content"

   This could be sent by a server to indicate progress of generation of
   content.

      Progress: 20480/UNKNOWN "Download in progress"

   Could be sent by an upstream proxy that is retrieving a message body,
   has received 20480 bytes, and doesn't know the content length.

      Progress: 1200000/1200000 "Download complete, scanning"

   Could be sent by an upstream proxy that has just completed retrieving
   a message body, has received 1200000 of 1200000 bytes, and is about
   to scan the content before sending it on to the client.

      Progress: %25 "Scanning content for virii"

   Could be sent by an upstream proxy that is currently 25% through
   virus scanning of a message body.


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4.  Timing

4.1 Progress intervals

   The client Progress header indicates a time in seconds which is the
   time within which it expects a response (either final or interim
   containing progress information).  The server or proxy SHOULD use
   this specified time as the initial time and periodic time for
   updates, or choose another time.   If the server chooses to use
   another periodic interval, this should be one chosen with regard to
   the usefulness of the interval to a waiting human, and it is
   suggested that an interval of about 5 - 10 seconds would be
   appropriate.

   Agents generating progress notifications MAY choose to send a
   notification whenever any significant change in state occurs.

   However in the interests of bandwidth, agents SHOULD NOT send
   progress notifications more frequently than once per second.
   This includes an intermediary which may be generating notifications
   and relaying notifications from upstream.

   It is left up to the implementor of intermediaries to choose which
   notifications they may choose to relay or generate themselves,
   remembering that this is intended for a human user, but will be
   useful to automated agents as well.

























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5.   Example

   +-------------------+------------------------+--------------------+
   |       Client      |      Intermediary      |       Server       |
   +-------------------+------------------------+--------------------+

   Connects to intermediary

   ->
   GET http://www.wingate.com/bigfile.zip HTTP/1.1
   Host: www.wingate.com
   Progress: 10

                      ->
                      GET /bigfile.zip HTTP/1.1
                      Host: www.wingate.com
                      Progress: 10

                                              <-
                                              HTTP/1.1 200 OK
                                              Content-Length: 20000000
                                              ...

                         time elapses
                      <-
                      HTTP/1,1 102 Processing
                      Progress: 1000000/20000000 "Downloading"

                         time elapses
                      <-
                      HTTP/1,1 102 Processing
                      Progress: 20000000/20000000 "Downloaded, Scanning"

                         time elapses
                      <-
                      HTTP/1,1 102 Processing
                      Progress: %25 "Scanning"

                         time elapses
                      <-
                      HTTP/1,1 102 Processing
                      Progress: %75 "Scanning"

                      <-
                      HTTP/1.1 200 OK
                      Content-Length: 20000000
                      ...
                      Transfers resource to client.



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6. Compatibilty issues.

   None identified.  RFC2616 already requires that any agent must be
   able to cope with multiple interim responses.

   A server not understanding the Progress header in a request will
   not generate progress notifications.

   A client unaware of this document will not generate requests with
   the Progress header.

   A proxy not understanding the Progress header already should be
   passing unknown headers through to upstream, and also passing back
   1XX responses.






































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7.  Implementation Notes

   Most user agents provide screen real-estate to display progress,
   often in the "status bar" of the window.  It is envisaged that the
   progress notifications outlined in this document would be shown in
   there.













































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8.  Security Considerations

   No security issues identified with use of this proposal.
















































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9.  Notes & TODO

   * modified from version 00 to remove sections on flow control issues.

   * modified from version 01 to allow for internationalisation of
     strings, slight modification to syntax.  Minor editorial changes.













































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10. IANA Considerations

   None.
















































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11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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.

   [RFC2047]  Moore, K., "MIME (Multipurpose Internet Mail Extensions)
              Part Three: Message Header Extensions for Non-ASCII Text",
              RFC 2047, November 1996.





































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Author's Address

   Adrien de Croy
   Qbik New Zealand Limited
   PO Box 3548
   Shortland St
   Auckland
   New Zealand

   Email: adrien@qbik.com
   URI:   http://www.wingate.com/








































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