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Versions: 00 01 02 03

HYBI                                                          M. Thomson
Internet-Draft                                                 Microsoft
Intended status: Standards Track                               S. Loreto
Expires: January 18, 2013                                       Ericsson
                                                              G. Wilkins
                                                                 Intalio
                                                           July 17, 2012


          Hypertext Transfer Protocol (HTTP) Keep-Alive Header
                   draft-thomson-hybi-http-timeout-03

Abstract

   A Keep-Alive header is defined for HTTP.  This hop-by-hop header
   informs hosts about connection management policies.  A parameters is
   defined for idle connection timeout.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 18, 2013.

Copyright Notice

   Copyright (c) 2012 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
   (http://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



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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Idle Connection Timeouts and Connection Reuse  . . . . . .  3
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Keep-Alive Header  . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  'timeout' Parameter  . . . . . . . . . . . . . . . . . . .  4
     2.2.  Other Header Parameters  . . . . . . . . . . . . . . . . .  5
       2.2.1.  'max' Parameter  . . . . . . . . . . . . . . . . . . .  5
   3.  Existing Intermediaries  . . . . . . . . . . . . . . . . . . .  5
   4.  Upgraded HTTP Connections  . . . . . . . . . . . . . . . . . .  6
   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
     7.1.  Registration for Keep-Alive Header . . . . . . . . . . . .  8
     7.2.  Registry for Keep-Alive Information  . . . . . . . . . . .  8
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  9
   9.  Change Log . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     10.1. Normative References . . . . . . . . . . . . . . . . . . .  9
     10.2. Informative References . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10


























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1.  Introduction

   This document describes the "Keep-Alive" header.  The "Keep-Alive"
   header provides Hypertext Transfer Protocol (HTTP)
   [I-D.ietf-httpbis-p1-messaging] clients, servers and intermediaries
   with information about the connection use policies of their peers.

   The "timeout" Keep-Alive parameter indicates the time that a
   connection will be allowed to remain idle before it is closed.

   Some HTTP implementations already provide an implementation for this
   header.  Not all of those implementations are interoperable due to
   significant differences in the header format.  This draft defines a
   single format for the header and ascribes specific semantics to the
   header parameters.

1.1.  Idle Connection Timeouts and Connection Reuse

   Management of idle HTTP connections has an impact on long-lived
   communications between hosts.  Hosts are able to close idle
   connections in order to reduce resource consumption.

   Many clients choose not to send non-idempotent requests on idle
   connections.  If the intermediary or server holding the other end of
   the connection chooses to close the connection while a non-idempotent
   request is in transit, the client has no way to tell if the request
   has succeeded.  For this reason, many clients establish a new
   connection for every non-idempotent request.  This is inefficient if
   the existing connection is a usable connection: establishing a new
   connection adds significantly to the latency of the request.

   Connection resources can be more efficiently used when an idle
   connection timeout is known.  A client that only periodically sends
   request can learn about the possibility of a connection timeout and
   can act to create a new connection for requests or send requests that
   keep the connection from timing out.  Alternatively, a client that
   knows that more requests on a connection are unlikely within the
   discovered timeout interval can close the connection immediately
   after a poll, releasing resources.

1.2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
   RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
   described in BCP 14, RFC 2119 [RFC2119] and indicate requirement
   levels for compliant implementations.




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2.  Keep-Alive Header

   The "Keep-Alive" header is a hop-by-hop header that provides
   information about a persistent connection.  Both client and server
   are able to provide information independently.

   Keep-Alive           = "Keep-Alive" ":" 1#keep-alive-info
   keep-alive-info      =   "timeout" "=" delta-seconds
                          / keep-alive-extension
   keep-alive-extension = token [ "=" ( token / quoted-string ) ]

   This header is sent by either host participating in a persistent
   connection.  The values might be set based on policy implemented by
   servers, clients and intermediaries.  Values might also be set based
   on knowledge that a host has about lower layer intermediaries in the
   path of the request, such as a TCP middlebox.  Such middleboxes, in
   particular network address translators (NATs), frequently discard
   mappings for idle connections, causing the connection to fail after a
   certain duration of inactivity.

   The value of Keep-Alive parameters can change on each request or
   response sent on a connection.  Absence of the header or any
   parameter implies that any previously provided value still applies.

   As a hop-by-hop header, this header only applies to a single
   transport-level connection.  If a Keep-Alive header is added to a
   request or response, the Connection header MUST include the tag
   "Keep-Alive".  This ensures that compliant intermediaries that do not
   recognize this header remove it before forwarding a request.

2.1.  'timeout' Parameter

   A host sets the value of the "timeout" parameter to the time that the
   host will allow an idle connection to remain open before it is
   closed.  A connection is idle if no data is sent or received by a
   host.

   The value of the "timeout" parameter is a single integer in seconds.

   A host MAY keep an idle connection open for longer than the time that
   it indicates, but it SHOULD attempt to retain a connection for at
   least as long as indicated.

   Each peer, client or server, has a different view of the time that a
   connection becomes idle.  Packet transmission at one peer necessarily
   occurs before receipt, meaning that the sending peer perceives the
   connection as being idle earlier to the receiving peer.  Similarly,
   the buffering or retransmission of data by lower layers of the stack,



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   which is unlikely to be visible to the HTTP implementation, compounds
   this effect.  Clients are advised to make allowances for delays in
   determining whether to reuse an idle connection.

2.2.  Other Header Parameters

   The Keep-Alive header can be extended by adding any number of keep-
   alive-extension values to the header.  Any extension that is not
   understood MUST be ignored.

   The HTTP Keep-Alive Information Registry defines the namespace for
   Keep-Alive extensions.  Section 7.2 describes this registry.

2.2.1.  'max' Parameter

   The "max" parameter has been used to indicate the maximum number of
   requests that would be made on the connection.  This parameter is
   deprecated.  Any limit on requests can be enforced by sending
   "Connection: close" and closing the connection.


3.  Existing Intermediaries

   The exact impact of an intermediary on an HTTP request with a Keep-
   Alive header depends on the type of intermediary.

   An intermediary that is compliant with HTTP/1.1, but does not
   implement Keep-Alive, ignores and discards this header before
   forwarding a request.  Since it is unaware of the semantics of the
   header it could drop an idle connection at any time (see Section
   7.1.4 of [I-D.ietf-httpbis-p1-messaging]).

   A non-compliant "transparent" intermediary could pass this header on
   to the next hop.  This results in errors of the sort that are
   described in Section A.1.2 of [I-D.ietf-httpbis-p1-messaging].
   Clients that send this header to HTTP/1.0 servers or proxies SHOULD
   monitor for "hung" connections and avoid sending the header if a
   connection appears to hang.

   A network address translation (NAT) device or other middlebox might
   cause a connection to become unavailable prior to the advertised
   timeout.

   A client or intermediary can revise or remove the Keep-Alive header
   for subsequent requests to the same resource or origin server if it
   detects non-compliant intermediaries or middleboxes that have shorter
   timeout periods.




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4.  Upgraded HTTP Connections

   A connection timeout can apply to a connection that is subsequently
   upgraded to another protocol [RFC2817], such as the websocket
   protocol [RFC6455].

   The idle connection timeout applies to the upgraded connection,
   unless the upgraded protocol provides another method for indicating
   idle timeouts.

   A server, client or intermediary might apply different policies to an
   upgraded protocol.

   Upgraded protocols might establish an end-to-end connection.  As a
   hop-by-hop header, the values in the "Keep-Alive" on each hop apply
   to every hop equally.  For "timeout", this means that the lowest
   value from any hop applies to the connection.

   Intermediaries that support this header SHOULD determine the impact
   of a header parameter on dependent hops and reflect that in the
   values they set.  For "timeout", this means that the lowest value
   from the values seen and the local value is provided in outgoing
   messages.


5.  Examples

   The example in Figure 1 shows how a Keep-Alive header could be used.
   All connections are independently negotiated.  In this example, the
   client indicates a timeout of 600 seconds (10 minutes), but the proxy
   is prepared to retain the connection for up to 3600 seconds (1 hour).
   On the link between proxy and server, the proxy requests a timeout of
   1200 seconds and the server indicates a lower limit of 300 seconds.

    Client                        Proxy                         Server
      |                             |                              |
      +- Keep-Alive: timeout=600 -->|                              |
      |  Connection: Keep-Alive     |                              |
      |                             +- Keep-Alive: timeout=1200 -->|
      |                             |  Connection: Keep-Alive      |
      |                             |                              |
      |                             |<-- Keep-Alive: timeout=300 --+
      |                             |    Connection: Keep-Alive    |
      |<- Keep-Alive: timeout=3600 -+                              |
      |    Connection: Keep-Alive   |                              |
      |                             |                              |

                      Figure 1: Independent HTTP Hops



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   As this example shows, the timeout policies maintained by the proxy
   are different for each connection.  Each connection hop is
   independent.

   The example in Figure 2 shows the headers included in an upgrade from
   HTTP/1.1 to WebSocket [RFC6455].  With a websocket upgrade, the
   connections on each hop cannot have independent lifecycles on either
   side of an intermediary.  After the upgrade, timeout policies cannot
   be independent for each hop.  The proxy adjusts the timeout value to
   reflect the lower of the values set by client and the proxy policies
   so that the server is aware of the connection characteristics;
   similarly, the value from the server is provided to the client.

    Client                        Proxy                         Server
      |                             |                              |
      |  Upgrade: websocket         |                              |
      +- Keep-Alive: timeout=600 -->|                              |
      |  Connection: Keep-Alive,    |                              |
      |              Upgrade        |                              |
      |                             |  Upgrade: websocket          |
      |                             +- Keep-Alive: timeout=600 --->|
      |                             |  Connection: Keep-Alive,     |
      |                             |              Upgrade         |
      |                             |                              |
      |                             |    Upgrade: websocket        |
      |                             |<-- Keep-Alive: timeout=300 --+
      |                             |    Connection: Keep-Alive,   |
      |                             |                Upgrade       |
      |   Upgrade: websocket        |                              |
      |<- Keep-Alive: timeout=300 --+                              |
      |   Connection: Keep-Alive,   |                              |
      |               Upgrade       |                              |
      |                             |                              |

             Figure 2: Interdependent Connections with Upgrade


6.  Security Considerations

   Establishing a persistent connection requires a commitment of
   resources at a host.  The Keep-Alive header are used to express host
   policy that could alter the way that a host allocates connection
   resources.  Since these policies can be enacted without this
   feedback, these indications have little effect on security other than
   exposing specifics of policy.

   A host can close a non-idle connection sooner than the indicated time
   if necessary or as dictated by local policy (see Section 7.1.4 of



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   [I-D.ietf-httpbis-p1-messaging]).


7.  IANA Considerations

   [[Note to IANA/RFC Editor: Please replace instance of RFCXXXX with
   the number of the published RFC and remove this note.]]

7.1.  Registration for Keep-Alive Header

   This document registers the HTTP "Keep-Alive" header in the
   "Permanent Message Header Fields" registry established by [RFC3864]

   Header field:  Keep-Alive

   Applicable protocol:  HTTP

   Status:  standard

   Author/change controller:  Internet Engineering Task Force, IETF
      (iesg@ietf.org)

   Specification document(s):  RFCXXXX (this document)

7.2.  Registry for Keep-Alive Information

   This document establishes a registry for Keep-Alive Information.

   Registrations are subject to Specification Required [RFC5226].  The
   designated expert is advised to review registrations and work with
   the submitter to ensure that:

   o  the registration name conforms to the HTTP "token" grammar

   o  a stable specification exists that is sufficient for interoperable
      implementation

   o  the registration does not duplicate an existing entry

   The registry includes the following initial values:

   timeout  See Section 2.1 of this document.

   max  Deprecated.  See Section 2.2.1 of this document.







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8.  Acknowledgments

   Jamie Lokier provided valuable contributions of experience, insight
   and text suggestions to this document.  Roy Fielding provided
   information on existing implementations of the poorly documented
   header.  Also provided useful feedback: Patrick McManus, Dave Thaler,
   Konstantinos Pentikousis.


9.  Change Log

   Since -01:

   o  Deprecated 'max'

   o  Corrected badly misleading examples

   o  Loosened the registry policy from IETF Review

   Since -00:

   o  Removed Request-Timeout in favor of the wait parameter of the
      Prefer header.

   o  Connection-Timeout has now been replaced with the zombie spawn of
      Keep-Alive.  This means that it picks up the 'max' parameter as
      baggage.  Open question: should 'max' be deprecated?

   Since draft-loreto-http-timeout:

   o  Changed Timeout to Request-Timeout to avoid a conflict with an
      existing header definition.

   o  Added note about the application of Connection-Timeout to upgraded
      protocols.


10.  References

10.1.  Normative References

   [I-D.ietf-httpbis-p1-messaging]
              Fielding, R., Lafon, Y., and J. Reschke, "HTTP/1.1, part
              1: Message Routing and Syntax"",
              draft-ietf-httpbis-p1-messaging-20 (work in progress),
              July 2012.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate



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              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", BCP 90, RFC 3864,
              September 2004.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

10.2.  Informative References

   [RFC2068]  Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.
              Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
              RFC 2068, January 1997.

   [RFC2817]  Khare, R. and S. Lawrence, "Upgrading to TLS Within
              HTTP/1.1", RFC 2817, May 2000.

   [RFC6455]  Fette, I. and A. Melnikov, "The WebSocket Protocol",
              RFC 6455, December 2011.


Authors' Addresses

   Martin Thomson
   Microsoft
   3210 Porter Drive
   Palo Alto, CA  94304
   US

   Phone: +1 650-353-1925
   Email: martin.thomson@skype.net


   Salvatore Loreto
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: salvatore.loreto@ericsson.com









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   Greg Wilkins
   Intalio
   644 Emerson Street, Suite 200
   Palo Alto  94301
   USA

   Email: gregw@intalio.com












































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