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HYBI                                                          M. Thomson
Internet-Draft                                                     Skype
Intended status: Standards Track                               S. Loreto
Expires: September 13, 2012                                     Ericsson
                                                              G. Wilkins
                                                                 Intalio
                                                          March 12, 2012


          Hypertext Transfer Protocol (HTTP) Keep-Alive Header
                   draft-thomson-hybi-http-timeout-01

Abstract

   A Keep-Alive header is defined for HTTP.  This hop-by-hop header
   informs hosts about connection management policies.  Parameters are
   defined for idle connection timeout and maximum request count.

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 September 13, 2012.

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.  'max' Parameter  . . . . . . . . . . . . . . . . . . . . .  5
     2.3.  Keep-Alive Extensions  . . . . . . . . . . . . . . . . . .  5
   3.  Existing Intermediaries  . . . . . . . . . . . . . . . . . . .  5
   4.  Upgraded HTTP Connections  . . . . . . . . . . . . . . . . . .  6
   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   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" header parameter indicates the time that a connection
   will be allowed to remain idle before it is closed.

   The "max" header parameter indicates the maximum number of requests
   that will be permitted before the connection 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



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   described in BCP 14, RFC 2119 [RFC2119] and indicate requirement
   levels for compliant implementations.


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
                          / "max" "=" 1*DIGIT
                          / 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 allows 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.




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   The perception of idleness for a connection can be affected by
   buffering in network stacks and other local considerations.  Clients
   and servers can also have different views of idleness.  In
   particular, network transit adds delays that skew the subjective
   perception of whether a connection is idle.  Clients are advised to
   make allowances for delays in determining whether to reuse an idle
   connection.

2.2.  'max' Parameter

   The "max" parameter indicates the maximum number of requests that a
   client will make, or that a server will allow to be made on the
   persistent connection.  Once the specified number of requests and
   responses have been sent, the host that included the parameter could
   close the connection.

   The value of the "max" parameter counts the number of requests since
   the connection was created.

   For clients, receiving this parameter in a response allows the client
   to limit the number of requests that it sends.  A client that
   pipelines request can use this information to constrain the length of
   a pipeline.

   For servers, receiving this parameter in a request allows the server
   to close the connection after the final response has been sent.

2.3.  Keep-Alive Extensions

   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.


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 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



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   to the next hop.  This results in errors of the sort that are
   described in Section 19.7.1 of [RFC2068].

   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 might revise the Keep-Alive header that it
   sends in subsequent requests to the same resource or origin server if
   it detects non-compliant intermediaries or middleboxes that have
   shorter timeout periods.


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.  The maximum request count does not apply to the
   upgraded connection; the upgrade request and subsequent exchange are
   regarded as a single HTTP request.

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


5.  Examples

   The following example 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 only prepared to retain the connection for at least 120 seconds (2
   minutes).  On the link between proxy and server, the proxy requests a
   timeout of 1200 seconds and the server reduces this to 300 seconds.














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    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=5000 -+                              |
      |    Connection: Keep-Alive   |                              |
      |                             |                              |

                           Independent HTTP Hops

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

   The following example 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 connection.  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=3000 -+
      |                             |    Connection: Keep-Alive,   |
      |                             |                Upgrade       |
      |   Upgrade: websocket        |                              |
      |<- Keep-Alive: timeout=3000 -+                              |
      |   Connection: Keep-Alive,   |                              |
      |               Upgrade       |                              |



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      |                             |                              |

                  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 indicates have little effect on security.

   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
   [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.

   Each registration MUST include a name that conforms to the HTTP
   'token' grammar and a reference to a specification.  Registrations
   are subject to IETF review [RFC5226].

   The registry includes the following initial values:



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   timeout  See Section 2.1 of this document.

   max  See Section 2.2 of this document.


8.  Acknowledgments

   Jamie Lokier provided valuable contributions of experience, insight
   and text suggestions to this document.  Roy Fielding provided
   information on the poorly documented Keep-Alive header.


9.  Change Log

   Since draft-thomson-hybi-http-timeout:

   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., Gettys, J., Mogul, J., Nielsen, H.,
              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., and
              J. Reschke, "HTTP/1.1, part 1: URIs, Connections, and
              Message Parsing", draft-ietf-httpbis-p1-messaging-18 (work
              in progress), January 2012.

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



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              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
   Skype
   3210 Porter Drive
   Palo Alto, CA  94304
   US

   Phone: +1 650-353-1925
   Email: martin.thomson@gmail.com


   Salvatore Loreto
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: salvatore.loreto@ericsson.com


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

   Email: gregw@intalio.com




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