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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
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carefully, as they describe your rights and restrictions with respect
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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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