Internet DRAFT - draft-thomson-hybi-http-timeout
draft-thomson-hybi-http-timeout
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
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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
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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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