Internet DRAFT - draft-thomson-http-nice
draft-thomson-http-nice
HTTPBIS M. Thomson
Internet-Draft Mozilla
Intended status: Standards Track November 10, 2014
Expires: May 14, 2015
Marking HTTP Requests as Unimportant
draft-thomson-http-nice-02
Abstract
An HTTP "Nice" header field is defined. "Nice" marks a request as
low priority. Gateways can choose to discard or delay the request,
or provide a response from cache rather than forwarding it to an
origin server. This enables constrained origin servers, such as
those that rely on battery power, to avoid expending limited
resources on serving requests.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 14, 2015.
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the Trust Legal Provisions and are provided without warranty as
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions and Terminology . . . . . . . . . . . . . . . 3
2. The Nice Header Field . . . . . . . . . . . . . . . . . . . . 3
2.1. Policies for Treatment of Nice Requests . . . . . . . . . 4
2.2. Polling with Nice Requests . . . . . . . . . . . . . . . 5
2.3. Store and Forward . . . . . . . . . . . . . . . . . . . . 6
3. Security Considerations . . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
HTTP [RFC2616] servers are beginning to appear as the interface to a
wide array of devices. Management interfaces in many devices have
classically been provided as HTTP servers, but this trend now extends
to HTTP APIs on a range of devices, including constrained devices.
Constrained devices are those with limited processing power, network
connectivity or battery capacity.
The Constrained Application Protocol (CoAP) [RFC7252] in particular
is designed to provide devices with extremely limited capabilities a
way to provide an HTTP-compatible interface to the information and
services they provide. A CoAP-HTTP gateway
[I-D.ietf-core-http-mapping] provides HTTP-capable clients a means of
accessing these devices.
For a device that operates based on a battery, it is often crucial
that the device remain dormant for extended periods. Radio
communication in particular consumes a significant amount of power.
Frequent communication limits the length of time that the device can
operate. It is often the case that communication can be initiated,
but this could require a significant expenditure of stored energy.
Many constrained devices rely on intermediaries such as the CoAP-HTTP
gateway to terminate requests and mediate access. Clients that
access the services provided by such limited devices can be unaware
of the limited nature of the device serving the request, since they
actually interact with the gateway. Even when the client is aware of
these limitatons, it is not always possible for clients to learn
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whether any given request would cause significant expenditure of
resources at the constrained device.
A push server [I-D.thomson-webpush-http2] provides similar
functionality for devices with constrained resources. Providing a
standard way to indicate that a request is not urgent allows a push
server to discriminate between requests that the sender considers
urgent and those that are unimportant.
This document defines an HTTP header field, "Nice" that can be used
by clients to indicate that a request is not urgent or important
enough to cause a constrained server to expend special effort to
serve. An gateway that is aware that the origin server is unable to
handle the request can instead terminate the request. The request is
forwarded as normal to an origin server that is available.
An gateway can generate an error or 203 (Non-Authoritative
Information) response in response to a nice request, avoiding the
need to contact the constrained origin server. Alternatively, the
gateway could delay the request until the origin server becomes
available or serve a response from cache if that is possible.
No specific mechanism is defined for an origin server to inform
gateways of absence or other indisposition.
1.1. Conventions and Terminology
At times, this document falls back on shorthands for establishing
interoperability requirements on implementations: the capitalized
words "MUST", "SHOULD" and "MAY". The meaning of these is described
in [RFC2119].
The terms "intermediary" and "gateway" are defined in [RFC7230].
2. The Nice Header Field
The "Nice" header field indicates that a request is less important
than a request that doesn't bear this header.
The value of the header field is a decimal number between 0 and 3
inclusive. Values greater than zero indicate increasing levels of
unimportance. A lower value indicates greater urgency; for example,
a value of 3 is less urgent or important than a value of 1. A value
of 0 (or an absent "Nice" header field) indicates that the request is
to be forwarded as normal.
Nice = "Nice" ":" ("3" / "2" / "1" / "0")
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Multiple values for the header field MUST NOT be included. If
multiple values are present, a gateway MAY choose to treat the
request in any way it chooses.
For example, the following request indicates that it is not urgent:
GET /m HTTP/1.1
Host: device9710.example.net:11453
Nice: 2
An gateway might reject this request, indicating that the origin
server is not available using a 503 status code.
HTTP/1.1 503 Service Unavailable
Date: Fri, 26 Jul 2013
Content-Type: text/plain;charset=utf8
Content-Length: 63
The server is asleep, don't disturb it unless it's urgent.
A key characteristic of this header field is that intermediaries and
clients that do not understand its semantics treat requests so marked
no different to any other requests. An intermediary that has no
special information about the availability of the origin server will
also forward the request. That means that requests from a client
that does not include this header will always reach the origin
server.
2.1. Policies for Treatment of Nice Requests
An origin server or gateway might use several inputs in determing the
threshold at which a request is forwarded to the origin server. An
origin server might either directly instruct the gateway about the
threshold, or it might be provide specific information that can be
used, in conjunction with knowledge the gateway has of the origin
server, as input to an algorithm for determining the threshold.
Potential inputs include:
o The relative cost of awakening a dormant server. Depending on the
server, this cost may be assessed in different ways, including
monetary, battery or time.
o The last time that the server was in active communication.
Typically, wireless devices have a period of heightened
availability just after sending or receiving data. During this
period activation and communication can be significantly more
efficient.
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o Application preferences or context. For example, a server might
be configured to be more highly responsive to requests during
certain times.
The following describes a potential set of policies regarding
selection and treatment of "Nice" header field value:
nice: 1 = The client regards the request as relatively urgent, but
not critically so. An gateway might use a heuristic with
a moderate risk of false positives in determining whether
the server is available. A gateway might also forward a
request so marked to a dormant device that has a
relatively low activation cost.
nice: 2 = The client regards the request as not urgent. A gateway
might attempt to minimize the probability that it awakens
a server, if it uses a heuristic in determining whether to
forward requests.
nice: 3 = The client regards the request as being of trivial
importance. A gateway might avoid forwarding requests
unless there is strong indication that the origin server
is available and willing to communicate.
Many different policies can be applied to the selection of a value
for the "Nice" header field, as well as to the treatment of requests
so marked. Specific applications might define a means for providing
more specific policies.
2.2. Polling with Nice Requests
Marking a request as nice is quite useful for requests that do not
require immediate action. Clients might wish to have the request
fulfilled, but are willing to wait until the origin server is
present. Such requests might be sent periodically until they
succeed.
In some cases, origin server availability is predictable and known to
the gateway. Some devices have predictable cycles of availability,
which are used for brief bursts of communication. If the next time
that the origin server is available is known, a gateway can include a
"Retry-After" header field in a generated error response.
For example:
HTTP/1.1 503 Service Unavailable
Date: Fri, 26 Jul 2013 03:34:19 GMT
Retry-After: 4
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2.3. Store and Forward
A gateway MAY hold requests for a limited amount of time, to be
forwarded when the origin server becomes available (i.e., a "store
and forward" mode of operation). Including a "Prefer" header field
[RFC7240] with the "wait" tag provides the gateway information about
how long the client is prepared to await a response. This could
allow the gateway to reject the request immediately if the device is
known to be unreachable for the entire duration.
Gateways MAY alternatively accept a request and return an immediate
response, such as a 202 (Accepted) status code. Use of the "respond-
async" token in the "Prefer" header field allows clients to expressly
request this behavior.
3. Security Considerations
Lowering the priority with which a request is handled is unlikely to
cause any special concern with respect to security.
Intermediaries that do not support the "Nice" header field might
erroneously cache a response from an intermediary that handles the
request without forwarding to the origin server. Intermediaries MUST
NOT generate cacheable responses to requests containing an "Nice"
header field. Intermediaries MAY however provide cached responses
originally provided by the origin server.
4. IANA Considerations
The permanent message header field registry (see [RFC3864]) has been
updated with the following registration:
Header field name: Nice
Applicable protocol: http
Status: standard
Author/Change controller: IETF
Specification document: this specification (Section 2)
5. Acknowledgements
The original idea for this header field was devised by Matthew
Kaufman and Bruce Lowekamp, who realized the importance of making the
header a negative rather than positive expression of priority.
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6. References
6.1. 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.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.
[RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Message Syntax and Routing", RFC 7230, June
2014.
6.2. Informative References
[I-D.ietf-core-http-mapping]
Castellani, A., Loreto, S., Rahman, A., Fossati, T., and
E. Dijk, "Guidelines for HTTP-CoAP Mapping
Implementations", draft-ietf-core-http-mapping-03 (work in
progress), February 2014.
[I-D.thomson-webpush-http2]
Thomson, M., "Generic Event Delivery Using HTTP Push",
draft-thomson-webpush-http2-00 (work in progress), May
2014.
[RFC7240] Snell, J., "Prefer Header for HTTP", RFC 7240, June 2014.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, June 2014.
Author's Address
Martin Thomson
Mozilla
331 E Evelyn Street
Mountain View, CA 94041
US
Email: martin.thomson@gmail.com
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