One document matched: draft-nottingham-http-browser-hints-01.xml
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<rfc ipr="trust200902" docName="draft-nottingham-http-browser-hints-01" category="info">
<front>
<title>HTTP Browser Hints</title>
<author initials="M." surname="Nottingham" fullname="Mark Nottingham">
<organization></organization>
<address>
<email>mnot@mnot.net</email>
<uri>http://www.mnot.net/</uri>
</address>
</author>
<date year="2011"/>
<abstract>
<t>Over time, Web browsers have adapted how they use HTTP based upon
common server configurations and behaviours. While this is necessary
in the common case, it can be detrimental for performance and
interoperability.</t>
<t>This document establishes a mechanism whereby origin servers can make
available hints for browsers about their preferences and
capabilities, without imposing overhead on their interactions or
requiring support for them.</t>
<t>This is intended to allow browsers to safely optimise connections
to servers.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>HTTP <xref target="RFC2616"/> clients -- especially browsers --
typically use hardcoded values or heuristics to determine how many TCP
connections to use to a server, based on common-case server behaviours
and limitations.</t>
<t>Likewise, they often send voluminous request headers (e.g., in
User-Agent and Allow) because they fear that changing those headers'
values will break some sites that depend upon specific values.</t>
<t>These are just two examples of common, conservative behaviour by
browsers that is good for interoperability, but potentially bad
for performance in certain circumstances.</t>
<t>This memo proposes a mechanism whereby a HTTP server can advertise
hints for browsers (and other clients), so that communication with
them can be optimised.</t>
<t>It does so by defining a file format for such Browser Hints <xref
target="format"/>, and defining how clients can discover it for a
given Web site <xref target="discover"/>. Finally, an extensible
vocabulary of hints is defined <xref target="hints"/>.</t>
<t>Feedback for this draft should take place on the
apps-discuss@ietf.org mailing list
<eref target="https://www.ietf.org/mailman/listinfo/apps-discuss"/>.
</t>
</section>
<section title="Requirements">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in <xref
target="RFC2119"/>.</t>
</section>
<section title="A file format for Browser Hints" anchor="format">
<t>Browser hints are indicating using a JSON <xref target="RFC4627"/>
formatted file, containing a single object whose member's names are
browser hints, as defined by the registry <xref
target="registry"/>.</t>
<t>For example;</t>
<figure><artwork>
{
"max-conns": 5,
"small-hdrs": true
}
</artwork></figure>
<t>By their nature, all browser hints are optional; i.e., browsers are
free to ignore them.</t>
</section>
<section title="Discovering Browser Hints for a Web site" anchor="discover">
<t>The hints relevant to a given site can be determined by fetching
the URI path "/.well-known/browser-hints" for that site.</t>
<t>Typically, clients (especially browsers) will not block other
requests to a site while fetching the browser hints (because
they're optional); instead, it will usually be done concurrently
with other requests, or on idle connections for future use.</t>
<t>In this specification, "site" is scoped by the URI scheme and
authority. As such, all of the following are considered to be
different sites, and therefore have different browser hints:</t>
<t><list style="symbols">
<t>http://foo.com/</t>
<t>https://foo.com/</t>
<t>http://foo.com:8000/</t>
<t>http://www.foo.com/</t>
</list></t>
<t>Clients SHOULD follow HTTP 3xx redirects when retrieving
hints.</t>
<t>A successful response is valid for its associated site for as long
as it can be cached in HTTP.</t>
<t>If the response has a 200 status code but no explicit freshness
(e.g., a Cache-Control: max-age or Expires: header), browsers SHOULD
cache the response heuristically for a generous fixed period (e.g., 30
days).</t>
</section>
<section title="Pre-defined Browser Hints" anchor="hints">
<section title="max-conns">
<t>
<list style="symbols">
<t>Browser Hint Name: max-conns</t>
<t>Description: When present, this hint indicates the maximum
number of concurrent persistent connections that the site
would like clients to use.</t>
<t>Value Type: number </t>
<t>Contact: mnot@mnot.net</t>
</list>
</t>
</section>
<section title="pconn-ip">
<t>
<list style="symbols">
<t>Browser Hint Name: pconn-ip</t>
<t>Description: When true, this hint indicates that the site
allows clients to reuse persistent connections keyed by IP
address, rather than by hostname. Note that all sites that are
sharing the connection MUST declare this hint for it to be
used, and if a transport-layer certificate is in use
(e.g., for TLS <xref target="RFC5246"/>), it MUST be valid
for all sites.</t>
<t>Value Type: true | false </t>
<t>Contact: mnot@mnot.net</t>
<t>Specification: [this document]</t>
</list>
</t>
<t>In other words, if both www.example.com and foo.example.org resolve
to the address 192.0.2.5, and indicate this hint, then clients
can send a request to www.example.com and then a request to
foo.example.org on the same TCP connection to that address.</t>
<t>If any of the sites grouped together for the purposes of
pconn-ip declare a max-conns hint, the max-conns value for that
address is considered to be the maximum of the declared
max-conn hints present.</t>
</section>
<section title="max-pipeline-depth">
<t>
<list style="symbols">
<t>Browser Hint Name: max-pipeline-depth</t>
<t>Description: When present, this hint indicates the maximum
number of pipelined requests per connection that the site would
like clients to use.</t>
<t>Value Type: number </t>
<t>Contact: mnot@mnot.net</t>
</list>
</t>
</section>
<section title="small-hdrs">
<t>
<list style="symbols">
<t>Browser Hint Name: small-hdrs</t>
<t>Description: When true, this hint indicates that clients
can omit the Accept and Accept-Charset request headers when
communicating with the site, and that they can use a shortened
version of the User-Agent header.</t>
<t>Value Type: true | false </t>
<t>Contact: mnot@mnot.net</t>
</list>
</t>
</section>
<section title="no-referer">
<t>
<list style="symbols">
<t>Browser Hint Name: no-referer</t>
<t>Description: When true, this hint indicates that clients
can omit the Referer HTTP request header when sending requests
to the site.</t>
<t>Value Type: true | false </t>
<t>Contact: mnot@mnot.net</t>
</list>
</t>
</section>
<section title="send-ref">
<t>
<list style="symbols">
<t>Browser Hint Name: send-ref</t>
<t>Description: When true, this hint indicates that clients
can omit the Referer HTTP request header when sending requests
to the site, if they instead send a Ref HTTP request header
(see <xref target="ref"/>).</t>
<t>Value Type: true | false </t>
<t>Contact: mnot@mnot.net</t>
</list>
</t>
</section>
<section title="chunk-req-bodies">
<t>
<list style="symbols">
<t>Browser Hint Name: chunk-req-bodies</t>
<t>Description: When true, this hint indicates that the server
can successfully process a request with a chunk-encoded body;
i.e., that it should not return a 411 Length Required status.
Note that clients may still require a 411 response status, even
in when this hint is present. When false, the server may or may
not require a Content-Length on requests with bodies.</t>
<t>Value Type: true | false </t>
<t>Contact: mnot@mnot.net</t>
</list>
</t>
</section>
<section title="omit-cookies">
<t>
<list style="symbols">
<t>Browser Hint Name: omit-cookies</t>
<t>Description: This hint contains a list of cookie <xref
target="RFC6265"/> cookie-names which can be omitted in requests
sent to this site.</t>
<t>Value Type: Array of strings</t>
<t>Contact: mnot@mnot.net</t>
</list>
</t>
</section>
</section>
<section title="The Ref HTTP Request Header" anchor="ref">
<t>TBD: relative URI referer header</t>
</section>
<section title="Security Considerations">
<t>TBD</t>
</section>
<section title="IANA Considerations">
<section title="The 'browser-hints' Well-Known URI">
<t>This document defines the "browser-hints" Well-Known URI
<xref target="RFC5785"/>.</t>
<t><list style="symbols">
<t>URI suffix: browser-hints</t>
<t>Change controller: mnot@mnot.net</t>
<t>Specification document(s): [this document]</t>
<t>Related information:</t>
</list></t>
</section>
<section title="The HTTP Browser Hints Registry" anchor="registry">
<t>This document establishes the HTTP Browser Hints Registry.</t>
<t>New hints are registered First Come First Served (see
<xref target="RFC5226"/>), by sending e-mail to <eref
target="mailto:iana@iana.org"/> (or using other mechanisms, as
established by IANA).</t>
<t>Registration requests MUST use the following template:</t>
<t>
<list style="symbols">
<t>Browser Hint Name: [name of hint]</t>
<t>Description: [description of hint]</t>
<t>Value Type: [JSON value type] </t>
<t>Contact: [e-mail address(es)]</t>
<t>Specification: [optional; reference or URI to more info]</t>
</list>
</t>
<t>New hints MUST be optional; they cannot place requirements upon
implementations.</t>
<t>Likewise, new hints MUST be relevant to browser use
cases; other non-browsing hints and metadata would make the hints
response undesirably large. However, note that non-browser clients
MAY use them.</t>
<t>Finally, new hints MUST NOT make communication non-conformant with
HTTP itself; i.e., this is not a mechanism for changing the HTTP
protocol in incompatible ways. For example, if a hint indicates
that browsers can compress request headers using GZIP, intermediaries
that are interposed are likely to fail.</t>
<t>The initial contents of the registry are defined in
<xref target="hints"/>.</t>
</section>
</section>
</middle>
<back>
<references title="Normative References">
&rfc2119; &rfc2616; &rfc4627;
</references>
<references title="Informative References">
&rfc5226; &rfc5246; &rfc5785; &rfc6265;
</references>
<section title="Acknowledgements">
<t>Thanks to
Mike Belshe,
Poul-Henning Kamp,
Anirban Kundu,
Patrick McManus, and
Steve Souders
for their suggestions and feedback.
</t>
<t>The author takes all responsibility for errors and
omissions.</t>
</section>
</back>
</rfc>
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