Hello,
I am having trouble with content negotiation due to some Accept
headers not clearly specifying an order amongst all desired media
types. For example, Safari provides:
> application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Right now, if a Rails resource can be represented both in html and
application/xml, rails will return an application/xml representation.
Asking about it in the rest-discuss mailing list, the http specs do
not provide any guide on which media-type to pick if multiple ones
have the same q value. In Safari's example, there are three possible
media types that can be picked.
Other language and frameworks have decided to use a first-q value,
second-alphabetical sorting of the list and find the first one that it
is capable of providing. This solves the problem for typical
representations because json and xml comes after html.
I am attaching my original question on the rest-discuss list and
mike's answer which mentions the first framework (his link shows other
- python and erlang - frameworks that chose the same path).
The rails code that affects it is within the mime_responds.rb:
if ActionController::Base.use_accept_header
@mime_type_priority = Array(Mime::Type.lookup_by_extension
(@request.parameters[:format]) || @request.accepts)
else
@mime_type_priority = [[email protected]]
end
The issue with Rails by default is that the first priority for Safari
in the list is priority = 'application/xml' and @responses do not
include it (Rails registered xml only, not application/xml):
if @responses[priority]
@responses[priority].call
return # mime type match found, be happy and return
end
If we register a application/xml, then Safari starts getting a xml
representation, where most would give back a html representation back.
Any suggestions?
note: the sorting is according to the name after the /
Regards
Guilherme Silveira
Caelum | Ensino e Inovação
http://www.caelum.com.br/
---------- Forwarded message ----------
From: mike amundsen <[email protected]>
Date: 2009/12/18
Subject: Re: [rest-discuss] content type negotiation: multiple entries
with same quality value
To: Guilherme Silveira <[email protected]>
Cc: rest-discuss <[email protected]>
Check the the mimeparse project [1]. The last thread there talks about
just this case, handling clients where more than one media-type has
the same q-value [2].
The most recent build orders the acceptable items in q-value, alpha
order and takes the first.
FWIW, I have a mod that also lets the server decide based on a
resource preference (the default for the resource, if one is given). I
also have a mod (in a mess, right now) that handles some "broken"
agents. For example, MS-Excel sends an accept header that prefers HTML
over CSV and I usually ignore that and send CSV anyway.
mca
http://amundsen.com/blog/
[1] http://code.google.com/p/mimeparse/
[2]
http://groups.google.com/group/mimeparse-dev/browse_thread/thread/2ec7e38517fad9be
On Fri, Dec 18, 2009 at 08:10, Guilherme Silveira
<[email protected]> wrote:
> Hello guys,
>
> Safari sends the following accept header, due to webkit's code [1]:
> application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
>
> I could not find in section 12 or the Accept header definition in http
> 1.1 what to do if there is more than one content-type with the same
> q-value. In the above example, it seems like the server is free to
> decide whether to send application/xml, application/xhtml+xml or
> text/html.
>
> Any opinions on that? Should it be followed left to right
> (application/xml first)? Should the server decide?
>
> Regards
>
> [1]
> http://www.newmediacampaigns.com/page/webkit-team-admits-accept-header-error
>
> Guilherme Silveira
> Caelum | Ensino e Inovação
> http://www.caelum.com.br/
>
>
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