Rack::Accept is a suite of tools for Ruby/Rack applications that eases the complexity of building and interpreting the Accept* family of HTTP request headers.

Some features of the library are:

• Strict adherence to RFC 2616, specifically section 14
• Full support for the Accept, Accept-Charset, Accept-Encoding, and Accept-Language HTTP request headers
• May be used as Rack middleware or standalone
• A comprehensive test suite that covers many edge cases

Using RubyGems:

$ sudo gem install rack-accept

From a local copy:

$ git clone git://github.com/mjijackson/rack-accept.git
$ cd rack-accept
$ rake package && sudo rake install

Rack::Accept implements the Rack middleware interface and may be used with any Rack-based application. Simply insert the Rack::Accept module in your Rack middleware pipeline and access the Rack::Accept::Request object in the rack-accept.request environment key, as in the following example.

require 'rack/accept'

use Rack::Accept

app = lambda do |env|
  accept = env['rack-accept.request']
  response = Rack::Response.new

  if accept.media_type?('text/html')
    response['Content-Type'] = 'text/html'
    response.write "<p>Hello. You accept text/html!</p>"
  else
    response['Content-Type'] = 'text/plain'
    response.write "Apparently you don't accept text/html. Too bad."
  end

  response.finish
end

run app

Rack::Accept can also construct automatic 406 responses if you set up the types of media, character sets, encoding, or languages your server is able to serve ahead of time. If you pass a configuration block to your use statement it will yield the Rack::Accept::Context object that is used for that invocation.

require 'rack/accept'

use(Rack::Accept) do |context|
  # We only ever serve content in English or Japanese from this site, so if
  # the user doesn't accept either of these we will respond with a 406.
  context.languages = %w< en jp >
end

app = ...

run app

Note: You should think carefully before using Rack::Accept in this way. Many user agents are careless about the types of Accept headers they send, and depend on apps not being too picky. Instead of automatically sending a 406, you should probably only send one when absolutely necessary.

Additionally, Rack::Accept may be used outside of a Rack context to provide any Ruby app the ability to construct and interpret Accept headers.

require 'rack/accept'

mtype = Rack::Accept::MediaType.new
mtype.qvalues = { 'text/html' => 1, 'text/*' => 0.8, '*/*' => 0.5 }
mtype.to_s # => "Accept: text/html, text/*;q=0.8, */*;q=0.5"

cset = Rack::Accept::Charset.new('unicode-1-1, iso-8859-5;q=0.8')
cset.best_of(%w< iso-8859-5 unicode-1-1 >)  # => "unicode-1-1"
cset.accept?('iso-8859-1')                  # => true

The very last line in this example may look like a mistake to someone not familiar with the intricacies of the spec, but it's actually correct. It just puts emphasis on the convenience of using this library so you don't have to worry about these kinds of details.

• Spec: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html
• Code: http://github.com/mjijackson/rack-accept
• Bugs: http://github.com/mjijackson/rack-accept/issues
• Docs: http://mjijackson.github.com/rack-accept

Copyright 2012 Michael Jackson

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

The software is provided "as is", without warranty of any kind, express or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose and noninfringement. In no event shall the authors or copyright holders be liable for any claim, damages or other liability, whether in an action of contract, tort or otherwise, arising from, out of or in connection with the software or the use or other dealings in the software.