HTTP Accept* for Ruby/Rack with accept-extension parameter support
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I'm working on a replacement for this gem called accept_headers.

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

This is a fork of rack-accept. The major addition being accept-extension parameter support.

Some features of the library are:


Add this line to your application's Gemfile:

gem 'rack-accept_headers'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rack-accept_headers

Or install it from a local copy:

$ git clone git://
$ cd rack-accept_headers
$ rake package
$ rake install


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

require 'rack/accept_headers'

use Rack::AcceptHeaders

app = lambda do |env|
  accept = env['rack-accept_headers.request']
  response =

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


run app

Rack::AcceptHeaders 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::AcceptHeaders::Context object that is used for that invocation.

require 'rack/accept_headers'

use(Rack::AcceptHeaders) 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 >

app = ...

run app

Note: You should think carefully before using Rack::AcceptHeaders 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.

Rack::AcceptHeaders supports accept-extension parameter support. Here's an example:

require 'rack/accept_headers'

use Rack::AcceptHeaders

app = lambda do |env|
      "text/html" => :html
      "application/json" => :json,
      "text/xml" => :xml

  accept = env['rack-accept_headers.request']
  response =

  if accept
    media_type = accept.media_type.best_of(SUPPORTED_MEDIA_TYPES.keys)

    # Here, I would return a 415 Unsupported media type, if media_type is nil
    # The unsupported_media_type call is left unimplemented here
    # unsupported_media_type unless media_type

    # To output the media_type symbol
    # puts SUPPORTED_MEDIA_TYPES[media_type]

    # To return a hash of accept-extension params for the given media type
    # puts accept.media_type.params(media_type)

    response['Content-Type'] = media_type
    response.write %Q{{ "message" : "Hello. You accept #{media_type}" }}
    media_type = "*/*"
    response['Content-Type'] = SUPPORTED_MEDIA_TYPES.keys.first
    response.write "Defaulting to #{response['Content-Type']}."


run app

So, given this Accept header:

Accept: application/json;version=1.0;q=0.1
accept = env['rack-accept_headers.request']
params = accept.media_type.params['application/json')

The params hash will end up with this value:

  "application/json" : {
    "q" : 0.1,
    "version" : "1.0"

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

require 'rack/accept_headers'

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

cset ='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.

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