HTTP::Accept

Provides a robust set of parsers for dealing with HTTP Accept, Accept-Language, Accept-Encoding, Accept-Charset headers.

I've been developing some tools for building RESTful endpoints and part of that involved versioning. After reviewing the options, I settled on using the Accept: application/json;version=1 method as outlined here.

The version=1 part of the media-type is a parameter as defined by RFC7231 Section 3.1.1.1. After reviewing several existing different options for parsing the Accept: header, I noticed a disturbing trend: header.split(','). Because parameters may contain quoted strings which contain commas, this is clearly not an appropriate way to parse the header.

I am concerned about correctness, security and performance. As such, I implemented this gem to provide a simple high level interface for both parsing and correctly interpreting these headers.

Add this line to your application's Gemfile:

gem 'http-accept'

And then execute:

$ bundle

Or install it yourself as:

$ gem install http-accept

You can then require it in your code like so:

require 'http/accept'

Here are some examples of how to parse various headers.

You can parse the incoming Accept: header:

media_types = HTTP::Accept::MediaTypes.parse("text/html;q=0.5, application/json; version=1")

expect(media_types[0].mime_type).to be == "application/json"
expect(media_types[0].parameters).to be == {'version' => '1'}
expect(media_types[1].mime_type).to be == "text/html"
expect(media_types[1].parameters).to be == {'q' => '0.5'}

Normally, you'd want to match the media types against some set of available mime types:

module ToJSON
  def content_type
    HTTP::Accept::ContentType.new("application", "json", charset: 'utf-8')
  end

  # Used for inserting into map.
  def split(*args)
    content_type.split(*args)
  end

  def convert(object, options)
    object.to_json
  end
end

module ToXML
  # Are you kidding?
end

map = HTTP::Accept::MediaTypes::Map.new
map << ToJSON
map << ToXML

object, media_range = map.for(media_types)
content = object.convert(model, media_range.parameters)
response = [200, {'Content-Type' => object.content_type}, [content]]

You can parse the incoming Accept-Language: header:

languages = HTTP::Accept::Languages.parse("da, en-gb;q=0.8, en;q=0.7")

expect(languages[0].locale).to be == "da"
expect(languages[1].locale).to be == "en-gb"
expect(languages[2].locale).to be == "en"

Normally, you'd want to match the languages against some set of available localizations:

available_localizations = HTTP::Accept::Languages::Locales.new(["en-nz", "en-us"])

# Given the languages that the user wants, and the localizations available, compute the set of desired localizations.
desired_localizations = available_localizations & languages

The desired_localizations in the example above is a subset of available_localizations.

HTTP::Accept::Languages::Locales provides an efficient data-structure for matching the Accept-Languages header to set of available localizations according to https://tools.ietf.org/html/rfc7231#section-5.3.5 and https://tools.ietf.org/html/rfc4647#section-2.3

We welcome contributions to this project.

1. Fork it.
2. Create your feature branch (git checkout -b my-new-feature).
3. Commit your changes (git commit -am 'Add some feature').
4. Push to the branch (git push origin my-new-feature).
5. Create new Pull Request.

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