MediaTypes::Deserialization

Add media types supported deserialization using your favourite deserializer, and (when supported and provided) media type validation.

Installation

Add this line to your application's Gemfile:

gem 'media_types-deserialization'

And then execute:

$ bundle

Or install it yourself as:

$ gem install media_types-deserialization

Usage

All logic lives in the MediaTypes::Deserialization and the main method you'll use is media_type_params. This works very similarly as params in Rack (and therefore Rails) applications, but only gives back what the implicit or explicit deserializer gives back.

require 'media_types/deserialization'

class BaseController
  include MediaTypes::Deserialization

  rescue_from ContentFormatError, with: :bad_request # 400
  rescue_from ContentTypeNotRecognised, with: :unsupported_media_type # 415
  rescue_from ContentDoesNotMatchContentType, with: :unprocessable_entity # 422 
end

Content Type lookup (symbol)

If you don't provide the lookup_content_type_symbol configuration, it requires 'action_dispatch/http/mime_type' to be present in order to look-up the content type symbol. This is true for Rails applications by default.

MediaTypes::Deserialization.configure do
  self.lookup_content_type_symbol = lambda do |content_type|
    # For example use a lookup map
    KNOWN_CONTENT_TYPES_TO_SYMBOL[content_type]

    # Or alternatively use matching
    content_type.include?('json') ? :json : nil 
  end
end

See below if you're using the media_types gem.

Deserializer lookup

If you don't provide the lookup_deserializer_by_symbol configuration, it currently can only deserialize json and will only do so if the symbol is :json, requiring oj. If you don't want this behaviour, define it.

MediaTypes::Deserialization.configure do
  self.lookup_deserializer_by_symbol = lambda do |symbol|
    case symbol
      when :json
        return CustomJsonDeserializer
      when :xml
      when :html
      when :xhtml
        return CustomXmlDeserializer
    else
      nil
    end
  end
end

Media Type lookup and validation

If you want media type validation, for example via the media_types gem, provide the lookup_media_type_by_symbol option and return the media types. The easiest way to accomplish this is tracking your registerables when you register the media types, and creating a Lookup Map like so:

# In some initializer that defines the media types,
#   given a module MyDomain::MediaTypes which holds many media types

require 'my_domain/media_types'
require 'media_types/integrations/actionpack'

registerables = []
MyDomain::MediaTypes.module_exec do
  registerables.concat self::Author.register
  registerables.concat self::Book.register
  registerables.concat self::Configuration.register
  registerables.concat self::Errors.register 
  registerables.concat self::Signature.register

  # Create lookup table by string (content-type) => media type
  lookup = registerables.flatten.each_with_object({}) do |registerable, hash|
    [registerable.media_type, *registerable.aliases].each do |type|
      hash[String(type)] = registerable
    end
  end.freeze

  # Create lookup table by symbol => media_type
  lookup_by_symbol = registerables.flatten.each_with_object({}) do |registerable, hash|
    hash[String(registerable.symbol).to_sym] = registerable
  end.freeze

  const_set(:LOOKUP, lookup)
  const_set(:LOOKUP_BY_SYMBOL, lookup_by_symbol)
end 

At this point you can re-use those lookup tables for both the media type lookup and the symbol lookup:

MediaTypes::Deserialization.configure do
  self.lookup_content_type_symbol = lambda do |content_type|
    registerable = MyDomain::MediaTypes.const_get(:Lookup).fetch(content_type) { nil }
    registerable&.symbol
  end

  self.lookup_media_type_by_symbol = lambda do |symbol|
    registerable = MyDomain::MediaTypes.const_get(:LOOKUP_BY_SYMBOL).fetch(symbol) { nil }
    registerable&.media_type
  end
end

Related

• MediaTypes: :gem: Library to create media type definitions, schemes and validations
• MediaTypes::Serialization: :cyclone: Add media types supported serialization using your favourite serializer
• MediaTypes::Validation: :heavy_exclamation_mark: Response validations according to a media-type

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at XPBytes/media_types-deserialization.