Rack::BodyParser

Rack middleware for parsing incoming request body per content type.

Inspiration

Rack::BodyParser is heavily inspired by Rack::Parser, but behaves a bit different. See Key Features.

Key Features; Differences to Rack::Parser

1. Rack::BodyParser only parses the request body.

2. Rack::BodyParser does not touch or replace the original params or request.params, and does not mix params and body payload. Instead the parsed result is stored in a separate key parsed_body in Rack's env.

3. (optional) patching of Rack::Request with support for custom getter method Parsed result available as request.parsed_body with support for custom request.#{your_key_here} per parser. Enable with :patch_request => true.

4. (optional) access to headers/env. If your parser respond_to? :env=, this setter method will be invoked with Rack's env just before running call on your parser.

Batteries not included

Rack::BodyParser does not contain any parsers out of the box.

Installation

Available through RubyGems:

gem install rack-bodyparser

Usage

Define your :parsers per media-type, which is the content-type without media type parameters; e.g., when content-type is text/plain;charset=utf-8, the media-type is text/plain.

Parsers configuration accepts a String or Regexp as media-type key, and anything that respond_to? 'call' as parser.

Sinatra example:

# app.rb

use Rack::BodyParser, :parsers => { 
  'application/json' => proc { |data| JSON.parse data },
  'application/xml'  => proc { |data| XML.parse data },
  /msgpack/          => proc { |data| Msgpack.parse data }
}

post '/' do
  puts env['parsed_body']
end

Error Handling

Rack::BodyParser has one default error handler that can be overridden by setting the 'default' handler. As with parsers, you can use a String or Regexp as media-type key and anything that respond_to? 'call' as the error handler. The error handler must accept the two parameters Error and type (the media type).

use Rack::Parser, :handlers => {
  'default' => proc { |e, type| 
    [400, {}, ['[Rack::BodyParser] Failed to parse %s: %s' % [type, e.to_s]]] 
  },
  'application/xml' => proc { [400, {}, 'Error: XML unsupported'] }
}

Note: the error handler rescues exceptions that descend from StandardError. See http://www.mikeperham.com/2012/03/03/the-perils-of-rescue-exception/

Logging

Rack::BodyParser will try to warn if a logger is present.

Patch Rack::Request

Setting up Rack::BodyParser with :patch_request => true will add a parsed_body getter method to Rack::Request. Parsers can also provide a :rack_request_key to define a custom key per parser:

# gem 'jsonapi_parser'
require 'json/api' # JSONAPI document parser/validator
module Rack::BodyParser::JSONAPI
  module Parser
    # This defines the getter key for Rack::Request
    def self.rack_request_key; :document; end

    def self.call(body)
      JSON::API.parse(JSON.parse(body))
    end
  end

  module Error
    def self.call(e, type)
      payload = {
        errors: {
          title: 'Failed to parse body as JSONAPI document',
          detail: e.message
        }
      }.to_json
      [422, {}, [payload]]
    end
  end
end

use Rack::BodyParser, :patch_request => true,
  :parsers  => { 
    'application/vnd.api+json' => Rack::BodyParser::JSONAPI::Parser
  },
  :handlers => {
    'application/vnd.api+json' => Rack::BodyParser::JSONAPI::Error
  }

post '/' do
  # These all output the same
  puts env['parsed_body']
  puts request.parsed_body
  puts request.document
end

Request headers/environment

Need headers or other data from Rack's env in your parser? Set up your parser with a setter method, respond_to? :env=, and it will be invoked just before running the main call method.

module ThisParserNeedsHeaders
  def self.env=(env)
    @env = env
  end

  def self.call(body)
    # @env available here for your parsing pleasure.
  end
end

use Rack::BodyParser, :parsers => { 
  'plain/text' => ThisParserNeedsHeaders 
}

Copyright

Copyright © 2016, 2017 Aaron Heesakkers.

See MIT-LICENSE for details.