Jay, trying to remember...

Lost sleep over JSON and Rack::PostBodyContentTypeParser

I’ve been fighting this issue the last couple nights. I wrote earlier about how Rack::PostBodyContentTypeParser can automagically turn a posted JSON object into a Rack / Sinatra params hash. So, I wrote some tests to make sure this was the case and moved on. Well, it turns out in real life things weren’t working and I couldn’t figure out why. Everything looked cool, but the hash wasn’t getting set when I did an AJAX call in the browser - everything was empty. I looked at everything, from the server, to the JS library, to the browser, to setting different content types in prototype.js etc… UGH!

The short of it is that Rack::PostBodyContentTypeParser requires exactly application/json in order to automagically turn the posted JSON object into Rack params and prototype.js (and jquery.js were adding an encoding type of charset=UTF-8 so the entire header entry was coming across as this CONTENT_TYPE: application/json; charset=UTF-8. So, as a fix, I’m just including the Rack::PostBodyContentTypeParser in the Sinatra application with one small change. Here’s the code:

module Rack
 
  # A Rack middleware for parsing POST/PUT body data when Content-Type is
  # not one of the standard supported types, like application/json.
  #
  # TODO: Find a better name.
  #
  class PostBodyContentTypeParser
 
    # Constants
    #
    CONTENT_TYPE = 'CONTENT_TYPE'.freeze
    POST_BODY = 'rack.input'.freeze
    FORM_INPUT = 'rack.request.form_input'.freeze
    FORM_HASH = 'rack.request.form_hash'.freeze
 
    # Supported Content-Types
    #

    ################## turned into regex so it matches type with encoding data...
    #APPLICATION_JSON = 'application/json'.freeze
    APPLICATION_JSON = /^application\/json/.freeze
 
    def initialize(app)
      @app = app
    end
 
    def call(env)
      case env[CONTENT_TYPE]
      when APPLICATION_JSON
env.update(FORM_HASH => JSON.parse(env[POST_BODY].read), FORM_INPUT => env[POST_BODY])
      end
      @app.call(env)
    end
 
  end
end

I tested that this worked by writing the following:

def test_post_as_json_converts_to_params
  # sanity check that post with normal params works...
  post '/test_params_as_json', :param1=>"param one"
  assert_equal last_response.body,"params[:param1]=param one"
  post '/test_params_as_json', {:param1=>"param one"}.to_json, "CONTENT_TYPE"=>"application/json"
  assert_equal last_response.body,"params[:param1]=param one"
  # this is the problem, adding a charset to the content type seems to breaks rack-contrib/post_body_content_type_parser.rb
  post '/test_params_as_json', {:param1=>"param one"}.to_json, "CONTENT_TYPE"=>"application/json; charset=UTF-8"
  assert_equal last_response.body,"params[:param1]=param one"    
end


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