How to intercept and rewrite damaged JSON calls with Middleware

Question

I'm trying to find the best place to do this. My middleware looks like this :

class Fixer
  def initialize app
    @app = app
  end

  def call env
   if env["HTTP_ORIGIN"] == "https://where_i_expect_it_to_come_from.com/"
     env['rack.input'] = StringIO.new('{"yo":"momma"}') # <--  But this info is not actually written before the call is passed!
   end

   env['rack.input'].rewind
   status, headers, response = @app.call env
   return [status, headers, response]

  end
end

Rails.application.config.middleware.insert_before ActionDispatch::ParamsParser, Fixer

It seems that even when I rewrite the call here, the info is not actually rewritten properly. Any ideas how I can have my content written before its bubbled up?

score 1 · Accepted Answer · edited May 23 '17 at 12:24

1

i think this problem is the same as here: https://stackoverflow.com/questions/22712663/getting-a-routing-error-when-my-routes-are-clearly-marked and here I have a third party service that I believe is sending me malformed JSON

from what i understand you want to fix some incoming request-data.

as a simplified example:

curl -X PUT -d "user[name]=something" http://localhost:3000/users/123

i change something to phoet in the fixer

class Fixer
  def initialize(app)
    @app = app
  end

  def call(env)
    env['rack.input'] = StringIO.new("user[name]=phoet")
    @app.call(env)
  end
end

and add it to application.rb

config.middleware.insert_before "ActionDispatch::ParamsParser", "Fixer"

when i request my app now, i see the logs

[localhost] [fdff4eb0-8387-41] Started PUT "/users/123" for 127.0.0.1 at 2014-03-30 13:16:02 -0400
[localhost] [fdff4eb0-8387-41] Processing by UsersController#update as */*
[localhost] [fdff4eb0-8387-41]   Parameters: {"user"=>{"name"=>"phoet"}, "id"=>"123"}

edited May 23 '17 at 12:24

Community

1
1

answered Mar 30 '14 at 17:18

phoet

18,688
4
46
74

Fair enough. This wraps up this part which was essentially answered in my other question. – Trip Mar 30 '14 at 22:24
@Trip i might misunderstand your questions. what OTHER problem do you have? – phoet Mar 30 '14 at 23:12
Whatever URL I rewrite to within my Rack engine, Rails can not find that route unless I rewrite the route to `/`, which redirects to `/quizzes` . http://stackoverflow.com/questions/22712663/getting-a-routing-error-when-my-routes-are-clearly-marked – Trip Mar 31 '14 at 06:58
why do you need to rewrite anything? – phoet Apr 04 '14 at 01:55
Thanks for this response. I'm coming back to this a year later, and finally understand this. – Trip Apr 06 '16 at 12:11

How to intercept and rewrite damaged JSON calls with Middleware

1 Answers1