Twirp::Service.error_response(twerr) method

[marioizquierdo]

Allows to easily make valid error responses from outside Twirp:

twerr = Twirp::Error.internal("Oops")
[status, headers, body] = Twirp::Service.error_response(twerr)

For example, from Rack middleware:

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

  def call(env)      
    // do some stuff and decide to return an early Twirp error
    if not_cool(env)
      twerr = Twirp::Error.invalid_argument("not cool", foo: "bar-meta")
      return Twirp::Service.error_response(twerr)
    end

    @app.call(env)   
  end                
end