Sending response before all request data was received

[janko]

In tus-ruby-server I'm handling large file uploads. When the user makes a PATCH request with a chunk of the file, the app first validates request headers, and if they're invalid it returns, it returns an error response without even reading the request body.

I'm using goliath-rack_proxy as a glue between Goliath and the tus-ruby-server Rack app, and I'm trying to figure out how to return the response early with Goliath. The reason I want that is because I would like to avoid happily accepting multiple gigabytes of request body from a client, only to return an error response because the request headers were invalid. I would like to utilize Goliath's ability to act as soon as request headers are received.

The problem is that .succeed is called on the Goliath::Request only after all request body has been receved, and all of the env[ASYNC_*] procs use callback { }, which means they will send the response only after all request data has been received (e.g. I tried using env[ASYNC_CALLBACK]). I wrote the following proof-of-concept, which uses hacks to access the Goliath::Request object (already discussed in #341) and use Goliath::Connection#send_data directly:

require "goliath"

class App < Goliath::API
  def on_headers(env, headers)
    request    = env[ASYNC_CALLBACK].receiver
    connection = request.conn
    response   = request.response

    response.status = 200
    response.headers = { "Foo" => "Bar" }
    response.body = "This is a response"

    response.each { |data| connection.send_data(data) }
    connection.terminate_request(false)
  end

  def response(env)
  end
end

I'm pretty sure that returning a response early is valid HTTP interaction, because curl-ing this app returns the response without any errors.

Are you open to support this in Goliath? If yes, I could come up with a PR.

[igrigorik]

I'm pretty sure that returning a response early is valid HTTP interaction...

Yes, I think so. What would you propose as an API to address this? The main complication I can anticipate here is not breaking all the other Goliath clients.