HTTP server for incoming payload

Simple server

So the main idea is to write an eslint bot for GitHub. It’ll be listening on given port any POST request and deal with it. GitHub has webhooks guide, which API provided.

Main workflow looks like this (it’s based on excellent work by Bernardstanislas)

• run node server on given port
• listen incoming events
• get commits given in this event
• run linter on it
• push comments to commit using GitHub API

Today I’ll try to ‘mimic’ events using CURL.

We have our simple server that’s listening on port 8080. I want to listen only for POST request. So only post on ‘/’ should be handled. Otherwise - return 405.

I don’t know how to unit test this yet :) So I’ll use CURL.

Let’s start with 405 always. It should be easier. Probably setStatusCode function should be used here. Let’s try.

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main = do
  server <- createServer respond
  listen server 8080 $ log "Server started"
  where
  respond req res = do
    setStatusCode res 405
    end (responseAsStream res) (return unit)

So far so good. psci run and on second terminal:

$ curl -v :8080
* Rebuilt URL to: :8080/
*   Trying ::1...
* Connected to  (::1) port 8080 (#0)
> GET / HTTP/1.1
> Host: :8080
> User-Agent: curl/7.43.0
> Accept: */*
>
< HTTP/1.1 405 Method Not Allowed
< Date: Thu, 21 Jan 2016 20:08:09 GMT
< Connection: keep-alive
< Content-Length: 0
<
* Connection #0 to host  left intact

As we can see - returns 405!

Using function from module we set status code on stream - line 6. Easy. Following node.js practice - we end a stream (first we need to get a writable stream).

(return unit) has something to do with effects. There’s a blog post I should get familiar with. It’ll take probably whole day. Some future day :)

Just one thing at the end - (return unit) probably means - we do not want to use any effects.

Proper server

We want to handle “POST” method, so we need to modify the code a bit, but it’s rather straightforward - we can just use case

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main = do
  server <- createServer respond
  listen server 8080 (return unit)
  where
  respond req res = do
    let method = requestMethod req
    case method of
      "POST" -> do
         setStatusCode res 200
         void $ pipe (requestAsStream req) (responseAsStream res)
      _     -> do
         setStatusCode res 405
         end (responseAsStream res) (return unit)

Easy as pie. If it’s “POST” - pipe input to output. If not - return 405.

Do some testing:

$ curl localhost:8080 --data '{ "test_key": "test_value"}' | jq
{
  "test_key": "test_value"
}

Input copied to output, as we expected!

Summary

First part of our puzzle is in place. Server is up & running and ready to receive payload from GitHub.

Code is at the step2 tag.