documentation of koa support

[kmathmann]

• I've searched for any related issues and avoided creating a duplicate issue.

Description

The usage of ws with express is documented in the readme but the usage of ws with koa is not documented.

The only information that i get if i search for "ws koa" or "ws koa2" are third party npm packages and the old issue #868.

But instead of using third party npm packages it's possible to use ws with koa2 like it is possible with express.

const app = new Koa();
const server = http.createServer(app.callback());

Can we add the documentation of koa2 support?

Attachments:

const Koa = require('koa');
const http = require('http');
const url = require('url');
const WebSocket = require('ws');

const app = new Koa();

app.use(async ctx => {
  ctx.body = 'Hello World';
});

const server = http.createServer(app.callback());
const wss = new WebSocket.Server({ server });

wss.on('connection', function connection(ws, req) {
  const location = url.parse(req.url, true);
  // You might use location.query.access_token to authenticate or share sessions
  // or req.headers.cookie (see http://stackoverflow.com/a/16395220/151312)

  ws.on('message', function incoming(message) {
    console.log('received: %s', message);
  });

  ws.send('something');
});

server.listen(8080, function listening() {
  console.log('Listening on %d', server.address().port);
});

[lpinca]

The only difference is app.callback(), isn't it better to only document that instead of copying the whole example?

[lpinca]

Also if we do it for koa we open the doors to any other framework out there. I think the example should only show how to use an externally created server without focusing on any particular framework.

[kmathmann]

Yes your argumentation makes sense. Adding examples for each framework isn't a solution.
Instead we should change the ExpressJS example to an general example how to use ws next to frameworks such as express, koa and others.

[lpinca]

Feel free to open a PR.