Server(config, callback).start() causes node process to hang

[joshuafodera]

Expected behaviour

When a karma server has finished running, it should clean up so that node can exit, e.g.:

new Server(config, callback).start()

Actual behaviour

The node process hangs, and doesn't exit for upwards of a few minutes.

Environment Details

• Latest Karma version (1.7.1/master branch):
• Uses the repo karma.conf.js file: test/client/karma.conf.js with ChromeHeadless as the browser

Steps to reproduce the behaviour

Note: This isn't 100% repo (as sometimes writeBuffer is empty when karma server calls .disconnect on the socket, see below for more details).

1. Create a karma test runner file, e.g.:

var Server = require('./lib/server')

new Server({
    configFile: "...karma-master/test/client/karma.conf.js",
    reporters: ['dots'],
    singleRun: true
}, (exitCode) => {
    console.log(`Exited with code: ${exitCode}`)
}).start()

2. run from commandline: node runkarma.js
3. re-run if repo doesn't hit

Cause

From debugging under node --inspect I see an engine.io socket stays alive preventing node from exiting.
Furthermore I see its caused by the writeBuffer containing messages preventing closeTransport from being called.
file: engine.io\lib\socket.js

Socket.prototype.close = function (discard) {
  if ('open' !== this.readyState) return;

  this.readyState = 'closing';

  if (this.writeBuffer.length) {
    this.once('drain', this.closeTransport.bind(this, discard));
    return;
  }

  this.closeTransport(discard);
};

Even more specifically its because the socket needs to cleanup the pingTimeout, which is done inside onClose which is called by closeTransport.

Note

Although the default behavior is to have the callback call process.exit, it doesn't work in our environment because:

1. We use karma inside a gulp task, which then runs subsequent tasks, so we don't want to exit straight away
2. We use "gulp watch" to run build/test tasks and this causes the subsequent watch tasks to stall
3. I see in the main repo they use grunt to spawn a child process, however we use JavaScript to configure the karma config, so that won't be a clean solution, and

[johnjbarton]

Can you create a (failing) test in this repo as a PR to illustrate the problem?

[joshuafodera]

I can attempt to make one, its a little tricky because the bug is in karma not releasing the node instance, so the test would have to verify that the node instance exited (I'm not familiar with writing a test like that).

[filipesilva]

Heya, I was faced with a similar problem today. As far as I can tell, it's because browser disconnection is setup on single run mode:
https://github.com/karma-runner/karma/blob/master/lib/server.js#L380-L383

But not on watch mode. So on watch mode even if you do something like

const karmaServer = new karma.Server({singleRun: false, configFile: '...'});
karmaServer.start();
karmaServer.emit('exit', () => { });

Karma would never really exit since the browsers are not disconnected.

I tried my hand at a PR for this in #2946.

[filipesilva]

Actually, now that I read the original issue again, I'm not too sure my analysis and fix suit. The original issue is for singleRun mode only, whereas my problem is on watch mode only.