Occasional "No inspectable targets" error when launching chrome with a very short connectionPollInterval

[robbertbrak]

To reproduce, create and run a Node script such as the one below:

const chromeLauncher = require('chrome-launcher');
const CDP = require('chrome-remote-interface');

let opts = {
  connectionPollInterval: 2,
  chromeFlags: ['--headless'],
};

(async() => {
  for (let i = 0; i < 100; i++) {
    let chrome = await chromeLauncher.launch(opts);
    let client = await CDP({port: chrome.port});
    console.log(i, chrome.port);
    client.close();
    chrome.kill();
  }
})().catch(error => { 
  console.log(error); 
  process.exit(1) 
});

After an unpredictable number of loops, the script (usually) crashes with a stacktrace:

Error: No inspectable targets
    at defaultTarget (.../node_modules/chrome-remote-interface/lib/chrome.js:47:23)
    at Chrome._fetchDebuggerURL (.../node_modules/chrome-remote-interface/lib/chrome.js:188:32)
    at process.internalTickCallback (internal/process/next_tick.js:77:7)

It looks like chrome-launcher occasionally reports that the launched Chrome instance is ready and has a debugging port, even though it isn't actually ready to accept a debug session yet.

[patrickhulce]

Thanks very much for filing with a simple repro case!

That's correct chrome-launcher resolves as soon as Chrome has begun listening on the debugging port and not necessarily when a target/the requested launch page is available for inspection.

If you'd be interested in adding this functionality to chrome-launcher, I'd bet some other folks might end up making use of it as well :)

I imagine it just might involve polling http://127.0.0.1:<port>/json/list until it has an entry if you wanted to do it yourself.

[robbertbrak]

@patrickhulce It's great to get such a fast response!

But I'm a little unsure of what you're suggesting. Do you consider the issue I reported to be a bug or normal/expected behavior? In the latter case, would adding a flag (e.g. waitForInspectableTarget) to the launch options be an acceptable solution, or do you have something else in mind?

[patrickhulce]

Do you consider the issue I reported to be a bug or normal/expected behavior?

I consider it to be expected behavior, but I understand your use case is a common one that could be worthwhile to support in the library (waitForInspectableTarget sounds great to me 👍 ).