Better waiting for chrome instance to launch

[andrewvy]

Instead of polling blindly right when we launch the chrome process with erl-exec, a hacky-way is to wait for stdout before polling.

[andrewvy]

Looks like there is already discussion of "pre-opening a socket" before exec a chrome instance, and then passing it in as an option at startup: https://bugs.chromium.org/p/chromium/issues/detail?id=624837

Though, I'm not sure if erlexec is able to handle this.

Additional docs: https://unix.stackexchange.com/questions/248408/file-descriptors-across-exec

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Actually, there's a hackier workaround if ^ doesn't work. (Comment #4)

[andrewvy]

Some options:

• Wait for stdout message that has a format of DevTools listening on 127.0.0.1:9222, then poll. (This is what puppeteer does, not sure why it's a separate implementation from chrome-launcher)

• Wait for DevToolsActivePort file to get created in --user-data-dir, then poll.

• Figure out how to pass file descriptors // pre-open socket and pass it into chrome

[bcardarella]

Wait for stdout message that has a format of

I don't think this is a viable option. Headless outputs everything to stderr. I logged a bug about this last week and it was marked as wontfix

https://bugs.chromium.org/p/chromium/issues/detail?id=773572&can=1&q=stderr&colspec=ID%20Pri%20M%20Stars%20ReleaseBlock%20Component%20Status%20Owner%20Summary%20OS%20Modified