I wasn't able to repro this locally. Could you provide more details please?
- How do you setup port forwarding?
- Do you run desktop chrome (or any other) with --remote-debugging-port?
- Do you enter the url to a desktop or mobile chrome?
- What is the exact version of desktop Chrome and mobile Chrome?

I'm not the OP but I'm able to reproduce this.

- How do you setup port forwarding?

    adb forward tcp:9222 localabstract:chrome_devtools_remote

- Do you run desktop chrome (or any other) with --remote-debugging-port?

No, in fact there's no desktop Chrome instance running.

- Do you enter the url to a desktop or mobile chrome?

No, I simply run:

    $ curl http://localhost:9222/json/protocol
    curl: (52) Empty reply from server

- What is the exact version of desktop Chrome and mobile Chrome?

    Mobile: 66.0.3359.126
    Desktop: 66.0.3359.139 (but not used)

---

In short this is enough to reproduce this issue:

1. attach the phone via the USB cable to the PC (this assuming that the USB debugging is enabled);

2. unlock the phone and open Chrome;

3. in a terminal run: adb forward tcp:9222 localabstract:chrome_devtools_remote

4. in a terminal run: curl http://localhost:9222/json/protocol

On the phone appears the message: "Unfortunately, Chrome has stopped."

Thanks for following up! I'll try to repro locally.

Note that "this should fetch protocol" won't happen - we do not bundle protocol on the mobile device. I can fix the crash though :)

Do you really need to fetch protocol from a mobile device? Perhaps, working around through browser version and git commit hash is fine?

> Note that "this should fetch protocol" won't happen - we do not bundle protocol on the mobile device.

Oh, this is new to me.

> Do you really need to fetch protocol from a mobile device?

Well the rationale is the same as being able to fetch the protocol from a desktop Chrome, that is to make sure that the client (e.g., chrome-remote-interface) knows what features are available in the instrumented Chrome. There's really no differences from this point of view IMO.

> Perhaps, working around through browser version and git commit hash is fine?

What is an *easy* way for users to manually fetch the proper protocol given the version and/or hash? chrome-remote-interface comes with a bundled version which is fetched from time to time from the ChromeDevTools/devtools-protocol repo, but there's no guarantee that it will work fine with the Chrome version at hand.