Allow the client to supply multiple ports

[DanTup]

This extends the --port option to accept a comma-separated list of ports so that if a client has a preference for ports they can be tried in-order. We could do this in the client, but it feels a bit clumsy to keep trying to spawn processes repeatedly until it works, so I thought this would be cleaner (though if you think it's weird putting this here, we could do that).

This is working towards supporting DevTools on CrOS without Linux Chrome. It will still rely on the VM service being also being available on an exposed port (I haven't dug into that yet).

Example output below. First we bind something to port 8000:

$ dart bin/devtools.dart --port 8000
Serving DevTools at http://127.0.0.1:8000

If we attempt to bind to it again:

$ dart bin/devtools.dart --port 8000
Unable to bind to port 8000: SocketException: Failed to create server socket (OS Error: Address already in use, errno = 48), address = 127.0.0.1, port = 8000
Unable to bind to any of the supplied ports. Include 0 in the list of ports to accept a randomly assign available port.

Machine output looks like this:

$ dart bin/devtools.dart --port 8000 --machine
{"method":"server.log","params":{"level":"info","message":"Unable to bind to port 8000: SocketException: Failed to create server socket (OS Error: Address already in use, errno = 48), address = 127.0.0.1, port = 8000"}}
{"method":"server.error","params":{"message":"Unable to bind to any of the supplied ports.","fatal":true}}

If we provide additional ports, it will try them in-order:

$ dart bin/devtools.dart --port 8000,8001
Unable to bind to port 8000: SocketException: Failed to create server socket (OS Error: Address already in use, errno = 48), address = 127.0.0.1, port = 8000
Serving DevTools at http://127.0.0.1:8001

And machine output:

$ dart bin/devtools.dart --port 8000,8001 --machine
{"method":"server.log","params":{"level":"info","message":"Unable to bind to port 8000: SocketException: Failed to create server socket (OS Error: Address already in use, errno = 48), address = 127.0.0.1, port = 8000"}}
{"method":"server.started","params":{"host":"127.0.0.1","port":8001,"pid":20416}}

Finally, if you want - you can include 0 in the list to accept any port (as before):

$ dart bin/devtools.dart --port 8000,0 --machine
{"method":"server.log","params":{"level":"info","message":"Unable to bind to port 8000: SocketException: Failed to create server socket (OS Error: Address already in use, errno = 48), address = 127.0.0.1, port = 8000"}}
{"method":"server.started","params":{"host":"127.0.0.1","port":52956,"pid":20553}}

I did consider including a flag that tries the CrOS-exposed ports to avoid clients having to deal with it, but it seemed a little specific. LMK if you'd prefer that though. We could even change the default from 9100 to 8000, 8008, 808, 8085, 8888, 9005, 3000, 4200, 5000, 9100 but that also looks kinda specific. Note: as far as I can tell, there's no easy way to detect when running in a CrOS Linux container besides hostname == 'penguin' which may not be reliable.

Also something I haven't done, but we could - is make the default normally 9100,0. This would avoid failures if the port was already bound while still having a preference for 9100 to avoid the randomness if you want to bookmark/whatever.

[jacob314]

remove the comment about the ports allowed on chromeos?

[jacob314]

only show this message if binding to all ports fail?

[jacob314]

never mind. this is fine.

[DanTup]

Holding off on merging this for now - as well as conflicting with @kenzieschmoll's other PR, I think there may be other blockers to running on CrOS in this way (we'd need the VM and Flutter to have some equivalent of this).

[DanTup]

Haven't forgotten about this - just unclear if we'll need it now (and it doesn't make sense to land if we won't use it). If it's not clear we'll use it soon, I'll just close it.

[DanTup]

There's a better solution on the way, so for now we're just going to use a single hard-coded port and don't need this.