Use IP address as hostname when configured

[jonatanklosko]

Closes #1180.

[jonatanklosko]

This isn't perfect, because running locally with Docker the URL will include 0.0.0.0 (which works, but it should be localhost anyway).

[jonatanklosko]

One option would be to support LIVEBOOK_HOST and set it to localhost in the Dockerfile. In that case, do we want --host as well? (I'd say it's not necessary)

[josevalim]

@jonatanklosko should we convert 127.0.0.1 and 0.0.0.0 tuples to localhost?

[aseigo]

This appears to work for me. Thanks @jonatanklosko !

@josevalim 0.0.0.0 isn't a synonym for localhost, though; it binds to all available IP addresses, including but not limited to localhost. So that might be dangerously misleading, as 0.0.0.0 opens livebook to the network beyond that machine but saying it is on localhost would not communicate that. So, for me, 127.0.0. => localhost makes sense, but perhaps not 0.0.0.0

(I can't comment on the Docker situation.)

[jonatanklosko]

That's what I've been thinking, but actually 0.0.0.0 isn't a valid destination address, so technically http://0.0.0.0:8080 is invalid, browsers just decide to treat it as localhost (ref). When we bind the server to 0.0.0.0, showing localhost URL is actually fine because it's one of the valid addresses for accessing the server. It could be slightly better to show machine hostname or IP, but this wouldn't work for the Docker case. Given that we bind to 0.0.0.0 only via explicit option, I think showing just localhost for access is alright.

[aseigo]

Yes, browsers redirect the address to localhost; however, in this case it is configuration for cowboy which causes it to bind to all available IP addresses, not just localhost. 0.0.0.0 is a synonym for INADDR_ANY.

For me this is a salient issue as livebook (by default, at least) exposes the local filesystem to a limited extent, even allowing the creation of local directories, and many devs often equate 0.0.0.0 with localhost (probably because browsers treat it that way on the client side ..)

Perhaps a useful compromise would be to emit a separate line on the console when 0.0.0.0 is provided as the address nothing that Livebook is listening on all available addresses, including potentially externally reachable ones?

[josevalim]

We don't use 0.0.0.0 by default, so I am not worried about it. If someone is passing 0.0.0.0 explicitly, then I hope they know they are doing and the implications of it. So showing 0.0.0.0 on the terminal is fine.

[jonatanklosko]

So showing 0.0.0.0 on the terminal is fine.

@josevalim did you mean localhost?

[josevalim]

I meant 0.0.0.0. So we don't hide it and the browser redirects it anyway.

[jonatanklosko]

I see, so we are back to the Docker question. Inside Docker we use 0.0.0.0, but for the user binding container ports it's actually just localhost, and showing 0.0.0.0 may give a wrong impression that we are exposing too much. So do we want LIVEBOOK_HOST or any other ideas?

[josevalim]

But docker can also bind to a different port, can't it? So we can't assume we know how it is accessed. Maybe we should change the message to say "Livebook listening to address: ..."?

[jonatanklosko]

So we can't assume we know how it is accessed

Ah right, good call!