Receiving events

[danbo]

Hi @toots,

I'm interested in having external processes receive events from liquidsoap, ie onTrack, onFrame, metadata etc. I could make a web request, but having an open stream / socket would be ideal.

I found #2014 but file.open it creates a file by default and it is unclear how to create a named socket, ie /tmp/liqevents.sock

Can you provide a snippet which shows how to have liquidsoap create this socket so that my liq script could then write to it in the on_x events?

PS I tried having an external process create the socket (socat) and gave a+x permissions but liquidsoap still complained it couldn't open the socket with an error

Below is how a normal liq server socket looks like on my system:

srw------- 1 10000     10001       0 Oct 22 22:53 liq.sock

Here is what I have created with socat:

socat UNIX-LISTEN:/tmp/liqevents.sock,reuseaddr,fork TCP-LISTEN:11111
srwxrwxrwx 1 10000     10001       0 Oct 22 22:55 liqevents.sock

In the liq script:

fd = file.open(write=true, "/tmp/liqevents.sock")

When starting...

Error 14: Uncaught runtime error:
type: file,
message: "No such device or address in open(/tmp/liqevents.sock)\nBacktrace:\nRaised by primitive operation at Builtins_file                          s.(fun) in file \"builtins/builtins_files.ml\", line 203, characters 10-47\n",
stack: at /test.liq, line 13, char 5-49

Looks like liquidsoap thinks its a file and can't access it, similar to how if I try to cp the socket, bash tells me cannot open for reading - no such device or address.

Tried with the latest 2.1.2 rolling release:

Liquidsoap 2.1.3+git@bf6eca1f
Copyright (c) 2003-2022 Savonet team
Liquidsoap is open-source software, released under GNU General Public License.

[toots]

Hi! That's an interesting use-case.

From a POSIX/unix point of view, there should be no reason for the call to fail here as opposed to doing it with a regular files. My suspicion would be that the access rights are not allowing the liquidsoap process to access the file.

[toots]

Wait my bad, I can reproduce. Let me get back to you!

[toots]

Ok, unix/posix openfile call does not in fact support named sockets. I am adding the whole socket API in this PR: #2722 which will include support for named sockets. However, this will have to be for the next major release.

Meanwhile, I'd suggest to use process.run with socat, which should allow you to communicate with the named socket via the local shell.