# Varlink with Vali

[varlink][1] is a neat little standard for doing debuggable IPC. It takes some
of the nice properties of DBUS, like the introspection capabilities, and
combines them with simple standard tools/technologies in the form of unix
sockets and JSON.

For C, there is a library by [emersion][2] called vali, which does pretty much
everything all you need to get going:  
https://emersion.fr/blog/2025/announcing-vali/

When you have written your service, here is how to interact with it just using
standard utils, socat and jq:

```sh
cat <<-EOF | jq --raw-output0 | socat STDIO UNIX-CONNECT:"$SOCKET" | jq
    {
        "method": "org.varlink.service.GetInfo",
    }
EOF
```

This is equivalent to using the varlink cli tool and running:
`varlink info $SOCKET`

```sh
cat <<-EOF | jq --raw-output0 | socat STDIO UNIX-CONNECT:"$SOCKET" | jq
    {
        "method": "org.varlink.service.GetInterfaceDescription",
        "parameters": {
            "interface": "com.example.Foobar"
        }
    }
EOF
```

This will return the service interface, if the service listening at the socket
actually implements it.

Note the use of `jq --raw-output0`. It is possible to omit the jq invocations,
the input JSON data should be followed by a NUL byte.


[1]: https://varlink.org
[2]: https://emersion.fr