Datagram Connection (unix domain)

## 21.5 Datagram Connection (unix domain)

This is similar to datagram connection in the internet domain, except that it is limited to communications between two processes on the same Unix machine.
Again, like in the internet domain, the connection needs to be established in both directions if bi-direction communication is required:

>     server:
>         % Make a named socket and read two terms from it
>         [eclipse 10]: socket(unix, datagram, s), bind(s, '/tmp/sock').

>         yes.
>         [eclipse 11]: read(s, X), read(s, Y).

>     process1:
>         % Connect a socket to the server and write one term
>         [eclipse 32]: socket(unix, datagram, s), connect(s, '/tmp/sock').

>         yes.
>         [eclipse 33]: printf(s, "%w. %b", message(process1)).

>     process2:
>         % Connect a named socket to the server and write another term
>         [eclipse 15]: socket(unix, datagram, s), connect(s, '/tmp/sock'),
>             bind(s, '/tmp/socka').

>         yes.
>         [eclipse 16]: printf(s, "%w. %b", message(process2)).

>         yes.
>         % And now disconnect the output socket from the server
>         [eclipse 17]: connect(s, 0).

>         yes.

>     server:
>         % Now the server can read the two terms
>         X = message(process1)
>         Y = message(process2)
>         yes.
>         % and it writes one term to the second process on the same socket
>         [eclipse 12]: connect(s, '/tmp/socka'),
>             printf(s, "%w. %b", message(server)).

>     process2:
>         %
>         [eclipse 18]: read(s, Msg).

>         Msg = message(server)
>         yes.