Re: UDP Sockets

[Daniel Diaz]

Hi All,

Since the are (were) some questions about sockets, I enclose a piece of
code managing a client and a server.
The client finds (several) solutions to a given problem and sends them
to the server (which simply displays them). You can modify the host and
the port number used (here localhost:7000). This is obviously a very
simple example but should be a good starting point for more complex
applications.

Predicates provided:

server/0 starts the server (should be done before starting the client),
waits for the client, and then receive the terms and displays them, at
the end the server-side communication.

client_init/0 initializes the communication with the server (on the
other process, server/0 should been launched).

client_send/1 sends the term passed to the server.

client_term/0 closes the client-side communication.


How to use them: 

start a gprolog process (called p1), load this file (called x.pl) and
start the server:

$ gprolog
GNU Prolog 1.2.8
By Daniel Diaz
Copyright (C) 1999-2001 Daniel Diaz
| ?- [x].
compiling /home/diaz/x.pl for byte code...
/home/diaz/x.pl compiled, 1550 lines read - 127107 bytes written, 561 ms
 
(100 ms) yes
| ?- server.

here the server waits for a connection...

start another gprolog process (call p2), load x.pl and start the client.

$ gprolog
GNU Prolog 1.2.8
By Daniel Diaz
Copyright (C) 1999-2001 Daniel Diaz
| ?- [x].
ccompiling /home/diaz/x.pl for byte code...
/home/diaz/x.pl compiled, 1550 lines read - 127107 bytes written, 455 ms

(100 ms) yes
| ?- client_init.
 
(10 ms) yes

this awakes p1 which displays:
accepting a connection from client : 127.0.0.1

then send some terms to the server, e.g. typing in p2:

| ?- client_send(foo).
 
yes

and p1 displays:
foo

repeat this as long as needed and then, stop the client (in p2):
| ?- client_term.
 
yes


this finished server/0 in p1 which then displays:

(10 ms) yes
| ?-


you can restart the server in p1.

| ?- server.

here the server waits for a connection...


and send all operators to p1, typing in p2:

| ?- client_init, current_op(X,Y,Z), client_send(op(X,Y,Z)), fail ;
client_term.

(10 ms) yes

and in p1 all operators are displayed:
accepting a connection from client : 127.0.0.1
op(1200,fx,:-)
op(1200,xfx,:-)
op(700,xfx,\=)
op(700,xfx,=:=)
op(700,xfx,#>=)
op(700,xfx,#<#)
op(700,xfx,@>=)
op(1200,xfx,-->)
...
op(700,xfx,#<)
op(700,xfx,@<)
 
yes


Here is a the code (file x.pl)

server :-
        socket('AF_INET', Sock),
        socket_bind(Sock, 'AF_INET'(localhost, 7000)),
        socket_listen(Sock, 4),
        socket_accept(Sock, C, SI, SO),
        close(SO),
        format('accepting a connection from client : ~a~n', [C]),
        repeat,
        read(SI, T),
        (   T \== end_of_file ->
            write(T), nl,
            fail
        ;   !),
        close(SI),
        socket_close(Sock).


client_init :-
        socket('AF_INET',Socket),
        socket_connect(Socket,'AF_INET'(localhost,7000), SI, SO),
        close(SI),
        add_stream_alias(SO, out),
        set_stream_buffering(out, line).

client_send(T):-
        format(out, '~q.~n',[T]).

client_term :-
        close(out).


Hope this helps.

PS: Carlos, in your example:
  - initialize the server as above
  - initialize the client before starting go/2,
  - define client(X,Y) :- client_send(sol(X,Y)).
  - call client_term at the end.