Simple example of socket programming for Erlang

In Erlang, gen_tcp is used to write TCP programs, and GEN_UDP is used to write UDP programs. A simple example of a TCP server echo:

Start_echo_server ()

{ok,listen}= Gen_tcp:listen (1234,[binary,{packet,4},{reuseaddr,true},{active,true}]),

{ok,socket}=get_tcp:accept (Listen),

Gen_tcp:close (Listen),

Loop (Socket).

Loop (Socket),

Receive

{Tcp,socket,bin}

Io:format ("serverreceived binary = ~p~n", [Bin])

Str= binary_to_term (Bin),

Io:format ("Server (unpacked) ~p~n", [Str]),

reply= Lib_misc:string2value (STR),

Io:format ("serverreplying = ~p~n", [Reply]),

Gen_tcp:send (Socket,term_to_binary (Reply)),

Loop (Socket);

{Tcp_closed,socket}

Io:format ("ServerSocket closed ~n")

End.

Example of the Echo Client for TCP:

Echo_client_eval (STR)

{Ok,socket} = gen_tcp:connect ("localhost", 2345,[binary,{packet,4}]),

ok= gen_tcp:send (Socket, Term_to_binary (STR)),

Receive

{tcp,socket,bin}->

Io:format ("clientreceived binary = ~p~n", [Bin]),

Val=binary_to_term (Bin),

Io:format ("Clientresult = ~p~n", [Val]),

Gen_tcp:close (Socket)

End.

UDP Server Sample

Udp_demo_server (Port),

{ok,socket}= Gen_udp:open (open,[binary]),

Loop (Socket).

Loop (Socket),

Receive

{udp,socket,host,port,bin}->

Binreply= ...,

Gen_udp:send (socket,host,port,binreply),

Loop (Socket)

End.

UDP Client Example:

Udp_demo_client (Request)

{ok,socket}= Gen_udp:open (0,[binary]),

ok= gen_udp:send (Socket, "localhost", 1234,request),

Value= Receive

{udp,socket,_,_,bin}-> {Ok,bin}

after2000-Error

End

Gen_udp:close (Socket),

Value

Note that because UDP is unreliable, be sure to set a time-out period, and reqeust preferably less than 500 bytes.

WebSocket, JS and Erlang combine to achieve most of the web's functionality.

Simple example of socket programming for Erlang