Question

I’m a erlang newbie.
When I read the Socket chapter from “Programming Erlang” and doing some examples according to the tutorial, there is a problem.

In the chapter “The Hybrid Approach (Partial Blocking)”, I do the following:

loop(Socket)->
receive
{tcp, Socket, Bin} ->
    io:format("Server received binary = ~p~n",[Bin]),
    Str = binary_to_term(Bin),
    io:format("Server (unpacked) ~p~n",[Str]),
    Reply = lib_misc:string2value(Str),
    io:format("Server replying = ~p~n",[Reply]),
    gen_tcp:send(Socket, term_to_binary(Reply)),

    inet:setopts(Socket,[binary,{active, once}]), %Configure socket as active
    loop(Socket);
{tcp_closed, Socket} ->
    io:format("Server socket closed~n")
end.

start()->
{ok,Listen} = gen_tcp:listen(2345,[binary,{packet,4},
                   {reuseaddr, true},
                   {active, once}]),
{ok, Socket} = gen_tcp:accept(Listen),
loop(Socket).

sendData(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("Client received binary = ~p~n",[Bin]),
    Val = binary_to_term(Bin),
    io:format("Client result=~p~n",[Val])
   % gen_tcp:close(Socket)
end.

Then I open one terminal like this:
$erl

server:start().

and open another terminal like this:
$erl

client:sendData(“1233”).

At server, it will output:
Server received binary = <<131,107,0,3,49,50,51>>
Server (unpacked) “123”
Server replying = 123

At client, it will output:
Client received binary = <<131,97,123>>
Client result=123

But when the client sendData second time, there is not any response at server.
Is there something wrong? Thank you.

Answer 1

You server listen only one connection. You start function should be in another loop too.