Talking to TCP server from shell

Magnus Leone magnus.falk@REDACTED
Fri Nov 12 02:24:44 CET 2021


I'm working on making a very basic talk about networking, and eventually a
webserver, but I thought I'd start with the very basic parts; just a TCP
echo server. The thing is that the talk is not specifically about Erlang,
I'm just using that as I'm most familiar with it (and hey, if I get some
people interested, that's great). So I wanted the client side to be just a
regular shell.

Here is where my problem comes in - I can't seem to get the server process
to accept the incoming connection when it comes from a shell. The code is
pretty much straight out of Joe's book and it works fine as long as the
other side is also an Erlang process. What I've tried so far:

>telnet localhost 7777
telnet: Unable to connect to remote host: Connection refused

>netcat localhost 7777
*no output*

Does anyone know how I can use bash to connect to a TCP socket in this


start(Port) ->
    {ok, ListenSocket} =
        gen_tcp:listen(Port, [list, {packet, 0},
                                    {reuseaddr, true},
                                    {active, true}]),
    {ok, Socket} = gen_tcp:accept(ListenSocket),
    ok = gen_tcp:close(ListenSocket),
    io:format("Server accepted connection on port ~p~n", [Port]),

loop(Socket) ->
        {tcp, Socket, StringMsg} ->
            io:format("Server received message: ~p~n", [StringMsg]),
            Reply = "Echo " ++ StringMsg,
            io:format("Server replying: ~p~n", [Reply]),
            gen_tcp:send(Socket, Reply),
        {tcp_closed, Socket} ->
            io:format("Server socket closed - shutting down...~n")
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