Non blocking server example

echo_server.erl:

-module(echo_server).
-behaviour(sockerl).

%% API:
-export([start/1
        ,packet_count/1]).


%% sockerl callbacks:
-export([listen_init/2
        ,connector_init/2
        ,handle_packet/3
        ,handle_disconnect/2
        ,handle_call/4
        ,terminate/3
        ,code_change/3]).





start(Port) ->
    RegisterName = {local, ?MODULE}, %% Optional
    CallbackMod = ?MODULE,
    InitArg = null,
    StartOpts = [],
    sockerl:start_link_server(RegisterName
                             ,CallbackMod
                             ,InitArg
                             ,Port
                             ,StartOpts).





packet_count(Con) ->
    gen_server:call(Con, how_much).





listen_init(null, _ListenSock) ->
    {ok, null2}.





%% SMD: #sockerl_metadata{} is and Erlang record containing useful things.
connector_init(null2, _SMD) ->
    {ok, [{state, 0}]}.





handle_packet(Pkt, Count = _MyState, _SMD) ->
    {ok, [{state, Count + 1}, {packet, Pkt}]}.





handle_call(how_much, From, Count, _SMD) ->
    {ok, [{reply, From, Count}]}.





handle_disconnect(_Count, _SMD) ->
    %% If client closes connection, 
    %% Server connection process will crash with reason 'normal'
    {stop, normal}.





terminate(_Reason, _State, _SMD) ->
    ok.





code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

Compile and go to the Erlang shell (You should add path for echo_server.beam and sockerl and its dependencies):

Erlang/OTP 19 [erts-8.2.2] [source-1ca84a4] [64-bit] [smp:4:4] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V8.2.2  (abort with ^G)
1> echo_server:start(8080).
{ok,<0.104.0>}

%% Getting all available server connections:
2> sockerl:get_server_connections(echo_server).
[]

Make a telnet connection to server:

$ telnet 127.0.0.1 8080

Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.

Get server connections again:

3> sockerl:get_server_connections(echo_server).
[{#Port<0.7532>,<0.116.0>}]

Send some texts in telnet connection:

foo
foo
2
2
3
3
4
4
5
5

Server replies after sending every text.
Check packet count for connection:

%% Getting pid of our connection process
4> [{_, Con}] = sockerl:get_server_connections(echo_server).
[{#Port<0.7532>,<0.116.0>}]

5> echo_server:packet_count(Con).
5