CODEWITHSUNDEEP
tcperlang
Grimless
Grimless

Reputation: 1266

Erlang TCP server handling

I am starting to learn Erlang in the hopes of creating a game server to real-time multiplayer games. Currently, I am trying to estimate the amount of work and headache Erlang would cause vs. Scala. So, to start, I am creating a simple Erlang server process. I found a nice tutorial by Jesse Farmer which I have modified to learn more. My modified code is meant to be similar to his echo server, except it takes in English words and simply returns the Lojban equivalent. However, only the wildcard case is ever selected. Here is the code:

-module(translate).
-export([listen/1]).
-import(string).

-define(TCP_OPTIONS, [binary, {packet, 0}, {active, false}, {reuseaddr, true}]).

% Call echo:listen(Port) to start the service.
listen(Port) ->
    {ok, LSocket} = gen_tcp:listen(Port, ?TCP_OPTIONS),
    accept(LSocket).

% Wait for incoming connections and spawn the echo loop when we get one.
accept(LSocket) ->
    {ok, Socket} = gen_tcp:accept(LSocket),
    spawn(fun() -> loop(Socket) end),
    accept(LSocket).

% Echo back whatever data we receive on Socket.
loop(Socket) ->
    case gen_tcp:recv(Socket, 0) of
        {ok, Data} ->
            case Data of
                "Hello" -> gen_tcp:send(Socket, "coi\n");
                "Hello\n" -> gen_tcp:send(Socket, "coi\n");
                'Hello' -> gen_tcp:send(Socket, "coi\n");
                <<"Hello">> -> gen_tcp:send(Socket, "coi\n");
                <<"Hello\n">> -> gen_tcp:send(Socket, "coi\n");
                _ -> gen_tcp:send(Socket, "I don't understand")
            end,
            loop(Socket);
        {error, closed} ->
            ok
    end.

My current test is to open two terminal windows and execute

[CONSOLE 1]
erl
c(translate).
translate:listen(8888).

[CONSOLE 2]
telnet localhost 8888
whatever
Hello

And the output becomes:

I don't understand
I don't understand

How can I parse the incoming data? This style of pattern matching seems to be failing completely. Thanks!

Upvotes: 2

Views: 861

Answers (1)

Oleksii Kachaiev
Oleksii Kachaiev

Reputation: 6234

Try this one:

case binary_to_list(Data) of
    "Hello\r\n" -> gen_tcp:send(Socket, "this will be good variant\n");
    _ -> gen_tcp:send(Socket, "I don't understand")
end,

Or without explicit convert:

case Data of
    <<"Hello\r\n">> -> gen_tcp:send(Socket, "this will be good variant\n");
    _ -> gen_tcp:send(Socket, "I don't understand")
end,

Updated from comments

To work with more complicated matching remove "\r\n" suffix first:

Content = list_to_binary(lists:subtract(binary_to_list(Data), "\r\n")),
case Content of
    <<"Hello">> -> gen_tcp:send(Socket, <<"Good day!\n">>);
    <<"My name is, ", Name/binary>> -> gen_tcp:send(Socket, <<"Hello ", Name/binary, "!\n">>);
    _ -> gen_tcp:send(Socket, "I don't understand")
end,

Upvotes: 2

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