| Author |
Message |
< Erlang ~ simple TCP problem |
| dijxtra |
 Posted: Tue May 10, 2011 2:28 am |
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Joined: 07 Mar 2011
Posts: 6
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I'm trying to write a TCP server: http://pastebin.com/aCeZh3mW
It works, except for the fact that client desn't get the result. Server receives the value, evaluates it, prints the result, but telnet just hangs outputs nothing. Any ideas where to start looking?
Regards,
dijxtra |
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| rvirding |
| Posted: Fri May 13, 2011 4:03 pm |
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User
Joined: 30 Aug 2006
Posts: 452
Location: Stockholm, Sweden
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Could you give some more details? Which system are you running on and which client are you using?
I would say that the probable cause is that you are using the wrong socket. You save and then use the listen socket for communication. This is wrong, the only thing you do with a listen socket is to accept connection requests on it. You should be saving the socket returned from gen_tcp:accept and using that for selecting input and sending output.
So I would have something like:
Code: -record(interface_state, {port,lsock,sock,buffer}).
...
exec_call(State) ->
Socket = State#interface_state.sock, %Use right socket
Buffer = State#interface_state.buffer,
...
gen_tcp:send(Socket, io_lib:fwrite("~p~n", [Result])),
io:format("~w~n", [Result]).
...
handle_info(timeout, #interface_state{lsock = LSock} = State) ->
{ok, Sock} = gen_tcp:accept(LSock),
{noreply, State#interface_state{sock=Sock}}.
A few other points:
- It is very unsafe to assume how tcp packets are delivered, in this case to assume that your commands will arrive as a stream of packets with the last packet containing only \r\n. Tcp is stream based so there are no guarantees at all.
- You shouldn't suspend behaviours the way you do in gen_tcp:accept as they use messages to interact with the rest of OTP. So your server will be completely unresponsive while it is waiting for connect request. If you want to use a gen_server here it would probably be better to have a top-level process which does listen/accept and then start a gen_server to handle the requests. |
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Robert Virding, Erlang Solutions Ltd. |
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| zhuyifan1129 |
| Posted: Sun May 15, 2011 6:21 am |
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| dijxtra |
| Posted: Sun May 15, 2011 9:12 am |
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Joined: 07 Mar 2011
Posts: 6
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rvirding wrote: I would say that the probable cause is that you are using the wrong socket.
That's it! Thanks!
rvirding wrote:
A few other points:
Thanks for the hints. I'm aware this code is horrible, I'm working on fixking it 
Thank you for your response! |
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| raymondb |
| Posted: Thu Jun 09, 2011 3:39 am |
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Joined: 08 Jun 2011
Posts: 4
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I do not think this is a common problem and would probably be because of a wrong setting in your ip protocol. Probably a wrong socket as what is already suggested.
I have used it for quite a while now and luckily have not run into those types of problems. |
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| Emmarogers |
| Posted: Sat Sep 17, 2011 11:18 am |
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Joined: 17 Sep 2011
Posts: 1
Location: 23306 Three Notch Rd California, MD 20619
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| Great work rvirding, i never thought that the problem could be with the socket.. |
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SaaS Companies |
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| wuji |
| Posted: Thu Aug 16, 2012 8:01 am |
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| dongdongwu |
| Posted: Thu Sep 20, 2012 5:23 am |
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