Problems using gets() on a socket

Hi,

I have built a telnet “chat server” using TCPserver and a select
statement.

If a client exits “cleanly” (such as by closing the shell in which
telnet is running), I can recognize the socket as being terminated using
sock.eof? and everything’s fine.

But if a client does wacky stuff like suspend their telnet process with
ctrl+z, then my server hangs at this line:

s = sock.gets()

(where s is a string and sock is the socket of the client)

I tried using s = sock.read and the server could not get past that line,
even for successfully connected clients. I tried using s =
sock.recvfrom(500)[0] but when the client hits that line I get the error
“in `recvfrom’: recv for buffered IO (IOError)”.

Any help you can provide would be gratefully received!

Very best,

  • Andrew

On 28.08.2010 23:24, Geometric Patterns wrote:

s = sock.gets()

(where s is a string and sock is the socket of the client)

Well, that’s perfectly OK since from the socket connection’s point of
view nothing changed. The process is still there and both ends can
still exchange data (after the client has been woken up which can happen
at any point in time).

I tried using s = sock.read and the server could not get past that line,
even for successfully connected clients. I tried using s =
sock.recvfrom(500)[0] but when the client hits that line I get the error
“in `recvfrom’: recv for buffered IO (IOError)”.

Any help you can provide would be gratefully received!

If you want to deal with those situations you probably need to extend
your protocol to be able to intermediately park a chat session and
resume it later. You could even release the socket in between to not
waste too many resources. This also requires that your client process
catches the signal, notifies the server from the session park and
release the socket. (Note, I am not 100% sure that you can do this and
still put the process to sleep.)

You can as well simply do nothing because only these things can happen:

  1. somebody wakes up the client process and communication resumes
    normally.

  2. somebody kills the client in which case the socket is released and
    the server will eventually throw an exception or return nil from #gets.

  3. network is disconnected or some other error in which case the server
    likely gets an exception.

Kind regards

robert

But if a client does wacky stuff like suspend their telnet process with
ctrl+z, then my server hangs at this line:

s = sock.gets()

This socket tutorial might help you:
http://en.wikibooks.org/wiki/Ruby_Programming/Reference/Objects/Socket

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