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#1
03-18-2008
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tcp server listening, client connecting problems
hello everyone. I tried searching for something related to this, but I figured it was time to ask my own question. I am experiencing these problems using Ubuntu 7.04
I am starting up a TCP listener/server and once connected, will act as a communication/control link with a program on another computer. In the final iteration I want it to run it like a daemon, disconnected from a controlling process so I am going to do: Code:
result = fork()
if (result == 0){
//close stdio handles and reopen to /dev/null
setsig()
umask(0)
socket()
bind()
listen()
accept()
}
else
_exit(0)
If I do NOT run the fork and just run the socket->bind->listen->accept I get the same problems. The problem is: The client connecting, whether it is my client, or even netcat will connect properly, but then the server immediately sends a disconnect. The server does not get out of accept() during this, and even stranger it is random, and sometimes it works (60%), and sometimes it doesn't (40%). I could tell it connected and disconnected right away by using wireshark, I got a SYN -> SYN/ACK -> ACK and then right away FIN/ACK -> FIN/ACK -> FIN. Using netstat -ta also shows the ports getting gummed up in TIME_WAIT as though it did connect and disconnect. What i think could be the problem Two things I have done: one is to not set the SO_REUSEADDR parameter, and it then works as expected, although I have not done as much testing because it requires you to wait for a minute after each test for the TIME_WAIT to clean up. two, before I set up the socket, I read some parameters from a config file, by opening and closing it. If I comment this out and hard-code the port to listen on, etc, the occurance of it is MUCH less, although can still happen. I am at my wits end with this. Is there anything I can do to figure this out or help debug it. I am pretty sure it has to do with file handles getting gummed up or something like that. But i have no Idea! Thanks for reading! 
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#3
03-19-2008
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Sorry. You are right. After a successful accept() I go into a while loop where I read and do various things. I just wrote slimmed down code to give an over-view of what I was doing. I am doing all the error checking and never return a -1. The program, when a proper connection does happen, works perfectly, however, the chances of getting an accept is about 50/50, BUT the client DOES briefly connect.
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