tcp server listening, client connecting problems


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# 1  
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)

This is simplified as i am using functions and setting socket options, particularily the SO_REUSEADDR option.

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!
# 2  
Dont you need a loop with read() after accept()?
# 3  
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.
# 4  
Hi,

My suggestion: check for ECONREFUSED error in client.
I think the old connections can affect newly relaunched server
and maybe they overflow listen specified queue length.
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