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While developing a client and server (both using blocking mode calls) I got into a few minor problems.
The client I'm creating should get one response for every time it does a request to the server. Once this "ping - pong" is done the client should disconnect and cleanup gracefully. This includes memory and the open socket.

A typical sequense goes like this.

1. Client sends request for server.
2. Server gives exactly one response.
...
3. Goto 1
...
4. Client is done and calls shutdown with parameter SD_BOTH and then closesocket.
5. Server will do a recv() call where it gets 0 as return value and assume the client is disconnecting.
6. Server calls shutdown with SD_BOTH param calls closesocket() and free's the memory used by the client.

So both the server and client runs the same sequense.
Now I shut down both programs and netstat shows this:

TCP cyber_server:4823 PII-400:6500 TIME_WAIT
TCP cyber_server:4824 PII-400:6500 TIME_WAIT
TCP cyber_server:4825 PII-400:6500 TIME_WAIT
TCP cyber_server:4826 PII-400:6500 TIME_WAIT
TCP cyber_server:4827 PII-400:6500 TIME_WAIT
TCP cyber_server:4828 PII-400:6500 TIME_WAIT
TCP cyber_server:4829 PII-400:6500 TIME_WAIT
TCP cyber_server:4830 PII-400:6500 TIME_WAIT
TCP cyber_server:4831 PII-400:6500 TIME_WAIT
TCP cyber_server:4832 PII-400:6500 TIME_WAIT
(This test was made by running the client in a endless loop)
The first column is the client and the server is second column which listens on port 6500.

So how can the socket stay open even though I closed it?

The other problem I'm having is a slow DNS lookup. On one of the machines I have it can take up to about 20-30 seconds to make a dns lookup even though it's on local network. The following code (written in C) is what I use to get the server ip:

// Try to use the host as a ip
sin.sin_addr.s_addr = inet_addr(szHost);
if (sin.sin_addr.s_addr == INADDR_NONE)
{
// Make a dns request
if ((lpHost = gethostbyname(szHost)) == NULL)
{
printf("DNS lookup of server failed\n");
return false;
}
sin.sin_addr.s_addr = *((unsigned long *) lpHost->h_addr);
}

It seems the process called System is taking all cpu time in the time the lookup happens. The odd thing is though that a few times in a row the lookup can be fast while most of the time it's slow. Is this a correct way to do DNS lookups?

All tests were made under Windows 2000.

Thanks in advance.

// CyberHeg

I just checked with ping command on the same machine and it acts the same way so I conclude it's some mess with bad dns setup.

Thanks again.

// CyberHeg