Non-blocking reuseable socket

[ktsangop]

Hi there!
I would like a little help regarding the following code.

The following code will wait for a non-blocking socket connection, and then wait to receive a certain packet. When the packet arrives, it will do something and then close connection and reinitialize it in order to be able to accept again. The client side closes it's connection also that's why i completely shutdown this one's also.

The problem is that the first time of the loop the operation is successful, but on second attempt, it cannot accept a socket connection and blocks on accept().

On client side i when i try to connect second time, i get a WSAECONNREFUSED error.

I am quite sure that this is the server's side problem because i used a couple of TCP socket testers available online and they all get a connection refused on the second attempt. That's why i didn't post the client side.

while(1)
{

	WSADATA WsaDat;
	if(WSAStartup(MAKEWORD(2,2),&WsaDat)!=0)
	{
		TRACE("---------WSA Initialization failed!----------\r\n");
		WSACleanup();
		return 0;
	}
	
	SOCKET Socket=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
	if(Socket==INVALID_SOCKET)
	{
		TRACE("---------Socket creation failed.----------\r\n");
		WSACleanup();
		return 0;
	}
					
	SOCKADDR_IN serverInf;
	serverInf.sin_family=AF_INET;
	serverInf.sin_addr.s_addr=INADDR_ANY;
	serverInf.sin_port=htons(2224);

	///TRY TO REUSE ADDRESS
	char reuse_add = '1';
	int reuseerr = setsockopt(Socket, SOL_SOCKET, SO_REUSEADDR, &reuse_add, sizeof (reuse_add));
	///TRY TO REUSE ADDRESS
					
	if(bind(Socket,(SOCKADDR*)(&serverInf),sizeof(serverInf))==SOCKET_ERROR)
	{
		TRACE("------------Unable to bind socket!-----------\r\n");
		WSACleanup();
		return 0;
	}
		
	int err = listen(Socket,1);
					
	SOCKET TempSock=SOCKET_ERROR;
	while(TempSock==SOCKET_ERROR)
	{
		TRACE("-----------Waiting for incoming connections...-----------\r\n");
		TempSock=accept(Socket,NULL,NULL);
	}
	
	
	// If iMode!=0, non-blocking mode is enabled.
	u_long iMode=1;
	ioctlsocket(Socket,FIONBIO,&iMode);
					
	Socket=TempSock;
	TRACE("---------------Client connected!----------------\r\n");

	while(1)
	{
		char buffer[1000];
		memset(buffer,0,999);
	
		recv(Socket,buffer,1000,0);
		if (strstr("MY_PACKET",buffer)!=NULL)
		{
			TRACE("---------------MY_PACKET RECEIVED!!!---------------------");
			break;
		}
		Sleep(30);
	}

	//////////////////////DO SOME STUFF I WANT
	Sleep(100);

	shutdown(Socket,SD_BOTH);
	closesocket(Socket);
	WSACleanup(); // NOT NECESSARY???


}

My guess :
1) setsockopt() with SO_REUSEADDR option is not working correctly because i am not sure if i use it correctly.
2) Although i use shutdown and closesocket, the connection is not terminated correctly?

Anyway after a lot of debugging i couldn't come to an answer.

Thanks in advance!

[nezachem]

This is a quite unusual way to serve connections. You don't need to shutdown a listening socket; the same one will accept new connections as many times as you want:

listen(serverSocket, 1);
    while(1) {
        clientSocket = accept(serverSocket, 0, 0);
        do_stuff(clientSocket);
        shutdown(clientSocket, SD_BOTH);
        closeSocket(clientSocket);
    }

In your code, after the line 51 you lose the handle to the listening socket forever. It is not affected by shutdown/closesocket anymore. The socket object is still sitting there interfering with a next one you are trying to create.

[ktsangop]

Thanks for the answer. I have no experience with socket programming so my code is mostly from tutorials.

I changed my code but still i get the same error when connecting with my client, but not with an external TCP tester i downloaded. Now it seems that i should change my client.

I think that my client shouldn't terminate/destroy the socket either but it's really hard to change the structure of my client now..
:(

I will try to work around this and if i find anything intersting i will post it.
Else, i will just mark this thread as solved sooner or later..

Any other suggestions still welcome..

Thanks!
:)

[ktsangop]

For what is worth i switched to udp sockets and solved my problem using the following library which i found extremely helpful.

Practical Sockets

Thanks for the help!