Listening TCP Socket

TCP is a connection-oriented transport protocol which means that end points have to establish a connection prior to sending any (payload) data. Server opens one socket only for listening for incoming connection requests that come from clients. When placing a socket into a listening state, a maximum number of pending incoming connections is set. Those connections are waiting to be accepted and when backlog gets full no new connections are accepted.

Operations on listening socket are:

• socket()
• bind()
• listen()
• accept()
• closesocket()

Listening socket never gets into connected state and shutdown() called on it yields socket error 10057 - WSAENOTCONN (Socket is not connected).

Here is the timeline of one simple dialogue between the client and the server:

Client	Server
sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)	sockListen= socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)
-	sockaddr_in sSockAddr; sSockAddr.sin_family = AF_INET; sSockAddr.sin_addr.s_addr = inet_addr("192.168.0.24"); sSockAddr.sin_port = htons(43501); bind(sockListen, (SOCKADDR*)&sSockAddr, sizeof(sSockAddr));
-	listen(sockListen, MAXPENDING)
struct sockaddr_in sockAddrRemoteNode; memset(&sockAddrRemoteNode, 0, sizeof(sockAddrRemoteNode)); sockAddrRemoteNode.sin_family = AF_INET; sockAddrRemoteNode.sin_addr.s_addr = inet_addr("192.168.0.24"); sockAddrRemoteNode.sin_port = htons(43501); connect(sock, (struct sockaddr*) &sockAddrRemoteNode, sizeof(sockAddrRemoteNode));	struct sockaddr sockAddrClt; int nSockAddrLen = sizeof(sockAddrClt); sockClient = accept(sockListen, (struct sockaddr*) &sockAddrClt, &nSockAddrLen);
send(sock, buffSend, SEND_BUFF_SIZE, 0)	int recvPacketLen = recv(sockClient, buffRecv, RECV_BUFF_SIZE, 0)
shutdown(sock, SD_BOTH)	shutdown(sockClient, SD_BOTH)
closesocket(sock)	closesocket(sockClient)
-	closesocket(sockListen)