C++ Builder XE2, receiving tcp requests - c++

Question

I want to write a tcp-listener within my application, so it can be controlled by others applications.
For that I use the following snippet I found (as an example for the use of listener).
I worked with p2p-connections and Sockets once already in C#.NET, but it's either too long ago or too differently. I expect the code to stop at the listen() command and wait until there is a connection request at that port. However, instead it just continues with the next lines. Usually my Firewall should also tell me, if there is some internet-activity-attempt, but it stays silent.
What would be the next step to actually know whether there is a connection request?
Can I trigger that with a HTTP-request for 127.0.0.1:27015 using a browser?
Or could this be archived easier?
#include <winsock.h>
#pragma comment(lib, "Ws2_32.lib")
int portlisten(){
WSADATA wsaData;
int iResult = 0;
SOCKET ListenSocket = INVALID_SOCKET;
sockaddr_in service;
iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
if (iResult != NO_ERROR) {
wprintf(L"WSAStartup() failed with error: %d\n", iResult);
return 1;
}
//----------------------
// Create a SOCKET for listening for incoming connection requests.
ListenSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (ListenSocket == INVALID_SOCKET) {
wprintf(L"socket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}
//----------------------
// The sockaddr_in structure specifies the address family,
// IP address, and port for the socket that is being bound.
service.sin_family = AF_INET;
service.sin_addr.s_addr = inet_addr("127.0.0.1");
service.sin_port = htons(27015);
iResult = bind(ListenSocket, (SOCKADDR *) & service, sizeof (service));
if (iResult == SOCKET_ERROR) {
wprintf(L"bind function failed with error %d\n", WSAGetLastError());
iResult = closesocket(ListenSocket);
if (iResult == SOCKET_ERROR)
wprintf(L"closesocket function failed with error %d\n", WSAGetLastError());
WSACleanup();
return 1;
}
//----------------------
// Listen for incoming connection requests
// on the created socket
if (listen(ListenSocket, 5) == SOCKET_ERROR)
wprintf(L"listen function failed with error: %d\n", WSAGetLastError());
wprintf(L"Listening on socket...\n");
iResult = closesocket(ListenSocket);
if (iResult == SOCKET_ERROR) {
wprintf(L"closesocket function failed with error %d\n", WSAGetLastError());
WSACleanup();
return 1;
}
WSACleanup();
return 0;
}

Answer 1

I expect the code to stop at the listen() command and wait until there is a connection request at that port.
No. You are thinking of accept() instead. listen() merely opens the port and then exits immediately. You have to then use accept() in a loop to accept individual client connections. It returns a new SOCKET that you use to exchange data with that specific client. You can use select() to know when a new client is trying to connect before then calling accept(), or you can let accept() block the calling thread until a client connects.
Instead of writing your own socket API code, you should use a pre-existing TCP server component, like the VCL's native TServerSocket component, or Indy's TIdTCPServer component.