I'm trying to write a simple server application using Winsock2. I have a socket listening on port 80 (for http traffic). When I run the program and use my browser to connect to 127.0.0.1, the server receives the connection and displays it as expected.

New Connection

Recieved message:
GET / HTTP/1.1
Host: 127.0.0.1
Connection: keep-alive
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.102 Safari/537.36
DNT: 1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9

The problem comes when I try to close the socket. I'm using the following two commands: 

closesocket(currentSocket);
FD_CLR(currentSocket, &socketList);

When I do this, the program keeps repeating the output as if it was getting the same request over and over. If I remove either of these commands it only displays the output once, as it should.

The complete source code is as follows. This is a simplified version of the code that will duplicate the behavior, so I've omitted certain checks for clarity.

#ifndef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN
#endif // !WIN32_LEAN_AND_MEAN

#pragma comment(lib, "ws2_32.lib")
#include <WinSock2.h>

#include <iostream>

void runTest()
{
	////// SETUP ///////
	const int LISTENING_PORT = 80;
	const int BUFFER_SIZE = 4098;

	WSADATA wsa;
	sockaddr_in listeningAddress;
	listeningAddress.sin_family = AF_INET;
	listeningAddress.sin_port = htons(LISTENING_PORT);
	listeningAddress.sin_addr.S_un.S_addr = INADDR_ANY;

	WSAStartup(MAKEWORD(2, 2), &wsa);
	SOCKET listeningSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
	bind(listeningSocket, (sockaddr*)&listeningAddress, sizeof(listeningAddress));
	listen(listeningSocket, SOMAXCONN);

	fd_set socketList;
	FD_ZERO(&socketList);
	FD_SET(listeningSocket, &socketList);

	////// MAIN LOOP ///////////
	bool isRunning = true;
	while(isRunning)	// endless loop, normally has interupt mechanism
	{
		fd_set socketListCopy = socketList;
		int socketCount = select(0, &socketListCopy, nullptr, nullptr, nullptr);

		for (int i = 0; i < socketCount; i++)
		{
			SOCKET currentSocket = socketListCopy.fd_array[i];
			if (currentSocket == listeningSocket)
			{
				std::cout << "New Connection\n";
				SOCKET client = accept(listeningSocket, nullptr, nullptr);
				FD_SET(client, &socketList);
			}
			else
			{
				char buffer[BUFFER_SIZE];
				memset(buffer, 0, BUFFER_SIZE);
				int bytesIn = recv(currentSocket, buffer, BUFFER_SIZE, 0);

				std::cout << "\nRecieved message:\n" << buffer << '\n';

				// Using the following two lines causes the output to loop
				closesocket(currentSocket);
				FD_CLR(currentSocket, &socketList);
			}
		}
	}
	WSACleanup();
}

Thanks for the help. You were right, it was the browser.

I just want to clarify the first point; If I understand correctly you just need a different place or structure to hold the sockets, but you can still use select to call them the same as before?

As for the second point, I did have error checking in my original code, I just left it out of my example code to keep it smaller and easier to read... maybe I left out a bit too much.