How to make server not wait on accept after first client? - c

Question

I have a tcp server and I want to make it so after it accepts the first client it doesn't wait on the accept function and just goes on if no-one else has connected
while (1)
{
SOCKET ClientSocket = accept(Socket, (sockaddr *)&Client, &ClientSize);
if(ClientSocket == INVALID_SOCKET)
{
Error("accept failed.\n");
}
ClientSockets[ClientSocketsIndex++] = ClientSocket;
Result = connect(ClientSocket, (sockaddr*)&Client, ClientSize);
sockaddr_in From;
int FromSize = sizeof(From);
Result = recv(ClientSocket, Message, sizeof(Message), 0);
if (Result == SOCKET_ERROR)
{
Error("recv failed.\n");
}
Result2 = getpeername(ClientSocket, (sockaddr*)&From, &FromSize);
if (Result2 == SOCKET_ERROR)
{
Error("getpeername failed.\n");
}
Here I take the ClientSocket with accept() and add it to an array where I store all ClientSockets and then receive a buffer. The problem is that after each loop it waits for a new ClientSocket.
The Error() function is just a one I made for printing to the console and quitting if I encounter an Error btw.

Answer 1

First off, calling connect() on the SOCKET returned by accept() is wrong. Get rid of that.
Second, if you want your loop to service multiple clients properly, then use select() (or equivalent). Don't call accept() until select() tells you that a new client is waiting to be accepted. Likewise, don't call recv() until select() tells you that a client in your array is waiting to be read from.
Try something more like this:
const size_t MAX_SOCKETS = ...;
SOCKET ClientSockets[MAX_SOCKETS];
size_t NumClientSockets = 0;
...
while (true)
{
fd_set readfds;
FD_ZERO(&readfds);
FD_SET(Socket, &readfds);
for(int i = 0; i < NumClientSockets; ++i)
{
FD_SET(ClientSockets[i], &readfds);
}
if (select(0, &readfds, NULL, NULL, NULL) > 0)
{
if (FD_ISSET(Socket, &readfds))
{
ClientSize = sizeof(Client);
SOCKET ClientSocket = accept(Socket, (sockaddr *)&Client, &ClientSize);
if (ClientSocket == INVALID_SOCKET)
{
Error("accept failed.\n");
}
else if (NumClientSockets == MAX_SOCKETS)
{
closesocket(ClientSocket);
}
else
{
ClientSockets[NumClientSockets] = ClientSocket;
++NumClientSockets;
}
}
size_t i = 0;
while (i < NumClientSockets)
{
if (!FD_ISSET(ClientSockets[i], &readfds))
{
++i;
continue;
}
Result = recv(ClientSockets[i], Message, sizeof(Message), 0);
if (Result <= 0)
{
if (Result == SOCKET_ERROR)
Error("recv failed.\n");
for(size_t j = i + 1; j < NumClientSockets; ++j)
{
ClientSockets[j - 1] = ClientSockets[j];
}
--NumClientSockets;
continue;
}
// use Message up to Result bytes as needed...
++i;
}
}
}