Set monitor connections to non-blocking

Better to just drop monitor connections when the quality is bad than to
risk blocking the shard thread.

src/CNProtocol.cpp

@@ -214,7 +214,7 @@ void CNSocket::step() {
     }
 }
 
-static bool setSockNonblocking(SOCKET listener, SOCKET newSock) {
+bool setSockNonblocking(SOCKET listener, SOCKET newSock) {
 #ifdef _WIN32
     unsigned long mode = 1;
     if (ioctlsocket(newSock, FIONBIO, &mode) != 0) {

src/CNProtocol.hpp

@@ -117,6 +117,8 @@ inline bool validInVarPacket(size_t base, int32_t npayloads, size_t plsize, size
     return true;
 }
 
+bool setSockNonblocking(SOCKET listener, SOCKET newSock);
+
 namespace CNSocketEncryption {
     // you won't believe how complicated they made it in the client :facepalm:
     static constexpr const char* defaultKey = "m@rQn~W#";

src/Monitor.cpp

@@ -46,6 +46,16 @@ void Monitor::init() {
         exit(1);
     }
 
+#ifdef _WIN32
+    unsigned long mode = 1;
+    if (ioctlsocket(listener, FIONBIO, &mode) != 0) {
+#else
+    if (fcntl(listener, F_SETFL, (fcntl(listener, F_GETFL, 0) | O_NONBLOCK)) != 0) {
+#endif
+        std::cerr << "[FATAL] OpenFusion: fcntl failed" << std::endl;
+        exit(EXIT_FAILURE);
+    }
+
     std::cout << "Monitor listening on *:" << settings::MONITORPORT << std::endl;
 
     REGISTER_SHARD_TIMER(tick, settings::MONITORINTERVAL);
@@ -117,6 +127,8 @@ void Monitor::start(void *unused) {
         if (SOCKETERROR(sock))
             continue;
 
+        setSockNonblocking(listener, sock);
+
         std::cout << "[INFO] New monitor connection from " << inet_ntoa(address.sin_addr) << std::endl;
 
         {