windows: SO_EXCLUSIVEADDRUSE

https://github.com/warmcat/libwebsockets/issues/942

lib/libwebsockets.h

@@ -1800,6 +1800,12 @@ enum lws_context_options {
 	/**< (VH) All connections to this vhost / port are RAW as soon as
 	 * the connection is accepted, no HTTP is going to be coming.
 	 */
+	LWS_SERVER_OPTION_ALLOW_LISTEN_SHARE			= (1 << 23),
+	/**< (VH) Set to allow multiple listen sockets on one interface +
+	 * address + port.  The default is to strictly allow only one
+	 * listen socket at a time.  This is automatically selected if you
+	 * have multiple service threads.
+	 */
 
 	/****** add new things just above ---^ ******/
 };

lib/server.c

@@ -65,6 +65,7 @@ lws_context_init_server(struct lws_context_creation_info *info,
 	}
 
 #if LWS_POSIX
+	(void)n;
 #if defined(__linux__)
 	limit = vhost->context->count_threads;
 #endif
@@ -93,6 +94,24 @@ lws_context_init_server(struct lws_context_creation_info *info,
 		return 1;
 	}
 #if LWS_POSIX && !defined(LWS_WITH_ESP32)
+
+#if (defined(WIN32) || defined(_WIN32)) && defined(SO_EXCLUSIVEADDRUSE)
+	/*
+	 * only accept that we are the only listener on the port
+	 * https://msdn.microsoft.com/zh-tw/library/windows/desktop/ms740621(v=vs.85).aspx
+	 *
+	 * for lws, to match Linux, we default to exclusive listen
+	 */
+	if (!lws_check_opt(vhost->options, LWS_SERVER_OPTION_ALLOW_LISTEN_SHARE)) {
+		if (setsockopt(sockfd, SOL_SOCKET, SO_EXCLUSIVEADDRUSE,
+			       (const void *)&opt, sizeof(opt)) < 0) {
+			lwsl_err("reuseaddr failed\n");
+			compatible_close(sockfd);
+			return 1;
+		}
+	} else
+#endif
+
 	/*
 	 * allow us to restart even if old sockets in TIME_WAIT
 	 */
@@ -116,7 +135,13 @@ lws_context_init_server(struct lws_context_creation_info *info,
 	}
 #endif
 
-#if defined(__linux__) && defined(SO_REUSEPORT) && LWS_MAX_SMP > 1
+#if defined(__linux__) && defined(SO_REUSEPORT)
+	n = lws_check_opt(vhost->options, LWS_SERVER_OPTION_ALLOW_LISTEN_SHARE);
+#if LWS_MAX_SMP > 1
+	n = 1;
+#endif
+
+	if (n)
 		if (vhost->context->count_threads > 1)
 			if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEPORT,
 					(const void *)&opt, sizeof(opt)) < 0) {