allow_random_ports: Let the OS choose an open port

src/socket_utils.cpp

@@ -23,32 +23,25 @@ uint16_t bind_port_in_range_(Socket &sock, Protocol protocol) {
 		if (!ec) return port;
 	}
 	if (cfg->allow_random_ports()) {
-		for (int k = 0; k < 100; ++k) {
-			uint16_t port = 1025 + rand() % 64000;
-			sock.bind(typename Protocol::endpoint(protocol, port), ec);
-			if (ec == lslboost::system::errc::address_in_use) continue;
-			if (!ec) return port;
-		}
+		// bind to port 0, i.e. let the operating system select a free port
+		sock.bind(typename Protocol::endpoint(protocol, 0), ec);
+		// query and return the port the socket was bound to
+		if (!ec) return sock.local_endpoint().port();
 	}
-	return 0;
+	throw std::runtime_error(
+		"All local ports were found occupied. You may have more open outlets on this machine "
+		"than your PortRange setting allows (see "
+		"https://labstreaminglayer.readthedocs.io/info/network-connectivity.html"
+		") or you have a problem with your network configuration.");
 }
 
-const std::string all_ports_bound_msg(
-	"All local ports were found occupied. You may have more open outlets on this machine than your "
-	"PortRange setting allows (see "
-	"https://labstreaminglayer.readthedocs.io/info/network-connectivity.html"
-	") or you have a problem with your network configuration.");
-
 uint16_t lsl::bind_port_in_range(asio::ip::udp::socket &sock, asio::ip::udp protocol) {
-	uint16_t port = bind_port_in_range_(sock, protocol);
-	if (!port) throw std::runtime_error(all_ports_bound_msg);
-	return port;
+	return bind_port_in_range_(sock, protocol);
 }
 
 uint16_t lsl::bind_and_listen_to_port_in_range(
 	asio::ip::tcp::acceptor &acc, asio::ip::tcp protocol, int backlog) {
 	uint16_t port = bind_port_in_range_(acc, protocol);
-	if (!port) throw std::runtime_error(all_ports_bound_msg);
 	acc.listen(backlog);
 	return port;
 }