net: new function to determine connected socket

src/knot/server/net.c

@@ -143,3 +143,10 @@ int net_connected_socket(int type, const struct sockaddr_storage *dst_addr,
 
 	return socket;
 }
+
+int net_is_connected(int fd)
+{
+	struct sockaddr_in6 ss;
+	socklen_t len = sizeof(ss);
+	return getpeername(fd, &ss, &len) == 0;
+}

src/knot/server/net.h

@@ -65,6 +65,16 @@ int net_bound_socket(int type, const struct sockaddr_storage *ss);
 int net_connected_socket(int type, const struct sockaddr_storage *dst_addr,
                          const struct sockaddr_storage *src_addr, unsigned flags);
 
+/*!
+ * \brief Return true if the socket is connected.
+ *
+ * @note This could be used to identify connected TCP from UDP sockets.
+ *
+ * \param fd Socket.
+ *
+ * \return true if connected
+ */
+int net_is_connected(int fd);
 
 #endif // _KNOTD_NET_H_