-int speaker_recv(int fd, struct speaker_message *sm, int *datafd);
-/* Receive a message. If DATAFD is not null then can receive an FD. Return 0
- * on EOF, +ve if a message is read, -1 on EAGAIN, terminates on any other
- * error. */
+/** @brief A connection for track @c id arrived */
+#define SM_ARRIVED 134
+
+void speaker_send(int fd, const struct speaker_message *sm);
+/* Send a message. */
+
+int speaker_recv(int fd, struct speaker_message *sm);
+/* Receive a message. Return 0 on EOF, +ve if a message is read, -1 on EAGAIN,
+ * terminates on any other error. */