px4_daemon: fixes for packet length computation

The enum change from uint8_t to an int avoids uninitialized bytes,
which led to valgrind warnings (no error though).

platforms/posix/src/px4_daemon/client.cpp

@@ -165,7 +165,7 @@ Client::_send_cmds(const int argc, const char **argv)
 	strcpy((char *)packet.payload.execute_msg.cmd, cmd_buf.c_str());
 
 	// The size is +1 because we want to include the null termination.
-	packet.header.payload_length = cmd_buf.size() + 1;
+	packet.header.payload_length = cmd_buf.size() + 1 + sizeof(packet.payload.execute_msg.is_atty);
 
 	_client_send_pipe_fd = open(get_client_send_pipe_path(_instance_id).c_str(), O_WRONLY);
 
@@ -214,7 +214,7 @@ Client::_listen()
 
 			// Again, we only read as much as we need because otherwise we need
 			// hold a buffer and parse it.
-			bytes_read = read(client_recv_pipe_fd, (char *)&packet_recv + bytes_read, payload_to_read);
+			bytes_read = read(client_recv_pipe_fd, ((uint8_t *)&packet_recv) + bytes_read, payload_to_read);
 
 			if (bytes_read > 0) {
 
@@ -293,7 +293,7 @@ Client::_stdout_msg_packet(const client_recv_packet_s &packet)
 		return 0;
 
 	} else {
-		PX4_ERR("payload size wrong");
+		PX4_ERR("payload size wrong (%i > %i)", packet.header.payload_length, sizeof(packet.payload.stdout_msg.text));
 		return -1;
 	}
 }

platforms/posix/src/px4_daemon/pipe_protocol.cpp

@@ -53,7 +53,7 @@ namespace px4_daemon
 
 unsigned get_client_send_packet_length(const client_send_packet_s *packet)
 {
-	return sizeof(client_send_packet_s) - sizeof(packet->payload) + packet->header.payload_length + sizeof(uint8_t);
+	return sizeof(client_send_packet_s) - sizeof(packet->payload) + packet->header.payload_length;
 }
 
 unsigned get_client_recv_packet_length(const client_recv_packet_s *packet)

platforms/posix/src/px4_daemon/pipe_protocol.h

@@ -46,13 +46,16 @@ namespace px4_daemon
 
 static const unsigned RECV_PIPE_PATH_LEN = 64;
 
+// The packet size is no more than 512 bytes, because that is the minimum guaranteed size
+// for a pipe to avoid interleaving of messages when multiple clients write at the same time
+// (atomic writes).
 struct client_send_packet_s {
 	struct message_header_s {
-		enum class e_msg_id : uint8_t {
+		uint64_t client_uuid;
+		enum class e_msg_id : int {
 			EXECUTE,
 			KILL
 		} msg_id;
-		uint64_t client_uuid;
 		unsigned payload_length;
 	} header;
 
@@ -70,7 +73,7 @@ struct client_send_packet_s {
 // We have per client receiver a pipe with the uuid in its file path.
 struct client_recv_packet_s {
 	struct message_header_s {
-		enum class e_msg_id : uint8_t {
+		enum class e_msg_id : int {
 			RETVAL,
 			STDOUT
 		} msg_id;
@@ -82,7 +85,7 @@ struct client_recv_packet_s {
 			int retval;
 		} retval_msg;
 		struct stdout_msg_s {
-			uint8_t text[512 - sizeof(message_header_s)];
+			uint8_t text[512 - sizeof(message_header_s)]; ///< null-terminated string (payload_length includes the null)
 		} stdout_msg;
 	} payload;
 };

platforms/posix/src/px4_daemon/pxh.cpp

@@ -239,8 +239,6 @@ void Pxh::run_pxh()
 		}
 
 	}
-
-	return;
 }
 
 void Pxh::stop()