mavlink: support receiving multi-chunk statustexts

This adds support for mavlink statustext messages arriving in multiple
chunks.

src/modules/mavlink/MavlinkStatustextHandler.cpp

@@ -0,0 +1,121 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2021 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+#include "MavlinkStatustextHandler.hpp"
+#include <mathlib/mathlib.h>
+
+bool MavlinkStatustextHandler::should_publish_previous(const mavlink_statustext_t &msg_statustext)
+{
+	// Check if the previous message has not been published yet. This can
+	// happen if the last chunk has been dropped, let's publish what we have.
+	if (_last_log_id > 0 && msg_statustext.id != _last_log_id) {
+		// We add a note that a part is missing at the end.
+		const size_t offset = strlen(_log_msg.text);
+		strncpy(_log_msg.text + offset, "[ missing ... ]",
+			sizeof(_log_msg.text) - offset);
+		_log_msg.text[sizeof(_log_msg.text) - 1] = '\0';
+
+		return true;
+	}
+
+	return false;
+}
+
+bool MavlinkStatustextHandler::should_publish_current(const mavlink_statustext_t &msg_statustext, const uint64_t &now)
+{
+	if (msg_statustext.id > 0) {
+		// Multi statustext message.
+		if (_last_log_id != msg_statustext.id) {
+			// On the first one arriving, we save the timestamp and severity.
+			_log_msg.timestamp = now;
+			_log_msg.severity = msg_statustext.severity;
+		}
+
+		if (msg_statustext.chunk_seq == 0) {
+			// We start from 0 with a new message.
+			strncpy(_log_msg.text, msg_statustext.text,
+				math::min(sizeof(_log_msg.text), sizeof(msg_statustext.text)));
+			_log_msg.text[sizeof(msg_statustext.text)] = '\0';
+
+		} else {
+			if (msg_statustext.chunk_seq != _last_log_chunk_seq + 1) {
+				const size_t offset = strlen(_log_msg.text);
+				strncpy(_log_msg.text + offset, "[ missing ... ]",
+					sizeof(_log_msg.text) - offset);
+				_log_msg.text[sizeof(_log_msg.text) - offset - 1] = '\0';
+			}
+
+			// We add a consecutive chunk.
+			const size_t offset = strlen(_log_msg.text);
+			const size_t max_to_add = math::min(sizeof(_log_msg.text) - offset - 1, sizeof(msg_statustext.text));
+			strncpy(_log_msg.text + offset, msg_statustext.text, max_to_add);
+			_log_msg.text[math::min(offset + max_to_add, sizeof(_log_msg.text) - 1)] = '\0';
+		}
+
+		_last_log_chunk_seq = msg_statustext.chunk_seq;
+
+		const bool publication_message_is_full = sizeof(_log_msg.text) - 1 == strlen(_log_msg.text);
+		const bool found_zero_termination = strnlen(msg_statustext.text,
+						    sizeof(msg_statustext.text)) < sizeof(msg_statustext.text);
+
+		if (publication_message_is_full || found_zero_termination) {
+			_last_log_id = 0;
+			_last_log_chunk_seq = -1;
+			return true;
+
+		} else {
+			_last_log_id = msg_statustext.id;
+			return false;
+		}
+
+	} else {
+		// Single statustext message.
+		_log_msg.timestamp = now;
+		_log_msg.severity = msg_statustext.severity;
+
+		static_assert(sizeof(_log_msg.text) > sizeof(msg_statustext.text),
+			      "_log_msg.text not big enough to hold msg_statustext.text");
+
+		strncpy(_log_msg.text, msg_statustext.text,
+			math::min(sizeof(_log_msg.text),
+				  sizeof(msg_statustext.text)));
+
+		// We need to 0-terminate after the copied text which does not have to be
+		// 0-terminated on the wire.
+		_log_msg.text[sizeof(msg_statustext.text) - 1] = '\0';
+
+		_last_log_id = 0;
+		return true;
+
+	}
+}