logger: add unit test for ULog INFO message serialization

Add a gtest that validates the exact binary layout of INFO and
INFO_MULTIPLE messages against the ULog spec. This exercises the same
packing logic as write_info/write_info_multiple and will catch any
accidental changes to the wire format (e.g. including a null terminator
in msg_size).

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

src/modules/logger/CMakeLists.txt

@@ -60,3 +60,5 @@ px4_add_module(
 		version
 		component_general_json # for checksums.h
 	)
+
+px4_add_unit_gtest(SRC ULogMessageInfoTest.cpp)

src/modules/logger/ULogMessageInfoTest.cpp

@@ -0,0 +1,106 @@
+/****************************************************************************
+ *
+ *   Copyright (C) 2025 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 <gtest/gtest.h>
+#include <cstdio>
+#include <cstring>
+#include "messages.h"
+
+TEST(ULogMessageInfo, InfoMessageLayout)
+{
+	const char *name  = "hello";
+	const char *value = "world";
+	const size_t vlen = strlen(value);
+
+	ulog_message_info_s msg = {};
+	uint8_t *buffer = reinterpret_cast<uint8_t *>(&msg);
+	msg.msg_type = static_cast<uint8_t>(ULogMessageType::INFO);
+
+	msg.key_len = snprintf(msg.key_value_str, sizeof(msg.key_value_str),
+			       "char[%zu] %s", vlen, name);
+	size_t msg_size = sizeof(msg) - sizeof(msg.key_value_str) + msg.key_len;
+
+	ASSERT_LT(vlen, sizeof(msg) - msg_size);
+	memcpy(&buffer[msg_size], value, vlen);
+	msg_size += vlen;
+
+	msg.msg_size = msg_size - ULOG_MSG_HEADER_LEN;
+
+	// msg_size == key_len + vlen + 1 (the +1 is the key_len field itself)
+	EXPECT_EQ(msg.msg_size, msg.key_len + vlen + 1);
+	EXPECT_EQ(msg.msg_type, static_cast<uint8_t>('I'));
+
+	const char expected_key[] = "char[5] hello";
+	EXPECT_EQ(msg.key_len, strlen(expected_key));
+
+	const size_t header_size = sizeof(msg) - sizeof(msg.key_value_str);
+	const uint8_t *value_start = &buffer[header_size + msg.key_len];
+	EXPECT_EQ(memcmp(value_start, "world", vlen), 0);
+
+	// msg_size must not account for a null terminator
+	EXPECT_EQ(msg_size, header_size + msg.key_len + vlen);
+}
+
+TEST(ULogMessageInfo, InfoMultipleMessageLayout)
+{
+	const char *name  = "ver";
+	const char *value = "1.0";
+	const size_t vlen = strlen(value);
+
+	ulog_message_info_multiple_s msg = {};
+	uint8_t *buffer = reinterpret_cast<uint8_t *>(&msg);
+	msg.msg_type = static_cast<uint8_t>(ULogMessageType::INFO_MULTIPLE);
+	msg.is_continued = false;
+
+	msg.key_len = snprintf(msg.key_value_str, sizeof(msg.key_value_str),
+			       "char[%zu] %s", vlen, name);
+	size_t msg_size = sizeof(msg) - sizeof(msg.key_value_str) + msg.key_len;
+
+	ASSERT_LT(vlen, sizeof(msg) - msg_size);
+	memcpy(&buffer[msg_size], value, vlen);
+	msg_size += vlen;
+
+	msg.msg_size = msg_size - ULOG_MSG_HEADER_LEN;
+
+	const size_t header_size = sizeof(msg) - sizeof(msg.key_value_str);
+	EXPECT_EQ(msg.msg_size, msg_size - ULOG_MSG_HEADER_LEN);
+	EXPECT_EQ(msg.msg_type, static_cast<uint8_t>('M'));
+
+	const char expected_key[] = "char[3] ver";
+	EXPECT_EQ(msg.key_len, strlen(expected_key));
+
+	const uint8_t *value_start = &buffer[header_size + msg.key_len];
+	EXPECT_EQ(memcmp(value_start, "1.0", vlen), 0);
+
+	EXPECT_EQ(msg_size, header_size + msg.key_len + vlen);
+}