logging: backend: mqtt

Added MQTT logging backend

Signed-off-by: Arif Balik <arifbalik@outlook.com>

Author: arifbalik

include/zephyr/logging/log_backend_mqtt.h

@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2024 Arif Balik <arifbalik@outlook.com>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_LOGGING_LOG_BACKEND_MQTT_H_
+#define ZEPHYR_INCLUDE_LOGGING_LOG_BACKEND_MQTT_H_
+
+#include <zephyr/net/mqtt.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief MQTT log backend API
+ * @defgroup log_backend_mqtt MQTT log backend API
+ * @ingroup log_backend
+ * @{
+ */
+
+/**
+ * @brief Set the MQTT client instance to be able to publish application's log messages to broker.
+ *
+ * This function allows the application to provide its own initialized
+ * MQTT client to the log backend. The backend will use this client
+ * exclusively for publishing log messages via mqtt_publish().
+ *
+ * @param client Pointer to an initialized and connected MQTT client.
+ *               The client must remain valid for the lifetime of the
+ *               log backend usage. Pass NULL to disable MQTT logging.
+ *
+ * @return 0 on success, negative error code on failure.
+ *
+ * @note The MQTT client must be connected before calling this function.
+ * @note The backend will not manage the client connection - this is the
+ *       responsibility of the application.
+ * @note The backend will only use mqtt_publish() and will not perform
+ *       any other operations on the client.
+ */
+int log_backend_mqtt_client_set(struct mqtt_client *client);
+
+/**
+ * @brief Set the MQTT topic to which log messages will be published.
+ *
+ * Allows the application to specify the MQTT topic that the log backend
+ * will use for publishing log messages to.
+ *
+ * @param topic Pointer to a null-terminated string containing the MQTT topic.
+ *              The topic must remain valid for the lifetime of the log backend usage.
+ *
+ * @return 0 on success, negative error code on failure.
+ *
+ * @note The topic must be a valid UTF-8 string, null-terminated and should not exceed
+ *       the maximum length supported by the MQTT broker.
+ */
+int log_backend_mqtt_topic_set(const char *topic);
+
+/**
+ * @}
+ */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* ZEPHYR_INCLUDE_LOGGING_LOG_BACKEND_MQTT_H_ */

subsys/logging/backends/CMakeLists.txt

@@ -25,6 +25,11 @@ zephyr_sources_ifdef(
   log_backend_fs.c
 )
 
+zephyr_sources_ifdef(
+  CONFIG_LOG_BACKEND_MQTT
+  log_backend_mqtt.c
+)
+
 zephyr_sources_ifdef(
   CONFIG_LOG_BACKEND_NATIVE_POSIX
   log_backend_native_posix.c

subsys/logging/backends/Kconfig

@@ -8,6 +8,7 @@ rsource "Kconfig.adsp_mtrace"
 rsource "Kconfig.ble"
 rsource "Kconfig.efi_console"
 rsource "Kconfig.fs"
+rsource "Kconfig.mqtt"
 rsource "Kconfig.native_posix"
 rsource "Kconfig.net"
 rsource "Kconfig.ws"

subsys/logging/backends/Kconfig.mqtt

@@ -0,0 +1,49 @@
+# Copyright (c) 2024 Arif Balik <arifbalik@outlook.com>
+# SPDX-License-Identifier: Apache-2.0
+
+config LOG_BACKEND_MQTT
+	bool "MQTT backend"
+	depends on MQTT_LIB && !LOG_MODE_IMMEDIATE
+	help
+	  Send log messages to an MQTT broker using an external MQTT client.
+	  This backend publishes log messages to a configurable MQTT topic
+	  using an MQTT client provided by the application via the
+	  log_backend_mqtt_client_set() API. The application is responsible
+	  for initializing, connecting, and managing the MQTT client lifecycle.
+
+if LOG_BACKEND_MQTT
+
+config LOG_BACKEND_MQTT_TOPIC_DEFAULT
+	string "Default MQTT topic for log messages"
+	default "zephyr/logs"
+	help
+	  Default MQTT topic for log messages. Use log backend MQTT API to change it at runtime.
+
+config LOG_BACKEND_MQTT_QOS
+	int "MQTT Quality of Service level"
+	default 0
+	range 0 2
+	help
+	  QoS level for published log messages:
+	  0 - At most once delivery (fire and forget)
+	  1 - At least once delivery (acknowledged delivery)
+	  2 - Exactly once delivery (assured delivery)
+
+config LOG_BACKEND_MQTT_RETAIN
+	bool "Retain MQTT messages"
+	help
+	  When enabled, published log messages will be retained by the broker
+	  and delivered to new subscribers immediately upon subscription.
+
+config LOG_BACKEND_MQTT_MAX_MSG_SIZE
+	int "Maximum log message size"
+	default 256
+	range 64 1024
+	help
+	  Maximum size of a single log message in bytes.
+
+backend = MQTT
+backend-str = mqtt
+source "subsys/logging/Kconfig.template.log_format_config"
+
+endif # LOG_BACKEND_MQTT

subsys/logging/backends/log_backend_mqtt.c

@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 2024 Arif Balik <arifbalik@outlook.com>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/logging/log.h>
+LOG_MODULE_REGISTER(log_backend_mqtt, CONFIG_LOG_DEFAULT_LEVEL);
+
+#include <zephyr/kernel.h>
+#include <zephyr/logging/log_backend.h>
+#include <zephyr/logging/log_ctrl.h>
+#include <zephyr/logging/log_backend_std.h>
+#include <zephyr/logging/log_backend_mqtt.h>
+#include <zephyr/logging/log_core.h>
+#include <zephyr/logging/log_output.h>
+#include <zephyr/net/mqtt.h>
+#include <zephyr/sys/util.h>
+#include <zephyr/random/random.h>
+
+#include <string.h>
+#include <errno.h>
+
+static bool panic;
+static char *mqtt_topic = CONFIG_LOG_BACKEND_MQTT_TOPIC_DEFAULT;
+static uint8_t log_buf[CONFIG_LOG_BACKEND_MQTT_MAX_MSG_SIZE];
+static uint32_t log_format_current = CONFIG_LOG_BACKEND_MQTT_OUTPUT_DEFAULT;
+
+static int log_output_func(uint8_t *data, size_t length, void *output_ctx)
+{
+	__ASSERT(output_ctx != NULL, "Output context must not be NULL");
+
+	struct mqtt_client *client = (struct mqtt_client *)output_ctx;
+	struct mqtt_publish_param param = {0};
+
+	param.message.topic.topic.utf8 = (uint8_t *)mqtt_topic;
+	param.message.topic.topic.size = strlen(mqtt_topic);
+	param.message.topic.qos = CONFIG_LOG_BACKEND_MQTT_QOS;
+	param.message.payload.data = data;
+	param.message.payload.len = length;
+	param.retain_flag = IS_ENABLED(CONFIG_LOG_BACKEND_MQTT_RETAIN);
+
+#if (CONFIG_LOG_BACKEND_MQTT_QOS > MQTT_QOS_0_AT_MOST_ONCE)
+	param.message_id = sys_rand32_get();
+#endif
+
+	int ret = mqtt_publish(client, &param);
+
+	if (ret != 0) {
+		return ret;
+	}
+
+	return length;
+}
+
+LOG_OUTPUT_DEFINE(log_output_mqtt, log_output_func, log_buf, sizeof(log_buf));
+
+static void mqtt_backend_process(const struct log_backend *const backend,
+				 union log_msg_generic *msg)
+{
+	if (panic) {
+		return;
+	}
+
+	uint32_t flags = log_backend_std_get_flags();
+
+	log_format_func_t log_output_func = log_format_func_t_get(log_format_current);
+
+	log_output_ctx_set(&log_output_mqtt, backend->cb->ctx);
+
+	log_output_func(&log_output_mqtt, &msg->log, flags);
+}
+
+static int mqtt_backend_format_set(const struct log_backend *const backend, uint32_t log_type)
+{
+	ARG_UNUSED(backend);
+	log_format_current = log_type;
+	return 0;
+}
+
+static void mqtt_backend_panic(const struct log_backend *const backend)
+{
+	ARG_UNUSED(backend);
+	panic = true;
+}
+
+const struct log_backend_api log_backend_mqtt_api = {
+	.process = mqtt_backend_process,
+	.format_set = mqtt_backend_format_set,
+	.panic = mqtt_backend_panic,
+};
+
+LOG_BACKEND_DEFINE(log_backend_mqtt, log_backend_mqtt_api, false);
+
+int log_backend_mqtt_client_set(struct mqtt_client *client)
+{
+	log_backend_disable(&log_backend_mqtt);
+
+	if (client != NULL) {
+		log_backend_enable(&log_backend_mqtt, (void *)client, CONFIG_LOG_MAX_LEVEL);
+	}
+
+	return 0;
+}
+
+int log_backend_mqtt_topic_set(const char *topic)
+{
+	if (topic == NULL || strlen(topic) == 0) {
+		return -EINVAL;
+	}
+
+	mqtt_topic = topic;
+
+	return 0;
+}