Add a MongoDB connector to the exporting engine (#8416)

* Copy files from the MongoDB backend

* Update the documentation

* Rename functions in the MongoDB backend

* Add the connector to the Netdata build

* Add an initializer and a worker

* Add specific configuration options

* Initialize the connector

* Add a ring buffer for inserting data to a MongoDB database

* Add unit tests

4 files changed, 385 insertions, 0 deletions

diff --git a/exporting/mongodb/Makefile.am b/exporting/mongodb/Makefile.am
new file mode 100644
index 0000000000..161784b8f6
--- /dev/null
+++ b/exporting/mongodb/Makefile.am
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+AUTOMAKE_OPTIONS = subdir-objects
+MAINTAINERCLEANFILES = $(srcdir)/Makefile.in
+
+dist_noinst_DATA = \
+    README.md \
+    $(NULL)
diff --git a/exporting/mongodb/README.md b/exporting/mongodb/README.md
new file mode 100644
index 0000000000..f8cb82e1ab
--- /dev/null
+++ b/exporting/mongodb/README.md
@@ -0,0 +1,31 @@
+# MongoDB exporting connector
+
+You can use the MongoDB connector and the experimental [exporting engine](../README.md) to archive your agent's metrics
+to a MongoDB database for long-term storage, further analysis, or correlation with data from other sources.
+
+## Prerequisites
+
+To use MongoDB as an external storage for long-term archiving, you should first
+[install](http://mongoc.org/libmongoc/current/installing.html) `libmongoc` 1.7.0 or higher. Next, re-install Netdata
+from the source, which detects that the required library is now available.
+
+## Configuration
+
+To enable data exporting to a MongoDB database, run `./edit-config exporting.conf`
+in the Netdata configuration directory and set the following options:
+
+```conf
+[mongodb:my_instance]
+    enabled = yes
+    destination = mongodb://<hostname>
+    database = your_database_name
+    collection = your_collection_name
+```
+
+You can find more information about the `destination` string URI format in the MongoDB
+[documentation](https://docs.mongodb.com/manual/reference/connection-string/)
+
+The default socket timeout depends on the exporting connector update interval. The timeout is 500 ms shorter than the
+interval (but not less than 1000 ms). You can alter the timeout using the `sockettimeoutms` MongoDB URI option.
+
+[![analytics](https://www.google-analytics.com/collect?v=1&aip=1&t=pageview&_s=1&ds=github&dr=https%3A%2F%2Fgithub.com%2Fnetdata%2Fnetdata&dl=https%3A%2F%2Fmy-netdata.io%2Fgithub%2Fexporting%2Fmongodb%2FREADME&_u=MAC~&cid=5792dfd7-8dc4-476b-af31-da2fdb9f93d2&tid=UA-64295674-3)](<>)
diff --git a/exporting/mongodb/mongodb.c b/exporting/mongodb/mongodb.c
new file mode 100644
index 0000000000..b10a8fa664
--- /dev/null
+++ b/exporting/mongodb/mongodb.c
@@ -0,0 +1,313 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#define EXPORTING_INTERNALS
+#include "mongodb.h"
+
+#define CONFIG_FILE_LINE_MAX ((CONFIG_MAX_NAME + CONFIG_MAX_VALUE + 1024) * 2)
+
+/**
+ * Initialize MongoDB connector specific data, including a ring buffer
+ *
+ * @param instance an instance data structure.
+ * @return Returns 0 on success, 1 on failure.
+ */
+int mongodb_init(struct instance *instance)
+{
+    struct mongodb_specific_config *connector_specific_config = instance->config.connector_specific_config;
+    mongoc_uri_t *uri;
+    bson_error_t bson_error;
+
+    if (unlikely(!connector_specific_config->collection || !*connector_specific_config->collection)) {
+        error("EXPORTING: collection name is a mandatory MongoDB parameter, but it is not configured");
+        return 1;
+    }
+
+    uri = mongoc_uri_new_with_error(instance->config.destination, &bson_error);
+    if (unlikely(!uri)) {
+        error(
+            "EXPORTING: failed to parse URI: %s. Error message: %s", instance->config.destination, bson_error.message);
+        return 1;
+    }
+
+    int32_t socket_timeout =
+        mongoc_uri_get_option_as_int32(uri, MONGOC_URI_SOCKETTIMEOUTMS, instance->config.timeoutms);
+    if (!mongoc_uri_set_option_as_int32(uri, MONGOC_URI_SOCKETTIMEOUTMS, socket_timeout)) {
+        error("EXPORTING: failed to set %s to the value %d", MONGOC_URI_SOCKETTIMEOUTMS, socket_timeout);
+        return 1;
+    };
+
+    struct mongodb_specific_data *connector_specific_data =
+        (struct mongodb_specific_data *)instance->connector_specific_data;
+
+    connector_specific_data->client = mongoc_client_new_from_uri(uri);
+    if (unlikely(!connector_specific_data->client)) {
+        error("EXPORTING: failed to create a new client");
+        return 1;
+    }
+
+    if (!mongoc_client_set_appname(connector_specific_data->client, "netdata")) {
+        error("EXPORTING: failed to set client appname");
+    };
+
+    connector_specific_data->collection = mongoc_client_get_collection(
+        connector_specific_data->client, connector_specific_config->database, connector_specific_config->collection);
+
+    mongoc_uri_destroy(uri);
+
+    // create a ring buffer
+    struct bson_buffer *first_buffer = NULL;
+
+    if (instance->config.buffer_on_failures < 2)
+        instance->config.buffer_on_failures = 1;
+    else
+        instance->config.buffer_on_failures -= 1;
+
+    for (int i = 0; i < instance->config.buffer_on_failures; i++) {
+        struct bson_buffer *current_buffer = callocz(1, sizeof(struct bson_buffer));
+
+        if (!connector_specific_data->first_buffer)
+            first_buffer = current_buffer;
+        else
+            current_buffer->next = connector_specific_data->first_buffer;
+
+        connector_specific_data->first_buffer = current_buffer;
+    }
+
+    first_buffer->next = connector_specific_data->first_buffer;
+    connector_specific_data->last_buffer = connector_specific_data->first_buffer;
+
+    return 0;
+}
+
+/**
+ * Clean a MongoDB connector instance up
+ *
+ * @param instance an instance data structure.
+ */
+void mongodb_cleanup(struct instance *instance)
+{
+    struct mongodb_specific_data *connector_specific_data =
+        (struct mongodb_specific_data *)instance->connector_specific_data;
+
+    mongoc_collection_destroy(connector_specific_data->collection);
+    mongoc_client_destroy(connector_specific_data->client);
+
+    return;
+}
+
+/**
+ * Initialize a MongoDB connector instance
+ *
+ * @param instance an instance data structure.
+ * @return Returns 0 on success, 1 on failure.
+ */
+int init_mongodb_instance(struct instance *instance)
+{
+    instance->worker = mongodb_connector_worker;
+
+    instance->start_batch_formatting = NULL;
+    instance->start_host_formatting = format_host_labels_json_plaintext;
+    instance->start_chart_formatting = NULL;
+
+    if (EXPORTING_OPTIONS_DATA_SOURCE(instance->config.options) == EXPORTING_SOURCE_DATA_AS_COLLECTED)
+        instance->metric_formatting = format_dimension_collected_json_plaintext;
+    else
+        instance->metric_formatting = format_dimension_stored_json_plaintext;
+
+    instance->end_chart_formatting = NULL;
+    instance->end_host_formatting = flush_host_labels;
+    instance->end_batch_formatting = format_batch_mongodb;
+
+    instance->send_header = NULL;
+    instance->check_response = NULL;
+
+    instance->buffer = (void *)buffer_create(0);
+    if (!instance->buffer) {
+        error("EXPORTING: cannot create buffer for MongoDB exporting connector instance %s", instance->config.name);
+        return 1;
+    }
+    if (uv_mutex_init(&instance->mutex))
+        return 1;
+    if (uv_cond_init(&instance->cond_var))
+        return 1;
+
+    struct mongodb_specific_data *connector_specific_data = callocz(1, sizeof(struct mongodb_specific_data));
+    instance->connector_specific_data = (void *)connector_specific_data;
+
+    instance->config.timeoutms =
+        (instance->config.update_every >= 2) ? (instance->engine->config.update_every * MSEC_PER_SEC - 500) : 1000;
+
+    if (!instance->engine->mongoc_initialized) {
+        mongoc_init();
+        instance->engine->mongoc_initialized = 1;
+    }
+
+    if (unlikely(mongodb_init(instance))) {
+        error("EXPORTING: cannot initialize MongoDB exporting connector");
+        return 1;
+    }
+
+    return 0;
+}
+
+/**
+ * Free an array of BSON structures
+ *
+ * @param insert an array of documents.
+ * @param documents_inserted the number of documents inserted.
+ */
+void free_bson(bson_t **insert, size_t documents_inserted)
+{
+    size_t i;
+
+    for (i = 0; i < documents_inserted; i++)
+        bson_destroy(insert[i]);
+
+    freez(insert);
+}
+
+/**
+ * Format a batch for the MongoDB connector
+ *
+ * @param instance an instance data structure.
+ * @return Returns 0 on success, 1 on failure.
+ */
+int format_batch_mongodb(struct instance *instance)
+{
+    struct mongodb_specific_data *connector_specific_data =
+        (struct mongodb_specific_data *)instance->connector_specific_data;
+    struct stats *stats = &instance->stats;
+
+    bson_t **insert = connector_specific_data->last_buffer->insert;
+    if (insert) {
+        // ring buffer is full, reuse the oldest element
+        connector_specific_data->first_buffer = connector_specific_data->first_buffer->next;
+        free_bson(insert, connector_specific_data->last_buffer->documents_inserted);
+    }
+    insert = callocz((size_t)stats->chart_buffered_metrics, sizeof(bson_t *));
+    connector_specific_data->last_buffer->insert = insert;
+
+    BUFFER *buffer = (BUFFER *)instance->buffer;
+    char *start = (char *)buffer_tostring(buffer);
+    char *end = start;
+
+    size_t documents_inserted = 0;
+
+    while (*end && documents_inserted <= (size_t)stats->chart_buffered_metrics) {
+        while (*end && *end != '\n')
+            end++;
+
+        if (likely(*end)) {
+            *end = '\0';
+            end++;
+        } else {
+            break;
+        }
+
+        bson_error_t bson_error;
+        insert[documents_inserted] = bson_new_from_json((const uint8_t *)start, -1, &bson_error);
+
+        if (unlikely(!insert[documents_inserted])) {
+            error("EXPORTING: %s", bson_error.message);
+            free_bson(insert, documents_inserted);
+            return 1;
+        }
+
+        start = end;
+
+        documents_inserted++;
+    }
+
+    buffer_flush(buffer);
+
+    connector_specific_data->last_buffer->documents_inserted = documents_inserted;
+    connector_specific_data->last_buffer = connector_specific_data->last_buffer->next;
+
+    return 0;
+}
+
+/**
+ * MongoDB connector worker
+ *
+ * Runs in a separate thread for every instance.
+ *
+ * @param instance_p an instance data structure.
+ */
+void mongodb_connector_worker(void *instance_p)
+{
+    struct instance *instance = (struct instance *)instance_p;
+    struct mongodb_specific_config *connector_specific_config = instance->config.connector_specific_config;
+    struct mongodb_specific_data *connector_specific_data =
+        (struct mongodb_specific_data *)instance->connector_specific_data;
+
+    while (!netdata_exit) {
+        struct stats *stats = &instance->stats;
+
+        uv_mutex_lock(&instance->mutex);
+        uv_cond_wait(&instance->cond_var, &instance->mutex);
+
+        bson_t **insert = connector_specific_data->first_buffer->insert;
+        size_t documents_inserted = connector_specific_data->first_buffer->documents_inserted;
+
+        connector_specific_data->first_buffer->insert = NULL;
+        connector_specific_data->first_buffer->documents_inserted = 0;
+        connector_specific_data->first_buffer = connector_specific_data->first_buffer->next;
+
+        uv_mutex_unlock(&instance->mutex);
+
+        size_t data_size = 0;
+        for (size_t i = 0; i < documents_inserted; i++) {
+            data_size += insert[i]->len;
+        }
+
+        debug(
+            D_BACKEND,
+            "EXPORTING: mongodb_insert(): destination = %s, database = %s, collection = %s, data size = %zu",
+            instance->config.destination,
+            connector_specific_config->database,
+            connector_specific_config->collection,
+            data_size);
+
+        if (unlikely(documents_inserted == 0))
+            continue;
+
+        bson_error_t bson_error;
+        if (likely(mongoc_collection_insert_many(
+                connector_specific_data->collection,
+                (const bson_t **)insert,
+                documents_inserted,
+                NULL,
+                NULL,
+                &bson_error))) {
+            stats->chart_sent_bytes += data_size;
+            stats->chart_transmission_successes++;
+            stats->chart_receptions++;
+        } else {
+            // oops! we couldn't send (all or some of the) data
+            error("EXPORTING: %s", bson_error.message);
+            error(
+                "EXPORTING: failed to write data to the database '%s'. "
+                "Willing to write %zu bytes, wrote %zu bytes.",
+                instance->config.destination, data_size, 0UL);
+
+            stats->chart_transmission_failures++;
+            stats->chart_data_lost_events++;
+            stats->chart_lost_bytes += data_size;
+            stats->chart_lost_metrics += stats->chart_buffered_metrics;
+        }
+
+        free_bson(insert, documents_inserted);
+
+        if (unlikely(netdata_exit))
+            break;
+
+        stats->chart_sent_bytes += data_size;
+        stats->chart_sent_metrics = stats->chart_buffered_metrics;
+
+#ifdef UNIT_TESTING
+        break;
+#endif
+    }
+
+    mongodb_cleanup(instance);
+}
diff --git a/exporting/mongodb/mongodb.h b/exporting/mongodb/mongodb.h
new file mode 100644
index 0000000000..0f23705f55
--- /dev/null
+++ b/exporting/mongodb/mongodb.h
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#ifndef NETDATA_EXPORTING_MONGODB_H
+#define NETDATA_EXPORTING_MONGODB_H
+
+#include "exporting/exporting_engine.h"
+#include "exporting/json/json.h"
+#include <mongoc.h>
+
+struct bson_buffer {
+    bson_t **insert;
+    size_t documents_inserted;
+
+    struct bson_buffer *next;
+};
+
+struct mongodb_specific_data {
+    mongoc_client_t *client;
+    mongoc_collection_t *collection;
+
+    bson_t **current_insert;
+    struct bson_buffer *first_buffer;
+    struct bson_buffer *last_buffer;
+};
+
+int mongodb_init(struct instance *instance);
+void mongodb_cleanup(struct instance *instance);
+
+int init_mongodb_instance(struct instance *instance);
+int format_batch_mongodb(struct instance *instance);
+void mongodb_connector_worker(void *instance_p);
+
+#endif //NETDATA_EXPORTING_MONGODB_H