From 2d3de46a48ca24b092b46b2bee839374423217f0 Mon Sep 17 00:00:00 2001
From: Anton Zhurba <zhurba.anton@outlook.com>
Date: Sat, 21 Oct 2023 22:51:12 +0300
Subject: [PATCH] Add expire time to metrics in prometheus_exporter

---
 include/fluent-bit/flb_hash_table.h    |  2 ++
 plugins/out_prometheus_exporter/prom.c | 12 +++++++++++-
 plugins/out_prometheus_exporter/prom.h |  3 +++
 src/flb_hash_table.c                   | 27 ++++++++++++++++++++++++++
 4 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/include/fluent-bit/flb_hash_table.h b/include/fluent-bit/flb_hash_table.h
index 115088d4f6e..cf711024ecd 100644
--- a/include/fluent-bit/flb_hash_table.h
+++ b/include/fluent-bit/flb_hash_table.h
@@ -86,4 +86,6 @@ int flb_hash_table_del(struct flb_hash_table *ht, const char *key);
 int flb_hash_table_del_ptr(struct flb_hash_table *ht, const char *key, int key_len,
                            void *ptr);
 
+void flb_hash_table_clear(struct flb_hash_table *ht);
+
 #endif
diff --git a/plugins/out_prometheus_exporter/prom.c b/plugins/out_prometheus_exporter/prom.c
index d471d2bab57..deb12e9425c 100644
--- a/plugins/out_prometheus_exporter/prom.c
+++ b/plugins/out_prometheus_exporter/prom.c
@@ -97,7 +97,7 @@ static int cb_prom_init(struct flb_output_instance *ins,
     }
 
     /* Hash table for metrics */
-    ctx->ht_metrics = flb_hash_table_create(FLB_HASH_TABLE_EVICT_NONE, 32, 0);
+    ctx->ht_metrics = flb_hash_table_create_with_ttl(ctx->ttl, FLB_HASH_TABLE_EVICT_NONE, 32, 0);
     if (!ctx->ht_metrics) {
         flb_plg_error(ctx->ins, "could not initialize hash table for metrics");
         return -1;
@@ -179,6 +179,9 @@ static void cb_prom_flush(struct flb_event_chunk *event_chunk,
     struct cmt *cmt;
     struct prom_exporter *ctx = out_context;
 
+    /* Clear old metrics */
+    flb_hash_table_clear(ctx->ht_metrics);
+
     /*
      * A new set of metrics has arrived, perform decoding, apply labels,
      * convert to Prometheus text format and store the output in the
@@ -229,6 +232,7 @@ static void cb_prom_flush(struct flb_event_chunk *event_chunk,
 
     /* retrieve a full copy of all metrics */
     metrics = hash_format_metrics(ctx);
+
     if (!metrics) {
         flb_plg_error(ctx->ins, "could not retrieve metrics");
         FLB_OUTPUT_RETURN(FLB_ERROR);
@@ -281,6 +285,12 @@ static struct flb_config_map config_map[] = {
      "TCP port for listening for HTTP connections."
     },
 
+    {
+     FLB_CONFIG_MAP_TIME, "ttl", "0s",
+     0, FLB_TRUE, offsetof(struct prom_exporter, ttl),
+     "Expiring time for metrics"
+    },
+
     /* EOF */
     {0}
 };
diff --git a/plugins/out_prometheus_exporter/prom.h b/plugins/out_prometheus_exporter/prom.h
index 1cbab6a5940..5da4bfe2ac6 100644
--- a/plugins/out_prometheus_exporter/prom.h
+++ b/plugins/out_prometheus_exporter/prom.h
@@ -33,6 +33,9 @@ struct prom_exporter {
     /* add timestamp to every metric */
     int add_timestamp;
 
+    /* expiry time for metrics in the hash table */
+    time_t ttl;
+
     /* config reader for 'add_label' */
     struct mk_list *add_labels;
 
diff --git a/src/flb_hash_table.c b/src/flb_hash_table.c
index d31c4259179..0b01e75030f 100644
--- a/src/flb_hash_table.c
+++ b/src/flb_hash_table.c
@@ -537,3 +537,30 @@ int flb_hash_table_del(struct flb_hash_table *ht, const char *key)
 
     return 0;
 }
+
+void flb_hash_table_clear(struct flb_hash_table *ht)
+{
+    int i;
+    struct mk_list *tmp;
+    struct mk_list *head;
+    struct flb_hash_table_entry *entry;
+    struct flb_hash_table_chain *table;
+    time_t expiration;
+
+    if (ht->cache_ttl <= 0) {
+        return;
+    }
+
+    for (i = 0; i < ht->size; i++) {
+        table = &ht->table[i];
+        mk_list_foreach_safe(head, tmp, &table->chains) {
+            entry = mk_list_entry(head, struct flb_hash_table_entry, _head);
+            
+            expiration = entry->created + ht->cache_ttl;
+
+            if (time(NULL) > expiration) {
+                flb_hash_table_entry_free(ht, entry);
+            }
+        }
+    }
+}