6 files changed, 44 insertions, 7 deletions
diff --git a/src/lib/metrics/metrics_common.c b/src/lib/metrics/metrics_common.c
index 5941a4d892..f3f7e22d88 100644
--- a/src/lib/metrics/metrics_common.c
+++ b/src/lib/metrics/metrics_common.c
@@ -11,6 +11,7 @@
 #include "orconfig.h"
 
 #include "lib/log/util_bug.h"
+#include "lib/string/printf.h"
 
 #include "lib/metrics/metrics_common.h"
 
@@ -27,3 +28,15 @@ metrics_type_to_str(const metrics_type_t type)
     tor_assert_unreached();
   }
 }
+
+/** Return a static buffer pointer that contains a formatted label on the form
+ * of key=value.
+ *
+ * Subsequent call to this function invalidates the previous buffer. */
+const char *
+metrics_format_label(const char *key, const char *value)
+{
+  static char buf[128];
+  tor_snprintf(buf, sizeof(buf), "%s=\"%s\"", key, value);
+  return buf;
+}
diff --git a/src/lib/metrics/metrics_common.h b/src/lib/metrics/metrics_common.h
index 59aa9c0e90..3644ad3d50 100644
--- a/src/lib/metrics/metrics_common.h
+++ b/src/lib/metrics/metrics_common.h
@@ -42,4 +42,7 @@ typedef struct metrics_gauge_t {
 
 const char *metrics_type_to_str(const metrics_type_t type);
 
+/* Helpers. */
+const char *metrics_format_label(const char *key, const char *value);
+
 #endif /* !defined(TOR_LIB_METRICS_METRICS_COMMON_H) */
diff --git a/src/lib/metrics/metrics_store.c b/src/lib/metrics/metrics_store.c
index 4cab5245f3..33b1780438 100644
--- a/src/lib/metrics/metrics_store.c
+++ b/src/lib/metrics/metrics_store.c
@@ -34,7 +34,8 @@ struct metrics_store_t {
 };
 
 /** Function pointer to the format function of a specific driver. */
-typedef void (fmt_driver_fn_t)(const metrics_store_entry_t *, buf_t *);
+typedef void (fmt_driver_fn_t)(const metrics_store_entry_t *, buf_t *,
+                               bool no_comment);
 
 /** Helper: Free a single entry in a metrics_store_t taking a void pointer
  * parameter. */
@@ -47,6 +48,8 @@ metrics_store_free_void(void *p)
   smartlist_free(list);
 }
 
+#include <stdio.h>
+
 /** Put the given store output in the buffer data and use the format function
  * given in fmt to get it for each entry. */
 static void
@@ -57,8 +60,11 @@ get_output(const metrics_store_t *store, buf_t *data, fmt_driver_fn_t fmt)
   tor_assert(fmt);
 
   STRMAP_FOREACH(store->entries, key, const smartlist_t *, entries) {
+    /* Indicate that we've formatted the coment already for the entries. */
+    bool comment_formatted = false;
     SMARTLIST_FOREACH_BEGIN(entries, const metrics_store_entry_t *, entry) {
-      fmt(entry, data);
+      fmt(entry, data, comment_formatted);
+      comment_formatted = true;
     } SMARTLIST_FOREACH_END(entry);
   } STRMAP_FOREACH_END;
 }
@@ -138,3 +144,14 @@ metrics_store_get_output(const metrics_format_t fmt,
     // LCOV_EXCL_STOP
   }
 }
+
+/** Reset a store as in free its content. */
+void
+metrics_store_reset(metrics_store_t *store)
+{
+  if (store == NULL) {
+    return;
+  }
+  strmap_free(store->entries, metrics_store_free_void);
+  store->entries = strmap_new();
+}
diff --git a/src/lib/metrics/metrics_store.h b/src/lib/metrics/metrics_store.h
index 42bc56e8fd..d85f484bd6 100644
--- a/src/lib/metrics/metrics_store.h
+++ b/src/lib/metrics/metrics_store.h
@@ -28,6 +28,7 @@ metrics_store_t *metrics_store_new(void);
 metrics_store_entry_t *metrics_store_add(metrics_store_t *store,
                                          metrics_type_t type,
                                          const char *name, const char *help);
+void metrics_store_reset(metrics_store_t *store);
 
 /* Accessors. */
 smartlist_t *metrics_store_get_all(const metrics_store_t *store,
diff --git a/src/lib/metrics/prometheus.c b/src/lib/metrics/prometheus.c
index 65241ed6c1..aac23ac92e 100644
--- a/src/lib/metrics/prometheus.c
+++ b/src/lib/metrics/prometheus.c
@@ -42,14 +42,17 @@ format_labels(smartlist_t *labels)
 
 /** Format the given entry in to the buffer data. */
 void
-prometheus_format_store_entry(const metrics_store_entry_t *entry, buf_t *data)
+prometheus_format_store_entry(const metrics_store_entry_t *entry, buf_t *data,
+                              bool no_comment)
 {
   tor_assert(entry);
   tor_assert(data);
 
-  buf_add_printf(data, "# HELP %s %s\n", entry->name, entry->help);
-  buf_add_printf(data, "# TYPE %s %s\n", entry->name,
-                 metrics_type_to_str(entry->type));
+  if (!no_comment) {
+    buf_add_printf(data, "# HELP %s %s\n", entry->name, entry->help);
+    buf_add_printf(data, "# TYPE %s %s\n", entry->name,
+                   metrics_type_to_str(entry->type));
+  }
   buf_add_printf(data, "%s%s %" PRIi64 "\n", entry->name,
                  format_labels(entry->labels),
                  metrics_store_entry_get_value(entry));
diff --git a/src/lib/metrics/prometheus.h b/src/lib/metrics/prometheus.h
index 19770e7911..faa7681daa 100644
--- a/src/lib/metrics/prometheus.h
+++ b/src/lib/metrics/prometheus.h
@@ -13,6 +13,6 @@
 #include "lib/metrics/metrics_store_entry.h"
 
 void prometheus_format_store_entry(const metrics_store_entry_t *entry,
-                                   buf_t *data);
+                                   buf_t *data, bool no_comment);
 
 #endif /* !defined(TOR_LIB_METRICS_PROMETHEUS_H) */