metrics: Move helper function to lib/metrics

It is a common function that a lot of subsystem can use which is to
format a label so move it out of the HS subsystem into the more generic
metrics library.

Signed-off-by: David Goulet <dgoulet@torproject.org>

2 files changed, 16 insertions, 0 deletions

diff --git a/src/lib/metrics/metrics_common.c b/src/lib/metrics/metrics_common.c
index 5941a4d892..c0352b6646 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) */