From bc16feb6cf0aefd4f04687e35320184112186a8d Mon Sep 17 00:00:00 2001
From: David Ashpole <dashpole@google.com>
Date: Fri, 1 Sep 2023 17:39:55 +0000
Subject: [PATCH] add _total suffix to prometheus counters

---
 CHANGELOG.md                                  |  3 ++
 .../exporters/prometheus/exporter_utils.h     |  2 +
 exporters/prometheus/src/exporter_utils.cc    | 41 +++++++++++++------
 .../prometheus/test/exporter_utils_test.cc    |  2 +-
 4 files changed, 35 insertions(+), 13 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0c4ce6f45f..71ac83b1a0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,9 @@ Increment the:
 
 ## [Unreleased]
 
+* [EXPORTER] Add _total suffixes to Prometheus counters
+  [#2288](https://github.com/open-telemetry/opentelemetry-cpp/pull/2288)
+
 ## [1.11.0] 2023-08-21
 
 * [BUILD] Fix more cases for symbol name for 32-bit win32 DLL build
diff --git a/exporters/prometheus/include/opentelemetry/exporters/prometheus/exporter_utils.h b/exporters/prometheus/include/opentelemetry/exporters/prometheus/exporter_utils.h
index ce7f0a1191..9ca7a5d7e1 100644
--- a/exporters/prometheus/include/opentelemetry/exporters/prometheus/exporter_utils.h
+++ b/exporters/prometheus/include/opentelemetry/exporters/prometheus/exporter_utils.h
@@ -44,6 +44,8 @@ class PrometheusExporterUtils
   static opentelemetry::sdk::metrics::AggregationType getAggregationType(
       const opentelemetry::sdk::metrics::PointType &point_type);
 
+  inline bool endsWith(std::string const & value, std::string const & ending);
+
   /**
    * Translate the OTel metric type to Prometheus metric type
    */
diff --git a/exporters/prometheus/src/exporter_utils.cc b/exporters/prometheus/src/exporter_utils.cc
index 966d665df6..a44c1b64b3 100644
--- a/exporters/prometheus/src/exporter_utils.cc
+++ b/exporters/prometheus/src/exporter_utils.cc
@@ -38,24 +38,35 @@ std::vector<prometheus_client::MetricFamily> PrometheusExporterUtils::TranslateT
   {
     for (const auto &metric_data : instrumentation_info.metric_data_)
     {
-      auto origin_name = metric_data.instrument_descriptor.name_;
-      auto unit        = metric_data.instrument_descriptor.unit_;
-      auto sanitized   = SanitizeNames(origin_name);
+      if (metric_data.point_data_attr_.empty()) {
+        continue;
+      }
       prometheus_client::MetricFamily metric_family;
+      auto front        = metric_data.point_data_attr_.front();
+      auto kind         = getAggregationType(front.point_data);
+      bool is_monotonic = true;
+      if (kind == sdk::metrics::AggregationType::kSum)
+      {
+        is_monotonic =
+            nostd::get<sdk::metrics::SumPointData>(front.point_data).is_monotonic_;
+      }
+      auto type = TranslateType(kind, is_monotonic);
+      metric_family.type = type;
+      auto origin_name   = metric_data.instrument_descriptor.name_;
+      auto unit          = metric_data.instrument_descriptor.unit_;
+      auto sanitized     = SanitizeNames(origin_name);
+      if (type == prometheus_client::MetricType::Counter && endsWith(sanitized,"_total")) {
+        // trim _total from counters, since it will be appended after the unit.
+        sanitized = sanitized.substr(0, sanitized.length() - sizeof("_total"));
+      }
       metric_family.name = sanitized + "_" + unit;
+      if (type == prometheus_client::MetricType::Counter) {
+        metric_family.name += "_total";
+      }
       metric_family.help = metric_data.instrument_descriptor.description_;
       auto time          = metric_data.end_ts.time_since_epoch();
       for (const auto &point_data_attr : metric_data.point_data_attr_)
       {
-        auto kind         = getAggregationType(point_data_attr.point_data);
-        bool is_monotonic = true;
-        if (kind == sdk::metrics::AggregationType::kSum)
-        {
-          is_monotonic =
-              nostd::get<sdk::metrics::SumPointData>(point_data_attr.point_data).is_monotonic_;
-        }
-        const prometheus_client::MetricType type = TranslateType(kind, is_monotonic);
-        metric_family.type                       = type;
         if (type == prometheus_client::MetricType::Histogram)  // Histogram
         {
           auto histogram_point_data =
@@ -121,6 +132,12 @@ std::vector<prometheus_client::MetricFamily> PrometheusExporterUtils::TranslateT
   return output;
 }
 
+inline bool PrometheusExporterUtils::endsWith(std::string const & value, std::string const & ending)
+{
+    if (ending.size() > value.size()) return false;
+    return std::equal(ending.rbegin(), ending.rend(), value.rbegin());
+}
+
 /**
  * Sanitize the given metric name or label according to Prometheus rule.
  *
diff --git a/exporters/prometheus/test/exporter_utils_test.cc b/exporters/prometheus/test/exporter_utils_test.cc
index 2eac7a6d8b..8e01c9a687 100644
--- a/exporters/prometheus/test/exporter_utils_test.cc
+++ b/exporters/prometheus/test/exporter_utils_test.cc
@@ -114,7 +114,7 @@ TEST(PrometheusExporterUtils, TranslateToPrometheusIntegerCounter)
 
   auto metric1          = translated[0];
   std::vector<int> vals = {10};
-  assert_basic(metric1, "library_name", "description", prometheus_client::MetricType::Counter, 1,
+  assert_basic(metric1, "library_name_total", "description", prometheus_client::MetricType::Counter, 1,
                vals);
 }