Add scope info and version to Prometheus exporter

examples/AspNetCore/Instrumentation.cs

@@ -22,7 +22,7 @@ public Instrumentation()
         string? version = typeof(Instrumentation).Assembly.GetName().Version?.ToString();
         this.ActivitySource = new ActivitySource(ActivitySourceName, version);
         this.meter = new Meter(MeterName, version);
-        this.FreezingDaysCounter = this.meter.CreateCounter<long>("weather.days.freezing", "The number of days where the temperature is below freezing");
+        this.FreezingDaysCounter = this.meter.CreateCounter<long>("weather.days.freezing", description: "The number of days where the temperature is below freezing");
     }
 
     public ActivitySource ActivitySource { get; }

src/OpenTelemetry.Exporter.Prometheus.AspNetCore/CHANGELOG.md

@@ -3,6 +3,7 @@
 ## Unreleased
 
 * Export OpenMetrics format from Prometheus exporters ([#5107](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5107))
+* For scrape requests with OpenMetrics format, otel_scope_info is automatically added ([#5086](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5086))
 
 ## 1.7.0-rc.1
 

src/OpenTelemetry.Exporter.Prometheus.HttpListener/CHANGELOG.md

@@ -3,6 +3,7 @@
 ## Unreleased
 
 * Export OpenMetrics format from Prometheus exporters ([#5107](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5107))
+* For scrape requests with OpenMetrics format, otel_scope_info is automatically added ([#5086](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5086))
 
 ## 1.7.0-rc.1
 

src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusCollectionManager.cs

@@ -14,6 +14,7 @@ internal sealed class PrometheusCollectionManager
     private readonly int scrapeResponseCacheDurationMilliseconds;
     private readonly Func<Batch<Metric>, ExportResult> onCollectRef;
     private readonly Dictionary<Metric, PrometheusMetric> metricsCache;
+    private readonly HashSet<string> scopes;
     private int metricsCacheCount;
     private byte[] buffer = new byte[85000]; // encourage the object to live in LOH (large object heap)
     private int globalLockState;
@@ -29,6 +30,7 @@ public PrometheusCollectionManager(PrometheusExporter exporter)
         this.scrapeResponseCacheDurationMilliseconds = this.exporter.ScrapeResponseCacheDurationMilliseconds;
         this.onCollectRef = this.OnCollect;
         this.metricsCache = new Dictionary<Metric, PrometheusMetric>();
+        this.scopes = new HashSet<string>();
     }
 
 #if NET6_0_OR_GREATER
@@ -170,6 +172,39 @@ private ExportResult OnCollect(Batch<Metric> metrics)
 
         try
         {
+            this.scopes.Clear();
+
+            foreach (var metric in metrics)
+            {
+                if (PrometheusSerializer.CanWriteMetric(metric))
+                {
+                    this.scopes.Add(metric.MeterName);
+                }
+            }
+
+            foreach (var scope in this.scopes)
+            {
+                try
+                {
+                    cursor = PrometheusSerializer.WriteScopeInfo(this.buffer, cursor, scope);
+
+                    break;
+                }
+                catch (IndexOutOfRangeException)
+                {
+                    if (!this.IncreaseBufferSize())
+                    {
+                        // there are two cases we might run into the following condition:
+                        // 1. we have many metrics to be exported - in this case we probably want
+                        //    to put some upper limit and allow the user to configure it.
+                        // 2. we got an IndexOutOfRangeException which was triggered by some other
+                        //    code instead of the buffer[cursor++] - in this case we should give up
+                        //    at certain point rather than allocating like crazy.
+                        throw;
+                    }
+                }
+            }
+
             foreach (var metric in metrics)
             {
                 if (!PrometheusSerializer.CanWriteMetric(metric))
@@ -194,12 +229,6 @@ private ExportResult OnCollect(Batch<Metric> metrics)
                     {
                         if (!this.IncreaseBufferSize())
                         {
-                            // there are two cases we might run into the following condition:
-                            // 1. we have many metrics to be exported - in this case we probably want
-                            //    to put some upper limit and allow the user to configure it.
-                            // 2. we got an IndexOutOfRangeException which was triggered by some other
-                            //    code instead of the buffer[cursor++] - in this case we should give up
-                            //    at certain point rather than allocating like crazy.
                             throw;
                         }
                     }

src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusSerializer.cs

@@ -5,6 +5,7 @@
 using System.Globalization;
 using System.Runtime.CompilerServices;
 using OpenTelemetry.Internal;
+using OpenTelemetry.Metrics;
 
 namespace OpenTelemetry.Exporter.Prometheus;
 
@@ -313,6 +314,31 @@ public static int WriteUnitMetadata(byte[] buffer, int cursor, PrometheusMetric
         return cursor;
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static int WriteScopeInfo(byte[] buffer, int cursor, string scopeName)
+    {
+        if (string.IsNullOrEmpty(scopeName))
+        {
+            return cursor;
+        }
+
+        cursor = WriteAsciiStringNoEscape(buffer, cursor, "# TYPE otel_scope_info info");
+        buffer[cursor++] = ASCII_LINEFEED;
+
+        cursor = WriteAsciiStringNoEscape(buffer, cursor, "# HELP otel_scope_info Scope metadata");
+        buffer[cursor++] = ASCII_LINEFEED;
+
+        cursor = WriteAsciiStringNoEscape(buffer, cursor, "otel_scope_info");
+        buffer[cursor++] = unchecked((byte)'{');
+        cursor = WriteLabel(buffer, cursor, "otel_scope_name", scopeName);
+        buffer[cursor++] = unchecked((byte)'}');
+        buffer[cursor++] = unchecked((byte)' ');
+        buffer[cursor++] = unchecked((byte)'1');
+        buffer[cursor++] = ASCII_LINEFEED;
+
+        return cursor;
+    }
+
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static int WriteTimestamp(byte[] buffer, int cursor, long value, bool useOpenMetrics)
     {
@@ -339,6 +365,37 @@ public static int WriteTimestamp(byte[] buffer, int cursor, long value, bool use
         return WriteLong(buffer, cursor, value);
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static int WriteTags(byte[] buffer, int cursor, Metric metric, ReadOnlyTagCollection tags, bool writeEnclosingBraces = true)
+    {
+        if (writeEnclosingBraces)
+        {
+            buffer[cursor++] = unchecked((byte)'{');
+        }
+
+        cursor = WriteLabel(buffer, cursor, "otel_scope_name", metric.MeterName);
+        buffer[cursor++] = unchecked((byte)',');
+
+        if (!string.IsNullOrEmpty(metric.MeterVersion))
+        {
+            cursor = WriteLabel(buffer, cursor, "otel_scope_version", metric.MeterVersion);
+            buffer[cursor++] = unchecked((byte)',');
+        }
+
+        foreach (var tag in tags)
+        {
+            cursor = WriteLabel(buffer, cursor, tag.Key, tag.Value);
+            buffer[cursor++] = unchecked((byte)',');
+        }
+
+        if (writeEnclosingBraces)
+        {
+            buffer[cursor - 1] = unchecked((byte)'}'); // Note: We write the '}' over the last written comma, which is extra.
+        }
+
+        return cursor;
+    }
+
     private static string MapPrometheusType(PrometheusType type)
     {
         return type switch

src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusSerializerExt.cs

@@ -32,24 +32,11 @@ public static int WriteMetric(byte[] buffer, int cursor, Metric metric, Promethe
         {
             foreach (ref readonly var metricPoint in metric.GetMetricPoints())
             {
-                var tags = metricPoint.Tags;
                 var timestamp = metricPoint.EndTime.ToUnixTimeMilliseconds();
 
                 // Counter and Gauge
                 cursor = WriteMetricName(buffer, cursor, prometheusMetric);
-
-                if (tags.Count > 0)
-                {
-                    buffer[cursor++] = unchecked((byte)'{');
-
-                    foreach (var tag in tags)
-                    {
-                        cursor = WriteLabel(buffer, cursor, tag.Key, tag.Value);
-                        buffer[cursor++] = unchecked((byte)',');
-                    }
-
-                    buffer[cursor - 1] = unchecked((byte)'}'); // Note: We write the '}' over the last written comma, which is extra.
-                }
+                cursor = WriteTags(buffer, cursor, metric, metricPoint.Tags);
 
                 buffer[cursor++] = unchecked((byte)' ');
 
@@ -100,12 +87,7 @@ public static int WriteMetric(byte[] buffer, int cursor, Metric metric, Promethe
 
                     cursor = WriteMetricName(buffer, cursor, prometheusMetric);
                     cursor = WriteAsciiStringNoEscape(buffer, cursor, "_bucket{");
-
-                    foreach (var tag in tags)
-                    {
-                        cursor = WriteLabel(buffer, cursor, tag.Key, tag.Value);
-                        buffer[cursor++] = unchecked((byte)',');
-                    }
+                    cursor = WriteTags(buffer, cursor, metric, tags, writeEnclosingBraces: false);
 
                     cursor = WriteAsciiStringNoEscape(buffer, cursor, "le=\"");
 
@@ -131,19 +113,7 @@ public static int WriteMetric(byte[] buffer, int cursor, Metric metric, Promethe
                 // Histogram sum
                 cursor = WriteMetricName(buffer, cursor, prometheusMetric);
                 cursor = WriteAsciiStringNoEscape(buffer, cursor, "_sum");
-
-                if (tags.Count > 0)
-                {
-                    buffer[cursor++] = unchecked((byte)'{');
-
-                    foreach (var tag in tags)
-                    {
-                        cursor = WriteLabel(buffer, cursor, tag.Key, tag.Value);
-                        buffer[cursor++] = unchecked((byte)',');
-                    }
-
-                    buffer[cursor - 1] = unchecked((byte)'}'); // Note: We write the '}' over the last written comma, which is extra.
-                }
+                cursor = WriteTags(buffer, cursor, metric, metricPoint.Tags);
 
                 buffer[cursor++] = unchecked((byte)' ');
 
@@ -157,19 +127,7 @@ public static int WriteMetric(byte[] buffer, int cursor, Metric metric, Promethe
                 // Histogram count
                 cursor = WriteMetricName(buffer, cursor, prometheusMetric);
                 cursor = WriteAsciiStringNoEscape(buffer, cursor, "_count");
-
-                if (tags.Count > 0)
-                {
-                    buffer[cursor++] = unchecked((byte)'{');
-
-                    foreach (var tag in tags)
-                    {
-                        cursor = WriteLabel(buffer, cursor, tag.Key, tag.Value);
-                        buffer[cursor++] = unchecked((byte)',');
-                    }
-
-                    buffer[cursor - 1] = unchecked((byte)'}'); // Note: We write the '}' over the last written comma, which is extra.
-                }
+                cursor = WriteTags(buffer, cursor, metric, metricPoint.Tags);
 
                 buffer[cursor++] = unchecked((byte)' ');
 

test/OpenTelemetry.Exporter.Prometheus.AspNetCore.Tests/PrometheusExporterMiddlewareTests.cs

@@ -19,6 +19,8 @@ namespace OpenTelemetry.Exporter.Prometheus.AspNetCore.Tests;
 
 public sealed class PrometheusExporterMiddlewareTests
 {
+    private const string MeterVersion = "1.0.1";
+
     private static readonly string MeterName = Utils.GetCurrentMethodName();
 
     [Fact]
@@ -281,7 +283,7 @@ public Task PrometheusExporterMiddlewareIntegration_UseOpenMetricsVersionHeader(
             new KeyValuePair<string, object>("key2", "value2"),
         };
 
-        using var meter = new Meter(MeterName);
+        using var meter = new Meter(MeterName, MeterVersion);
 
         var beginTimestamp = DateTimeOffset.Now.ToUnixTimeMilliseconds();
 
@@ -320,11 +322,17 @@ public Task PrometheusExporterMiddlewareIntegration_UseOpenMetricsVersionHeader(
             string content = await response.Content.ReadAsStringAsync();
 
             string expected = requestOpenMetrics
-                ? "# TYPE counter_double_total counter\n"
-                  + "counter_double_total{key1='value1',key2='value2'} 101.17 (\\d+\\.\\d{3})\n"
+                ? "# TYPE otel_scope_info info\n"
+                  + "# HELP otel_scope_info Scope metadata\n"
+                  + $"otel_scope_info{{otel_scope_name='{MeterName}'}} 1\n"
+                  + "# TYPE counter_double_total counter\n"
+                  + $"counter_double_total{{otel_scope_name='{MeterName}',otel_scope_version='{MeterVersion}',key1='value1',key2='value2'}} 101.17 (\\d+\\.\\d{{3}})\n"
                   + "# EOF\n"
-                : "# TYPE counter_double_total counter\n"
-                  + "counter_double_total{key1='value1',key2='value2'} 101.17 (\\d+)\n"
+                : "# TYPE otel_scope_info info\n"
+                  + "# HELP otel_scope_info Scope metadata\n"
+                  + $"otel_scope_info{{otel_scope_name='{MeterName}'}} 1\n"
+                  + "# TYPE counter_double_total counter\n"
+                  + $"counter_double_total{{otel_scope_name='{MeterName}',otel_scope_version='{MeterVersion}',key1='value1',key2='value2'}} 101.17 (\\d+)\n"
                   + "# EOF\n";
 
             var matches = Regex.Matches(content, ("^" + expected + "$").Replace('\'', '"'));

test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/PrometheusHttpListenerTests.cs

@@ -14,7 +14,9 @@ namespace OpenTelemetry.Exporter.Prometheus.Tests;
 
 public class PrometheusHttpListenerTests
 {
-    private readonly string meterName = Utils.GetCurrentMethodName();
+    private const string MeterVersion = "1.0.1";
+
+    private static readonly string MeterName = Utils.GetCurrentMethodName();
 
     [Theory]
     [InlineData("http://+:9464")]
@@ -99,7 +101,7 @@ private async Task RunPrometheusExporterHttpServerIntegrationTest(bool skipMetri
         string address = null;
 
         MeterProvider provider = null;
-        using var meter = new Meter(this.meterName);
+        using var meter = new Meter(MeterName, MeterVersion);
 
         while (retryAttempts-- != 0)
         {
@@ -110,7 +112,10 @@ private async Task RunPrometheusExporterHttpServerIntegrationTest(bool skipMetri
             {
                 provider = Sdk.CreateMeterProviderBuilder()
                     .AddMeter(meter.Name)
-                    .AddPrometheusHttpListener(options => options.UriPrefixes = new string[] { address })
+                    .AddPrometheusHttpListener(options =>
+                    {
+                        options.UriPrefixes = new string[] { address };
+                    })
                     .Build();
 
                 break;
@@ -165,11 +170,17 @@ private async Task RunPrometheusExporterHttpServerIntegrationTest(bool skipMetri
             var content = await response.Content.ReadAsStringAsync();
 
             var expected = requestOpenMetrics
-                ? "# TYPE counter_double_total counter\n"
-                  + "counter_double_total{key1='value1',key2='value2'} 101.17 \\d+\\.\\d{3}\n"
+                ? "# TYPE otel_scope_info info\n"
+                  + "# HELP otel_scope_info Scope metadata\n"
+                  + $"otel_scope_info{{otel_scope_name='{MeterName}'}} 1\n"
+                  + "# TYPE counter_double_total counter\n"
+                  + $"counter_double_total{{otel_scope_name='{MeterName}',otel_scope_version='{MeterVersion}',key1='value1',key2='value2'}} 101.17 (\\d+\\.\\d{{3}})\n"
                   + "# EOF\n"
-                : "# TYPE counter_double_total counter\n"
-                  + "counter_double_total{key1='value1',key2='value2'} 101.17 \\d+\n"
+                : "# TYPE otel_scope_info info\n"
+                  + "# HELP otel_scope_info Scope metadata\n"
+                  + $"otel_scope_info{{otel_scope_name='{MeterName}'}} 1\n"
+                  + "# TYPE counter_double_total counter\n"
+                  + $"counter_double_total{{otel_scope_name='{MeterName}',otel_scope_version='{MeterVersion}',key1='value1',key2='value2'}} 101.17 (\\d+)\n"
                   + "# EOF\n";
 
             Assert.Matches(("^" + expected + "$").Replace('\'', '"'), content);