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/.publicApi/PublicAPI.Unshipped.txt

@@ -2,6 +2,8 @@ Microsoft.AspNetCore.Builder.PrometheusExporterApplicationBuilderExtensions
 Microsoft.AspNetCore.Builder.PrometheusExporterEndpointRouteBuilderExtensions
 OpenTelemetry.Exporter.PrometheusAspNetCoreOptions
 OpenTelemetry.Exporter.PrometheusAspNetCoreOptions.PrometheusAspNetCoreOptions() -> void
+OpenTelemetry.Exporter.PrometheusAspNetCoreOptions.ScopeInfoEnabled.get -> bool
+OpenTelemetry.Exporter.PrometheusAspNetCoreOptions.ScopeInfoEnabled.set -> void
 OpenTelemetry.Exporter.PrometheusAspNetCoreOptions.ScrapeEndpointPath.get -> string
 OpenTelemetry.Exporter.PrometheusAspNetCoreOptions.ScrapeEndpointPath.set -> void
 OpenTelemetry.Exporter.PrometheusAspNetCoreOptions.ScrapeResponseCacheDurationMilliseconds.get -> int

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))
+* Added ability to export otel_scope_info from Prometheus exporters ([#5086](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5086))
 
 ## 1.7.0-rc.1
 

src/OpenTelemetry.Exporter.Prometheus.AspNetCore/PrometheusAspNetCoreOptions.cs

@@ -29,5 +29,14 @@ public int ScrapeResponseCacheDurationMilliseconds
         set => this.ExporterOptions.ScrapeResponseCacheDurationMilliseconds = value;
     }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether to export scope info. Default value: true.
+    /// </summary>
+    public bool ScopeInfoEnabled
+    {
+        get => this.ExporterOptions.ScopeInfoEnabled;
+        set => this.ExporterOptions.ScopeInfoEnabled = value;
+    }
+
     internal PrometheusExporterOptions ExporterOptions { get; } = new();
 }

src/OpenTelemetry.Exporter.Prometheus.HttpListener/.publicApi/PublicAPI.Unshipped.txt

@@ -1,4 +1,6 @@
 OpenTelemetry.Exporter.PrometheusHttpListenerOptions
+OpenTelemetry.Exporter.PrometheusHttpListenerOptions.ScopeInfoEnabled.get -> bool
+OpenTelemetry.Exporter.PrometheusHttpListenerOptions.ScopeInfoEnabled.set -> void
 OpenTelemetry.Exporter.PrometheusHttpListenerOptions.UriPrefixes.get -> System.Collections.Generic.IReadOnlyCollection<string>
 OpenTelemetry.Exporter.PrometheusHttpListenerOptions.UriPrefixes.set -> void
 OpenTelemetry.Exporter.PrometheusHttpListenerOptions.PrometheusHttpListenerOptions() -> void

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))
+* Added ability to export otel_scope_info from Prometheus exporters ([#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 +172,42 @@ private ExportResult OnCollect(Batch<Metric> metrics)
 
         try
         {
+            if (this.exporter.ScopeInfoEnabled && this.exporter.OpenMetricsRequested)
+            {
+                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))
@@ -186,20 +224,15 @@ private ExportResult OnCollect(Batch<Metric> metrics)
                             cursor,
                             metric,
                             this.GetPrometheusMetric(metric),
-                            this.exporter.OpenMetricsRequested);
+                            this.exporter.OpenMetricsRequested,
+                            this.exporter.ScopeInfoEnabled);
 
                         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;
                         }
                     }

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

@@ -25,6 +25,7 @@ public PrometheusExporter(PrometheusExporterOptions options)
         Guard.ThrowIfNull(options);
 
         this.ScrapeResponseCacheDurationMilliseconds = options.ScrapeResponseCacheDurationMilliseconds;
+        this.ScopeInfoEnabled = options.ScopeInfoEnabled;
 
         this.CollectionManager = new PrometheusCollectionManager(this);
     }
@@ -52,6 +53,8 @@ internal Func<Batch<Metric>, ExportResult> OnExport
 
     internal bool OpenMetricsRequested { get; set; }
 
+    internal bool ScopeInfoEnabled { get; set; }
+
     /// <inheritdoc/>
     public override ExportResult Export(in Batch<Metric> metrics)
     {

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

@@ -28,4 +28,9 @@ public int ScrapeResponseCacheDurationMilliseconds
             this.scrapeResponseCacheDurationMilliseconds = value;
         }
     }
+
+    /// <summary>
+    /// Gets or sets a value indicating whether to export scope info. Default value: true.
+    /// </summary>
+    public bool ScopeInfoEnabled { get; set; } = true;
 }

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 +365,43 @@ 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 scopeInfoEnabled, bool writeEnclosingBraces = true)
+    {
+        if (tags.Count > 0 || scopeInfoEnabled)
+        {
+            if (writeEnclosingBraces)
+            {
+                buffer[cursor++] = unchecked((byte)'{');
+            }
+
+            if (scopeInfoEnabled)
+            {
+                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

@@ -22,7 +22,7 @@ public static bool CanWriteMetric(Metric metric)
         return true;
     }
 
-    public static int WriteMetric(byte[] buffer, int cursor, Metric metric, PrometheusMetric prometheusMetric, bool openMetricsRequested = false)
+    public static int WriteMetric(byte[] buffer, int cursor, Metric metric, PrometheusMetric prometheusMetric, bool openMetricsRequested = false, bool scopeInfoEnabled = true)
     {
         cursor = WriteTypeMetadata(buffer, cursor, prometheusMetric);
         cursor = WriteUnitMetadata(buffer, cursor, prometheusMetric);
@@ -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, scopeInfoEnabled);
 
                 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, scopeInfoEnabled, 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, scopeInfoEnabled);
 
                 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, scopeInfoEnabled);
 
                 buffer[cursor++] = unchecked((byte)' ');
 

src/OpenTelemetry.Exporter.Prometheus.HttpListener/PrometheusHttpListenerMeterProviderBuilderExtensions.cs

@@ -65,7 +65,11 @@ public static MeterProviderBuilder AddPrometheusHttpListener(
     private static MetricReader BuildPrometheusHttpListenerMetricReader(
         PrometheusHttpListenerOptions options)
     {
-        var exporter = new PrometheusExporter(new PrometheusExporterOptions { ScrapeResponseCacheDurationMilliseconds = 0 });
+        var exporter = new PrometheusExporter(new PrometheusExporterOptions
+        {
+            ScrapeResponseCacheDurationMilliseconds = 0,
+            ScopeInfoEnabled = options.ScopeInfoEnabled,
+        });
 
         var reader = new BaseExportingMetricReader(exporter)
         {

src/OpenTelemetry.Exporter.Prometheus.HttpListener/PrometheusHttpListenerOptions.cs

@@ -17,6 +17,11 @@ public class PrometheusHttpListenerOptions
     /// </summary>
     public string ScrapeEndpointPath { get; set; } = "/metrics";
 
+    /// <summary>
+    /// Gets or sets a value indicating whether to export scope info. Default value: true.
+    /// </summary>
+    public bool ScopeInfoEnabled { get; set; } = true;
+
     /// <summary>
     /// Gets or sets the URI (Uniform Resource Identifier) prefixes to use for the http listener.
     /// Default value: <c>["http://localhost:9464/"]</c>.