[DNM/DNR] Prometheus compatibility fixes

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

@@ -26,53 +26,82 @@ Notes](../../RELEASENOTES.md).
 
 * Fix non-ASCII characters in metric names and unit strings not being sanitized
   correctly during Prometheus serialization.
-  ([#7184](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7184))
+  ([#7184](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7184))
 
 * Fix case where reader tracking could be reset while readers were still active.
   ([#7190](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7190))
 
 * Improve `Accept` header handling for format negotiation so OpenMetrics is
   selected correctly by considering whitespace and `q` weights.
-  ([#7208](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7208))
+  ([#7208](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7208))
 
 * Emit OpenMetrics exemplars for counters and histogram buckets.
-  ([#7222](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7222))
+  ([#7222](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7222))
 
 * Fix incorrect handling of untyped metrics when using OpenMetrics format.
-  ([#7219](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7219))
+  ([#7219](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7219))
 
 * Fix Prometheus/OpenMetrics serialization to emit metric and label names
-  containing `_` instead of dropping them and prefixing leading digits.
+  containing `:` and `_` instead of dropping them and prefixing leading digits.
   Invalid characters are replaced with `_` instead of being dropped.
-  ([#7209](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7209))
+  ([#7209](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7209))
 
 * Add `escaping=underscores` to the `Accept` header handling for content
   negotiation so OpenMetrics are handled correctly.
-  ([#7209](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7209))
+  ([#7209](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7209))
+
+* Use the canonical representation for histogram "le" label values when using
+  OpenMetrics.
+  ([#7218](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7218))
 
 * Omit histogram `_sum` and `_count` in OpenMetrics when negative bucket
   thresholds are present.
-  ([#7221](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7221))
+  ([#7221](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7221))
 
 * Fix `ArgumentException` if `OTEL_SDK_DISABLED=true`.
-  ([#7273](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7273))
+  ([#7273](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7273))
 
 * Update `Accept` header parsing to more closely follow the Prometheus
   [Scrape protocol content negotiation](https://prometheus.io/docs/instrumenting/content_negotiation/)
   specification.
-  ([#7266](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7266))
+  ([#7266](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7266))
 
 * Abort scrape request processing if request exceeds the value specified by the
   `X-Prometheus-Scrape-Timeout-Seconds` HTTP request header.
-  ([#7252](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7252))
+  ([#7252](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7252))
+
+* GZip compress scrape endpoint responses when `Accept-Encoding: gzip` is
+  specified by the HTTP request headers.
+  ([#7274](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7274))
+
+* Export `{name}_created` series for counters and histograms when using
+  OpenMetrics and a start time is available.
+  ([#7223](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7223))
+
+* Emit OpenMetrics scope metadata as a single `otel_scope` metric family with
+  `otel_scope_info` samples instead of repeating metadata for every scope.
+  ([#7237](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7237))
+
+* Include instrumentation scope metadata on samples using `otel_scope_*` labels
+  including scope version, schema URL, and prefixed scope attributes.
+  ([#7237](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7237))
+
+* Drop conflicting scope attributes named `name`, `version`, and `schema_url`.
+  ([#7237](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7237))
+
+* Add Prometheus text fallback `target_info` output as a gauge.
+  ([#7238](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7238))
+
+* Merge colliding sanitized label keys.
+  ([#7239](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7239))
 
 ## 1.15.3-beta.1
 
 Released 2026-Apr-21
 
 * Fixed metric unit strings containing invalid Prometheus characters (e.g. `# RU`)
   not being sanitized, resulting in malformed metric names.
-  ([#6187](https://github.com/open-telemetry/opentelemetry-dotnet/issues/6187))
+  ([#6187](https://github.com/open-telemetry/opentelemetry-dotnet/pull/6187))
 
 * Fixed Prometheus metric serialization to handle empty label names without
   throwing during scrape rendering.

src/OpenTelemetry.Exporter.Prometheus.AspNetCore/OpenTelemetry.Exporter.Prometheus.AspNetCore.csproj

@@ -7,6 +7,7 @@
     <PackageTags>$(PackageTags);prometheus;metrics</PackageTags>
     <MinVerTagPrefix>coreunstable-</MinVerTagPrefix>
     <DefineConstants>$(DefineConstants);PROMETHEUS_ASPNETCORE</DefineConstants>
+    <NoWarn>$(NoWarn);CA2007</NoWarn>
   </PropertyGroup>
 
   <ItemGroup Condition="'$(RunningDotNetPack)' != 'true'">

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

@@ -5,7 +5,9 @@
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
+using System.IO.Compression;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Headers;
 using Microsoft.Net.Http.Headers;
 using OpenTelemetry.Exporter.Prometheus;
 using OpenTelemetry.Internal;
@@ -73,9 +75,11 @@ public async Task InvokeAsync(HttpContext httpContext)
 
             using var linkedCts = CancellationTokenSource.CreateLinkedTokenSource(requestCancelled.Token, httpContext.RequestAborted);
 
-            var protocol = Negotiate(httpContext.Request);
+            var requestHeaders = httpContext.Request.GetTypedHeaders();
 
-            var collectionResponse = await this.exporter.CollectionManager.EnterCollect(protocol.IsOpenMetrics).ConfigureAwait(false);
+            var protocol = Negotiate(requestHeaders);
+
+            var collectionResponse = await this.exporter.CollectionManager.EnterCollect(protocol.IsOpenMetrics);
 
             try
             {
@@ -90,7 +94,7 @@ public async Task InvokeAsync(HttpContext httpContext)
                     response.Headers.Append("Last-Modified", collectionResponse.GeneratedAtUtc.ToString("R"));
                     response.ContentType = PrometheusProtocol.GetContentType(protocol);
 
-                    await response.Body.WriteAsync(dataView.Array.AsMemory(0, dataView.Count), linkedCts.Token).ConfigureAwait(false);
+                    await WriteResponseAsync(response, dataView.Array.AsMemory(0, dataView.Count), AcceptsGZip(requestHeaders), linkedCts.Token);
                 }
                 else
                 {
@@ -144,9 +148,9 @@ static bool TryGetScrapeTimeout(
         }
     }
 
-    internal static PrometheusProtocol Negotiate(HttpRequest request)
+    internal static PrometheusProtocol Negotiate(RequestHeaders headers)
     {
-        var acceptHeader = request.GetTypedHeaders().Accept;
+        var acceptHeader = headers.Accept;
 
         if (acceptHeader is not { Count: > 0 })
         {
@@ -284,4 +288,44 @@ private static bool TryParse(
         protocol = new(mediaType, escaping, version, isOpenMetrics);
         return true;
     }
+
+    private static bool AcceptsGZip(RequestHeaders headers)
+    {
+        if (headers.AcceptEncoding is { Count: > 0 } acceptEncoding)
+        {
+            foreach (var parameter in acceptEncoding)
+            {
+                if (parameter.Value.Equals("gzip", StringComparison.OrdinalIgnoreCase))
+                {
+                    return true;
+                }
+            }
+        }
+
+        return false;
+    }
+
+    private static async Task WriteResponseAsync(
+        HttpResponse response,
+        ReadOnlyMemory<byte> content,
+        bool compress,
+        CancellationToken cancellationToken)
+    {
+        if (compress)
+        {
+            response.Headers.Append("Content-Encoding", "gzip");
+
+            await using var gzip = new GZipStream(
+                response.Body,
+                CompressionLevel.Optimal,
+                leaveOpen: true);
+
+            await gzip.WriteAsync(content, cancellationToken);
+            await gzip.FlushAsync(cancellationToken);
+        }
+        else
+        {
+            await response.BodyWriter.WriteAsync(content, cancellationToken);
+        }
+    }
 }

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

@@ -32,7 +32,7 @@ Notes](../../RELEASENOTES.md).
 
 * Fix non-ASCII characters in metric names and unit strings not being sanitized
   correctly during Prometheus serialization.
-  ([#7184](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7184))
+  ([#7184](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7184))
 
 * Add support for caching the scrape endpoint HTTP responses using the
   `PrometheusHttpListenerOptions.ScrapeResponseCacheDurationMilliseconds` option.
@@ -45,13 +45,13 @@ Notes](../../RELEASENOTES.md).
 
 * Improve `Accept` header handling for format negotiation so OpenMetrics is
   selected correctly by considering whitespace and `q` weights.
-  ([#7208](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7208))
+  ([#7208](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7208))
 
 * Emit OpenMetrics exemplars for counters and histogram buckets.
-  ([#7222](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7222))
+  ([#7222](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7222))
 
 * Fix incorrect handling of untyped metrics when using OpenMetrics format.
-  ([#7219](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7219))
+  ([#7219](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7219))
 
 * Add support for configuring the HTTP listener endpoint host and port using
   the `OTEL_EXPORTER_PROMETHEUS_HOST` and `OTEL_EXPORTER_PROMETHEUS_PORT`
@@ -60,34 +60,67 @@ Notes](../../RELEASENOTES.md).
   [#7255](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7255))
 
 * Fix Prometheus/OpenMetrics serialization to emit metric and label names
-  containing and `_` instead of dropping them and prefixing leading digits.
+  containing `_` instead of dropping them and prefixing leading digits.
   Invalid characters are replaced with `_` instead of being dropped.
-  ([#7209](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7209))
+  ([#7209](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7209))
 
 * Add `escaping=underscores` to the `Accept` header handling for content
   negotiation so OpenMetrics are handled correctly.
-  ([#7209](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7209))
+  ([#7209](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7209))
 
 * Omit histogram `_sum` and `_count` in OpenMetrics when negative bucket
   thresholds are present.
-  ([#7221](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7221))
+  ([#7221](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7221))
 
 * Update `Accept` header parsing to more closely follow the Prometheus
   [Scrape protocol content negotiation](https://prometheus.io/docs/instrumenting/content_negotiation/)
   specification.
-  ([#7266](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7266))
+  ([#7266](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7266))
 
 * Abort scrape request processing if request exceeds the value specified by the
   `X-Prometheus-Scrape-Timeout-Seconds` HTTP request header.
-  ([#7252](https://github.com/open-telemetry/opentelemetry-dotnet/issues/7252))
+  ([#7252](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7252))
+
+* Add `escaping=underscores` to the `Accept` header handling for content
+  negotiation so OpenMetrics are handled correctly.
+  ([#7209](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7209))
+
+* Use the canonical representation for histogram "le" label values when using
+  OpenMetrics.
+  ([#7218](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7218))
+
+* Omit histogram `_sum` and `_count` in OpenMetrics when negative bucket
+  thresholds are present.
+  ([#7221](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7221))
+
+* Export `{name}_created` series for counters and histograms when using
+  OpenMetrics and a start time is available.
+  ([#7223](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7223))
+
+* Emit OpenMetrics scope metadata as a single `otel_scope` metric family with
+  `otel_scope_info` samples instead of repeating metadata for every scope.
+  ([#7237](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7237))
+
+* Include instrumentation scope metadata on samples using `otel_scope_*` labels
+  including scope version, schema URL, and prefixed scope attributes.
+  ([#7237](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7237))
+
+* Drop conflicting scope attributes named `name`, `version`, and `schema_url`.
+  ([#7237](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7237))
+
+* Add Prometheus text fallback `target_info` output as a gauge.
+  ([#7238](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7238))
+
+* Merge colliding sanitized label keys.
+  ([#7239](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7239))
 
 ## 1.15.3-beta.1
 
 Released 2026-Apr-21
 
 * Fixed metric unit strings containing invalid Prometheus characters (e.g. `# RU`)
   not being sanitized, resulting in malformed metric names.
-  ([#6187](https://github.com/open-telemetry/opentelemetry-dotnet/issues/6187))
+  ([#7033](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7033))
 
 * Fixed Prometheus metric serialization to handle empty label names without
   throwing during scrape rendering.
@@ -383,7 +416,7 @@ Released 2022-Feb-02
 Released 2021-Nov-29
 
 * Bug fix for handling Histogram with empty buckets.
-  ([#2651](https://github.com/open-telemetry/opentelemetry-dotnet/issues/2651))
+  ([#2651](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2651))
 
 ## 1.2.0-beta2
 

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

@@ -20,7 +20,8 @@ internal sealed class PrometheusCollectionManager
     private int metricsCacheCount;
     private byte[] plainTextBuffer = new byte[85000]; // encourage the object to live in LOH (large object heap)
     private byte[] openMetricsBuffer = new byte[85000]; // encourage the object to live in LOH (large object heap)
-    private int targetInfoBufferLength = -1; // zero or positive when target_info has been written for the first time
+    private int plainTextTargetInfoBufferLength = -1;
+    private int openMetricsTargetInfoBufferLength = -1;
     private ArraySegment<byte> previousPlainTextDataView;
     private ArraySegment<byte> previousOpenMetricsDataView;
     private int globalLockState;
@@ -237,11 +238,12 @@ private ExportResult OnCollect(in Batch<Metric> metrics)
 
         try
         {
+            cursor = this.WriteTargetInfo(ref buffer);
+
             if (this.exporter.OpenMetricsRequested)
             {
-                cursor = this.WriteTargetInfo(ref buffer);
-
                 this.scopes.Clear();
+                var scopeInfoMetadataWritten = false;
 
                 foreach (var metric in metrics)
                 {
@@ -250,13 +252,19 @@ private ExportResult OnCollect(in Batch<Metric> metrics)
                         continue;
                     }
 
-                    if (this.scopes.Add(metric.MeterName))
+                    if (this.scopes.Add(PrometheusSerializer.CreateScopeIdentity(metric)))
                     {
                         while (true)
                         {
                             try
                             {
-                                cursor = PrometheusSerializer.WriteScopeInfo(buffer, cursor, metric.MeterName, openMetricsRequested: true);
+                                if (!scopeInfoMetadataWritten)
+                                {
+                                    cursor = PrometheusSerializer.WriteScopeInfoMetadata(buffer, cursor);
+                                    scopeInfoMetadataWritten = true;
+                                }
+
+                                cursor = PrometheusSerializer.WriteScopeInfoMetric(buffer, cursor, metric);
 
                                 break;
                             }
@@ -292,11 +300,11 @@ private ExportResult OnCollect(in Batch<Metric> metrics)
                             metricState.Metric,
                             metricState.PrometheusMetric,
                             this.exporter.OpenMetricsRequested,
-                            metricState.WriteType,
-                            metricState.WriteUnit,
-                            metricState.WriteHelp,
-                            metricState.Unit,
-                            metricState.Help);
+                            writeType: metricState.WriteType,
+                            writeUnit: metricState.WriteUnit,
+                            writeHelp: metricState.WriteHelp,
+                            unitOverride: metricState.Unit,
+                            helpOverride: metricState.Help);
 
                         break;
                     }
@@ -356,13 +364,18 @@ private ExportResult OnCollect(in Batch<Metric> metrics)
 
     private int WriteTargetInfo(ref byte[] buffer)
     {
-        if (this.targetInfoBufferLength < 0)
+        ref var targetInfoBufferLength = ref this.exporter.OpenMetricsRequested
+            ? ref this.openMetricsTargetInfoBufferLength
+            : ref this.plainTextTargetInfoBufferLength;
+
+        if (targetInfoBufferLength < 0)
         {
             while (true)
             {
                 try
                 {
-                    this.targetInfoBufferLength = PrometheusSerializer.WriteTargetInfo(buffer, 0, this.exporter.Resource, openMetricsRequested: true);
+                    targetInfoBufferLength = PrometheusSerializer.WriteTargetInfo(buffer, 0, this.exporter.Resource, this.exporter.OpenMetricsRequested);
+                    targetInfoBufferLength = PrometheusSerializer.WriteTargetInfo(buffer, 0, this.exporter.Resource, this.exporter.OpenMetricsRequested);
 
                     break;
                 }
@@ -376,7 +389,7 @@ private int WriteTargetInfo(ref byte[] buffer)
             }
         }
 
-        return this.targetInfoBufferLength;
+        return targetInfoBufferLength;
     }
 
     private PrometheusMetric GetPrometheusMetric(Metric metric)