Export OpenMetrics format for prometheus exporters (#5107)

Author: robertcoltheart

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

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+* Export OpenMetrics format from Prometheus exporters ([#5107](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5107))
+
 ## 1.7.0-rc.1
 
 Released 2023-Nov-29

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

@@ -28,6 +28,7 @@
     <Compile Include="$(RepoRoot)\src\OpenTelemetry.Exporter.Prometheus.HttpListener\Internal\PrometheusSerializerExt.cs" Link="Includes/PrometheusSerializerExt.cs" />
     <Compile Include="$(RepoRoot)\src\OpenTelemetry.Exporter.Prometheus.HttpListener\Internal\PrometheusType.cs" Link="Includes/PrometheusType.cs" />
     <Compile Include="$(RepoRoot)\src\OpenTelemetry.Exporter.Prometheus.HttpListener\Internal\PrometheusMetric.cs" Link="Includes/PrometheusMetric.cs" />
+    <Compile Include="$(RepoRoot)\src\OpenTelemetry.Exporter.Prometheus.HttpListener\Internal\PrometheusHeadersParser.cs" Link="Includes/PrometheusHeadersParser.cs" />
     <Compile Include="$(RepoRoot)\src\Shared\ExceptionExtensions.cs" Link="Includes\ExceptionExtensions.cs" />
   </ItemGroup>
 

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

@@ -16,6 +16,7 @@
 
 using System.Diagnostics;
 using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.Primitives;
 using OpenTelemetry.Exporter.Prometheus;
 using OpenTelemetry.Internal;
 using OpenTelemetry.Metrics;
@@ -64,7 +65,9 @@ public async Task InvokeAsync(HttpContext httpContext)
 
         try
         {
-            var collectionResponse = await this.exporter.CollectionManager.EnterCollect().ConfigureAwait(false);
+            var openMetricsRequested = AcceptsOpenMetrics(httpContext.Request);
+            var collectionResponse = await this.exporter.CollectionManager.EnterCollect(openMetricsRequested).ConfigureAwait(false);
+
             try
             {
                 if (collectionResponse.View.Count > 0)
@@ -75,7 +78,9 @@ public async Task InvokeAsync(HttpContext httpContext)
 #else
                     response.Headers.Add("Last-Modified", collectionResponse.GeneratedAtUtc.ToString("R"));
 #endif
-                    response.ContentType = "text/plain; charset=utf-8; version=0.0.4";
+                    response.ContentType = openMetricsRequested
+                        ? "application/openmetrics-text; version=1.0.0; charset=utf-8"
+                        : "text/plain; charset=utf-8; version=0.0.4";
 
                     await response.Body.WriteAsync(collectionResponse.View.Array, 0, collectionResponse.View.Count).ConfigureAwait(false);
                 }
@@ -102,4 +107,24 @@ public async Task InvokeAsync(HttpContext httpContext)
 
         this.exporter.OnExport = null;
     }
+
+    private static bool AcceptsOpenMetrics(HttpRequest request)
+    {
+        var acceptHeader = request.Headers.Accept;
+
+        if (StringValues.IsNullOrEmpty(acceptHeader))
+        {
+            return false;
+        }
+
+        foreach (var header in acceptHeader)
+        {
+            if (PrometheusHeadersParser.AcceptsOpenMetrics(header))
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
 }

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

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+* Export OpenMetrics format from Prometheus exporters ([#5107](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5107))
+
 ## 1.7.0-rc.1
 
 Released 2023-Nov-29

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

@@ -45,9 +45,9 @@ public PrometheusCollectionManager(PrometheusExporter exporter)
     }
 
 #if NET6_0_OR_GREATER
-    public ValueTask<CollectionResponse> EnterCollect()
+    public ValueTask<CollectionResponse> EnterCollect(bool openMetricsRequested)
 #else
-    public Task<CollectionResponse> EnterCollect()
+    public Task<CollectionResponse> EnterCollect(bool openMetricsRequested)
 #endif
     {
         this.EnterGlobalLock();
@@ -93,7 +93,7 @@ public Task<CollectionResponse> EnterCollect()
         this.ExitGlobalLock();
 
         CollectionResponse response;
-        var result = this.ExecuteCollect();
+        var result = this.ExecuteCollect(openMetricsRequested);
         if (result)
         {
             this.previousDataViewGeneratedAtUtc = DateTime.UtcNow;
@@ -168,9 +168,10 @@ private void WaitForReadersToComplete()
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    private bool ExecuteCollect()
+    private bool ExecuteCollect(bool openMetricsRequested)
     {
         this.exporter.OnExport = this.onCollectRef;
+        this.exporter.OpenMetricsRequested = openMetricsRequested;
         var result = this.exporter.Collect(Timeout.Infinite);
         this.exporter.OnExport = null;
         return result;
@@ -193,7 +194,13 @@ private ExportResult OnCollect(Batch<Metric> metrics)
                 {
                     try
                     {
-                        cursor = PrometheusSerializer.WriteMetric(this.buffer, cursor, metric, this.GetPrometheusMetric(metric));
+                        cursor = PrometheusSerializer.WriteMetric(
+                            this.buffer,
+                            cursor,
+                            metric,
+                            this.GetPrometheusMetric(metric),
+                            this.exporter.OpenMetricsRequested);
+
                         break;
                     }
                     catch (IndexOutOfRangeException)

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

@@ -63,6 +63,8 @@ internal Func<Batch<Metric>, ExportResult> OnExport
 
     internal int ScrapeResponseCacheDurationMilliseconds { get; }
 
+    internal bool OpenMetricsRequested { get; set; }
+
     /// <inheritdoc/>
     public override ExportResult Export(in Batch<Metric> metrics)
     {

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

@@ -0,0 +1,60 @@
+// <copyright file="PrometheusHeadersParser.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+namespace OpenTelemetry.Exporter.Prometheus;
+
+internal static class PrometheusHeadersParser
+{
+    private const string OpenMetricsMediaType = "application/openmetrics-text";
+
+    internal static bool AcceptsOpenMetrics(string contentType)
+    {
+        var value = contentType.AsSpan();
+
+        while (value.Length > 0)
+        {
+            var headerValue = SplitNext(ref value, ',');
+            var mediaType = SplitNext(ref headerValue, ';');
+
+            if (mediaType.Equals(OpenMetricsMediaType.AsSpan(), StringComparison.Ordinal))
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    private static ReadOnlySpan<char> SplitNext(ref ReadOnlySpan<char> span, char character)
+    {
+        var index = span.IndexOf(character);
+
+        if (index == -1)
+        {
+            var part = span;
+            span = span.Slice(span.Length);
+
+            return part;
+        }
+        else
+        {
+            var part = span.Slice(0, index);
+            span = span.Slice(index + 1);
+
+            return part;
+        }
+    }
+}

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

@@ -326,6 +326,32 @@ public static int WriteUnitMetadata(byte[] buffer, int cursor, PrometheusMetric
         return cursor;
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static int WriteTimestamp(byte[] buffer, int cursor, long value, bool useOpenMetrics)
+    {
+        if (useOpenMetrics)
+        {
+            cursor = WriteLong(buffer, cursor, value / 1000);
+            buffer[cursor++] = unchecked((byte)'.');
+
+            long millis = value % 1000;
+
+            if (millis < 100)
+            {
+                buffer[cursor++] = unchecked((byte)'0');
+            }
+
+            if (millis < 10)
+            {
+                buffer[cursor++] = unchecked((byte)'0');
+            }
+
+            return WriteLong(buffer, cursor, millis);
+        }
+
+        return WriteLong(buffer, cursor, value);
+    }
+
     private static string MapPrometheusType(PrometheusType type)
     {
         return type switch

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

@@ -35,7 +35,7 @@ public static bool CanWriteMetric(Metric metric)
         return true;
     }
 
-    public static int WriteMetric(byte[] buffer, int cursor, Metric metric, PrometheusMetric prometheusMetric)
+    public static int WriteMetric(byte[] buffer, int cursor, Metric metric, PrometheusMetric prometheusMetric, bool openMetricsRequested = false)
     {
         cursor = WriteTypeMetadata(buffer, cursor, prometheusMetric);
         cursor = WriteUnitMetadata(buffer, cursor, prometheusMetric);
@@ -94,7 +94,7 @@ public static int WriteMetric(byte[] buffer, int cursor, Metric metric, Promethe
 
                 buffer[cursor++] = unchecked((byte)' ');
 
-                cursor = WriteLong(buffer, cursor, timestamp);
+                cursor = WriteTimestamp(buffer, cursor, timestamp, openMetricsRequested);
 
                 buffer[cursor++] = ASCII_LINEFEED;
             }
@@ -136,7 +136,7 @@ public static int WriteMetric(byte[] buffer, int cursor, Metric metric, Promethe
                     cursor = WriteLong(buffer, cursor, totalCount);
                     buffer[cursor++] = unchecked((byte)' ');
 
-                    cursor = WriteLong(buffer, cursor, timestamp);
+                    cursor = WriteTimestamp(buffer, cursor, timestamp, openMetricsRequested);
 
                     buffer[cursor++] = ASCII_LINEFEED;
                 }
@@ -163,7 +163,7 @@ public static int WriteMetric(byte[] buffer, int cursor, Metric metric, Promethe
                 cursor = WriteDouble(buffer, cursor, metricPoint.GetHistogramSum());
                 buffer[cursor++] = unchecked((byte)' ');
 
-                cursor = WriteLong(buffer, cursor, timestamp);
+                cursor = WriteTimestamp(buffer, cursor, timestamp, openMetricsRequested);
 
                 buffer[cursor++] = ASCII_LINEFEED;
 
@@ -189,14 +189,12 @@ public static int WriteMetric(byte[] buffer, int cursor, Metric metric, Promethe
                 cursor = WriteLong(buffer, cursor, metricPoint.GetHistogramCount());
                 buffer[cursor++] = unchecked((byte)' ');
 
-                cursor = WriteLong(buffer, cursor, timestamp);
+                cursor = WriteTimestamp(buffer, cursor, timestamp, openMetricsRequested);
 
                 buffer[cursor++] = ASCII_LINEFEED;
             }
         }
 
-        buffer[cursor++] = ASCII_LINEFEED;
-
         return cursor;
     }
 }

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

@@ -110,6 +110,18 @@ public void Dispose()
         }
     }
 
+    private static bool AcceptsOpenMetrics(HttpListenerRequest request)
+    {
+        var acceptHeader = request.Headers["Accept"];
+
+        if (string.IsNullOrEmpty(acceptHeader))
+        {
+            return false;
+        }
+
+        return PrometheusHeadersParser.AcceptsOpenMetrics(acceptHeader);
+    }
+
     private void WorkerProc()
     {
         this.httpListener.Start();
@@ -148,15 +160,19 @@ private async Task ProcessRequestAsync(HttpListenerContext context)
     {
         try
         {
-            var collectionResponse = await this.exporter.CollectionManager.EnterCollect().ConfigureAwait(false);
+            var openMetricsRequested = AcceptsOpenMetrics(context.Request);
+            var collectionResponse = await this.exporter.CollectionManager.EnterCollect(openMetricsRequested).ConfigureAwait(false);
+
             try
             {
                 context.Response.Headers.Add("Server", string.Empty);
                 if (collectionResponse.View.Count > 0)
                 {
                     context.Response.StatusCode = 200;
                     context.Response.Headers.Add("Last-Modified", collectionResponse.GeneratedAtUtc.ToString("R"));
-                    context.Response.ContentType = "text/plain; charset=utf-8; version=0.0.4";
+                    context.Response.ContentType = openMetricsRequested
+                        ? "application/openmetrics-text; version=1.0.0; charset=utf-8"
+                        : "text/plain; charset=utf-8; version=0.0.4";
 
                     await context.Response.OutputStream.WriteAsync(collectionResponse.View.Array, 0, collectionResponse.View.Count).ConfigureAwait(false);
                 }