Prometheus Exporter - New .MapPrometheusScrapingEndpoint() Extension Method

src/OpenTelemetry.Exporter.Prometheus/PrometheusExporterEndpointRouteBuilderExtensions.cs

@@ -0,0 +1,112 @@
+// <copyright file="PrometheusExporterEndpointRouteBuilderExtensions.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>
+
+#if NETCOREAPP3_1_OR_GREATER
+
+using System;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Routing;
+using Microsoft.Extensions.DependencyInjection;
+using OpenTelemetry.Exporter;
+using OpenTelemetry.Exporter.Prometheus;
+using OpenTelemetry.Internal;
+using OpenTelemetry.Metrics;
+
+namespace Microsoft.AspNetCore.Builder
+{
+    /// <summary>
+    /// Provides extension methods for <see cref="IEndpointRouteBuilder"/> to add
+    /// Prometheus scraping endpoint.
+    /// </summary>
+    public static class PrometheusExporterEndpointRouteBuilderExtensions
+    {
+        /// <summary>
+        /// Adds OpenTelemetry Prometheus scraping endpoint middleware to an
+        /// <see cref="IEndpointRouteBuilder"/> instance.
+        /// </summary>
+        /// <remarks>Note: A branched pipeline is created for the route
+        /// specified by <see
+        /// cref="PrometheusExporterOptions.ScrapeEndpointPath"/>.</remarks>
+        /// <param name="endpoints">The <see cref="IEndpointRouteBuilder"/> to add
+        /// middleware to.</param>
+        /// <returns>A convention routes for the Prometheus scraping endpoint.</returns>
+        public static IEndpointConventionBuilder MapPrometheusScrapingEndpoint(this IEndpointRouteBuilder endpoints)
+            => MapPrometheusScrapingEndpoint(endpoints, path: null, meterProvider: null, configureBranchedPipeline: null);
+
+        /// <summary>
+        /// Adds OpenTelemetry Prometheus scraping endpoint middleware to an
+        /// <see cref="IEndpointRouteBuilder"/> instance.
+        /// </summary>
+        /// <param name="endpoints">The <see cref="IEndpointRouteBuilder"/> to add
+        /// middleware to.</param>
+        /// <param name="path">The path to use for the branched pipeline.</param>
+        /// <returns>A convention routes for the Prometheus scraping endpoint.</returns>
+        public static IEndpointConventionBuilder MapPrometheusScrapingEndpoint(this IEndpointRouteBuilder endpoints, string path)
+        {
+            Guard.ThrowIfNull(path);
+            return MapPrometheusScrapingEndpoint(endpoints, path, meterProvider: null, configureBranchedPipeline: null);
+        }
+
+        /// <summary>
+        /// Adds OpenTelemetry Prometheus scraping endpoint middleware to an
+        /// <see cref="IEndpointRouteBuilder"/> instance.
+        /// </summary>
+        /// <param name="endpoints">The <see cref="IEndpointRouteBuilder"/> to add
+        /// middleware to.</param>
+        /// <param name="path">Optional path to use for the branched pipeline.
+        /// If not provided then <see cref="PrometheusExporterOptions.ScrapeEndpointPath"/>
+        /// is used.</param>
+        /// <param name="meterProvider">Optional <see cref="MeterProvider"/>
+        /// containing a <see cref="PrometheusExporter"/> otherwise the primary
+        /// SDK provider will be resolved using application services.</param>
+        /// <param name="configureBranchedPipeline">Optional callback to
+        /// configure the branched pipeline. Called before registration of the
+        /// Prometheus middleware.</param>
+        /// <returns>A convention routes for the Prometheus scraping endpoint.</returns>
+        public static IEndpointConventionBuilder MapPrometheusScrapingEndpoint(
+            this IEndpointRouteBuilder endpoints,
+            string path = null,
+            MeterProvider meterProvider = null,
+            Action<IApplicationBuilder> configureBranchedPipeline = null)
+        {
+            var builder = endpoints.CreateApplicationBuilder();
+
+            // Note: Order is important here. MeterProvider is accessed before
+            // GetOptions<PrometheusExporterOptions> so that any changes made to
+            // PrometheusExporterOptions in deferred AddPrometheusExporter
+            // configure actions are reflected.
+            meterProvider ??= builder.ApplicationServices.GetRequiredService<MeterProvider>();
+
+            if (path == null)
+            {
+                var options = builder.ApplicationServices.GetOptions<PrometheusExporterOptions>();
+                path = options.ScrapeEndpointPath ?? PrometheusExporterOptions.DefaultScrapeEndpointPath;
+            }
+
+            if (!path.StartsWith("/"))
+            {
+                path = $"/{path}";
+            }
+
+            configureBranchedPipeline?.Invoke(builder);
+
+            builder.UseMiddleware<PrometheusExporterMiddleware>(meterProvider);
+
+            return endpoints.Map(new PathString(path), builder.Build());
+        }
+    }
+}
+#endif

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

@@ -167,6 +167,42 @@ public Task PrometheusExporterMiddlewareIntegration_NoMetrics()
                 skipMetrics: true);
         }
 
+        [Fact]
+        public Task PrometheusExporterMiddlewareIntegration_MapEndpoint()
+        {
+            return RunPrometheusExporterMiddlewareIntegrationTest(
+                "/metrics",
+                app => app.UseRouting().UseEndpoints(builder => builder.MapPrometheusScrapingEndpoint()),
+                services => services.AddRouting());
+        }
+
+        [Fact]
+        public Task PrometheusExporterMiddlewareIntegration_MapEndpoint_WithPathOverride()
+        {
+            return RunPrometheusExporterMiddlewareIntegrationTest(
+                "/metrics_path",
+                app => app.UseRouting().UseEndpoints(builder => builder.MapPrometheusScrapingEndpoint("metrics_path")),
+                services => services.AddRouting());
+        }
+
+        [Fact]
+        public async Task PrometheusExporterMiddlewareIntegration_MapEndpoint_WithMeterProvider()
+        {
+            using MeterProvider meterProvider = Sdk.CreateMeterProviderBuilder()
+                .AddMeter(MeterName)
+                .AddPrometheusExporter()
+                .Build();
+
+            await RunPrometheusExporterMiddlewareIntegrationTest(
+                "/metrics",
+                app => app.UseRouting().UseEndpoints(builder => builder.MapPrometheusScrapingEndpoint(
+                    path: null,
+                    meterProvider: meterProvider,
+                    configureBranchedPipeline: null)),
+                services => services.AddRouting(),
+                registerMeterProvider: false).ConfigureAwait(false);
+        }
+
         private static async Task RunPrometheusExporterMiddlewareIntegrationTest(
             string path,
             Action<IApplicationBuilder> configure,