[Exporter.PrometherusHttpListener] Restore ScrapeResponseCacheDuratio…

…nMilliseconds

src/OpenTelemetry.Exporter.Prometheus.HttpListener/.publicApi/net462/PublicAPI.Unshipped.txt

@@ -1,4 +1,6 @@
 OpenTelemetry.Exporter.PrometheusHttpListenerOptions
+OpenTelemetry.Exporter.PrometheusHttpListenerOptions.ScrapeResponseCacheDurationMilliseconds.get -> int
+OpenTelemetry.Exporter.PrometheusHttpListenerOptions.ScrapeResponseCacheDurationMilliseconds.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/.publicApi/netstandard2.0/PublicAPI.Unshipped.txt

@@ -2,6 +2,8 @@ OpenTelemetry.Exporter.PrometheusHttpListenerOptions
 OpenTelemetry.Exporter.PrometheusHttpListenerOptions.PrometheusHttpListenerOptions() -> void
 OpenTelemetry.Exporter.PrometheusHttpListenerOptions.ScrapeEndpointPath.get -> string
 OpenTelemetry.Exporter.PrometheusHttpListenerOptions.ScrapeEndpointPath.set -> void
+OpenTelemetry.Exporter.PrometheusHttpListenerOptions.ScrapeResponseCacheDurationMilliseconds.get -> int
+OpenTelemetry.Exporter.PrometheusHttpListenerOptions.ScrapeResponseCacheDurationMilliseconds.set -> void
 OpenTelemetry.Exporter.PrometheusHttpListenerOptions.UriPrefixes.get -> System.Collections.Generic.IReadOnlyCollection<string>
 OpenTelemetry.Exporter.PrometheusHttpListenerOptions.UriPrefixes.set -> void
 OpenTelemetry.Metrics.PrometheusHttpListenerMeterProviderBuilderExtensions

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

@@ -5,6 +5,9 @@
 * Bug fix for Prometheus Exporter reporting StatusCode 204
   instead of 200, when no metrics are collected
   ([#3643](https://github.com/open-telemetry/opentelemetry-dotnet/pull/3643))
+* Bug fix, restore endpoint response caching feature &
+  `ScrapeResponseCacheDurationMilliseconds` option
+  ([#3694](https://github.com/open-telemetry/opentelemetry-dotnet/pull/3694))
 * Added overloads which accept a name to the `MeterProviderBuilder`
   `AddPrometheusHttpListener` extension to allow for more fine-grained options
   management

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

@@ -15,6 +15,7 @@
 // </copyright>
 
 using System;
+using System.Collections.Generic;
 using System.Net;
 using System.Threading;
 using System.Threading.Tasks;
@@ -35,16 +36,18 @@ internal sealed class PrometheusHttpListener : IDisposable
         /// <summary>
         /// Initializes a new instance of the <see cref="PrometheusHttpListener"/> class.
         /// </summary>
-        /// <param name="exporter"><see cref="PrometheusExporter"/>The exporter instance.</param>
-        /// <param name="options"><see cref="PrometheusHttpListenerOptions"/>The configured HttpListener options.</param>
-        public PrometheusHttpListener(PrometheusExporter exporter, PrometheusHttpListenerOptions options)
+        /// <param name="exporter"><see cref="PrometheusExporter"/>The path to use for the scraping endpoint.</param>
+        /// <param name="scrapeEndpointPath">The configured HttpListener options.</param>
+        /// <param name="uriPrefixes">The URI (Uniform Resource Identifier) prefixes to use for the http listener.</param>
+        public PrometheusHttpListener(PrometheusExporter exporter, string scrapeEndpointPath, IEnumerable<string> uriPrefixes)
         {
             Guard.ThrowIfNull(exporter);
-            Guard.ThrowIfNull(options);
+            Guard.ThrowIfNullOrWhitespace(scrapeEndpointPath);
+            Guard.ThrowIfNull(uriPrefixes);
 
             this.exporter = exporter;
 
-            string path = options.ScrapeEndpointPath;
+            string path = scrapeEndpointPath;
 
             if (!path.StartsWith("/"))
             {
@@ -56,7 +59,7 @@ public PrometheusHttpListener(PrometheusExporter exporter, PrometheusHttpListene
                 path = $"{path}/";
             }
 
-            foreach (string uriPrefix in options.UriPrefixes)
+            foreach (string uriPrefix in uriPrefixes)
             {
                 this.httpListener.Prefixes.Add($"{uriPrefix.TrimEnd('/')}{path}");
             }

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

@@ -80,7 +80,7 @@ private static MeterProviderBuilder AddPrometheusHttpListener(
             MeterProviderBuilder builder,
             PrometheusHttpListenerOptions options)
         {
-            var exporter = new PrometheusExporter();
+            var exporter = new PrometheusExporter(options.ScrapeResponseCacheDurationMilliseconds);
 
             var reader = new BaseExportingMetricReader(exporter)
             {
@@ -89,7 +89,7 @@ private static MeterProviderBuilder AddPrometheusHttpListener(
 
             try
             {
-                var listener = new PrometheusHttpListener(exporter, options);
+                var listener = new PrometheusHttpListener(exporter, options.ScrapeEndpointPath, options.UriPrefixes);
                 exporter.OnDispose = () => listener.Dispose();
                 listener.Start();
             }

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

@@ -25,13 +25,31 @@ namespace OpenTelemetry.Exporter
     /// </summary>
     public class PrometheusHttpListenerOptions
     {
-        private IReadOnlyCollection<string> uriPrefixes = new string[] { "http://localhost:9464/" };
+        private int scrapeResponseCacheDurationMilliseconds = 300;
+        private IReadOnlyCollection<string> uriPrefixes = new[] { "http://localhost:9464/" };
 
         /// <summary>
         /// Gets or sets the path to use for the scraping endpoint. Default value: "/metrics".
         /// </summary>
         public string ScrapeEndpointPath { get; set; } = "/metrics";
 
+        /// <summary>
+        /// Gets or sets the cache duration in milliseconds for scrape responses. Default value: 300.
+        /// </summary>
+        /// <remarks>
+        /// Note: Specify 0 to disable response caching.
+        /// </remarks>
+        public int ScrapeResponseCacheDurationMilliseconds
+        {
+            get => this.scrapeResponseCacheDurationMilliseconds;
+            set
+            {
+                Guard.ThrowIfOutOfRange(value, min: 0);
+
+                this.scrapeResponseCacheDurationMilliseconds = value;
+            }
+        }
+
         /// <summary>
         /// Gets or sets the URI (Uniform Resource Identifier) prefixes to use for the http listener.
         /// Default value: <c>["http://localhost:9464/"]</c>.

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

@@ -42,6 +42,12 @@ for more details.
 
 Defines the Prometheus scrape endpoint path. Default value: `"/metrics"`.
 
+### ScrapeResponseCacheDurationMilliseconds
+
+Configures scrape endpoint response caching. Multiple scrape requests within the
+cache duration time period will receive the same previously generated response.
+The default value is `300`. Set to `0` to disable response caching.
+
 ## Troubleshooting
 
 This component uses an

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

@@ -29,11 +29,7 @@ namespace OpenTelemetry.Exporter.Prometheus.Tests
 {
     public sealed class PrometheusCollectionManagerTests
     {
-#if PROMETHEUS_HTTP_LISTENER
-        [Fact(Skip = "Might be flaky. Might be a bug. See: https://github.com/open-telemetry/opentelemetry-dotnet/issues/3679")]
-#else
         [Fact]
-#endif
         public async Task EnterExitCollectTest()
         {
             using var meter = new Meter(Utils.GetCurrentMethodName());