[prometheus-httplistener] Throw an exception if the listener cannot b…

…e started (#5304)
open-telemetry · Feb 1, 2024 · 8b54074 · 8b54074
1 parent 9fd01f7
commit 8b54074
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Showing 4 changed files with 87 additions and 18 deletions.
diff --git a/src/OpenTelemetry.Exporter.Prometheus.HttpListener/CHANGELOG.md b/src/OpenTelemetry.Exporter.Prometheus.HttpListener/CHANGELOG.md
@@ -2,11 +2,17 @@
 
 ## Unreleased
 
-* Export OpenMetrics format from Prometheus exporters ([#5107](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5107))
+* Export OpenMetrics format from Prometheus exporters
+  ([#5107](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5107))
+
 * For requests with OpenMetrics format, scope info is automatically added
   ([#5086](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5086)
   [#5182](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5182))
 
+* **Breaking change** Updated the `PrometheusHttpListener` to throw an exception
+  if it can't be started.
+  ([#5304](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5304))
+
 ## 1.7.0-rc.1
 
 Released 2023-Nov-29

diff --git a/src/OpenTelemetry.Exporter.Prometheus.HttpListener/PrometheusHttpListener.cs b/src/OpenTelemetry.Exporter.Prometheus.HttpListener/PrometheusHttpListener.cs
@@ -59,6 +59,8 @@ public void Start(CancellationToken token = default)
                 return;
             }
 
+            this.httpListener.Start();
+
             // link the passed in token if not null
             this.tokenSource = token == default ?
                 new CancellationTokenSource() :
@@ -91,7 +93,7 @@ public void Dispose()
     {
         this.Stop();
 
-        if (this.httpListener != null && this.httpListener.IsListening)
+        if (this.httpListener.IsListening)
         {
             this.httpListener.Close();
         }
@@ -111,8 +113,6 @@ private static bool AcceptsOpenMetrics(HttpListenerRequest request)
 
     private void WorkerProc()
     {
-        this.httpListener.Start();
-
         try
         {
             using var scope = SuppressInstrumentationScope.Begin();

diff --git a/...rometheus.HttpListener.Tests/PrometheusHttpListenerMeterProviderBuilderExtensionsTests.cs b/...rometheus.HttpListener.Tests/PrometheusHttpListenerMeterProviderBuilderExtensionsTests.cs
@@ -23,7 +23,7 @@ public void TestAddPrometheusHttpListener_NamedOptions()
                 services.Configure<PrometheusHttpListenerOptions>("Exporter2", o => namedExporterOptionsConfigureOptionsInvocations++);
             })
             .AddPrometheusHttpListener()
-            .AddPrometheusHttpListener("Exporter2", o => { })
+            .AddPrometheusHttpListener("Exporter2", o => o.ScrapeEndpointPath = "/metrics2")
             .Build();
 
         Assert.Equal(1, defaultExporterOptionsConfigureOptionsInvocations);

diff --git a/test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/PrometheusHttpListenerTests.cs b/test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/PrometheusHttpListenerTests.cs
@@ -29,19 +29,15 @@ public class PrometheusHttpListenerTests
     [InlineData("http://example.com")]
     public void UriPrefixesPositiveTest(params string[] uriPrefixes)
     {
-        using MeterProvider meterProvider = Sdk.CreateMeterProviderBuilder()
-            .AddPrometheusHttpListener(options => options.UriPrefixes = uriPrefixes)
-            .Build();
+        TestPrometheusHttpListenerUriPrefixOptions(uriPrefixes);
     }
 
     [Fact]
     public void UriPrefixesNull()
     {
         Assert.Throws<ArgumentNullException>(() =>
         {
-            using MeterProvider meterProvider = Sdk.CreateMeterProviderBuilder()
-                .AddPrometheusHttpListener(options => options.UriPrefixes = null)
-                .Build();
+            TestPrometheusHttpListenerUriPrefixOptions(null);
         });
     }
 
@@ -50,20 +46,16 @@ public void UriPrefixesEmptyList()
     {
         Assert.Throws<ArgumentException>(() =>
         {
-            using MeterProvider meterProvider = Sdk.CreateMeterProviderBuilder()
-                .AddPrometheusHttpListener(options => options.UriPrefixes = new string[] { })
-                .Build();
+            TestPrometheusHttpListenerUriPrefixOptions(new string[] { });
         });
     }
 
     [Fact]
     public void UriPrefixesInvalid()
     {
-        Assert.Throws<InvalidOperationException>(() =>
+        Assert.Throws<ArgumentException>(() =>
         {
-            using MeterProvider meterProvider = Sdk.CreateMeterProviderBuilder()
-                .AddPrometheusHttpListener(options => options.UriPrefixes = new string[] { "ftp://example.com" })
-                .Build();
+            TestPrometheusHttpListenerUriPrefixOptions(new string[] { "ftp://example.com" });
         });
     }
 
@@ -91,6 +83,77 @@ public async Task PrometheusExporterHttpServerIntegration_UseOpenMetricsVersionH
         await this.RunPrometheusExporterHttpServerIntegrationTest(acceptHeader: "application/openmetrics-text; version=1.0.0");
     }
 
+    [Fact]
+    public void PrometheusHttpListenerThrowsOnStart()
+    {
+        Random random = new Random();
+        int retryAttempts = 5;
+        int port = 0;
+        string address = null;
+
+        PrometheusExporter exporter = null;
+        PrometheusHttpListener listener = null;
+
+        // Step 1: Start a listener on a random port.
+        while (retryAttempts-- != 0)
+        {
+            port = random.Next(2000, 5000);
+            address = $"http://localhost:{port}/";
+
+            try
+            {
+                exporter = new PrometheusExporter(new());
+                listener = new PrometheusHttpListener(
+                    exporter,
+                    new()
+                    {
+                        UriPrefixes = new string[] { address },
+                    });
+
+                listener.Start();
+
+                break;
+            }
+            catch
+            {
+                // ignored
+            }
+        }
+
+        if (retryAttempts == 0)
+        {
+            throw new InvalidOperationException("PrometheusHttpListener could not be started");
+        }
+
+        // Step 2: Make sure if we start a second listener on the same port an exception is thrown.
+        Assert.Throws<HttpListenerException>(() =>
+        {
+            using var exporter = new PrometheusExporter(new());
+            using var listener = new PrometheusHttpListener(
+                exporter,
+                new()
+                {
+                    UriPrefixes = new string[] { address },
+                });
+
+            listener.Start();
+        });
+
+        exporter?.Dispose();
+        listener?.Dispose();
+    }
+
+    private static void TestPrometheusHttpListenerUriPrefixOptions(string[] uriPrefixes)
+    {
+        using var exporter = new PrometheusExporter(new());
+        using var listener = new PrometheusHttpListener(
+            exporter,
+            new()
+            {
+                UriPrefixes = uriPrefixes,
+            });
+    }
+
     private async Task RunPrometheusExporterHttpServerIntegrationTest(bool skipMetrics = false, string acceptHeader = "application/openmetrics-text")
     {
         var requestOpenMetrics = acceptHeader.StartsWith("application/openmetrics-text");