Add OTEL tracing support for Wiremock + automatic OTEL for Aspire integration (#1418)

* Update aspire to 13.1 (examples + code)

Allows usage of aspire CLI which is very useful for dev in codespaces (for my next PR).

* Add OTEL support

* Initial PR feedback

* PR feedback

* PR feedback

* PR feedback

* Cleanup.

* Cleanup

* Fix

* Fix

* Rename stuff around to be more accurate

* PR feedback

* Update WireMock.Net.OpenTelemetry.csproj

Update <Authors>

* PR feedback parser

* PR feedback package versions

* Status code feedback.

* Update preprocessor directives to to Activity Tracing instead of OpenTelemetry. Is more descriptive.

* Add tests

* Improve tests

---------

Co-authored-by: Stef Heyenrath <Stef.Heyenrath@gmail.com>

src/WireMock.Net.Aspire/WireMockServerArguments.cs

@@ -79,6 +79,22 @@ public class WireMockServerArguments
     /// </summary>
     public Dictionary<string, string[]> ProtoDefinitions { get; set; } = [];
 
+    /// <summary>
+    /// Gets or sets a value indicating whether OpenTelemetry tracing is enabled.
+    /// When enabled, WireMock.Net will emit distributed traces for request processing.
+    /// Default value is <c>false</c>.
+    /// </summary>
+    public bool OpenTelemetryEnabled { get; set; }
+
+    /// <summary>
+    /// Gets or sets the OTLP exporter endpoint URL.
+    /// When set, traces will be exported to this endpoint using the OTLP protocol.
+    /// Example: "http://localhost:4317" for gRPC or "http://localhost:4318" for HTTP.
+    /// If not set, the OTLP exporter will use the <c>OTEL_EXPORTER_OTLP_ENDPOINT</c> environment variable,
+    /// or fall back to the default endpoint (<c>http://localhost:4317</c> for gRPC).
+    /// </summary>
+    public string? OpenTelemetryOtlpExporterEndpoint { get; set; }
+
     /// <summary>
     /// Add an additional Urls on which WireMock should listen.
     /// </summary>
@@ -138,6 +154,20 @@ public class WireMockServerArguments
             Add(args, "--WatchStaticMappingsInSubdirectories", "true");
         }
 
+        if (OpenTelemetryEnabled)
+        {
+            // Enable activity tracing (creates System.Diagnostics.Activity objects)
+            Add(args, "--ActivityTracingEnabled", "true");
+            
+            // Enable OpenTelemetry exporter
+            Add(args, "--OpenTelemetryEnabled", "true");
+            
+            if (!string.IsNullOrEmpty(OpenTelemetryOtlpExporterEndpoint))
+            {
+                Add(args, "--OpenTelemetryOtlpExporterEndpoint", OpenTelemetryOtlpExporterEndpoint);
+            }
+        }
+
         if (AdditionalUrls.Count > 0)
         {
             Add(args, "--Urls", $"http://*:{HttpContainerPort} {string.Join(' ', AdditionalUrls)}");

src/WireMock.Net.Aspire/WireMockServerBuilderExtensions.cs

@@ -287,6 +287,40 @@ public static class WireMockServerBuilderExtensions
         return wiremock;
     }
 
+    /// <summary>
+    /// Configures OpenTelemetry distributed tracing for the WireMock.Net server.
+    /// This enables automatic trace export to the Aspire dashboard.
+    /// </summary>
+    /// <param name="wiremock">The <see cref="IResourceBuilder{WireMockServerResource}"/>.</param>
+    /// <returns>A reference to the <see cref="IResourceBuilder{WireMockServerResource}"/>.</returns>
+    /// <remarks>
+    /// When enabled, WireMock.Net will emit distributed traces for each request processed,
+    /// including information about:
+    /// <list type="bullet">
+    ///   <item>HTTP method, URL, and status code</item>
+    ///   <item>Mapping match results and scores</item>
+    ///   <item>Request processing duration</item>
+    /// </list>
+    /// The traces will automatically appear in the Aspire dashboard.
+    /// </remarks>
+    public static IResourceBuilder<WireMockServerResource> WithOpenTelemetry(this IResourceBuilder<WireMockServerResource> wiremock)
+    {
+        Guard.NotNull(wiremock);
+
+        // Enable OpenTelemetry in WireMock server arguments
+        wiremock.Resource.Arguments.OpenTelemetryEnabled = true;
+
+        // Use Aspire's standard WithOtlpExporter to configure OTEL environment variables for the container
+        // This sets OTEL_EXPORTER_OTLP_ENDPOINT which the OTLP exporter reads automatically
+        var containerBuilder = wiremock as IResourceBuilder<ContainerResource>;
+        if (containerBuilder != null)
+        {
+            containerBuilder.WithOtlpExporter();
+        }
+
+        return wiremock;
+    }
+
     private static Task<ExecuteCommandResult> OnRunOpenInspectorCommandAsync(IResourceBuilder<WireMockServerResource> builder)
     {
         WireMockInspector.Inspect(builder.Resource.GetEndpoint().Url);