Introduce TelemetryResilienceStrategyOptions.ResultFormatter (#1294)

src/Polly.Extensions/Polly.Extensions.csproj

@@ -28,5 +28,6 @@
     <PackageReference Include="Microsoft.Extensions.Options" />
     <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" />
     <PackageReference Include="System.Diagnostics.DiagnosticSource" />
+    <Reference Include="System.Net.Http" Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'"/>
   </ItemGroup>
 </Project>

src/Polly.Extensions/Telemetry/TelemetryResilienceStrategy.cs

@@ -12,14 +12,16 @@ internal sealed class TelemetryResilienceStrategy : ResilienceStrategy
     private readonly string? _strategyKey;
     private readonly List<Action<EnrichmentContext>> _enrichers;
     private readonly ILogger _logger;
+    private readonly Func<ResilienceContext, object?, object?> _resultFormatter;
 
     // Temporary only, until the TimeProvider is exposed
     public TelemetryResilienceStrategy(
         string builderName,
         string? strategyKey,
         ILoggerFactory loggerFactory,
+        Func<ResilienceContext, object?, object?> resultFormatter,
         List<Action<EnrichmentContext>> enrichers)
-        : this(TimeProvider.System, builderName, strategyKey, loggerFactory, enrichers)
+        : this(TimeProvider.System, builderName, strategyKey, loggerFactory, resultFormatter, enrichers)
     {
     }
 
@@ -28,11 +30,13 @@ public TelemetryResilienceStrategy(
         string? builderName,
         string? strategyKey,
         ILoggerFactory loggerFactory,
+        Func<ResilienceContext, object?, object?> resultFormatter,
         List<Action<EnrichmentContext>> enrichers)
     {
         _timeProvider = timeProvider;
         _builderName = builderName;
         _strategyKey = strategyKey;
+        _resultFormatter = resultFormatter;
         _enrichers = enrichers;
         _logger = loggerFactory.CreateLogger(TelemetryUtil.PollyDiagnosticSource);
         ExecutionDuration = ResilienceTelemetryDiagnosticSource.Meter.CreateHistogram<double>(
@@ -59,7 +63,7 @@ protected override async ValueTask<Outcome<TResult>> ExecuteCoreAsync<TResult, T
             _builderName,
             _strategyKey,
             context.GetResultType(),
-            ExpandOutcome(outcome),
+            ExpandOutcome(context, outcome),
             context.GetExecutionHealth(),
             duration.TotalMilliseconds,
             outcome.Exception);
@@ -85,9 +89,9 @@ private static Outcome<object> CreateOutcome<TResult>(Outcome<TResult> outcome)
             new Outcome<object>(outcome.Result) :
             new Outcome<object>(outcome.Exception!);
 
-    private static object? ExpandOutcome<TResult>(Outcome<TResult> outcome)
+    private object? ExpandOutcome<TResult>(ResilienceContext context, Outcome<TResult> outcome)
     {
         // stryker disable once all: no means to test this
-        return (object)outcome.Exception?.Message! ?? outcome.Result;
+        return (object)outcome.Exception?.Message! ?? _resultFormatter(context, outcome.Result);
     }
 }

src/Polly.Extensions/Telemetry/TelemetryResilienceStrategyBuilderExtensions.cs

@@ -60,6 +60,7 @@ public static TBuilder EnableTelemetry<TBuilder>(this TBuilder builder, Telemetr
                 builder.BuilderName,
                 builder.Properties.GetValue(TelemetryUtil.StrategyKey, null!),
                 options.LoggerFactory,
+                options.ResultFormatter,
                 options.Enrichers.ToList());
 
             strategies.Insert(0, telemetryStrategy);

src/Polly.Extensions/Telemetry/TelemetryResilienceStrategyOptions.cs

@@ -1,4 +1,6 @@
+using System;
 using System.ComponentModel.DataAnnotations;
+using System.Net.Http;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
 
@@ -25,4 +27,20 @@ public class TelemetryResilienceStrategyOptions
     /// Defaults to an empty collection.
     /// </remarks>
     public ICollection<Action<EnrichmentContext>> Enrichers { get; } = new List<Action<EnrichmentContext>>();
+
+    /// <summary>
+    /// Gets or sets the result formatter.
+    /// </summary>
+    /// <remarks>
+    /// Defaults to a formatter that returns a status code for HTTP based responses and the result as-is for all other result types.
+    /// <para>
+    /// This property is required.
+    /// </para>
+    /// </remarks>
+    [Required]
+    public Func<ResilienceContext, object?, object?> ResultFormatter { get; set; } = (_, result) => result switch
+    {
+        HttpResponseMessage response => (int)response.StatusCode,
+        _ => result,
+    };
 }

test/Polly.Extensions.Tests/Telemetry/TelemetryResilienceStrategyOptionsTests.cs

@@ -1,3 +1,5 @@
+using System.Net;
+using System.Net.Http;
 using Microsoft.Extensions.Logging.Abstractions;
 using Polly.Extensions.Telemetry;
 
@@ -12,5 +14,11 @@ public void Ctor_EnsureDefaults()
 
         options.Enrichers.Should().BeEmpty();
         options.LoggerFactory.Should().Be(NullLoggerFactory.Instance);
+        var resilienceContext = ResilienceContext.Get();
+        options.ResultFormatter(resilienceContext, null).Should().BeNull();
+        options.ResultFormatter(resilienceContext, "dummy").Should().Be("dummy");
+
+        using var response = new HttpResponseMessage(HttpStatusCode.OK);
+        options.ResultFormatter(resilienceContext, response).Should().Be(200);
     }
 }

test/Polly.Extensions.Tests/Telemetry/TelemetryResilienceStrategyTests.cs

@@ -165,7 +165,8 @@ public void Execute_WithResult_EnsureMetered(bool healthy)
         }
     }
 
-    private TelemetryResilienceStrategy CreateStrategy() => new("my-builder", "my-key", _loggerFactory, new List<Action<EnrichmentContext>> { c => _enricher?.Invoke(c) });
+    private TelemetryResilienceStrategy CreateStrategy() => new("my-builder", "my-key", _loggerFactory, (_, r) => r, new List<Action<EnrichmentContext>> { c => _enricher?.Invoke(c) });
+
     public void Dispose()
     {
         _metering.Dispose();