Adding generated correlation id to response

sample/SampleWebApp/SampleWebApp.csproj

@@ -8,9 +8,12 @@
 
   <ItemGroup>
     <PackageReference Include="Serilog.AspNetCore" Version="8.0.2" />
-    <PackageReference Include="Serilog.Enrichers.ClientInfo" Version="2.1.1" />
     <PackageReference Include="Serilog.Sinks.Console" Version="6.0.0" />
     <PackageReference Include="Serilog.Sinks.File" Version="6.0.0" />
     <PackageReference Include="Swashbuckle.AspNetCore" Version="6.8.1" />
   </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Serilog.Enrichers.ClientInfo\Serilog.Enrichers.ClientInfo.csproj" />
+  </ItemGroup>
 </Project>

src/Serilog.Enrichers.ClientInfo/Enrichers/CorrelationIdEnricher.cs

@@ -1,19 +1,18 @@
-using System;
-using Microsoft.AspNetCore.Http;
-using Microsoft.Extensions.Primitives;
+using Microsoft.AspNetCore.Http;
 using Serilog.Core;
 using Serilog.Events;
+using Serilog.Preparers.CorrelationIds;
 
+#nullable enable
 namespace Serilog.Enrichers;
 
 /// <inheritdoc />
 public class CorrelationIdEnricher : ILogEventEnricher
 {
     private const string CorrelationIdItemKey = "Serilog_CorrelationId";
     private const string PropertyName = "CorrelationId";
-    private readonly bool _addValueIfHeaderAbsence;
     private readonly IHttpContextAccessor _contextAccessor;
-    private readonly string _headerKey;
+    private readonly CorrelationIdPreparerOptions _options;
 
     /// <summary>
     ///     Initializes a new instance of the <see cref="CorrelationIdEnricher" /> class.
@@ -24,15 +23,22 @@ public class CorrelationIdEnricher : ILogEventEnricher
     /// <param name="addValueIfHeaderAbsence">
     ///     Determines whether to add a new correlation ID value if the header is absent.
     /// </param>
-    public CorrelationIdEnricher(string headerKey, bool addValueIfHeaderAbsence)
-        : this(headerKey, addValueIfHeaderAbsence, new HttpContextAccessor())
+    public CorrelationIdEnricher(
+        string headerKey,
+        bool addValueIfHeaderAbsence)
+        : this(
+              headerKey,
+              addValueIfHeaderAbsence,
+              new HttpContextAccessor())
     {
     }
 
-    internal CorrelationIdEnricher(string headerKey, bool addValueIfHeaderAbsence, IHttpContextAccessor contextAccessor)
+    internal CorrelationIdEnricher(
+        string headerKey,
+        bool addValueIfHeaderAbsence,
+        IHttpContextAccessor contextAccessor)
     {
-        _headerKey = headerKey;
-        _addValueIfHeaderAbsence = addValueIfHeaderAbsence;
+        _options = new CorrelationIdPreparerOptions(addValueIfHeaderAbsence, headerKey);
         _contextAccessor = contextAccessor;
     }
 
@@ -42,39 +48,30 @@ public void Enrich(LogEvent logEvent, ILogEventPropertyFactory propertyFactory)
         HttpContext httpContext = _contextAccessor.HttpContext;
         if (httpContext == null) return;
 
-        if (httpContext.Items.TryGetValue(CorrelationIdItemKey, out object value) &&
+        if (httpContext.Items.TryGetValue(CorrelationIdItemKey, out object? value) &&
             value is LogEventProperty logEventProperty)
         {
             logEvent.AddPropertyIfAbsent(logEventProperty);
 
             // Ensure the string value is also available if not already stored
             if (!httpContext.Items.ContainsKey(Constants.CorrelationIdValueKey))
             {
-                string correlationIdValue = ((ScalarValue)logEventProperty.Value).Value as string;
+                string? correlationIdValue = ((ScalarValue)logEventProperty.Value).Value as string;
                 httpContext.Items.Add(Constants.CorrelationIdValueKey, correlationIdValue);
             }
 
             return;
         }
 
-        StringValues requestHeader = httpContext.Request.Headers[_headerKey];
-        StringValues responseHeader = httpContext.Response.Headers[_headerKey];
+        ICorrelationIdPreparer correlationIdPreparer = httpContext.GetCorrelationIdPreparer();
 
-        string correlationId;
-
-        if (!string.IsNullOrWhiteSpace(requestHeader))
-            correlationId = requestHeader;
-        else if (!string.IsNullOrWhiteSpace(responseHeader))
-            correlationId = responseHeader;
-        else if (_addValueIfHeaderAbsence)
-            correlationId = Guid.NewGuid().ToString();
-        else
-            correlationId = null;
+        string? correlationId = correlationIdPreparer.PrepareCorrelationId(httpContext, _options);
 
         LogEventProperty correlationIdProperty = new(PropertyName, new ScalarValue(correlationId));
         logEvent.AddOrUpdateProperty(correlationIdProperty);
 
         httpContext.Items.Add(CorrelationIdItemKey, correlationIdProperty);
         httpContext.Items.Add(Constants.CorrelationIdValueKey, correlationId);
     }
-}
+}
+#nullable disable

src/Serilog.Enrichers.ClientInfo/Extensions/HttpContextExtensions.cs

@@ -1,4 +1,6 @@
 using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.DependencyInjection;
+using Serilog.Preparers.CorrelationIds;
 
 namespace Serilog.Enrichers;
 
@@ -14,4 +16,12 @@ public static class HttpContextExtensions
     /// <returns>The correlation ID as a string, or null if not available.</returns>
     public static string GetCorrelationId(this HttpContext httpContext)
         => httpContext?.Items[Constants.CorrelationIdValueKey] as string;
+
+    /// <summary>
+    /// Retrieves the correlation ID preparer for processing the current HTTP context.
+    /// </summary>
+    /// <param name="httpContext">The HTTP context.</param>
+    /// <returns>Correlation ID preparer.</returns>
+    internal static ICorrelationIdPreparer GetCorrelationIdPreparer(this HttpContext httpContext)
+        => httpContext.RequestServices.GetService<ICorrelationIdPreparer>() ?? new CorrelationIdPreparer();
 }

src/Serilog.Enrichers.ClientInfo/Preparers/CorrelationIds/CorrelationIdPreparer.cs

@@ -0,0 +1,52 @@
+using System;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.Primitives;
+
+#nullable enable
+namespace Serilog.Preparers.CorrelationIds
+{
+    internal class CorrelationIdPreparer : ICorrelationIdPreparer
+    {
+        protected string? CorrelationId { get; set; }
+
+        /// <inheritdoc/>
+        public string? PrepareCorrelationId(
+            HttpContext httpContext,
+            CorrelationIdPreparerOptions correlationIdPreparerOptions)
+        {
+            if (string.IsNullOrEmpty(CorrelationId))
+            {
+                CorrelationId = PrepareValueForCorrelationId(httpContext, correlationIdPreparerOptions);
+            }
+
+            return CorrelationId;
+        }
+
+        protected string? PrepareValueForCorrelationId(
+            HttpContext httpContext,
+            CorrelationIdPreparerOptions correlationIdPreparerOptions)
+        {
+            StringValues requestHeader = httpContext.Request.Headers[correlationIdPreparerOptions.HeaderKey];
+
+            if (!string.IsNullOrWhiteSpace(requestHeader))
+            {
+                return requestHeader;
+            }
+
+            StringValues responseHeader = httpContext.Response.Headers[correlationIdPreparerOptions.HeaderKey];
+
+            if (!string.IsNullOrWhiteSpace(responseHeader))
+            {
+                return responseHeader;
+            }
+
+            if (correlationIdPreparerOptions.AddValueIfHeaderAbsence)
+            {
+                return Guid.NewGuid().ToString();
+            }
+
+            return null;
+        }
+    }
+}
+#nullable disable

src/Serilog.Enrichers.ClientInfo/Preparers/CorrelationIds/CorrelationIdPreparerOptions.cs

@@ -0,0 +1,31 @@
+namespace Serilog.Preparers.CorrelationIds
+{
+    /// <summary>
+    /// Settings for <see cref="ICorrelationIdPreparer"/>.
+    /// </summary>
+    public class CorrelationIdPreparerOptions
+    {
+        /// <summary>
+        /// Determines whether to add a new correlation ID value if the header is absent.
+        /// </summary>
+        public bool AddValueIfHeaderAbsence { get; }
+
+        /// <summary>
+        /// The header key used to retrieve the correlation ID from the HTTP request or response headers.
+        /// </summary>
+        public string HeaderKey { get; }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="CorrelationIdPreparerOptions" /> class.
+        /// </summary>
+        /// <param name="addValueIfHeaderAbsence">Determines whether to add a new correlation ID value if the header is absent.</param>
+        /// <param name="headerKey">The header key used to retrieve the correlation ID from the HTTP request or response headers.</param>
+        public CorrelationIdPreparerOptions(
+            bool addValueIfHeaderAbsence,
+            string headerKey)
+        {
+            AddValueIfHeaderAbsence = addValueIfHeaderAbsence;
+            HeaderKey = headerKey;
+        }
+    }
+}

src/Serilog.Enrichers.ClientInfo/Preparers/CorrelationIds/ICorrelationIdPreparer.cs

@@ -0,0 +1,22 @@
+using Microsoft.AspNetCore.Http;
+
+#nullable enable
+namespace Serilog.Preparers.CorrelationIds
+{
+    /// <summary>
+    /// Preparer for correlation ID.
+    /// </summary>
+    public interface ICorrelationIdPreparer
+    {
+        /// <summary>
+        /// Prepares the correlation ID.
+        /// </summary>
+        /// <param name="httpContext">The HTTP context.</param>
+        /// <param name="correlationIdPreparerOptions">Options for preparation.</param>
+        /// <returns>The correlation ID.</returns>
+        string? PrepareCorrelationId(
+            HttpContext httpContext,
+            CorrelationIdPreparerOptions correlationIdPreparerOptions);
+    }
+}
+#nullable disable

test/Serilog.Enrichers.ClientInfo.Tests/CorrelationIdEnricherTests.cs

@@ -1,8 +1,11 @@
-using Microsoft.AspNetCore.Http;
+using System;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.DependencyInjection;
 using NSubstitute;
+using NSubstitute.ReturnsExtensions;
 using Serilog.Core;
 using Serilog.Events;
-using System;
+using Serilog.Preparers.CorrelationIds;
 using Xunit;
 
 namespace Serilog.Enrichers.ClientInfo.Tests;
@@ -15,18 +18,44 @@ public class CorrelationIdEnricherTests
 
     public CorrelationIdEnricherTests()
     {
-        DefaultHttpContext httpContext = new();
+        IServiceProvider serviceProvider = Substitute.For<IServiceProvider>();
+        serviceProvider.GetService<ICorrelationIdPreparer>().ReturnsNull();
+
+        DefaultHttpContext httpContext = new DefaultHttpContext
+        {
+            RequestServices = serviceProvider
+        };
         _contextAccessor = Substitute.For<IHttpContextAccessor>();
         _contextAccessor.HttpContext.Returns(httpContext);
     }
 
     [Fact]
-    public void EnrichLogWithCorrelationId_WhenHttpRequestContainCorrelationHeader_ShouldCreateCorrelationIdProperty()
+    public void EnrichLogWithCorrelationId_WhenRequestServicesContainsICorrelationIdPreparer_ShouldUseCorrelationIdPreparerFromRequestServices()
     {
         // Arrange
         string correlationId = Guid.NewGuid().ToString();
-        _contextAccessor.HttpContext!.Request!.Headers[HeaderKey] = correlationId;
-        CorrelationIdEnricher correlationIdEnricher = new(HeaderKey, false, _contextAccessor);
+
+        ICorrelationIdPreparer correlationIdPreparer = Substitute.For<ICorrelationIdPreparer>();
+        IServiceProvider serviceProvider = Substitute.For<IServiceProvider>();
+
+        DefaultHttpContext httpContext = new DefaultHttpContext
+        {
+            RequestServices = serviceProvider
+        };
+        CorrelationIdPreparerOptions correlationIdPreparerOptions = new CorrelationIdPreparerOptions(false, HeaderKey);
+
+        correlationIdPreparer.PrepareCorrelationId(
+            httpContext,
+            Arg.Is<CorrelationIdPreparerOptions>(x =>
+                x.AddValueIfHeaderAbsence == correlationIdPreparerOptions.AddValueIfHeaderAbsence &&
+                x.HeaderKey == correlationIdPreparerOptions.HeaderKey))
+            .Returns(correlationId);
+
+        serviceProvider.GetService<ICorrelationIdPreparer>().Returns(correlationIdPreparer);
+        IHttpContextAccessor contextAccessor = Substitute.For<IHttpContextAccessor>();
+        contextAccessor.HttpContext.Returns(httpContext);
+
+        CorrelationIdEnricher correlationIdEnricher = new(correlationIdPreparerOptions.HeaderKey, correlationIdPreparerOptions.AddValueIfHeaderAbsence, contextAccessor);
 
         LogEvent evt = null;
         Logger log = new LoggerConfiguration()
@@ -44,8 +73,7 @@ public void EnrichLogWithCorrelationId_WhenHttpRequestContainCorrelationHeader_S
     }
 
     [Fact]
-    public void
-        EnrichLogWithCorrelationId_WhenHttpRequestContainCorrelationHeader_ShouldCreateCorrelationIdPropertyHasValue()
+    public void EnrichLogWithCorrelationId_WhenHttpRequestContainCorrelationHeader_ShouldCreateCorrelationIdProperty()
     {
         // Arrange
         string correlationId = Guid.NewGuid().ToString();