Workaround for Kestrel bleeding AsyncLocal across requests (#9)

Author: alefranz

src/HeaderPropagationMiddleware.cs

@@ -33,7 +33,8 @@ public HeaderPropagationMiddleware(RequestDelegate next, IOptions<HeaderPropagat
             _values = values ?? throw new ArgumentNullException(nameof(values));
         }
 
-        public Task Invoke(HttpContext context)
+        // This needs to be async as otherwise the AsyncLocal could bleed across requests, see https://github.com/aspnet/AspNetCore/issues/13991.
+        public async Task Invoke(HttpContext context)
         {
             // We need to intialize the headers because the message handler will use this to detect misconfiguration.
             var headers = _values.Headers ??= new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase);
@@ -56,7 +57,7 @@ public Task Invoke(HttpContext context)
                 }
             }
 
-            return _next.Invoke(context);
+            await _next.Invoke(context);
         }
 
         private static StringValues GetValue(HttpContext context, HeaderPropagationEntry entry)

test/HeaderPropagationMiddlewareTest.cs

@@ -1,6 +1,8 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
+using System.Collections.Generic;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.Options;
@@ -14,7 +16,11 @@ public class HeaderPropagationMiddlewareTest
         public HeaderPropagationMiddlewareTest()
         {
             Context = new DefaultHttpContext();
-            Next = ctx => Task.CompletedTask;
+            Next = ctx =>
+            {
+                CapturedHeaders = State.Headers;
+                return Task.CompletedTask;
+            };
             Configuration = new HeaderPropagationOptions();
             State = new HeaderPropagationValues();
             Middleware = new HeaderPropagationMiddleware(Next,
@@ -24,8 +30,10 @@ public HeaderPropagationMiddlewareTest()
 
         public DefaultHttpContext Context { get; set; }
         public RequestDelegate Next { get; set; }
+        public Action Assertion { get; set; }
         public HeaderPropagationOptions Configuration { get; set; }
         public HeaderPropagationValues State { get; set; }
+        public IDictionary<string, StringValues> CapturedHeaders { get; set; }
         public HeaderPropagationMiddleware Middleware { get; set; }
 
         [Fact]
@@ -39,8 +47,8 @@ public async Task HeaderInRequest_AddCorrectValue()
             await Middleware.Invoke(Context);
 
             // Assert
-            Assert.Contains("in", State.Headers.Keys);
-            Assert.Equal(new[] { "test" }, State.Headers["in"]);
+            Assert.Contains("in", CapturedHeaders.Keys);
+            Assert.Equal(new[] { "test" }, CapturedHeaders["in"]);
         }
 
         [Fact]
@@ -53,7 +61,7 @@ public async Task NoHeaderInRequest_DoesNotAddIt()
             await Middleware.Invoke(Context);
 
             // Assert
-            Assert.Empty(State.Headers);
+            Assert.Empty(CapturedHeaders);
         }
 
         [Fact]
@@ -66,7 +74,7 @@ public async Task HeaderInRequest_NotInOptions_DoesNotAddIt()
             await Middleware.Invoke(Context);
 
             // Assert
-            Assert.Empty(State.Headers);
+            Assert.Empty(CapturedHeaders);
         }
 
         [Fact]
@@ -82,10 +90,10 @@ public async Task MultipleHeadersInRequest_AddAllHeaders()
             await Middleware.Invoke(Context);
 
             // Assert
-            Assert.Contains("in", State.Headers.Keys);
-            Assert.Equal(new[] { "test" }, State.Headers["in"]);
-            Assert.Contains("another", State.Headers.Keys);
-            Assert.Equal(new[] { "test2" }, State.Headers["another"]);
+            Assert.Contains("in", CapturedHeaders.Keys);
+            Assert.Equal(new[] { "test" }, CapturedHeaders["in"]);
+            Assert.Contains("another", CapturedHeaders.Keys);
+            Assert.Equal(new[] { "test2" }, CapturedHeaders["another"]);
         }
 
         [Theory]
@@ -101,7 +109,7 @@ public async Task HeaderEmptyInRequest_DoesNotAddIt(string headerValue)
             await Middleware.Invoke(Context);
 
             // Assert
-            Assert.DoesNotContain("in", State.Headers.Keys);
+            Assert.DoesNotContain("in", CapturedHeaders.Keys);
         }
 
         [Theory]
@@ -127,8 +135,8 @@ public async Task UsesValueFilter(string[] filterValues, string[] expectedValues
             await Middleware.Invoke(Context);
 
             // Assert
-            Assert.Contains("in", State.Headers.Keys);
-            Assert.Equal(expectedValues, State.Headers["in"]);
+            Assert.Contains("in", CapturedHeaders.Keys);
+            Assert.Equal(expectedValues, CapturedHeaders["in"]);
             Assert.Equal("in", receivedName);
             Assert.Equal(new StringValues("value"), receivedValue);
             Assert.Same(Context, receivedContext);
@@ -145,8 +153,8 @@ public async Task PreferValueFilter_OverRequestHeader()
             await Middleware.Invoke(Context);
 
             // Assert
-            Assert.Contains("in", State.Headers.Keys);
-            Assert.Equal("test", State.Headers["in"]);
+            Assert.Contains("in", CapturedHeaders.Keys);
+            Assert.Equal("test", CapturedHeaders["in"]);
         }
 
         [Fact]
@@ -159,7 +167,7 @@ public async Task EmptyValuesFromValueFilter_DoesNotAddIt()
             await Middleware.Invoke(Context);
 
             // Assert
-            Assert.DoesNotContain("in", State.Headers.Keys);
+            Assert.DoesNotContain("in", CapturedHeaders.Keys);
         }
 
         [Fact]
@@ -174,8 +182,8 @@ public async Task MultipleEntries_AddsFirstToProduceValue()
             await Middleware.Invoke(Context);
 
             // Assert
-            Assert.Contains("in", State.Headers.Keys);
-            Assert.Equal("Test", State.Headers["in"]);
+            Assert.Contains("in", CapturedHeaders.Keys);
+            Assert.Equal("Test", CapturedHeaders["in"]);
         }
     }
 }