Fix for: Minimal APIs and controllers treat header arrays differently

src/Http/Http.Extensions/gen/StaticRouteHandlerModel/Emitters/EndpointParameterEmitter.cs

@@ -18,9 +18,12 @@ internal static void EmitQueryOrHeaderParameterPreparation(this EndpointParamete
     {
         codeWriter.WriteLine(endpointParameter.EmitParameterDiagnosticComment());
 
-        var assigningCode = endpointParameter.Source is EndpointParameterSource.Header
-            ? $"httpContext.Request.Headers[\"{endpointParameter.LookupName}\"]"
-            : $"httpContext.Request.Query[\"{endpointParameter.LookupName}\"]";
+        var assigningCode = (endpointParameter.Source, endpointParameter.IsArray) switch
+        {
+            (EndpointParameterSource.Header, true) => $"httpContext.Request.Headers.GetCommaSeparatedValues(\"{endpointParameter.LookupName}\")",
+            (EndpointParameterSource.Header, false) => $"httpContext.Request.Headers[\"{endpointParameter.LookupName}\"]",
+            _ => $"httpContext.Request.Query[\"{endpointParameter.LookupName}\"]"
+        };
         codeWriter.WriteLine($"var {endpointParameter.EmitAssigningCodeResult()} = {assigningCode};");
 
         // If we are not optional, then at this point we can just assign the string value to the handler argument,

src/Http/Http.Extensions/src/RequestDelegateFactory.cs

@@ -1955,8 +1955,17 @@ private static Expression BindParameterFromExpression(
                 Expression.Convert(Expression.Constant(parameter.DefaultValue), parameter.ParameterType)));
     }
 
-    private static Expression BindParameterFromProperty(ParameterInfo parameter, MemberExpression property, PropertyInfo itemProperty, string key, RequestDelegateFactoryContext factoryContext, string source) =>
-        BindParameterFromValue(parameter, GetValueFromProperty(property, itemProperty, key, GetExpressionType(parameter.ParameterType)), factoryContext, source);
+    private static Expression BindParameterFromProperty(ParameterInfo parameter, MemberExpression property, PropertyInfo itemProperty, string key, RequestDelegateFactoryContext factoryContext, string source)
+    {
+        var valueExpression = (source == "header" && parameter.ParameterType.IsArray)
+            ? Expression.Call(
+                typeof(ParsingHelpers).GetMethod(nameof(ParsingHelpers.GetHeaderSplit), BindingFlags.Public | BindingFlags.Static, [typeof(IHeaderDictionary), typeof(string)])!,
+                property,
+                Expression.Constant(key))
+            : GetValueFromProperty(property, itemProperty, key, GetExpressionType(parameter.ParameterType));
+
+        return BindParameterFromValue(parameter, valueExpression, factoryContext, source);
+    }
 
     private static Type? GetExpressionType(Type type) =>
         type.IsArray ? typeof(string[]) :

src/Http/Http.Extensions/test/RequestDelegateFactoryTests.cs

@@ -3156,6 +3156,55 @@ static void TestAction([AsParameters] ParameterListRequiredNullableStringFromDif
         Assert.Null(httpContext.Items["RequiredHeaderParam"]);
     }
 
+    private class ParameterListFromHeaderCommaSeparatedValues
+    {
+        [FromHeader(Name = "q")]
+        public required StringValues? BoundToStringValues { get; set; }
+
+        [FromHeader(Name = "q")]
+        public string? BoundToString { get; set; }
+
+        [FromHeader(Name = "q")]
+        public string[]? BoundToStringArray { get; set; }
+
+        [FromHeader(Name = "q")]
+        public int[]? BoundToIntArray { get; set; }
+    }
+
+    [Theory]
+    [InlineData("", new string[] { }, new int[] {})]
+    [InlineData(" ", new string[] { }, new int[] { })]
+    [InlineData(",", new string[] { }, new int[] { })]
+    [InlineData("100", new string[] { "100" }, new int[] { 100 })]
+    [InlineData("1,2", new string[] { "1", "2" }, new int[] { 1, 2 })]
+    [InlineData("1, 2 ,  3", new string[] { "1", "2", "3" }, new int[] { 1, 2, 3 })]
+    public async Task RequestDelegateFactory_FromHeader_CommaSeparatedValues(string headerValue, string[] expectedStringArray, int[] expectedIntArray)
+    {
+        // Arrange
+        var httpContext = CreateHttpContext();
+        httpContext.Request.Headers["q"] = headerValue;
+
+        void TestAction([AsParameters] ParameterListFromHeaderCommaSeparatedValues args)
+        {
+            httpContext.Items[nameof(args.BoundToStringValues)] = args.BoundToStringValues;
+            httpContext.Items[nameof(args.BoundToString)] = args.BoundToString;
+            httpContext.Items[nameof(args.BoundToStringArray)] = args.BoundToStringArray;
+            httpContext.Items[nameof(args.BoundToIntArray)] = args.BoundToIntArray;
+        }
+
+        var factoryResult = RequestDelegateFactory.Create(TestAction);
+        var requestDelegate = factoryResult.RequestDelegate;
+
+        // Act
+        await requestDelegate(httpContext);
+
+        // Assert
+        Assert.Equal(headerValue, httpContext.Items[nameof(ParameterListFromHeaderCommaSeparatedValues.BoundToString)]);
+        Assert.Equal(new StringValues(headerValue), httpContext.Items[nameof(ParameterListFromHeaderCommaSeparatedValues.BoundToStringValues)]);
+        Assert.Equal(expectedStringArray, httpContext.Items[nameof(ParameterListFromHeaderCommaSeparatedValues.BoundToStringArray)]);
+        Assert.Equal(expectedIntArray, httpContext.Items[nameof(ParameterListFromHeaderCommaSeparatedValues.BoundToIntArray)]);
+    }
+
 #nullable disable
     private class ParameterListMixedRequiredStringsFromDifferentSources
     {

src/Http/Http.Extensions/test/RequestDelegateGenerator/Baselines/MapAction_ExplicitHeader_ComplexTypeArrayParam.generated.txt

@@ -108,7 +108,7 @@ namespace Microsoft.AspNetCore.Http.Generated
                 {
                     var wasParamCheckFailure = false;
                     // Endpoint Parameter: p (Type = Microsoft.AspNetCore.Http.Generators.Tests.ParsableTodo[], IsOptional = False, IsParsable = True, IsArray = True, Source = Header)
-                    var p_raw = httpContext.Request.Headers["p"];
+                    var p_raw = httpContext.Request.Headers.GetCommaSeparatedValues("p");
                     var p_temp = p_raw.ToArray();
                     global::Microsoft.AspNetCore.Http.Generators.Tests.ParsableTodo[] p_local = new global::Microsoft.AspNetCore.Http.Generators.Tests.ParsableTodo[p_temp.Length];
                     for (var i = 0; i < p_temp.Length; i++)
@@ -138,7 +138,7 @@ namespace Microsoft.AspNetCore.Http.Generated
                 {
                     var wasParamCheckFailure = false;
                     // Endpoint Parameter: p (Type = Microsoft.AspNetCore.Http.Generators.Tests.ParsableTodo[], IsOptional = False, IsParsable = True, IsArray = True, Source = Header)
-                    var p_raw = httpContext.Request.Headers["p"];
+                    var p_raw = httpContext.Request.Headers.GetCommaSeparatedValues("p");
                     var p_temp = p_raw.ToArray();
                     global::Microsoft.AspNetCore.Http.Generators.Tests.ParsableTodo[] p_local = new global::Microsoft.AspNetCore.Http.Generators.Tests.ParsableTodo[p_temp.Length];
                     for (var i = 0; i < p_temp.Length; i++)

src/Http/Http.Extensions/test/RequestDelegateGenerator/Baselines/MapAction_ExplicitHeader_NullableStringArrayParam.generated.txt

@@ -108,7 +108,7 @@ namespace Microsoft.AspNetCore.Http.Generated
                 {
                     var wasParamCheckFailure = false;
                     // Endpoint Parameter: p (Type = string?[], IsOptional = False, IsParsable = False, IsArray = True, Source = Header)
-                    var p_raw = httpContext.Request.Headers["p"];
+                    var p_raw = httpContext.Request.Headers.GetCommaSeparatedValues("p");
                     var p_temp = p_raw.ToArray();
                     string[] p_local = p_temp!;
 
@@ -125,7 +125,7 @@ namespace Microsoft.AspNetCore.Http.Generated
                 {
                     var wasParamCheckFailure = false;
                     // Endpoint Parameter: p (Type = string?[], IsOptional = False, IsParsable = False, IsArray = True, Source = Header)
-                    var p_raw = httpContext.Request.Headers["p"];
+                    var p_raw = httpContext.Request.Headers.GetCommaSeparatedValues("p");
                     var p_temp = p_raw.ToArray();
                     string[] p_local = p_temp!;
 

src/Http/Http.Extensions/test/RequestDelegateGenerator/Baselines/MapAction_ExplicitHeader_StringArrayParam.generated.txt

@@ -108,7 +108,7 @@ namespace Microsoft.AspNetCore.Http.Generated
                 {
                     var wasParamCheckFailure = false;
                     // Endpoint Parameter: p (Type = string[], IsOptional = False, IsParsable = False, IsArray = True, Source = Header)
-                    var p_raw = httpContext.Request.Headers["p"];
+                    var p_raw = httpContext.Request.Headers.GetCommaSeparatedValues("p");
                     var p_temp = p_raw.ToArray();
                     string[] p_local = p_temp!;
 
@@ -125,7 +125,7 @@ namespace Microsoft.AspNetCore.Http.Generated
                 {
                     var wasParamCheckFailure = false;
                     // Endpoint Parameter: p (Type = string[], IsOptional = False, IsParsable = False, IsArray = True, Source = Header)
-                    var p_raw = httpContext.Request.Headers["p"];
+                    var p_raw = httpContext.Request.Headers.GetCommaSeparatedValues("p");
                     var p_temp = p_raw.ToArray();
                     string[] p_local = p_temp!;
 

src/Http/Http.Extensions/test/RequestDelegateGenerator/RequestDelegateCreationTests.Arrays.cs

@@ -775,4 +775,23 @@ public async Task RequestDelegateHandlesArraysFromExplicitQueryStringSource()
         Assert.Equal(new[] { 4, 5, 6 }, (int[])httpContext.Items["headers"]!);
         Assert.Equal(new[] { 7, 8, 9 }, (int[])httpContext.Items["form"]!);
     }
+
+    [Theory]
+    [InlineData("""app.MapGet("/", ([FromHeader(Name = "q")] string[]? arr) => arr);""", "", "[]")]
+    [InlineData("""app.MapGet("/", ([FromHeader(Name = "q")] string[]? arr) => arr);""", "a,b,c", "[\"a\",\"b\",\"c\"]")]
+    [InlineData("""app.MapGet("/", ([FromHeader(Name = "q")] int[]? arr) => arr);""", "1,2,3", "[1,2,3]")]
+    public async Task MapMethods_Get_With_CommaSeparatedValues_InHeader_ShouldBindToArray(string source, string headerContent, string expectedBody)
+    {
+        var (_, compilation) = await RunGeneratorAsync(source);
+        var endpoints = GetEndpointsFromCompilation(compilation);
+
+        foreach (var endpoint in endpoints)
+        {
+            var httpContext = CreateHttpContext();
+            httpContext.Request.Headers["q"] = headerContent;
+            await endpoint.RequestDelegate(httpContext);
+
+            await VerifyResponseBodyAsync(httpContext, expectedBody);
+        }
+    }
 }