update EndpointParameterEmitter

Author: smnsht

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/test/RequestDelegateGenerator/CompileTimeCreationTests.cs

@@ -788,4 +788,23 @@ public async Task RequestDelegatePopulatesFromOptionalFormParameterStringArray()
 
         Assert.Equal<string[]>(["hello", "bye"], (string[])httpContext.Items["message"]);
     }
+
+    [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 RequestDelegateGenerator_FromHeader_CommaSeparatedValues(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);
+        }
+    }
 }