Fix file upload FormatException for parameterized Content-Type

src/HotChocolate/AspNetCore/src/Transport.Http/DefaultGraphQLHttpClient.cs

@@ -291,7 +291,7 @@ private static HttpContent CreateMultipartContent(
             var fileContent = new StreamContent(file.OpenReadStream());
             if (!string.IsNullOrEmpty(file.ContentType))
             {
-                fileContent.Headers.ContentType = new MediaTypeHeaderValue(file.ContentType);
+                fileContent.Headers.TryAddWithoutValidation("Content-Type", file.ContentType);
             }
 
             form.Add(fileContent, i.ToString(), file.Name);
@@ -394,7 +394,7 @@ private static HttpContent CreateMultipartContent(
             var fileContent = new StreamContent(fileInfo.File.OpenRead());
             if (!string.IsNullOrEmpty(fileInfo.File.ContentType))
             {
-                fileContent.Headers.ContentType = new MediaTypeHeaderValue(fileInfo.File.ContentType);
+                fileContent.Headers.TryAddWithoutValidation("Content-Type", fileInfo.File.ContentType);
             }
 
             form.Add(fileContent, fileInfo.Name, fileInfo.File.FileName);

src/HotChocolate/AspNetCore/test/Transport.Http.Tests/GraphQLHttpClientTests.cs

@@ -975,6 +975,7 @@ public async Task Get_Subscription_Over_SSE_With_Errors()
     [Theory]
     [InlineData((string?)null)]
     [InlineData("application/pdf")]
+    [InlineData("text/plain; charset=utf-8")]
     public async Task Post_GraphQL_FileUpload(string? contentType)
     {
         // arrange

src/HotChocolate/Fusion/test/Fusion.AspNetCore.Tests/FileUploadTests.cs

@@ -58,6 +58,54 @@ public async Task Upload_Single_File()
         await MatchSnapshotAsync(gateway, operation, result, rawRequest: rawRequest);
     }
 
+    [Fact]
+    public async Task Upload_Single_File_Should_Forward_Parameterized_ContentType()
+    {
+        // arrange
+        using var server1 = CreateSourceSchema(
+            "A",
+            b => b.AddQueryType<SourceSchema1.Query>().AddUploadType());
+
+        using var gateway = await CreateCompositeSchemaAsync(
+        [
+            ("A", server1)
+        ]);
+
+        // act
+        using var client = GraphQLHttpClient.Create(gateway.CreateClient());
+
+        var stream = new MemoryStream("abc"u8.ToArray());
+
+        var operation = new OperationRequest(
+            """
+            query ($file: Upload!) {
+              singleUpload(file: $file) {
+                fileName
+                contentType
+                content
+              }
+            }
+            """,
+            variables: new Dictionary<string, object?>
+            {
+                ["file"] = new FileReference(() => stream, "test.txt", "text/plain; charset=utf-8")
+            });
+
+        RawRequest? rawRequest = null;
+        var request = new GraphQLHttpRequest(operation, new Uri("http://localhost:5000/graphql"))
+        {
+            Method = GraphQLHttpMethod.Post,
+            EnableFileUploads = true,
+            OnMessageCreated = (_, request, _) => rawRequest = GetRawRequest(request)
+        };
+
+        // act
+        var result = await client.SendAsync(request, TestContext.Current.CancellationToken);
+
+        // assert
+        await MatchSnapshotAsync(gateway, operation, result, rawRequest: rawRequest);
+    }
+
     [Fact]
     public async Task Upload_Single_File_In_Input_Object()
     {

src/HotChocolate/Fusion/test/Fusion.AspNetCore.Tests/__snapshots__/FileUploadTests.Upload_Single_File_Should_Forward_Parameterized_ContentType.yaml

@@ -0,0 +1,146 @@
+title: Upload_Single_File_Should_Forward_Parameterized_ContentType
+request:
+  contentType: multipart/form-data; boundary="f56524ab-5626-4955-b296-234a097b44f6"
+  body: |
+    --f56524ab-5626-4955-b296-234a097b44f6
+    Content-Type: application/json; charset=utf-8
+    Content-Disposition: form-data; name=operations
+
+    {"query":"query ($file: Upload!) {\n  singleUpload(file: $file) {\n    fileName\n    contentType\n    content\n  }\n}","variables":{"file":null}}
+    --f56524ab-5626-4955-b296-234a097b44f6
+    Content-Type: application/json; charset=utf-8
+    Content-Disposition: form-data; name=map
+
+    {"0":["variables.file"]}
+    --f56524ab-5626-4955-b296-234a097b44f6
+    Content-Type: text/plain; charset=utf-8
+    Content-Disposition: form-data; name=0; filename=test.txt; filename*=utf-8''test.txt
+
+    abc
+    --f56524ab-5626-4955-b296-234a097b44f6--
+response:
+  body: |
+    {
+      "data": {
+        "singleUpload": {
+          "fileName": "test.txt",
+          "contentType": "text/plain; charset=utf-8",
+          "content": "abc"
+        }
+      }
+    }
+sourceSchemas:
+  - name: A
+    schema: |
+      schema {
+        query: Query
+      }
+
+      type Query {
+        singleUpload(file: Upload!): FileUploadResult!
+        nullableUpload(file: Upload): FileUploadResult
+        singleUploadWithInput(input: FileInput!): FileUploadResult!
+        multiUpload(files: [Upload!]!): [FileUploadResult!]!
+        multiUploadWithInput(input: FilesInput!): [FileUploadResult!]!
+      }
+
+      type FileUploadResult {
+        fileName: String!
+        contentType: String
+        content: String!
+      }
+
+      input FileInput {
+        file: Upload!
+      }
+
+      input FilesInput {
+        files: [Upload!]!
+      }
+
+      "Defines the possible serialization types for GraphQL scalar values."
+      enum ScalarSerializationType {
+        "The scalar serializes to a string value."
+        STRING
+        "The scalar serializes to a boolean value."
+        BOOLEAN
+        "The scalar serializes to an integer value."
+        INT
+        "The scalar serializes to a floating-point value."
+        FLOAT
+        "The scalar serializes to an object value."
+        OBJECT
+        "The scalar serializes to a list value."
+        LIST
+      }
+
+      "The `Upload` scalar type represents a file upload."
+      scalar Upload @serializeAs(type: STRING)
+
+      directive @serializeAs(
+        "The primitive type a scalar is serialized to."
+        type: [ScalarSerializationType!]!
+        "The ECMA-262 regex pattern that the serialized scalar value conforms to."
+        pattern: String
+      ) on SCALAR
+    interactions:
+      - request:
+          accept: application/graphql-response+json; charset=utf-8, application/json; charset=utf-8, application/jsonl; charset=utf-8, text/event-stream; charset=utf-8
+          contentType: multipart/form-data; boundary="f56524ab-5626-4955-b296-234a097b44f6"
+          body: |
+            --f56524ab-5626-4955-b296-234a097b44f6
+            Content-Type: application/json; charset=utf-8
+            Content-Disposition: form-data; name=operations
+
+            {"query":"query Op_6e1beb14_1($file: Upload!) {\n  singleUpload(file: $file) {\n    fileName\n    contentType\n    content\n  }\n}","variables":{"file":null}}
+            --f56524ab-5626-4955-b296-234a097b44f6
+            Content-Type: application/json; charset=utf-8
+            Content-Disposition: form-data; name=map
+
+            {"0":["variables.file"]}
+            --f56524ab-5626-4955-b296-234a097b44f6
+            Content-Type: text/plain; charset=utf-8
+            Content-Disposition: form-data; name=0; filename=test.txt; filename*=utf-8''test.txt
+
+            abc
+            --f56524ab-5626-4955-b296-234a097b44f6--
+        response:
+          results:
+            - |
+              {
+                "data": {
+                  "singleUpload": {
+                    "fileName": "test.txt",
+                    "contentType": "text/plain; charset=utf-8",
+                    "content": "abc"
+                  }
+                }
+              }
+operationPlan:
+  operation:
+    - document: |
+        query($file: Upload!) {
+          singleUpload(file: $file) {
+            fileName
+            contentType
+            content
+          }
+        }
+      hash: 6e1beb142822946e961b9f062df288a0
+      searchSpace: 1
+      expandedNodes: 1
+  nodes:
+    - id: 1
+      type: Operation
+      schema: A
+      operation: |
+        query Op_6e1beb14_1($file: Upload!) {
+          singleUpload(file: $file) {
+            fileName
+            contentType
+            content
+          }
+        }
+      forwardedVariables:
+        - file
+      requiresFileUpload: true