Add support for FileContentResult in OpenAPI schemas (#63504)

Updated OpenApiSchemaService to handle FileContentResult, ensuring schemas are generated as `string` with `binary` format.

Introduced a new test in OpenApiSchemaServiceTests to validate OpenAPI response handling for FileContentResult, ensuring correct schema and content type representation.

Author: marcominerva

src/OpenApi/src/Services/Schemas/OpenApiSchemaService.cs

@@ -58,9 +58,9 @@ internal sealed class OpenApiSchemaService(
         TransformSchemaNode = (context, schema) =>
         {
             var type = context.TypeInfo.Type;
-            // Fix up schemas generated for IFormFile, IFormFileCollection, Stream, and PipeReader
+            // Fix up schemas generated for IFormFile, IFormFileCollection, Stream, PipeReader and FileContentResult
             // that appear as properties within complex types.
-            if (type == typeof(IFormFile) || type == typeof(Stream) || type == typeof(PipeReader))
+            if (type == typeof(IFormFile) || type == typeof(Stream) || type == typeof(PipeReader) || type == typeof(Mvc.FileContentResult))
             {
                 schema = new JsonObject
                 {

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Extensions/JsonTypeInfoExtensionsTests.cs

@@ -63,6 +63,7 @@ public class Baz
         [typeof(JsonPatchDocument<Todo>), "JsonPatchDocument"],
         [typeof(Stream), "Stream"],
         [typeof(PipeReader), "PipeReader"],
+        [typeof(FileContentResult), "FileContentResult"],
         [typeof(Results<Ok<TodoWithDueDate>, Ok<Todo>>), "ResultsOfOkOfTodoWithDueDateAndOkOfTodo"],
         [typeof(Ok<Todo>), "OkOfTodo"],
         [typeof(NotFound<TodoWithDueDate>), "NotFoundOfTodoWithDueDate"],

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Services/OpenApiSchemaService/OpenApiSchemaService.ResponseSchemas.cs

@@ -3,6 +3,7 @@
 
 using System.ComponentModel;
 using System.Net.Http;
+using System.Net.Mime;
 using System.Text.Json.Nodes;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Http;
@@ -1031,6 +1032,29 @@ await VerifyOpenApiDocument(actionDescriptor, document =>
         });
     }
 
+    [Fact]
+    public async Task GetOpenApiResponse_HandlesFileContentResultTypeResponse()
+    {
+        // Arrange
+        var builder = CreateBuilder();
+
+        // Act
+        builder.MapPost("/filecontentresult", () => { return new FileContentResult([], MediaTypeNames.Application.Octet); })
+            .Produces<FileContentResult>(contentType: MediaTypeNames.Application.Octet);
+
+        // Assert
+        await VerifyOpenApiDocument(builder, document =>
+        {
+            var operation = document.Paths["/filecontentresult"].Operations[HttpMethod.Post];
+            var responses = Assert.Single(operation.Responses);
+            var response = responses.Value;
+            Assert.True(response.Content.TryGetValue("application/octet-stream", out var mediaType));
+            var schema = mediaType.Schema;
+            Assert.Equal(JsonSchemaType.String, schema.Type);
+            Assert.Equal("binary", schema.Format);
+        });
+    }
+
     [ApiController]
     [Produces("application/json")]
     public class TestController