[11.0 P1] What's New: OpenAPI: Binary File Response (#36747)

* [11.0 P1] What's New: OpenAPI: Binary File Response

* Update aspnetcore/release-notes/aspnetcore-11/includes/openapi-binary-file-response.md

Co-authored-by: Luke Latham <1622880+guardrex@users.noreply.github.com>

* Update aspnetcore/release-notes/aspnetcore-11/includes/openapi-binary-file-response.md

Co-authored-by: Luke Latham <1622880+guardrex@users.noreply.github.com>

---------

Co-authored-by: Luke Latham <1622880+guardrex@users.noreply.github.com>

Author: wadepickett

aspnetcore/release-notes/aspnetcore-11.md

@@ -37,6 +37,8 @@ This section describes new features for Minimal APIs.
 
 This section describes new features for OpenAPI.
 
+[!INCLUDE[](~/release-notes/aspnetcore-11/includes/openapi-binary-file-response.md)]
+
 ## Authentication and authorization
 
 This section describes new features for authentication and authorization.

aspnetcore/release-notes/aspnetcore-11/includes/openapi-binary-file-response.md

@@ -0,0 +1,57 @@
+### Describe binary file responses
+
+ASP.NET Core 11 introduces support for generating OpenAPI descriptions for operations that return binary file responses. This support maps the `FileContentResult` result type to an OpenAPI schema with `type: string` and `format: binary`.
+
+#### [Minimal APIs](#tab/minimal-apis)
+
+Use the `Produces<T>` extension method with `T` of `FileContentResult` to specify the response type and content type:
+<!-- UPDATE 11.0 - API cross-link needs to be entered in the line above for the new API
+such as: <xref:Microsoft.AspNetCore.NEW_API_TO_BE_ENTERED_>
+-->
+
+```csharp
+app.MapPost("/filecontentresult", () =>
+{
+    var content = "This endpoint returns a FileContentResult!"u8.ToArray();
+    return TypedResults.File(content);
+})
+.Produces<FileContentResult>(contentType: MediaTypeNames.Application.Octet);
+```
+
+#### [Controllers](#tab/controllers)
+
+Use the `ProducesResponseType<T>` attribute with `T` of `FileContentResult` to specify the response type and content type:
+
+```csharp
+[HttpPost("filecontentresult")]
+[ProducesResponseType<FileContentResult>(StatusCodes.Status200OK, MediaTypeNames.Application.Octet)]
+public IActionResult PostFileContentResult()
+{
+    var content = "This endpoint returns a FileContentResult!"u8.ToArray();
+    return new FileContentResult(content, MediaTypeNames.Application.Octet);
+}
+```
+
+---
+
+The generated OpenAPI document describes the endpoint response as:
+
+```yaml
+responses:
+  '200':
+    description: OK
+    content:
+      application/octet-stream:
+        schema:
+          $ref: '#/components/schemas/FileContentResult'
+```
+
+The `FileContentResult` is defined in `components/schemas` as:
+
+```yaml
+components:
+  schemas:
+    FileContentResult:
+      type: string
+      format: binary
+```