Missing "encoding" field

[JMLX42]

Hello,

I want to make sure the Swagger UI file dialog will limit the selectable file(s) to a specific extension (in this case .glb).
Based on my discussion with ChatGPT and my read of the OAS spec, it should be done using the encoding object.

How to reproduce

#[derive(ToSchema, MultipartForm)]
pub(crate) struct GlbFileUpload {
    /// The binary glTF (`.glb`) file to import.
    #[schema(format = Binary, encoding = "model/gltf-binary", value_type=Vec<u8>)]
    file: TempFile,
}

/// Import a glTF file
///
/// Imports a glTF file from a multipart form data.
/// This endpoint accepts a `.glb` file and supports additional query parameters.
#[utoipa::path(
    tag = "glTF",
    params(
        GltfResourceQueryParameters,
    ),
    request_body(content = inline(GlbFileUpload), content_type = "multipart/form-data"),
    responses(GltfResourceResponse),
)]
#[post("/gltf/import")]
pub async fn import_gltf_file(
    req: HttpRequest,
    db: web::Data<Database>,
    query: web::Query<GltfResourceQueryParameters>,
    MultipartForm(payload): MultipartForm<GlbFileUpload>,
) -> Result<HttpResponse<actix_web::body::BoxBody>, ErrorList> {
    info!(
        "received `{}` ({} bytes) for import",
        payload.file.file_name.unwrap(),
        payload.file.size
    );

    let file = Arc::new(payload.file.file);
    let db = db.into_inner();

    Ok(
        ResponseBuilder::<GltfResourceObject>::new(req.uri().clone())
            .relationship_resolver(AssetResolver::new(db.clone()))
            .relationship_resolver(SceneResolver::new(db.clone()))
            .query_parameters(query.into_inner())
            .data(Box::new(move || {
                let db = db.clone();
                let file = file.clone();

                Box::pin(async move {
                    gltf_live_importer::import_from_reader(file.as_ref(), &db)
                        .await
                        .map(|r| r.into_resource_object())
                })
            }))
            .build()
            .await
            .into(),
    )
}

OAS Spec

In the OpenAPI Specification (OAS) 3.0, the encoding field is used to describe how a specific property of a multipart/form-data request body is encoded. Specifically, it is used for properties that are defined as file uploads. Here is the relevant section from the OpenAPI Specification (3.0.3):
Encoding Object Definition (OAS 3.0.3)

The encoding object is defined as follows:

encoding: Map[string, Encoding Object
A map allowing additional information to be provided as headers, for example Content-Disposition. encoding is only > applicable to multipart and application/x-www-form-urlencoded request bodies.

Within the encoding object, you can use the contentType field to specify the MIME type for a particular property:

paths:
  /upload:
    post:
      summary: Upload a glTF .glb file
      requestBody:
        required: true
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                file:
                  type: string
                  format: binary
                  description: The glTF .glb file to upload
                  example: "file.glb"
            encoding:
              file:
                contentType: model/gltf-binary
      responses:
        '200':
          description: Successful upload
          content:
            application/json:
              schema:
                type: object
                properties:
                  message:
                    type: string

The key fields related to file uploads are:

• contentType (string): The Content-Type for encoding a specific property. This can be used to describe the media type for file uploads, such as model/gltf-binary for .glb files.
  - Example from OAS 3.0.3:
  - When this is a multipart content-type, this property is used to describe the media type of a file part.

https://spec.openapis.org/oas/v3.0.3#encoding-object

To Do

• Validate that this field is indeed missing
• Design an implementation
• Implement the validated design

[juhaku]

Yup, that is surely missing from the macro syntax as discussed here #811 (comment) #1055.

[juhaku]

I think we can verify that the the field is actually missing, from the generation side. I'll mark it as checked for the above todo list.