Binary response with */* and format: binary generates Blob but misses Axios responseType

[metinsut]

Hi,

I have a file download endpoint defined like this in my OpenAPI JSON:

{
  "/project/participant/generate-excel-template/{projectId}": {
    "get": {
      "tags": ["project-participant-controller"],
      "operationId": "generateExcelTemplate",
      "parameters": [
        {
          "name": "projectId",
          "in": "path",
          "required": true,
          "schema": {
            "type": "integer",
            "format": "int64"
          }
        }
      ],
      "responses": {
        "200": {
          "description": "OK",
          "content": {
            "*/*": {
              "schema": {
                "type": "string",
                "format": "binary"
              }
            }
          }
        }
      }
    }
  }
}

Orval generates the response type as Blob, which looks correct:

return customInstanceOrg<Blob>({
  url: `/project/participant/generate-excel-template/${projectId}`,
  method: "GET",
});

However, the generated Axios config does not include responseType: "blob". Because of that, the downloaded Excel file is corrupted / cannot be opened.

If I manually add responseType: "blob", the file downloads correctly:

return customInstanceOrg<Blob>({
  url: `/project/participant/generate-excel-template/${projectId}`,
  method: "GET",
  responseType: "blob",
});

My current workaround is to use an Orval transformer and normalize this binary response to application/octet-stream before generation.

What would be the recommended approach here?

1. Should the backend OpenAPI spec avoid */* and use application/octet-stream instead?
2. Should this be handled with a transformer or custom mutator?
3. Or should Orval generate responseType: "blob" whenever the response schema is type: string + format: binary, even if the content type is */*?

Thanks.

[melloware]

Yes you should declare octet-stream as the response type. That makes your API more semantically correct an obviously helps Orval as Orval assumes * is plain text