[BUG] [typescript-fetch] Not able to generate a `BlobApiResponse` with a binary response

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

Hello,

I'm currently trying to generate a typescript api client in which one endpoint should deliver a blob as an API response. But no matter how I define the endpoint in my API spec, the client always tries to convert it to a string.

I followed the recommendation when modelling binary responses by using return type string with format binary but that doesn't work.

It will generate the correct return type for the methods:

Promise<runtime.ApiResponse<Blob>>

But it wrongly tries to convert the response to a text instead of a blob.

openapi-generator version

7.14.0

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  title: Sample Attachment API
  version: '1.0'
paths:
  /attachment:
    get:
      operationId: getAttachment
      responses:
        default:
          description: Attachment as binary data.
          content:
            application/octet-stream:
              schema:
                type: string
                format: binary

Generation Details

java -jar openapi-generator-cli.jar generate -i api-docs/test-docs.yaml -g typescript-fetch -o src/test-api

Steps to reproduce

1. generate
2. look at apis/DefaultApi.ts

        if (this.isJsonMime(response.headers.get('content-type'))) {
            return new runtime.JSONApiResponse<Blob>(response);
        } else {
            return new runtime.TextApiResponse(response) as any;
        }

What should actually be generated is

        return new runtime.BlobApiResponse(response);

Related issues/PRs

Suggest a fix

Looking at the template https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache#L341 I can see the function I need to be generated is already there - but I haven't found a way to trigger the isResponseFile flag with my config.

Either I have a wrong api spec - in this case I would be very happy to be led in the right direction to fix it.

Or the generator has a bug in this case.

Start with the generated apis/DefaultApi.ts output and the typescript-fetch template at modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache, especially the isResponseFile branch around line 341. Trace how the binary response schema is represented during generation and why isResponseFile is not enabled. Done means the sample spec generates runtime.BlobApiResponse instead of TextApiResponse.