Request Header 'Content-Type' no longer set for requests with body serialized as FormData

[schuch]

Description

After upgrading openapi-fetch from 0.8.2 to 0.9.1 we see 415 Unsupported Media Type responses for multipart/form-data requests.

We have investigated how the request has changed as a result of the update. We noticed that the request header Content-Type: multipart/form-data; boundary=... is no longer sent with the request.

A copy from of the request (as cUrl) from the developer console:

curl 'https://...' \
  -H 'Accept: */*' \
  --data-raw $'------WebKitFormBoundary9Y0HMzSGLEhBsYQT\r\nContent-Disposition: form-data; name="file"; filename="test.pdf"\r\nContent-Type: application/pdf\r\n\r\n\r\n------WebKitFormBoundary9Y0HMzSGLEhBsYQT--\r\n' \
  --compressed

(omitted a few headers for better clarity)

Reproduction

We use the following code to perform the request:

await POST(`/...`, {
    params: {
      ...
    },
    body: {
      file
    },
    bodySerializer: (body) => {
      const formData = new FormData();
      for (const name in body) {
        formData.append(name, body[name as keyof typeof body]);
      }
      return formData;
    }
).then(...)

Expected result

openapi-fetch create a proper multipart form-data request, e.g.:

curl 'https://...' \
  -H 'Accept: */*' \
  -H 'Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryy81TvwmCQwmGHDDw' \
  --data-raw $'------WebKitFormBoundaryy81TvwmCQwmGHDDw\r\nContent-Disposition: form-data; name="file"; filename="test.pdf"\r\nContent-Type: application/pdf\r\n\r\n\r\n------WebKitFormBoundaryy81TvwmCQwmGHDDw--\r\n' \
  --compressed

(copied as cUrl from a successful request from the developer console, omitted a few headers for better clarity)

Checklist

• I’m willing to open a PR (see CONTRIBUTING.md)

[shirish87]

I have the same issue. Inspecting the Request object in openapi-fetch shows the content-type header that used to be set in 0.8.2 multipart/form-data; boundary=----formdata-undici-0.6228903411172271 is no longer set in 0.9.x

[lukasbash]

Is there a chance to get this in a patch release as soon as merged? Would be awesome!

[drwpow]

Released in 0.9.2!