Q&A (please complete the following information)

• OS: macOS
• Environment: Chrome 80, Node.js v12.9.1
• Method of installation: npm
• Swagger-Client version: 3.9.5, 3.10.0
• Swagger/OpenAPI version: OpenAPI 3.0.2

Content & configuration

Swagger/OpenAPI definition:

openapi: 3.0.2
info:
  title: test
  version: 1.0.0
paths:
  "/foo":
    post:
      operationId: foo
      requestBody:
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                a:
                  type: number
                b:
                  type: number
      responses:
        '200':
          description: bar

Swagger-Client usage:

There is no some specific configuration, just:

new SwaggerClient({ spec })

Describe the bug you're encountering

swagger-client generates an invalid value "multipart/form-data" for the header "Content-Type" when there is a request with FormData as the body. The parameter "boundary" is missed in the header value.

To reproduce...

1. Clone a repository with an example:

git clone https://github.com/nikolaas/swagger-client-multipart-bug.git

2. Install dependencies:

cd swagger-client-multipart-bug
npm install

3. Run the example:

node index.js

4. See the output:

{
  url: '/foo',
  credentials: 'same-origin',
  headers: { 'Content-Type': 'multipart/form-data' }, // <-- the invalid header
  method: 'POST',
  body: FormData {
     // FormData content here
  }
}

Expected behavior

The expected value of the header is "multipart/form-data; boundary=some-boundary".

Additional context or thoughts

By RFC 2046 the header "Content-Type" for multipart requests must contain parameter "boundary":

The Content-Type field for multipart entities requires one parameter, "boundary".

In my opinion, the bug affects the basic functionality. I bumped with it when I tried to send the first multipart request. I don't know why nobody reported it before.

I'm confused. Maybe I don't understand something. Can you tell me this behavior is a bug? Or maybe am I doing something wrong?

Workaround

To workaround the bug you can override the HTTP client. The overridden HTTP client must remove the invalid header "Content-Type". After that, the browser will generate a valid value of the header based on the request body:

const http = (req) => fetch(fixMultipartContentType(req));
const swagger = new Swagger({ spec, http });

function fixMultipartContentType(req) {
    if (req.headers == undefined) {
        return req;
    }
    if (req.headers['Content-Type'] !== 'multipart/form-data') {
        return req;
    }
    if (!(req.body instanceof FormData)) {
        return req;
    }
    const headers = { ...req.headers };
    delete headers['Content-Type'];
    return { ...req, headers };
}