Strange behaviour with request.file() when filename in form is not specified

[giovanni-bertoncelli]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Fastify version

4.23.2

Plugin version

8.1.0

Node.js version

20.x

Operating system

macOS

Operating system version (i.e. 20.04, 11.3, 10)

Sonoma 14.2

Description

I encountered a strange behavior in the request.file() method when I send a multipart (using form-auto-content) without specifying the filename of the sent file. The method returns undefined. I do not know if it is a form-auto-content issue, if this is the expected behaviour or not. If it is expected I'll close this.

Steps to Reproduce

Reproduction example: https://codesandbox.io/p/devbox/fastify-multipart-filename-nxnqgd

• Setup a fastify server with the @fastify/multipart plugin with a route calling req.file()
• Setup a simple client using form-auto-content and appending a file specifying the contentType but not the filename
• Call the endpoint

Expected Behavior

I expect an error (if multipart with part missing the filename are considered malformed) or otherwise the parsed file.

[gurgunday]

For now, we definitely don’t throw in many cases where we maybe should, this could be an interesting change that I support

Silent errors should be opt-in

[decipher-cs]

Seconded. This should most definitely throw an error or warning of some kind. In the meantime, I highly recommend adding a note in the README that documents this behavior.

data will be undefined in this case unless I add the name attribute to the input in my client code

fastify.post("/upload", async function handler(request, reply) {
  const data = await request.file();
  log(data?.file); //undefined
  return "done";
});

<form method="post" action="upload" enctype="multipart/form-data">
  <input type="file" />
  <button type="submit">send</button>
</form>

the code will work.

<input 
        type="file" 
++      name="some-name"
    />