Missing '\r\n' in last boundary of FormData #4197

Bug Description

When we send a POST request containing a FormData with fetch, the server never responds (as if still waiting for data). We end up going into timeout.

Reproducible By

const form = new FormData();
form.append('hash', 'abc123deadbeef');

let timer:any ;
const resp = Promise.race([
fetch('http://localhost:3000/api', {
method: 'POST',
body: form
}),
new Promise((_,rejection) => timer = setTimeout(rejection, 10000, exception))
]).finally(() => clearTimeout(timer)) ;

Expected Behavior

The last boundary should end with a new line '\r\n' allowing the server to know that all data has been sent.

Logs & Screenshots

Environment

Node v22.15.0