Environment

• Environment: Netlify, indicates nodejs:18.v18.
• h3: 1.8.2
• nitropack: 2.7.2

Note: This is not a nitropack bug because the fault lies with the utilities provided by h3.
It is possible to create a workaround using different h3 functions, therefor the failing function is faulty.

Reproduction

1. Create a nitro project, add a route containing the following handler:

   export default defineEventHandler(async event => {
     if (event.method !== 'POST') {
       return `<form action="${getRequestURL(event)}" method=POST><button name=btn autofocus>Submit`;
     } else {
       return Object.fromEntries((await readFormData(event)).entries());
     }
   });

2. Publish on netlify
3. Open the route in a browser
4. Click submit button
5. 💥

Locally, you get what you expect:

{"btn": ""}

Describe the bug

Using readFormData crashes the server, not even allowing an error to be caught with catch or similar mechanisms.

I cannot see exactly why the server crashes, as I only receive a cryptic error back:

error decoding lambda response: invalid status code returned from lambda: 0

Additional context

Root cause of nitrojs/nitro#1721

That said, I do know that toWebRequest() is the function within readFormData that is at fault.
The event.node.req.body field is a string containing the POST body of the request before calling into readFormData.

Using the following implementation of readFormData can succesfully read the data:

async function readFormData_fixed(event: H3Event) : Promise<FormData> {
  const request = new Request(getRequestURL(event), {
    // @ts-ignore Undici option
    duplex: 'half',
    method: event.method,
    headers: event.headers,
    body: await readRawBody(event),
  } as RequestInit);
  return await request.formData();
}

Here readRawBody short-circuits because event.node.req.body is set and RequestInit.body is allowed to be of type string.

Logs

Logging statements directly before `await readFormData(...)` show up in netlify's function log.
Logging statements directly after `await readFormData(...)` do not.