How to create file from /api in NextJS? - next.js

Question

I am currently trying to create a temp file from /api/sendEmail.js with fs.mkdirSync
fs.mkdirSync(path.join(__dirname, "../../public"));
but on Vercel (where my app is running) all folders are read-only and I can't create any temp files.
Error:
ERROR
Error: EROFS: read-only file system, mkdir '/var/task/.next/server/public'
As I can see there are some questions about this but no clear answer, have any of you guys managed to do this?

Answer 1

Vercel allows creation of files in /tmp directory. However, there are limitations with this. https://github.com/vercel/vercel/discussions/5320
An example of /api function that writes and reads files is:
import fs from 'fs';
export default async function handler(req, res) {
const {
method,
body,
} = req
try {
switch (method) {
case 'GET': {
// read
// This line opens the file as a readable stream
const readStream = fs.createReadStream('/tmp/text.txt')
// This will wait until we know the readable stream is actually valid before piping
readStream.on('open', function () {
// This just pipes the read stream to the response object (which goes to the client)
readStream.pipe(res)
})
// This catches any errors that happen while creating the readable stream (usually invalid names)
readStream.on('error', function (err) {
res.end(err)
})
return
}
case 'POST':
// write
fs.writeFileSync('./test.txt', JSON.stringify(body))
break
default:
res.setHeader('Allow', ['GET', 'POST'])
res.status(405).end(`Method ${method} Not Allowed`)
}
// send result
return res.status(200).json({ message: 'Success' })
} catch (error) {
return res.status(500).json(error)
}
}
}
Also see: https://vercel.com/support/articles/how-can-i-use-files-in-serverless-functions