fastify-multipart v 3.0 not able to access key/value pairs with upload binary file

🐛 Bug Report

Thanks for improving this plugin to make it easier for files upload. I’ve switched over to v3.0 and tried out the new API but it’s not letting me access the fields data like the legacy version

To Reproduce

Steps to reproduce the behavior:

Client form

    const formData = new FormData();
    formData.append("avatar", file, file.name); // <input type="file" />
    formData.append("testData", JSON.stringify({ name: "Foo" })); 

    fetch("/", {
      method: "POST",
      body: formData
    })

Server

    fastify.post('/', async function (req, reply) {
        const data = await req.file()

        data.file // stream
        data.fields // other parsed parts
        data.fieldname
        data.filename
        data.encoding
        data.mimetype

        console.log(JSON.parse(data.fields))

        await pump(data.file, fs.createWriteStream(data.filename))

        reply.send()
    })

Expected behavior

print out { name: ‘Foo’ }

in the legacy version, i could access it under this:

  mp.on('field', function (key, value) {
    console.log(JSON.parse(value))
  })

Your Environment

• node version: 12
• fastify version: >=3.0.0
• os: Mac

[StarpTech]

We can’t parse out of sync because files must be handled first. In order to achieve your result, you have to reorder your form

	formData.append("testData", JSON.stringify({ name: "Foo" }));
    formData.append("avatar", file, file.name); // <input type="file" /> 

[StarpTech]

or you use multipartIterator() to iterate over field and files.