Tus plugin onBeforeRequest does not support Promises

[vp-aridhia]

Hello, I found a small issue with the tus plugin. We're using uppy and tus for file uploads and came across a auth token issue raised internally. I found that onBeforeRequest will solve our issue, by adding the latest auth token in this handler and not using the headers options which aren't synced with ongoing uploads, on the condition it supports promises.

Our used versions are:

@uppy/[email protected]
@uppy/[email protected]
@uppy/[email protected]
@uppy/[email protected]
@uppy/[email protected]
@uppy/[email protected]
@uppy/[email protected]
@uppy/[email protected]
@uppy/[email protected]
@uppy/[email protected]
@uppy/[email protected]
@uppy/[email protected]
@uppy/[email protected]
@uppy/[email protected]
[email protected]

There's a slight mismatch in the @uppy/tus plugin, at the onBeforeRequest optional function.

https://github.com/tus/tus-js-client/blob/master/docs/api.md#onbeforerequest

You can also return a Promise if you need to perform some calculations before the request is sent:

onBeforeRequest: function (req) {
    return new Promise(resolve => {
        var xhr = req.getUnderlyingObect()
        xhr.withCredentials = true
        resolve()
    })
}

Tus supports promises, but @uppy/tus plugin wraps the optional function and calls it without handling the case when it's a promise.

https://github.com/transloadit/uppy/blob/main/packages/%40uppy/tus/src/index.js#L211

if (typeof opts.onBeforeRequest === 'function') {
  opts.onBeforeRequest(req)
}

I think it would be a good addition to also have promises enabled on this endpoint. Currently, I'm subclassing the plugin and replacing the bits I need.

Let me know if I missed something. I might be able to help with a PR

[aduh95]

Thanks for the report, I've opened #3712 to address this.