Upload componet ignores server validation of small files.

[AndreRisnes]

Description

We have an Upload + TransferProgressAwareHandler with a handleUploadRequest() that calls notifyError() to signal a failed upload (because of a file validation error). This works when uploading large files, but for small files, the client seemingly decides that the upload was successful before handleUploadRequest has a say in it, and displays failed files as successful in the Upload component's file list.

notifyError is called on the server, but the client still sends this:

Sending xhr message to server: {"csrfToken":"943b511e-da80-450d-9fa6-c0aba20effcc","rpc":[{"type":"event","node":561,"event":"upload-success","data":{"element.files":[{"loaded":32768,"held":false,"status":"","xhr":{},"uploadTarget":"VAADIN/dynamic/resource/0/863e8c02-6d46-45f5-af39-991b00327859/upload","indeterminate":false,"uploading":false,"error":false,"abort":false,"complete":true,"progress":100}]}}],"syncId":31,"clientId":31}

Expected outcome

I expect that errors signaled in handleUploadRequest are reflected in the file list, regardless of file size

Minimal reproducible example

class ReproUploadHandler extends TransferProgressAwareHandler<UploadEvent, ReproUploadHandler> implements UploadHandler {
    @Override
    public void handleUploadRequest(UploadEvent event) throws IOException {
        notifyError(event, new IOException("test error"));
    }

    @Override
    protected TransferContext getTransferContext(UploadEvent transferEvent) {
        return new TransferContext(transferEvent.getRequest(),
                transferEvent.getResponse(), transferEvent.getSession(),
                transferEvent.getFileName(), transferEvent.getOwningElement(),
                transferEvent.getFileSize());
    }
}

And in some view class:

var upload = new Upload(new ReproUploadHandler());
upload.setMaxFiles(1);  //Not sure if this is significant 
// add upload to the view.

Steps to reproduce

Create a view and add an Upload with the code above. Try to upload a small file (my test file is 32K).

Environment

Vaadin version(s): 25.0.5
OS: Ubuntu 20.04.6
Browser: FF 136.0 (not sure if significant)

Browsers

Firefox

[sissbruecker]

As mentioned in the JavaDoc of notifyError, its purpose is to notify custom application listeners that can be added through the TransferProgressAwareHandler interface. However, it is not responsible for marking an upload request as failed, which requires an additional step, which is either:

• (Re)throw an exception from handleUploadRequest
• Call event.rejected() from handleUploadRequest

Both will result in setting an HTTP status code on the response that indicates a failure to the upload component. Optionally you can override responseHandled to customize the response status code.

In general this is somewhat covered in the Upload documentation, although the documentation could use some improvements to:

• Provide a concrete example for custom validation and how to make an upload request fail when an error occurs
• Clearly point out the purpose of notifyError

[AndreRisnes]

I can't see a rejected() method on UploadEvent in 25.0.6.

Re-throwing somewhat works, but the progress bar for the failed file gets stuck in "indefinite processing" mode.

I'd prefer to not re-throw the exception, since it causes logging at ERROR level in TransferUtil.

[Artur-]

The reject API was added in vaadin/flow#22814 to deal with the exception logging and unclear API. Would be great if you want to try out an 25.1 alpha to see if it solves your issues