[Upload] Provide single event with all rejected files

[guygoldwasser]

Description

B"H
Hi,
assuming developer block usage to pdf types only,
but customer enforce selections to take lets say 4 file that are not pdf.
rejection event will happened 4 times.
the AllFinished event will happened if and only if at least single file path the validations.

But, what i really want is a single generation of error.
e.g. I have my own error dialog, and i don't want to open it 4 times, only once.
I don't see how I can reach it with current.

consistently get AllFinished event might help in such case.
is there any other way to acheve same?

Expected outcome

A single final event knowing all done,

Minimal reproducible example

upload.addFileRejectedListener(event -> {
			if (failMessage == null) {
				failMessage = Lists.newArrayList();
			}
			failMessage.add(event.getFileName() + " - " + event.getErrorMessage());
		});
upload.addAllFinishedListener(event ->{
			if(failMessage == null || failMessage.isEmpty()) {
				logger.debug("All files uploaded successfully.");
				//do what need to do
			} else {
				logger.warn("Some files failed to upload: {}", String.join(", ", failMessage));
				//e.g.  my notification showError("...", failMessage);
				failMessage = null;
			}
		});

Steps to reproduce

1. create upload with multiply
2. restrict for some type e.g. application/pdf
3. load few jpg files

Environment

Vaadin version(s):
OS:

Browsers

No response

[Artur-]

This is slightly related to the PR for rejecting files vaadin/flow#22814 although the errors there would be shown in the upload component, not in a separate dialog

[Artur-]

There is also UploadHandler.responseHandled today which should be called when all uploads are complete. Not sure if it can be used for this case

[rolfsmeds]

JavaDoc says AllFinishedEvent should trigger regardless of whether all the receptions were successful or not, which implies that it should also trigger when none of them are. Thus, this is a bug.
As this is a behavior altering change that may cause issues in existing apps, we'll target this for a patch in 25.0, and not backport to V24 by default.

[sissbruecker]

Since rejected files never get added to the list of files to upload, using the all finished event is probably not a good choice. These are two different things:

• All finished: Is for giving feedback about success or failure of the actual upload operation
• Rejected: Is for giving validation feedback that some files the user dropped / selected were not added to the file list in the first place

This was discussed previously in #3088, where users also voiced their opinion that they would not expected rejected files to trigger an all finished event.

Instead of repurposing the all finished event, we could:

• Introduce a new "Files rejected" (plural) event that lists all files that were not added after the user dropped or selected files
• Deprecate and later remove the current file rejected event, as the event providing the list of files should be more practical in all cases where you want to give feedback to the user

That should make it easier to give feedback to users why some files did not end up in the list. Having a single event for rejections would also allow combining feedback about rejections with finished / failed uploads by doing something like this:

private List<String> rejections = new ArrayList<>();

upload.addFilesRejectedListener(e -> {
    rejections.addAll(e.getFileNames());
    if (!upload.isUploading()) {
        showFeedback();
    }
});

upload.addAllFinishedListener(e -> {
    showFeedback();
});

[guygoldwasser]

B"H
Well,

1. i still found this is a bug and not just enhancement, currently i have no good way to express the user what is going on, else i will hack something.
2. Assuming i have list of rejections and list of success, not clear to me how can i handle it in single shot.
   e.g. i might want to block the process, or continue partially etc.
   this split without single point of truth make it a dizzy api from my opinion and really wonder how it is going to work.