Expose .abort() method in S3OutputStream for cancelling partially completed uploads

[zhemaituk]

Type: Feature

Is your feature request related to a problem? Please describe.
If writing a file through S3OutputStream has started - there is no possibility to abort the upload.
My scenario:

1. User uploads large file via UI
2. Backend accepts the file, starts validating file and proxy writes it to S3 for storage
3. Something goes wrong (user abandons the upload, file turns out invalid, etc.)

Sample code:

try (
    S3OutputStream s3Stream = inMemoryBufferingS3StreamProvider.create(uploadLocation,
            ObjectMetadata.builder()
                    .contentType("text/csv")
                    .build());
    CSVWriter writer = new CSVWriter(new OutputStreamWriter(s3Stream))
) {
    try {
        String[] headers = reader.readNext();
        validateHeaders(headers);
        writer.writeNext(headers);

        String[] row;
        while ((row = reader.readNext()) != null) {
            // Further data validation is done at this stage.
            writer.writeNext(row);
        }
    } catch (CsvValidationException|IOException e) {
        // TODO: Abort the upload?!
        // TODO: s3Stream.abort();
    }
}

Describe the solution you'd like
New method S3OutputStream#abort which can be called if the stream is not closed yet.

Describe alternatives you've considered

1. Use reflection to call InMemoryBufferingS3OutputStream#abortMultiPartUpload
2. Delete the file if upload (partially) fails. Does not work that well on versioned buckets/objects.
3. Copy-paste InMemoryBufferingS3OutputStream and expose abort method
   None of the alternatives are appealing.

Additional context

[maciejwalkowiak]

As I understand exposing this method would make sense for InMemoryBufferingS3OutputStream but not for all the implementations of S3OutputStream. Would you like to submit a PR?

[zhemaituk]

Created #1221 PR.
It seems applicable for the other implementations of S3OutputStream , e.g. if a user needs to cancel the upload mid-way using the stream.
E.g. currently DiskBufferingS3OutputStream#close would always result in a file on S3, even if the user's code fails to write everything what was intended. #abort gives the user ability to cancel if required.

[maciejwalkowiak]

Fixed in #1221