Does offset > fileSize really mean success, or maybe something went wrong?

Something is wrong here. We've defined earlier

this->fileSize = getBucket(s3Path.getBucketName())
                           .getObjectSize(s3Path.getObjectName());

then we're creating a new variable

const size_t fileSize =
          bucket.getObjectSize(this->s3Path.getObjectName());

And check this->fileSize.
So the variable fileSize is never used.

It looks like we should either check this->fileSize where it is defined or check fileSize here instead

Is there a good reason for using a raw pointer and new here?