Hi, I’m working on the tarfile module to add support for file objects whose size is not know beforehand (https://bugs.python.org/issue35227).

In doing so, I need to adapt `tarfile.copyfileobj` to return the length of the file after it has been copied.

Calling this function with `length=None` currently leads to data being copied but without adding the necessary padding. This seems weird to me, I do not understand why this would be needed and this behaviour is currently not used.

This function is not documented in Python documentation so nobody is probably using it.

Can I safely change `tarfile.copyfileobj` to make it write the padding when `length=None`?

Thanks, Rémi