User.RevokeFile: Revoke file access
===================================

.. function:: RevokeFile(filename string, targetUsername string) (error)

    You may assume this function will only be called by the file owner.

    Revokes access to the given file from ``targetUsername`` and any other users
    with whom ``targetUsername`` has shared the file. The secure file share
    invitation(s) should be revoked even if the recipient has not yet called
    ``ReceiveFile()``.

    Revoked users cannot take any actions on the file (see
    :ref:`requirement_sharing_and_revoking`).

    Returns an error if:

      - the given file does not exist in the caller's personal file namespace;
        or

      - the given file is not currently shared with ``targetUsername``; or

      - revocation cannot complete due to malicious action.

    :param filename: The name of the file in the caller's personal file
                     namespace.
    :type filename: string
    :param targetUsername: Username of the user to revoke access from.
    :type targetUsername: string

    :rtype: error

.. warning::
    Do not forget that your design must satisfy **all** requirements, including:

    #. All :ref:`requirement_access_tokens` requirements.

    #. All :ref:`requirement_sharing_and_revoking` requirements.