'Return the boundary associated with the payload if present.
The boundary is extracted from the Content-Type header\'s `boundary\'
parameter, and it is unquoted.'

def get_boundary(self, failobj=None):

    missing = object()
    boundary = self.get_param('boundary', missing)
    if (boundary is missing):
        return failobj
    return utils.collapse_rfc2231_value(boundary).rstrip()
