'Create a file to which an incoming message may be written.
@type octets: L{int}
@param octets: The number of octets which will be written to the file
@rtype: Any object which implements C{write(string)} and
C{seek(int, int)}
@return: A file-like object'

def messageFile(self, octets):

    if (octets > self._memoryFileLimit):
        return tempfile.TemporaryFile()
    else:
        return BytesIO()
