'Compute the string to use for the value of the I{Host} header, based on
the given scheme, host name, and port number.'

def _computeHostValue(self, scheme, host, port):

    if isIPv6Address(nativeString(host)):
        host = (('[' + host) + ']')
    if ((scheme, port) in (('http', 80), ('https', 443))):
        return host
    return ((host + ':') + intToBytes(port))
