unify common parts of build_register_command

        # Maybe the script was read from stdin; in any case don't guess at the directory.

        raise ValueError("Can't find executable directory for registration helpers")

    # "common" is options shared by every registration helper.

    common = []

    if method not in ("http", "appspot", "email"):

        raise ValueError("Unknown registration method \"%s\"" % method)

    args = []

    # facilitator selection

    if method == "http":

        if options.facilitator_url is not None:

            args += ["-f", options.facilitator_url]

    else:

        if options.facilitator_pubkey_filename is not None:

            args += ["--facilitator-pubkey", options.facilitator_pubkey_filename]

    # options shared by every registration helper.

    if options.address_family == socket.AF_INET:

        common += ["-4"]

        args += ["-4"]

    elif options.address_family == socket.AF_INET6:

        common += ["-6"]

        args += ["-6"]

    if options.transport is not None:

        common += ["--transport", options.transport]

        args += ["--transport", options.transport]

    if not options.safe_logging:

        common += ["--unsafe-logging"]

        args += ["--unsafe-logging"]

    if method == "appspot":

        command = [os.path.join(script_dir, "flashproxy-reg-appspot")] + common

        if options.facilitator_pubkey_filename is not None:

            command += ["--facilitator-pubkey", options.facilitator_pubkey_filename]

        return command

    elif method == "email":

        command = [os.path.join(script_dir, "flashproxy-reg-email")] + common

        if options.facilitator_pubkey_filename is not None:

            command += ["--facilitator-pubkey", options.facilitator_pubkey_filename]

        return command

    elif method == "http":

        command = [os.path.join(script_dir, "flashproxy-reg-http")] + common

        if options.facilitator_url is not None:

            command += ["-f", options.facilitator_url]

        return command

    else:

        raise ValueError("Unknown registration method \"%s\"" % method)

    prog = os.path.join(script_dir, "flashproxy-reg-%s" % method)

    return [prog] + args

def pt_escape(s):

    result = []