# Copyright (C) 2011 Canonical Ltd.
# Copyright (C) 2012, 2013 Hewlett-Packard Development Company, L.P.
#
# Author: Scott Moser <scott.moser@canonical.com>
# Author: Juerg Haefliger <juerg.haefliger@hp.com>
#
# This file is part of cloud-init. See LICENSE file for license information.

"""
Set Hostname
------------
**Summary:** set hostname and fqdn

This module handles setting the system hostname and fqdn. If
``preserve_hostname`` is set, then the hostname will not be altered.

A hostname and fqdn can be provided by specifying a full domain name under the
``fqdn`` key. Alternatively, a hostname can be specified using the ``hostname``
key, and the fqdn of the cloud wil be used. If a fqdn specified with the
``hostname`` key, it will be handled properly, although it is better to use
the ``fqdn`` config key. If both ``fqdn`` and ``hostname`` are set,
it is distro dependent whether ``hostname`` or ``fqdn`` is used,
unless the ``prefer_fqdn_over_hostname`` option is true and fqdn is set
it will force the use of FQDN in all distros, and if false then it will
force the hostname use.

This module will run in the init-local stage before networking is configured
if the hostname is set by metadata or user data on the local system.

This will occur on datasources like nocloud and ovf where metadata and user
data are available locally. This ensures that the desired hostname is applied
before any DHCP requests are preformed on these platforms where dynamic DNS is
based on initial hostname.

**Internal name:** ``cc_set_hostname``

**Module frequency:** always

**Supported distros:** all

**Config keys**::

    preserve_hostname: <true/false>
    prefer_fqdn_over_hostname: <true/false>
    fqdn: <fqdn>
    hostname: <fqdn/hostname>
"""

import os


from cloudinit.atomic_helper import write_json
from cloudinit import util


class SetHostnameError(Exception):
    """Raised when the distro runs into an exception when setting hostname.

    This may happen if we attempt to set the hostname early in cloud-init's
    init-local timeframe as certain services may not be running yet.
    """


def handle(name, cfg, cloud, log, _args):
    if util.get_cfg_option_bool(cfg, "preserve_hostname", False):
        log.debug(("Configuration option 'preserve_hostname' is set,"
                   " not setting the hostname in module %s"), name)
        return

    # Set prefer_fqdn_over_hostname value in distro
    hostname_fqdn = util.get_cfg_option_bool(cfg,
                                             "prefer_fqdn_over_hostname",
                                             None)
    if hostname_fqdn is not None:
        cloud.distro.set_option('prefer_fqdn_over_hostname', hostname_fqdn)

    (hostname, fqdn) = util.get_hostname_fqdn(cfg, cloud)
    # Check for previous successful invocation of set-hostname

    # set-hostname artifact file accounts for both hostname and fqdn
    # deltas. As such, it's format is different than cc_update_hostname's
    # previous-hostname file which only contains the base hostname.
    # TODO consolidate previous-hostname and set-hostname artifact files and
    # distro._read_hostname implementation so we only validate  one artifact.
    prev_fn = os.path.join(cloud.get_cpath('data'), "set-hostname")
    prev_hostname = {}
    if os.path.exists(prev_fn):
        prev_hostname = util.load_json(util.load_file(prev_fn))
    hostname_changed = (hostname != prev_hostname.get('hostname') or
                        fqdn != prev_hostname.get('fqdn'))
    if not hostname_changed:
        log.debug('No hostname changes. Skipping set-hostname')
        return
    log.debug("Setting the hostname to %s (%s)", fqdn, hostname)
    try:
        cloud.distro.set_hostname(hostname, fqdn)
    except Exception as e:
        msg = "Failed to set the hostname to %s (%s)" % (fqdn, hostname)
        util.logexc(log, msg)
        raise SetHostnameError("%s: %s" % (msg, e)) from e
    write_json(prev_fn, {'hostname': hostname, 'fqdn': fqdn})

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