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//usr/lib/python3/dist-packages/cloudinit/handlers/cloud_config.py

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

import jsonpatch

from cloudinit import handlers
from cloudinit import log as logging
from cloudinit import mergers
from cloudinit import util
from cloudinit import safeyaml

from cloudinit.settings import (PER_ALWAYS)

LOG = logging.getLogger(__name__)

MERGE_HEADER = 'Merge-Type'

# Due to the way the loading of yaml configuration was done previously,
# where previously each cloud config part was appended to a larger yaml
# file and then finally that file was loaded as one big yaml file we need
# to mimic that behavior by altering the default strategy to be replacing
# keys of prior merges.
#
#
# For example
# #file 1
# a: 3
# #file 2
# a: 22
# #combined file (comments not included)
# a: 3
# a: 22
#
# This gets loaded into yaml with final result {'a': 22}
DEF_MERGERS = mergers.string_extract_mergers('dict(replace)+list()+str()')
CLOUD_PREFIX = "#cloud-config"
JSONP_PREFIX = "#cloud-config-jsonp"

class CloudConfigPartHandler(handlers.Handler):

# The content prefixes this handler understands.
    prefixes = [CLOUD_PREFIX, JSONP_PREFIX]

def __init__(self, paths, **_kwargs):
        handlers.Handler.__init__(self, PER_ALWAYS, version=3)
        self.cloud_buf = None
        self.cloud_fn = paths.get_ipath("cloud_config")
        if 'cloud_config_path' in _kwargs:
            self.cloud_fn = paths.get_ipath(_kwargs["cloud_config_path"])
        self.file_names = []

def _write_cloud_config(self):
        if not self.cloud_fn:
            return
        # Capture which files we merged from...
        file_lines = []
        if self.file_names:
            file_lines.append("# from %s files" % (len(self.file_names)))
            for fn in self.file_names:
                if not fn:
                    fn = '?'
                file_lines.append("# %s" % (fn))
            file_lines.append("")
        if self.cloud_buf is not None:
            # Something was actually gathered....
            lines = [
                CLOUD_PREFIX,
                '',
            ]
            lines.extend(file_lines)
            lines.append(safeyaml.dumps(self.cloud_buf))
        else:
            lines = []
        util.write_file(self.cloud_fn, "\n".join(lines), 0o600)

def _extract_mergers(self, payload, headers):
        merge_header_headers = ''
        for h in [MERGE_HEADER, 'X-%s' % (MERGE_HEADER)]:
            tmp_h = headers.get(h, '')
            if tmp_h:
                merge_header_headers = tmp_h
                break
        # Select either the merge-type from the content
        # or the merge type from the headers or default to our own set
        # if neither exists (or is empty) from the later.
        payload_yaml = util.load_yaml(payload)
        mergers_yaml = mergers.dict_extract_mergers(payload_yaml)
        mergers_header = mergers.string_extract_mergers(merge_header_headers)
        all_mergers = []
        all_mergers.extend(mergers_yaml)
        all_mergers.extend(mergers_header)
        if not all_mergers:
            all_mergers = DEF_MERGERS
        return (payload_yaml, all_mergers)

def _merge_patch(self, payload):
        # JSON doesn't handle comments in this manner, so ensure that
        # if we started with this 'type' that we remove it before
        # attempting to load it as json (which the jsonpatch library will
        # attempt to do).
        payload = payload.lstrip()
        payload = util.strip_prefix_suffix(payload, prefix=JSONP_PREFIX)
        patch = jsonpatch.JsonPatch.from_string(payload)
        LOG.debug("Merging by applying json patch %s", patch)
        self.cloud_buf = patch.apply(self.cloud_buf, in_place=False)

def _merge_part(self, payload, headers):
        (payload_yaml, my_mergers) = self._extract_mergers(payload, headers)
        LOG.debug("Merging by applying %s", my_mergers)
        merger = mergers.construct(my_mergers)
        self.cloud_buf = merger.merge(self.cloud_buf, payload_yaml)

def _reset(self):
        self.file_names = []
        self.cloud_buf = None

def handle_part(self, data, ctype, filename, payload, frequency, headers):
        if ctype == handlers.CONTENT_START:
            self._reset()
            return
        if ctype == handlers.CONTENT_END:
            self._write_cloud_config()
            self._reset()
            return
        try:
            # First time through, merge with an empty dict...
            if self.cloud_buf is None or not self.file_names:
                self.cloud_buf = {}
            if ctype == handlers.INCLUSION_TYPES_MAP[JSONP_PREFIX]:
                self._merge_patch(payload)
            else:
                self._merge_part(payload, headers)
            # Ensure filename is ok to store
            for i in ("\n", "\r", "\t"):
                filename = filename.replace(i, " ")
            self.file_names.append(filename.strip())
        except Exception:
            util.logexc(LOG, "Failed at merging in cloud config part from %s",
                        filename)

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