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✏️ Editing: atomic_helper.py

# This file is part of cloud-init. See LICENSE file for license information.

import json
import logging
import os
import stat
import tempfile
from base64 import b64decode, b64encode

_DEF_PERMS = 0o644
LOG = logging.getLogger(__name__)

def b64d(source):
    # Base64 decode some data, accepting bytes or unicode/str, and returning
    # str/unicode if the result is utf-8 compatible, otherwise returning bytes.
    decoded = b64decode(source)
    try:
        return decoded.decode("utf-8")
    except UnicodeDecodeError:
        return decoded

def b64e(source):
    # Base64 encode some data, accepting bytes or unicode/str, and returning
    # str/unicode if the result is utf-8 compatible, otherwise returning bytes.
    if not isinstance(source, bytes):
        source = source.encode("utf-8")
    return b64encode(source).decode("utf-8")

def write_file(
    filename, content, mode=_DEF_PERMS, omode="wb", preserve_mode=False
):
    # open filename in mode 'omode', write content, set permissions to 'mode'

if preserve_mode:
        try:
            file_stat = os.stat(filename)
            mode = stat.S_IMODE(file_stat.st_mode)
        except OSError:
            pass

tf = None
    try:
        tf = tempfile.NamedTemporaryFile(
            dir=os.path.dirname(filename), delete=False, mode=omode
        )
        LOG.debug(
            "Atomically writing to file %s (via temporary file %s) - %s: [%o]"
            " %d bytes/chars",
            filename,
            tf.name,
            omode,
            mode,
            len(content),
        )
        tf.write(content)
        tf.close()
        os.chmod(tf.name, mode)
        os.rename(tf.name, filename)
    except Exception as e:
        if tf is not None:
            os.unlink(tf.name)
        raise e

def json_serialize_default(_obj):
    """Handler for types which aren't json serializable."""
    try:
        return "ci-b64:{0}".format(b64e(_obj))
    except AttributeError:
        return "Warning: redacted unserializable type {0}".format(type(_obj))

def json_dumps(data):
    """Return data in nicely formatted json."""
    return json.dumps(
        data,
        indent=1,
        sort_keys=True,
        separators=(",", ": "),
        default=json_serialize_default,
    )

def write_json(filename, data, mode=_DEF_PERMS):
    # dump json representation of data to file filename.
    return write_file(
        filename,
        json_dumps(data) + "\n",
        omode="w",
        mode=mode,
    )

MR SKB