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Filename : sys_conf.py
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# Copyright (C) 2012 Yahoo! Inc.
#
# Author: Joshua Harlow <harlowja@yahoo-inc.com>
#
# This file is part of cloud-init. See LICENSE file for license information.

import re
import shlex
from io import StringIO

# This library is used to parse/write
# out the various sysconfig files edited (best attempt effort)
#
# It has to be slightly modified though
# to ensure that all values are quoted/unquoted correctly
# since these configs are usually sourced into
# bash scripts...
import configobj

# See: http://pubs.opengroup.org/onlinepubs/000095399/basedefs/xbd_chap08.html
# or look at the 'param_expand()' function in the subst.c file in the bash
# source tarball...
SHELL_VAR_RULE = r"[a-zA-Z_]+[a-zA-Z0-9_]*"
SHELL_VAR_REGEXES = [
    # Basic variables
    re.compile(r"\$" + SHELL_VAR_RULE),
    # Things like $?, $0, $-, $@
    re.compile(r"\$[0-9#\?\-@\*]"),
    # Things like ${blah:1} - but this one
    # gets very complex so just try the
    # simple path
    re.compile(r"\$\{.+\}"),
]


def _contains_shell_variable(text):
    for r in SHELL_VAR_REGEXES:
        if r.search(text):
            return True
    return False


class SysConf(configobj.ConfigObj):
    """A configobj.ConfigObj subclass specialised for sysconfig files.

    :param contents:
        The sysconfig file to parse, in a format accepted by
        ``configobj.ConfigObj.__init__`` (i.e. "a filename, file like object,
        or list of lines").
    """

    def __init__(self, contents):
        configobj.ConfigObj.__init__(
            self, contents, interpolation=False, write_empty_values=True
        )

    def __str__(self):
        contents = self.write()
        out_contents = StringIO()
        if isinstance(contents, (list, tuple)):
            out_contents.write("\n".join(contents))
        else:
            out_contents.write(str(contents))
        return out_contents.getvalue()

    def _quote(self, value, multiline=False):
        if not isinstance(value, str):
            raise ValueError('Value "%s" is not a string' % (value))
        if len(value) == 0:
            return ""
        quot_func = None
        if value[0] in ['"', "'"] and value[-1] in ['"', "'"]:
            if len(value) == 1:
                quot_func = (
                    lambda x: self._get_single_quote(x) % x
                )  # noqa: E731
        else:
            # Quote whitespace if it isn't the start + end of a shell command
            if value.strip().startswith("$(") and value.strip().endswith(")"):
                pass
            else:
                if re.search(r"[\t\r\n ]", value):
                    if _contains_shell_variable(value):
                        # If it contains shell variables then we likely want to
                        # leave it alone since the shlex.quote function likes
                        # to use single quotes which won't get expanded...
                        if re.search(r"[\n\"']", value):
                            quot_func = (
                                lambda x: self._get_triple_quote(x) % x
                            )  # noqa: E731
                        else:
                            quot_func = (
                                lambda x: self._get_single_quote(x) % x
                            )  # noqa: E731
                    else:
                        quot_func = shlex.quote
        if not quot_func:
            return value
        return quot_func(value)

    def _write_line(self, indent_string, entry, this_entry, comment):
        # Ensure it is formatted fine for
        # how these sysconfig scripts are used
        val = self._decode_element(self._quote(this_entry))
        key = self._decode_element(self._quote(entry))
        cmnt = self._decode_element(comment)
        return "%s%s%s%s%s" % (
            indent_string,
            key,
            "=",
            val,
            cmnt,
        )