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|
#!/usr/bin/python3
# Copyright (C) 2017
import posixpath
import logging
import os
import collections
from augeas import Augeas
AUGEAS_LOAD_PATH = '/augeas/load/'
AUGEAS_FILES_PATH = '/files/'
AUGEAS_ERROR_PATH = '//error'
log = logging.getLogger('augeas')
def join(*paths):
"""
join two Augeas tree paths
FIXME: Beware: // is normalized to /
"""
norm_paths = [posixpath.normpath(path) for path in paths]
# first path must be absolute
assert norm_paths[0][0] == '/'
new_paths = [norm_paths[0]]
# relativize all other paths so join works as expected
for path in norm_paths[1:]:
if path.startswith('/'):
path = path[1:]
new_paths.append(path)
new_path = posixpath.join(*new_paths)
log.debug("join: new_path %s", new_path)
return posixpath.normpath(new_path)
class AugeasWrapper:
"""python-augeas higher-level wrapper.
Load single augeas lens and configuration file.
Exposes configuration file as AugeasNode object with dict-like interface.
AugeasWrapper can be used in with statement in the same way as file does.
"""
def __init__(self, confpath, lens, root=None, loadpath=None,
flags=Augeas.NO_MODL_AUTOLOAD | Augeas.NO_LOAD | Augeas.ENABLE_SPAN):
"""Parse configuration file using given lens.
Params:
confpath (str): Absolute path to the configuration file
lens (str): Name of module containing Augeas lens
root: passed down to original Augeas
flags: passed down to original Augeas
loadpath: passed down to original Augeas
flags: passed down to original Augeas
"""
log.debug('loadpath: %s', loadpath)
log.debug('confpath: %s', confpath)
self._aug = Augeas(root=root, loadpath=loadpath, flags=flags)
# /augeas/load/{lens}
aug_load_path = join(AUGEAS_LOAD_PATH, lens)
# /augeas/load/{lens}/lens = {lens}.lns
self._aug.set(join(aug_load_path, 'lens'), '%s.lns' % lens)
# /augeas/load/{lens}/incl[0] = {confpath}
self._aug.set(join(aug_load_path, 'incl[0]'), confpath)
self._aug.load()
errors = self._aug.match(AUGEAS_ERROR_PATH)
if errors:
err_msg = '\n'.join(
["{}: {}".format(e, self._aug.get(e)) for e in errors]
)
raise RuntimeError(err_msg)
path = join(AUGEAS_FILES_PATH, confpath)
paths = self._aug.match(path)
if len(paths) != 1:
raise ValueError('path %s did not match exactly once' % path)
self.tree = AugeasNode(self._aug, path)
self._loaded = True
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
self.save()
self.close()
def save(self):
"""Save Augeas tree to its original file."""
assert self._loaded
try:
self._aug.save()
except IOError as exc:
log.exception(exc)
for err_path in self._aug.match('//error'):
log.error('%s: %s', err_path,
self._aug.get(os.path.join(err_path, 'message')))
raise
def close(self):
"""
close Augeas library
After calling close() the object must not be used anymore.
"""
assert self._loaded
self._aug.close()
del self._aug
self._loaded = False
def match(self, path):
"""Yield AugeasNodes matching given expression."""
assert self._loaded
assert path
log.debug('tree match %s', path)
for matched_path in self._aug.match(path):
yield AugeasNode(self._aug, matched_path)
class AugeasNode(collections.MutableMapping):
"""One Augeas tree node with dict-like interface."""
def __init__(self, aug, path):
"""
Args:
aug (AugeasWrapper or Augeas): Augeas library instance
path (str): absolute path in Augeas tree matching single node
BEWARE: There are no sanity checks of given path for performance reasons.
"""
assert aug
assert path
assert path.startswith('/')
self._aug = aug
self._path = path
self._span = None
@property
def path(self):
"""canonical path in Augeas tree, read-only"""
return self._path
@property
def value(self):
"""
get value of this node in Augeas tree
"""
value = self._aug.get(self._path)
log.debug('tree get: %s = %s', self._path, value)
return value
@value.setter
def value(self, value):
"""
set value of this node in Augeas tree
"""
log.debug('tree set: %s = %s', self._path, value)
self._aug.set(self._path, value)
@property
def span(self):
if self._span is None:
self._span = "char position %s" % self._aug.span(self._path)[5]
return self._span
@property
def char(self):
return self._aug.span(self._path)[5]
def __len__(self):
"""
number of items matching this path
It is always 1 after __init__() but it may change
as Augeas tree changes.
"""
return len(self._aug.match(self._path))
def __getitem__(self, key):
if isinstance(key, int):
# int is a shortcut to write [int]
target_path = '%s[%s]' % (self._path, key)
else:
target_path = self._path + key
log.debug('tree getitem: target_path %s', target_path)
paths = self._aug.match(target_path)
if len(paths) != 1:
raise KeyError('path %s did not match exactly once' % target_path)
return AugeasNode(self._aug, target_path)
def __delitem__(self, key):
log.debug('tree delitem: %s + %s', self._path, key)
target_path = self._path + key
log.debug('tree delitem: target_path %s', target_path)
self._aug.remove(target_path)
def __setitem__(self, key, value):
assert isinstance(value, AugeasNode)
target_path = self.path + key
self._aug.copy(value.path, target_path)
def __iter__(self):
self_path_len = len(self._path)
assert self_path_len > 0
log.debug('tree iter: %s', self._path)
for new_path in self._aug.match(self._path):
if len(new_path) == self_path_len:
yield ''
else:
yield new_path[self_path_len - 1:]
def match(self, subpath):
"""Yield AugeasNodes matching given sub-expression."""
assert subpath.startswith("/")
match_path = "%s%s" % (self._path, subpath)
log.debug('tree match %s: %s', match_path, self._path)
for matched_path in self._aug.match(match_path):
yield AugeasNode(self._aug, matched_path)
def __repr__(self):
return 'AugeasNode(%s)' % self._path
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