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[DataIO] Atomically save json (#372)

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Should put an end to the corruption issues
This commit is contained in:
Twentysix 2016-09-13 00:33:37 +02:00 committed by GitHub
parent f95b7c1fee
commit 60f4a16828
1 changed files with 23 additions and 38 deletions
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57
cogs/utils/dataIO.py
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@ -1,48 +1,45 @@
import json import json
import os import os
import logging import logging
from shutil import copy from random import randint
class InvalidFileIO(Exception): class InvalidFileIO(Exception):
pass pass
class CorruptedJSON(Exception):
pass
class DataIO(): class DataIO():
def __init__(self): def __init__(self):
self.logger = logging.getLogger("red") self.logger = logging.getLogger("red")
def save_json(self, filename, data): def save_json(self, filename, data):
"""Saves and backups json file""" """Atomically saves json file"""
bak_file = os.path.splitext(filename)[0]+'.bak' rnd = randint(1000, 9999)
self._save_json(filename, data) path, ext = os.path.splitext(filename)
copy(filename, bak_file) # Backup copy tmp_file = "{}-{}.tmp".format(path, rnd)
self._save_json(tmp_file, data)
try:
self._read_json(tmp_file)
except json.decoder.JSONDecodeError:
self.logger.exception("Attempted to write file {} but JSON "
"integrity check on tmp file has failed. "
"The original file is unaltered."
"".format(filename))
return False
os.replace(tmp_file, filename)
return True
def load_json(self, filename): def load_json(self, filename):
"""Loads json file and restores backup copy in case of corrupted file""" """Loads json file"""
try:
return self._read_json(filename) return self._read_json(filename)
except json.decoder.JSONDecodeError:
result = self._restore_json(filename)
if result:
return self._read_json(filename) # Which hopefully will work
else:
raise CorruptedJSON("{} is corrupted and no backup copy is"
" available.".format(filename))
def is_valid_json(self, filename): def is_valid_json(self, filename):
"""Returns True if readable json file, False if not existing. """Verifies if json file exists / is readable"""
Tries to restore backup copy if corrupted"""
try: try:
data = self._read_json(filename) self._read_json(filename)
return True
except FileNotFoundError: except FileNotFoundError:
return False return False
except json.decoder.JSONDecodeError: except json.decoder.JSONDecodeError:
result = self._restore_json(filename) return False
return result # If False, no backup copy, might as well
else: # allow the overwrite
return True
def _read_json(self, filename): def _read_json(self, filename):
with open(filename, encoding='utf-8', mode="r") as f: with open(filename, encoding='utf-8', mode="r") as f:
@ -55,18 +52,6 @@ class DataIO():
separators=(',',' : ')) separators=(',',' : '))
return data return data
def _restore_json(self, filename):
bak_file = os.path.splitext(filename)[0]+'.bak'
if os.path.isfile(bak_file):
copy(bak_file, filename) # Restore last working copy
self.logger.warning("{} was corrupted. Restored "
"backup copy.".format(filename))
return True
else:
self.logger.critical("{} is corrupted and there is no "
"backup copy available.".format(filename))
return False
def _legacy_fileio(self, filename, IO, data=None): def _legacy_fileio(self, filename, IO, data=None):
"""Old fileIO provided for backwards compatibility""" """Old fileIO provided for backwards compatibility"""
if IO == "save" and data != None: if IO == "save" and data != None: