#!/usr/bin/python """ This module makes it possible to ensure that data is not corrupted between files whose version numbers are not important but must be synchronized. It protects these files from crashes. It does, however, require that critical files do not disappear between executions. It can only account for cases where the computer does not do what it is told, not cases where it does what it is not told. Copyright (c) 2008 Collin Ross Mechlowitz Stocks This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see . """ import os class SyncFiles(object): def __init__(self,pathcons,*paths): self.pathcons=pathcons self.paths=list(paths) self.TEMP="-temp~" self.BACK="-back~" self.PACKETSIZE=1<<20 def _testfiles(self): if os.path.exists(self.pathcons): #update had not even been called yet, so temps are bad #and currs are not bad return False,False tempsaregood=True currsarebad1=False currsarebad2=False if not os.path.exists(self.pathcons+self.TEMP): tempsaregood=False currsarebad1=True else: currsarebad2=True for path in self.paths: if not os.path.exists(path+self.TEMP): tempsaregood=False currsarebad1=True else: currsarebad2=True return tempsaregood,(currsarebad1 and currsarebad2) def _safeupdatefrom(self,ext): for path in self.paths: fread=open(path+ext,"rb") fwrite=open(path,"wb") data=fread.read(self.PACKETSIZE) while data: fwrite.write(data) data=fread.read(self.PACKETSIZE) fread.close() fwrite.close() def openread(self): ret=[] tempsaregood,currsarebad=self._testfiles() if tempsaregood: self._safeupdatefrom(self.TEMP) for path in self.paths: ret.append(open(path,"rb")) elif currsarebad: for path in self.paths: ret.append(open(path+self.BACK,"rb")) else: for path in self.paths: ret.append(open(path,"rb")) return ret def openwrite(self): ret=[] firsttime=True for path in self.paths: if os.path.exists(path): firsttime=False if not firsttime: tempsaregood,currsarebad=self._testfiles() if tempsaregood: self._safeupdatefrom(self.TEMP) elif currsarebad: self._safeupdatefrom(self.BACK) open(self.pathcons,"wb").close() for path in self.paths: ret.append(open(path+self.TEMP,"wb")) return ret def update(self): os.remove(self.pathcons) open(self.pathcons+self.TEMP,"wb").close() for path in self.paths: try: os.remove(path+self.BACK) except OSError: pass for path in self.paths: try: os.rename(path,path+self.BACK) except OSError: pass os.remove(self.pathcons+self.TEMP) for path in self.paths: os.rename(path+self.TEMP,path)