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#!/usr/bin/python
import Alchemist
import os
import re
import exceptions
import string
def VersionList(cache_dir,template):
"""
Utility function.
We build a list of the versions available of a given template file in
a cache directory. the files will resemble /cache_dir/version.template
"""
version_list = []
cache_match = re.compile(r'(\d+)\.cache.' + re.escape(template))
for file in os.listdir(cache_dir):
match = cache_match.match(file)
if match:
version_list.append(string.atoi(match.groups(0)[0]))
version_list.sort()
return version_list
def getBox(box_cfg):
"""
getBox: get a BlackBox from this module
@box_cfg: a box_cfg conformant AdmList element containing
the following elements:
path: type string, the path to the context file (required)
returns: CacheBlackBox object
"""
return CacheBlackBox(box_cfg)
class CacheBlackBox(Alchemist.BlackBox):
"""
The CacheBlackBox class provides a class to read and write Contexts
from and to files.
"""
def __init__ (self, box_cfg):
"""
__init__: Initialize a BlackBox
@self: the class instance
@box_cfg: a box_cfg conformant AdmList element containing
the following elements:
cache_dir : a string
template : a string
mode : an integer
"""
self.status = 0
self.me = self.__class__.__module__
self._errNo = 0
self._errStr = None
self.writable = 1
Alchemist.validateBoxCfg(box_cfg)
try:
self.cache_dir = box_cfg.getChildByName("cache_dir").getValue()
except:
raise ValueError, "CacheBlackBox box_cfg must contain a 'cache_dir' entry"
try:
self.template = box_cfg.getChildByName("template").getValue()
except:
raise ValueError, "CacheBlackBox box_cfg must contain a 'template' entry"
try:
self.mode = box_cfg.getChildByName("mode").getValue()
except:
raise ValueError, "CacheBlackBox box_cfg must contain a 'mode' entry"
try:
self.depth = box_cfg.getChildByName("depth").getValue()
except:
raise ValueError, "CacheBlackBox box_cfg must contain a 'dapth' entry"
def isReadable (self):
"""
isReadable: if a read were attempted now, would it succede?
@self: this BlackBox instance
"""
vlist = VersionList(self.cache_dir, self.template)
if len(vlist) > 0:
return 1
return 0
def readVersion(self, version):
"""
readVersion: reads a specific version from the cache directiry, if it exists.
"""
try:
path = self.cache_dir + '/' + repr(version) + '.cache.' + self.template
return Alchemist.ReadContextFromFile(path)
except:
return None
def read (self):
"""
read: read the contents of the CacheBlackBox
@self: this CacheBlackBox instance
"""
vlist = VersionList(self.cache_dir, self.template)
if len(vlist) == 0:
return None
# Read the highest version in the list
return self.readVersion(vlist[-1])
def version(self):
"""
version: returns the version of this CacheBlackBox's context
@self: this CacheBlackBox instance
"""
vlist = VersionList(self.cache_dir, self.template)
if len(vlist) != 0:
return vlist[-1]
return None
def write (self, context):
"""
write: write the contents of the CacheBlackBox
@self: this CacheBlackBox instance
This function is callable multiple times. It writes a
Context out to the file the CacheBlackBox is initialized with.
It returns 0 on failure, and a non-zero, positive integer
on success.
"""
serial = context.getIdentityRoot().getSerial()
path = self.cache_dir + '/' + repr(serial) + '.cache.' + self.template
try:
Alchemist.WriteContextToFile(path, context, mode = self.mode)
# Trash the bottom of the context stack if we've over flowed it.
vlist = VersionList(self.cache_dir, self.template)
if len(vlist) > self.depth:
os.unlink(self.cache_dir + '/' + repr(vlist[0]) + '.' + self.template)
return 1
except Exception, e:
if len(e.args) == 1:
self._errNo = 1
self._errStr = e.args[0]
else:
self._errStr = e.args[1]
self._errNo = e.args[0]
return 0
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