cvs2svn_lib/serializer.py

   1 # (Be in -*- python -*- mode.)
   2 #
   3 # ====================================================================
   4 # Copyright (c) 2000-2008 CollabNet.  All rights reserved.
   5 #
   6 # This software is licensed as described in the file COPYING, which
   7 # you should have received as part of this distribution.  The terms
   8 # are also available at http://subversion.tigris.org/license-1.html.
   9 # If newer versions of this license are posted there, you may use a
  10 # newer version instead, at your option.
  11 #
  12 # This software consists of voluntary contributions made by many
  13 # individuals.  For exact contribution history, see the revision
  14 # history and logs, available at http://cvs2svn.tigris.org/.
  15 # ====================================================================
  16
  17 """Picklers and unpicklers that are primed with known objects."""
  18
  19
  20 import cStringIO
  21 import marshal
  22 import cPickle
  23 import zlib
  24
  25
  26 class Serializer:
  27   """An object able to serialize/deserialize some class of objects."""
  28
  29   def dumpf(self, f, object):
  30     """Serialize OBJECT to file-like object F."""
  31
  32     raise NotImplementedError()
  33
  34   def dumps(self, object):
  35     """Return a string containing OBJECT in serialized form."""
  36
  37     raise NotImplementedError()
  38
  39   def loadf(self, f):
  40     """Return the next object deserialized from file-like object F."""
  41
  42     raise NotImplementedError()
  43
  44   def loads(self, s):
  45     """Return the object deserialized from string S."""
  46
  47     raise NotImplementedError()
  48
  49
  50 class MarshalSerializer(Serializer):
  51   """This class uses the marshal module to serialize/deserialize.
  52
  53   This means that it shares the limitations of the marshal module,
  54   namely only being able to serialize a few simple python data types
  55   without reference loops."""
  56
  57   def dumpf(self, f, object):
  58     marshal.dump(object, f)
  59
  60   def dumps(self, object):
  61     return marshal.dumps(object)
  62
  63   def loadf(self, f):
  64     return marshal.load(f)
  65
  66   def loads(self, s):
  67     return marshal.loads(s)
  68
  69
  70 class PrimedPickleSerializer(Serializer):
  71   """This class acts as a pickler/unpickler with a pre-initialized memo.
  72
  73   The picklers and unpicklers are 'pre-trained' to recognize the
  74   objects that are in the primer.  If objects are recognized
  75   from PRIMER, then only their persistent IDs need to be pickled
  76   instead of the whole object.  (Note that the memos needed for
  77   pickling and unpickling are different.)
  78
  79   A new pickler/unpickler is created for each use, each time with the
  80   memo initialized appropriately for pickling or unpickling."""
  81
  82   def __init__(self, primer):
  83     """Prepare to make picklers/unpicklers with the specified primer.
  84
  85     The Pickler and Unpickler are 'primed' by pre-pickling PRIMER,
  86     which can be an arbitrary object (e.g., a list of objects that are
  87     expected to occur frequently in the objects to be serialized)."""
  88
  89     f = cStringIO.StringIO()
  90     pickler = cPickle.Pickler(f, -1)
  91     pickler.dump(primer)
  92     self.pickler_memo = pickler.memo
  93
  94     unpickler = cPickle.Unpickler(cStringIO.StringIO(f.getvalue()))
  95     unpickler.load()
  96     self.unpickler_memo = unpickler.memo
  97
  98   def dumpf(self, f, object):
  99     """Serialize OBJECT to file-like object F."""
 100
 101     pickler = cPickle.Pickler(f, -1)
 102     pickler.memo = self.pickler_memo.copy()
 103     pickler.dump(object)
 104
 105   def dumps(self, object):
 106     """Return a string containing OBJECT in serialized form."""
 107
 108     f = cStringIO.StringIO()
 109     self.dumpf(f, object)
 110     return f.getvalue()
 111
 112   def loadf(self, f):
 113     """Return the next object deserialized from file-like object F."""
 114
 115     unpickler = cPickle.Unpickler(f)
 116     unpickler.memo = self.unpickler_memo.copy()
 117     return unpickler.load()
 118
 119   def loads(self, s):
 120     """Return the object deserialized from string S."""
 121
 122     return self.loadf(cStringIO.StringIO(s))
 123
 124
 125 class CompressingSerializer(Serializer):
 126   """This class wraps other Serializers to compress their serialized data."""
 127
 128   def __init__(self, wrapee):
 129     """Constructor.  WRAPEE is the Serializer whose bitstream ought to be
 130     compressed."""
 131
 132     self.wrapee = wrapee
 133
 134   def dumpf(self, f, object):
 135     marshal.dump(zlib.compress(self.wrapee.dumps(object), 9), f)
 136
 137   def dumps(self, object):
 138     return marshal.dumps(zlib.compress(self.wrapee.dumps(object), 9))
 139
 140   def loadf(self, f):
 141     return self.wrapee.loads(zlib.decompress(marshal.load(f)))
 142
 143   def loads(self, s):
 144     return self.wrapee.loads(zlib.decompress(marshal.loads(s)))
 145
 146