serializer.py

#
#

# Copyright (C) 2007, 2008 Google Inc.
#
# 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 2 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, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301, USA.

"""Serializer abstraction module

This module introduces a simple abstraction over the serialization
backend (currently json).

"""
# pylint: disable-msg=C0103

# C0103: Invalid name, since pylint doesn't see that Dump points to a
# function and not a constant

import simplejson
import re
import hmac

from ganeti import errors

try:
  from hashlib import sha1
except ImportError:
  import sha as sha1


_JSON_INDENT = 2

_RE_EOLSP = re.compile('[ \t]+$', re.MULTILINE)


def _GetJsonDumpers(_encoder_class=simplejson.JSONEncoder):
  """Returns two JSON functions to serialize data.

  @rtype: (callable, callable)
  @return: The function to generate a compact form of JSON and another one to
           generate a more readable, indented form of JSON (if supported)

  """
  plain_encoder = _encoder_class(sort_keys=True)

  # Check whether the simplejson module supports indentation
  try:
    indent_encoder = _encoder_class(indent=_JSON_INDENT, sort_keys=True)
  except TypeError:
    # Indentation not supported
    indent_encoder = plain_encoder

  return (plain_encoder.encode, indent_encoder.encode)


(_DumpJson, _DumpJsonIndent) = _GetJsonDumpers()


def DumpJson(data, indent=True):
  """Serialize a given object.

  @param data: the data to serialize
  @param indent: whether to indent output (depends on simplejson version)

  @return: the string representation of data

  """
  if indent:
    fn = _DumpJsonIndent
  else:
    fn = _DumpJson

  txt = _RE_EOLSP.sub("", fn(data))
  if not txt.endswith('\n'):
    txt += '\n'

  return txt


def LoadJson(txt):
  """Unserialize data from a string.

  @param txt: the json-encoded form

  @return: the original data

  """
  return simplejson.loads(txt)


def DumpSignedJson(data, key, salt=None):
  """Serialize a given object and authenticate it.

  @param data: the data to serialize
  @param key: shared hmac key
  @return: the string representation of data signed by the hmac key

  """
  txt = DumpJson(data, indent=False)
  if salt is None:
    salt = ''
  signed_dict = {
    'msg': txt,
    'salt': salt,
    'hmac': hmac.new(key, salt + txt, sha1).hexdigest(),
  }
  return DumpJson(signed_dict, indent=False)


def LoadSignedJson(txt, key):
  """Verify that a given message was signed with the given key, and load it.

  @param txt: json-encoded hmac-signed message
  @param key: shared hmac key
  @rtype: tuple of original data, string
  @return: original data, salt
  @raises errors.SignatureError: if the message signature doesn't verify

  """
  signed_dict = LoadJson(txt)
  if not isinstance(signed_dict, dict):
    raise errors.SignatureError('Invalid external message')
  try:
    msg = signed_dict['msg']
    salt = signed_dict['salt']
    hmac_sign = signed_dict['hmac']
  except KeyError:
    raise errors.SignatureError('Invalid external message')

  if hmac.new(key, salt + msg, sha1).hexdigest() != hmac_sign:
    raise errors.SignatureError('Invalid Signature')

  return LoadJson(msg), salt


Dump = DumpJson
Load = LoadJson
DumpSigned = DumpSignedJson
LoadSigned = LoadSignedJson