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#

#

# 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).

"""

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():

  """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_dump = simplejson.dumps

  # Check whether the simplejson module supports indentation

  try:

    simplejson.dumps(1, indent=_JSON_INDENT)

  except TypeError:

    # Indentation not supported

    indent_dump = plain_dump

  else:

    # Indentation supported

    indent_dump = lambda data: simplejson.dumps(data, indent=_JSON_INDENT)

  assert callable(plain_dump)

  assert callable(indent_dump)

  return (plain_dump, indent_dump)

(_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