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=C0103

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

import re

# Python 2.6 and above contain a JSON module based on simplejson. Unfortunately
# the standard library version is significantly slower than the external
# module. While it should be better from at least Python 3.2 on (see Python
# issue 7451), for now Ganeti needs to work well with older Python versions
# too.
import simplejson

from ganeti import errors
from ganeti import utils


_RE_EOLSP = re.compile("[ \t]+$", re.MULTILINE)


def DumpJson(data):
  """Serialize a given object.

  @param data: the data to serialize
  @return: the string representation of data

  """
  encoded = simplejson.dumps(data)

  txt = _RE_EOLSP.sub("", encoded)
  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, key_selector=None):
  """Serialize a given object and authenticate it.

  @param data: the data to serialize
  @param key: shared hmac key
  @param key_selector: name/id that identifies the key (in case there are
    multiple keys in use, e.g. in a multi-cluster environment)
  @return: the string representation of data signed by the hmac key

  """
  txt = DumpJson(data)
  if salt is None:
    salt = ""
  signed_dict = {
    "msg": txt,
    "salt": salt,
    }

  if key_selector:
    signed_dict["key_selector"] = key_selector
  else:
    key_selector = ""

  signed_dict["hmac"] = utils.Sha1Hmac(key, txt, salt=salt + key_selector)

  return DumpJson(signed_dict)


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: the shared hmac key or a callable taking one argument (the key
    selector), which returns the hmac key belonging to the key selector.
    Typical usage is to pass a reference to the get method of a dict.
  @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 callable(key):
    # pylint: disable=E1103
    key_selector = signed_dict.get("key_selector", None)
    hmac_key = key(key_selector)
    if not hmac_key:
      raise errors.SignatureError("No key with key selector '%s' found" %
                                  key_selector)
  else:
    key_selector = ""
    hmac_key = key

  if not utils.VerifySha1Hmac(hmac_key, msg, hmac_sign,
                              salt=salt + key_selector):
    raise errors.SignatureError("Invalid Signature")

  return LoadJson(msg), salt


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