evennia/evennia/utils/dbserialize.py

"""
This module handles serialization of arbitrary python structural data,
intended primarily to be stored in the database. It also supports
storing Django model instances (which plain pickle cannot do).

This serialization is used internally by the server, notably for
storing data in Attributes and for piping data to process pools.

The purpose of dbserialize is to handle all forms of data. For
well-structured non-arbitrary exchange, such as communicating with a
rich web client, a simpler JSON serialization makes more sense.

This module also implements the `SaverList`, `SaverDict` and `SaverSet`
classes. These are iterables that track their position in a nested
structure and makes sure to send updates up to their root. This is
used by Attributes - without it, one would not be able to update mutables
in-situ, e.g `obj.db.mynestedlist[3][5] = 3` would never be saved and
be out of sync with the database.

"""
from builtins import object, int

from functools import update_wrapper
from collections import defaultdict, MutableSequence, MutableSet, MutableMapping
try:
    from cPickle import dumps, loads
except ImportError:
    from pickle import dumps, loads
from django.core.exceptions import ObjectDoesNotExist
from django.contrib.contenttypes.models import ContentType
from evennia.utils.utils import to_str, uses_database
from evennia.utils import logger

__all__ = ("to_pickle", "from_pickle", "do_pickle", "do_unpickle",
            "dbserialize", "dbunserialize")

PICKLE_PROTOCOL = 2

def _get_mysql_db_version(self):
    """
    This is a helper method for specifically getting the version
    string of a MySQL database.

    Returns:
        mysql_version (str): The currently used mysql database
            version.

    """
    from django.db import connection
    conn = connection.cursor()
    conn.execute("SELECT VERSION()")
    version = conn.fetchone()
    return version and str(version[0]) or ""

# initialization and helpers

_GA = object.__getattribute__
_SA = object.__setattr__
_FROM_MODEL_MAP = None
_TO_MODEL_MAP = None
_SESSION_HANDLER = None
_IS_PACKED_DBOBJ = lambda o: type(o) == tuple and len(o) == 4 and o[0] == '__packed_dbobj__'
_IS_PACKED_SESSION = lambda o: type(o) == tuple and len(o) == 3 and o[0] == '__packed_session__'
if uses_database("mysql") and _get_mysql_db_version() < '5.6.4':
    # mysql <5.6.4 don't support millisecond precision
    _DATESTRING = "%Y:%m:%d-%H:%M:%S:000000"
else:
    _DATESTRING = "%Y:%m:%d-%H:%M:%S:%f"


def _TO_DATESTRING(obj):
    """
    Creates datestring hash.

    Args:
        obj (Object): Database object.

    Returns:
        datestring (str): A datestring hash.

    """
    try:
        return _GA(obj, "db_date_created").strftime(_DATESTRING)
    except AttributeError:
        # this can happen if object is not yet saved - no datestring is then set
        obj.save()
        return _GA(obj, "db_date_created").strftime(_DATESTRING)


def _init_globals():
    "Lazy importing to avoid circular import issues"
    global _FROM_MODEL_MAP, _TO_MODEL_MAP, _SESSION_HANDLER
    if not _FROM_MODEL_MAP:
        _FROM_MODEL_MAP = defaultdict(str)
        _FROM_MODEL_MAP.update(dict((c.model, c.natural_key()) for c in ContentType.objects.all()))
    if not _TO_MODEL_MAP:
        _TO_MODEL_MAP = defaultdict(str)
        _TO_MODEL_MAP.update(dict((c.natural_key(), c.model_class()) for c in ContentType.objects.all()))
    if not _SESSION_HANDLER:
        from evennia.server.sessionhandler import SESSION_HANDLER as _SESSION_HANDLER

#
# SaverList, SaverDict, SaverSet - Attribute-specific helper classes and functions
#


def _save(method):
    "method decorator that saves data to Attribute"
    def save_wrapper(self, *args, **kwargs):
        self.__doc__ = method.__doc__
        ret = method(self, *args, **kwargs)
        self._save_tree()
        return ret
    return update_wrapper(save_wrapper, method)


class _SaverMutable(object):
    """
    Parent class for properly handling  of nested mutables in
    an Attribute. If not used something like
     obj.db.mylist[1][2] = "test" (allocation to a nested list)
    will not save the updated value to the database.
    """
    def __init__(self, *args, **kwargs):
        "store all properties for tracking the tree"
        self._parent = kwargs.pop("parent", None)
        self._db_obj = kwargs.pop("db_obj", None)
        self._data = None

    def _save_tree(self):
        "recursively traverse back up the tree, save when we reach the root"
        if self._parent:
            self._parent._save_tree()
        elif self._db_obj:
            self._db_obj.value = self
        else:
            logger.log_err("_SaverMutable %s has no root Attribute to save to." % self)

    def _convert_mutables(self, data):
        "converts mutables to Saver* variants and assigns .parent property"
        def process_tree(item, parent):
            "recursively populate the tree, storing parents"
            dtype = type(item)
            if dtype in (basestring, int, float, bool, tuple):
                return item
            elif dtype == list:
                dat = _SaverList(parent=parent)
                dat._data.extend(process_tree(val, dat) for val in item)
                return dat
            elif dtype == dict:
                dat = _SaverDict(parent=parent)
                dat._data.update((key, process_tree(val, dat)) for key, val in item.items())
                return dat
            elif dtype == set:
                dat = _SaverSet(parent=parent)
                dat._data.update(process_tree(val, dat) for val in item)
                return dat
            return item
        return process_tree(data, self)

    def __repr__(self):
        return self._data.__repr__()

    def __len__(self):
        return self._data.__len__()

    def __iter__(self):
        return self._data.__iter__()

    def __getitem__(self, key):
        return self._data.__getitem__(key)

    @_save
    def __setitem__(self, key, value):
        self._data.__setitem__(key, self._convert_mutables(value))

    @_save
    def __delitem__(self, key):
        self._data.__delitem__(key)


class _SaverList(_SaverMutable, MutableSequence):
    """
    A list that saves itself to an Attribute when updated.
    """
    def __init__(self, *args, **kwargs):
        super(_SaverList, self).__init__(*args, **kwargs)
        self._data = list(*args)

    @_save
    def __add__(self, otherlist):
        self._data = self._data.__add__(otherlist)
        return self._data

    @_save
    def insert(self, index, value):
        self._data.insert(index, self._convert_mutables(value))


class _SaverDict(_SaverMutable, MutableMapping):
    """
    A dict that stores changes to an Attribute when updated
    """
    def __init__(self, *args, **kwargs):
        super(_SaverDict, self).__init__(*args, **kwargs)
        self._data = dict(*args)

    def has_key(self, key):
        return key in self._data


class _SaverSet(_SaverMutable, MutableSet):
    """
    A set that saves to an Attribute when updated
    """
    def __init__(self, *args, **kwargs):
        super(_SaverSet, self).__init__(*args, **kwargs)
        self._data = set(*args)

    def __contains__(self, value):
        return self._data.__contains__(value)

    @_save
    def add(self, value):
        self._data.add(self._convert_mutables(value))

    @_save
    def discard(self, value):
        self._data.discard(value)

#
# serialization helpers
#

def pack_dbobj(item):
    """
    Check and convert django database objects to an internal representation.

    Args:
        item (any): A database entity to pack

    Returns:
        packed (any or tuple): Either returns the original input item
            or the packing tuple `("__packed_dbobj__", key, creation_time, id)`.

    """
    _init_globals()
    obj = item
    natural_key = _FROM_MODEL_MAP[hasattr(obj, "id") and hasattr(obj, "db_date_created") and
                                  hasattr(obj, '__dbclass__') and obj.__dbclass__.__name__.lower()]
    # build the internal representation as a tuple
    #  ("__packed_dbobj__", key, creation_time, id)
    return natural_key and ('__packed_dbobj__', natural_key,
                             _TO_DATESTRING(obj), _GA(obj, "id")) or item


def unpack_dbobj(item):
    """
    Check and convert internal representations back to Django database
    models.

    Args:
        item (packed_dbobj): The fact that item is a packed dbobj
            should be checked before this call.

    Returns:
        unpacked (any): Either the original input or converts the
            internal store back to a database representation (its
            typeclass is returned if applicable).

    """
    _init_globals()
    try:
        obj = item[3] and _TO_MODEL_MAP[item[1]].objects.get(id=item[3])
    except ObjectDoesNotExist:
        return None
    # even if we got back a match, check the sanity of the date (some
    # databases may 're-use' the id)
    return _TO_DATESTRING(obj) == item[2] and obj or None


def pack_session(item):
    """
    Handle the safe serializion of Sessions objects (these contain
    hidden references to database objects (players, puppets) so they
    can't be safely serialized).

    Args:
        item (packed_session): The fact that item is a packed Session
            should be checked before this call.

    Returns:
        unpacked (any): Either the original input or converts the
            internal store back to a Session. If the Session no longer
            exists, None is returned.

    """
    _init_globals()
    return item.conn_time and item.sessid and ('__packed_session__',
                                              _GA(item, "sessid"),
                                              _GA(item, "conn_time"))

def unpack_session(item):
    """
    Check and convert internal representations back to Sessions.

    Args:
        item (packed_session): The fact that item is a packed session
            should be checked before this call.

    Returns:
        unpacked (any): Either the original input or converts the
            internal store back to a Session. If Session no longer
            exists, None will be returned.
    """
    _init_globals()
    session = _SESSION_HANDLER.get(item[1])
    if session and session.conn_time == item[2]:
        # we require connection times to be identical for the Session
        # to be accepted as the same as the one stored (sessids gets
        # reused all the time).
        return session
    return None

#
# Access methods
#

def to_pickle(data):
    """
    This prepares data on arbitrary form to be pickled. It handles any
    nested structure and returns data on a form that is safe to pickle
    (including having converted any database models to their internal
    representation).  We also convert any Saver*-type objects back to
    their normal representations, they are not pickle-safe.

    Args:
        data (any): Data to pickle.

    Returns:
        data (any): Pickled data.

    """
    def process_item(item):
        "Recursive processor and identification of data"
        dtype = type(item)
        if dtype in (basestring, int, float, bool):
            return item
        elif dtype == tuple:
            return tuple(process_item(val) for val in item)
        elif dtype in (list, _SaverList):
            return [process_item(val) for val in item]
        elif dtype in (dict, _SaverDict):
            return dict((process_item(key), process_item(val)) for key, val in item.items())
        elif dtype in (set, _SaverSet):
            return set(process_item(val) for val in item)
        elif hasattr(item, '__iter__'):
            # we try to conserve the iterable class, if not convert to list
            try:
                return item.__class__([process_item(val) for val in item])
            except (AttributeError, TypeError):
                return [process_item(val) for val in item]
        elif hasattr(item, "sessid") and hasattr(item, "conn_time") and item.sessid in _SESSION_HANDLER:
            return pack_session(item)
        return pack_dbobj(item)
    return process_item(data)


#@transaction.autocommit
def from_pickle(data, db_obj=None):
    """
    This should be fed a just de-pickled data object. It will be converted back
    to a form that may contain database objects again. Note that if a database
    object was removed (or changed in-place) in the database, None will be
    returned.

    Args_
        data (any): Pickled data to unpickle.
        db_obj (Atribute, any): This is the model instance (normally
            an Attribute) that _Saver*-type iterables (_SaverList etc)
            will save to when they update. It must have a 'value' property
            that saves assigned data to the database. Skip if not
            serializing onto a given object.  If db_obj is given, this
            function will convert lists, dicts and sets to their
            _SaverList, _SaverDict and _SaverSet counterparts.

    Returns:
        data (any): Unpickled data.

    """
    def process_item(item):
        "Recursive processor and identification of data"
        dtype = type(item)
        if dtype in (basestring, int, float, bool):
            return item
        elif _IS_PACKED_DBOBJ(item):
            # this must be checked before tuple
            return unpack_dbobj(item)
        elif _IS_PACKED_SESSION(item):
            return unpack_session(item)
        elif dtype == tuple:
            return tuple(process_item(val) for val in item)
        elif dtype == dict:
            return dict((process_item(key), process_item(val)) for key, val in item.items())
        elif dtype == set:
            return set(process_item(val) for val in item)
        elif hasattr(item, '__iter__'):
            try:
                # we try to conserve the iterable class if
                # it accepts an iterator
                return item.__class__(process_item(val) for val in item)
            except (AttributeError, TypeError):
                return [process_item(val) for val in item]
        return item

    def process_tree(item, parent):
        "Recursive processor, building a parent-tree from iterable data"
        dtype = type(item)
        if dtype in (basestring, int, float, bool):
            return item
        elif _IS_PACKED_DBOBJ(item):
            # this must be checked before tuple
            return unpack_dbobj(item)
        elif dtype == tuple:
            return tuple(process_tree(val, item) for val in item)
        elif dtype == list:
            dat = _SaverList(parent=parent)
            dat._data.extend(process_tree(val, dat) for val in item)
            return dat
        elif dtype == dict:
            dat = _SaverDict(parent=parent)
            dat._data.update(dict((process_item(key), process_tree(val, dat))
                                   for key, val in item.items()))
            return dat
        elif dtype == set:
            dat = _SaverSet(parent=parent)
            dat._data.update(set(process_tree(val, dat) for val in item))
            return dat
        elif hasattr(item, '__iter__'):
            try:
                # we try to conserve the iterable class if it
                # accepts an iterator
                return item.__class__(process_tree(val, parent) for val in item)
            except (AttributeError, TypeError):
                dat = _SaverList(parent=parent)
                dat._data.extend(process_tree(val, dat) for val in item)
                return dat
        return item

    if db_obj:
        # convert lists, dicts and sets to their Saved* counterparts. It
        # is only relevant if the "root" is an iterable of the right type.
        dtype = type(data)
        if dtype == list:
            dat = _SaverList(db_obj=db_obj)
            dat._data.extend(process_tree(val, parent=dat) for val in data)
            return dat
        elif dtype == dict:
            dat = _SaverDict(db_obj=db_obj)
            dat._data.update((process_item(key), process_tree(val, parent=dat))
                              for key, val in data.items())
            return dat
        elif dtype == set:
            dat = _SaverSet(db_obj=db_obj)
            dat._data.update(process_tree(val, parent=dat) for val in data)
            return dat
    return process_item(data)


def do_pickle(data):
    "Perform pickle to string"
    return to_str(dumps(data, protocol=PICKLE_PROTOCOL))


def do_unpickle(data):
    "Retrieve pickle from pickled string"
    return loads(to_str(data))


def dbserialize(data):
    "Serialize to pickled form in one step"
    return do_pickle(to_pickle(data))


def dbunserialize(data, db_obj=None):
    "Un-serialize in one step. See from_pickle for help db_obj."
    return from_pickle(do_unpickle(data), db_obj=db_obj)