Move source files to subfolder.

5 files changed, 801 insertions, 0 deletions

diff --git a/soledad/backends/__init__.py b/soledad/backends/__init__.py
new file mode 100644
index 00000000..61438e8a
--- /dev/null
+++ b/soledad/backends/__init__.py
@@ -0,0 +1,9 @@
+"""
+Backends that extend U1DB functionality.
+"""
+
+import objectstore
+
+
+__all__ = [
+    'objectstore']
diff --git a/soledad/backends/couch.py b/soledad/backends/couch.py
new file mode 100644
index 00000000..b7a77054
--- /dev/null
+++ b/soledad/backends/couch.py
@@ -0,0 +1,270 @@
+"""A U1DB backend that uses CouchDB as its persistence layer."""
+
+# general imports
+import uuid
+from base64 import b64encode, b64decode
+import re
+# u1db
+from u1db import errors
+from u1db.sync import LocalSyncTarget
+from u1db.backends.inmemory import InMemoryIndex
+from u1db.remote.server_state import ServerState
+from u1db.errors import DatabaseDoesNotExist
+# couchdb
+from couchdb.client import Server, Document as CouchDocument
+from couchdb.http import ResourceNotFound
+# leap
+from leap.soledad.backends.objectstore import (
+    ObjectStoreDatabase,
+    ObjectStoreSyncTarget,
+)
+from leap.soledad.backends.leap_backend import LeapDocument
+
+try:
+    import simplejson as json
+except ImportError:
+    import json  # noqa
+
+
+class InvalidURLError(Exception):
+    """Exception raised when Soledad encounters a malformed URL."""
+    pass
+
+
+class CouchDatabase(ObjectStoreDatabase):
+    """A U1DB backend that uses Couch as its persistence layer."""
+
+    @classmethod
+    def open_database(cls, url, create):
+        """Open a U1DB database using CouchDB as backend."""
+        # get database from url
+        m = re.match('(^https?://[^/]+)/(.+)$', url)
+        if not m:
+            raise InvalidURLError
+        url = m.group(1)
+        dbname = m.group(2)
+        server = Server(url=url)
+        try:
+            server[dbname]
+        except ResourceNotFound:
+            if not create:
+                raise DatabaseDoesNotExist()
+        return cls(url, dbname)
+
+    def __init__(self, url, database, replica_uid=None, full_commit=True,
+                 session=None):
+        """Create a new Couch data container."""
+        self._url = url
+        self._full_commit = full_commit
+        self._session = session
+        self._server = Server(url=self._url,
+                              full_commit=self._full_commit,
+                              session=self._session)
+        self._dbname = database
+        # this will ensure that transaction and sync logs exist and are
+        # up-to-date.
+        try:
+            self._database = self._server[database]
+        except ResourceNotFound:
+            self._server.create(database)
+            self._database = self._server[database]
+        super(CouchDatabase, self).__init__(replica_uid=replica_uid,
+                                            document_factory=LeapDocument)
+
+    #-------------------------------------------------------------------------
+    # methods from Database
+    #-------------------------------------------------------------------------
+
+    def _get_doc(self, doc_id, check_for_conflicts=False):
+        """Get just the document content, without fancy handling."""
+        cdoc = self._database.get(doc_id)
+        if cdoc is None:
+            return None
+        has_conflicts = False
+        if check_for_conflicts:
+            has_conflicts = self._has_conflicts(doc_id)
+        doc = self._factory(
+            doc_id=doc_id,
+            rev=cdoc['u1db_rev'],
+            has_conflicts=has_conflicts)
+        contents = self._database.get_attachment(cdoc, 'u1db_json')
+        if contents:
+            doc.content = json.loads(contents.getvalue())
+        else:
+            doc.make_tombstone()
+        return doc
+
+    def get_all_docs(self, include_deleted=False):
+        """Get the JSON content for all documents in the database."""
+        generation = self._get_generation()
+        results = []
+        for doc_id in self._database:
+            if doc_id == self.U1DB_DATA_DOC_ID:
+                continue
+            doc = self._get_doc(doc_id, check_for_conflicts=True)
+            if doc.content is None and not include_deleted:
+                continue
+            results.append(doc)
+        return (generation, results)
+
+    def _put_doc(self, doc):
+        """Store document in database."""
+        # prepare couch's Document
+        cdoc = CouchDocument()
+        cdoc['_id'] = doc.doc_id
+        # we have to guarantee that couch's _rev is cosistent
+        old_cdoc = self._database.get(doc.doc_id)
+        if old_cdoc is not None:
+            cdoc['_rev'] = old_cdoc['_rev']
+        # store u1db's rev
+        cdoc['u1db_rev'] = doc.rev
+        # save doc in db
+        self._database.save(cdoc)
+        # store u1db's content as json string
+        if not doc.is_tombstone():
+            self._database.put_attachment(cdoc, doc.get_json(),
+                                          filename='u1db_json')
+        else:
+            self._database.delete_attachment(cdoc, 'u1db_json')
+
+    def get_sync_target(self):
+        """
+        Return a SyncTarget object, for another u1db to synchronize with.
+        """
+        return CouchSyncTarget(self)
+
+    def create_index(self, index_name, *index_expressions):
+        """
+        Create a named index, which can then be queried for future lookups.
+        """
+        if index_name in self._indexes:
+            if self._indexes[index_name]._definition == list(
+                    index_expressions):
+                return
+            raise errors.IndexNameTakenError
+        index = InMemoryIndex(index_name, list(index_expressions))
+        for doc_id in self._database:
+            if doc_id == self.U1DB_DATA_DOC_ID:
+                continue
+            doc = self._get_doc(doc_id)
+            if doc.content is not None:
+                index.add_json(doc_id, doc.get_json())
+        self._indexes[index_name] = index
+        # save data in object store
+        self._store_u1db_data()
+
+    def close(self):
+        """Release any resources associated with this database."""
+        # TODO: fix this method so the connection is properly closed and
+        # test_close (+tearDown, which deletes the db) works without problems.
+        self._url = None
+        self._full_commit = None
+        self._session = None
+        #self._server = None
+        self._database = None
+        return True
+
+    def sync(self, url, creds=None, autocreate=True):
+        """Synchronize documents with remote replica exposed at url."""
+        from u1db.sync import Synchronizer
+        return Synchronizer(self, CouchSyncTarget(url, creds=creds)).sync(
+            autocreate=autocreate)
+
+    #-------------------------------------------------------------------------
+    # methods from ObjectStoreDatabase
+    #-------------------------------------------------------------------------
+
+    def _init_u1db_data(self):
+        if self._replica_uid is None:
+            self._replica_uid = uuid.uuid4().hex
+        doc = self._factory(doc_id=self.U1DB_DATA_DOC_ID)
+        doc.content = {'transaction_log': [],
+                       'conflicts': b64encode(json.dumps({})),
+                       'other_generations': {},
+                       'indexes': b64encode(json.dumps({})),
+                       'replica_uid': self._replica_uid}
+        self._put_doc(doc)
+
+    def _fetch_u1db_data(self):
+        # retrieve u1db data from couch db
+        cdoc = self._database.get(self.U1DB_DATA_DOC_ID)
+        jsonstr = self._database.get_attachment(cdoc, 'u1db_json').getvalue()
+        content = json.loads(jsonstr)
+        # set u1db database info
+        #self._sync_log = content['sync_log']
+        self._transaction_log = content['transaction_log']
+        self._conflicts = json.loads(b64decode(content['conflicts']))
+        self._other_generations = content['other_generations']
+        self._indexes = self._load_indexes_from_json(
+            b64decode(content['indexes']))
+        self._replica_uid = content['replica_uid']
+        # save couch _rev
+        self._couch_rev = cdoc['_rev']
+
+    def _store_u1db_data(self):
+        doc = self._factory(doc_id=self.U1DB_DATA_DOC_ID)
+        doc.content = {
+            'transaction_log': self._transaction_log,
+            # Here, the b64 encode ensures that document content
+            # does not cause strange behaviour in couchdb because
+            # of encoding.
+            'conflicts': b64encode(json.dumps(self._conflicts)),
+            'other_generations': self._other_generations,
+            'indexes': b64encode(self._dump_indexes_as_json()),
+            'replica_uid': self._replica_uid,
+            '_rev': self._couch_rev}
+        self._put_doc(doc)
+
+    #-------------------------------------------------------------------------
+    # Couch specific methods
+    #-------------------------------------------------------------------------
+
+    def delete_database(self):
+        """Delete a U1DB CouchDB database."""
+        del(self._server[self._dbname])
+
+    def _dump_indexes_as_json(self):
+        indexes = {}
+        for name, idx in self._indexes.iteritems():
+            indexes[name] = {}
+            for attr in ['name', 'definition', 'values']:
+                indexes[name][attr] = getattr(idx, '_' + attr)
+        return json.dumps(indexes)
+
+    def _load_indexes_from_json(self, indexes):
+        dict = {}
+        for name, idx_dict in json.loads(indexes).iteritems():
+            idx = InMemoryIndex(name, idx_dict['definition'])
+            idx._values = idx_dict['values']
+            dict[name] = idx
+        return dict
+
+
+class CouchSyncTarget(ObjectStoreSyncTarget):
+    pass
+
+
+class CouchServerState(ServerState):
+    """Inteface of the WSGI server with the CouchDB backend."""
+
+    def __init__(self, couch_url):
+        self.couch_url = couch_url
+
+    def open_database(self, dbname):
+        """Open a database at the given location."""
+        # TODO: open couch
+        from leap.soledad.backends.couch import CouchDatabase
+        return CouchDatabase.open_database(self.couch_url + '/' + dbname,
+                                           create=False)
+
+    def ensure_database(self, dbname):
+        """Ensure database at the given location."""
+        from leap.soledad.backends.couch import CouchDatabase
+        db = CouchDatabase.open_database(self.couch_url + '/' + dbname,
+                                         create=True)
+        return db, db._replica_uid
+
+    def delete_database(self, dbname):
+        """Delete database at the given location."""
+        from leap.soledad.backends.couch import CouchDatabase
+        CouchDatabase.delete_database(self.couch_url + '/' + dbname)
diff --git a/soledad/backends/leap_backend.py b/soledad/backends/leap_backend.py
new file mode 100644
index 00000000..a37f9d25
--- /dev/null
+++ b/soledad/backends/leap_backend.py
@@ -0,0 +1,224 @@
+"""
+A U1DB backend that encrypts data before sending to server and decrypts after
+receiving.
+"""
+
+try:
+    import simplejson as json
+except ImportError:
+    import json  # noqa
+
+from u1db import Document
+from u1db.remote import utils
+from u1db.remote.http_target import HTTPSyncTarget
+from u1db.remote.http_database import HTTPDatabase
+from u1db.errors import BrokenSyncStream
+
+import uuid
+
+
+class NoDefaultKey(Exception):
+    """
+    Exception to signal that there's no default OpenPGP key configured.
+    """
+    pass
+
+
+class NoSoledadInstance(Exception):
+    """
+    Exception to signal that no Soledad instance was found.
+    """
+    pass
+
+
+class DocumentNotEncrypted(Exception):
+    """
+    Exception to signal failures in document encryption.
+    """
+    pass
+
+
+class LeapDocument(Document):
+    """
+    Encryptable and syncable document.
+
+    LEAP Documents are standard u1db documents with cabability of returning an
+    encrypted version of the document json string as well as setting document
+    content based on an encrypted version of json string.
+    """
+
+    def __init__(self, doc_id=None, rev=None, json='{}', has_conflicts=False,
+                 encrypted_json=None, soledad=None, syncable=True):
+        super(LeapDocument, self).__init__(doc_id, rev, json, has_conflicts)
+        self._soledad = soledad
+        self._syncable = syncable
+        if encrypted_json:
+            self.set_encrypted_json(encrypted_json)
+
+    def get_encrypted_content(self):
+        """
+        Return an encrypted JSON serialization of document's contents.
+        """
+        if not self._soledad:
+            raise NoSoledadInstance()
+        return self._soledad.encrypt_symmetric(self.doc_id,
+                                               self.get_json())
+
+    def set_encrypted_content(self, cyphertext):
+        """
+        Set document's content based on an encrypted JSON serialization of
+        contents.
+        """
+        plaintext = self._soledad.decrypt_symmetric(self.doc_id, cyphertext)
+        return self.set_json(plaintext)
+
+    def get_encrypted_json(self):
+        """
+        Return a valid JSON string containing document's content encrypted to
+        the user's public key.
+        """
+        return json.dumps({'_encrypted_json': self.get_encrypted_content()})
+
+    def set_encrypted_json(self, encrypted_json):
+        """
+        Set document's content based on a valid JSON string containing the
+        encrypted document's contents.
+        """
+        if not self._soledad:
+            raise NoSoledadInstance()
+        cyphertext = json.loads(encrypted_json)['_encrypted_json']
+        self.set_encrypted_content(cyphertext)
+
+    def _get_syncable(self):
+        return self._syncable
+
+    def _set_syncable(self, syncable=True):
+        self._syncable = syncable
+
+    syncable = property(
+        _get_syncable,
+        _set_syncable,
+        doc="Determine if document should be synced with server."
+    )
+
+    # Returning the revision as string solves the following exception in
+    # Twisted web:
+    #     exceptions.TypeError: Can only pass-through bytes on Python 2
+    def _get_rev(self):
+        if self._rev is None:
+            return None
+        return str(self._rev)
+
+    def _set_rev(self, rev):
+        self._rev = rev
+
+    rev = property(
+        _get_rev,
+        _set_rev,
+        doc="Wrapper to ensure `doc.rev` is always returned as bytes.")
+
+
+class LeapSyncTarget(HTTPSyncTarget):
+    """
+    A SyncTarget that encrypts data before sending and decrypts data after
+    receiving.
+    """
+
+    def __init__(self, url, creds=None, soledad=None):
+        super(LeapSyncTarget, self).__init__(url, creds)
+        self._soledad = soledad
+
+    def _parse_sync_stream(self, data, return_doc_cb, ensure_callback=None):
+        """
+        Does the same as parent's method but ensures incoming content will be
+        decrypted.
+        """
+        parts = data.splitlines()  # one at a time
+        if not parts or parts[0] != '[':
+            raise BrokenSyncStream
+        data = parts[1:-1]
+        comma = False
+        if data:
+            line, comma = utils.check_and_strip_comma(data[0])
+            res = json.loads(line)
+            if ensure_callback and 'replica_uid' in res:
+                ensure_callback(res['replica_uid'])
+            for entry in data[1:]:
+                if not comma:  # missing in between comma
+                    raise BrokenSyncStream
+                line, comma = utils.check_and_strip_comma(entry)
+                entry = json.loads(line)
+                # decrypt after receiving from server.
+                if not self._soledad:
+                    raise NoSoledadInstance()
+                enc_json = json.loads(entry['content'])['_encrypted_json']
+                if not self._soledad.is_encrypted_sym(enc_json):
+                    raise DocumentNotEncrypted(
+                        "Incoming document from sync is not encrypted.")
+                doc = LeapDocument(entry['id'], entry['rev'],
+                                   encrypted_json=entry['content'],
+                                   soledad=self._soledad)
+                return_doc_cb(doc, entry['gen'], entry['trans_id'])
+        if parts[-1] != ']':
+            try:
+                partdic = json.loads(parts[-1])
+            except ValueError:
+                pass
+            else:
+                if isinstance(partdic, dict):
+                    self._error(partdic)
+            raise BrokenSyncStream
+        if not data or comma:  # no entries or bad extra comma
+            raise BrokenSyncStream
+        return res
+
+    def sync_exchange(self, docs_by_generations, source_replica_uid,
+                      last_known_generation, last_known_trans_id,
+                      return_doc_cb, ensure_callback=None):
+        """
+        Does the same as parent's method but encrypts content before syncing.
+        """
+        self._ensure_connection()
+        if self._trace_hook:  # for tests
+            self._trace_hook('sync_exchange')
+        url = '%s/sync-from/%s' % (self._url.path, source_replica_uid)
+        self._conn.putrequest('POST', url)
+        self._conn.putheader('content-type', 'application/x-u1db-sync-stream')
+        for header_name, header_value in self._sign_request('POST', url, {}):
+            self._conn.putheader(header_name, header_value)
+        entries = ['[']
+        size = 1
+
+        def prepare(**dic):
+            entry = comma + '\r\n' + json.dumps(dic)
+            entries.append(entry)
+            return len(entry)
+
+        comma = ''
+        size += prepare(
+            last_known_generation=last_known_generation,
+            last_known_trans_id=last_known_trans_id,
+            ensure=ensure_callback is not None)
+        comma = ','
+        for doc, gen, trans_id in docs_by_generations:
+            if doc.syncable:
+                # encrypt and verify before sending to server.
+                enc_json = json.loads(
+                    doc.get_encrypted_json())['_encrypted_json']
+                if not self._soledad.is_encrypted_sym(enc_json):
+                    raise DocumentNotEncrypted(
+                        "Could not encrypt document before sync.")
+                size += prepare(id=doc.doc_id, rev=doc.rev,
+                                content=doc.get_encrypted_json(),
+                                gen=gen, trans_id=trans_id)
+        entries.append('\r\n]')
+        size += len(entries[-1])
+        self._conn.putheader('content-length', str(size))
+        self._conn.endheaders()
+        for entry in entries:
+            self._conn.send(entry)
+        entries = None
+        data, _ = self._response()
+        res = self._parse_sync_stream(data, return_doc_cb, ensure_callback)
+        data = None
+        return res['new_generation'], res['new_transaction_id']
diff --git a/soledad/backends/objectstore.py b/soledad/backends/objectstore.py
new file mode 100644
index 00000000..7c5d1177
--- /dev/null
+++ b/soledad/backends/objectstore.py
@@ -0,0 +1,135 @@
+"""
+Abstract U1DB backend to handle storage using object stores (like CouchDB, for
+example.
+
+Right now, this is only used by CouchDatabase backend, but can also be
+extended to implement OpenStack or Amazon S3 storage, for example.
+"""
+
+from u1db.backends.inmemory import (
+    InMemoryDatabase,
+    InMemorySyncTarget,
+)
+from u1db import errors
+
+
+class ObjectStoreDatabase(InMemoryDatabase):
+    """
+    A backend for storing u1db data in an object store.
+    """
+
+    @classmethod
+    def open_database(cls, url, create, document_factory=None):
+        raise NotImplementedError(cls.open_database)
+
+    def __init__(self, replica_uid=None, document_factory=None):
+        super(ObjectStoreDatabase, self).__init__(
+            replica_uid,
+            document_factory=document_factory)
+        # sync data in memory with data in object store
+        if not self._get_doc(self.U1DB_DATA_DOC_ID):
+            self._init_u1db_data()
+        self._fetch_u1db_data()
+
+    #-------------------------------------------------------------------------
+    # methods from Database
+    #-------------------------------------------------------------------------
+
+    def _set_replica_uid(self, replica_uid):
+        super(ObjectStoreDatabase, self)._set_replica_uid(replica_uid)
+        self._store_u1db_data()
+
+    def _put_doc(self, doc):
+        raise NotImplementedError(self._put_doc)
+
+    def _get_doc(self, doc):
+        raise NotImplementedError(self._get_doc)
+
+    def get_all_docs(self, include_deleted=False):
+        raise NotImplementedError(self.get_all_docs)
+
+    def delete_doc(self, doc):
+        """Mark a document as deleted."""
+        old_doc = self._get_doc(doc.doc_id, check_for_conflicts=True)
+        if old_doc is None:
+            raise errors.DocumentDoesNotExist
+        if old_doc.rev != doc.rev:
+            raise errors.RevisionConflict()
+        if old_doc.is_tombstone():
+            raise errors.DocumentAlreadyDeleted
+        if old_doc.has_conflicts:
+            raise errors.ConflictedDoc()
+        new_rev = self._allocate_doc_rev(doc.rev)
+        doc.rev = new_rev
+        doc.make_tombstone()
+        self._put_and_update_indexes(old_doc, doc)
+        return new_rev
+
+    # index-related methods
+
+    def create_index(self, index_name, *index_expressions):
+        """
+        Create an named index, which can then be queried for future lookups.
+        """
+        raise NotImplementedError(self.create_index)
+
+    def delete_index(self, index_name):
+        """Remove a named index."""
+        super(ObjectStoreDatabase, self).delete_index(index_name)
+        self._store_u1db_data()
+
+    def _replace_conflicts(self, doc, conflicts):
+        super(ObjectStoreDatabase, self)._replace_conflicts(doc, conflicts)
+        self._store_u1db_data()
+
+    def _do_set_replica_gen_and_trans_id(self, other_replica_uid,
+                                         other_generation,
+                                         other_transaction_id):
+        super(ObjectStoreDatabase, self)._do_set_replica_gen_and_trans_id(
+            other_replica_uid,
+            other_generation,
+            other_transaction_id)
+        self._store_u1db_data()
+
+    #-------------------------------------------------------------------------
+    # implemented methods from CommonBackend
+    #-------------------------------------------------------------------------
+
+    def _put_and_update_indexes(self, old_doc, doc):
+        for index in self._indexes.itervalues():
+            if old_doc is not None and not old_doc.is_tombstone():
+                index.remove_json(old_doc.doc_id, old_doc.get_json())
+            if not doc.is_tombstone():
+                index.add_json(doc.doc_id, doc.get_json())
+        trans_id = self._allocate_transaction_id()
+        self._put_doc(doc)
+        self._transaction_log.append((doc.doc_id, trans_id))
+        self._store_u1db_data()
+
+    #-------------------------------------------------------------------------
+    # methods specific for object stores
+    #-------------------------------------------------------------------------
+
+    U1DB_DATA_DOC_ID = 'u1db_data'
+
+    def _fetch_u1db_data(self):
+        """
+        Fetch u1db configuration data from backend storage.
+        """
+        NotImplementedError(self._fetch_u1db_data)
+
+    def _store_u1db_data(self):
+        """
+        Save u1db configuration data on backend storage.
+        """
+        NotImplementedError(self._store_u1db_data)
+
+    def _init_u1db_data(self):
+        """
+        Initialize u1db configuration data on backend storage.
+        """
+        NotImplementedError(self._init_u1db_data)
+
+
+class ObjectStoreSyncTarget(InMemorySyncTarget):
+    pass
diff --git a/soledad/backends/sqlcipher.py b/soledad/backends/sqlcipher.py
new file mode 100644
index 00000000..5d2569bf
--- /dev/null
+++ b/soledad/backends/sqlcipher.py
@@ -0,0 +1,163 @@
+"""A U1DB backend that uses SQLCipher as its persistence layer."""
+
+import os
+from pysqlcipher import dbapi2
+import time
+
+from leap import util
+from u1db.backends import sqlite_backend
+util.logger.debug(
+    "Monkey-patching u1db.backends.sqlite_backend with pysqlcipher.dbapi2..."
+)
+sqlite_backend.dbapi2 = dbapi2
+
+from u1db import (
+    errors,
+)
+
+from leap.soledad.backends.leap_backend import LeapDocument
+
+
+def open(path, password, create=True, document_factory=None, soledad=None):
+    """Open a database at the given location.
+
+    Will raise u1db.errors.DatabaseDoesNotExist if create=False and the
+    database does not already exist.
+
+    :param path: The filesystem path for the database to open.
+    :param create: True/False, should the database be created if it doesn't
+        already exist?
+    :param document_factory: A function that will be called with the same
+        parameters as Document.__init__.
+    :return: An instance of Database.
+    """
+    return SQLCipherDatabase.open_database(
+        path, password, create=create, document_factory=document_factory,
+        soledad=soledad)
+
+
+class DatabaseIsNotEncrypted(Exception):
+    """
+    Exception raised when trying to open non-encrypted databases.
+    """
+    pass
+
+
+class SQLCipherDatabase(sqlite_backend.SQLitePartialExpandDatabase):
+    """A U1DB implementation that uses SQLCipher as its persistence layer."""
+
+    _index_storage_value = 'expand referenced encrypted'
+
+    @classmethod
+    def set_pragma_key(cls, db_handle, key):
+        db_handle.cursor().execute("PRAGMA key = '%s'" % key)
+
+    def __init__(self, sqlite_file, password, document_factory=None,
+                 soledad=None):
+        """Create a new sqlcipher file."""
+        self._check_if_db_is_encrypted(sqlite_file)
+        self._db_handle = dbapi2.connect(sqlite_file)
+        SQLCipherDatabase.set_pragma_key(self._db_handle, password)
+        self._real_replica_uid = None
+        self._ensure_schema()
+        self._soledad = soledad
+
+        def factory(doc_id=None, rev=None, json='{}', has_conflicts=False,
+                    encrypted_json=None, syncable=True):
+            return LeapDocument(doc_id=doc_id, rev=rev, json=json,
+                                has_conflicts=has_conflicts,
+                                encrypted_json=encrypted_json,
+                                syncable=syncable, soledad=self._soledad)
+        self.set_document_factory(factory)
+
+    def _check_if_db_is_encrypted(self, sqlite_file):
+        if not os.path.exists(sqlite_file):
+            return
+        else:
+            try:
+                # try to open an encrypted database with the regular u1db
+                # backend should raise a DatabaseError exception.
+                sqlite_backend.SQLitePartialExpandDatabase(sqlite_file)
+                raise DatabaseIsNotEncrypted()
+            except dbapi2.DatabaseError:
+                pass
+
+    @classmethod
+    def _open_database(cls, sqlite_file, password, document_factory=None,
+                       soledad=None):
+        if not os.path.isfile(sqlite_file):
+            raise errors.DatabaseDoesNotExist()
+        tries = 2
+        while True:
+            # Note: There seems to be a bug in sqlite 3.5.9 (with python2.6)
+            #       where without re-opening the database on Windows, it
+            #       doesn't see the transaction that was just committed
+            db_handle = dbapi2.connect(sqlite_file)
+            SQLCipherDatabase.set_pragma_key(db_handle, password)
+            c = db_handle.cursor()
+            v, err = cls._which_index_storage(c)
+            db_handle.close()
+            if v is not None:
+                break
+            # possibly another process is initializing it, wait for it to be
+            # done
+            if tries == 0:
+                raise err  # go for the richest error?
+            tries -= 1
+            time.sleep(cls.WAIT_FOR_PARALLEL_INIT_HALF_INTERVAL)
+        return SQLCipherDatabase._sqlite_registry[v](
+            sqlite_file, password, document_factory=document_factory,
+            soledad=soledad)
+
+    @classmethod
+    def open_database(cls, sqlite_file, password, create, backend_cls=None,
+                      document_factory=None, soledad=None):
+        """Open U1DB database using SQLCipher as backend."""
+        try:
+            return cls._open_database(sqlite_file, password,
+                                      document_factory=document_factory,
+                                      soledad=soledad)
+        except errors.DatabaseDoesNotExist:
+            if not create:
+                raise
+            if backend_cls is None:
+                # default is SQLCipherPartialExpandDatabase
+                backend_cls = SQLCipherDatabase
+            return backend_cls(sqlite_file, password,
+                               document_factory=document_factory,
+                               soledad=soledad)
+
+    def sync(self, url, creds=None, autocreate=True):
+        """
+        Synchronize encrypted documents with remote replica exposed at url.
+        """
+        from u1db.sync import Synchronizer
+        from leap.soledad.backends.leap_backend import LeapSyncTarget
+        return Synchronizer(
+            self,
+            LeapSyncTarget(url,
+                           creds=creds,
+                           soledad=self._soledad)).sync(autocreate=autocreate)
+
+    def _extra_schema_init(self, c):
+        c.execute(
+            'ALTER TABLE document '
+            'ADD COLUMN syncable BOOL NOT NULL DEFAULT TRUE')
+
+    def _put_and_update_indexes(self, old_doc, doc):
+        super(SQLCipherDatabase, self)._put_and_update_indexes(old_doc, doc)
+        c = self._db_handle.cursor()
+        c.execute('UPDATE document SET syncable=? WHERE doc_id=?',
+                  (doc.syncable, doc.doc_id))
+
+    def _get_doc(self, doc_id, check_for_conflicts=False):
+        doc = super(SQLCipherDatabase, self)._get_doc(doc_id,
+                                                      check_for_conflicts)
+        if doc:
+            c = self._db_handle.cursor()
+            c.execute('SELECT syncable FROM document WHERE doc_id=?',
+                      (doc.doc_id,))
+            doc.syncable = bool(c.fetchone()[0])
+        return doc
+
+sqlite_backend.SQLiteDatabase.register_implementation(SQLCipherDatabase)