[refactor] split out backend from couch database

First step of splitting classes across files on common.
backend.py holds SoledadBackend (generic backend logic)
couch/ is now a directory with old code inside __init__.py and
CouchServerState on state.py
Also removed mock IndexedSoledadBackend, since Soledad does not support
indexing due to encryption on server side.
Also fixed DesignDocUnknownError to show up what is the message of the
original exception. It was being lost.

11 files changed, 1593 insertions, 1650 deletions

diff --git a/common/src/leap/soledad/common/backend.py b/common/src/leap/soledad/common/backend.py
new file mode 100644
index 00000000..cb37b4ac
--- /dev/null
+++ b/common/src/leap/soledad/common/backend.py
@@ -0,0 +1,681 @@
+# -*- coding: utf-8 -*-
+# backend.py
+# Copyright (C) 2015 LEAP
+#
+# 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 3 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, see <http://www.gnu.org/licenses/>.
+
+
+"""A U1DB generic backend."""
+
+
+from u1db import vectorclock
+from u1db.errors import (
+    RevisionConflict,
+    InvalidDocId,
+    ConflictedDoc,
+    DocumentDoesNotExist,
+    DocumentAlreadyDeleted,
+)
+from u1db.backends import CommonBackend
+from u1db.backends import CommonSyncTarget
+from leap.soledad.common.document import CouchDocument
+
+
+class SoledadBackend(CommonBackend):
+
+    """
+    A U1DB backend implementation.
+    """
+
+    def __init__(self, database, replica_uid=None):
+        """
+        Create a new backend.
+
+        :param database: the database implementation
+        :type database: Database
+        :param replica_uid: an optional unique replica identifier
+        :type replica_uid: str
+        """
+        # save params
+        self._factory = CouchDocument
+        self._real_replica_uid = None
+        self._cache = None
+        self._dbname = database._dbname
+        self._database = database
+        if replica_uid is not None:
+            self._set_replica_uid(replica_uid)
+
+    @property
+    def cache(self):
+        if self._cache is not None:
+            return self._cache
+        else:
+            return {}
+
+    def init_caching(self, cache):
+        """
+        Start using cache by setting internal _cache attribute.
+
+        :param cache: the cache instance, anything that behaves like a dict
+        :type cache: dict
+        """
+        self._cache = cache
+
+    def get_sync_target(self):
+        """
+        Return a SyncTarget object, for another u1db to synchronize with.
+
+        :return: The sync target.
+        :rtype: SoledadSyncTarget
+        """
+        return SoledadSyncTarget(self)
+
+    def delete_database(self):
+        """
+        Delete a U1DB CouchDB database.
+        """
+        self._database.delete_database()
+
+    def close(self):
+        """
+        Release any resources associated with this database.
+
+        :return: True if db was succesfully closed.
+        :rtype: bool
+        """
+        self._database.close()
+        return True
+
+    def __del__(self):
+        """
+        Close the database upon garbage collection.
+        """
+        self.close()
+
+    def _set_replica_uid(self, replica_uid):
+        """
+        Force the replica uid to be set.
+
+        :param replica_uid: The new replica uid.
+        :type replica_uid: str
+        """
+        self._database.set_replica_uid(replica_uid)
+        self._real_replica_uid = replica_uid
+        self.cache['replica_uid'] = self._real_replica_uid
+
+    def _get_replica_uid(self):
+        """
+        Get the replica uid.
+
+        :return: The replica uid.
+        :rtype: str
+        """
+        if self._real_replica_uid is not None:
+            self.cache['replica_uid'] = self._real_replica_uid
+            return self._real_replica_uid
+        if 'replica_uid' in self.cache:
+            return self.cache['replica_uid']
+        self._real_replica_uid = self._database.get_replica_uid()
+        self._set_replica_uid(self._real_replica_uid)
+        return self._real_replica_uid
+
+    _replica_uid = property(_get_replica_uid, _set_replica_uid)
+
+    replica_uid = property(_get_replica_uid)
+
+    def _get_generation(self):
+        """
+        Return the current generation.
+
+        :return: The current generation.
+        :rtype: int
+
+        :raise MissingDesignDocError: Raised when tried to access a missing
+                                      design document.
+        :raise MissingDesignDocListFunctionError: Raised when trying to access
+                                                  a missing list function on a
+                                                  design document.
+        :raise MissingDesignDocNamedViewError: Raised when trying to access a
+                                               missing named view on a design
+                                               document.
+        :raise MissingDesignDocDeletedError: Raised when trying to access a
+                                             deleted design document.
+        :raise MissingDesignDocUnknownError: Raised when failed to access a
+                                             design document for an yet
+                                             unknown reason.
+        """
+        return self._get_generation_info()[0]
+
+    def _get_generation_info(self):
+        """
+        Return the current generation.
+
+        :return: A tuple containing the current generation and transaction id.
+        :rtype: (int, str)
+
+        :raise MissingDesignDocError: Raised when tried to access a missing
+                                      design document.
+        :raise MissingDesignDocListFunctionError: Raised when trying to access
+                                                  a missing list function on a
+                                                  design document.
+        :raise MissingDesignDocNamedViewError: Raised when trying to access a
+                                               missing named view on a design
+                                               document.
+        :raise MissingDesignDocDeletedError: Raised when trying to access a
+                                             deleted design document.
+        :raise MissingDesignDocUnknownError: Raised when failed to access a
+                                             design document for an yet
+                                             unknown reason.
+        """
+        if self.replica_uid + '_gen' in self.cache:
+            response = self.cache[self.replica_uid + '_gen']
+            return response
+        cur_gen, newest_trans_id = self._database._get_generation_info()
+        self.cache[self.replica_uid + '_gen'] = (cur_gen, newest_trans_id)
+        return (cur_gen, newest_trans_id)
+
+    def _get_trans_id_for_gen(self, generation):
+        """
+        Get the transaction id corresponding to a particular generation.
+
+        :param generation: The generation for which to get the transaction id.
+        :type generation: int
+
+        :return: The transaction id for C{generation}.
+        :rtype: str
+
+        """
+        return self._database._get_trans_id_for_gen(generation)
+
+    def _get_transaction_log(self):
+        """
+        This is only for the test suite, it is not part of the api.
+
+        :return: The complete transaction log.
+        :rtype: [(str, str)]
+
+        """
+        return self._database._get_transaction_log()
+
+    def _get_doc(self, doc_id, check_for_conflicts=False):
+        """
+        Extract the document from storage.
+
+        This can return None if the document doesn't exist.
+
+        :param doc_id: The unique document identifier
+        :type doc_id: str
+        :param check_for_conflicts: If set to False, then the conflict check
+                                    will be skipped.
+        :type check_for_conflicts: bool
+
+        :return: The document.
+        :rtype: CouchDocument
+        """
+        return self._database._get_doc(doc_id, check_for_conflicts)
+
+    def get_doc(self, doc_id, include_deleted=False):
+        """
+        Get the JSON string for the given document.
+
+        :param doc_id: The unique document identifier
+        :type doc_id: str
+        :param include_deleted: If set to True, deleted documents will be
+            returned with empty content. Otherwise asking for a deleted
+            document will return None.
+        :type include_deleted: bool
+
+        :return: A document object.
+        :rtype: CouchDocument.
+        """
+        doc = self._get_doc(doc_id, check_for_conflicts=True)
+        if doc is None:
+            return None
+        if doc.is_tombstone() and not include_deleted:
+            return None
+        return doc
+
+    def get_all_docs(self, include_deleted=False):
+        """
+        Get the JSON content for all documents in the database.
+
+        :param include_deleted: If set to True, deleted documents will be
+                                returned with empty content. Otherwise deleted
+                                documents will not be included in the results.
+        :type include_deleted: bool
+
+        :return: (generation, [CouchDocument])
+            The current generation of the database, followed by a list of all
+            the documents in the database.
+        :rtype: (int, [CouchDocument])
+        """
+        return self._database.get_all_docs(include_deleted)
+
+    def _put_doc(self, old_doc, doc):
+        """
+        Put the document in the Couch backend database.
+
+        Note that C{old_doc} must have been fetched with the parameter
+        C{check_for_conflicts} equal to True, so we can properly update the
+        new document using the conflict information from the old one.
+
+        :param old_doc: The old document version.
+        :type old_doc: CouchDocument
+        :param doc: The document to be put.
+        :type doc: CouchDocument
+        """
+        last_transaction =\
+            self._database.save_document(old_doc, doc,
+                                         self._allocate_transaction_id())
+        if self.replica_uid + '_gen' in self.cache:
+            gen, trans = self.cache[self.replica_uid + '_gen']
+            gen += 1
+            trans = last_transaction
+            self.cache[self.replica_uid + '_gen'] = (gen, trans)
+
+    def put_doc(self, doc):
+        """
+        Update a document.
+
+        If the document currently has conflicts, put will fail.
+        If the database specifies a maximum document size and the document
+        exceeds it, put will fail and raise a DocumentTooBig exception.
+
+        :param doc: A Document with new content.
+        :return: new_doc_rev - The new revision identifier for the document.
+            The Document object will also be updated.
+
+        :raise InvalidDocId: Raised if the document's id is invalid.
+        :raise DocumentTooBig: Raised if the document size is too big.
+        :raise ConflictedDoc: Raised if the document has conflicts.
+        """
+        if doc.doc_id is None:
+            raise InvalidDocId()
+        self._check_doc_id(doc.doc_id)
+        self._check_doc_size(doc)
+        old_doc = self._get_doc(doc.doc_id, check_for_conflicts=True)
+        if old_doc and old_doc.has_conflicts:
+            raise ConflictedDoc()
+        if old_doc and doc.rev is None and old_doc.is_tombstone():
+            new_rev = self._allocate_doc_rev(old_doc.rev)
+        else:
+            if old_doc is not None:
+                    if old_doc.rev != doc.rev:
+                        raise RevisionConflict()
+            else:
+                if doc.rev is not None:
+                    raise RevisionConflict()
+            new_rev = self._allocate_doc_rev(doc.rev)
+        doc.rev = new_rev
+        self._put_doc(old_doc, doc)
+        return new_rev
+
+    def whats_changed(self, old_generation=0):
+        """
+        Return a list of documents that have changed since old_generation.
+
+        :param old_generation: The generation of the database in the old
+                               state.
+        :type old_generation: int
+
+        :return: (generation, trans_id, [(doc_id, generation, trans_id),...])
+                 The current generation of the database, its associated
+                 transaction id, and a list of of changed documents since
+                 old_generation, represented by tuples with for each document
+                 its doc_id and the generation and transaction id corresponding
+                 to the last intervening change and sorted by generation (old
+                 changes first)
+        :rtype: (int, str, [(str, int, str)])
+        """
+        return self._database.whats_changed(old_generation)
+
+    def delete_doc(self, doc):
+        """
+        Mark a document as deleted.
+
+        Will abort if the current revision doesn't match doc.rev.
+        This will also set doc.content to None.
+
+        :param doc: The document to mark as deleted.
+        :type doc: CouchDocument.
+
+        :raise DocumentDoesNotExist: Raised if the document does not
+                                            exist.
+        :raise RevisionConflict: Raised if the revisions do not match.
+        :raise DocumentAlreadyDeleted: Raised if the document is
+                                              already deleted.
+        :raise ConflictedDoc: Raised if the doc has conflicts.
+        """
+        old_doc = self._get_doc(doc.doc_id, check_for_conflicts=True)
+        if old_doc is None:
+            raise DocumentDoesNotExist
+        if old_doc.rev != doc.rev:
+            raise RevisionConflict()
+        if old_doc.is_tombstone():
+            raise DocumentAlreadyDeleted
+        if old_doc.has_conflicts:
+            raise ConflictedDoc()
+        new_rev = self._allocate_doc_rev(doc.rev)
+        doc.rev = new_rev
+        doc.make_tombstone()
+        self._put_doc(old_doc, doc)
+        return new_rev
+
+    def get_doc_conflicts(self, doc_id, couch_rev=None):
+        """
+        Get the conflicted versions of a document.
+
+        If the C{couch_rev} parameter is not None, conflicts for a specific
+        document's couch revision are returned.
+
+        :param couch_rev: The couch document revision.
+        :type couch_rev: str
+
+        :return: A list of conflicted versions of the document.
+        :rtype: list
+        """
+        return self._database.get_doc_conflicts(doc_id, couch_rev)
+
+    def _get_replica_gen_and_trans_id(self, other_replica_uid):
+        """
+        Return the last known generation and transaction id for the other db
+        replica.
+
+        When you do a synchronization with another replica, the Database keeps
+        track of what generation the other database replica was at, and what
+        the associated transaction id was.  This is used to determine what data
+        needs to be sent, and if two databases are claiming to be the same
+        replica.
+
+        :param other_replica_uid: The identifier for the other replica.
+        :type other_replica_uid: str
+
+        :return: A tuple containing the generation and transaction id we
+                 encountered during synchronization. If we've never
+                 synchronized with the replica, this is (0, '').
+        :rtype: (int, str)
+        """
+        return self._database._get_replica_gen_and_trans_id(other_replica_uid)
+
+    def _set_replica_gen_and_trans_id(self, other_replica_uid,
+                                      other_generation, other_transaction_id,
+                                      number_of_docs=None, doc_idx=None,
+                                      sync_id=None):
+        """
+        Set the last-known generation and transaction id for the other
+        database replica.
+
+        We have just performed some synchronization, and we want to track what
+        generation the other replica was at. See also
+        _get_replica_gen_and_trans_id.
+
+        :param other_replica_uid: The U1DB identifier for the other replica.
+        :type other_replica_uid: str
+        :param other_generation: The generation number for the other replica.
+        :type other_generation: int
+        :param other_transaction_id: The transaction id associated with the
+            generation.
+        :type other_transaction_id: str
+        :param number_of_docs: The total amount of documents sent on this sync
+                               session.
+        :type number_of_docs: int
+        :param doc_idx: The index of the current document being sent.
+        :type doc_idx: int
+        :param sync_id: The id of the current sync session.
+        :type sync_id: str
+        """
+        if other_replica_uid is not None and other_generation is not None:
+            self._do_set_replica_gen_and_trans_id(
+                other_replica_uid, other_generation, other_transaction_id,
+                number_of_docs=number_of_docs, doc_idx=doc_idx,
+                sync_id=sync_id)
+
+    def _do_set_replica_gen_and_trans_id(
+            self, other_replica_uid, other_generation, other_transaction_id,
+            number_of_docs=None, doc_idx=None, sync_id=None):
+        """
+        Set the last-known generation and transaction id for the other
+        database replica.
+
+        We have just performed some synchronization, and we want to track what
+        generation the other replica was at. See also
+        _get_replica_gen_and_trans_id.
+
+        :param other_replica_uid: The U1DB identifier for the other replica.
+        :type other_replica_uid: str
+        :param other_generation: The generation number for the other replica.
+        :type other_generation: int
+        :param other_transaction_id: The transaction id associated with the
+                                     generation.
+        :type other_transaction_id: str
+        :param number_of_docs: The total amount of documents sent on this sync
+                               session.
+        :type number_of_docs: int
+        :param doc_idx: The index of the current document being sent.
+        :type doc_idx: int
+        :param sync_id: The id of the current sync session.
+        :type sync_id: str
+        """
+        self.cache[other_replica_uid] = (other_generation,
+                                         other_transaction_id)
+        self._database._do_set_replica_gen_and_trans_id(other_replica_uid,
+                                                        other_generation,
+                                                        other_transaction_id)
+
+    def _force_doc_sync_conflict(self, doc):
+        """
+        Add a conflict and force a document put.
+
+        :param doc: The document to be put.
+        :type doc: CouchDocument
+        """
+        my_doc = self._get_doc(doc.doc_id)
+        self._prune_conflicts(doc, vectorclock.VectorClockRev(doc.rev))
+        doc.add_conflict(self._factory(doc.doc_id, my_doc.rev,
+                                       my_doc.get_json()))
+        doc.has_conflicts = True
+        self._put_doc(my_doc, doc)
+
+    def resolve_doc(self, doc, conflicted_doc_revs):
+        """
+        Mark a document as no longer conflicted.
+
+        We take the list of revisions that the client knows about that it is
+        superseding. This may be a different list from the actual current
+        conflicts, in which case only those are removed as conflicted.  This
+        may fail if the conflict list is significantly different from the
+        supplied information. (sync could have happened in the background from
+        the time you GET_DOC_CONFLICTS until the point where you RESOLVE)
+
+        :param doc: A Document with the new content to be inserted.
+        :type doc: CouchDocument
+        :param conflicted_doc_revs: A list of revisions that the new content
+                                    supersedes.
+        :type conflicted_doc_revs: [str]
+
+        :raise MissingDesignDocError: Raised when tried to access a missing
+                                      design document.
+        :raise MissingDesignDocListFunctionError: Raised when trying to access
+                                                  a missing list function on a
+                                                  design document.
+        :raise MissingDesignDocNamedViewError: Raised when trying to access a
+                                               missing named view on a design
+                                               document.
+        :raise MissingDesignDocDeletedError: Raised when trying to access a
+                                             deleted design document.
+        :raise MissingDesignDocUnknownError: Raised when failed to access a
+                                             design document for an yet
+                                             unknown reason.
+        """
+        cur_doc = self._get_doc(doc.doc_id, check_for_conflicts=True)
+        new_rev = self._ensure_maximal_rev(cur_doc.rev,
+                                           conflicted_doc_revs)
+        superseded_revs = set(conflicted_doc_revs)
+        doc.rev = new_rev
+        # this backend stores conflicts as properties of the documents, so we
+        # have to copy these conflicts over to the document being updated.
+        if cur_doc.rev in superseded_revs:
+            # the newer doc version will supersede the one in the database, so
+            # we copy conflicts before updating the backend.
+            doc.set_conflicts(cur_doc.get_conflicts())  # copy conflicts over.
+            doc.delete_conflicts(superseded_revs)
+            self._put_doc(cur_doc, doc)
+        else:
+            # the newer doc version does not supersede the one in the
+            # database, so we will add a conflict to the database and copy
+            # those over to the document the user has in her hands.
+            cur_doc.add_conflict(doc)
+            cur_doc.delete_conflicts(superseded_revs)
+            self._put_doc(cur_doc, cur_doc)  # just update conflicts
+            # backend has been updated with current conflicts, now copy them
+            # to the current document.
+            doc.set_conflicts(cur_doc.get_conflicts())
+
+    def _put_doc_if_newer(self, doc, save_conflict, replica_uid, replica_gen,
+                          replica_trans_id='', number_of_docs=None,
+                          doc_idx=None, sync_id=None):
+        """
+        Insert/update document into the database with a given revision.
+
+        This api is used during synchronization operations.
+
+        If a document would conflict and save_conflict is set to True, the
+        content will be selected as the 'current' content for doc.doc_id,
+        even though doc.rev doesn't supersede the currently stored revision.
+        The currently stored document will be added to the list of conflict
+        alternatives for the given doc_id.
+
+        This forces the new content to be 'current' so that we get convergence
+        after synchronizing, even if people don't resolve conflicts. Users can
+        then notice that their content is out of date, update it, and
+        synchronize again. (The alternative is that users could synchronize and
+        think the data has propagated, but their local copy looks fine, and the
+        remote copy is never updated again.)
+
+        :param doc: A document object
+        :type doc: CouchDocument
+        :param save_conflict: If this document is a conflict, do you want to
+                              save it as a conflict, or just ignore it.
+        :type save_conflict: bool
+        :param replica_uid: A unique replica identifier.
+        :type replica_uid: str
+        :param replica_gen: The generation of the replica corresponding to the
+                            this document. The replica arguments are optional,
+                            but are used during synchronization.
+        :type replica_gen: int
+        :param replica_trans_id: The transaction_id associated with the
+                                 generation.
+        :type replica_trans_id: str
+        :param number_of_docs: The total amount of documents sent on this sync
+                               session.
+        :type number_of_docs: int
+        :param doc_idx: The index of the current document being sent.
+        :type doc_idx: int
+        :param sync_id: The id of the current sync session.
+        :type sync_id: str
+
+        :return: (state, at_gen) -  If we don't have doc_id already, or if
+                 doc_rev supersedes the existing document revision, then the
+                 content will be inserted, and state is 'inserted'.  If
+                 doc_rev is less than or equal to the existing revision, then
+                 the put is ignored and state is respecitvely 'superseded' or
+                 'converged'.  If doc_rev is not strictly superseded or
+                 supersedes, then state is 'conflicted'. The document will not
+                 be inserted if save_conflict is False.  For 'inserted' or
+                 'converged', at_gen is the insertion/current generation.
+        :rtype: (str, int)
+        """
+        if not isinstance(doc, CouchDocument):
+            doc = self._factory(doc.doc_id, doc.rev, doc.get_json())
+        my_doc = self._get_doc(doc.doc_id, check_for_conflicts=True)
+        if my_doc:
+            doc.set_conflicts(my_doc.get_conflicts())
+        return CommonBackend._put_doc_if_newer(self, doc, save_conflict,
+                                               replica_uid, replica_gen,
+                                               replica_trans_id)
+
+    def _put_and_update_indexes(self, cur_doc, doc):
+        self._put_doc(cur_doc, doc)
+
+    def get_docs(self, doc_ids, check_for_conflicts=True,
+                 include_deleted=False):
+        """
+        Get the JSON content for many documents.
+
+        :param doc_ids: A list of document identifiers or None for all.
+        :type doc_ids: list
+        :param check_for_conflicts: If set to False, then the conflict check
+                                    will be skipped, and 'None' will be
+                                    returned instead of True/False.
+        :type check_for_conflicts: bool
+        :param include_deleted: If set to True, deleted documents will be
+                                returned with empty content. Otherwise deleted
+                                documents will not be included in the results.
+        :return: iterable giving the Document object for each document id
+                 in matching doc_ids order.
+        :rtype: iterable
+        """
+        return self._database.get_docs(doc_ids, check_for_conflicts,
+                                       include_deleted)
+
+    def _prune_conflicts(self, doc, doc_vcr):
+        """
+        Prune conflicts that are older then the current document's revision, or
+        whose content match to the current document's content.
+        Originally in u1db.CommonBackend
+
+        :param doc: The document to have conflicts pruned.
+        :type doc: CouchDocument
+        :param doc_vcr: A vector clock representing the current document's
+                        revision.
+        :type doc_vcr: u1db.vectorclock.VectorClock
+        """
+        if doc.has_conflicts:
+            autoresolved = False
+            c_revs_to_prune = []
+            for c_doc in doc._conflicts:
+                c_vcr = vectorclock.VectorClockRev(c_doc.rev)
+                if doc_vcr.is_newer(c_vcr):
+                    c_revs_to_prune.append(c_doc.rev)
+                elif doc.same_content_as(c_doc):
+                    c_revs_to_prune.append(c_doc.rev)
+                    doc_vcr.maximize(c_vcr)
+                    autoresolved = True
+            if autoresolved:
+                doc_vcr.increment(self._replica_uid)
+                doc.rev = doc_vcr.as_str()
+            doc.delete_conflicts(c_revs_to_prune)
+
+
+class SoledadSyncTarget(CommonSyncTarget):
+
+    """
+    Functionality for using a SoledadBackend as a synchronization target.
+    """
+
+    def get_sync_info(self, source_replica_uid):
+        source_gen, source_trans_id = self._db._get_replica_gen_and_trans_id(
+            source_replica_uid)
+        my_gen, my_trans_id = self._db._get_generation_info()
+        return (
+            self._db._replica_uid, my_gen, my_trans_id, source_gen,
+            source_trans_id)
+
+    def record_sync_info(self, source_replica_uid, source_replica_generation,
+                         source_replica_transaction_id):
+        if self._trace_hook:
+            self._trace_hook('record_sync_info')
+        self._db._set_replica_gen_and_trans_id(
+            source_replica_uid, source_replica_generation,
+            source_replica_transaction_id)
diff --git a/common/src/leap/soledad/common/couch.py b/common/src/leap/soledad/common/couch.py
deleted file mode 100644
index d4f67696..00000000
--- a/common/src/leap/soledad/common/couch.py
+++ /dev/null
@@ -1,1514 +0,0 @@
-# -*- coding: utf-8 -*-
-# couch.py
-# Copyright (C) 2013 LEAP
-#
-# 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 3 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, see <http://www.gnu.org/licenses/>.
-
-
-"""A U1DB backend that uses CouchDB as its persistence layer."""
-
-
-import json
-import re
-import uuid
-import logging
-import binascii
-import time
-
-
-from StringIO import StringIO
-from urlparse import urljoin
-from contextlib import contextmanager
-from multiprocessing.pool import ThreadPool
-
-
-from couchdb.client import Server, Database
-from couchdb.multipart import MultipartWriter
-from couchdb.http import (
-    ResourceConflict,
-    ResourceNotFound,
-    ServerError,
-    Session,
-    urljoin as couch_urljoin,
-    Resource,
-)
-from u1db import vectorclock
-from u1db.errors import (
-    DatabaseDoesNotExist,
-    InvalidGeneration,
-    RevisionConflict,
-    InvalidDocId,
-    ConflictedDoc,
-    DocumentDoesNotExist,
-    DocumentAlreadyDeleted,
-    Unauthorized,
-)
-from u1db.backends import CommonBackend, CommonSyncTarget
-from u1db.remote import http_app
-from u1db.remote.server_state import ServerState
-
-
-from leap.soledad.common import ddocs
-from leap.soledad.common.errors import raise_server_error
-from leap.soledad.common.errors import raise_missing_design_doc_error
-from leap.soledad.common.errors import InvalidURLError
-from leap.soledad.common.command import exec_validated_cmd
-from leap.soledad.common.document import CouchDocument
-
-
-logger = logging.getLogger(__name__)
-
-
-COUCH_TIMEOUT = 120  # timeout for transfers between Soledad server and Couch
-
-
-def list_users_dbs(couch_url):
-    """
-    Retrieves a list with all databases that starts with 'user-' on CouchDB.
-    Those databases belongs to users. So, the list will contain all the
-    database names in the form of 'user-{uuid4}'.
-
-    :param couch_url: The couch url with needed credentials
-    :type couch_url: str
-
-    :return: The list of all database names from users.
-    :rtype: [str]
-    """
-    with couch_server(couch_url) as server:
-        users = [dbname for dbname in server if dbname.startswith('user-')]
-    return users
-
-# monkey-patch the u1db http app to use CouchDocument
-http_app.Document = CouchDocument
-
-
-@contextmanager
-def couch_server(url):
-    """
-    Provide a connection to a couch server and cleanup after use.
-
-    For database creation and deletion we use an ephemeral connection to the
-    couch server. That connection has to be properly closed, so we provide it
-    as a context manager.
-
-    :param url: The URL of the Couch server.
-    :type url: str
-    """
-    session = Session(timeout=COUCH_TIMEOUT)
-    server = Server(url=url, full_commit=False, session=session)
-    yield server
-
-
-THREAD_POOL = ThreadPool(20)
-
-
-class SoledadBackend(CommonBackend):
-
-    """
-    A U1DB implementation that uses CouchDB as its persistence layer.
-    """
-
-    @classmethod
-    def open_database(cls, url, create, replica_uid=None, ensure_ddocs=False,
-                      database_security=None):
-        """
-        Open a U1DB database using CouchDB as backend.
-
-        :param url: the url of the database replica
-        :type url: str
-        :param create: should the replica be created if it does not exist?
-        :type create: bool
-        :param replica_uid: an optional unique replica identifier
-        :type replica_uid: str
-        :param ensure_ddocs: Ensure that the design docs exist on server.
-        :type ensure_ddocs: bool
-
-        :return: the database instance
-        :rtype: SoledadBackend
-        """
-        db = CouchDatabase.open_database(url, create, ensure_ddocs)
-        return cls(
-            db, replica_uid=replica_uid)
-
-    def __init__(self, database, replica_uid=None):
-        """
-        Create a new Couch data container.
-
-        :param url: the url of the couch database
-        :type url: str
-        :param dbname: the database name
-        :type dbname: str
-        :param replica_uid: an optional unique replica identifier
-        :type replica_uid: str
-        :param ensure_ddocs: Ensure that the design docs exist on server.
-        :type ensure_ddocs: bool
-        """
-        # save params
-        self._factory = CouchDocument
-        self._real_replica_uid = None
-        # configure couch
-        self._cache = None
-        self._dbname = database._dbname
-        self._database = database
-        if replica_uid is not None:
-            self._set_replica_uid(replica_uid)
-
-    @property
-    def cache(self):
-        if self._cache is not None:
-            return self._cache
-        else:
-            return {}
-
-    def init_caching(self, cache):
-        """
-        Start using cache by setting internal _cache attribute.
-
-        :param cache: the cache instance, anything that behaves like a dict
-        :type cache: dict
-        """
-        self._cache = cache
-
-    def get_sync_target(self):
-        """
-        Return a SyncTarget object, for another u1db to synchronize with.
-
-        :return: The sync target.
-        :rtype: CouchSyncTarget
-        """
-        return CouchSyncTarget(self)
-
-    def delete_database(self):
-        """
-        Delete a U1DB CouchDB database.
-        """
-        self._database.delete_database()
-
-    def close(self):
-        """
-        Release any resources associated with this database.
-
-        :return: True if db was succesfully closed.
-        :rtype: bool
-        """
-        self._database.close()
-        return True
-
-    def __del__(self):
-        """
-        Close the database upon garbage collection.
-        """
-        self.close()
-
-    def _set_replica_uid(self, replica_uid):
-        """
-        Force the replica uid to be set.
-
-        :param replica_uid: The new replica uid.
-        :type replica_uid: str
-        """
-        self._database.set_replica_uid(replica_uid)
-        self._real_replica_uid = replica_uid
-        self.cache['replica_uid'] = self._real_replica_uid
-
-    def _get_replica_uid(self):
-        """
-        Get the replica uid.
-
-        :return: The replica uid.
-        :rtype: str
-        """
-        if self._real_replica_uid is not None:
-            self.cache['replica_uid'] = self._real_replica_uid
-            return self._real_replica_uid
-        if 'replica_uid' in self.cache:
-            return self.cache['replica_uid']
-        self._real_replica_uid = self._database.get_replica_uid()
-        self._set_replica_uid(self._real_replica_uid)
-        return self._real_replica_uid
-
-    _replica_uid = property(_get_replica_uid, _set_replica_uid)
-
-    replica_uid = property(_get_replica_uid)
-
-    def _get_generation(self):
-        """
-        Return the current generation.
-
-        :return: The current generation.
-        :rtype: int
-
-        :raise MissingDesignDocError: Raised when tried to access a missing
-                                      design document.
-        :raise MissingDesignDocListFunctionError: Raised when trying to access
-                                                  a missing list function on a
-                                                  design document.
-        :raise MissingDesignDocNamedViewError: Raised when trying to access a
-                                               missing named view on a design
-                                               document.
-        :raise MissingDesignDocDeletedError: Raised when trying to access a
-                                             deleted design document.
-        :raise MissingDesignDocUnknownError: Raised when failed to access a
-                                             design document for an yet
-                                             unknown reason.
-        """
-        return self._get_generation_info()[0]
-
-    def _get_generation_info(self):
-        """
-        Return the current generation.
-
-        :return: A tuple containing the current generation and transaction id.
-        :rtype: (int, str)
-
-        :raise MissingDesignDocError: Raised when tried to access a missing
-                                      design document.
-        :raise MissingDesignDocListFunctionError: Raised when trying to access
-                                                  a missing list function on a
-                                                  design document.
-        :raise MissingDesignDocNamedViewError: Raised when trying to access a
-                                               missing named view on a design
-                                               document.
-        :raise MissingDesignDocDeletedError: Raised when trying to access a
-                                             deleted design document.
-        :raise MissingDesignDocUnknownError: Raised when failed to access a
-                                             design document for an yet
-                                             unknown reason.
-        """
-        if self.replica_uid + '_gen' in self.cache:
-            response = self.cache[self.replica_uid + '_gen']
-            return response
-        cur_gen, newest_trans_id = self._database._get_generation_info()
-        self.cache[self.replica_uid + '_gen'] = (cur_gen, newest_trans_id)
-        return (cur_gen, newest_trans_id)
-
-    def _get_trans_id_for_gen(self, generation):
-        """
-        Get the transaction id corresponding to a particular generation.
-
-        :param generation: The generation for which to get the transaction id.
-        :type generation: int
-
-        :return: The transaction id for C{generation}.
-        :rtype: str
-
-        """
-        return self._database._get_trans_id_for_gen(generation)
-
-    def _get_transaction_log(self):
-        """
-        This is only for the test suite, it is not part of the api.
-
-        :return: The complete transaction log.
-        :rtype: [(str, str)]
-
-        """
-        return self._database._get_transaction_log()
-
-    def _get_doc(self, doc_id, check_for_conflicts=False):
-        """
-        Extract the document from storage.
-
-        This can return None if the document doesn't exist.
-
-        :param doc_id: The unique document identifier
-        :type doc_id: str
-        :param check_for_conflicts: If set to False, then the conflict check
-                                    will be skipped.
-        :type check_for_conflicts: bool
-
-        :return: The document.
-        :rtype: CouchDocument
-        """
-        return self._database._get_doc(doc_id, check_for_conflicts)
-
-    def get_doc(self, doc_id, include_deleted=False):
-        """
-        Get the JSON string for the given document.
-
-        :param doc_id: The unique document identifier
-        :type doc_id: str
-        :param include_deleted: If set to True, deleted documents will be
-            returned with empty content. Otherwise asking for a deleted
-            document will return None.
-        :type include_deleted: bool
-
-        :return: A document object.
-        :rtype: CouchDocument.
-        """
-        doc = self._get_doc(doc_id, check_for_conflicts=True)
-        if doc is None:
-            return None
-        if doc.is_tombstone() and not include_deleted:
-            return None
-        return doc
-
-    def get_all_docs(self, include_deleted=False):
-        """
-        Get the JSON content for all documents in the database.
-
-        :param include_deleted: If set to True, deleted documents will be
-                                returned with empty content. Otherwise deleted
-                                documents will not be included in the results.
-        :type include_deleted: bool
-
-        :return: (generation, [CouchDocument])
-            The current generation of the database, followed by a list of all
-            the documents in the database.
-        :rtype: (int, [CouchDocument])
-        """
-        return self._database.get_all_docs(include_deleted)
-
-    def _put_doc(self, old_doc, doc):
-        """
-        Put the document in the Couch backend database.
-
-        Note that C{old_doc} must have been fetched with the parameter
-        C{check_for_conflicts} equal to True, so we can properly update the
-        new document using the conflict information from the old one.
-
-        :param old_doc: The old document version.
-        :type old_doc: CouchDocument
-        :param doc: The document to be put.
-        :type doc: CouchDocument
-        """
-        last_transaction =\
-            self._database.save_document(old_doc, doc,
-                                         self._allocate_transaction_id())
-        if self.replica_uid + '_gen' in self.cache:
-            gen, trans = self.cache[self.replica_uid + '_gen']
-            gen += 1
-            trans = last_transaction
-            self.cache[self.replica_uid + '_gen'] = (gen, trans)
-
-    def put_doc(self, doc):
-        """
-        Update a document.
-
-        If the document currently has conflicts, put will fail.
-        If the database specifies a maximum document size and the document
-        exceeds it, put will fail and raise a DocumentTooBig exception.
-
-        :param doc: A Document with new content.
-        :return: new_doc_rev - The new revision identifier for the document.
-            The Document object will also be updated.
-
-        :raise InvalidDocId: Raised if the document's id is invalid.
-        :raise DocumentTooBig: Raised if the document size is too big.
-        :raise ConflictedDoc: Raised if the document has conflicts.
-        """
-        if doc.doc_id is None:
-            raise InvalidDocId()
-        self._check_doc_id(doc.doc_id)
-        self._check_doc_size(doc)
-        old_doc = self._get_doc(doc.doc_id, check_for_conflicts=True)
-        if old_doc and old_doc.has_conflicts:
-            raise ConflictedDoc()
-        if old_doc and doc.rev is None and old_doc.is_tombstone():
-            new_rev = self._allocate_doc_rev(old_doc.rev)
-        else:
-            if old_doc is not None:
-                    if old_doc.rev != doc.rev:
-                        raise RevisionConflict()
-            else:
-                if doc.rev is not None:
-                    raise RevisionConflict()
-            new_rev = self._allocate_doc_rev(doc.rev)
-        doc.rev = new_rev
-        self._put_doc(old_doc, doc)
-        return new_rev
-
-    def whats_changed(self, old_generation=0):
-        """
-        Return a list of documents that have changed since old_generation.
-
-        :param old_generation: The generation of the database in the old
-                               state.
-        :type old_generation: int
-
-        :return: (generation, trans_id, [(doc_id, generation, trans_id),...])
-                 The current generation of the database, its associated
-                 transaction id, and a list of of changed documents since
-                 old_generation, represented by tuples with for each document
-                 its doc_id and the generation and transaction id corresponding
-                 to the last intervening change and sorted by generation (old
-                 changes first)
-        :rtype: (int, str, [(str, int, str)])
-        """
-        return self._database.whats_changed(old_generation)
-
-    def delete_doc(self, doc):
-        """
-        Mark a document as deleted.
-
-        Will abort if the current revision doesn't match doc.rev.
-        This will also set doc.content to None.
-
-        :param doc: The document to mark as deleted.
-        :type doc: CouchDocument.
-
-        :raise DocumentDoesNotExist: Raised if the document does not
-                                            exist.
-        :raise RevisionConflict: Raised if the revisions do not match.
-        :raise DocumentAlreadyDeleted: Raised if the document is
-                                              already deleted.
-        :raise ConflictedDoc: Raised if the doc has conflicts.
-        """
-        old_doc = self._get_doc(doc.doc_id, check_for_conflicts=True)
-        if old_doc is None:
-            raise DocumentDoesNotExist
-        if old_doc.rev != doc.rev:
-            raise RevisionConflict()
-        if old_doc.is_tombstone():
-            raise DocumentAlreadyDeleted
-        if old_doc.has_conflicts:
-            raise ConflictedDoc()
-        new_rev = self._allocate_doc_rev(doc.rev)
-        doc.rev = new_rev
-        doc.make_tombstone()
-        self._put_doc(old_doc, doc)
-        return new_rev
-
-    def get_doc_conflicts(self, doc_id, couch_rev=None):
-        """
-        Get the conflicted versions of a document.
-
-        If the C{couch_rev} parameter is not None, conflicts for a specific
-        document's couch revision are returned.
-
-        :param couch_rev: The couch document revision.
-        :type couch_rev: str
-
-        :return: A list of conflicted versions of the document.
-        :rtype: list
-        """
-        return self._database.get_doc_conflicts(doc_id, couch_rev)
-
-    def _get_replica_gen_and_trans_id(self, other_replica_uid):
-        """
-        Return the last known generation and transaction id for the other db
-        replica.
-
-        When you do a synchronization with another replica, the Database keeps
-        track of what generation the other database replica was at, and what
-        the associated transaction id was.  This is used to determine what data
-        needs to be sent, and if two databases are claiming to be the same
-        replica.
-
-        :param other_replica_uid: The identifier for the other replica.
-        :type other_replica_uid: str
-
-        :return: A tuple containing the generation and transaction id we
-                 encountered during synchronization. If we've never
-                 synchronized with the replica, this is (0, '').
-        :rtype: (int, str)
-        """
-        return self._database._get_replica_gen_and_trans_id(other_replica_uid)
-
-    def _set_replica_gen_and_trans_id(self, other_replica_uid,
-                                      other_generation, other_transaction_id,
-                                      number_of_docs=None, doc_idx=None,
-                                      sync_id=None):
-        """
-        Set the last-known generation and transaction id for the other
-        database replica.
-
-        We have just performed some synchronization, and we want to track what
-        generation the other replica was at. See also
-        _get_replica_gen_and_trans_id.
-
-        :param other_replica_uid: The U1DB identifier for the other replica.
-        :type other_replica_uid: str
-        :param other_generation: The generation number for the other replica.
-        :type other_generation: int
-        :param other_transaction_id: The transaction id associated with the
-            generation.
-        :type other_transaction_id: str
-        :param number_of_docs: The total amount of documents sent on this sync
-                               session.
-        :type number_of_docs: int
-        :param doc_idx: The index of the current document being sent.
-        :type doc_idx: int
-        :param sync_id: The id of the current sync session.
-        :type sync_id: str
-        """
-        if other_replica_uid is not None and other_generation is not None:
-            self._do_set_replica_gen_and_trans_id(
-                other_replica_uid, other_generation, other_transaction_id,
-                number_of_docs=number_of_docs, doc_idx=doc_idx,
-                sync_id=sync_id)
-
-    def _do_set_replica_gen_and_trans_id(
-            self, other_replica_uid, other_generation, other_transaction_id,
-            number_of_docs=None, doc_idx=None, sync_id=None):
-        """
-        Set the last-known generation and transaction id for the other
-        database replica.
-
-        We have just performed some synchronization, and we want to track what
-        generation the other replica was at. See also
-        _get_replica_gen_and_trans_id.
-
-        :param other_replica_uid: The U1DB identifier for the other replica.
-        :type other_replica_uid: str
-        :param other_generation: The generation number for the other replica.
-        :type other_generation: int
-        :param other_transaction_id: The transaction id associated with the
-                                     generation.
-        :type other_transaction_id: str
-        :param number_of_docs: The total amount of documents sent on this sync
-                               session.
-        :type number_of_docs: int
-        :param doc_idx: The index of the current document being sent.
-        :type doc_idx: int
-        :param sync_id: The id of the current sync session.
-        :type sync_id: str
-        """
-        self.cache[other_replica_uid] = (other_generation,
-                                         other_transaction_id)
-        self._database._do_set_replica_gen_and_trans_id(other_replica_uid,
-                                                        other_generation,
-                                                        other_transaction_id)
-
-    def _force_doc_sync_conflict(self, doc):
-        """
-        Add a conflict and force a document put.
-
-        :param doc: The document to be put.
-        :type doc: CouchDocument
-        """
-        my_doc = self._get_doc(doc.doc_id)
-        self._prune_conflicts(doc, vectorclock.VectorClockRev(doc.rev))
-        doc.add_conflict(self._factory(doc.doc_id, my_doc.rev,
-                                       my_doc.get_json()))
-        doc.has_conflicts = True
-        self._put_doc(my_doc, doc)
-
-    def resolve_doc(self, doc, conflicted_doc_revs):
-        """
-        Mark a document as no longer conflicted.
-
-        We take the list of revisions that the client knows about that it is
-        superseding. This may be a different list from the actual current
-        conflicts, in which case only those are removed as conflicted.  This
-        may fail if the conflict list is significantly different from the
-        supplied information. (sync could have happened in the background from
-        the time you GET_DOC_CONFLICTS until the point where you RESOLVE)
-
-        :param doc: A Document with the new content to be inserted.
-        :type doc: CouchDocument
-        :param conflicted_doc_revs: A list of revisions that the new content
-                                    supersedes.
-        :type conflicted_doc_revs: [str]
-
-        :raise MissingDesignDocError: Raised when tried to access a missing
-                                      design document.
-        :raise MissingDesignDocListFunctionError: Raised when trying to access
-                                                  a missing list function on a
-                                                  design document.
-        :raise MissingDesignDocNamedViewError: Raised when trying to access a
-                                               missing named view on a design
-                                               document.
-        :raise MissingDesignDocDeletedError: Raised when trying to access a
-                                             deleted design document.
-        :raise MissingDesignDocUnknownError: Raised when failed to access a
-                                             design document for an yet
-                                             unknown reason.
-        """
-        cur_doc = self._get_doc(doc.doc_id, check_for_conflicts=True)
-        new_rev = self._ensure_maximal_rev(cur_doc.rev,
-                                           conflicted_doc_revs)
-        superseded_revs = set(conflicted_doc_revs)
-        doc.rev = new_rev
-        # this backend stores conflicts as properties of the documents, so we
-        # have to copy these conflicts over to the document being updated.
-        if cur_doc.rev in superseded_revs:
-            # the newer doc version will supersede the one in the database, so
-            # we copy conflicts before updating the backend.
-            doc.set_conflicts(cur_doc.get_conflicts())  # copy conflicts over.
-            doc.delete_conflicts(superseded_revs)
-            self._put_doc(cur_doc, doc)
-        else:
-            # the newer doc version does not supersede the one in the
-            # database, so we will add a conflict to the database and copy
-            # those over to the document the user has in her hands.
-            cur_doc.add_conflict(doc)
-            cur_doc.delete_conflicts(superseded_revs)
-            self._put_doc(cur_doc, cur_doc)  # just update conflicts
-            # backend has been updated with current conflicts, now copy them
-            # to the current document.
-            doc.set_conflicts(cur_doc.get_conflicts())
-
-    def _put_doc_if_newer(self, doc, save_conflict, replica_uid, replica_gen,
-                          replica_trans_id='', number_of_docs=None,
-                          doc_idx=None, sync_id=None):
-        """
-        Insert/update document into the database with a given revision.
-
-        This api is used during synchronization operations.
-
-        If a document would conflict and save_conflict is set to True, the
-        content will be selected as the 'current' content for doc.doc_id,
-        even though doc.rev doesn't supersede the currently stored revision.
-        The currently stored document will be added to the list of conflict
-        alternatives for the given doc_id.
-
-        This forces the new content to be 'current' so that we get convergence
-        after synchronizing, even if people don't resolve conflicts. Users can
-        then notice that their content is out of date, update it, and
-        synchronize again. (The alternative is that users could synchronize and
-        think the data has propagated, but their local copy looks fine, and the
-        remote copy is never updated again.)
-
-        :param doc: A document object
-        :type doc: CouchDocument
-        :param save_conflict: If this document is a conflict, do you want to
-                              save it as a conflict, or just ignore it.
-        :type save_conflict: bool
-        :param replica_uid: A unique replica identifier.
-        :type replica_uid: str
-        :param replica_gen: The generation of the replica corresponding to the
-                            this document. The replica arguments are optional,
-                            but are used during synchronization.
-        :type replica_gen: int
-        :param replica_trans_id: The transaction_id associated with the
-                                 generation.
-        :type replica_trans_id: str
-        :param number_of_docs: The total amount of documents sent on this sync
-                               session.
-        :type number_of_docs: int
-        :param doc_idx: The index of the current document being sent.
-        :type doc_idx: int
-        :param sync_id: The id of the current sync session.
-        :type sync_id: str
-
-        :return: (state, at_gen) -  If we don't have doc_id already, or if
-                 doc_rev supersedes the existing document revision, then the
-                 content will be inserted, and state is 'inserted'.  If
-                 doc_rev is less than or equal to the existing revision, then
-                 the put is ignored and state is respecitvely 'superseded' or
-                 'converged'.  If doc_rev is not strictly superseded or
-                 supersedes, then state is 'conflicted'. The document will not
-                 be inserted if save_conflict is False.  For 'inserted' or
-                 'converged', at_gen is the insertion/current generation.
-        :rtype: (str, int)
-        """
-        if not isinstance(doc, CouchDocument):
-            doc = self._factory(doc.doc_id, doc.rev, doc.get_json())
-        my_doc = self._get_doc(doc.doc_id, check_for_conflicts=True)
-        if my_doc:
-            doc.set_conflicts(my_doc.get_conflicts())
-        return CommonBackend._put_doc_if_newer(self, doc, save_conflict,
-                                               replica_uid, replica_gen,
-                                               replica_trans_id)
-
-    def _put_and_update_indexes(self, cur_doc, doc):
-        self._put_doc(cur_doc, doc)
-
-    def get_docs(self, doc_ids, check_for_conflicts=True,
-                 include_deleted=False):
-        """
-        Get the JSON content for many documents.
-
-        :param doc_ids: A list of document identifiers or None for all.
-        :type doc_ids: list
-        :param check_for_conflicts: If set to False, then the conflict check
-                                    will be skipped, and 'None' will be
-                                    returned instead of True/False.
-        :type check_for_conflicts: bool
-        :param include_deleted: If set to True, deleted documents will be
-                                returned with empty content. Otherwise deleted
-                                documents will not be included in the results.
-        :return: iterable giving the Document object for each document id
-                 in matching doc_ids order.
-        :rtype: iterable
-        """
-        return self._database.get_docs(doc_ids, check_for_conflicts,
-                                       include_deleted)
-
-    def _prune_conflicts(self, doc, doc_vcr):
-        """
-        Prune conflicts that are older then the current document's revision, or
-        whose content match to the current document's content.
-        Originally in u1db.CommonBackend
-
-        :param doc: The document to have conflicts pruned.
-        :type doc: CouchDocument
-        :param doc_vcr: A vector clock representing the current document's
-                        revision.
-        :type doc_vcr: u1db.vectorclock.VectorClock
-        """
-        if doc.has_conflicts:
-            autoresolved = False
-            c_revs_to_prune = []
-            for c_doc in doc._conflicts:
-                c_vcr = vectorclock.VectorClockRev(c_doc.rev)
-                if doc_vcr.is_newer(c_vcr):
-                    c_revs_to_prune.append(c_doc.rev)
-                elif doc.same_content_as(c_doc):
-                    c_revs_to_prune.append(c_doc.rev)
-                    doc_vcr.maximize(c_vcr)
-                    autoresolved = True
-            if autoresolved:
-                doc_vcr.increment(self._replica_uid)
-                doc.rev = doc_vcr.as_str()
-            doc.delete_conflicts(c_revs_to_prune)
-
-
-class CouchDatabase(object):
-    """
-    Holds CouchDB related code.
-    This class gives methods to encapsulate database operations and hide
-    CouchDB details from backend code.
-    """
-
-    @classmethod
-    def open_database(cls, url, create, ensure_ddocs=False):
-        """
-        Open a U1DB database using CouchDB as backend.
-
-        :param url: the url of the database replica
-        :type url: str
-        :param create: should the replica be created if it does not exist?
-        :type create: bool
-        :param replica_uid: an optional unique replica identifier
-        :type replica_uid: str
-        :param ensure_ddocs: Ensure that the design docs exist on server.
-        :type ensure_ddocs: bool
-
-        :return: the database instance
-        :rtype: SoledadBackend
-        """
-        # get database from url
-        m = re.match('(^https?://[^/]+)/(.+)$', url)
-        if not m:
-            raise InvalidURLError
-        url = m.group(1)
-        dbname = m.group(2)
-        with couch_server(url) as server:
-            try:
-                server[dbname]
-            except ResourceNotFound:
-                if not create:
-                    raise DatabaseDoesNotExist()
-                server.create(dbname)
-        return cls(
-            url, dbname, ensure_ddocs=ensure_ddocs)
-
-    def __init__(self, url, dbname, ensure_ddocs=True,
-                 database_security=None):
-        self._session = Session(timeout=COUCH_TIMEOUT)
-        self._url = url
-        self._dbname = dbname
-        self._database = Database(
-            urljoin(url, dbname),
-            self._session)
-        self._database.info()
-        if ensure_ddocs:
-            self.ensure_ddocs_on_db()
-            self.ensure_security_ddoc(database_security)
-
-    def ensure_ddocs_on_db(self):
-        """
-        Ensure that the design documents used by the backend exist on the
-        couch database.
-        """
-        for ddoc_name in ['docs', 'syncs', 'transactions']:
-            try:
-                self._database.resource('_design',
-                                        ddoc_name, '_info').get_json()
-            except ResourceNotFound:
-                ddoc = json.loads(
-                    binascii.a2b_base64(
-                        getattr(ddocs, ddoc_name)))
-                self._database.save(ddoc)
-
-    def ensure_security_ddoc(self, security_config=None):
-        """
-        Make sure that only soledad user is able to access this database as
-        an unprivileged member, meaning that administration access will
-        be forbidden even inside an user database.
-        The goal is to make sure that only the lowest access level is given
-        to the unprivileged CouchDB user set on the server process.
-        This is achieved by creating a _security design document, see:
-        http://docs.couchdb.org/en/latest/api/database/security.html
-
-        :param database_security: security configuration parsed from conf file
-        :type cache: dict
-        """
-        security_config = security_config or {}
-        security = self._database.resource.get_json('_security')[2]
-        security['members'] = {'names': [], 'roles': []}
-        security['members']['names'] = security_config.get('members',
-                                                           ['soledad'])
-        security['members']['roles'] = security_config.get('members_roles', [])
-        security['admins'] = {'names': [], 'roles': []}
-        security['admins']['names'] = security_config.get('admins', [])
-        security['admins']['roles'] = security_config.get('admins_roles', [])
-        self._database.resource.put_json('_security', body=security)
-
-    def delete_database(self):
-        """
-        Delete a U1DB CouchDB database.
-        """
-        with couch_server(self._url) as server:
-            del(server[self._dbname])
-
-    def set_replica_uid(self, replica_uid):
-        """
-        Force the replica uid to be set.
-
-        :param replica_uid: The new replica uid.
-        :type replica_uid: str
-        """
-        try:
-            # set on existent config document
-            doc = self._database['u1db_config']
-            doc['replica_uid'] = replica_uid
-        except ResourceNotFound:
-            # or create the config document
-            doc = {
-                '_id': 'u1db_config',
-                'replica_uid': replica_uid,
-            }
-        self._database.save(doc)
-
-    def get_replica_uid(self):
-        """
-        Get the replica uid.
-
-        :return: The replica uid.
-        :rtype: str
-        """
-        try:
-            # grab replica_uid from server
-            doc = self._database['u1db_config']
-            replica_uid = doc['replica_uid']
-            return replica_uid
-        except ResourceNotFound:
-            # create a unique replica_uid
-            replica_uid = uuid.uuid4().hex
-            self.set_replica_uid(replica_uid)
-            return replica_uid
-
-    def close(self):
-        self._database = None
-
-    def get_all_docs(self, include_deleted=False):
-        """
-        Get the JSON content for all documents in the database.
-
-        :param include_deleted: If set to True, deleted documents will be
-                                returned with empty content. Otherwise deleted
-                                documents will not be included in the results.
-        :type include_deleted: bool
-
-        :return: (generation, [CouchDocument])
-            The current generation of the database, followed by a list of all
-            the documents in the database.
-        :rtype: (int, [CouchDocument])
-        """
-
-        generation, _ = self._get_generation_info()
-        results = list(self.get_docs(self._database,
-                                     include_deleted=include_deleted))
-        return (generation, results)
-
-    def get_docs(self, doc_ids, check_for_conflicts=True,
-                 include_deleted=False):
-        """
-        Get the JSON content for many documents.
-
-        :param doc_ids: A list of document identifiers or None for all.
-        :type doc_ids: list
-        :param check_for_conflicts: If set to False, then the conflict check
-                                    will be skipped, and 'None' will be
-                                    returned instead of True/False.
-        :type check_for_conflicts: bool
-        :param include_deleted: If set to True, deleted documents will be
-                                returned with empty content. Otherwise deleted
-                                documents will not be included in the results.
-        :return: iterable giving the Document object for each document id
-                 in matching doc_ids order.
-        :rtype: iterable
-        """
-        # Workaround for:
-        #
-        #   http://bugs.python.org/issue7980
-        #   https://leap.se/code/issues/5449
-        #
-        # python-couchdb uses time.strptime, which is not thread safe. In
-        # order to avoid the problem described on the issues above, we preload
-        # strptime here by evaluating the conversion of an arbitrary date.
-        # This will not be needed when/if we switch from python-couchdb to
-        # paisley.
-        time.strptime('Mar 8 1917', '%b %d %Y')
-        get_one = lambda doc_id: self._get_doc(doc_id, check_for_conflicts)
-        docs = [THREAD_POOL.apply_async(get_one, [doc_id])
-                for doc_id in doc_ids]
-        for doc in docs:
-            doc = doc.get()
-            if not doc or not include_deleted and doc.is_tombstone():
-                continue
-            yield doc
-
-    def _get_doc(self, doc_id, check_for_conflicts=False):
-        """
-        Extract the document from storage.
-
-        This can return None if the document doesn't exist.
-
-        :param doc_id: The unique document identifier
-        :type doc_id: str
-        :param check_for_conflicts: If set to False, then the conflict check
-                                    will be skipped.
-        :type check_for_conflicts: bool
-
-        :return: The document.
-        :rtype: CouchDocument
-        """
-        # get document with all attachments (u1db content and eventual
-        # conflicts)
-        try:
-            result = \
-                self._database.resource(doc_id).get_json(
-                    attachments=True)[2]
-        except ResourceNotFound:
-            return None
-        return self.__parse_doc_from_couch(result, doc_id, check_for_conflicts)
-
-    def __parse_doc_from_couch(self, result, doc_id,
-                               check_for_conflicts=False):
-        # restrict to u1db documents
-        if 'u1db_rev' not in result:
-            return None
-        doc = CouchDocument(doc_id, result['u1db_rev'])
-        # set contents or make tombstone
-        if '_attachments' not in result \
-                or 'u1db_content' not in result['_attachments']:
-            doc.make_tombstone()
-        else:
-            doc.content = json.loads(
-                binascii.a2b_base64(
-                    result['_attachments']['u1db_content']['data']))
-        # determine if there are conflicts
-        if check_for_conflicts \
-                and '_attachments' in result \
-                and 'u1db_conflicts' in result['_attachments']:
-            doc.set_conflicts(
-                self._build_conflicts(
-                    doc.doc_id,
-                    json.loads(binascii.a2b_base64(
-                        result['_attachments']['u1db_conflicts']['data']))))
-        # store couch revision
-        doc.couch_rev = result['_rev']
-        # store transactions
-        doc.transactions = result['u1db_transactions']
-        return doc
-
-    def _build_conflicts(self, doc_id, attached_conflicts):
-        """
-        Build the conflicted documents list from the conflicts attachment
-        fetched from a couch document.
-
-        :param attached_conflicts: The document's conflicts as fetched from a
-                                   couch document attachment.
-        :type attached_conflicts: dict
-        """
-        conflicts = []
-        for doc_rev, content in attached_conflicts:
-            doc = CouchDocument(doc_id, doc_rev)
-            if content is None:
-                doc.make_tombstone()
-            else:
-                doc.content = content
-            conflicts.append(doc)
-        return conflicts
-
-    def _get_trans_id_for_gen(self, generation):
-        """
-        Get the transaction id corresponding to a particular generation.
-
-        :param generation: The generation for which to get the transaction id.
-        :type generation: int
-
-        :return: The transaction id for C{generation}.
-        :rtype: str
-
-        :raise InvalidGeneration: Raised when the generation does not exist.
-        :raise MissingDesignDocError: Raised when tried to access a missing
-                                      design document.
-        :raise MissingDesignDocListFunctionError: Raised when trying to access
-                                                  a missing list function on a
-                                                  design document.
-        :raise MissingDesignDocNamedViewError: Raised when trying to access a
-                                               missing named view on a design
-                                               document.
-        :raise MissingDesignDocDeletedError: Raised when trying to access a
-                                             deleted design document.
-        :raise MissingDesignDocUnknownError: Raised when failed to access a
-                                             design document for an yet
-                                             unknown reason.
-        """
-        if generation == 0:
-            return ''
-        # query a couch list function
-        ddoc_path = [
-            '_design', 'transactions', '_list', 'trans_id_for_gen', 'log'
-        ]
-        res = self._database.resource(*ddoc_path)
-        try:
-            response = res.get_json(gen=generation)
-            if response[2] == {}:
-                raise InvalidGeneration
-            return response[2]['transaction_id']
-        except ResourceNotFound as e:
-            raise_missing_design_doc_error(e, ddoc_path)
-        except ServerError as e:
-            raise_server_error(e, ddoc_path)
-
-    def _get_replica_gen_and_trans_id(self, other_replica_uid):
-        """
-        Return the last known generation and transaction id for the other db
-        replica.
-
-        When you do a synchronization with another replica, the Database keeps
-        track of what generation the other database replica was at, and what
-        the associated transaction id was.  This is used to determine what data
-        needs to be sent, and if two databases are claiming to be the same
-        replica.
-
-        :param other_replica_uid: The identifier for the other replica.
-        :type other_replica_uid: str
-
-        :return: A tuple containing the generation and transaction id we
-                 encountered during synchronization. If we've never
-                 synchronized with the replica, this is (0, '').
-        :rtype: (int, str)
-        """
-        doc_id = 'u1db_sync_%s' % other_replica_uid
-        try:
-            doc = self._database[doc_id]
-        except ResourceNotFound:
-            doc = {
-                '_id': doc_id,
-                'generation': 0,
-                'transaction_id': '',
-            }
-            self._database.save(doc)
-        result = doc['generation'], doc['transaction_id']
-        return result
-
-    def get_doc_conflicts(self, doc_id, couch_rev=None):
-        """
-        Get the conflicted versions of a document.
-
-        If the C{couch_rev} parameter is not None, conflicts for a specific
-        document's couch revision are returned.
-
-        :param couch_rev: The couch document revision.
-        :type couch_rev: str
-
-        :return: A list of conflicted versions of the document.
-        :rtype: list
-        """
-        # request conflicts attachment from server
-        params = {}
-        conflicts = []
-        if couch_rev is not None:
-            params['rev'] = couch_rev  # restric document's couch revision
-        else:
-            # TODO: move into resource logic!
-            first_entry = self._get_doc(doc_id, check_for_conflicts=True)
-            conflicts.append(first_entry)
-        resource = self._database.resource(doc_id, 'u1db_conflicts')
-        try:
-            response = resource.get_json(**params)
-            return conflicts + self._build_conflicts(
-                doc_id, json.loads(response[2].read()))
-        except ResourceNotFound:
-            return []
-
-    def _do_set_replica_gen_and_trans_id(
-            self, other_replica_uid, other_generation, other_transaction_id,
-            number_of_docs=None, doc_idx=None, sync_id=None):
-        """
-        Set the last-known generation and transaction id for the other
-        database replica.
-
-        We have just performed some synchronization, and we want to track what
-        generation the other replica was at. See also
-        _get_replica_gen_and_trans_id.
-
-        :param other_replica_uid: The U1DB identifier for the other replica.
-        :type other_replica_uid: str
-        :param other_generation: The generation number for the other replica.
-        :type other_generation: int
-        :param other_transaction_id: The transaction id associated with the
-                                     generation.
-        :type other_transaction_id: str
-        :param number_of_docs: The total amount of documents sent on this sync
-                               session.
-        :type number_of_docs: int
-        :param doc_idx: The index of the current document being sent.
-        :type doc_idx: int
-        :param sync_id: The id of the current sync session.
-        :type sync_id: str
-        """
-        doc_id = 'u1db_sync_%s' % other_replica_uid
-        try:
-            doc = self._database[doc_id]
-        except ResourceNotFound:
-            doc = {'_id': doc_id}
-        doc['generation'] = other_generation
-        doc['transaction_id'] = other_transaction_id
-        self._database.save(doc)
-
-    def _get_transaction_log(self):
-        """
-        This is only for the test suite, it is not part of the api.
-
-        :return: The complete transaction log.
-        :rtype: [(str, str)]
-
-        :raise MissingDesignDocError: Raised when tried to access a missing
-                                      design document.
-        :raise MissingDesignDocListFunctionError: Raised when trying to access
-                                                  a missing list function on a
-                                                  design document.
-        :raise MissingDesignDocNamedViewError: Raised when trying to access a
-                                               missing named view on a design
-                                               document.
-        :raise MissingDesignDocDeletedError: Raised when trying to access a
-                                             deleted design document.
-        :raise MissingDesignDocUnknownError: Raised when failed to access a
-                                             design document for an yet
-                                             unknown reason.
-        """
-        # query a couch view
-        ddoc_path = ['_design', 'transactions', '_view', 'log']
-        res = self._database.resource(*ddoc_path)
-        try:
-            response = res.get_json()
-            return map(
-                lambda row: (row['id'], row['value']),
-                response[2]['rows'])
-        except ResourceNotFound as e:
-            raise_missing_design_doc_error(e, ddoc_path)
-
-    def whats_changed(self, old_generation=0):
-        """
-        Return a list of documents that have changed since old_generation.
-
-        :param old_generation: The generation of the database in the old
-                               state.
-        :type old_generation: int
-
-        :return: (generation, trans_id, [(doc_id, generation, trans_id),...])
-                 The current generation of the database, its associated
-                 transaction id, and a list of of changed documents since
-                 old_generation, represented by tuples with for each document
-                 its doc_id and the generation and transaction id corresponding
-                 to the last intervening change and sorted by generation (old
-                 changes first)
-        :rtype: (int, str, [(str, int, str)])
-
-        :raise MissingDesignDocError: Raised when tried to access a missing
-                                      design document.
-        :raise MissingDesignDocListFunctionError: Raised when trying to access
-                                                  a missing list function on a
-                                                  design document.
-        :raise MissingDesignDocNamedViewError: Raised when trying to access a
-                                               missing named view on a design
-                                               document.
-        :raise MissingDesignDocDeletedError: Raised when trying to access a
-                                             deleted design document.
-        :raise MissingDesignDocUnknownError: Raised when failed to access a
-                                             design document for an yet
-                                             unknown reason.
-        """
-        # query a couch list function
-        ddoc_path = [
-            '_design', 'transactions', '_list', 'whats_changed', 'log'
-        ]
-        res = self._database.resource(*ddoc_path)
-        try:
-            response = res.get_json(old_gen=old_generation)
-            results = map(
-                lambda row:
-                    (row['generation'], row['doc_id'], row['transaction_id']),
-                response[2]['transactions'])
-            results.reverse()
-            cur_gen = old_generation
-            seen = set()
-            changes = []
-            newest_trans_id = ''
-            for generation, doc_id, trans_id in results:
-                if doc_id not in seen:
-                    changes.append((doc_id, generation, trans_id))
-                    seen.add(doc_id)
-            if changes:
-                cur_gen = changes[0][1]  # max generation
-                newest_trans_id = changes[0][2]
-                changes.reverse()
-            else:
-                cur_gen, newest_trans_id = self._get_generation_info()
-
-            return cur_gen, newest_trans_id, changes
-        except ResourceNotFound as e:
-            raise_missing_design_doc_error(e, ddoc_path)
-        except ServerError as e:
-            raise_server_error(e, ddoc_path)
-
-    def _get_generation_info(self):
-        """
-        Return the current generation.
-
-        :return: A tuple containing the current generation and transaction id.
-        :rtype: (int, str)
-
-        :raise MissingDesignDocError: Raised when tried to access a missing
-                                      design document.
-        :raise MissingDesignDocListFunctionError: Raised when trying to access
-                                                  a missing list function on a
-                                                  design document.
-        :raise MissingDesignDocNamedViewError: Raised when trying to access a
-                                               missing named view on a design
-                                               document.
-        :raise MissingDesignDocDeletedError: Raised when trying to access a
-                                             deleted design document.
-        :raise MissingDesignDocUnknownError: Raised when failed to access a
-                                             design document for an yet
-                                             unknown reason.
-        """
-        # query a couch list function
-        ddoc_path = ['_design', 'transactions', '_list', 'generation', 'log']
-        res = self._database.resource(*ddoc_path)
-        try:
-            response = res.get_json()
-            return (response[2]['generation'], response[2]['transaction_id'])
-        except ResourceNotFound as e:
-            raise_missing_design_doc_error(e, ddoc_path)
-        except ServerError as e:
-            raise_server_error(e, ddoc_path)
-
-    def save_document(self, old_doc, doc, transaction_id):
-        """
-        Put the document in the Couch backend database.
-
-        Note that C{old_doc} must have been fetched with the parameter
-        C{check_for_conflicts} equal to True, so we can properly update the
-        new document using the conflict information from the old one.
-
-        :param old_doc: The old document version.
-        :type old_doc: CouchDocument
-        :param doc: The document to be put.
-        :type doc: CouchDocument
-
-        :raise RevisionConflict: Raised when trying to update a document but
-                                 couch revisions mismatch.
-        :raise MissingDesignDocError: Raised when tried to access a missing
-                                      design document.
-        :raise MissingDesignDocListFunctionError: Raised when trying to access
-                                                  a missing list function on a
-                                                  design document.
-        :raise MissingDesignDocNamedViewError: Raised when trying to access a
-                                               missing named view on a design
-                                               document.
-        :raise MissingDesignDocDeletedError: Raised when trying to access a
-                                             deleted design document.
-        :raise MissingDesignDocUnknownError: Raised when failed to access a
-                                             design document for an yet
-                                             unknown reason.
-        """
-        attachments = {}  # we save content and conflicts as attachments
-        parts = []  # and we put it using couch's multipart PUT
-        # save content as attachment
-        if doc.is_tombstone() is False:
-            content = doc.get_json()
-            attachments['u1db_content'] = {
-                'follows': True,
-                'content_type': 'application/octet-stream',
-                'length': len(content),
-            }
-            parts.append(content)
-        # save conflicts as attachment
-        if doc.has_conflicts is True:
-            conflicts = json.dumps(
-                map(lambda cdoc: (cdoc.rev, cdoc.content),
-                    doc.get_conflicts()))
-            attachments['u1db_conflicts'] = {
-                'follows': True,
-                'content_type': 'application/octet-stream',
-                'length': len(conflicts),
-            }
-            parts.append(conflicts)
-        # store old transactions, if any
-        transactions = old_doc.transactions[:] if old_doc is not None else []
-        # create a new transaction id and timestamp it so the transaction log
-        # is consistent when querying the database.
-        transactions.append(
-            # here we store milliseconds to keep consistent with javascript
-            # Date.prototype.getTime() which was used before inside a couchdb
-            # update handler.
-            (int(time.time() * 1000),
-             transaction_id))
-        # build the couch document
-        couch_doc = {
-            '_id': doc.doc_id,
-            'u1db_rev': doc.rev,
-            'u1db_transactions': transactions,
-            '_attachments': attachments,
-        }
-        # if we are updating a doc we have to add the couch doc revision
-        if old_doc is not None:
-            couch_doc['_rev'] = old_doc.couch_rev
-        # prepare the multipart PUT
-        buf = StringIO()
-        headers = {}
-        envelope = MultipartWriter(buf, headers=headers, subtype='related')
-        envelope.add('application/json', json.dumps(couch_doc))
-        for part in parts:
-            envelope.add('application/octet-stream', part)
-        envelope.close()
-        # try to save and fail if there's a revision conflict
-        try:
-            resource = self._new_resource()
-            resource.put_json(
-                doc.doc_id, body=str(buf.getvalue()), headers=headers)
-        except ResourceConflict:
-            raise RevisionConflict()
-        return transactions[-1][1]
-
-    def _new_resource(self, *path):
-        """
-        Return a new resource for accessing a couch database.
-
-        :return: A resource for accessing a couch database.
-        :rtype: couchdb.http.Resource
-        """
-        # Workaround for: https://leap.se/code/issues/5448
-        url = couch_urljoin(self._database.resource.url, *path)
-        resource = Resource(url, Session(timeout=COUCH_TIMEOUT))
-        resource.credentials = self._database.resource.credentials
-        resource.headers = self._database.resource.headers.copy()
-        return resource
-
-
-class CouchSyncTarget(CommonSyncTarget):
-
-    """
-    Functionality for using a SoledadBackend as a synchronization target.
-    """
-
-    def get_sync_info(self, source_replica_uid):
-        source_gen, source_trans_id = self._db._get_replica_gen_and_trans_id(
-            source_replica_uid)
-        my_gen, my_trans_id = self._db._get_generation_info()
-        return (
-            self._db._replica_uid, my_gen, my_trans_id, source_gen,
-            source_trans_id)
-
-    def record_sync_info(self, source_replica_uid, source_replica_generation,
-                         source_replica_transaction_id):
-        if self._trace_hook:
-            self._trace_hook('record_sync_info')
-        self._db._set_replica_gen_and_trans_id(
-            source_replica_uid, source_replica_generation,
-            source_replica_transaction_id)
-
-
-def is_db_name_valid(name):
-    """
-    Validate a user database using a regular expression.
-
-    :param name: database name.
-    :type name: str
-
-    :return: boolean for name vailidity
-    :rtype: bool
-    """
-    db_name_regex = "^user-[a-f0-9]+$"
-    return re.match(db_name_regex, name) is not None
-
-
-class CouchServerState(ServerState):
-
-    """
-    Inteface of the WSGI server with the CouchDB backend.
-    """
-
-    def __init__(self, couch_url, create_cmd=None):
-        """
-        Initialize the couch server state.
-
-        :param couch_url: The URL for the couch database.
-        :type couch_url: str
-        """
-        self.couch_url = couch_url
-        self.create_cmd = create_cmd
-
-    def open_database(self, dbname):
-        """
-        Open a couch database.
-
-        :param dbname: The name of the database to open.
-        :type dbname: str
-
-        :return: The SoledadBackend object.
-        :rtype: SoledadBackend
-        """
-        url = urljoin(self.couch_url, dbname)
-        db = SoledadBackend.open_database(url, create=False,
-                                          ensure_ddocs=False)
-        return db
-
-    def ensure_database(self, dbname):
-        """
-        Ensure couch database exists.
-
-        :param dbname: The name of the database to ensure.
-        :type dbname: str
-
-        :raise Unauthorized: If disabled or other error was raised.
-
-        :return: The SoledadBackend object and its replica_uid.
-        :rtype: (SoledadBackend, str)
-        """
-        if not self.create_cmd:
-            raise Unauthorized()
-        else:
-            code, out = exec_validated_cmd(self.create_cmd, dbname,
-                                           validator=is_db_name_valid)
-            if code is not 0:
-                logger.error("""
-                    Error while creating database (%s) with (%s) command.
-                    Output: %s
-                    Exit code: %d
-                    """ % (dbname, self.create_cmd, out, code))
-                raise Unauthorized()
-        db = self.open_database(dbname)
-        return db, db.replica_uid
-
-    def delete_database(self, dbname):
-        """
-        Delete couch database.
-
-        :param dbname: The name of the database to delete.
-        :type dbname: str
-
-        :raise Unauthorized: Always, because Soledad server is not allowed to
-                             delete databases.
-        """
-        raise Unauthorized()
diff --git a/common/src/leap/soledad/common/couch/__init__.py b/common/src/leap/soledad/common/couch/__init__.py
new file mode 100644
index 00000000..727f033f
--- /dev/null
+++ b/common/src/leap/soledad/common/couch/__init__.py
@@ -0,0 +1,746 @@
+# -*- coding: utf-8 -*-
+# couch.py
+# Copyright (C) 2013 LEAP
+#
+# 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 3 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, see <http://www.gnu.org/licenses/>.
+
+
+"""A U1DB backend that uses CouchDB as its persistence layer."""
+
+
+import json
+import re
+import uuid
+import binascii
+import time
+
+
+from StringIO import StringIO
+from urlparse import urljoin
+from contextlib import contextmanager
+from multiprocessing.pool import ThreadPool
+
+
+from couchdb.client import Server, Database
+from couchdb.multipart import MultipartWriter
+from couchdb.http import (
+    ResourceConflict,
+    ResourceNotFound,
+    ServerError,
+    Session,
+    urljoin as couch_urljoin,
+    Resource,
+)
+from u1db.errors import (
+    DatabaseDoesNotExist,
+    InvalidGeneration,
+    RevisionConflict,
+)
+from u1db.remote import http_app
+
+
+from leap.soledad.common import ddocs
+from leap.soledad.common.errors import raise_server_error
+from leap.soledad.common.errors import raise_missing_design_doc_error
+from leap.soledad.common.errors import InvalidURLError
+from leap.soledad.common.document import CouchDocument
+from leap.soledad.common.backend import SoledadBackend
+
+
+COUCH_TIMEOUT = 120  # timeout for transfers between Soledad server and Couch
+
+
+def list_users_dbs(couch_url):
+    """
+    Retrieves a list with all databases that starts with 'user-' on CouchDB.
+    Those databases belongs to users. So, the list will contain all the
+    database names in the form of 'user-{uuid4}'.
+
+    :param couch_url: The couch url with needed credentials
+    :type couch_url: str
+
+    :return: The list of all database names from users.
+    :rtype: [str]
+    """
+    with couch_server(couch_url) as server:
+        users = [dbname for dbname in server if dbname.startswith('user-')]
+    return users
+
+
+# monkey-patch the u1db http app to use CouchDocument
+http_app.Document = CouchDocument
+
+
+@contextmanager
+def couch_server(url):
+    """
+    Provide a connection to a couch server and cleanup after use.
+
+    For database creation and deletion we use an ephemeral connection to the
+    couch server. That connection has to be properly closed, so we provide it
+    as a context manager.
+
+    :param url: The URL of the Couch server.
+    :type url: str
+    """
+    session = Session(timeout=COUCH_TIMEOUT)
+    server = Server(url=url, full_commit=False, session=session)
+    yield server
+
+
+THREAD_POOL = ThreadPool(20)
+
+
+class CouchDatabase(object):
+    """
+    Holds CouchDB related code.
+    This class gives methods to encapsulate database operations and hide
+    CouchDB details from backend code.
+    """
+
+    @classmethod
+    def open_database(cls, url, create, ensure_ddocs=False, replica_uid=None,
+                      database_security=None):
+        """
+        Open a U1DB database using CouchDB as backend.
+
+        :param url: the url of the database replica
+        :type url: str
+        :param create: should the replica be created if it does not exist?
+        :type create: bool
+        :param replica_uid: an optional unique replica identifier
+        :type replica_uid: str
+        :param ensure_ddocs: Ensure that the design docs exist on server.
+        :type ensure_ddocs: bool
+
+        :return: the database instance
+        :rtype: SoledadBackend
+        """
+        # get database from url
+        m = re.match('(^https?://[^/]+)/(.+)$', url)
+        if not m:
+            raise InvalidURLError
+        url = m.group(1)
+        dbname = m.group(2)
+        with couch_server(url) as server:
+            try:
+                server[dbname]
+            except ResourceNotFound:
+                if not create:
+                    raise DatabaseDoesNotExist()
+                server.create(dbname)
+        db = cls(url,
+                 dbname, ensure_ddocs=ensure_ddocs,
+                 database_security=database_security)
+        return SoledadBackend(
+            db, replica_uid=replica_uid)
+
+    def __init__(self, url, dbname, ensure_ddocs=True,
+                 database_security=None):
+        self._session = Session(timeout=COUCH_TIMEOUT)
+        self._url = url
+        self._dbname = dbname
+        self._database = Database(
+            urljoin(url, dbname),
+            self._session)
+        self._database.info()
+        if ensure_ddocs:
+            self.ensure_ddocs_on_db()
+            self.ensure_security_ddoc(database_security)
+
+    def ensure_ddocs_on_db(self):
+        """
+        Ensure that the design documents used by the backend exist on the
+        couch database.
+        """
+        for ddoc_name in ['docs', 'syncs', 'transactions']:
+            try:
+                self._database.resource('_design',
+                                        ddoc_name, '_info').get_json()
+            except ResourceNotFound:
+                ddoc = json.loads(
+                    binascii.a2b_base64(
+                        getattr(ddocs, ddoc_name)))
+                self._database.save(ddoc)
+
+    def ensure_security_ddoc(self, security_config=None):
+        """
+        Make sure that only soledad user is able to access this database as
+        an unprivileged member, meaning that administration access will
+        be forbidden even inside an user database.
+        The goal is to make sure that only the lowest access level is given
+        to the unprivileged CouchDB user set on the server process.
+        This is achieved by creating a _security design document, see:
+        http://docs.couchdb.org/en/latest/api/database/security.html
+
+        :param database_security: security configuration parsed from conf file
+        :type cache: dict
+        """
+        security_config = security_config or {}
+        security = self._database.resource.get_json('_security')[2]
+        security['members'] = {'names': [], 'roles': []}
+        security['members']['names'] = security_config.get('members',
+                                                           ['soledad'])
+        security['members']['roles'] = security_config.get('members_roles', [])
+        security['admins'] = {'names': [], 'roles': []}
+        security['admins']['names'] = security_config.get('admins', [])
+        security['admins']['roles'] = security_config.get('admins_roles', [])
+        self._database.resource.put_json('_security', body=security)
+
+    def delete_database(self):
+        """
+        Delete a U1DB CouchDB database.
+        """
+        with couch_server(self._url) as server:
+            del(server[self._dbname])
+
+    def set_replica_uid(self, replica_uid):
+        """
+        Force the replica uid to be set.
+
+        :param replica_uid: The new replica uid.
+        :type replica_uid: str
+        """
+        try:
+            # set on existent config document
+            doc = self._database['u1db_config']
+            doc['replica_uid'] = replica_uid
+        except ResourceNotFound:
+            # or create the config document
+            doc = {
+                '_id': 'u1db_config',
+                'replica_uid': replica_uid,
+            }
+        self._database.save(doc)
+
+    def get_replica_uid(self):
+        """
+        Get the replica uid.
+
+        :return: The replica uid.
+        :rtype: str
+        """
+        try:
+            # grab replica_uid from server
+            doc = self._database['u1db_config']
+            replica_uid = doc['replica_uid']
+            return replica_uid
+        except ResourceNotFound:
+            # create a unique replica_uid
+            replica_uid = uuid.uuid4().hex
+            self.set_replica_uid(replica_uid)
+            return replica_uid
+
+    def close(self):
+        self._database = None
+
+    def get_all_docs(self, include_deleted=False):
+        """
+        Get the JSON content for all documents in the database.
+
+        :param include_deleted: If set to True, deleted documents will be
+                                returned with empty content. Otherwise deleted
+                                documents will not be included in the results.
+        :type include_deleted: bool
+
+        :return: (generation, [CouchDocument])
+            The current generation of the database, followed by a list of all
+            the documents in the database.
+        :rtype: (int, [CouchDocument])
+        """
+
+        generation, _ = self._get_generation_info()
+        results = list(self.get_docs(self._database,
+                                     include_deleted=include_deleted))
+        return (generation, results)
+
+    def get_docs(self, doc_ids, check_for_conflicts=True,
+                 include_deleted=False):
+        """
+        Get the JSON content for many documents.
+
+        :param doc_ids: A list of document identifiers or None for all.
+        :type doc_ids: list
+        :param check_for_conflicts: If set to False, then the conflict check
+                                    will be skipped, and 'None' will be
+                                    returned instead of True/False.
+        :type check_for_conflicts: bool
+        :param include_deleted: If set to True, deleted documents will be
+                                returned with empty content. Otherwise deleted
+                                documents will not be included in the results.
+        :return: iterable giving the Document object for each document id
+                 in matching doc_ids order.
+        :rtype: iterable
+        """
+        # Workaround for:
+        #
+        #   http://bugs.python.org/issue7980
+        #   https://leap.se/code/issues/5449
+        #
+        # python-couchdb uses time.strptime, which is not thread safe. In
+        # order to avoid the problem described on the issues above, we preload
+        # strptime here by evaluating the conversion of an arbitrary date.
+        # This will not be needed when/if we switch from python-couchdb to
+        # paisley.
+        time.strptime('Mar 8 1917', '%b %d %Y')
+        get_one = lambda doc_id: self._get_doc(doc_id, check_for_conflicts)
+        docs = [THREAD_POOL.apply_async(get_one, [doc_id])
+                for doc_id in doc_ids]
+        for doc in docs:
+            doc = doc.get()
+            if not doc or not include_deleted and doc.is_tombstone():
+                continue
+            yield doc
+
+    def _get_doc(self, doc_id, check_for_conflicts=False):
+        """
+        Extract the document from storage.
+
+        This can return None if the document doesn't exist.
+
+        :param doc_id: The unique document identifier
+        :type doc_id: str
+        :param check_for_conflicts: If set to False, then the conflict check
+                                    will be skipped.
+        :type check_for_conflicts: bool
+
+        :return: The document.
+        :rtype: CouchDocument
+        """
+        # get document with all attachments (u1db content and eventual
+        # conflicts)
+        try:
+            result = \
+                self._database.resource(doc_id).get_json(
+                    attachments=True)[2]
+        except ResourceNotFound:
+            return None
+        return self.__parse_doc_from_couch(result, doc_id, check_for_conflicts)
+
+    def __parse_doc_from_couch(self, result, doc_id,
+                               check_for_conflicts=False):
+        # restrict to u1db documents
+        if 'u1db_rev' not in result:
+            return None
+        doc = CouchDocument(doc_id, result['u1db_rev'])
+        # set contents or make tombstone
+        if '_attachments' not in result \
+                or 'u1db_content' not in result['_attachments']:
+            doc.make_tombstone()
+        else:
+            doc.content = json.loads(
+                binascii.a2b_base64(
+                    result['_attachments']['u1db_content']['data']))
+        # determine if there are conflicts
+        if check_for_conflicts \
+                and '_attachments' in result \
+                and 'u1db_conflicts' in result['_attachments']:
+            doc.set_conflicts(
+                self._build_conflicts(
+                    doc.doc_id,
+                    json.loads(binascii.a2b_base64(
+                        result['_attachments']['u1db_conflicts']['data']))))
+        # store couch revision
+        doc.couch_rev = result['_rev']
+        # store transactions
+        doc.transactions = result['u1db_transactions']
+        return doc
+
+    def _build_conflicts(self, doc_id, attached_conflicts):
+        """
+        Build the conflicted documents list from the conflicts attachment
+        fetched from a couch document.
+
+        :param attached_conflicts: The document's conflicts as fetched from a
+                                   couch document attachment.
+        :type attached_conflicts: dict
+        """
+        conflicts = []
+        for doc_rev, content in attached_conflicts:
+            doc = CouchDocument(doc_id, doc_rev)
+            if content is None:
+                doc.make_tombstone()
+            else:
+                doc.content = content
+            conflicts.append(doc)
+        return conflicts
+
+    def _get_trans_id_for_gen(self, generation):
+        """
+        Get the transaction id corresponding to a particular generation.
+
+        :param generation: The generation for which to get the transaction id.
+        :type generation: int
+
+        :return: The transaction id for C{generation}.
+        :rtype: str
+
+        :raise InvalidGeneration: Raised when the generation does not exist.
+        :raise MissingDesignDocError: Raised when tried to access a missing
+                                      design document.
+        :raise MissingDesignDocListFunctionError: Raised when trying to access
+                                                  a missing list function on a
+                                                  design document.
+        :raise MissingDesignDocNamedViewError: Raised when trying to access a
+                                               missing named view on a design
+                                               document.
+        :raise MissingDesignDocDeletedError: Raised when trying to access a
+                                             deleted design document.
+        :raise MissingDesignDocUnknownError: Raised when failed to access a
+                                             design document for an yet
+                                             unknown reason.
+        """
+        if generation == 0:
+            return ''
+        # query a couch list function
+        ddoc_path = [
+            '_design', 'transactions', '_list', 'trans_id_for_gen', 'log'
+        ]
+        res = self._database.resource(*ddoc_path)
+        try:
+            response = res.get_json(gen=generation)
+            if response[2] == {}:
+                raise InvalidGeneration
+            return response[2]['transaction_id']
+        except ResourceNotFound as e:
+            raise_missing_design_doc_error(e, ddoc_path)
+        except ServerError as e:
+            raise_server_error(e, ddoc_path)
+
+    def _get_replica_gen_and_trans_id(self, other_replica_uid):
+        """
+        Return the last known generation and transaction id for the other db
+        replica.
+
+        When you do a synchronization with another replica, the Database keeps
+        track of what generation the other database replica was at, and what
+        the associated transaction id was.  This is used to determine what data
+        needs to be sent, and if two databases are claiming to be the same
+        replica.
+
+        :param other_replica_uid: The identifier for the other replica.
+        :type other_replica_uid: str
+
+        :return: A tuple containing the generation and transaction id we
+                 encountered during synchronization. If we've never
+                 synchronized with the replica, this is (0, '').
+        :rtype: (int, str)
+        """
+        doc_id = 'u1db_sync_%s' % other_replica_uid
+        try:
+            doc = self._database[doc_id]
+        except ResourceNotFound:
+            doc = {
+                '_id': doc_id,
+                'generation': 0,
+                'transaction_id': '',
+            }
+            self._database.save(doc)
+        result = doc['generation'], doc['transaction_id']
+        return result
+
+    def get_doc_conflicts(self, doc_id, couch_rev=None):
+        """
+        Get the conflicted versions of a document.
+
+        If the C{couch_rev} parameter is not None, conflicts for a specific
+        document's couch revision are returned.
+
+        :param couch_rev: The couch document revision.
+        :type couch_rev: str
+
+        :return: A list of conflicted versions of the document.
+        :rtype: list
+        """
+        # request conflicts attachment from server
+        params = {}
+        conflicts = []
+        if couch_rev is not None:
+            params['rev'] = couch_rev  # restric document's couch revision
+        else:
+            # TODO: move into resource logic!
+            first_entry = self._get_doc(doc_id, check_for_conflicts=True)
+            conflicts.append(first_entry)
+        resource = self._database.resource(doc_id, 'u1db_conflicts')
+        try:
+            response = resource.get_json(**params)
+            return conflicts + self._build_conflicts(
+                doc_id, json.loads(response[2].read()))
+        except ResourceNotFound:
+            return []
+
+    def _do_set_replica_gen_and_trans_id(
+            self, other_replica_uid, other_generation, other_transaction_id,
+            number_of_docs=None, doc_idx=None, sync_id=None):
+        """
+        Set the last-known generation and transaction id for the other
+        database replica.
+
+        We have just performed some synchronization, and we want to track what
+        generation the other replica was at. See also
+        _get_replica_gen_and_trans_id.
+
+        :param other_replica_uid: The U1DB identifier for the other replica.
+        :type other_replica_uid: str
+        :param other_generation: The generation number for the other replica.
+        :type other_generation: int
+        :param other_transaction_id: The transaction id associated with the
+                                     generation.
+        :type other_transaction_id: str
+        :param number_of_docs: The total amount of documents sent on this sync
+                               session.
+        :type number_of_docs: int
+        :param doc_idx: The index of the current document being sent.
+        :type doc_idx: int
+        :param sync_id: The id of the current sync session.
+        :type sync_id: str
+        """
+        doc_id = 'u1db_sync_%s' % other_replica_uid
+        try:
+            doc = self._database[doc_id]
+        except ResourceNotFound:
+            doc = {'_id': doc_id}
+        doc['generation'] = other_generation
+        doc['transaction_id'] = other_transaction_id
+        self._database.save(doc)
+
+    def _get_transaction_log(self):
+        """
+        This is only for the test suite, it is not part of the api.
+
+        :return: The complete transaction log.
+        :rtype: [(str, str)]
+
+        :raise MissingDesignDocError: Raised when tried to access a missing
+                                      design document.
+        :raise MissingDesignDocListFunctionError: Raised when trying to access
+                                                  a missing list function on a
+                                                  design document.
+        :raise MissingDesignDocNamedViewError: Raised when trying to access a
+                                               missing named view on a design
+                                               document.
+        :raise MissingDesignDocDeletedError: Raised when trying to access a
+                                             deleted design document.
+        :raise MissingDesignDocUnknownError: Raised when failed to access a
+                                             design document for an yet
+                                             unknown reason.
+        """
+        # query a couch view
+        ddoc_path = ['_design', 'transactions', '_view', 'log']
+        res = self._database.resource(*ddoc_path)
+        try:
+            response = res.get_json()
+            return map(
+                lambda row: (row['id'], row['value']),
+                response[2]['rows'])
+        except ResourceNotFound as e:
+            raise_missing_design_doc_error(e, ddoc_path)
+
+    def whats_changed(self, old_generation=0):
+        """
+        Return a list of documents that have changed since old_generation.
+
+        :param old_generation: The generation of the database in the old
+                               state.
+        :type old_generation: int
+
+        :return: (generation, trans_id, [(doc_id, generation, trans_id),...])
+                 The current generation of the database, its associated
+                 transaction id, and a list of of changed documents since
+                 old_generation, represented by tuples with for each document
+                 its doc_id and the generation and transaction id corresponding
+                 to the last intervening change and sorted by generation (old
+                 changes first)
+        :rtype: (int, str, [(str, int, str)])
+
+        :raise MissingDesignDocError: Raised when tried to access a missing
+                                      design document.
+        :raise MissingDesignDocListFunctionError: Raised when trying to access
+                                                  a missing list function on a
+                                                  design document.
+        :raise MissingDesignDocNamedViewError: Raised when trying to access a
+                                               missing named view on a design
+                                               document.
+        :raise MissingDesignDocDeletedError: Raised when trying to access a
+                                             deleted design document.
+        :raise MissingDesignDocUnknownError: Raised when failed to access a
+                                             design document for an yet
+                                             unknown reason.
+        """
+        # query a couch list function
+        ddoc_path = [
+            '_design', 'transactions', '_list', 'whats_changed', 'log'
+        ]
+        res = self._database.resource(*ddoc_path)
+        try:
+            response = res.get_json(old_gen=old_generation)
+            results = map(
+                lambda row:
+                    (row['generation'], row['doc_id'], row['transaction_id']),
+                response[2]['transactions'])
+            results.reverse()
+            cur_gen = old_generation
+            seen = set()
+            changes = []
+            newest_trans_id = ''
+            for generation, doc_id, trans_id in results:
+                if doc_id not in seen:
+                    changes.append((doc_id, generation, trans_id))
+                    seen.add(doc_id)
+            if changes:
+                cur_gen = changes[0][1]  # max generation
+                newest_trans_id = changes[0][2]
+                changes.reverse()
+            else:
+                cur_gen, newest_trans_id = self._get_generation_info()
+
+            return cur_gen, newest_trans_id, changes
+        except ResourceNotFound as e:
+            raise_missing_design_doc_error(e, ddoc_path)
+        except ServerError as e:
+            raise_server_error(e, ddoc_path)
+
+    def _get_generation_info(self):
+        """
+        Return the current generation.
+
+        :return: A tuple containing the current generation and transaction id.
+        :rtype: (int, str)
+
+        :raise MissingDesignDocError: Raised when tried to access a missing
+                                      design document.
+        :raise MissingDesignDocListFunctionError: Raised when trying to access
+                                                  a missing list function on a
+                                                  design document.
+        :raise MissingDesignDocNamedViewError: Raised when trying to access a
+                                               missing named view on a design
+                                               document.
+        :raise MissingDesignDocDeletedError: Raised when trying to access a
+                                             deleted design document.
+        :raise MissingDesignDocUnknownError: Raised when failed to access a
+                                             design document for an yet
+                                             unknown reason.
+        """
+        # query a couch list function
+        ddoc_path = ['_design', 'transactions', '_list', 'generation', 'log']
+        res = self._database.resource(*ddoc_path)
+        try:
+            response = res.get_json()
+            return (response[2]['generation'], response[2]['transaction_id'])
+        except ResourceNotFound as e:
+            raise_missing_design_doc_error(e, ddoc_path)
+        except ServerError as e:
+            raise_server_error(e, ddoc_path)
+
+    def save_document(self, old_doc, doc, transaction_id):
+        """
+        Put the document in the Couch backend database.
+
+        Note that C{old_doc} must have been fetched with the parameter
+        C{check_for_conflicts} equal to True, so we can properly update the
+        new document using the conflict information from the old one.
+
+        :param old_doc: The old document version.
+        :type old_doc: CouchDocument
+        :param doc: The document to be put.
+        :type doc: CouchDocument
+
+        :raise RevisionConflict: Raised when trying to update a document but
+                                 couch revisions mismatch.
+        :raise MissingDesignDocError: Raised when tried to access a missing
+                                      design document.
+        :raise MissingDesignDocListFunctionError: Raised when trying to access
+                                                  a missing list function on a
+                                                  design document.
+        :raise MissingDesignDocNamedViewError: Raised when trying to access a
+                                               missing named view on a design
+                                               document.
+        :raise MissingDesignDocDeletedError: Raised when trying to access a
+                                             deleted design document.
+        :raise MissingDesignDocUnknownError: Raised when failed to access a
+                                             design document for an yet
+                                             unknown reason.
+        """
+        attachments = {}  # we save content and conflicts as attachments
+        parts = []  # and we put it using couch's multipart PUT
+        # save content as attachment
+        if doc.is_tombstone() is False:
+            content = doc.get_json()
+            attachments['u1db_content'] = {
+                'follows': True,
+                'content_type': 'application/octet-stream',
+                'length': len(content),
+            }
+            parts.append(content)
+        # save conflicts as attachment
+        if doc.has_conflicts is True:
+            conflicts = json.dumps(
+                map(lambda cdoc: (cdoc.rev, cdoc.content),
+                    doc.get_conflicts()))
+            attachments['u1db_conflicts'] = {
+                'follows': True,
+                'content_type': 'application/octet-stream',
+                'length': len(conflicts),
+            }
+            parts.append(conflicts)
+        # store old transactions, if any
+        transactions = old_doc.transactions[:] if old_doc is not None else []
+        # create a new transaction id and timestamp it so the transaction log
+        # is consistent when querying the database.
+        transactions.append(
+            # here we store milliseconds to keep consistent with javascript
+            # Date.prototype.getTime() which was used before inside a couchdb
+            # update handler.
+            (int(time.time() * 1000),
+             transaction_id))
+        # build the couch document
+        couch_doc = {
+            '_id': doc.doc_id,
+            'u1db_rev': doc.rev,
+            'u1db_transactions': transactions,
+            '_attachments': attachments,
+        }
+        # if we are updating a doc we have to add the couch doc revision
+        if old_doc is not None:
+            couch_doc['_rev'] = old_doc.couch_rev
+        # prepare the multipart PUT
+        buf = StringIO()
+        headers = {}
+        envelope = MultipartWriter(buf, headers=headers, subtype='related')
+        envelope.add('application/json', json.dumps(couch_doc))
+        for part in parts:
+            envelope.add('application/octet-stream', part)
+        envelope.close()
+        # try to save and fail if there's a revision conflict
+        try:
+            resource = self._new_resource()
+            resource.put_json(
+                doc.doc_id, body=str(buf.getvalue()), headers=headers)
+        except ResourceConflict:
+            raise RevisionConflict()
+        return transactions[-1][1]
+
+    def _new_resource(self, *path):
+        """
+        Return a new resource for accessing a couch database.
+
+        :return: A resource for accessing a couch database.
+        :rtype: couchdb.http.Resource
+        """
+        # Workaround for: https://leap.se/code/issues/5448
+        url = couch_urljoin(self._database.resource.url, *path)
+        resource = Resource(url, Session(timeout=COUCH_TIMEOUT))
+        resource.credentials = self._database.resource.credentials
+        resource.headers = self._database.resource.headers.copy()
+        return resource
diff --git a/common/src/leap/soledad/common/couch/state.py b/common/src/leap/soledad/common/couch/state.py
new file mode 100644
index 00000000..39d49fa0
--- /dev/null
+++ b/common/src/leap/soledad/common/couch/state.py
@@ -0,0 +1,114 @@
+# -*- coding: utf-8 -*-
+# state.py
+# Copyright (C) 2015 LEAP
+#
+# 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 3 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, see <http://www.gnu.org/licenses/>.
+"""
+Server state using CouchDatabase as backend.
+"""
+import re
+import logging
+from urlparse import urljoin
+
+from u1db.remote.server_state import ServerState
+from leap.soledad.common.command import exec_validated_cmd
+from leap.soledad.common.couch import CouchDatabase
+from u1db.errors import Unauthorized
+
+
+logger = logging.getLogger(__name__)
+
+
+def is_db_name_valid(name):
+    """
+    Validate a user database using a regular expression.
+
+    :param name: database name.
+    :type name: str
+
+    :return: boolean for name vailidity
+    :rtype: bool
+    """
+    db_name_regex = "^user-[a-f0-9]+$"
+    return re.match(db_name_regex, name) is not None
+
+
+class CouchServerState(ServerState):
+
+    """
+    Inteface of the WSGI server with the CouchDB backend.
+    """
+
+    def __init__(self, couch_url, create_cmd=None):
+        """
+        Initialize the couch server state.
+
+        :param couch_url: The URL for the couch database.
+        :type couch_url: str
+        """
+        self.couch_url = couch_url
+        self.create_cmd = create_cmd
+
+    def open_database(self, dbname):
+        """
+        Open a couch database.
+
+        :param dbname: The name of the database to open.
+        :type dbname: str
+
+        :return: The SoledadBackend object.
+        :rtype: SoledadBackend
+        """
+        url = urljoin(self.couch_url, dbname)
+        db = CouchDatabase.open_database(url, create=False, ensure_ddocs=False)
+        return db
+
+    def ensure_database(self, dbname):
+        """
+        Ensure couch database exists.
+
+        :param dbname: The name of the database to ensure.
+        :type dbname: str
+
+        :raise Unauthorized: If disabled or other error was raised.
+
+        :return: The SoledadBackend object and its replica_uid.
+        :rtype: (SoledadBackend, str)
+        """
+        if not self.create_cmd:
+            raise Unauthorized()
+        else:
+            code, out = exec_validated_cmd(self.create_cmd, dbname,
+                                           validator=is_db_name_valid)
+            if code is not 0:
+                logger.error("""
+                    Error while creating database (%s) with (%s) command.
+                    Output: %s
+                    Exit code: %d
+                    """ % (dbname, self.create_cmd, out, code))
+                raise Unauthorized()
+        db = self.open_database(dbname)
+        return db, db.replica_uid
+
+    def delete_database(self, dbname):
+        """
+        Delete couch database.
+
+        :param dbname: The name of the database to delete.
+        :type dbname: str
+
+        :raise Unauthorized: Always, because Soledad server is not allowed to
+                             delete databases.
+        """
+        raise Unauthorized()
diff --git a/common/src/leap/soledad/common/errors.py b/common/src/leap/soledad/common/errors.py
index ea9d6ce4..84d8d813 100644
--- a/common/src/leap/soledad/common/errors.py
+++ b/common/src/leap/soledad/common/errors.py
@@ -266,4 +266,4 @@ def raise_server_error(exc, ddoc_path):
         if 'point is undefined' in exc.message[1][1]:
             raise MissingDesignDocListFunctionError
     # other errors are unknown for now
-    raise DesignDocUnknownError(path)
+    raise DesignDocUnknownError("%s: %s" % (path, str(exc.message)))
diff --git a/common/src/leap/soledad/common/tests/test_couch.py b/common/src/leap/soledad/common/tests/test_couch.py
index b3536a6a..1634d30c 100644
--- a/common/src/leap/soledad/common/tests/test_couch.py
+++ b/common/src/leap/soledad/common/tests/test_couch.py
@@ -36,6 +36,7 @@ from u1db import SyncTarget
 from u1db import vectorclock
 
 from leap.soledad.common import couch
+from leap.soledad.common import backend
 from leap.soledad.common import errors
 
 from leap.soledad.common.tests import u1db_tests as tests
@@ -56,7 +57,7 @@ from u1db.backends.inmemory import InMemoryIndex
 class TestCouchBackendImpl(CouchDBTestCase):
 
     def test__allocate_doc_id(self):
-        db = couch.SoledadBackend.open_database(
+        db = couch.CouchDatabase.open_database(
             urljoin(
                 'http://localhost:' + str(self.couch_port),
                 ('test-%s' % uuid4().hex)
@@ -78,7 +79,7 @@ class TestCouchBackendImpl(CouchDBTestCase):
 def make_couch_database_for_test(test, replica_uid):
     port = str(test.couch_port)
     dbname = ('test-%s' % uuid4().hex)
-    db = couch.SoledadBackend.open_database(
+    db = couch.CouchDatabase.open_database(
         urljoin('http://localhost:' + port, dbname),
         create=True,
         replica_uid=replica_uid or 'test',
@@ -91,7 +92,7 @@ def copy_couch_database_for_test(test, db):
     port = str(test.couch_port)
     couch_url = 'http://localhost:' + port
     new_dbname = db._dbname + '_copy'
-    new_db = couch.SoledadBackend.open_database(
+    new_db = couch.CouchDatabase.open_database(
         urljoin(couch_url, new_dbname),
         create=True,
         replica_uid=db._replica_uid or 'test')
@@ -529,89 +530,6 @@ class SoledadBackendSyncTargetTests(
         self.st.record_sync_info('replica', 0, 'T-sid')
         self.assertEqual(expected, called)
 
-
-# The following tests need that the database have an index, so we fake one.
-
-class IndexedSoledadBackend(couch.SoledadBackend):
-
-    def __init__(self, db, replica_uid=None):
-        old_class.__init__(self, db, replica_uid=replica_uid)
-        self._indexes = {}
-
-    def _put_doc(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())
-        old_class._put_doc(self, old_doc, doc)
-
-    def create_index(self, index_name, *index_expressions):
-        if index_name in self._indexes:
-            if self._indexes[index_name]._definition == list(
-                    index_expressions):
-                return
-            raise u1db_errors.IndexNameTakenError
-        index = InMemoryIndex(index_name, list(index_expressions))
-        _, all_docs = self.get_all_docs()
-        for doc in all_docs:
-            index.add_json(doc.doc_id, doc.get_json())
-        self._indexes[index_name] = index
-
-    def delete_index(self, index_name):
-        del self._indexes[index_name]
-
-    def list_indexes(self):
-        definitions = []
-        for idx in self._indexes.itervalues():
-            definitions.append((idx._name, idx._definition))
-        return definitions
-
-    def get_from_index(self, index_name, *key_values):
-        try:
-            index = self._indexes[index_name]
-        except KeyError:
-            raise u1db_errors.IndexDoesNotExist
-        doc_ids = index.lookup(key_values)
-        result = []
-        for doc_id in doc_ids:
-            result.append(self._get_doc(doc_id, check_for_conflicts=True))
-        return result
-
-    def get_range_from_index(self, index_name, start_value=None,
-                             end_value=None):
-        """Return all documents with key values in the specified range."""
-        try:
-            index = self._indexes[index_name]
-        except KeyError:
-            raise u1db_errors.IndexDoesNotExist
-        if isinstance(start_value, basestring):
-            start_value = (start_value,)
-        if isinstance(end_value, basestring):
-            end_value = (end_value,)
-        doc_ids = index.lookup_range(start_value, end_value)
-        result = []
-        for doc_id in doc_ids:
-            result.append(self._get_doc(doc_id, check_for_conflicts=True))
-        return result
-
-    def get_index_keys(self, index_name):
-        try:
-            index = self._indexes[index_name]
-        except KeyError:
-            raise u1db_errors.IndexDoesNotExist
-        keys = index.keys()
-        # XXX inefficiency warning
-        return list(set([tuple(key.split('\x01')) for key in keys]))
-
-
-# monkey patch SoledadBackend (once) to include virtual indexes
-if getattr(couch.SoledadBackend, '_old_class', None) is None:
-    old_class = couch.SoledadBackend
-    IndexedSoledadBackend._old_class = old_class
-    couch.SoledadBackend = IndexedSoledadBackend
-
-
 sync_scenarios = []
 for name, scenario in COUCH_SCENARIOS:
     scenario = dict(scenario)
@@ -921,7 +839,6 @@ class SoledadBackendSyncTests(
         self.db1 = self.create_database('test1', 'source')
         self.db2 = self.create_database('test2', 'target')
         doc = self.db2.create_doc_from_json(simple_doc)
-        self.db1.create_index('test-idx', 'key')
         self.assertEqual(0, self.sync(self.db1, self.db2))
         self.assertGetDoc(self.db1, doc.doc_id, doc.rev, simple_doc, False)
         self.assertEqual(1, self.db1._get_replica_gen_and_trans_id('test2')[0])
@@ -931,7 +848,7 @@ class SoledadBackendSyncTests(
             {'receive': {'docs': [], 'last_known_gen': 0},
              'return': {'docs': [(doc.doc_id, doc.rev)],
                         'last_gen': 1}})
-        self.assertEqual([doc], self.db1.get_from_index('test-idx', 'value'))
+        self.assertGetDoc(self.db2, doc.doc_id, doc.rev, simple_doc, False)
 
     def test_sync_pulling_doesnt_update_other_if_changed(self):
         self.db1 = self.create_database('test1', 'source')
@@ -1020,7 +937,7 @@ class SoledadBackendSyncTests(
         doc1 = self.db1.create_doc_from_json(simple_doc)
         doc_id = doc1.doc_id
         doc1_rev = doc1.rev
-        self.db1.create_index('test-idx', 'key')
+        # self.db1.create_index('test-idx', 'key')
         new_doc = '{"key": "altval"}'
         doc2 = self.db2.create_doc_from_json(new_doc, doc_id=doc_id)
         doc2_rev = doc2.rev
@@ -1036,18 +953,18 @@ class SoledadBackendSyncTests(
         self.assertTransactionLog([doc_id, doc_id], self.db1)
         self.assertGetDoc(self.db1, doc_id, doc2_rev, new_doc, True)
         self.assertGetDoc(self.db2, doc_id, doc2_rev, new_doc, False)
-        from_idx = self.db1.get_from_index('test-idx', 'altval')[0]
-        self.assertEqual(doc2.doc_id, from_idx.doc_id)
-        self.assertEqual(doc2.rev, from_idx.rev)
-        self.assertTrue(from_idx.has_conflicts)
-        self.assertEqual([], self.db1.get_from_index('test-idx', 'value'))
+        # soledad doesnt support index due to encryption
+        # from_idx = self.db1.get_from_index('test-idx', 'altval')[0]
+        # self.assertEqual(doc2.doc_id, from_idx.doc_id)
+        # self.assertEqual(doc2.rev, from_idx.rev)
+        # self.assertTrue(from_idx.has_conflicts)
+        # self.assertEqual([], self.db1.get_from_index('test-idx', 'value'))
 
     def test_sync_sees_remote_delete_conflicted(self):
         self.db1 = self.create_database('test1', 'source')
         self.db2 = self.create_database('test2', 'target')
         doc1 = self.db1.create_doc_from_json(simple_doc)
         doc_id = doc1.doc_id
-        self.db1.create_index('test-idx', 'key')
         self.sync(self.db1, self.db2)
         doc2 = self.make_document(doc1.doc_id, doc1.rev, doc1.get_json())
         new_doc = '{"key": "altval"}'
@@ -1067,7 +984,6 @@ class SoledadBackendSyncTests(
         self.assertGetDocIncludeDeleted(self.db1, doc_id, doc2.rev, None, True)
         self.assertGetDocIncludeDeleted(
             self.db2, doc_id, doc2.rev, None, False)
-        self.assertEqual([], self.db1.get_from_index('test-idx', 'value'))
 
     def test_sync_local_race_conflicted(self):
         self.db1 = self.create_database('test1', 'source')
@@ -1075,7 +991,7 @@ class SoledadBackendSyncTests(
         doc = self.db1.create_doc_from_json(simple_doc)
         doc_id = doc.doc_id
         doc1_rev = doc.rev
-        self.db1.create_index('test-idx', 'key')
+        # self.db1.create_index('test-idx', 'key')
         self.sync(self.db1, self.db2)
         content1 = '{"key": "localval"}'
         content2 = '{"key": "altval"}'
@@ -1094,21 +1010,22 @@ class SoledadBackendSyncTests(
         self.sync(self.db1, self.db2, trace_hook=after_whatschanged)
         self.assertEqual([True], triggered)
         self.assertGetDoc(self.db1, doc_id, doc2_rev2, content2, True)
-        from_idx = self.db1.get_from_index('test-idx', 'altval')[0]
-        self.assertEqual(doc.doc_id, from_idx.doc_id)
-        self.assertEqual(doc.rev, from_idx.rev)
-        self.assertTrue(from_idx.has_conflicts)
-        self.assertEqual([], self.db1.get_from_index('test-idx', 'value'))
-        self.assertEqual([], self.db1.get_from_index('test-idx', 'localval'))
+        # soledad doesnt support indexing due to encryption
+        # from_idx = self.db1.get_from_index('test-idx', 'altval')[0]
+        # self.assertEqual(doc.doc_id, from_idx.doc_id)
+        # self.assertEqual(doc.rev, from_idx.rev)
+        # self.assertTrue(from_idx.has_conflicts)
+        # self.assertEqual([], self.db1.get_from_index('test-idx', 'value'))
+        # self.assertEqual([], self.db1.get_from_index('test-idx', 'localval'))
 
     def test_sync_propagates_deletes(self):
         self.db1 = self.create_database('test1', 'source')
         self.db2 = self.create_database('test2', 'both')
         doc1 = self.db1.create_doc_from_json(simple_doc)
         doc_id = doc1.doc_id
-        self.db1.create_index('test-idx', 'key')
+        # self.db1.create_index('test-idx', 'key')
         self.sync(self.db1, self.db2)
-        self.db2.create_index('test-idx', 'key')
+        # self.db2.create_index('test-idx', 'key')
         self.db3 = self.create_database('test3', 'target')
         self.sync(self.db1, self.db3)
         self.db1.delete_doc(doc1)
@@ -1124,8 +1041,8 @@ class SoledadBackendSyncTests(
             self.db1, doc_id, deleted_rev, None, False)
         self.assertGetDocIncludeDeleted(
             self.db2, doc_id, deleted_rev, None, False)
-        self.assertEqual([], self.db1.get_from_index('test-idx', 'value'))
-        self.assertEqual([], self.db2.get_from_index('test-idx', 'value'))
+        # self.assertEqual([], self.db1.get_from_index('test-idx', 'value'))
+        # self.assertEqual([], self.db2.get_from_index('test-idx', 'value'))
         self.sync(self.db2, self.db3)
         self.assertLastExchangeLog(
             self.db3,
@@ -1324,9 +1241,11 @@ class SoledadBackendExceptionsTests(CouchDBTestCase):
     def create_db(self, ensure=True, dbname=None):
         if not dbname:
             dbname = ('test-%s' % uuid4().hex)
-        self.db = couch.CouchDatabase.open_database(
-            urljoin('http://127.0.0.1:%d' % self.couch_port, dbname),
-            create=True,
+        if dbname not in self.couch_server:
+            self.couch_server.create(dbname)
+        self.db = couch.CouchDatabase(
+            ('http://127.0.0.1:%d' % self.couch_port),
+            dbname,
             ensure_ddocs=ensure)
 
     def tearDown(self):
@@ -1520,14 +1439,14 @@ class SoledadBackendExceptionsTests(CouchDBTestCase):
 class DatabaseNameValidationTest(unittest.TestCase):
 
     def test_database_name_validation(self):
-        self.assertFalse(couch.is_db_name_valid("user-deadbeef | cat /secret"))
-        self.assertTrue(couch.is_db_name_valid("user-cafe1337"))
+        self.assertFalse(couch.state.is_db_name_valid("user-deadbeef | cat /secret"))
+        self.assertTrue(couch.state.is_db_name_valid("user-cafe1337"))
 
 
 class CommandBasedDBCreationTest(unittest.TestCase):
 
     def test_ensure_db_using_custom_command(self):
-        state = couch.CouchServerState("url", create_cmd="echo")
+        state = couch.state.CouchServerState("url", create_cmd="echo")
         mock_db = Mock()
         mock_db.replica_uid = 'replica_uid'
         state.open_database = Mock(return_value=mock_db)
@@ -1536,11 +1455,11 @@ class CommandBasedDBCreationTest(unittest.TestCase):
         self.assertEquals(mock_db.replica_uid, replica_uid)
 
     def test_raises_unauthorized_on_failure(self):
-        state = couch.CouchServerState("url", create_cmd="inexistent")
+        state = couch.state.CouchServerState("url", create_cmd="inexistent")
         self.assertRaises(u1db_errors.Unauthorized,
                           state.ensure_database, "user-1337")
 
     def test_raises_unauthorized_by_default(self):
-        state = couch.CouchServerState("url")
+        state = couch.state.CouchServerState("url")
         self.assertRaises(u1db_errors.Unauthorized,
                           state.ensure_database, "user-1337")
diff --git a/common/src/leap/soledad/common/tests/test_couch_operations_atomicity.py b/common/src/leap/soledad/common/tests/test_couch_operations_atomicity.py
index 2c2daf05..8cd3ae08 100644
--- a/common/src/leap/soledad/common/tests/test_couch_operations_atomicity.py
+++ b/common/src/leap/soledad/common/tests/test_couch_operations_atomicity.py
@@ -26,7 +26,8 @@ from twisted.internet import defer
 from uuid import uuid4
 
 from leap.soledad.client import Soledad
-from leap.soledad.common.couch import SoledadBackend, CouchServerState
+from leap.soledad.common.couch.state import CouchServerState
+from leap.soledad.common.couch import CouchDatabase
 
 from leap.soledad.common.tests.util import (
     make_token_soledad_app,
@@ -86,7 +87,7 @@ class CouchAtomicityTestCase(CouchDBTestCase, TestCaseWithServer):
         TestCaseWithServer.setUp(self)
         CouchDBTestCase.setUp(self)
         self.user = ('user-%s' % uuid4().hex)
-        self.db = SoledadBackend.open_database(
+        self.db = CouchDatabase.open_database(
             urljoin(self.couch_url, 'user-' + self.user),
             create=True,
             replica_uid='replica',
diff --git a/common/src/leap/soledad/common/tests/test_server.py b/common/src/leap/soledad/common/tests/test_server.py
index 5810ce31..d75275d6 100644
--- a/common/src/leap/soledad/common/tests/test_server.py
+++ b/common/src/leap/soledad/common/tests/test_server.py
@@ -29,10 +29,8 @@ from urlparse import urljoin
 from twisted.internet import defer
 from twisted.trial import unittest
 
-from leap.soledad.common.couch import (
-    CouchServerState,
-    SoledadBackend,
-)
+from leap.soledad.common.couch.state import CouchServerState
+from leap.soledad.common.couch import CouchDatabase
 from leap.soledad.common.tests.u1db_tests import TestCaseWithServer
 from leap.soledad.common.tests.test_couch import CouchDBTestCase
 from leap.soledad.common.tests.util import (
@@ -358,7 +356,7 @@ class EncryptedSyncTestCase(
             passphrase=passphrase)
 
         # ensure remote db exists before syncing
-        db = SoledadBackend.open_database(
+        db = CouchDatabase.open_database(
             urljoin(self.couch_url, 'user-' + user),
             create=True,
             ensure_ddocs=True)
@@ -488,7 +486,7 @@ class LockResourceTestCase(
         self.tempdir = tempfile.mkdtemp(prefix="leap_tests-")
         TestCaseWithServer.setUp(self)
         # create the databases
-        db = SoledadBackend.open_database(
+        db = CouchDatabase.open_database(
             urljoin(self.couch_url, ('shared-%s' % (uuid4().hex))),
             create=True,
             ensure_ddocs=True)
diff --git a/common/src/leap/soledad/common/tests/test_sync_mutex.py b/common/src/leap/soledad/common/tests/test_sync_mutex.py
index 35cecb8f..973a8587 100644
--- a/common/src/leap/soledad/common/tests/test_sync_mutex.py
+++ b/common/src/leap/soledad/common/tests/test_sync_mutex.py
@@ -33,7 +33,8 @@ from twisted.internet import defer
 
 from leap.soledad.client.sync import SoledadSynchronizer
 
-from leap.soledad.common import couch
+from leap.soledad.common.couch.state import CouchServerState
+from leap.soledad.common.couch import CouchDatabase
 from leap.soledad.common.tests.u1db_tests import TestCaseWithServer
 from leap.soledad.common.tests.test_couch import CouchDBTestCase
 
@@ -84,7 +85,7 @@ class TestSyncMutex(
     sync_target = soledad_sync_target
 
     def make_app(self):
-        self.request_state = couch.CouchServerState(self.couch_url)
+        self.request_state = CouchServerState(self.couch_url)
         return self.make_app_with_state(self.request_state)
 
     def setUp(self):
@@ -102,7 +103,7 @@ class TestSyncMutex(
         self.startServer()
 
         # ensure remote db exists before syncing
-        db = couch.SoledadBackend.open_database(
+        db = CouchDatabase.open_database(
             urljoin(self.couch_url, 'user-' + self.user),
             create=True,
             ensure_ddocs=True)
diff --git a/common/src/leap/soledad/common/tests/test_sync_target.py b/common/src/leap/soledad/common/tests/test_sync_target.py
index 0cf31c3f..f25e84dd 100644
--- a/common/src/leap/soledad/common/tests/test_sync_target.py
+++ b/common/src/leap/soledad/common/tests/test_sync_target.py
@@ -29,7 +29,6 @@ from uuid import uuid4
 
 from testscenarios import TestWithScenarios
 from twisted.internet import defer
-from urlparse import urljoin
 
 from leap.soledad.client import http_target as target
 from leap.soledad.client import crypto
@@ -37,7 +36,6 @@ from leap.soledad.client.sqlcipher import SQLCipherU1DBSync
 from leap.soledad.client.sqlcipher import SQLCipherOptions
 from leap.soledad.client.sqlcipher import SQLCipherDatabase
 
-from leap.soledad.common import couch
 from leap.soledad.common.document import SoledadDocument
 
 from leap.soledad.common.tests import u1db_tests as tests
@@ -265,9 +263,9 @@ class TestSoledadSyncTarget(
                                      replica_trans_id=replica_trans_id,
                                      number_of_docs=number_of_docs,
                                      doc_idx=doc_idx, sync_id=sync_id)
-        from leap.soledad.common.tests.test_couch import IndexedSoledadBackend
+        from leap.soledad.common.backend import SoledadBackend
         self.patch(
-            IndexedSoledadBackend, '_put_doc_if_newer', bomb_put_doc_if_newer)
+            SoledadBackend, '_put_doc_if_newer', bomb_put_doc_if_newer)
         remote_target = self.getSyncTarget(
             source_replica_uid='replica')
         other_changes = []
diff --git a/common/src/leap/soledad/common/tests/util.py b/common/src/leap/soledad/common/tests/util.py
index bfd06856..f7f9ebd0 100644
--- a/common/src/leap/soledad/common/tests/util.py
+++ b/common/src/leap/soledad/common/tests/util.py
@@ -27,7 +27,6 @@ import shutil
 import random
 import string
 import u1db
-import traceback
 import couchdb
 
 from uuid import uuid4
@@ -37,17 +36,17 @@ from StringIO import StringIO
 from pysqlcipher import dbapi2
 
 from u1db import sync
-from u1db.errors import DatabaseDoesNotExist
 from u1db.remote import http_database
 
 from twisted.trial import unittest
 
-from leap.common.files import mkdir_p
 from leap.common.testing.basetest import BaseLeapTest
 
 from leap.soledad.common import soledad_assert
 from leap.soledad.common.document import SoledadDocument
-from leap.soledad.common.couch import SoledadBackend, CouchServerState
+from leap.soledad.common.couch import CouchDatabase
+from leap.soledad.common.couch.state import CouchServerState
+
 from leap.soledad.common.crypto import ENC_SCHEME_KEY
 
 from leap.soledad.client import Soledad
@@ -379,7 +378,7 @@ class CouchServerStateForTests(CouchServerState):
         Create db and append to a list, allowing test to close it later
         """
         dbname = dbname or ('test-%s' % uuid4().hex)
-        db = SoledadBackend.open_database(
+        db = CouchDatabase.open_database(
             urljoin(self.couch_url, dbname),
             True,
             replica_uid=replica_uid or 'test',