[feature] use twisted.web.client in client sync

This change uses twisted deferreds for the whole syncing process and paves the
way to implementing other transport schemes. It removes a lot of threaded code
that used locks and was very difficult to maintain, and lets twisted to the
dirty work. Furthermore, all blocking network i/o is now handled
asynchronously by the twisted.

This commit removes the possibility of interrupting a sync, and we should
reimplement it using cancellable deferreds if we need it.

5 files changed, 634 insertions, 1549 deletions

diff --git a/client/src/leap/soledad/client/encdecpool.py b/client/src/leap/soledad/client/encdecpool.py
index 0c1f92ea..7c21c30e 100644
--- a/client/src/leap/soledad/client/encdecpool.py
+++ b/client/src/leap/soledad/client/encdecpool.py
@@ -789,12 +789,5 @@ class SyncDecrypterPool(SyncEncryptDecryptPool):
             self._exception = e
         self._finished.set()
 
-    def wait(self):
-        """
-        Wait for the decrypt-and-process loop to finish.
-        """
-        logger.debug("Waiting for asynchronous decryption of incoming documents...")
-        self._finished.wait()
-        logger.debug("Asynchronous decryption of incoming documents finished.")
-        if self._exception:
-            raise self._exception
+    def has_finished(self):
+        return self._finished.is_set()
diff --git a/client/src/leap/soledad/client/http_target.py b/client/src/leap/soledad/client/http_target.py
new file mode 100644
index 00000000..041180e6
--- /dev/null
+++ b/client/src/leap/soledad/client/http_target.py
@@ -0,0 +1,570 @@
+# -*- coding: utf-8 -*-
+# target.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 backend for encrypting data before sending to server and decrypting
+after receiving.
+"""
+
+import json
+import base64
+import logging
+
+from zope.proxy import setProxiedObject
+from zope.proxy import ProxyBase
+from uuid import uuid4
+from functools import partial
+from collections import defaultdict
+
+from twisted.internet import defer
+from twisted.internet import reactor
+from twisted.web.client import getPage
+
+from u1db import errors
+from u1db import SyncTarget
+from u1db.remote import utils
+
+from leap.soledad.common.document import SoledadDocument
+
+from leap.soledad.client.crypto import is_symmetrically_encrypted
+from leap.soledad.client.crypto import encrypt_doc
+from leap.soledad.client.crypto import decrypt_doc
+from leap.soledad.client.events import SOLEDAD_SYNC_SEND_STATUS
+from leap.soledad.client.events import SOLEDAD_SYNC_RECEIVE_STATUS
+from leap.soledad.client.events import signal
+from leap.soledad.client.encdecpool import SyncDecrypterPool
+
+
+logger = logging.getLogger(__name__)
+
+
+class SoledadHTTPSyncTarget(SyncTarget):
+    """
+    A SyncTarget that encrypts data before sending and decrypts data after
+    receiving.
+
+    Normally encryption will have been written to the sync database upon
+    document modification. The sync database is also used to write temporarily
+    the parsed documents that the remote send us, before being decrypted and
+    written to the main database.
+    """
+
+    # will later keep a reference to the insert-doc callback
+    # passed to sync_exchange
+    _insert_doc_cb = defaultdict(lambda: ProxyBase(None))
+
+    def __init__(self, url, source_replica_uid, creds, crypto,
+            sync_db=None, sync_enc_pool=None):
+        """
+        Initialize the sync target.
+
+        :param url: The server sync url.
+        :type url: str
+        :param source_replica_uid: The source replica uid which we use when
+                                   deferring decryption.
+        :type source_replica_uid: str
+        :param url: The url of the target replica to sync with.
+        :type url: str
+        :param creds: A dictionary containing the uuid and token.
+        :type creds: creds
+        :param crypto: An instance of SoledadCrypto so we can encrypt/decrypt
+                        document contents when syncing.
+        :type crypto: soledad.crypto.SoledadCrypto
+        :param sync_db: Optional. handler for the db with the symmetric
+                        encryption of the syncing documents. If
+                        None, encryption will be done in-place,
+                        instead of retreiving it from the dedicated
+                        database.
+        :type sync_db: Sqlite handler
+        """
+        if url.endswith("/"):
+            url = url[:-1]
+        self._url = str(url) + "/sync-from/" + source_replica_uid
+        self.source_replica_uid = source_replica_uid
+        self._auth_header = None
+        self.set_creds(creds)
+        self._crypto = crypto
+        self._sync_db = sync_db
+        self._sync_enc_pool = sync_enc_pool
+        # asynchronous encryption/decryption attributes
+        self._decryption_callback = None
+        self._sync_decr_pool = None
+
+    def set_creds(self, creds):
+        """
+        Update credentials.
+
+        :param creds: A dictionary containing the uuid and token.
+        :type creds: dict
+        """
+        uuid = creds['token']['uuid']
+        token = creds['token']['token']
+        auth = '%s:%s' % (uuid, token)
+        b64_token = base64.b64encode(auth)
+        self._auth_header = {'Authorization': 'Token %s' % b64_token}
+
+    @property
+    def _defer_encryption(self):
+        return self._sync_enc_pool is not None
+
+    #
+    # SyncTarget API
+    # 
+
+    @defer.inlineCallbacks
+    def get_sync_info(self, source_replica_uid):
+        """
+        Return information about known state of remote database.
+
+        Return the replica_uid and the current database generation of the
+        remote database, and its last-seen database generation for the client
+        replica.
+
+        :param source_replica_uid: The client-size replica uid.
+        :type source_replica_uid: str
+
+        :return: A deferred which fires with (target_replica_uid,
+                 target_replica_generation, target_trans_id,
+                 source_replica_last_known_generation,
+                 source_replica_last_known_transaction_id)
+        :rtype: twisted.internet.defer.Deferred
+        """
+        raw = yield getPage(self._url, headers=self._auth_header)
+        res = json.loads(raw)
+        defer.returnValue([
+            res['target_replica_uid'],
+            res['target_replica_generation'],
+            res['target_replica_transaction_id'],
+            res['source_replica_generation'],
+            res['source_transaction_id']
+        ])
+
+    def record_sync_info(
+            self, source_replica_uid, source_replica_generation,
+            source_replica_transaction_id):
+        """
+        Record tip information for another replica.
+
+        After sync_exchange has been processed, the caller will have
+        received new content from this replica. This call allows the
+        source replica instigating the sync to inform us what their
+        generation became after applying the documents we returned.
+
+        This is used to allow future sync operations to not need to repeat data
+        that we just talked about. It also means that if this is called at the
+        wrong time, there can be database records that will never be
+        synchronized.
+
+        :param source_replica_uid: The identifier for the source replica.
+        :type source_replica_uid: str
+        :param source_replica_generation: The database generation for the
+                                          source replica.
+        :type source_replica_generation: int
+        :param source_replica_transaction_id: The transaction id associated
+                                              with the source replica
+                                              generation.
+        :type source_replica_transaction_id: str
+
+        :return: A deferred which fires with the result of the query.
+        :rtype: twisted.internet.defer.Deferred
+        """
+        data = json.dumps({
+            'generation': source_replica_generation,
+            'transaction_id': source_replica_transaction_id
+        })
+        headers = self._auth_header.copy()
+        headers.update({'content-type': 'application/json'})
+        return getPage(
+            self._url,
+            method='PUT',
+            headers=headers,
+            postdata=data)
+
+    @defer.inlineCallbacks
+    def sync_exchange(self, docs_by_generation, source_replica_uid,
+                      last_known_generation, last_known_trans_id,
+                      return_doc_cb, ensure_callback=None,
+                      defer_decryption=True, sync_id=None):
+        """
+        Find out which documents the remote database does not know about,
+        encrypt and send them. After that, receive documents from the remote
+        database.
+
+        :param docs_by_generations: A list of (doc_id, generation, trans_id)
+                                    of local documents that were changed since
+                                    the last local generation the remote
+                                    replica knows about.
+        :type docs_by_generations: list of tuples
+
+        :param source_replica_uid: The uid of the source replica.
+        :type source_replica_uid: str
+
+        :param last_known_generation: Target's last known generation.
+        :type last_known_generation: int
+
+        :param last_known_trans_id: Target's last known transaction id.
+        :type last_known_trans_id: str
+
+        :param return_doc_cb: A callback for inserting received documents from
+                              target. If not overriden, this will call u1db
+                              insert_doc_from_target in synchronizer, which
+                              implements the TAKE OTHER semantics.
+        :type return_doc_cb: function
+
+        :param ensure_callback: A callback that ensures we know the target
+                                replica uid if the target replica was just
+                                created.
+        :type ensure_callback: function
+
+        :param defer_decryption: Whether to defer the decryption process using
+                                 the intermediate database. If False,
+                                 decryption will be done inline.
+        :type defer_decryption: bool
+
+        :return: A deferred which fires with the new generation and
+                 transaction id of the target replica.
+        :rtype: twisted.internet.defer.Deferred
+        """
+
+        self._ensure_callback = ensure_callback
+
+        if sync_id is None:
+            sync_id = str(uuid4())
+        self.source_replica_uid = source_replica_uid
+
+        # let the decrypter pool access the passed callback to insert docs
+        setProxiedObject(self._insert_doc_cb[source_replica_uid],
+                         return_doc_cb)
+
+        gen_after_send, trans_id_after_send = yield self._send_docs(
+            docs_by_generation,
+            last_known_generation,
+            last_known_trans_id,
+            sync_id)
+
+        cur_target_gen, cur_target_trans_id = yield self._receive_docs(
+            last_known_generation, last_known_trans_id,
+            return_doc_cb, ensure_callback, sync_id,
+            defer_decryption=defer_decryption)
+
+        # update gen and trans id info in case we just sent and did not
+        # receive docs.
+        if gen_after_send is not None and gen_after_send > cur_target_gen:
+            cur_target_gen = gen_after_send
+            cur_target_trans_id = trans_id_after_send
+
+        defer.returnValue([cur_target_gen, cur_target_trans_id])
+
+    #
+    # methods to send docs
+    #
+
+    def _prepare(self, comma, entries, **dic):
+        entry = comma + '\r\n' + json.dumps(dic)
+        entries.append(entry)
+        return len(entry)
+
+    @defer.inlineCallbacks
+    def _send_docs(self, docs_by_generation, last_known_generation,
+            last_known_trans_id, sync_id):
+
+        if not docs_by_generation:
+            defer.returnValue([None, None])
+
+        headers = self._auth_header.copy()
+        headers.update({'content-type': 'application/x-soledad-sync-put'})
+        # add remote replica metadata to the request
+        first_entries = ['[']
+        self._prepare(
+            '', first_entries,
+            last_known_generation=last_known_generation,
+            last_known_trans_id=last_known_trans_id,
+            sync_id=sync_id,
+            ensure=self._ensure_callback is not None)
+        idx = 0
+        total = len(docs_by_generation)
+        for doc, gen, trans_id in docs_by_generation:
+            idx += 1
+            result = yield self._send_one_doc(
+                headers, first_entries, doc,
+                gen, trans_id, total, idx)
+            if self._defer_encryption:
+                self._sync_enc_pool.delete_encrypted_doc(
+                    doc.doc_id, doc.rev)
+            signal(SOLEDAD_SYNC_SEND_STATUS,
+                "Soledad sync send status: %d/%d"
+                % (idx, total))
+        response_dict = json.loads(result)[0]
+        gen_after_send = response_dict['new_generation']
+        trans_id_after_send = response_dict['new_transaction_id']
+        defer.returnValue([gen_after_send, trans_id_after_send])
+
+    @defer.inlineCallbacks
+    def _send_one_doc(self, headers, first_entries, doc, gen, trans_id,
+            number_of_docs, doc_idx):
+        entries = first_entries[:]
+        # add the document to the request
+        content = yield self._encrypt_doc(doc)
+        self._prepare(
+            ',', entries,
+            id=doc.doc_id, rev=doc.rev, content=content, gen=gen,
+            trans_id=trans_id, number_of_docs=number_of_docs,
+            doc_idx=doc_idx)
+        entries.append('\r\n]')
+        data = ''.join(entries)
+        result = yield getPage(
+            self._url,
+            method='POST',
+            headers=headers,
+            postdata=data)
+        defer.returnValue(result)
+
+    def _encrypt_doc(self, doc):
+        d = None
+        if doc.is_tombstone():
+            d = defer.succeed(None)
+        elif not self._defer_encryption:
+            # fallback case, for tests
+            d = defer.succeed(encrypt_doc(self._crypto, doc))
+        else:
+
+            def _maybe_encrypt_doc_inline(doc_json):
+                if doc_json is None:
+                    # the document is not marked as tombstone, but we got
+                    # nothing from the sync db. As it is not encrypted
+                    # yet, we force inline encryption.
+                    return encrypt_doc(self._crypto, doc)
+                return doc_json
+
+            d = self._sync_enc_pool.get_encrypted_doc(doc.doc_id, doc.rev)
+            d.addCallback(_maybe_encrypt_doc_inline)
+        return d
+    
+    #
+    # methods to receive doc
+    #
+
+    @defer.inlineCallbacks
+    def _receive_docs(self, last_known_generation, last_known_trans_id,
+                      return_doc_cb, ensure_callback, sync_id,
+                      defer_decryption):
+        # we keep a reference to the callback in case we defer the decryption
+        self._return_doc_cb = return_doc_cb
+        self._queue_for_decrypt = defer_decryption \
+            and self._sync_db is not None
+
+        new_generation = last_known_generation
+        new_transaction_id = last_known_trans_id
+
+        if self._queue_for_decrypt:
+            logger.debug(
+                "Soledad sync: will queue received docs for decrypting.")
+
+        if defer_decryption:
+            self._setup_sync_decr_pool()
+
+        headers = self._auth_header.copy()
+        headers.update({'content-type': 'application/x-soledad-sync-get'})
+
+        # maybe get one doc
+        d = self._receive_one_doc(
+            headers, last_known_generation, last_known_trans_id,
+            sync_id, 0)
+        d.addCallback(partial(self._insert_received_doc, 1, 1))
+        number_of_changes, ngen, ntrans = yield d
+
+        if defer_decryption:
+            self._sync_decr_pool.set_docs_to_process(
+                number_of_changes)
+        idx = 1
+
+        # maybe get more documents
+        deferreds = []
+        while idx < number_of_changes:
+            d = self._receive_one_doc(
+                headers, last_known_generation,
+                last_known_trans_id, sync_id, idx)
+            d.addCallback(
+                partial(
+                    self._insert_received_doc,
+                    idx + 1,
+                    number_of_changes))
+            deferreds.append(d)
+            idx += 1
+        results = yield defer.gatherResults(deferreds)
+
+        # get genration and transaction id of target after insertions
+        if deferreds:
+            _, new_generation, new_transaction_id = results.pop()
+
+        # get current target gen and trans id in case no documents were
+        def _shutdown_and_finish(res):
+            self._sync_decr_pool.close()
+            return new_generation, new_transaction_id
+
+        d = defer.Deferred()
+        d.addCallback(_shutdown_and_finish)
+
+        def _wait_or_finish():
+            if not self._sync_decr_pool.has_finished():
+                reactor.callLater(
+                    SyncDecrypterPool.DECRYPT_LOOP_PERIOD,
+                    _wait_or_finish)
+            else:
+                d.callback(None)
+
+        # decrypt docs in case of deferred decryption
+        if defer_decryption:
+            _wait_or_finish()
+        else:
+            d.callback(None)
+
+        new_generation, new_transaction_id = yield d
+        defer.returnValue([new_generation, new_transaction_id])
+
+    def _receive_one_doc(self, headers, last_known_generation,
+            last_known_trans_id, sync_id, received):
+        entries = ['[']
+        # add remote replica metadata to the request
+        self._prepare(
+            '', entries,
+            last_known_generation=last_known_generation,
+            last_known_trans_id=last_known_trans_id,
+            sync_id=sync_id,
+            ensure=self._ensure_callback is not None)
+        # inform server of how many documents have already been received
+        self._prepare(
+            ',', entries, received=received)
+        entries.append('\r\n]')
+        # send headers
+        return getPage(
+            self._url,
+            method='POST',
+            headers=headers,
+            postdata=''.join(entries))
+
+    def _insert_received_doc(self, idx, total, response):
+        """
+        Insert a received document into the local replica.
+
+        :param idx: The index count of the current operation.
+        :type idx: int
+        :param total: The total number of operations.
+        :type total: int
+        :param response: The body and headers of the response.
+        :type response: tuple(str, dict)
+        """
+        new_generation, new_transaction_id, number_of_changes, doc_id, \
+            rev, content, gen, trans_id = \
+            self._parse_received_doc_response(response)
+        if doc_id is not None:
+            print doc_id
+            # decrypt incoming document and insert into local database
+            # -------------------------------------------------------------
+            # symmetric decryption of document's contents
+            # -------------------------------------------------------------
+            # If arriving content was symmetrically encrypted, we decrypt it.
+            # We do it inline if defer_decryption flag is False or no sync_db
+            # was defined, otherwise we defer it writing it to the received
+            # docs table.
+            doc = SoledadDocument(doc_id, rev, content)
+            if is_symmetrically_encrypted(doc):
+                if self._queue_for_decrypt:
+                    self._sync_decr_pool.insert_encrypted_received_doc(
+                        doc.doc_id, doc.rev, doc.content, gen, trans_id,
+                        idx)
+                else:
+                    # defer_decryption is False or no-sync-db fallback
+                    doc.set_json(decrypt_doc(self._crypto, doc))
+                    self._return_doc_cb(doc, gen, trans_id)
+            else:
+                # not symmetrically encrypted doc, insert it directly
+                # or save it in the decrypted stage.
+                if self._queue_for_decrypt:
+                    self._sync_decr_pool.insert_received_doc(
+                        doc.doc_id, doc.rev, doc.content, gen, trans_id,
+                        idx)
+                else:
+                    self._return_doc_cb(doc, gen, trans_id)
+            # -------------------------------------------------------------
+            # end of symmetric decryption
+            # -------------------------------------------------------------
+        msg = "%d/%d" % (idx, total)
+        signal(SOLEDAD_SYNC_RECEIVE_STATUS, msg)
+        logger.debug("Soledad sync receive status: %s" % msg)
+        return number_of_changes, new_generation, new_transaction_id
+
+    def _parse_received_doc_response(self, response):
+        """
+        Parse the response from the server containing the received document.
+
+        :param response: The body and headers of the response.
+        :type response: tuple(str, dict)
+
+        :return: (new_gen, new_trans_id, number_of_changes, doc_id, rev,
+                 content, gen, trans_id)
+        :rtype: tuple
+        """
+        # decode incoming stream
+        parts = response.splitlines()
+        if not parts or parts[0] != '[' or parts[-1] != ']':
+            raise errors.BrokenSyncStream
+        data = parts[1:-1]
+        # decode metadata
+        line, comma = utils.check_and_strip_comma(data[0])
+        metadata = None
+        try:
+            metadata = json.loads(line)
+            new_generation = metadata['new_generation']
+            new_transaction_id = metadata['new_transaction_id']
+            number_of_changes = metadata['number_of_changes']
+        except (json.JSONDecodeError, KeyError):
+            raise errors.BrokenSyncStream
+        # make sure we have replica_uid from fresh new dbs
+        if self._ensure_callback and 'replica_uid' in metadata:
+            self._ensure_callback(metadata['replica_uid'])
+        # parse incoming document info
+        doc_id = None
+        rev = None
+        content = None
+        gen = None
+        trans_id = None
+        if number_of_changes > 0:
+            try:
+                entry = json.loads(data[1])
+                doc_id = entry['id']
+                rev = entry['rev']
+                content = entry['content']
+                gen = entry['gen']
+                trans_id = entry['trans_id']
+            except (IndexError, KeyError):
+                raise errors.BrokenSyncStream
+        return new_generation, new_transaction_id, number_of_changes, \
+            doc_id, rev, content, gen, trans_id
+
+    def _setup_sync_decr_pool(self):
+        """
+        Set up the SyncDecrypterPool for deferred decryption.
+        """
+        if self._sync_decr_pool is None and self._sync_db is not None:
+            # initialize syncing queue decryption pool
+            self._sync_decr_pool = SyncDecrypterPool(
+                self._crypto,
+                self._sync_db,
+                insert_doc_cb=self._insert_doc_cb,
+                source_replica_uid=self.source_replica_uid)
diff --git a/client/src/leap/soledad/client/sqlcipher.py b/client/src/leap/soledad/client/sqlcipher.py
index 16241621..53afbda8 100644
--- a/client/src/leap/soledad/client/sqlcipher.py
+++ b/client/src/leap/soledad/client/sqlcipher.py
@@ -53,20 +53,17 @@ from u1db.backends import sqlite_backend
 from hashlib import sha256
 from contextlib import contextmanager
 from collections import defaultdict
-from httplib import CannotSendRequest
 from functools import partial
 
 from pysqlcipher import dbapi2 as sqlcipher_dbapi2
 
 from twisted.internet import reactor
-from twisted.internet.task import LoopingCall
 from twisted.internet.threads import deferToThreadPool
 from twisted.python.threadpool import ThreadPool
-from twisted.python import log
 from twisted.enterprise import adbapi
 
 from leap.soledad.client import encdecpool
-from leap.soledad.client.target import SoledadSyncTarget
+from leap.soledad.client.http_target import SoledadHTTPSyncTarget
 from leap.soledad.client.sync import SoledadSynchronizer
 
 from leap.soledad.client import pragmas
@@ -590,33 +587,13 @@ class SQLCipherU1DBSync(SQLCipherDatabase):
             before the synchronisation was performed.
         :rtype: Deferred
         """
-        kwargs = {'creds': creds, 'autocreate': autocreate,
-                  'defer_decryption': defer_decryption}
-        return self._defer_to_sync_threadpool(self._sync, url, **kwargs)
-
-    def _sync(self, url, creds=None, autocreate=True, defer_decryption=True):
-        res = None
-
         # the following context manager blocks until the syncing lock can be
         # acquired.
-        # TODO review, I think this is no longer needed with a 1-thread
-        # threadpool.
-
-        log.msg("in _sync")
-        self.__url = url
         with self._syncer(url, creds=creds) as syncer:
             # XXX could mark the critical section here...
-            try:
-                log.msg('syncer sync...')
-                res = syncer.sync(autocreate=autocreate,
-                                  defer_decryption=defer_decryption)
-            except CannotSendRequest:
-                logger.warning("Connection with sync target couldn't be "
-                               "established. Resetting connection...")
-                # closing the connection it will be recreated in the next try
-                syncer.sync_target.close()
-                return
-        return res
+            return syncer.sync(
+                autocreate=autocreate,
+                defer_decryption=defer_decryption)
 
     def stop_sync(self):
         """
@@ -673,13 +650,14 @@ class SQLCipherU1DBSync(SQLCipherDatabase):
         if syncer is None or h != cur_h:
             syncer = SoledadSynchronizer(
                 self,
-                SoledadSyncTarget(url,
-                                  # XXX is the replica_uid ready?
-                                  self._replica_uid,
-                                  creds=creds,
-                                  crypto=self._crypto,
-                                  sync_db=self._sync_db,
-                                  sync_enc_pool=self._sync_enc_pool))
+                SoledadHTTPSyncTarget(
+                    url,
+                    # XXX is the replica_uid ready?
+                    self._replica_uid,
+                    creds=creds,
+                    crypto=self._crypto,
+                    sync_db=self._sync_db,
+                    sync_enc_pool=self._sync_enc_pool))
             self._syncers[url] = (h, syncer)
         # in order to reuse the same synchronizer multiple times we have to
         # reset its state (i.e. the number of documents received from target
diff --git a/client/src/leap/soledad/client/sync.py b/client/src/leap/soledad/client/sync.py
index d4ca4258..f8f74ce7 100644
--- a/client/src/leap/soledad/client/sync.py
+++ b/client/src/leap/soledad/client/sync.py
@@ -25,9 +25,10 @@ Extend u1db Synchronizer with the ability to:
     * Be interrupted and recovered.
 """
 import logging
-import traceback
 from threading import Lock
 
+from twisted.internet import defer
+
 from u1db import errors
 from u1db.sync import Synchronizer
 
@@ -90,6 +91,7 @@ class SoledadSynchronizer(Synchronizer):
             # Synchronizer may be reused later.
             self.release_syncing_lock()
 
+    @defer.inlineCallbacks
     def _sync(self, autocreate=False, defer_decryption=True):
         """
         Helper function, called from the main `sync` method.
@@ -102,7 +104,7 @@ class SoledadSynchronizer(Synchronizer):
         ensure_callback = None
         try:
             (self.target_replica_uid, target_gen, target_trans_id,
-             target_my_gen, target_my_trans_id) = \
+             target_my_gen, target_my_trans_id) = yield \
                 sync_target.get_sync_info(self.source._replica_uid)
         except errors.DatabaseDoesNotExist:
             if not autocreate:
@@ -151,15 +153,15 @@ class SoledadSynchronizer(Synchronizer):
                     self.target_replica_uid)
         logger.debug(
             "Soledad source sync info:\n"
-            "  source target gen: %d\n"
-            "  source target trans_id: %s"
+            "  last target gen known to source: %d\n"
+            "  last target trans_id known to source: %s"
             % (target_last_known_gen, target_last_known_trans_id))
 
         # validate transaction ids
         if not changes and target_last_known_gen == target_gen:
             if target_trans_id != target_last_known_trans_id:
                 raise errors.InvalidTransactionId
-            return my_gen
+            defer.returnValue(my_gen)
 
         # prepare to send all the changed docs
         changed_doc_ids = [doc_id for doc_id, _, _ in changes]
@@ -177,33 +179,26 @@ class SoledadSynchronizer(Synchronizer):
         #
         # The sync_exchange method may be interrupted, in which case it will
         # return a tuple of Nones.
-        try:
-            new_gen, new_trans_id = sync_target.sync_exchange(
-                docs_by_generation, self.source._replica_uid,
-                target_last_known_gen, target_last_known_trans_id,
-                self._insert_doc_from_target, ensure_callback=ensure_callback,
-                defer_decryption=defer_decryption)
-            logger.debug(
-                "Soledad source sync info after sync exchange:\n"
-                "  source target gen: %d\n"
-                "  source target trans_id: %s"
-                % (new_gen, new_trans_id))
-            info = {
-                "target_replica_uid": self.target_replica_uid,
-                "new_gen": new_gen,
-                "new_trans_id": new_trans_id,
-                "my_gen": my_gen
-            }
-            self._syncing_info = info
-            self.complete_sync()
-        except Exception as e:
-            logger.error("Soledad sync error: %s" % str(e))
-            logger.error(traceback.format_exc())
-            sync_target.stop()
-        finally:
-            sync_target.close()
-
-        return my_gen
+        new_gen, new_trans_id = yield sync_target.sync_exchange(
+            docs_by_generation, self.source._replica_uid,
+            target_last_known_gen, target_last_known_trans_id,
+            self._insert_doc_from_target, ensure_callback=ensure_callback,
+            defer_decryption=defer_decryption)
+        logger.debug(
+            "Soledad source sync info after sync exchange:\n"
+            "  source known target gen: %d\n"
+            "  source known target trans_id: %s"
+            % (new_gen, new_trans_id))
+        info = {
+            "target_replica_uid": self.target_replica_uid,
+            "new_gen": new_gen,
+            "new_trans_id": new_trans_id,
+            "my_gen": my_gen
+        }
+        self._syncing_info = info
+        yield self.complete_sync()
+
+        defer.returnValue(my_gen)
 
     def complete_sync(self):
         """
@@ -211,6 +206,9 @@ class SoledadSynchronizer(Synchronizer):
             (a) record last known generation and transaction uid for the remote
             replica, and
             (b) make target aware of our current reached generation.
+
+        :return: A deferred which will fire when the sync has been completed.
+        :rtype: twisted.internet.defer.Deferred
         """
         logger.debug("Completing deferred last step in SYNC...")
 
@@ -221,7 +219,26 @@ class SoledadSynchronizer(Synchronizer):
             info["target_replica_uid"], info["new_gen"], info["new_trans_id"])
 
         # if gapless record current reached generation with target
-        self._record_sync_info_with_the_target(info["my_gen"])
+        return self._record_sync_info_with_the_target(info["my_gen"])
+
+    def _record_sync_info_with_the_target(self, start_generation):
+        """
+        Store local replica metadata in server.
+
+        :param start_generation: The local generation when the sync was
+                                 started.
+        :type start_generation: int
+
+        :return: A deferred which will fire when the operation has been
+                 completed.
+        :rtype: twisted.internet.defer.Deferred
+        """
+        cur_gen, trans_id = self.source._get_generation_info()
+        if (cur_gen == start_generation + self.num_inserted
+                and self.num_inserted > 0):
+            return self.sync_target.record_sync_info(
+                self.source._replica_uid, cur_gen, trans_id)
+        return defer.succeed(None)
 
     @property
     def syncing(self):
diff --git a/client/src/leap/soledad/client/target.py b/client/src/leap/soledad/client/target.py
deleted file mode 100644
index 667aab15..00000000
--- a/client/src/leap/soledad/client/target.py
+++ /dev/null
@@ -1,1473 +0,0 @@
-# -*- coding: utf-8 -*-
-# target.py
-# Copyright (C) 2013, 2014 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 for encrypting data before sending to server and decrypting
-after receiving.
-"""
-import cStringIO
-import gzip
-import logging
-import re
-import urllib
-import threading
-
-from collections import defaultdict
-from time import sleep
-from uuid import uuid4
-from functools import partial
-
-import simplejson as json
-
-from u1db import errors
-from u1db.remote import utils, http_errors
-from u1db.remote.http_target import HTTPSyncTarget
-from u1db.remote.http_client import _encode_query_parameter, HTTPClientBase
-from zope.proxy import ProxyBase
-from zope.proxy import setProxiedObject
-
-from twisted.internet import defer
-
-from leap.soledad.common.document import SoledadDocument
-from leap.soledad.client.auth import TokenBasedAuth
-from leap.soledad.client.crypto import is_symmetrically_encrypted
-from leap.soledad.client.crypto import encrypt_doc, decrypt_doc
-from leap.soledad.client.encdecpool import SyncDecrypterPool
-from leap.soledad.client.events import SOLEDAD_SYNC_SEND_STATUS
-from leap.soledad.client.events import SOLEDAD_SYNC_RECEIVE_STATUS
-from leap.soledad.client.events import signal
-
-
-logger = logging.getLogger(__name__)
-
-
-def _gunzip(data):
-    """
-    Uncompress data that is gzipped.
-
-    :param data: gzipped data
-    :type data: basestring
-    """
-    buffer = cStringIO.StringIO()
-    buffer.write(data)
-    buffer.seek(0)
-    try:
-        data = gzip.GzipFile(mode='r', fileobj=buffer).read()
-    except Exception:
-        logger.warning("Error while decrypting gzipped data")
-    buffer.close()
-    return data
-
-
-class DocumentSyncerThread(threading.Thread):
-    """
-    A thread that knowns how to either send or receive a document during the
-    sync process.
-    """
-
-    def __init__(self, doc_syncer, release_method, failed_method,
-                 idx, total, last_request_lock=None, last_callback_lock=None):
-        """
-        Initialize a new syncer thread.
-
-        :param doc_syncer: A document syncer.
-        :type doc_syncer: HTTPDocumentSyncer
-        :param release_method: A method to be called when finished running.
-        :type release_method: callable(DocumentSyncerThread)
-        :param failed_method: A method to be called when we failed.
-        :type failed_method: callable(DocumentSyncerThread)
-        :param idx: The index count of the current operation.
-        :type idx: int
-        :param total: The total number of operations.
-        :type total: int
-        :param last_request_lock: A lock to wait for before actually performing
-                                  the request.
-        :type last_request_lock: threading.Lock
-        :param last_callback_lock: A lock to wait for before actually running
-                                  the success callback.
-        :type last_callback_lock: threading.Lock
-        """
-        threading.Thread.__init__(self)
-        self._doc_syncer = doc_syncer
-        self._release_method = release_method
-        self._failed_method = failed_method
-        self._idx = idx
-        self._total = total
-        self._last_request_lock = last_request_lock
-        self._last_callback_lock = last_callback_lock
-        self._response = None
-        self._exception = None
-        self._result = None
-        self._success = False
-        self.started = threading.Event()
-        # a lock so we can signal when we're finished
-        self._request_lock = threading.Lock()
-        self._request_lock.acquire()
-        self._callback_lock = threading.Lock()
-        self._callback_lock.acquire()
-        # make thread interruptable
-        self._stopped = None
-        self._stop_lock = threading.Lock()
-
-    def run(self):
-        """
-        Run the HTTP request and store results.
-
-        This method will block and wait for an eventual previous operation to
-        finish before actually performing the request. It also traps any
-        exception and register any failure with the request.
-        """
-        self.started.set()
-
-        with self._stop_lock:
-            if self._stopped is None:
-                self._stopped = False
-            else:
-                return
-
-        # eventually wait for the previous thread to finish
-        if self._last_request_lock is not None:
-            self._last_request_lock.acquire()
-
-        # bail out in case we've been interrupted
-        if self.stopped is True:
-            return
-
-        try:
-            self._response = self._doc_syncer.do_request()
-            self._request_lock.release()
-
-            # run success callback
-            if self._doc_syncer.success_callback is not None:
-
-                # eventually wait for callback lock release
-                if self._last_callback_lock is not None:
-                    self._last_callback_lock.acquire()
-
-                # bail out in case we've been interrupted
-                if self._stopped is True:
-                    return
-
-                self._result = self._doc_syncer.success_callback(
-                    self._idx, self._total, self._response)
-                self._success = True
-                doc_syncer = self._doc_syncer
-                self._release_method(self, doc_syncer)
-                self._doc_syncer = None
-                # let next thread executed its callback
-                self._callback_lock.release()
-
-        # trap any exception and signal failure
-        except Exception as e:
-            self._exception = e
-            self._success = False
-            # run failure callback
-            if self._doc_syncer.failure_callback is not None:
-
-                # eventually wait for callback lock release
-                if self._last_callback_lock is not None:
-                    self._last_callback_lock.acquire()
-
-                # bail out in case we've been interrupted
-                if self.stopped is True:
-                    return
-
-                self._doc_syncer.failure_callback(
-                    self._idx, self._total, self._exception)
-
-                self._failed_method()
-                # we do not release the callback lock here because we
-                # failed and so we don't want other threads to succeed.
-
-    @property
-    def doc_syncer(self):
-        return self._doc_syncer
-
-    @property
-    def response(self):
-        return self._response
-
-    @property
-    def exception(self):
-        return self._exception
-
-    @property
-    def callback_lock(self):
-        return self._callback_lock
-
-    @property
-    def request_lock(self):
-        return self._request_lock
-
-    @property
-    def success(self):
-        return self._success
-
-    def stop(self):
-        with self._stop_lock:
-            self._stopped = True
-
-    @property
-    def stopped(self):
-        with self._stop_lock:
-            return self._stopped
-
-    @property
-    def result(self):
-        return self._result
-
-
-class DocumentSyncerPool(object):
-    """
-    A pool of reusable document syncers.
-    """
-
-    POOL_SIZE = 10
-    """
-    The maximum amount of syncer threads running at the same time.
-    """
-
-    def __init__(self, raw_url, raw_creds, query_string, headers,
-                 ensure_callback, stop_method):
-        """
-        Initialize the document syncer pool.
-
-        :param raw_url: The complete raw URL for the HTTP request.
-        :type raw_url: str
-        :param raw_creds: The credentials for the HTTP request.
-        :type raw_creds: dict
-        :param query_string: The query string for the HTTP request.
-        :type query_string: str
-        :param headers: The headers for the HTTP request.
-        :type headers: dict
-        :param ensure_callback: A callback to ensure we have the correct
-                                target_replica_uid, if it was just created.
-        :type ensure_callback: callable
-
-        """
-        # save syncer params
-        self._raw_url = raw_url
-        self._raw_creds = raw_creds
-        self._query_string = query_string
-        self._headers = headers
-        self._ensure_callback = ensure_callback
-        self._stop_method = stop_method
-        # pool attributes
-        self._failures = False
-        self._semaphore_pool = threading.BoundedSemaphore(
-            DocumentSyncerPool.POOL_SIZE)
-        self._pool_access_lock = threading.Lock()
-        self._doc_syncers = []
-        self._threads = []
-
-    def new_syncer_thread(self, idx, total, last_request_lock=None,
-                          last_callback_lock=None):
-        """
-        Yield a new document syncer thread.
-
-        :param idx: The index count of the current operation.
-        :type idx: int
-        :param total: The total number of operations.
-        :type total: int
-        :param last_request_lock: A lock to wait for before actually performing
-                                  the request.
-        :type last_request_lock: threading.Lock
-        :param last_callback_lock: A lock to wait for before actually running
-                                   the success callback.
-        :type last_callback_lock: threading.Lock
-        """
-        t = None
-        # wait for available threads
-        self._semaphore_pool.acquire()
-        with self._pool_access_lock:
-            if self._failures is True:
-                return None
-            # get a syncer
-            doc_syncer = self._get_syncer()
-            # we rely on DocumentSyncerThread.run() to release the lock using
-            # self.release_syncer so we can launch a new thread.
-            t = DocumentSyncerThread(
-                doc_syncer, self.release_syncer, self.stop_threads,
-                idx, total,
-                last_request_lock=last_request_lock,
-                last_callback_lock=last_callback_lock)
-            self._threads.append(t)
-            return t
-
-    def _failed(self):
-        with self._pool_access_lock:
-            self._failures = True
-
-    @property
-    def failures(self):
-        return self._failures
-
-    def _get_syncer(self):
-        """
-        Get a document syncer from the pool.
-
-        This method will create a new syncer whenever there is no syncer
-        available in the pool.
-
-        :return: A syncer.
-        :rtype: HTTPDocumentSyncer
-        """
-        syncer = None
-        # get an available syncer or create a new one
-        try:
-            syncer = self._doc_syncers.pop()
-        except IndexError:
-            syncer = HTTPDocumentSyncer(
-                self._raw_url, self._raw_creds, self._query_string,
-                self._headers, self._ensure_callback)
-        return syncer
-
-    def release_syncer(self, syncer_thread, doc_syncer):
-        """
-        Return a syncer to the pool after use and check for any failures.
-
-        :param syncer: The syncer to be returned to the pool.
-        :type syncer: HTTPDocumentSyncer
-        """
-        with self._pool_access_lock:
-            self._doc_syncers.append(doc_syncer)
-            if syncer_thread.success is True:
-                self._threads.remove(syncer_thread)
-            self._semaphore_pool.release()
-
-    def stop_threads(self, fail=True):
-        """
-        Stop all threads in the pool.
-
-        :param fail: Whether we are stopping because of a failure.
-        :type fail: bool
-        """
-        # stop sync
-        self._stop_method()
-        stopped = []
-        # stop all threads
-        with self._pool_access_lock:
-            if fail:
-                self._failures = True
-                logger.error("sync failed: cancelling sync threads...")
-            while self._threads:
-                t = self._threads.pop(0)
-                t.stop()
-                self._doc_syncers.append(t.doc_syncer)
-                stopped.append(t)
-        # release locks and join
-        while stopped:
-            t = stopped.pop(0)
-            t.request_lock.acquire(False)   # just in case
-            t.request_lock.release()
-            t.callback_lock.acquire(False)  # just in case
-            t.callback_lock.release()
-        # release any blocking semaphores
-        for i in xrange(DocumentSyncerPool.POOL_SIZE):
-            try:
-                self._semaphore_pool.release()
-            except ValueError:
-                break
-        if fail:
-            logger.error("Soledad sync: cancelled sync threads.")
-
-    def cleanup(self):
-        """
-        Close and remove any syncers from the pool.
-        """
-        with self._pool_access_lock:
-            while self._doc_syncers:
-                syncer = self._doc_syncers.pop()
-                syncer.close()
-                del syncer
-
-
-class HTTPDocumentSyncer(HTTPClientBase, TokenBasedAuth):
-
-    def __init__(self, raw_url, creds, query_string, headers, ensure_callback):
-        """
-        Initialize the client.
-
-        :param raw_url: The raw URL of the target HTTP server.
-        :type raw_url: str
-        :param creds: Authentication credentials.
-        :type creds: dict
-        :param query_string: The query string for the HTTP request.
-        :type query_string: str
-        :param headers: The headers for the HTTP request.
-        :type headers: dict
-        :param ensure_callback: A callback to ensure we have the correct
-                                target_replica_uid, if it was just created.
-        :type ensure_callback: callable
-        """
-        HTTPClientBase.__init__(self, raw_url, creds=creds)
-        # info needed to perform the request
-        self._query_string = query_string
-        self._headers = headers
-        self._ensure_callback = ensure_callback
-        # the actual request method
-        self._request_method = None
-        self._success_callback = None
-        self._failure_callback = None
-
-    def _reset(self):
-        """
-        Reset this document syncer so we can reuse it.
-        """
-        self._request_method = None
-        self._success_callback = None
-        self._failure_callback = None
-        self._request_method = None
-
-    def set_request_method(self, method, *args, **kwargs):
-        """
-        Set the actual method to perform the request.
-
-        :param method: Either 'get' or 'put'.
-        :type method: str
-        :param args: Arguments for the request method.
-        :type args: list
-        :param kwargs: Keyworded arguments for the request method.
-        :type kwargs: dict
-        """
-        self._reset()
-        # resolve request method
-        if method is 'get':
-            self._request_method = self._get_doc
-        elif method is 'put':
-            self._request_method = self._put_doc
-        else:
-            raise Exception
-        # store request method args
-        self._args = args
-        self._kwargs = kwargs
-
-    def set_success_callback(self, callback):
-        self._success_callback = callback
-
-    def set_failure_callback(self, callback):
-        self._failure_callback = callback
-
-    @property
-    def success_callback(self):
-        return self._success_callback
-
-    @property
-    def failure_callback(self):
-        return self._failure_callback
-
-    def do_request(self):
-        """
-        Actually perform the request.
-
-        :return: The body and headers of the response.
-        :rtype: tuple
-        """
-        self._ensure_connection()
-        args = self._args
-        kwargs = self._kwargs
-        return self._request_method(*args, **kwargs)
-
-    def _request(self, method, url_parts, params=None, body=None,
-                 content_type=None):
-        """
-        Perform an HTTP request.
-
-        :param method: The HTTP request method.
-        :type method: str
-        :param url_parts: A list representing the request path.
-        :type url_parts: list
-        :param params: Parameters for the URL query string.
-        :type params: dict
-        :param body: The body of the request.
-        :type body: str
-        :param content-type: The content-type of the request.
-        :type content-type: str
-
-        :return: The body and headers of the response.
-        :rtype: tuple
-
-        :raise errors.Unavailable: Raised after a number of unsuccesful
-                                   request attempts.
-        :raise Exception: Raised for any other exception ocurring during the
-                          request.
-        """
-
-        self._ensure_connection()
-        unquoted_url = url_query = self._url.path
-        if url_parts:
-            if not url_query.endswith('/'):
-                url_query += '/'
-                unquoted_url = url_query
-            url_query += '/'.join(urllib.quote(part, safe='')
-                                  for part in url_parts)
-            # oauth performs its own quoting
-            unquoted_url += '/'.join(url_parts)
-        encoded_params = {}
-        if params:
-            for key, value in params.items():
-                key = unicode(key).encode('utf-8')
-                encoded_params[key] = _encode_query_parameter(value)
-            url_query += ('?' + urllib.urlencode(encoded_params))
-        if body is not None and not isinstance(body, basestring):
-            body = json.dumps(body)
-            content_type = 'application/json'
-        headers = {}
-        if content_type:
-            headers['content-type'] = content_type
-
-        # Patched: We would like to receive gzip pretty please
-        # ----------------------------------------------------
-        headers['accept-encoding'] = "gzip"
-        # ----------------------------------------------------
-
-        headers.update(
-            self._sign_request(method, unquoted_url, encoded_params))
-
-        for delay in self._delays:
-            try:
-                self._conn.request(method, url_query, body, headers)
-                return self._response()
-            except errors.Unavailable, e:
-                sleep(delay)
-        raise e
-
-    def _response(self):
-        """
-        Return the response of the (possibly gzipped) HTTP request.
-
-        :return: The body and headers of the response.
-        :rtype: tuple
-        """
-        resp = self._conn.getresponse()
-        body = resp.read()
-        headers = dict(resp.getheaders())
-
-        # Patched: We would like to decode gzip
-        # ----------------------------------------------------
-        encoding = headers.get('content-encoding', '')
-        if "gzip" in encoding:
-            body = _gunzip(body)
-        # ----------------------------------------------------
-
-        if resp.status in (200, 201):
-            return body, headers
-        elif resp.status in http_errors.ERROR_STATUSES:
-            try:
-                respdic = json.loads(body)
-            except ValueError:
-                pass
-            else:
-                self._error(respdic)
-        # special case
-        if resp.status == 503:
-            raise errors.Unavailable(body, headers)
-        raise errors.HTTPError(resp.status, body, headers)
-
-    def _prepare(self, comma, entries, **dic):
-        """
-        Prepare an entry to be sent through a syncing POST request.
-
-        :param comma: A string to be prepended to the current entry.
-        :type comma: str
-        :param entries: A list of entries accumulated to be sent on the
-                        request.
-        :type entries: list
-        :param dic: The data to be included in this entry.
-        :type dic: dict
-
-        :return: The size of the prepared entry.
-        :rtype: int
-        """
-        entry = comma + '\r\n' + json.dumps(dic)
-        entries.append(entry)
-        return len(entry)
-
-    def _init_post_request(self, action, content_length):
-        """
-        Initiate a syncing POST request.
-
-        :param url: The syncing URL.
-        :type url: str
-        :param action: The syncing action, either 'get' or 'receive'.
-        :type action: str
-        :param headers: The initial headers to be sent on this request.
-        :type headers: dict
-        :param content_length: The content-length of the request.
-        :type content_length: int
-        """
-        self._conn.putrequest('POST', self._query_string)
-        self._conn.putheader(
-            'content-type', 'application/x-soledad-sync-%s' % action)
-        for header_name, header_value in self._headers:
-            self._conn.putheader(header_name, header_value)
-        self._conn.putheader('accept-encoding', 'gzip')
-        self._conn.putheader('content-length', str(content_length))
-        self._conn.endheaders()
-
-    def _get_doc(self, received, sync_id, last_known_generation,
-                 last_known_trans_id):
-        """
-        Get a sync document from server by means of a POST request.
-
-        :param received: The number of documents already received in the
-                         current sync session.
-        :type received: int
-        :param sync_id: The id for the current sync session.
-        :type sync_id: str
-        :param last_known_generation: Target's last known generation.
-        :type last_known_generation: int
-        :param last_known_trans_id: Target's last known transaction id.
-        :type last_known_trans_id: str
-
-        :return: The body and headers of the response.
-        :rtype: tuple
-        """
-        entries = ['[']
-        size = 1
-        # add remote replica metadata to the request
-        size += self._prepare(
-            '', entries,
-            last_known_generation=last_known_generation,
-            last_known_trans_id=last_known_trans_id,
-            sync_id=sync_id,
-            ensure=self._ensure_callback is not None)
-        # inform server of how many documents have already been received
-        size += self._prepare(
-            ',', entries, received=received)
-        entries.append('\r\n]')
-        size += len(entries[-1])
-        # send headers
-        self._init_post_request('get', size)
-        # get document
-        for entry in entries:
-            self._conn.send(entry)
-        return self._response()
-
-    def _put_doc(self, sync_id, last_known_generation, last_known_trans_id,
-                 id, rev, content, gen, trans_id, number_of_docs, doc_idx):
-        """
-        Put a sync document on server by means of a POST request.
-
-        :param sync_id: The id for the current sync session.
-        :type sync_id: str
-        :param last_known_generation: Target's last known generation.
-        :type last_known_generation: int
-        :param last_known_trans_id: Target's last known transaction id.
-        :type last_known_trans_id: str
-        :param id: The document id.
-        :type id: str
-        :param rev: The document revision.
-        :type rev: str
-        :param content: The serialized document content.
-        :type content: str
-        :param gen: The generation of the modification of the document.
-        :type gen: int
-        :param trans_id: The transaction id of the modification of the
-                         document.
-        :type 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
-
-        :return: The body and headers of the response.
-        :rtype: tuple
-        """
-        # prepare to send the document
-        entries = ['[']
-        size = 1
-        # add remote replica metadata to the request
-        size += self._prepare(
-            '', entries,
-            last_known_generation=last_known_generation,
-            last_known_trans_id=last_known_trans_id,
-            sync_id=sync_id,
-            ensure=self._ensure_callback is not None)
-        # add the document to the request
-        size += self._prepare(
-            ',', entries,
-            id=id, rev=rev, content=content, gen=gen, trans_id=trans_id,
-            number_of_docs=number_of_docs, doc_idx=doc_idx)
-        entries.append('\r\n]')
-        size += len(entries[-1])
-        # send headers
-        self._init_post_request('put', size)
-        # send document
-        for entry in entries:
-            self._conn.send(entry)
-        return self._response()
-
-    def _sign_request(self, method, url_query, params):
-        """
-        Return an authorization header to be included in the HTTP request.
-
-        :param method: The HTTP method.
-        :type method: str
-        :param url_query: The URL query string.
-        :type url_query: str
-        :param params: A list with encoded query parameters.
-        :type param: list
-
-        :return: The Authorization header.
-        :rtype: list of tuple
-        """
-        return TokenBasedAuth._sign_request(self, method, url_query, params)
-
-    def set_token_credentials(self, uuid, token):
-        """
-        Store given credentials so we can sign the request later.
-
-        :param uuid: The user's uuid.
-        :type uuid: str
-        :param token: The authentication token.
-        :type token: str
-        """
-        TokenBasedAuth.set_token_credentials(self, uuid, token)
-
-
-class SoledadSyncTarget(HTTPSyncTarget, TokenBasedAuth):
-    """
-    A SyncTarget that encrypts data before sending and decrypts data after
-    receiving.
-
-    Normally encryption will have been written to the sync database upon
-    document modification. The sync database is also used to write temporarily
-    the parsed documents that the remote send us, before being decrypted and
-    written to the main database.
-    """
-
-    # will later keep a reference to the insert-doc callback
-    # passed to sync_exchange
-    _insert_doc_cb = defaultdict(lambda: ProxyBase(None))
-
-    #
-    # Modified HTTPSyncTarget methods.
-    #
-
-    def __init__(self, url, source_replica_uid=None, creds=None, crypto=None,
-                 sync_db=None, sync_enc_pool=None):
-        """
-        Initialize the SoledadSyncTarget.
-
-        :param source_replica_uid: The source replica uid which we use when
-                                   deferring decryption.
-        :type source_replica_uid: str
-        :param url: The url of the target replica to sync with.
-        :type url: str
-        :param creds: Optional dictionary giving credentials.
-                      to authorize the operation with the server.
-        :type creds: dict
-        :param crypto: An instance of SoledadCrypto so we can encrypt/decrypt
-                        document contents when syncing.
-        :type crypto: soledad.crypto.SoledadCrypto
-        :param sync_db: Optional. handler for the db with the symmetric
-                        encryption of the syncing documents. If
-                        None, encryption will be done in-place,
-                        instead of retreiving it from the dedicated
-                        database.
-        :type sync_db: Sqlite handler
-        """
-        HTTPSyncTarget.__init__(self, url, creds)
-        self._raw_url = url
-        self._raw_creds = creds
-        self._crypto = crypto
-        self._stopped = True
-        self._stop_lock = threading.Lock()
-        self.source_replica_uid = source_replica_uid
-        self._syncer_pool = None
-
-        # asynchronous encryption/decryption attributes
-        self._sync_db = sync_db
-        self._sync_enc_pool = sync_enc_pool
-        self._decryption_callback = None
-        self._sync_decr_pool = None
-
-    def _setup_sync_decr_pool(self):
-        """
-        Set up the SyncDecrypterPool for deferred decryption.
-        """
-        if self._sync_decr_pool is None and self._sync_db is not None:
-            # initialize syncing queue decryption pool
-            self._sync_decr_pool = SyncDecrypterPool(
-                self._crypto,
-                self._sync_db,
-                insert_doc_cb=self._insert_doc_cb,
-                source_replica_uid=self.source_replica_uid)
-
-    def _teardown_sync_decr_pool(self):
-        """
-        Tear down the SyncDecrypterPool.
-        """
-        self._sync_decr_pool.close()
-        self._sync_decr_pool = None
-
-    def _get_replica_uid(self, url):
-        """
-        Return replica uid from the url, or None.
-
-        :param url: the replica url
-        :type url: str
-        """
-        replica_uid_match = re.findall("user-([0-9a-fA-F]+)", url)
-        return replica_uid_match[0] if len(replica_uid_match) > 0 else None
-
-    @staticmethod
-    def connect(url, source_replica_uid=None, crypto=None):
-        return SoledadSyncTarget(
-            url, source_replica_uid=source_replica_uid, crypto=crypto)
-
-    def _parse_received_doc_response(self, response):
-        """
-        Parse the response from the server containing the received document.
-
-        :param response: The body and headers of the response.
-        :type response: tuple(str, dict)
-        """
-        data, _ = response
-        # decode incoming stream
-        parts = data.splitlines()
-        if not parts or parts[0] != '[' or parts[-1] != ']':
-            raise errors.BrokenSyncStream
-        data = parts[1:-1]
-        # decode metadata
-        line, comma = utils.check_and_strip_comma(data[0])
-        metadata = None
-        try:
-            metadata = json.loads(line)
-            new_generation = metadata['new_generation']
-            new_transaction_id = metadata['new_transaction_id']
-            number_of_changes = metadata['number_of_changes']
-        except (json.JSONDecodeError, KeyError):
-            raise errors.BrokenSyncStream
-        # make sure we have replica_uid from fresh new dbs
-        if self._ensure_callback and 'replica_uid' in metadata:
-            self._ensure_callback(metadata['replica_uid'])
-        # parse incoming document info
-        doc_id = None
-        rev = None
-        content = None
-        gen = None
-        trans_id = None
-        if number_of_changes > 0:
-            try:
-                entry = json.loads(data[1])
-                doc_id = entry['id']
-                rev = entry['rev']
-                content = entry['content']
-                gen = entry['gen']
-                trans_id = entry['trans_id']
-            except (IndexError, KeyError):
-                raise errors.BrokenSyncStream
-        return new_generation, new_transaction_id, number_of_changes, \
-            doc_id, rev, content, gen, trans_id
-
-    def _insert_received_doc(self, idx, total, response):
-        """
-        Insert a received document into the local replica.
-
-        :param idx: The index count of the current operation.
-        :type idx: int
-        :param total: The total number of operations.
-        :type total: int
-        :param response: The body and headers of the response.
-        :type response: tuple(str, dict)
-        """
-        new_generation, new_transaction_id, number_of_changes, doc_id, \
-            rev, content, gen, trans_id = \
-            self._parse_received_doc_response(response)
-        if doc_id is not None:
-            # decrypt incoming document and insert into local database
-            # -------------------------------------------------------------
-            # symmetric decryption of document's contents
-            # -------------------------------------------------------------
-            # If arriving content was symmetrically encrypted, we decrypt it.
-            # We do it inline if defer_decryption flag is False or no sync_db
-            # was defined, otherwise we defer it writing it to the received
-            # docs table.
-            doc = SoledadDocument(doc_id, rev, content)
-            if is_symmetrically_encrypted(doc):
-                if self._queue_for_decrypt:
-                    self._enqueue_encrypted_received_doc(
-                        doc, gen, trans_id, idx, total)
-                else:
-                    # defer_decryption is False or no-sync-db fallback
-                    doc.set_json(decrypt_doc(self._crypto, doc))
-                    self._return_doc_cb(doc, gen, trans_id)
-            else:
-                # not symmetrically encrypted doc, insert it directly
-                # or save it in the decrypted stage.
-                if self._queue_for_decrypt:
-                    self._enqueue_received_doc(doc, gen, trans_id, idx, total)
-                else:
-                    self._return_doc_cb(doc, gen, trans_id)
-            # -------------------------------------------------------------
-            # end of symmetric decryption
-            # -------------------------------------------------------------
-        msg = "%d/%d" % (idx + 1, total)
-        signal(SOLEDAD_SYNC_RECEIVE_STATUS, msg)
-        logger.debug("Soledad sync receive status: %s" % msg)
-        return number_of_changes, new_generation, new_transaction_id
-
-    def _get_remote_docs(self, url, last_known_generation, last_known_trans_id,
-                         headers, return_doc_cb, ensure_callback, sync_id,
-                         defer_decryption=False):
-        """
-        Fetch sync documents from the remote database and insert them in the
-        local database.
-
-        If an incoming document's encryption scheme is equal to
-        EncryptionSchemes.SYMKEY, then this method will decrypt it with
-        Soledad's symmetric key.
-
-        :param url: The syncing URL.
-        :type url: str
-        :param last_known_generation: Target's last known generation.
-        :type last_known_generation: int
-        :param last_known_trans_id: Target's last known transaction id.
-        :type last_known_trans_id: str
-        :param headers: The headers of the HTTP request.
-        :type headers: dict
-        :param return_doc_cb: A callback to insert docs from target.
-        :type return_doc_cb: callable
-        :param ensure_callback: A callback to ensure we have the correct
-                                target_replica_uid, if it was just created.
-        :type ensure_callback: callable
-        :param sync_id: The id for the current sync session.
-        :type sync_id: str
-        :param defer_decryption: Whether to defer the decryption process using
-                                 the intermediate database. If False,
-                                 decryption will be done inline.
-        :type defer_decryption: bool
-
-        :raise BrokenSyncStream: If `data` is malformed.
-
-        :return: A dictionary representing the first line of the response got
-                 from remote replica.
-        :rtype: dict
-        """
-        # we keep a reference to the callback in case we defer the decryption
-        self._return_doc_cb = return_doc_cb
-        self._queue_for_decrypt = defer_decryption \
-            and self._sync_db is not None
-
-        new_generation = last_known_generation
-        new_transaction_id = last_known_trans_id
-
-        if self._queue_for_decrypt:
-            logger.debug(
-                "Soledad sync: will queue received docs for decrypting.")
-
-        idx = 0
-        number_of_changes = 1
-
-        first_request = True
-        last_callback_lock = None
-        threads = []
-
-        # get incoming documents
-        while idx < number_of_changes:
-            # bail out if sync process was interrupted
-            if self.stopped is True:
-                break
-
-            # launch a thread to fetch one document from target
-            t = self._syncer_pool.new_syncer_thread(
-                idx, number_of_changes,
-                last_callback_lock=last_callback_lock)
-
-            # bail out if any thread failed
-            if t is None:
-                self.stop(fail=True)
-                break
-
-            if defer_decryption:
-                self._setup_sync_decr_pool()
-
-            t.doc_syncer.set_request_method(
-                'get', idx, sync_id, last_known_generation,
-                last_known_trans_id)
-            t.doc_syncer.set_success_callback(self._insert_received_doc)
-
-            def _failure_callback(idx, total, exception):
-                _failure_msg = "Soledad sync: error while getting document " \
-                    "%d/%d: %s" \
-                    % (idx + 1, total, exception)
-                logger.warning("%s" % _failure_msg)
-                logger.warning("Soledad sync: failing gracefully, will "
-                               "recover on next sync.")
-
-            t.doc_syncer.set_failure_callback(_failure_callback)
-            threads.append(t)
-            t.start()
-            last_callback_lock = t.callback_lock
-            idx += 1
-
-            # if this is the first request, wait to update the number of
-            # changes
-            if first_request is True:
-                t.join()
-                if t.success:
-                    number_of_changes, _, _ = t.result
-                    if defer_decryption:
-                        self._sync_decr_pool.set_docs_to_process(
-                            number_of_changes)
-                else:
-                    raise t.exception
-                first_request = False
-
-        # make sure all threads finished and we have up-to-date info
-        last_successful_thread = None
-        while threads:
-            # check if there are failures
-            t = threads.pop(0)
-            t.join()
-            if t.success:
-                last_successful_thread = t
-            else:
-                raise t.exception
-
-        # get information about last successful thread
-        if last_successful_thread is not None:
-            body, _ = last_successful_thread.response
-            parsed_body = json.loads(body)
-            # get current target gen and trans id in case no documents were
-            # transferred
-            if len(parsed_body) == 1:
-                metadata = parsed_body[0]
-                new_generation = metadata['new_generation']
-                new_transaction_id = metadata['new_transaction_id']
-            # get current target gen and trans id from last transferred
-            # document
-            else:
-                doc_data = parsed_body[1]
-                new_generation = doc_data['gen']
-                new_transaction_id = doc_data['trans_id']
-
-        # decrypt docs in case of deferred decryption
-        if defer_decryption:
-            self._sync_decr_pool.wait()
-            self._teardown_sync_decr_pool()
-
-        return new_generation, new_transaction_id
-
-    @property
-    def _defer_encryption(self):
-        return self._sync_enc_pool is not None
-
-    @property
-    def _defer_decryption(self):
-        return self._sync_decr_pool is not None
-
-    def sync_exchange(self, docs_by_generations,
-                      source_replica_uid, last_known_generation,
-                      last_known_trans_id, return_doc_cb,
-                      ensure_callback=None, defer_decryption=True,
-                      sync_id=None):
-        """
-        Find out which documents the remote database does not know about,
-        encrypt and send them.
-
-        This does the same as the parent's method but encrypts content before
-        syncing.
-
-        :param docs_by_generations: A list of (doc_id, generation, trans_id)
-                                    of local documents that were changed since
-                                    the last local generation the remote
-                                    replica knows about.
-        :type docs_by_generations: list of tuples
-
-        :param source_replica_uid: The uid of the source replica.
-        :type source_replica_uid: str
-
-        :param last_known_generation: Target's last known generation.
-        :type last_known_generation: int
-
-        :param last_known_trans_id: Target's last known transaction id.
-        :type last_known_trans_id: str
-
-        :param return_doc_cb: A callback for inserting received documents from
-                              target. If not overriden, this will call u1db
-                              insert_doc_from_target in synchronizer, which
-                              implements the TAKE OTHER semantics.
-        :type return_doc_cb: function
-
-        :param ensure_callback: A callback that ensures we know the target
-                                replica uid if the target replica was just
-                                created.
-        :type ensure_callback: function
-
-        :param defer_decryption: Whether to defer the decryption process using
-                                 the intermediate database. If False,
-                                 decryption will be done inline.
-        :type defer_decryption: bool
-
-        :return: The new generation and transaction id of the target replica.
-        :rtype: tuple
-        """
-        self._ensure_callback = ensure_callback
-
-        self.start()
-
-        if sync_id is None:
-            sync_id = str(uuid4())
-        self.source_replica_uid = source_replica_uid
-        # let the decrypter pool access the passed callback to insert docs
-        setProxiedObject(self._insert_doc_cb[source_replica_uid],
-                         return_doc_cb)
-
-        self._ensure_connection()
-        if self._trace_hook:  # for tests
-            self._trace_hook('sync_exchange')
-        url = '%s/sync-from/%s' % (self._url.path, source_replica_uid)
-        headers = self._sign_request('POST', url, {})
-
-        cur_target_gen = last_known_generation
-        cur_target_trans_id = last_known_trans_id
-
-        # -------------------------------------------------------------------
-        # start of send documents to target
-        # -------------------------------------------------------------------
-        msg = "%d/%d" % (0, len(docs_by_generations))
-        signal(SOLEDAD_SYNC_SEND_STATUS, msg)
-        logger.debug("Soledad sync send status: %s" % msg)
-
-        self._syncer_pool = DocumentSyncerPool(
-            self._raw_url, self._raw_creds, url, headers, ensure_callback,
-            self.stop_syncer)
-        threads = []
-        last_callback_lock = None
-
-        sent = 0
-        total = len(docs_by_generations)
-
-        synced = []
-        number_of_docs = len(docs_by_generations)
-
-        last_request_lock = None
-        for doc, gen, trans_id in docs_by_generations:
-            # allow for interrupting the sync process
-            if self.stopped is True:
-                break
-
-            # skip non-syncable docs
-            if isinstance(doc, SoledadDocument) and not doc.syncable:
-                continue
-
-            # -------------------------------------------------------------
-            # symmetric encryption of document's contents
-            # -------------------------------------------------------------
-
-            # the following var will hold a deferred because we may try to
-            # fetch the encrypted document from the sync db
-            d = None
-
-            if doc.is_tombstone():
-                d = defer.succeed(None)
-            elif not self._defer_encryption:
-                # fallback case, for tests
-                d = defer.succeed(encrypt_doc(self._crypto, doc))
-            else:
-
-                def _maybe_encrypt_doc_inline(doc_json):
-                    if doc_json is None:
-                        # the document is not marked as tombstone, but we got
-                        # nothing from the sync db. As it is not encrypted
-                        # yet, we force inline encryption.
-                        # TODO: implement a queue to deal with these cases.
-                        return encrypt_doc(self._crypto, doc)
-                    return doc_json
-
-                d = self.get_encrypted_doc_from_db(doc.doc_id, doc.rev)
-                d.addCallback(_maybe_encrypt_doc_inline)
-            # -------------------------------------------------------------
-            # end of symmetric encryption
-            # -------------------------------------------------------------
-
-            t = self._syncer_pool.new_syncer_thread(
-                sent + 1, total, last_request_lock=last_request_lock,
-                last_callback_lock=last_callback_lock)
-
-            # bail out if creation of any thread failed
-            if t is None:
-                self.stop(fail=True)
-                break
-
-            # the following callback will be called when the document's
-            # encrypted content is available, either because it was found on
-            # the sync db or because it has been encrypted inline.
-
-            def _configure_and_start_thread(t, doc_json):
-                # set the request method
-                t.doc_syncer.set_request_method(
-                    'put', sync_id, cur_target_gen, cur_target_trans_id,
-                    id=doc.doc_id, rev=doc.rev, content=doc_json, gen=gen,
-                    trans_id=trans_id, number_of_docs=number_of_docs,
-                    doc_idx=sent + 1)
-                # set the success calback
-
-                def _success_callback(idx, total, response):
-                    _success_msg = "Soledad sync send status: %d/%d" \
-                                   % (idx, total)
-                    signal(SOLEDAD_SYNC_SEND_STATUS, _success_msg)
-                    logger.debug(_success_msg)
-
-                t.doc_syncer.set_success_callback(_success_callback)
-
-                # set the failure callback
-                def _failure_callback(idx, total, exception):
-                    _failure_msg = "Soledad sync: error while sending document " \
-                                   "%d/%d: %s" % (idx, total, exception)
-                    logger.warning("%s" % _failure_msg)
-                    logger.warning("Soledad sync: failing gracefully, will "
-                                   "recover on next sync.")
-
-                t.doc_syncer.set_failure_callback(_failure_callback)
-
-                # save thread and append
-                t.start()
-
-            d.addCallback(partial(_configure_and_start_thread, t))
-
-            threads.append((t, doc))
-
-            # update lock references so they can be used in next call to
-            # syncer_pool.new_syncer_thread() above
-            last_callback_lock = t.callback_lock
-            last_request_lock = t.request_lock
-
-            sent += 1
-
-        # make sure all threads finished and we have up-to-date info
-        last_successful_thread = None
-        while threads:
-            # check if there are failures
-            t, doc = threads.pop(0)
-            t.started.wait()
-            t.join()
-            if t.success:
-                synced.append((doc.doc_id, doc.rev))
-                last_successful_thread = t
-            else:
-                raise t.exception
-
-        # delete documents from the sync database
-        if self._defer_encryption:
-            self._delete_encrypted_docs_from_db(synced)
-
-        # get target gen and trans_id after docs
-        gen_after_send = None
-        trans_id_after_send = None
-        if last_successful_thread is not None:
-            response_dict = json.loads(last_successful_thread.response[0])[0]
-            gen_after_send = response_dict['new_generation']
-            trans_id_after_send = response_dict['new_transaction_id']
-        # -------------------------------------------------------------------
-        # end of send documents to target
-        # -------------------------------------------------------------------
-
-        # -------------------------------------------------------------------
-        # start of fetch documents from target
-        # -------------------------------------------------------------------
-        defer_decryption = defer_decryption and self._defer_decryption
-        if self.stopped is False:
-            cur_target_gen, cur_target_trans_id = self._get_remote_docs(
-                url,
-                last_known_generation, last_known_trans_id, headers,
-                return_doc_cb, ensure_callback, sync_id,
-                defer_decryption=defer_decryption)
-        # -------------------------------------------------------------------
-        # end of fetch documents from target
-        # -------------------------------------------------------------------
-
-        self._syncer_pool.cleanup()
-
-        # update gen and trans id info in case we just sent and did not
-        # receive docs.
-        if gen_after_send is not None and gen_after_send > cur_target_gen:
-            cur_target_gen = gen_after_send
-            cur_target_trans_id = trans_id_after_send
-
-        self.stop(fail=False)
-        self._syncer_pool = None
-        return cur_target_gen, cur_target_trans_id
-
-    def start(self):
-        """
-        Mark current sync session as running.
-        """
-        with self._stop_lock:
-            self._stopped = False
-
-    def stop_syncer(self):
-        with self._stop_lock:
-            self._stopped = True
-
-    def stop(self, fail=False):
-        """
-        Mark current sync session as stopped.
-
-        This will eventually interrupt the sync_exchange() method and return
-        enough information to the synchronizer so the sync session can be
-        recovered afterwards.
-
-        :param fail: Whether we are stopping because of a failure.
-        :type fail: bool
-        """
-        self.stop_syncer()
-        if self._syncer_pool:
-            self._syncer_pool.stop_threads(fail=fail)
-
-    @property
-    def stopped(self):
-        """
-        Return whether this sync session is stopped.
-
-        :return: Whether this sync session is stopped.
-        :rtype: bool
-        """
-        with self._stop_lock:
-            return self._stopped is True
-
-    #
-    # Symmetric encryption of syncing docs
-    #
-
-    def get_encrypted_doc_from_db(self, doc_id, doc_rev):
-        """
-        Retrieve encrypted document from the database of encrypted docs for
-        sync.
-
-        :param doc_id: The Document id.
-        :type doc_id: str
-
-        :param doc_rev: The document revision
-        :type doc_rev: str
-
-        :return: A deferred which is fired with the document's encrypted
-                 content or None if the document was not found on the sync db.
-        :rtype: twisted.internet.defer.Deferred
-        """
-        logger.debug("Looking for encrypted document on sync db: %s" % doc_id)
-        return self._sync_enc_pool.get_encrypted_doc(doc_id, doc_rev)
-
-    def _delete_encrypted_docs_from_db(self, docs):
-        """
-        Delete several encrypted documents from the database of symmetrically
-        encrypted docs to sync.
-
-        :param docs: an iterable with (doc_id, doc_rev) for all documents
-                     to be deleted.
-        :type docs: any iterable of tuples of str
-        """
-        for doc_id, doc_rev in docs:
-            logger.debug("Removing encrypted document on sync db: %s"
-                         % doc_id)
-            return self._sync_enc_pool.delete_encrypted_doc(doc_id, doc_rev)
-
-    #
-    # Symmetric decryption of syncing docs
-    #
-
-    def _enqueue_encrypted_received_doc(self, doc, gen, trans_id, idx, total):
-        """
-        Save a symmetrically encrypted incoming document into the received
-        docs table in the sync db. A decryption task will pick it up
-        from here in turn.
-
-        :param doc: The document to save.
-        :type doc: SoledadDocument
-        :param gen: The generation.
-        :type gen: str
-        :param  trans_id: Transacion id.
-
-        :param idx: The index count of the current operation.
-        :type idx: int
-        :param total: The total number of operations.
-        :type total: int
-        """
-        logger.debug("Enqueueing doc for decryption: %d/%d."
-                     % (idx + 1, total))
-        self._sync_decr_pool.insert_encrypted_received_doc(
-            doc.doc_id, doc.rev, doc.content, gen, trans_id, idx + 1)
-
-    def _enqueue_received_doc(self, doc, gen, trans_id, idx, total):
-        """
-        Save any incoming document into the received docs table in the sync db.
-
-        :param doc: The document to save.
-        :type doc: SoledadDocument
-        :param gen: The generation.
-        :type gen: str
-        :param  trans_id: Transacion id.
-        :type gen: str
-        :param idx: The index count of the current operation.
-        :type idx: int
-        :param total: The total number of operations.
-        :type total: int
-        """
-        logger.debug("Enqueueing doc, no decryption needed: %d/%d."
-                     % (idx + 1, total))
-        self._sync_decr_pool.insert_received_doc(
-            doc.doc_id, doc.rev, doc.content, gen, trans_id, idx + 1)
-
-    def set_decryption_callback(self, cb):
-        """
-        Set callback to be called when the decryption finishes.
-
-        :param cb: The callback to be set.
-        :type cb: callable
-        """
-        self._decryption_callback = cb
-
-    def has_decryption_callback(self):
-        """
-        Return True if there is a decryption callback set.
-        :rtype: bool
-        """
-        return self._decryption_callback is not None
-
-    #
-    # Authentication methods
-    #
-
-    def _sign_request(self, method, url_query, params):
-        """
-        Return an authorization header to be included in the HTTP request.
-
-        :param method: The HTTP method.
-        :type method: str
-        :param url_query: The URL query string.
-        :type url_query: str
-        :param params: A list with encoded query parameters.
-        :type param: list
-
-        :return: The Authorization header.
-        :rtype: list of tuple
-        """
-        return TokenBasedAuth._sign_request(self, method, url_query, params)
-
-    def set_token_credentials(self, uuid, token):
-        """
-        Store given credentials so we can sign the request later.
-
-        :param uuid: The user's uuid.
-        :type uuid: str
-        :param token: The authentication token.
-        :type token: str
-        """
-        TokenBasedAuth.set_token_credentials(self, uuid, token)