[feat] first draft of sync_state in memory

This commit changes sync_state to be in memory, with all tests passing.
The memory variable for now is a dict with each key composed by
source_replica_uid and sync_id, replicating CouchDB implementation. Next
steps includes migrating this to Beaker and refactor/clean up code.

Changed the module's INFO dict to use Beaker's caching and adapted
methods to get and save from it. Still needs refactoring, all tests
passes.

Beaker is now using memory as default; It is configurable, but we aren't
opening the possibility of config now for security. We need to check
what can be misconfigured first.

We are not sure if beaker will be the definitive solution for server
side caching. This change isolates it with more granularity.
In order to replace it, just change get_cache_for to return the proper
caching object using another implementation. This caching object is
supposed to behave as a dict.

3 files changed, 177 insertions, 171 deletions

diff --git a/server/src/leap/soledad/server/caching.py b/server/src/leap/soledad/server/caching.py
new file mode 100644
index 00000000..cd5d8dd4
--- /dev/null
+++ b/server/src/leap/soledad/server/caching.py
@@ -0,0 +1,32 @@
+# -*- coding: utf-8 -*-
+# caching.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 side caching. Using beaker for now.
+"""
+from beaker.cache import CacheManager
+
+
+def setup_caching():
+    _cache_manager = CacheManager(type='memory')
+    return _cache_manager
+
+
+_cache_manager = setup_caching()
+
+
+def get_cache_for(key):
+    return _cache_manager.get_cache(key)
diff --git a/server/src/leap/soledad/server/state.py b/server/src/leap/soledad/server/state.py
new file mode 100644
index 00000000..d1225170
--- /dev/null
+++ b/server/src/leap/soledad/server/state.py
@@ -0,0 +1,143 @@
+# -*- 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 side synchronization infrastructure.
+"""
+from leap.soledad.server import caching
+
+
+class ServerSyncState(object):
+    """
+    The state of one sync session, as stored on backend server.
+
+    On server side, the ongoing syncs metadata is maintained in a caching layer.
+    """
+
+    def __init__(self, source_replica_uid, sync_id):
+        """
+        Initialize the sync state object.
+
+        :param sync_id: The id of current sync
+        :type sync_id: str
+        :param source_replica_uid: The source replica uid
+        :type source_replica_uid: str
+        """
+        self._source_replica_uid = source_replica_uid
+        self._sync_id = sync_id
+        self._storage = caching.get_cache_for(source_replica_uid + sync_id)
+
+    def _put_dict_info(self, key, value):
+        """
+        Put some information about the sync state.
+
+        :param key: The key for the info to be put.
+        :type key: str
+        :param value: The value for the info to be put.
+        :type value: str
+        """
+        if key not in self._storage:
+            self._storage[key] = []
+        info_list = self._storage.get(key)
+        info_list.append(value)
+        self._storage[key] = info_list
+
+    def put_seen_id(self, seen_id, gen):
+        """
+        Put one seen id on the sync state.
+
+        :param seen_id: The doc_id of a document seen during sync.
+        :type seen_id: str
+        :param gen: The corresponding db generation for that document.
+        :type gen: int
+        """
+        self._put_dict_info(
+            'seen_id',
+            (seen_id, gen))
+
+    def seen_ids(self):
+        """
+        Return all document ids seen during the sync.
+
+        :return: A dict with doc ids seen during the sync.
+        :rtype: dict
+        """
+        if 'seen_id' in self._storage:
+            seen_ids = self._storage.get('seen_id')
+        else:
+            seen_ids = []
+        return dict(seen_ids)
+
+    def put_changes_to_return(self, gen, trans_id, changes_to_return):
+        """
+        Put the calculated changes to return in the backend sync state.
+
+        :param gen: The target database generation that will be synced.
+        :type gen: int
+        :param trans_id: The target database transaction id that will be
+                         synced.
+        :type trans_id: str
+        :param changes_to_return: A list of tuples with the changes to be
+                                  returned during the sync process.
+        :type changes_to_return: list
+        """
+        self._put_dict_info(
+            'changes_to_return',
+            {
+                'gen': gen,
+                'trans_id': trans_id,
+                'changes_to_return': changes_to_return,
+            }
+        )
+
+    def sync_info(self):
+        """
+        Return information about the current sync state.
+
+        :return: The generation and transaction id of the target database
+                 which will be synced, and the number of documents to return,
+                 or a tuple of Nones if those have not already been sent to
+                 server.
+        :rtype: tuple
+        """
+        info = self._storage.get('changes_to_return') if 'changes_to_return' in self._storage else None
+        gen = None
+        trans_id = None
+        number_of_changes = None
+        if info:
+            info = info[0]
+            gen = info['gen']
+            trans_id = info['trans_id']
+            number_of_changes = len(info['changes_to_return'])
+        return gen, trans_id, number_of_changes
+
+    def next_change_to_return(self, received):
+        """
+        Return the next change to be returned to the source syncing replica.
+
+        :param received: How many documents the source replica has already
+                         received during the current sync process.
+        :type received: int
+        """
+        info = self._storage.get('changes_to_return') if 'changes_to_return' in self._storage else None
+        gen = trans_id = next_change_to_return = None
+        if info:
+            info = info[0]
+            gen = info['gen']
+            trans_id = info['trans_id']
+            if received < len(info['changes_to_return']):
+                next_change_to_return = tuple(info['changes_to_return'][received])
+        return gen, trans_id, next_change_to_return
diff --git a/server/src/leap/soledad/server/sync.py b/server/src/leap/soledad/server/sync.py
index 18c4ee40..64f7e4e7 100644
--- a/server/src/leap/soledad/server/sync.py
+++ b/server/src/leap/soledad/server/sync.py
@@ -17,183 +17,15 @@
 """
 Server side synchronization infrastructure.
 """
-import json
-
-from leap.soledad.common.couch import CouchDatabase
 from u1db import sync, Document
 from u1db.remote import http_app
+from leap.soledad.server.state import ServerSyncState
 
 
 MAX_REQUEST_SIZE = 200  # in Mb
 MAX_ENTRY_SIZE = 200  # in Mb
 
 
-class ServerSyncState(object):
-    """
-    The state of one sync session, as stored on backend server.
-
-    This object performes queries to distinct design documents:
-
-        _design/syncs/_update/state
-        _design/syncs/_view/state
-        _design/syncs/_view/seen_ids
-        _design/syncs/_view/changes_to_return
-
-    On server side, the ongoing syncs metadata is maintained in a document
-    called 'u1db_sync_state'.
-    """
-
-    def __init__(self, db, source_replica_uid, sync_id):
-        """
-        Initialize the sync state object.
-
-        :param db: The target syncing database.
-        :type db: CouchDatabase.
-        :param source_replica_uid: CouchDatabase
-        :type source_replica_uid: str
-        """
-        self._db = db
-        self._source_replica_uid = source_replica_uid
-        self._sync_id = sync_id
-
-    def _key(self, key):
-        """
-        Format a key to be used on couch views.
-
-        :param key: The lookup key.
-        :type key: json serializable object
-
-        :return: The properly formatted key.
-        :rtype: str
-        """
-        return json.dumps(key, separators=(',', ':'))
-
-    def _put_info(self, key, value):
-        """
-        Put some information on the sync state document.
-
-        This method works in conjunction with the
-        _design/syncs/_update/state update handler couch backend.
-
-        :param key: The key for the info to be put.
-        :type key: str
-        :param value: The value for the info to be put.
-        :type value: str
-        """
-        ddoc_path = [
-            '_design', 'syncs', '_update', 'state',
-            'u1db_sync_state']
-        res = self._db._database.resource(*ddoc_path)
-        with CouchDatabase.sync_info_lock[self._db.replica_uid]:
-            res.put_json(
-                body={
-                    'sync_id': self._sync_id,
-                    'source_replica_uid': self._source_replica_uid,
-                    key: value,
-                },
-                headers={'content-type': 'application/json'})
-
-    def put_seen_id(self, seen_id, gen):
-        """
-        Put one seen id on the sync state document.
-
-        :param seen_id: The doc_id of a document seen during sync.
-        :type seen_id: str
-        :param gen: The corresponding db generation for that document.
-        :type gen: int
-        """
-        self._put_info(
-            'seen_id',
-            [seen_id, gen])
-
-    def seen_ids(self):
-        """
-        Return all document ids seen during the sync.
-
-        :return: A list with doc ids seen during the sync.
-        :rtype: list
-        """
-        ddoc_path = ['_design', 'syncs', '_view', 'seen_ids']
-        resource = self._db._database.resource(*ddoc_path)
-        response = resource.get_json(
-            key=self._key([self._source_replica_uid, self._sync_id]))
-        data = response[2]
-        if data['rows']:
-            entry = data['rows'].pop()
-            return entry['value']['seen_ids']
-        return []
-
-    def put_changes_to_return(self, gen, trans_id, changes_to_return):
-        """
-        Put the calculated changes to return in the backend sync state
-        document.
-
-        :param gen: The target database generation that will be synced.
-        :type gen: int
-        :param trans_id: The target database transaction id that will be
-                         synced.
-        :type trans_id: str
-        :param changes_to_return: A list of tuples with the changes to be
-                                  returned during the sync process.
-        :type changes_to_return: list
-        """
-        self._put_info(
-            'changes_to_return',
-            {
-                'gen': gen,
-                'trans_id': trans_id,
-                'changes_to_return': changes_to_return,
-            }
-        )
-
-    def sync_info(self):
-        """
-        Return information about the current sync state.
-
-        :return: The generation and transaction id of the target database
-                 which will be synced, and the number of documents to return,
-                 or a tuple of Nones if those have not already been sent to
-                 server.
-        :rtype: tuple
-        """
-        ddoc_path = ['_design', 'syncs', '_view', 'state']
-        resource = self._db._database.resource(*ddoc_path)
-        response = resource.get_json(
-            key=self._key([self._source_replica_uid, self._sync_id]))
-        data = response[2]
-        gen = None
-        trans_id = None
-        number_of_changes = None
-        if data['rows'] and data['rows'][0]['value'] is not None:
-            value = data['rows'][0]['value']
-            gen = value['gen']
-            trans_id = value['trans_id']
-            number_of_changes = value['number_of_changes']
-        return gen, trans_id, number_of_changes
-
-    def next_change_to_return(self, received):
-        """
-        Return the next change to be returned to the source syncing replica.
-
-        :param received: How many documents the source replica has already
-                         received during the current sync process.
-        :type received: int
-        """
-        ddoc_path = ['_design', 'syncs', '_view', 'changes_to_return']
-        resource = self._db._database.resource(*ddoc_path)
-        response = resource.get_json(
-            key=self._key(
-                [self._source_replica_uid, self._sync_id, received]))
-        data = response[2]
-        if not data['rows']:
-            return None, None, None
-        value = data['rows'][0]['value']
-        gen = value['gen']
-        trans_id = value['trans_id']
-        next_change_to_return = value['next_change_to_return']
-        return gen, trans_id, tuple(next_change_to_return)
-
-
 class SyncExchange(sync.SyncExchange):
 
     def __init__(self, db, source_replica_uid, last_known_generation, sync_id):
@@ -216,8 +48,7 @@ class SyncExchange(sync.SyncExchange):
         self.new_trans_id = None
         self._trace_hook = None
         # recover sync state
-        self._sync_state = ServerSyncState(
-            self._db, self.source_replica_uid, sync_id)
+        self._sync_state = ServerSyncState(self.source_replica_uid, sync_id)
 
     def find_changes_to_return(self, received):
         """