Merge branch 'release-v0.21.0' of github.com:matrix-org/synapse v0.21.0

6 files changed, 495 insertions, 84 deletions

diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index deee0f4904..861441708b 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -474,8 +474,13 @@ class FederationClient(FederationBase):
             content (object): Any additional data to put into the content field
                 of the event.
         Return:
-            A tuple of (origin (str), event (object)) where origin is the remote
-            homeserver which generated the event.
+            Deferred: resolves to a tuple of (origin (str), event (object))
+            where origin is the remote homeserver which generated the event.
+
+            Fails with a ``CodeMessageException`` if the chosen remote server
+            returns a 300/400 code.
+
+            Fails with a ``RuntimeError`` if no servers were reachable.
         """
         valid_memberships = {Membership.JOIN, Membership.LEAVE}
         if membership not in valid_memberships:
@@ -528,6 +533,27 @@ class FederationClient(FederationBase):
 
     @defer.inlineCallbacks
     def send_join(self, destinations, pdu):
+        """Sends a join event to one of a list of homeservers.
+
+        Doing so will cause the remote server to add the event to the graph,
+        and send the event out to the rest of the federation.
+
+        Args:
+            destinations (str): Candidate homeservers which are probably
+                participating in the room.
+            pdu (BaseEvent): event to be sent
+
+        Return:
+            Deferred: resolves to a dict with members ``origin`` (a string
+            giving the serer the event was sent to, ``state`` (?) and
+            ``auth_chain``.
+
+            Fails with a ``CodeMessageException`` if the chosen remote server
+            returns a 300/400 code.
+
+            Fails with a ``RuntimeError`` if no servers were reachable.
+        """
+
         for destination in destinations:
             if destination == self.server_name:
                 continue
@@ -635,6 +661,26 @@ class FederationClient(FederationBase):
 
     @defer.inlineCallbacks
     def send_leave(self, destinations, pdu):
+        """Sends a leave event to one of a list of homeservers.
+
+        Doing so will cause the remote server to add the event to the graph,
+        and send the event out to the rest of the federation.
+
+        This is mostly useful to reject received invites.
+
+        Args:
+            destinations (str): Candidate homeservers which are probably
+                participating in the room.
+            pdu (BaseEvent): event to be sent
+
+        Return:
+            Deferred: resolves to None.
+
+            Fails with a ``CodeMessageException`` if the chosen remote server
+            returns a non-200 code.
+
+            Fails with a ``RuntimeError`` if no servers were reachable.
+        """
         for destination in destinations:
             if destination == self.server_name:
                 continue
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index bc20b9c201..51e3fdea06 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -440,6 +440,16 @@ class FederationServer(FederationBase):
                         key_id: json.loads(json_bytes)
                     }
 
+        logger.info(
+            "Claimed one-time-keys: %s",
+            ",".join((
+                "%s for %s:%s" % (key_id, user_id, device_id)
+                for user_id, user_keys in json_result.iteritems()
+                for device_id, device_keys in user_keys.iteritems()
+                for key_id, _ in device_keys.iteritems()
+            )),
+        )
+
         defer.returnValue({"one_time_keys": json_result})
 
     @defer.inlineCallbacks
diff --git a/synapse/federation/send_queue.py b/synapse/federation/send_queue.py
index bbb0195228..93e5acebc1 100644
--- a/synapse/federation/send_queue.py
+++ b/synapse/federation/send_queue.py
@@ -31,21 +31,19 @@ Events are replicated via a separate events stream.
 
 from .units import Edu
 
+from synapse.storage.presence import UserPresenceState
 from synapse.util.metrics import Measure
 import synapse.metrics
 
 from blist import sorteddict
-import ujson
+from collections import namedtuple
 
+import logging
 
-metrics = synapse.metrics.get_metrics_for(__name__)
+logger = logging.getLogger(__name__)
 
 
-PRESENCE_TYPE = "p"
-KEYED_EDU_TYPE = "k"
-EDU_TYPE = "e"
-FAILURE_TYPE = "f"
-DEVICE_MESSAGE_TYPE = "d"
+metrics = synapse.metrics.get_metrics_for(__name__)
 
 
 class FederationRemoteSendQueue(object):
@@ -55,18 +53,19 @@ class FederationRemoteSendQueue(object):
         self.server_name = hs.hostname
         self.clock = hs.get_clock()
         self.notifier = hs.get_notifier()
+        self.is_mine_id = hs.is_mine_id
 
-        self.presence_map = {}
-        self.presence_changed = sorteddict()
+        self.presence_map = {}  # Pending presence map user_id -> UserPresenceState
+        self.presence_changed = sorteddict()  # Stream position -> user_id
 
-        self.keyed_edu = {}
-        self.keyed_edu_changed = sorteddict()
+        self.keyed_edu = {}  # (destination, key) -> EDU
+        self.keyed_edu_changed = sorteddict()  # stream position -> (destination, key)
 
-        self.edus = sorteddict()
+        self.edus = sorteddict()  # stream position -> Edu
 
-        self.failures = sorteddict()
+        self.failures = sorteddict()  # stream position -> (destination, Failure)
 
-        self.device_messages = sorteddict()
+        self.device_messages = sorteddict()  # stream position -> destination
 
         self.pos = 1
         self.pos_time = sorteddict()
@@ -122,7 +121,9 @@ class FederationRemoteSendQueue(object):
                 del self.presence_changed[key]
 
             user_ids = set(
-                user_id for uids in self.presence_changed.values() for _, user_id in uids
+                user_id
+                for uids in self.presence_changed.itervalues()
+                for user_id in uids
             )
 
             to_del = [
@@ -189,18 +190,20 @@ class FederationRemoteSendQueue(object):
 
         self.notifier.on_new_replication_data()
 
-    def send_presence(self, destination, states):
-        """As per TransactionQueue"""
+    def send_presence(self, states):
+        """As per TransactionQueue
+
+        Args:
+            states (list(UserPresenceState))
+        """
         pos = self._next_pos()
 
-        self.presence_map.update({
-            state.user_id: state
-            for state in states
-        })
+        # We only want to send presence for our own users, so lets always just
+        # filter here just in case.
+        local_states = filter(lambda s: self.is_mine_id(s.user_id), states)
 
-        self.presence_changed[pos] = [
-            (destination, state.user_id) for state in states
-        ]
+        self.presence_map.update({state.user_id: state for state in local_states})
+        self.presence_changed[pos] = [state.user_id for state in local_states]
 
         self.notifier.on_new_replication_data()
 
@@ -220,10 +223,15 @@ class FederationRemoteSendQueue(object):
     def get_current_token(self):
         return self.pos - 1
 
-    def get_replication_rows(self, token, limit, federation_ack=None):
-        """
+    def federation_ack(self, token):
+        self._clear_queue_before_pos(token)
+
+    def get_replication_rows(self, from_token, to_token, limit, federation_ack=None):
+        """Get rows to be sent over federation between the two tokens
+
         Args:
-            token (int)
+            from_token (int)
+            to_token(int)
             limit (int)
             federation_ack (int): Optional. The position where the worker is
                 explicitly acknowledged it has handled. Allows us to drop
@@ -232,9 +240,11 @@ class FederationRemoteSendQueue(object):
         # TODO: Handle limit.
 
         # To handle restarts where we wrap around
-        if token > self.pos:
-            token = -1
+        if from_token > self.pos:
+            from_token = -1
 
+        # list of tuple(int, BaseFederationRow), where the first is the position
+        # of the federation stream.
         rows = []
 
         # There should be only one reader, so lets delete everything its
@@ -244,62 +254,295 @@ class FederationRemoteSendQueue(object):
 
         # Fetch changed presence
         keys = self.presence_changed.keys()
-        i = keys.bisect_right(token)
-        dest_user_ids = set(
-            (pos, dest_user_id)
-            for pos in keys[i:]
-            for dest_user_id in self.presence_changed[pos]
-        )
+        i = keys.bisect_right(from_token)
+        j = keys.bisect_right(to_token) + 1
+        dest_user_ids = [
+            (pos, user_id)
+            for pos in keys[i:j]
+            for user_id in self.presence_changed[pos]
+        ]
 
-        for (key, (dest, user_id)) in dest_user_ids:
-            rows.append((key, PRESENCE_TYPE, ujson.dumps({
-                "destination": dest,
-                "state": self.presence_map[user_id].as_dict(),
-            })))
+        for (key, user_id) in dest_user_ids:
+            rows.append((key, PresenceRow(
+                state=self.presence_map[user_id],
+            )))
 
         # Fetch changes keyed edus
         keys = self.keyed_edu_changed.keys()
-        i = keys.bisect_right(token)
-        keyed_edus = set((k, self.keyed_edu_changed[k]) for k in keys[i:])
-
-        for (pos, (destination, edu_key)) in keyed_edus:
-            rows.append(
-                (pos, KEYED_EDU_TYPE, ujson.dumps({
-                    "key": edu_key,
-                    "edu": self.keyed_edu[(destination, edu_key)].get_internal_dict(),
-                }))
-            )
+        i = keys.bisect_right(from_token)
+        j = keys.bisect_right(to_token) + 1
+        # We purposefully clobber based on the key here, python dict comprehensions
+        # always use the last value, so this will correctly point to the last
+        # stream position.
+        keyed_edus = {self.keyed_edu_changed[k]: k for k in keys[i:j]}
+
+        for ((destination, edu_key), pos) in keyed_edus.iteritems():
+            rows.append((pos, KeyedEduRow(
+                key=edu_key,
+                edu=self.keyed_edu[(destination, edu_key)],
+            )))
 
         # Fetch changed edus
         keys = self.edus.keys()
-        i = keys.bisect_right(token)
-        edus = set((k, self.edus[k]) for k in keys[i:])
+        i = keys.bisect_right(from_token)
+        j = keys.bisect_right(to_token) + 1
+        edus = ((k, self.edus[k]) for k in keys[i:j])
 
         for (pos, edu) in edus:
-            rows.append((pos, EDU_TYPE, ujson.dumps(edu.get_internal_dict())))
+            rows.append((pos, EduRow(edu)))
 
         # Fetch changed failures
         keys = self.failures.keys()
-        i = keys.bisect_right(token)
-        failures = set((k, self.failures[k]) for k in keys[i:])
+        i = keys.bisect_right(from_token)
+        j = keys.bisect_right(to_token) + 1
+        failures = ((k, self.failures[k]) for k in keys[i:j])
 
         for (pos, (destination, failure)) in failures:
-            rows.append((pos, FAILURE_TYPE, ujson.dumps({
-                "destination": destination,
-                "failure": failure,
-            })))
+            rows.append((pos, FailureRow(
+                destination=destination,
+                failure=failure,
+            )))
 
         # Fetch changed device messages
         keys = self.device_messages.keys()
-        i = keys.bisect_right(token)
-        device_messages = set((k, self.device_messages[k]) for k in keys[i:])
+        i = keys.bisect_right(from_token)
+        j = keys.bisect_right(to_token) + 1
+        device_messages = {self.device_messages[k]: k for k in keys[i:j]}
 
-        for (pos, destination) in device_messages:
-            rows.append((pos, DEVICE_MESSAGE_TYPE, ujson.dumps({
-                "destination": destination,
-            })))
+        for (destination, pos) in device_messages.iteritems():
+            rows.append((pos, DeviceRow(
+                destination=destination,
+            )))
 
         # Sort rows based on pos
         rows.sort()
 
-        return rows
+        return [(pos, row.TypeId, row.to_data()) for pos, row in rows]
+
+
+class BaseFederationRow(object):
+    """Base class for rows to be sent in the federation stream.
+
+    Specifies how to identify, serialize and deserialize the different types.
+    """
+
+    TypeId = None  # Unique string that ids the type. Must be overriden in sub classes.
+
+    @staticmethod
+    def from_data(data):
+        """Parse the data from the federation stream into a row.
+
+        Args:
+            data: The value of ``data`` from FederationStreamRow.data, type
+                depends on the type of stream
+        """
+        raise NotImplementedError()
+
+    def to_data(self):
+        """Serialize this row to be sent over the federation stream.
+
+        Returns:
+            The value to be sent in FederationStreamRow.data. The type depends
+            on the type of stream.
+        """
+        raise NotImplementedError()
+
+    def add_to_buffer(self, buff):
+        """Add this row to the appropriate field in the buffer ready for this
+        to be sent over federation.
+
+        We use a buffer so that we can batch up events that have come in at
+        the same time and send them all at once.
+
+        Args:
+            buff (BufferedToSend)
+        """
+        raise NotImplementedError()
+
+
+class PresenceRow(BaseFederationRow, namedtuple("PresenceRow", (
+    "state",  # UserPresenceState
+))):
+    TypeId = "p"
+
+    @staticmethod
+    def from_data(data):
+        return PresenceRow(
+            state=UserPresenceState.from_dict(data)
+        )
+
+    def to_data(self):
+        return self.state.as_dict()
+
+    def add_to_buffer(self, buff):
+        buff.presence.append(self.state)
+
+
+class KeyedEduRow(BaseFederationRow, namedtuple("KeyedEduRow", (
+    "key",  # tuple(str) - the edu key passed to send_edu
+    "edu",  # Edu
+))):
+    """Streams EDUs that have an associated key that is ued to clobber. For example,
+    typing EDUs clobber based on room_id.
+    """
+
+    TypeId = "k"
+
+    @staticmethod
+    def from_data(data):
+        return KeyedEduRow(
+            key=tuple(data["key"]),
+            edu=Edu(**data["edu"]),
+        )
+
+    def to_data(self):
+        return {
+            "key": self.key,
+            "edu": self.edu.get_internal_dict(),
+        }
+
+    def add_to_buffer(self, buff):
+        buff.keyed_edus.setdefault(
+            self.edu.destination, {}
+        )[self.key] = self.edu
+
+
+class EduRow(BaseFederationRow, namedtuple("EduRow", (
+    "edu",  # Edu
+))):
+    """Streams EDUs that don't have keys. See KeyedEduRow
+    """
+    TypeId = "e"
+
+    @staticmethod
+    def from_data(data):
+        return EduRow(Edu(**data))
+
+    def to_data(self):
+        return self.edu.get_internal_dict()
+
+    def add_to_buffer(self, buff):
+        buff.edus.setdefault(self.edu.destination, []).append(self.edu)
+
+
+class FailureRow(BaseFederationRow, namedtuple("FailureRow", (
+    "destination",  # str
+    "failure",
+))):
+    """Streams failures to a remote server. Failures are issued when there was
+    something wrong with a transaction the remote sent us, e.g. it included
+    an event that was invalid.
+    """
+
+    TypeId = "f"
+
+    @staticmethod
+    def from_data(data):
+        return FailureRow(
+            destination=data["destination"],
+            failure=data["failure"],
+        )
+
+    def to_data(self):
+        return {
+            "destination": self.destination,
+            "failure": self.failure,
+        }
+
+    def add_to_buffer(self, buff):
+        buff.failures.setdefault(self.destination, []).append(self.failure)
+
+
+class DeviceRow(BaseFederationRow, namedtuple("DeviceRow", (
+    "destination",  # str
+))):
+    """Streams the fact that either a) there is pending to device messages for
+    users on the remote, or b) a local users device has changed and needs to
+    be sent to the remote.
+    """
+    TypeId = "d"
+
+    @staticmethod
+    def from_data(data):
+        return DeviceRow(destination=data["destination"])
+
+    def to_data(self):
+        return {"destination": self.destination}
+
+    def add_to_buffer(self, buff):
+        buff.device_destinations.add(self.destination)
+
+
+TypeToRow = {
+    Row.TypeId: Row
+    for Row in (
+        PresenceRow,
+        KeyedEduRow,
+        EduRow,
+        FailureRow,
+        DeviceRow,
+    )
+}
+
+
+ParsedFederationStreamData = namedtuple("ParsedFederationStreamData", (
+    "presence",  # list(UserPresenceState)
+    "keyed_edus",  # dict of destination -> { key -> Edu }
+    "edus",  # dict of destination -> [Edu]
+    "failures",  # dict of destination -> [failures]
+    "device_destinations",  # set of destinations
+))
+
+
+def process_rows_for_federation(transaction_queue, rows):
+    """Parse a list of rows from the federation stream and put them in the
+    transaction queue ready for sending to the relevant homeservers.
+
+    Args:
+        transaction_queue (TransactionQueue)
+        rows (list(synapse.replication.tcp.streams.FederationStreamRow))
+    """
+
+    # The federation stream contains a bunch of different types of
+    # rows that need to be handled differently. We parse the rows, put
+    # them into the appropriate collection and then send them off.
+
+    buff = ParsedFederationStreamData(
+        presence=[],
+        keyed_edus={},
+        edus={},
+        failures={},
+        device_destinations=set(),
+    )
+
+    # Parse the rows in the stream and add to the buffer
+    for row in rows:
+        if row.type not in TypeToRow:
+            logger.error("Unrecognized federation row type %r", row.type)
+            continue
+
+        RowType = TypeToRow[row.type]
+        parsed_row = RowType.from_data(row.data)
+        parsed_row.add_to_buffer(buff)
+
+    if buff.presence:
+        transaction_queue.send_presence(buff.presence)
+
+    for destination, edu_map in buff.keyed_edus.iteritems():
+        for key, edu in edu_map.items():
+            transaction_queue.send_edu(
+                edu.destination, edu.edu_type, edu.content, key=key,
+            )
+
+    for destination, edu_list in buff.edus.iteritems():
+        for edu in edu_list:
+            transaction_queue.send_edu(
+                edu.destination, edu.edu_type, edu.content, key=None,
+            )
+
+    for destination, failure_list in buff.failures.iteritems():
+        for failure in failure_list:
+            transaction_queue.send_failure(destination, failure)
+
+    for destination in buff.device_destinations:
+        transaction_queue.send_device_messages(destination)
diff --git a/synapse/federation/transaction_queue.py b/synapse/federation/transaction_queue.py
index c27ce7c5f3..a15198e05d 100644
--- a/synapse/federation/transaction_queue.py
+++ b/synapse/federation/transaction_queue.py
@@ -21,11 +21,10 @@ from .units import Transaction, Edu
 
 from synapse.api.errors import HttpResponseException
 from synapse.util.async import run_on_reactor
-from synapse.util.logcontext import preserve_context_over_fn
+from synapse.util.logcontext import preserve_context_over_fn, preserve_fn
 from synapse.util.retryutils import NotRetryingDestination, get_retry_limiter
 from synapse.util.metrics import measure_func
-from synapse.types import get_domain_from_id
-from synapse.handlers.presence import format_user_presence_state
+from synapse.handlers.presence import format_user_presence_state, get_interested_remotes
 import synapse.metrics
 
 import logging
@@ -41,6 +40,8 @@ sent_pdus_destination_dist = client_metrics.register_distribution(
 )
 sent_edus_counter = client_metrics.register_counter("sent_edus")
 
+sent_transactions_counter = client_metrics.register_counter("sent_transactions")
+
 
 class TransactionQueue(object):
     """This class makes sure we only have one transaction in flight at
@@ -77,8 +78,18 @@ class TransactionQueue(object):
         # destination -> list of tuple(edu, deferred)
         self.pending_edus_by_dest = edus = {}
 
-        # Presence needs to be separate as we send single aggragate EDUs
+        # Map of user_id -> UserPresenceState for all the pending presence
+        # to be sent out by user_id. Entries here get processed and put in
+        # pending_presence_by_dest
+        self.pending_presence = {}
+
+        # Map of destination -> user_id -> UserPresenceState of pending presence
+        # to be sent to each destinations
         self.pending_presence_by_dest = presence = {}
+
+        # Pending EDUs by their "key". Keyed EDUs are EDUs that get clobbered
+        # based on their key (e.g. typing events by room_id)
+        # Map of destination -> (edu_type, key) -> Edu
         self.pending_edus_keyed_by_dest = edus_keyed = {}
 
         metrics.register_callback(
@@ -113,6 +124,8 @@ class TransactionQueue(object):
         self._is_processing = False
         self._last_poked_id = -1
 
+        self._processing_pending_presence = False
+
     def can_send_to(self, destination):
         """Can we send messages to the given server?
 
@@ -169,15 +182,12 @@ class TransactionQueue(object):
                     # Otherwise if the last member on a server in a room is
                     # banned then it won't receive the event because it won't
                     # be in the room after the ban.
-                    users_in_room = yield self.state.get_current_user_in_room(
+                    destinations = yield self.state.get_current_hosts_in_room(
                         event.room_id, latest_event_ids=[
                             prev_id for prev_id, _ in event.prev_events
                         ],
                     )
 
-                    destinations = set(
-                        get_domain_from_id(user_id) for user_id in users_in_room
-                    )
                     if send_on_behalf_of is not None:
                         # If we are sending the event on behalf of another server
                         # then it already has the event and there is no reason to
@@ -224,17 +234,71 @@ class TransactionQueue(object):
                 self._attempt_new_transaction, destination
             )
 
-    def send_presence(self, destination, states):
-        if not self.can_send_to(destination):
-            return
+    @preserve_fn  # the caller should not yield on this
+    @defer.inlineCallbacks
+    def send_presence(self, states):
+        """Send the new presence states to the appropriate destinations.
 
-        self.pending_presence_by_dest.setdefault(destination, {}).update({
+        This actually queues up the presence states ready for sending and
+        triggers a background task to process them and send out the transactions.
+
+        Args:
+            states (list(UserPresenceState))
+        """
+
+        # First we queue up the new presence by user ID, so multiple presence
+        # updates in quick successtion are correctly handled
+        # We only want to send presence for our own users, so lets always just
+        # filter here just in case.
+        self.pending_presence.update({
             state.user_id: state for state in states
+            if self.is_mine_id(state.user_id)
         })
 
-        preserve_context_over_fn(
-            self._attempt_new_transaction, destination
-        )
+        # We then handle the new pending presence in batches, first figuring
+        # out the destinations we need to send each state to and then poking it
+        # to attempt a new transaction. We linearize this so that we don't
+        # accidentally mess up the ordering and send multiple presence updates
+        # in the wrong order
+        if self._processing_pending_presence:
+            return
+
+        self._processing_pending_presence = True
+        try:
+            while True:
+                states_map = self.pending_presence
+                self.pending_presence = {}
+
+                if not states_map:
+                    break
+
+                yield self._process_presence_inner(states_map.values())
+        finally:
+            self._processing_pending_presence = False
+
+    @measure_func("txnqueue._process_presence")
+    @defer.inlineCallbacks
+    def _process_presence_inner(self, states):
+        """Given a list of states populate self.pending_presence_by_dest and
+        poke to send a new transaction to each destination
+
+        Args:
+            states (list(UserPresenceState))
+        """
+        hosts_and_states = yield get_interested_remotes(self.store, states, self.state)
+
+        for destinations, states in hosts_and_states:
+            for destination in destinations:
+                if not self.can_send_to(destination):
+                    continue
+
+                self.pending_presence_by_dest.setdefault(
+                    destination, {}
+                ).update({
+                    state.user_id: state for state in states
+                })
+
+                preserve_fn(self._attempt_new_transaction)(destination)
 
     def send_edu(self, destination, edu_type, content, key=None):
         edu = Edu(
@@ -374,6 +438,7 @@ class TransactionQueue(object):
                     destination, pending_pdus, pending_edus, pending_failures,
                 )
                 if success:
+                    sent_transactions_counter.inc()
                     # Remove the acknowledged device messages from the database
                     # Only bother if we actually sent some device messages
                     if device_message_edus:
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 15a03378f5..52b2a717d2 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -193,6 +193,26 @@ class TransportLayerClient(object):
     @defer.inlineCallbacks
     @log_function
     def make_membership_event(self, destination, room_id, user_id, membership):
+        """Asks a remote server to build and sign us a membership event
+
+        Note that this does not append any events to any graphs.
+
+        Args:
+            destination (str): address of remote homeserver
+            room_id (str): room to join/leave
+            user_id (str): user to be joined/left
+            membership (str): one of join/leave
+
+        Returns:
+            Deferred: Succeeds when we get a 2xx HTTP response. The result
+            will be the decoded JSON body (ie, the new event).
+
+            Fails with ``HTTPRequestException`` if we get an HTTP response
+            code >= 300.
+
+            Fails with ``NotRetryingDestination`` if we are not yet ready
+            to retry this server.
+        """
         valid_memberships = {Membership.JOIN, Membership.LEAVE}
         if membership not in valid_memberships:
             raise RuntimeError(
@@ -201,11 +221,23 @@ class TransportLayerClient(object):
             )
         path = PREFIX + "/make_%s/%s/%s" % (membership, room_id, user_id)
 
+        ignore_backoff = False
+        retry_on_dns_fail = False
+
+        if membership == Membership.LEAVE:
+            # we particularly want to do our best to send leave events. The
+            # problem is that if it fails, we won't retry it later, so if the
+            # remote server was just having a momentary blip, the room will be
+            # out of sync.
+            ignore_backoff = True
+            retry_on_dns_fail = True
+
         content = yield self.client.get_json(
             destination=destination,
             path=path,
-            retry_on_dns_fail=False,
+            retry_on_dns_fail=retry_on_dns_fail,
             timeout=20000,
+            ignore_backoff=ignore_backoff,
         )
 
         defer.returnValue(content)
@@ -232,6 +264,12 @@ class TransportLayerClient(object):
             destination=destination,
             path=path,
             data=content,
+
+            # we want to do our best to send this through. The problem is
+            # that if it fails, we won't retry it later, so if the remote
+            # server was just having a momentary blip, the room will be out of
+            # sync.
+            ignore_backoff=True,
         )
 
         defer.returnValue(response)
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index c840da834c..3d676e7d8b 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -24,6 +24,7 @@ from synapse.http.servlet import (
 )
 from synapse.util.ratelimitutils import FederationRateLimiter
 from synapse.util.versionstring import get_version_string
+from synapse.util.logcontext import preserve_fn
 from synapse.types import ThirdPartyInstanceID
 
 import functools
@@ -79,6 +80,7 @@ class Authenticator(object):
     def __init__(self, hs):
         self.keyring = hs.get_keyring()
         self.server_name = hs.hostname
+        self.store = hs.get_datastore()
 
     # A method just so we can pass 'self' as the authenticator to the Servlets
     @defer.inlineCallbacks
@@ -138,6 +140,13 @@ class Authenticator(object):
         logger.info("Request from %s", origin)
         request.authenticated_entity = origin
 
+        # If we get a valid signed request from the other side, its probably
+        # alive
+        retry_timings = yield self.store.get_destination_retry_timings(origin)
+        if retry_timings and retry_timings["retry_last_ts"]:
+            logger.info("Marking origin %r as up", origin)
+            preserve_fn(self.store.set_destination_retry_timings)(origin, 0, 0)
+
         defer.returnValue(origin)