Change the way pagination works to support out of order events.

2 files changed, 64 insertions, 47 deletions

diff --git a/synapse/api/streams/__init__.py b/synapse/api/streams/__init__.py
index 989e63f9ec..44f4cc6078 100644
--- a/synapse/api/streams/__init__.py
+++ b/synapse/api/streams/__init__.py
@@ -20,23 +20,23 @@ class PaginationConfig(object):
 
     """A configuration object which stores pagination parameters."""
 
-    def __init__(self, from_tok=None, to_tok=None, limit=0):
+    def __init__(self, from_tok=None, to_tok=None, direction='f', limit=0):
         self.from_tok = from_tok
         self.to_tok = to_tok
+        self.direction = direction
         self.limit = limit
 
     @classmethod
     def from_request(cls, request, raise_invalid_params=True):
         params = {
-            "from_tok": PaginationStream.TOK_START,
-            "to_tok": PaginationStream.TOK_END,
-            "limit": 0
+            "direction": 'f',
         }
 
         query_param_mappings = [  # 3-tuple of qp_key, attribute, rules
             ("from", "from_tok", lambda x: type(x) == str),
             ("to", "to_tok", lambda x: type(x) == str),
-            ("limit", "limit", lambda x: x.isdigit())
+            ("limit", "limit", lambda x: x.isdigit()),
+            ("dir", "direction", lambda x: x == 'f' or x == 'b'),
         ]
 
         for qp, attr, is_valid in query_param_mappings:
@@ -48,12 +48,17 @@ class PaginationConfig(object):
 
         return PaginationConfig(**params)
 
+    def __str__(self):
+        return (
+            "<PaginationConfig from_tok=%s, to_tok=%s, "
+            "direction=%s, limit=%s>"
+        ) % (self.from_tok, self.to_tok, self.direction, self.limit)
+
 
 class PaginationStream(object):
 
     """ An interface for streaming data as chunks. """
 
-    TOK_START = "START"
     TOK_END = "END"
 
     def get_chunk(self, config=None):
@@ -76,7 +81,7 @@ class StreamData(object):
         self.hs = hs
         self.store = hs.get_datastore()
 
-    def get_rows(self, user_id, from_pkey, to_pkey, limit):
+    def get_rows(self, user_id, from_pkey, to_pkey, limit, direction):
         """ Get event stream data between the specified pkeys.
 
         Args:
diff --git a/synapse/api/streams/event.py b/synapse/api/streams/event.py
index 414b05be30..a5c8b2b31f 100644
--- a/synapse/api/streams/event.py
+++ b/synapse/api/streams/event.py
@@ -38,8 +38,8 @@ class EventsStreamData(StreamData):
         self.with_feedback = feedback
 
     @defer.inlineCallbacks
-    def get_rows(self, user_id, from_key, to_key, limit):
-        data, latest_ver = yield self.store.get_room_events_stream(
+    def get_rows(self, user_id, from_key, to_key, limit, direction):
+        data, latest_ver = yield self.store.get_room_events(
             user_id=user_id,
             from_key=from_key,
             to_key=to_key,
@@ -70,6 +70,15 @@ class EventStream(PaginationStream):
             pagination_config.from_tok)
         pagination_config.to_tok = yield self.fix_token(
             pagination_config.to_tok)
+
+        if (
+            not pagination_config.to_tok
+            and pagination_config.direction == 'f'
+        ):
+            pagination_config.to_tok = yield self.get_current_max_token()
+
+        logger.debug("pagination_config: %s", pagination_config)
+
         defer.returnValue(pagination_config)
 
     @defer.inlineCallbacks
@@ -81,39 +90,42 @@ class EventStream(PaginationStream):
         Returns:
             The fixed-up token, which may == token.
         """
-        # replace TOK_START and TOK_END with 0_0_0 or -1_-1_-1 depending.
-        replacements = [
-            (PaginationStream.TOK_START, "0"),
-            (PaginationStream.TOK_END, "-1")
-        ]
-        for magic_token, key in replacements:
-            if magic_token == token:
-                token = EventStream.SEPARATOR.join(
-                    [key] * len(self.stream_data)
-                )
-
-        # replace -1 values with an actual pkey
-        token_segments = self._split_token(token)
-        for i, tok in enumerate(token_segments):
-            if tok == -1:
-                # add 1 to the max token because results are EXCLUSIVE from the
-                # latest version.
-                token_segments[i] = 1 + (yield self.stream_data[i].max_token())
-        defer.returnValue(EventStream.SEPARATOR.join(
-            str(x) for x in token_segments
-        ))
+        if token == PaginationStream.TOK_END:
+            new_token = yield self.get_current_max_token()
+
+            logger.debug("fix_token: From %s to %s", token, new_token)
+
+            token = new_token
+
+        defer.returnValue(token)
 
     @defer.inlineCallbacks
-    def get_chunk(self, config=None):
+    def get_current_max_token(self):
+        new_token_parts = []
+        for s in self.stream_data:
+            mx = yield s.max_token()
+            new_token_parts.append(str(mx))
+
+        new_token = EventStream.SEPARATOR.join(new_token_parts)
+
+        logger.debug("get_current_max_token: %s", new_token)
+
+        defer.returnValue(new_token)
+
+    @defer.inlineCallbacks
+    def get_chunk(self, config):
         # no support for limit on >1 streams, makes no sense.
         if config.limit and len(self.stream_data) > 1:
             raise EventStreamError(
                 400, "Limit not supported on multiplexed streams."
             )
 
-        (chunk_data, next_tok) = yield self._get_chunk_data(config.from_tok,
-                                                            config.to_tok,
-                                                            config.limit)
+        chunk_data, next_tok = yield self._get_chunk_data(
+            config.from_tok,
+            config.to_tok,
+            config.limit,
+            config.direction,
+        )
 
         defer.returnValue({
             "chunk": chunk_data,
@@ -122,7 +134,7 @@ class EventStream(PaginationStream):
         })
 
     @defer.inlineCallbacks
-    def _get_chunk_data(self, from_tok, to_tok, limit):
+    def _get_chunk_data(self, from_tok, to_tok, limit, direction):
         """ Get event data between the two tokens.
 
         Tokens are SEPARATOR separated values representing pkey values of
@@ -140,11 +152,12 @@ class EventStream(PaginationStream):
             EventStreamError if something went wrong.
         """
         # sanity check
-        if (from_tok.count(EventStream.SEPARATOR) !=
-                to_tok.count(EventStream.SEPARATOR) or
-                (from_tok.count(EventStream.SEPARATOR) + 1) !=
-                len(self.stream_data)):
-            raise EventStreamError(400, "Token lengths don't match.")
+        if to_tok is not None:
+            if (from_tok.count(EventStream.SEPARATOR) !=
+                    to_tok.count(EventStream.SEPARATOR) or
+                    (from_tok.count(EventStream.SEPARATOR) + 1) !=
+                    len(self.stream_data)):
+                raise EventStreamError(400, "Token lengths don't match.")
 
         chunk = []
         next_ver = []
@@ -158,7 +171,7 @@ class EventStream(PaginationStream):
                 continue
 
             (event_chunk, max_pkey) = yield self.stream_data[i].get_rows(
-                self.user_id, from_pkey, to_pkey, limit
+                self.user_id, from_pkey, to_pkey, limit, direction,
             )
 
             chunk.extend([
@@ -177,9 +190,8 @@ class EventStream(PaginationStream):
         Returns:
             A list of ints.
         """
-        segments = token.split(EventStream.SEPARATOR)
-        try:
-            int_segments = [int(x) for x in segments]
-        except ValueError:
-            raise EventStreamError(400, "Bad token: %s" % token)
-        return int_segments
+        if token:
+            segments = token.split(EventStream.SEPARATOR)
+        else:
+            segments = [None] * len(self.stream_data)
+        return segments