gateway.websocket: do chunked sends on zlib stream

this should fix issues with big payloads being sent
as a single big websocket message to a client (potentially crashing it).

chunked sends split the payload into 1KB chunks that are each
sent through the websocket. clients are already supposed to handle
this behavior from the zlib-stream docs.

 - utils: add yield_chunks

litecord/gateway/gateway.py

@@ -54,8 +54,6 @@ async def websocket_handler(app, ws, url):
     if gw_compress and gw_compress not in ('zlib-stream',):
         return await ws.close(1000, 'Invalid gateway compress')
 
-    print('encoding', gw_encoding, 'compression', gw_compress)
-
     gws = GatewayWebsocket(ws, app, v=gw_version,
                            encoding=gw_encoding, compress=gw_compress)
     await gws.run()

litecord/gateway/websocket.py

@@ -32,7 +32,9 @@ import earl
 from litecord.auth import raw_token_check
 from litecord.enums import RelationshipType
 from litecord.schemas import validate, GW_STATUS_UPDATE
-from litecord.utils import task_wrapper, LitecordJSONEncoder
+from litecord.utils import (
+    task_wrapper, LitecordJSONEncoder, yield_chunks
+)
 from litecord.permissions import get_permissions
 
 from litecord.gateway.opcodes import OP
@@ -41,7 +43,7 @@ from litecord.gateway.state import GatewayState
 from litecord.errors import (
     WebsocketClose, Unauthorized, Forbidden, BadRequest
 )
-from .errors import (
+from litecord.gateway.errors import (
     DecodeError, UnknownOPCode, InvalidShard, ShardingRequired
 )
 
@@ -125,6 +127,8 @@ class GatewayWebsocket:
                                        zlib.compressobj(),
                                        {})
 
+        log.debug('websocket properties: {!r}', self.wsp)
+
         self.state = None
 
         self._set_encoders()
@@ -139,6 +143,41 @@ class GatewayWebsocket:
 
         self.encoder, self.decoder = encodings[encoding]
 
+    async def _chunked_send(self, data: bytes, chunk_size: int):
+        """Split data in chunk_size-big chunks and send them
+        over the websocket."""
+        total_chunks = 0
+        for chunk in yield_chunks(data, chunk_size):
+            total_chunks += 1
+            await self.ws.send(chunk)
+
+        log.debug('zlib-stream: sent {} chunks', total_chunks)
+
+    async def _zlib_stream_send(self, encoded):
+        """Sending a single payload across multiple compressed
+        websocket messages."""
+
+        # compress and flush (for the rest of compressed data + ZLIB_SUFFIX)
+        data1 = self.wsp.zctx.compress(encoded)
+        data2 = self.wsp.zctx.flush(zlib.Z_FULL_FLUSH)
+
+        log.debug('zlib-stream: length {} -> compressed ({} + {})',
+                  len(encoded), len(data1), len(data2))
+
+        # NOTE: the old approach was ws.send(data1 + data2).
+        #  I changed this to a chunked send of data1 and data2
+        #  because that can bring some problems to the network
+        #  since we can be potentially sending a really big packet
+        #  as a single message.
+
+        #  clients should handle chunked sends (via detection
+        #  of the ZLIB_SUFFIX suffix appended to data2), so
+        #  this shouldn't being problems.
+
+        # TODO: the chunks are 1024 bytes, 1KB, is this good enough?
+        await self._chunked_send(data1, 1024)
+        await self._chunked_send(data2, 1024)
+
     async def send(self, payload: Dict[str, Any]):
         """Send a payload to the websocket.
 
@@ -159,13 +198,11 @@ class GatewayWebsocket:
         if not isinstance(encoded, bytes):
             encoded = encoded.encode()
 
-        # handle zlib-stream, pure zlib or plain
         if self.wsp.compress == 'zlib-stream':
-            data1 = self.wsp.zctx.compress(encoded)
-            data2 = self.wsp.zctx.flush(zlib.Z_FULL_FLUSH)
-
-            await self.ws.send(data1 + data2)
+            await self._zlib_stream_send(encoded)
         elif self.state and self.state.compress and len(encoded) > 1024:
+            # TODO: should we only compress on >1KB packets? or maybe we
+            # should do all?
             await self.ws.send(zlib.compress(encoded))
         else:
             await self.ws.send(encoded.decode())

litecord/utils.py

@@ -158,3 +158,18 @@ async def pg_set_json(con):
         decoder=json.loads,
         schema='pg_catalog'
     )
+
+
+def yield_chunks(input_list: list, chunk_size: int):
+    """Yield successive n-sized chunks from l.
+
+    Taken from https://stackoverflow.com/a/312464.
+
+    Modified to make linter happy (variable name changes,
+    typing, comments).
+    """
+
+    # range accepts step param, so we use that to
+    # make the chunks
+    for idx in range(0, len(input_list), chunk_size):
+        yield input_list[idx:idx + chunk_size]