add drain method to StreamingHTTPResponse

sanic/response.py

@@ -120,6 +120,9 @@ class StreamingHTTPResponse(BaseHTTPResponse):
         self.headers = headers or {}
         self._cookies = None
 
+    async def drain():
+        await self.stream_writer.drain()
+
     def write(self, data):
         """Writes a chunk of data to the streaming response.
 

sanic/server.py

@@ -261,6 +261,7 @@ class HttpProtocol(asyncio.Protocol):
         try:
             keep_alive = self.keep_alive
             response.transport = self.transport
+            response.stream_writer = asyncio.StreamWriter(self.transport, self)
             await response.stream(
                 self.request.version, keep_alive, self.request_timeout)
             if self.has_log: