[PR #10088/29c3ca93 backport][3.11] Avoid calling len on the same data in the stream reader twice (#10090)

Co-authored-by: J. Nick Koston <nick@koston.org>

Author: patchback[bot]

aiohttp/streams.py

@@ -517,8 +517,9 @@ def _read_nowait_chunk(self, n: int) -> bytes:
         else:
             data = self._buffer.popleft()
 
-        self._size -= len(data)
-        self._cursor += len(data)
+        data_len = len(data)
+        self._size -= data_len
+        self._cursor += data_len
 
         chunk_splits = self._http_chunk_splits
         # Prevent memory leak: drop useless chunk splits