gh-99941: asyncio.Protocol.data_received now received immutable bytes

Lib/asyncio/proactor_events.py

@@ -288,7 +288,8 @@ def _loop_reading(self, fut=None):
                         # we got end-of-file so no need to reschedule a new read
                         return
 
-                    data = self._data[:length]
+                    # It's a new slice so make it immutable so protocols upstream don't have problems
+                    data = bytes(memoryview(self._data)[:length])
                 else:
                     # the future will be replaced by next proactor.recv call
                     fut.cancel()

Lib/asyncio/streams.py

@@ -688,7 +688,7 @@ async def read(self, n=-1):
             await self._wait_for_data('read')
 
         # This will work right even if buffer is less than n bytes
-        data = bytes(self._buffer[:n])
+        data = bytes(memoryview(self._buffer)[:n])
         del self._buffer[:n]
 
         self._maybe_resume_transport()
@@ -730,7 +730,7 @@ async def readexactly(self, n):
             data = bytes(self._buffer)
             self._buffer.clear()
         else:
-            data = bytes(self._buffer[:n])
+            data = bytes(memoryview(self._buffer)[:n])
             del self._buffer[:n]
         self._maybe_resume_transport()
         return data

Lib/test/test_asyncio/test_proactor_events.py

@@ -75,7 +75,10 @@ def test_loop_reading_data(self):
         called_buf = bytearray(self.buffer_size)
         called_buf[:len(buf)] = buf
         self.loop._proactor.recv_into.assert_called_with(self.sock, called_buf)
-        self.protocol.data_received.assert_called_with(bytearray(buf))
+        self.protocol.data_received.assert_called_with(buf)
+        # assert_called_with maps bytearray and bytes to the same thing so check manually
+        # regression test for https://github.com/python/cpython/issues/99941
+        self.assertIsInstance(self.protocol.data_received.call_args.args[0], bytes)
 
     @unittest.skipIf(sys.flags.optimize, "Assertions are disabled in optimized mode")
     def test_loop_reading_no_data(self):

Misc/NEWS.d/next/Windows/2022-12-06-11-16-46.gh-issue-99941.GmUQ6o.rst

@@ -0,0 +1,2 @@
+Ensure that :func:`asyncio.Protocol.data_received` receives an immutable
+:class:`bytes` object (as documented), instead of :class:`bytearray`.