python · gvanrossum · Dec 10, 2022 · Dec 6, 2022 · Dec 6, 2022 · Dec 6, 2022
@@ -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()

@@ -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

@@ -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):

diff --git a/Misc/NEWS.d/next/Windows/2022-12-06-11-16-46.gh-issue-99941.GmUQ6o.rst b/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`.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Ensure that :func:`asyncio.Protocol.data_received` receives an immutable
		:class:`bytes` object (as documented), instead of :class:`bytearray`.