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Raise ParsingError instead of asserting on oversized frame payload #763

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Raise ParsingError instead of asserting on oversized frame payload #763

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6 changes: 5 additions & 1 deletion bellows/ash.py
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Original file line number Diff line number Diff line change
Expand Up @@ -177,7 +177,11 @@ class DataFrame(AshFrame):

@staticmethod
def _randomize(data: bytes) -> bytes:
assert len(data) <= len(PSEUDO_RANDOM_DATA_SEQUENCE)
if len(data) > len(PSEUDO_RANDOM_DATA_SEQUENCE):
raise ParsingError(
f"Frame payload is too long: {len(data)} >"
f" {len(PSEUDO_RANDOM_DATA_SEQUENCE)} bytes"
)
return bytes([a ^ b for a, b in zip(data, PSEUDO_RANDOM_DATA_SEQUENCE)])

@classmethod
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12 changes: 12 additions & 0 deletions tests/test_ash.py
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Expand Up @@ -197,6 +197,18 @@ def test_frame_parsing_errors():
assert ash.RstFrame.from_bytes(b"\xC0\xAB\xCD")


def test_data_frame_payload_too_long():
seq_len = len(ash.PSEUDO_RANDOM_DATA_SEQUENCE)

# A payload of exactly the sequence length still parses.
ash.DataFrame.from_bytes(ash.AshFrame.append_crc(bytes([0x00]) + bytes(seq_len)))

@zigpy-review-bot zigpy-review-bot Oct 4, 2026

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Optional: this line only checks that no exception is raised. Asserting on the result would also pin that the derandomized payload isn't truncated at the boundary, e.g. assert len(ash.DataFrame.from_bytes(...).ezsp_frame) == seq_len.


# One byte longer must raise ParsingError, not an uncaught AssertionError.
too_long = ash.AshFrame.append_crc(bytes([0x00]) + bytes(seq_len + 1))
with pytest.raises(ash.ParsingError, match=r"too long"):
ash.DataFrame.from_bytes(too_long)


def test_rst_frame():
assert ash.RstFrame() == ash.RstFrame()
assert ash.RstFrame().to_bytes() == b"\xC0\x38\xBC"
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