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Allow OverlayStream overlay at offset 0 #116

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Merged
Schamper merged 1 commit into from
Jan 29, 2026
Merged

Allow OverlayStream overlay at offset 0 #116

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2 changes: 1 addition & 1 deletion dissect/util/stream.py
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Original file line number Diff line number Diff line change
Expand Up @@ -547,7 +547,7 @@ def _read(self, offset: int, length: int) -> bytes:
if length == 0:
break

if next_overlay_offset:
if next_overlay_offset is not None:
next_overlay_size, next_overlay_data = overlays[next_overlay_offset]
gap_to_next_overlay = next_overlay_offset - offset

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16 changes: 16 additions & 0 deletions tests/test_stream.py
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Expand Up @@ -194,6 +194,22 @@ def test_overlay_stream() -> None:
assert fh.read(100) == b"\x04" * 4


def test_overlay_stream_add_at_offset_zero() -> None:
buf = io.BytesIO(b"\x00" * 100)
fh = stream.OverlayStream(buf, size=100)

# Add a small overlay at offset zero
fh.add(0, b"MZ")

assert fh.read(2) == b"MZ"

fh.seek(0)
assert fh.read(100) == b"MZ" + (b"\x00" * 98)

fh.seek(0)
assert fh.read() == b"MZ" + (b"\x00" * 98)


def test_zlib_stream() -> None:
data = b"\x01" * 8192 + b"\x02" * 8192 + b"\x03" * 8192 + b"\x04" * 8192
fh = stream.ZlibStream(io.BytesIO(zlib.compress(data)), size=8192 * 4, align=512)
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