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Use bytearray instead of BytesIO in MspDecoder #9877

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Use bytearray instead of BytesIO in MspDecoder #9877

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eed2a0e
Rename variable
radarhere Aug 19, 2026
d0b6ba2
Use bytearray instead of BytesIO
radarhere Aug 19, 2026
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17 changes: 8 additions & 9 deletions src/PIL/MspImagePlugin.py
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Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,6 @@
# See also: https://www.fileformat.info/format/mspaint/egff.htm
from __future__ import annotations

import io
import struct
from typing import IO

Expand Down Expand Up @@ -115,7 +114,7 @@ class MspDecoder(ImageFile.PyDecoder):
def decode(self, buffer: Image.DecoderInput) -> tuple[int, int]:
assert self.fd is not None

img = io.BytesIO()
data = bytearray()
blank_line = bytearray((0xFF,) * ((self.state.xsize + 7) // 8))
try:
self.fd.seek(32)
Expand All @@ -126,33 +125,33 @@ def decode(self, buffer: Image.DecoderInput) -> tuple[int, int]:
msg = "Truncated MSP file in row map"
raise OSError(msg) from e

for x, rowlen in enumerate(rowmap):
for y, rowlen in enumerate(rowmap):
try:
if rowlen == 0:
img.write(blank_line)
data += blank_line
continue
row = self.fd.read(rowlen)
if len(row) != rowlen:
msg = f"Truncated MSP file, expected {rowlen} bytes on row {x}"
msg = f"Truncated MSP file, expected {rowlen} bytes on row {y}"
raise OSError(msg)
idx = 0
while idx < rowlen:
runtype = row[idx]
idx += 1
if runtype == 0:
runcount, runval = struct.unpack_from("Bc", row, idx)
img.write(runval * runcount)
data += runval * runcount
idx += 2
else:
runcount = runtype
img.write(row[idx : idx + runcount])
data += row[idx : idx + runcount]
idx += runcount

except struct.error as e:
msg = f"Corrupted MSP file in row {x}"
msg = f"Corrupted MSP file in row {y}"
raise OSError(msg) from e

self.set_as_raw(img.getvalue(), "1")
self.set_as_raw(bytes(data), "1")

return -1, 0

Expand Down