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Keep track of offsets within substreams where possible #1015

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Merged
arekbulski merged 1 commit into from
Oct 23, 2023
Merged

Keep track of offsets within substreams where possible #1015

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47 changes: 38 additions & 9 deletions construct/core.py
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Original file line number Diff line number Diff line change
Expand Up @@ -235,6 +235,29 @@ def stream_iseof(stream):
raise StreamError("stream. read() seek() tell() failed", path="???")


class BytesIOWithOffsets(io.BytesIO):
@staticmethod
def from_reading(stream, length: int, path: str):
offset = stream_tell(stream, path)
contents = stream_read(stream, length, path)
return BytesIOWithOffsets(contents, stream, offset)

def __init__(self, contents: bytes, parent_stream, offset: int):
super().__init__(contents)
self.parent_stream = parent_stream
self.parent_stream_offset = offset

def tell(self) -> int:
return super().tell() + self.parent_stream_offset

def seek(self, offset: int, whence: int = io.SEEK_SET) -> int:
if whence != io.SEEK_SET:
super().seek(offset, whence)
else:
super().seek(offset - self.parent_stream_offset)
return self.tell()


class CodeGen:
def __init__(self):
self.blocks = []
Expand Down Expand Up @@ -4520,8 +4543,8 @@ def _parse(self, stream, context, path):
endpos = stream_tell(stream, path)
stream_seek(stream, curpos, 0, path)
length = endpos + endoffset - curpos
data = stream_read(stream, length, path)
return self.subcon._parsereport(io.BytesIO(data), context, path)
substream = BytesIOWithOffsets.from_reading(stream, length, path)
return self.subcon._parsereport(substream, context, path)

def _build(self, obj, stream, context, path):
return self.subcon._build(obj, stream, context, path)
Expand Down Expand Up @@ -4834,8 +4857,8 @@ def _parse(self, stream, context, path):
length = self.lengthfield._parsereport(stream, context, path)
if self.includelength:
length -= self.lengthfield._sizeof(context, path)
data = stream_read(stream, length, path)
return self.subcon._parsereport(io.BytesIO(data), context, path)
substream = BytesIOWithOffsets.from_reading(stream, length, path)
return self.subcon._parsereport(substream, context, path)

def _build(self, obj, stream, context, path):
stream2 = io.BytesIO()
Expand Down Expand Up @@ -4956,8 +4979,8 @@ def _parse(self, stream, context, path):
length = evaluate(self.length, context)
if length < 0:
raise PaddingError("length cannot be negative", path=path)
data = stream_read(stream, length, path)
return self.subcon._parsereport(io.BytesIO(data), context, path)
substream = BytesIOWithOffsets.from_reading(stream, length, path)
return self.subcon._parsereport(substream, context, path)

def _build(self, obj, stream, context, path):
length = evaluate(self.length, context)
Expand Down Expand Up @@ -5026,6 +5049,7 @@ def _parse(self, stream, context, path):
if unit < 1:
raise PaddingError("NullTerminated term must be at least 1 byte", path=path)
data = b''
offset = stream_tell(stream, path)
while True:
try:
b = stream_read(stream, unit, path)
Expand All @@ -5041,7 +5065,8 @@ def _parse(self, stream, context, path):
stream_seek(stream, -unit, 1, path)
break
data += b
return self.subcon._parsereport(io.BytesIO(data), context, path)
substream = BytesIOWithOffsets(contents=data, parent_stream=stream, offset=offset)
return self.subcon._parsereport(substream, context, path)

def _build(self, obj, stream, context, path):
buildret = self.subcon._build(obj, stream, context, path)
Expand Down Expand Up @@ -5088,6 +5113,7 @@ def _parse(self, stream, context, path):
unit = len(pad)
if unit < 1:
raise PaddingError("NullStripped pad must be at least 1 byte", path=path)
offset = stream_tell(stream, path)
data = stream_read_entire(stream, path)
if unit == 1:
data = data.rstrip(pad)
Expand All @@ -5099,7 +5125,8 @@ def _parse(self, stream, context, path):
while end-unit >= 0 and data[end-unit:end] == pad:
end -= unit
data = data[:end]
return self.subcon._parsereport(io.BytesIO(data), context, path)
substream = BytesIOWithOffsets(contents=data, parent_stream=stream, offset=offset)
return self.subcon._parsereport(substream, context, path)

def _build(self, obj, stream, context, path):
return self.subcon._build(obj, stream, context, path)
Expand Down Expand Up @@ -5323,14 +5350,16 @@ def _parse(self, stream, context, path):
raise StringError("ProcessXor needs integer or bytes pad", path=path)
if isinstance(pad, bytestringtype) and len(pad) == 1:
pad = byte2int(pad)
offset = stream_tell(stream, path)
data = stream_read_entire(stream, path)
if isinstance(pad, integertypes):
if not (pad == 0):
data = integers2bytes( (b ^ pad) for b in data )
if isinstance(pad, bytestringtype):
if not (len(pad) <= 64 and pad == bytes(len(pad))):
data = integers2bytes( (b ^ p) for b,p in zip(data, itertools.cycle(pad)) )
return self.subcon._parsereport(io.BytesIO(data), context, path)
substream = BytesIOWithOffsets(data, stream, offset)
return self.subcon._parsereport(substream, context, path)

def _build(self, obj, stream, context, path):
pad = evaluate(self.padfunc, context)
Expand Down