Add custom stream type for compressed resources

rsrcfork/api.py

@@ -252,9 +252,8 @@ class Resource(object):
 			try:
 				return self._data_decompressed
 			except AttributeError:
-				with self.open_raw() as f:
-					f.seek(self.compressed_info.header_length)
-					self._data_decompressed = b"".join(compress.decompress_stream_parsed(self.compressed_info, f))
+				with self.open() as f:
+					self._data_decompressed = f.read()
 				return self._data_decompressed
 		else:
 			return self.data_raw
@@ -272,7 +271,12 @@ class Resource(object):
 		because the stream API does not require the entire resource data to be read (and possibly decompressed) in advance.
 		"""
 		
-		return io.BytesIO(self.data)
+		if self.compressed_info is None:
+			return self.open_raw()
+		else:
+			f = self.open_raw()
+			f.seek(self.compressed_info.header_length)
+			return compress.DecompressingStream(f, self.compressed_info, close_stream=True)
 
 
 class _LazyResourceMap(typing.Mapping[int, Resource]):

rsrcfork/compress/__init__.py

@@ -66,3 +66,88 @@ def decompress(data: bytes, *, debug: bool = False) -> bytes:
 	"""Decompress the given compressed resource data."""
 	
 	return b"".join(decompress_stream(io.BytesIO(data), debug=debug))
+
+
+class DecompressingStream(io.BufferedIOBase, typing.BinaryIO):
+	_compressed_stream: typing.BinaryIO
+	_close_stream: bool
+	_header_info: CompressedHeaderInfo
+	_decompress_iter: typing.Iterator[bytes]
+	_decompressed_stream: typing.BinaryIO
+	_seek_position: int
+	
+	def __init__(self, compressed_stream: typing.BinaryIO, header_info: typing.Optional[CompressedHeaderInfo], *, close_stream: bool = False) -> None:
+		super().__init__()
+		
+		self._compressed_stream = compressed_stream
+		self._close_stream = close_stream
+		
+		if header_info is not None:
+			self._header_info = header_info
+		else:
+			self._header_info = CompressedHeaderInfo.parse_stream(self._compressed_stream)
+		
+		self._decompress_iter = decompress_stream_parsed(self._header_info, self._compressed_stream)
+		self._decompressed_stream = io.BytesIO()
+		self._seek_position = 0
+	
+	# This override does nothing,
+	# but is needed to make mypy happy,
+	# otherwise it complains (apparently incorrectly) about the __enter__ definitions from IOBase and BinaryIO being incompatible with each other.
+	def __enter__(self: "DecompressingStream") -> "DecompressingStream":
+		return super().__enter__()
+	
+	def close(self) -> None:
+		super().close()
+		if self._close_stream:
+			self._compressed_stream.close()
+		del self._decompress_iter
+		self._decompressed_stream.close()
+	
+	def seekable(self) -> bool:
+		return True
+	
+	def tell(self) -> int:
+		return self._seek_position
+	
+	def seek(self, offset: int, whence: int = io.SEEK_SET) -> int:
+		if whence == io.SEEK_SET:
+			if offset < 0:
+				raise ValueError(f"Negative seek offset not allowed with SEEK_SET: {offset}")
+			
+			self._seek_position = offset
+		elif whence == io.SEEK_CUR:
+			self._seek_position += offset
+		elif whence == io.SEEK_END:
+			self._seek_position = self._header_info.decompressed_length - offset
+		else:
+			raise ValueError(f"Invalid whence value: {whence}")
+		
+		self._seek_position = max(0, min(self._header_info.decompressed_length, self._seek_position))
+		
+		return self._seek_position
+	
+	def readable(self) -> bool:
+		return True
+	
+	def read(self, size: typing.Optional[int] = -1) -> bytes:
+		if size is None:
+			size = -1
+		
+		self._decompressed_stream.seek(0, io.SEEK_END)
+		
+		if size < 0:
+			for chunk in self._decompress_iter:
+				self._decompressed_stream.write(chunk)
+		else:
+			if self._decompressed_stream.tell() - self._seek_position < size:
+				for chunk in self._decompress_iter:
+					self._decompressed_stream.write(chunk)
+					
+					if self._decompressed_stream.tell() - self._seek_position >= size:
+						break
+		
+		self._decompressed_stream.seek(self._seek_position)
+		ret = self._decompressed_stream.read(size)
+		self._seek_position += len(ret)
+		return ret