Add Resource.compressed_info attribute

This allows accessing a compressed resource's header data, without
having to decompress it or parse the compressed data manually.

rsrcfork/api.py

@@ -96,7 +96,7 @@ class ResourceAttrs(enum.Flag):
 class Resource(object):
 	"""A single resource from a resource file."""
 	
-	__slots__ = ("type", "id", "name", "attributes", "data_raw", "_data_decompressed")
+	__slots__ = ("type", "id", "name", "attributes", "data_raw", "_compressed_info", "_data_decompressed")
 	
 	def __init__(self, resource_type: bytes, resource_id: int, name: typing.Optional[bytes], attributes: ResourceAttrs, data_raw: bytes):
 		"""Create a new resource with the given type code, ID, name, attributes, and data."""
@@ -138,6 +138,22 @@ class Resource(object):
 		warnings.warn(DeprecationWarning("The resource_id attribute has been deprecated and will be removed in a future version. Please use the id attribute instead."))
 		return self.id
 	
+	@property
+	def compressed_info(self) -> typing.Optional[compress.common.CompressedHeaderInfo]:
+		"""The compressed resource header information, or None if this resource is not compressed.
+		
+		Accessing this attribute may raise a DecompressError if the resource data is compressed and the header could not be parsed. To access the unparsed header data, use the data_raw attribute.
+		"""
+		
+		if ResourceAttrs.resCompressed in self.attributes:
+			try:
+				return self._compressed_info
+			except AttributeError:
+				self._compressed_info = compress.common.CompressedHeaderInfo.parse(self.data_raw)
+				return self._compressed_info
+		else:
+			return None
+	
 	@property
 	def data(self) -> bytes:
 		"""The resource data, decompressed if necessary.
@@ -149,7 +165,7 @@ class Resource(object):
 			try:
 				return self._data_decompressed
 			except AttributeError:
-				self._data_decompressed = compress.decompress(self.data_raw)
+				self._data_decompressed = compress.decompress_parsed(self.compressed_info, self.data_raw[self.compressed_info.header_length:])
 				return self._data_decompressed
 		else:
 			return self.data_raw

rsrcfork/compress/__init__.py

@@ -19,6 +19,20 @@ DECOMPRESSORS = {
 }
 
 
+def decompress_parsed(header_info: CompressedHeaderInfo, data: bytes, *, debug: bool=False) -> bytes:
+	"""Decompress the given compressed resource data, whose header has already been removed and parsed into a CompressedHeaderInfo object."""
+	
+	try:
+		decompress_func = DECOMPRESSORS[header_info.dcmp_id]
+	except KeyError:
+		raise DecompressError(f"Unsupported 'dcmp' ID: {header_info.dcmp_id}")
+	
+	decompressed = decompress_func(header_info, data, debug=debug)
+	if len(decompressed) != header_info.decompressed_length:
+		raise DecompressError(f"Actual length of decompressed data ({len(decompressed)}) does not match length stored in resource ({header_info.decompressed_length})")
+	return decompressed
+
+
 def decompress(data: bytes, *, debug: bool=False) -> bytes:
 	"""Decompress the given compressed resource data."""
 	
@@ -27,12 +41,4 @@ def decompress(data: bytes, *, debug: bool=False) -> bytes:
 	if debug:
 		print(f"Compressed resource data header: {header_info}")
 	
-	try:
-		decompress_func = DECOMPRESSORS[header_info.dcmp_id]
-	except KeyError:
-		raise DecompressError(f"Unsupported 'dcmp' ID: {header_info.dcmp_id}")
-	
-	decompressed = decompress_func(header_info, data[header_info.header_length:], debug=debug)
-	if len(decompressed) != header_info.decompressed_length:
-		raise DecompressError(f"Actual length of decompressed data ({len(decompressed)}) does not match length stored in resource ({header_info.decompressed_length})")
-	return decompressed
+	return decompress_parsed(header_info, data[header_info.header_length:], debug=debug)