Macintosh-Tools/python-rsrcfork
1
0
Fork 0
mirror of https://github.com/dgelessus/python-rsrcfork.git synced 2024-06-08 05:29:40 +00:00
Code Issues Projects Releases Wiki Activity

Move decompressed data length field into common compressed header

Browse Source 
Previously it was handled separately (but identically) by both the
system and application decompression functions.
This commit is contained in:
dgelessus 2019-08-21 23:30:20 +02:00
parent 5bc2c0cc81
commit 3d444bda10
1 changed files with 17 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

36
rsrcfork/compress.py
View File

@ -18,15 +18,15 @@ COMPRESSED_TYPE_SYSTEM = 0x0901
# 4 bytes: Signature (see above).
# 2 bytes: Length of the complete header (this common part and the type-specific part that follows it). (This meaning is just a guess - the field's value is always 0x0012, so there's no way to know for certain what it means.)
# 2 bytes: Compression type. Known so far: 0x0901 is used in the System file's resources. 0x0801 is used in other files' resources.
STRUCT_COMPRESSED_HEADER = struct.Struct(">4sHH")
# 4 bytes: Length of the data after decompression.
STRUCT_COMPRESSED_HEADER = struct.Struct(">4sHHI")
# Header continuation part for an "application" compressed resource.
# 4 bytes: Length of the data after decompression.
# 1 byte: "Working buffer fractional size" - the ratio of the compressed data size to the uncompressed data size, times 256.
# 1 byte: "Expansion buffer size" - the maximum number of bytes that the data might grow during decompression.
# 2 bytes: The ID of the 'dcmp' resource that can decompress this resource. Currently only ID 0 is supported.
# 2 bytes: Reserved (always zero).
STRUCT_COMPRESSED_APPLICATION_HEADER = struct.Struct(">IBBhH")
STRUCT_COMPRESSED_APPLICATION_HEADER = struct.Struct(">BBhH")
# Lookup table for codes in range(0x4b, 0xfe) in "application" compressed resources.
# This table was obtained by decompressing a manually created compressed resource that refers to every possible table entry. Detailed steps:
@ -69,12 +69,11 @@ COMPRESSED_APPLICATION_TABLE = [COMPRESSED_APPLICATION_TABLE_DATA[i:i + 2] for i
assert len(COMPRESSED_APPLICATION_TABLE) == len(range(0x4b, 0xfe))
# Header continuation part for a "system" compressed resource.
# 4 bytes: Length of the data after decompression.
# 2 bytes: The ID of the 'dcmp' resource that can decompress this resource. Currently only ID 2 is supported.
# 2 bytes: Unknown meaning, doesn't appear to have any effect on the decompression algorithm. Usually zero, sometimes set to a small integer (< 10). On 'lpch' resources, the value is always nonzero, and sometimes larger than usual.
# 1 byte: Number of entries in the custom lookup table minus one. Set to zero if the default lookup table is used.
# 1 byte: Flags. See the CompressedSystemFlags enum below for details.
STRUCT_COMPRESSED_SYSTEM_HEADER = struct.Struct(">IhHBB")
STRUCT_COMPRESSED_SYSTEM_HEADER = struct.Struct(">hHBB")
# Default lookup table for "system" compressed resources.
# If the custom table flag is set, a custom table (usually with fewer than 256 entries) is used instead of this one.
@ -164,11 +163,10 @@ def _read_variable_length_integer(data: bytes, position: int) -> typing.Tuple[in
return int.from_bytes(data[position:position+1], "big", signed=True), 1
def _decompress_application(data: bytes, *, debug: bool=False) -> bytes:
decompressed_length, working_buffer_fractional_size, expansion_buffer_size, dcmp_id, reserved = STRUCT_COMPRESSED_APPLICATION_HEADER.unpack_from(data)
def _decompress_application(data: bytes, decompressed_length: int, *, debug: bool=False) -> bytes:
working_buffer_fractional_size, expansion_buffer_size, dcmp_id, reserved = STRUCT_COMPRESSED_APPLICATION_HEADER.unpack_from(data)
if debug:
print(f"Decompressed length: {decompressed_length}")
print(f"Working buffer fractional size: {working_buffer_fractional_size} (=> {len(data) * 256 / working_buffer_fractional_size})")
print(f"Expansion buffer size: {expansion_buffer_size}")
@ -431,9 +429,6 @@ def _decompress_application(data: bytes, *, debug: bool=False) -> bytes:
# This is necessary because nearly all codes generate data in groups of 2 or 4 bytes, so it is basically impossible to represent data with an odd length using this compression format.
decompressed = decompressed[:-1]
if len(decompressed) != decompressed_length:
raise DecompressError(f"Actual length of decompressed data ({len(decompressed)}) does not match length stored in resource ({decompressed_length})")
return decompressed
@ -494,8 +489,8 @@ def _decompress_system_tagged(data: bytes, decompressed_length: int, table: typi
return b"".join(parts)
def _decompress_system(data: bytes, *, debug: bool=False) -> bytes:
decompressed_length, dcmp_id, unknown, table_count_m1, flags_raw = STRUCT_COMPRESSED_SYSTEM_HEADER.unpack_from(data)
def _decompress_system(data: bytes, decompressed_length: int, *, debug: bool=False) -> bytes:
dcmp_id, unknown, table_count_m1, flags_raw = STRUCT_COMPRESSED_SYSTEM_HEADER.unpack_from(data)
if dcmp_id != 2:
raise DecompressError(f"Unsupported 'dcmp' ID: {dcmp_id}, expected 2")
if debug:
@ -534,17 +529,14 @@ def _decompress_system(data: bytes, *, debug: bool=False) -> bytes:
else:
decompress_func = _decompress_system_untagged
decompressed = decompress_func(data[data_start:], decompressed_length, table, debug=debug)
if len(decompressed) != decompressed_length:
raise DecompressError(f"Actual length of decompressed data ({len(decompressed)}) does not match length stored in resource ({decompressed_length})")
return decompressed
return decompress_func(data[data_start:], decompressed_length, table, debug=debug)
def decompress(data: bytes, *, debug: bool=False) -> bytes:
"""Decompress the given compressed resource data."""
try:
signature, header_length, compression_type = STRUCT_COMPRESSED_HEADER.unpack_from(data)
signature, header_length, compression_type, decompressed_length = STRUCT_COMPRESSED_HEADER.unpack_from(data)
except struct.error:
raise DecompressError(f"Invalid header")
if signature != COMPRESSED_SIGNATURE:
@ -559,4 +551,10 @@ def decompress(data: bytes, *, debug: bool=False) -> bytes:
else:
raise DecompressError(f"Unsupported compression type: 0x{compression_type:>04x}")
return decompress_func(data[STRUCT_COMPRESSED_HEADER.size:], debug=debug)
if debug:
print(f"Decompressed length: {decompressed_length}")
decompressed = decompress_func(data[STRUCT_COMPRESSED_HEADER.size:], decompressed_length, debug=debug)
if len(decompressed) != decompressed_length:
raise DecompressError(f"Actual length of decompressed data ({len(decompressed)}) does not match length stored in resource ({decompressed_length})")
return decompressed