diff --git a/rsrcfork/compress.py b/rsrcfork/compress.py index aad278a..23e7842 100644 --- a/rsrcfork/compress.py +++ b/rsrcfork/compress.py @@ -20,6 +20,54 @@ COMPRESSED_TYPE_SYSTEM = 0x0901 # 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") +# 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") + +# 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: +# 1. Create a file with a resource fork +# 2. Add a resource with the following contents: b'\xa8\x9fer\x00\x12\x08\x01\x00\x00\x01f\x80\x03\x00\x00\x00\x00' + bytes(range(0x4b, 0xfe)) + b'\xff' +# 3. Set the "compressed" flag (0x01) on the resource +# 4. Open the file in ResEdit +# 5. Duplicate the resource - this will decompress the original resource and write its contents uncompressed into the duplicate +# 6. Read the data from the duplicated resource +COMPRESSED_APPLICATION_TABLE_DATA = ( + # First line corresponds to codes in range(0x4b, 0x50). + b"\x00\x00N\xba\x00\x08Nu\x00\x0c" + # All following lines correspond to 8 codes each. + b"N\xad S/\x0ba\x00\x00\x10p\x00/\x00Hn" + b" P n/.\xff\xfcH\xe7?<\x00\x04\xff\xf8" + b"/\x0c \x06N\xedNV hN^\x00\x01X\x8f" + b"O\xef\x00\x02\x00\x18`\x00\xff\xffP\x8fN\x90\x00\x06" + b"&n\x00\x14\xff\xf4L\xee\x00\n\x00\x0eA\xeeL\xdf" + b"H\xc0\xff\xf0-@\x00\x120.p\x01/( T" + b"g\x00\x00 \x00\x1c _\x18\x00&oHx\x00\x16" + b"A\xfa0<(@r\x00(n \x0cf\x00 k" + b"/\x07U\x8f\x00(\xff\xfe\xff\xec\"\xd8 \x0b\x00\x0f" + b"Y\x8f/<\xff\x00\x01\x18\x81\xe1J\x00N\xb0\xff\xe8" + b"H\xc7\x00\x03\x00\"\x00\x07\x00\x1ag\x06g\x08N\xf9" + b"\x00$ x\x08\x00f\x04\x00*N\xd00(&_" + b"g\x04\x000C\xee?\x00 \x1f\x00\x1e\xff\xf6 ." + b"B\xa7 \x07\xff\xfa`\x02=@\x0c@f\x06\x00&" + b"-H/\x01p\xff`\x04\x18\x80J@\x00@\x00," + b"/\x08\x00\x11\xff\xe4!@&@\xff\xf2BnN\xb9" + b"=|\x008\x00\r`\x06B. \x00" + b"f\x0c.\x00\xff\xee m @\xff\xe0S@`\x08" + # Last line corresponds to codes in range(0xf8, 0xfe). + b"\x04\x80\x00h\x0b|D\x00A\xe8HA" +) +# Note: index 0 in this table corresponds to code 0x4b, index 1 to 0x4c, etc. +COMPRESSED_APPLICATION_TABLE = [COMPRESSED_APPLICATION_TABLE_DATA[i:i + 2] for i in range(0, len(COMPRESSED_APPLICATION_TABLE_DATA), 2)] +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. @@ -98,9 +146,295 @@ def _split_bits(i: int) -> typing.Tuple[bool, bool, bool, bool, bool, bool, bool bool(i & (1 << 0)), ) +def _read_variable_length_integer(data: bytes, position: int) -> typing.Tuple[int, int]: + """Read a variable-length integer starting at the given position in the data, and return the integer as well as the number of bytes consumed. + + This variable-length integer format is used by the 0xfe codes in "application" compressed resources. + """ + + assert len(data) > position + if data[position] == 0xff: + assert len(data) > position + 4 + return int.from_bytes(data[position+1:position+5], "big", signed=True), 5 + elif data[position] >= 0x80: + assert len(data) > position + 1 + data_modified = bytes([(data[position] - 0xc0) & 0xff, data[position+1]]) + return int.from_bytes(data_modified, "big", signed=True), 2 + else: + return int.from_bytes(data[position:position+1], "big", signed=True), 1 + def _decompress_application(data: bytes, *, debug: bool=False) -> bytes: - raise DecompressError('"Application" compression type not supported yet') + decompressed_length, 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}") + + if dcmp_id != 0: + raise DecompressError(f"Unsupported 'dcmp' ID: {dcmp_id}, expected 0") + + if reserved != 0: + raise DecompressError(f"Reserved field should be 0, not 0x{reserved:>04x}") + + prev_literals = [] + decompressed = b"" + + i = STRUCT_COMPRESSED_APPLICATION_HEADER.size + + while i < len(data): + byte = data[i] + if debug: + print(f"Tag byte 0x{byte:>02x}, at 0x{i:x}, decompressing to 0x{len(decompressed):x}") + + if byte in range(0x00, 0x20): + # Literal byte sequence. + if byte in (0x00, 0x10): + # The length of the literal data is stored in the next byte. + count_div2 = data[i+1] + begin = i + 2 + else: + # The length of the literal data is stored in the low nibble of the tag byte. + count_div2 = byte >> 0 & 0xf + begin = i + 1 + end = begin + 2*count_div2 + # Controls whether or not the literal is stored so that it can be referenced again later. + do_store = byte >= 0x10 + literal = data[begin:end] + if debug: + print(f"Literal (storing: {do_store})") + print(f"\t-> {literal}") + decompressed += literal + if do_store: + if debug: + print(f"\t-> stored as literal number 0x{len(prev_literals):x}") + prev_literals.append(literal) + i = end + elif byte in (0x20, 0x21): + # Backreference to a previous literal, 2-byte form. + # This can reference literals with index in range(0x28, 0x228). + table_index = 0x28 + ((byte - 0x20) << 8 | data[i+1]) + i += 2 + if debug: + print(f"Backreference (2-byte form) to 0x{table_index:>02x}") + literal = prev_literals[table_index] + if debug: + print(f"\t-> {literal}") + decompressed += literal + elif byte == 0x22: + # Backreference to a previous literal, 3-byte form. + # This can reference any literal with index 0x28 and higher, but is only necessary for literals with index 0x228 and higher. + table_index = 0x28 + int.from_bytes(data[i+1:i+3], "big", signed=False) + i += 3 + if debug: + print(f"Backreference (3-byte form) to 0x{table_index:>02x}") + literal = prev_literals[table_index] + if debug: + print(f"\t-> {literal}") + decompressed += literal + elif byte in range(0x23, 0x4b): + # Backreference to a previous literal, 1-byte form. + # This can reference literals with indices in range(0x28). + table_index = byte - 0x23 + i += 1 + if debug: + print(f"Backreference (1-byte form) to 0x{table_index:>02x}") + literal = prev_literals[table_index] + if debug: + print(f"\t-> {literal}") + decompressed += literal + elif byte in range(0x4b, 0xfe): + # Reference into a fixed table of two-byte literals. + # All compressed resource use the same table. + table_index = byte - 0x4b + i += 1 + if debug: + print(f"Fixed table reference to 0x{table_index:>02x}") + entry = COMPRESSED_APPLICATION_TABLE[table_index] + if debug: + print(f"\t-> {entry}") + decompressed += entry + elif byte == 0xfe: + # Extended code, whose meaning is controlled by the following byte. + + i += 1 + kind = data[i] + if debug: + print(f"Extended code: 0x{kind:>02x}") + i += 1 + + if kind == 0x00: + # Compact representation of (part of) a segment loader jump table, as used in 'CODE' (0) resources. + + if debug: + print(f"Segment loader jump table entries") + + # All generated jump table entries have the same segment number. + segment_number_int, length = _read_variable_length_integer(data, i) + i += length + if debug: + print(f"\t-> segment number: {segment_number_int:#x}") + + # The tail part of all jump table entries (i. e. everything except for the address). + entry_tail = b"?<" + segment_number_int.to_bytes(2, "big", signed=True) + b"\xa9\xf0" + if debug: + print(f"\t-> tail of first entry: {entry_tail}") + # The tail is output once *without* an address in front, i. e. the first entry's address must be generated manually by a previous code. + decompressed += entry_tail + + count, length = _read_variable_length_integer(data, i) + i += length + if count <= 0: + raise DecompressError(f"Jump table entry count must be greater than 0, not {count}") + + # The second entry's address is stored explicitly. + current_int, length = _read_variable_length_integer(data, i) + i += length + if debug: + print(f"-> address of second entry: {current_int:#x}") + entry = current_int.to_bytes(2, "big", signed=False) + entry_tail + if debug: + print(f"-> second entry: {entry}") + decompressed += entry + + for _ in range(1, count): + # All further entries' addresses are stored as differences relative to the previous entry's address. + diff, length = _read_variable_length_integer(data, i) + i += length + # For some reason, each difference is 6 higher than it should be. + diff -= 6 + + # Simulate 16-bit integer wraparound. + current_int = (current_int + diff) & 0xffff + if debug: + print(f"\t-> difference {diff:#x}: {current_int:#x}") + entry = current_int.to_bytes(2, "big", signed=False) + entry_tail + if debug: + print(f"\t-> {entry}") + decompressed += entry + elif kind in (0x02, 0x03): + # Repeat 1 or 2 bytes a certain number of times. + + if kind == 0x02: + byte_count = 1 + elif kind == 0x03: + byte_count = 2 + else: + raise AssertionError() + + if debug: + print(f"Repeat {byte_count}-byte value") + + # The byte(s) to repeat, stored as a variable-length integer. The value is treated as unsigned, i. e. the integer is never negative. + to_repeat_int, length = _read_variable_length_integer(data, i) + i += length + try: + to_repeat = to_repeat_int.to_bytes(byte_count, "big", signed=False) + except OverflowError: + raise DecompressError(f"Value to repeat out of range for {byte_count}-byte repeat: {to_repeat_int:#x}") + + count_m1, length = _read_variable_length_integer(data, i) + i += length + count = count_m1 + 1 + if count <= 0: + raise DecompressError(f"Repeat count must be positive: {count}") + + repeated = to_repeat * count + if debug: + print(f"\t-> {to_repeat} * {count}: {repeated}") + decompressed += repeated + elif kind == 0x04: + # A sequence of 16-bit signed integers, with each integer encoded as a difference relative to the previous integer. The first integer is stored explicitly. + + if debug: + print(f"Difference-encoded 16-bit integers") + + # The first integer is stored explicitly, as a signed value. + initial_int, length = _read_variable_length_integer(data, i) + i += length + try: + initial = initial_int.to_bytes(2, "big", signed=True) + except OverflowError: + raise DecompressError(f"Initial value out of range for 16-bit integer difference encoding: {initial_int:#x}") + if debug: + print(f"\t-> initial: {initial}") + decompressed += initial + + count, length = _read_variable_length_integer(data, i) + i += length + if count < 0: + raise DecompressError(f"Count cannot be negative: {count}") + + # To make the following calculations simpler, the signed initial_int value is converted to unsigned. + current_int = initial_int & 0xffff + for _ in range(count): + # The difference to the previous integer is stored as an 8-bit signed integer. + # The usual variable-length integer format is *not* used here. + diff = int.from_bytes(data[i:i+1], "big", signed=True) + i += 1 + + # Simulate 16-bit integer wraparound. + current_int = (current_int + diff) & 0xffff + current = current_int.to_bytes(2, "big", signed=False) + if debug: + print(f"\t-> difference {diff:#x}: {current}") + decompressed += current + elif kind == 0x06: + # A sequence of 32-bit signed integers, with each integer encoded as a difference relative to the previous integer. The first integer is stored explicitly. + + if debug: + print(f"Difference-encoded 16-bit integers") + + # The first integer is stored explicitly, as a signed value. + initial_int, length = _read_variable_length_integer(data, i) + i += length + try: + initial = initial_int.to_bytes(4, "big", signed=True) + except OverflowError: + raise DecompressError(f"Initial value out of range for 32-bit integer difference encoding: {initial_int:#x}") + if debug: + print(f"\t-> initial: {initial}") + decompressed += initial + + count, length = _read_variable_length_integer(data, i) + i += length + assert count >= 0 + + # To make the following calculations simpler, the signed initial_int value is converted to unsigned. + current_int = initial_int & 0xffffffff + for _ in range(count): + # The difference to the previous integer is stored as a variable-length integer, whose value may be negative. + diff, length = _read_variable_length_integer(data, i) + i += length + + # Simulate 32-bit integer wraparound. + current_int = (current_int + diff) & 0xffffffff + current = current_int.to_bytes(4, "big", signed=False) + if debug: + print(f"\t-> difference {diff:#x}: {current}") + decompressed += current + else: + raise DecompressError(f"Unknown extended code: 0x{kind:>02x}") + elif byte == 0xff: + # End of data marker, always occurs exactly once as the last byte of the compressed data. + if debug: + print("End marker") + if i != len(data) - 1: + raise DecompressError(f"End marker reached at {i}, before the expected end of data at {len(data) - 1}") + i += 1 + else: + raise DecompressError(f"Unknown tag byte: 0x{data[i]:>02x}") + + if decompressed_length % 2 != 0 and len(decompressed) == decompressed_length + 1: + # Special case: if the decompressed data length stored in the header is odd and one less than the length of the actual decompressed data, drop the last byte. + # 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 def _decompress_system_untagged(data: bytes, decompressed_length: int, table: typing.Sequence[bytes], *, debug: bool=False) -> bytes: