Add support for "application" compressed resources
This commit is contained in:
dgelessus
parent
360833f940
commit
5bc2c0cc81
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@ -20,6 +20,54 @@ COMPRESSED_TYPE_SYSTEM = 0x0901
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# 2 bytes: Compression type. Known so far: 0x0901 is used in the System file's resources. 0x0801 is used in other files' resources.
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STRUCT_COMPRESSED_HEADER = struct.Struct(">4sHH")
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# Header continuation part for an "application" compressed resource.
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# 4 bytes: Length of the data after decompression.
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# 1 byte: "Working buffer fractional size" - the ratio of the compressed data size to the uncompressed data size, times 256.
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# 1 byte: "Expansion buffer size" - the maximum number of bytes that the data might grow during decompression.
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# 2 bytes: The ID of the 'dcmp' resource that can decompress this resource. Currently only ID 0 is supported.
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# 2 bytes: Reserved (always zero).
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STRUCT_COMPRESSED_APPLICATION_HEADER = struct.Struct(">IBBhH")
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# Lookup table for codes in range(0x4b, 0xfe) in "application" compressed resources.
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# This table was obtained by decompressing a manually created compressed resource that refers to every possible table entry. Detailed steps:
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# 1. Create a file with a resource fork
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# 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'
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# 3. Set the "compressed" flag (0x01) on the resource
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# 4. Open the file in ResEdit
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# 5. Duplicate the resource - this will decompress the original resource and write its contents uncompressed into the duplicate
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# 6. Read the data from the duplicated resource
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COMPRESSED_APPLICATION_TABLE_DATA = (
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# First line corresponds to codes in range(0x4b, 0x50).
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b"\x00\x00N\xba\x00\x08Nu\x00\x0c"
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# All following lines correspond to 8 codes each.
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b"N\xad S/\x0ba\x00\x00\x10p\x00/\x00Hn"
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b" P n/.\xff\xfcH\xe7?<\x00\x04\xff\xf8"
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b"/\x0c \x06N\xedNV hN^\x00\x01X\x8f"
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b"O\xef\x00\x02\x00\x18`\x00\xff\xffP\x8fN\x90\x00\x06"
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b"&n\x00\x14\xff\xf4L\xee\x00\n\x00\x0eA\xeeL\xdf"
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b"H\xc0\xff\xf0-@\x00\x120.p\x01/( T"
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b"g\x00\x00 \x00\x1c _\x18\x00&oHx\x00\x16"
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b"A\xfa0<(@r\x00(n \x0cf\x00 k"
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b"/\x07U\x8f\x00(\xff\xfe\xff\xec\"\xd8 \x0b\x00\x0f"
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b"Y\x8f/<\xff\x00\x01\x18\x81\xe1J\x00N\xb0\xff\xe8"
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b"H\xc7\x00\x03\x00\"\x00\x07\x00\x1ag\x06g\x08N\xf9"
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b"\x00$ x\x08\x00f\x04\x00*N\xd00(&_"
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b"g\x04\x000C\xee?\x00 \x1f\x00\x1e\xff\xf6 ."
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b"B\xa7 \x07\xff\xfa`\x02=@\x0c@f\x06\x00&"
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b"-H/\x01p\xff`\x04\x18\x80J@\x00@\x00,"
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b"/\x08\x00\x11\xff\xe4!@&@\xff\xf2BnN\xb9"
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b"=|\x008\x00\r`\x06B. <g\x0c-h"
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b"f\x08J.J\xae\x00.H@\"_\"\x00g\n"
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b"0\x07Bg\x002 (\x00\tHz\x02\x00/+"
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b"\x00\x05\"nf\x02\xe5\x80g\x0ef\n\x00P>\x00"
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b"f\x0c.\x00\xff\xee m @\xff\xe0S@`\x08"
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# Last line corresponds to codes in range(0xf8, 0xfe).
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b"\x04\x80\x00h\x0b|D\x00A\xe8HA"
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)
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# Note: index 0 in this table corresponds to code 0x4b, index 1 to 0x4c, etc.
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COMPRESSED_APPLICATION_TABLE = [COMPRESSED_APPLICATION_TABLE_DATA[i:i + 2] for i in range(0, len(COMPRESSED_APPLICATION_TABLE_DATA), 2)]
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assert len(COMPRESSED_APPLICATION_TABLE) == len(range(0x4b, 0xfe))
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# Header continuation part for a "system" compressed resource.
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# 4 bytes: Length of the data after decompression.
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# 2 bytes: The ID of the 'dcmp' resource that can decompress this resource. Currently only ID 2 is supported.
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@ -98,9 +146,295 @@ def _split_bits(i: int) -> typing.Tuple[bool, bool, bool, bool, bool, bool, bool
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bool(i & (1 << 0)),
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)
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def _read_variable_length_integer(data: bytes, position: int) -> typing.Tuple[int, int]:
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"""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.
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This variable-length integer format is used by the 0xfe codes in "application" compressed resources.
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"""
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assert len(data) > position
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if data[position] == 0xff:
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assert len(data) > position + 4
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return int.from_bytes(data[position+1:position+5], "big", signed=True), 5
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elif data[position] >= 0x80:
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assert len(data) > position + 1
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data_modified = bytes([(data[position] - 0xc0) & 0xff, data[position+1]])
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return int.from_bytes(data_modified, "big", signed=True), 2
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else:
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return int.from_bytes(data[position:position+1], "big", signed=True), 1
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def _decompress_application(data: bytes, *, debug: bool=False) -> bytes:
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raise DecompressError('"Application" compression type not supported yet')
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decompressed_length, working_buffer_fractional_size, expansion_buffer_size, dcmp_id, reserved = STRUCT_COMPRESSED_APPLICATION_HEADER.unpack_from(data)
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if debug:
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print(f"Decompressed length: {decompressed_length}")
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print(f"Working buffer fractional size: {working_buffer_fractional_size} (=> {len(data) * 256 / working_buffer_fractional_size})")
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print(f"Expansion buffer size: {expansion_buffer_size}")
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if dcmp_id != 0:
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raise DecompressError(f"Unsupported 'dcmp' ID: {dcmp_id}, expected 0")
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if reserved != 0:
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raise DecompressError(f"Reserved field should be 0, not 0x{reserved:>04x}")
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prev_literals = []
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decompressed = b""
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i = STRUCT_COMPRESSED_APPLICATION_HEADER.size
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while i < len(data):
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byte = data[i]
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if debug:
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print(f"Tag byte 0x{byte:>02x}, at 0x{i:x}, decompressing to 0x{len(decompressed):x}")
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if byte in range(0x00, 0x20):
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# Literal byte sequence.
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if byte in (0x00, 0x10):
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# The length of the literal data is stored in the next byte.
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count_div2 = data[i+1]
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begin = i + 2
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else:
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# The length of the literal data is stored in the low nibble of the tag byte.
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count_div2 = byte >> 0 & 0xf
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begin = i + 1
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end = begin + 2*count_div2
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# Controls whether or not the literal is stored so that it can be referenced again later.
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do_store = byte >= 0x10
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literal = data[begin:end]
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if debug:
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print(f"Literal (storing: {do_store})")
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print(f"\t-> {literal}")
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decompressed += literal
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if do_store:
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if debug:
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print(f"\t-> stored as literal number 0x{len(prev_literals):x}")
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prev_literals.append(literal)
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i = end
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elif byte in (0x20, 0x21):
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# Backreference to a previous literal, 2-byte form.
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# This can reference literals with index in range(0x28, 0x228).
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table_index = 0x28 + ((byte - 0x20) << 8 | data[i+1])
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i += 2
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if debug:
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print(f"Backreference (2-byte form) to 0x{table_index:>02x}")
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literal = prev_literals[table_index]
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if debug:
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print(f"\t-> {literal}")
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decompressed += literal
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elif byte == 0x22:
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# Backreference to a previous literal, 3-byte form.
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# This can reference any literal with index 0x28 and higher, but is only necessary for literals with index 0x228 and higher.
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table_index = 0x28 + int.from_bytes(data[i+1:i+3], "big", signed=False)
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i += 3
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if debug:
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print(f"Backreference (3-byte form) to 0x{table_index:>02x}")
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literal = prev_literals[table_index]
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if debug:
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print(f"\t-> {literal}")
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decompressed += literal
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elif byte in range(0x23, 0x4b):
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# Backreference to a previous literal, 1-byte form.
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# This can reference literals with indices in range(0x28).
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table_index = byte - 0x23
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i += 1
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if debug:
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print(f"Backreference (1-byte form) to 0x{table_index:>02x}")
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literal = prev_literals[table_index]
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if debug:
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print(f"\t-> {literal}")
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decompressed += literal
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elif byte in range(0x4b, 0xfe):
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# Reference into a fixed table of two-byte literals.
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# All compressed resource use the same table.
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table_index = byte - 0x4b
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i += 1
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if debug:
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print(f"Fixed table reference to 0x{table_index:>02x}")
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entry = COMPRESSED_APPLICATION_TABLE[table_index]
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if debug:
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print(f"\t-> {entry}")
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decompressed += entry
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elif byte == 0xfe:
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# Extended code, whose meaning is controlled by the following byte.
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i += 1
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kind = data[i]
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if debug:
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print(f"Extended code: 0x{kind:>02x}")
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i += 1
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if kind == 0x00:
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# Compact representation of (part of) a segment loader jump table, as used in 'CODE' (0) resources.
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if debug:
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print(f"Segment loader jump table entries")
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# All generated jump table entries have the same segment number.
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segment_number_int, length = _read_variable_length_integer(data, i)
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i += length
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if debug:
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print(f"\t-> segment number: {segment_number_int:#x}")
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# The tail part of all jump table entries (i. e. everything except for the address).
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entry_tail = b"?<" + segment_number_int.to_bytes(2, "big", signed=True) + b"\xa9\xf0"
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if debug:
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print(f"\t-> tail of first entry: {entry_tail}")
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# 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.
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decompressed += entry_tail
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count, length = _read_variable_length_integer(data, i)
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i += length
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if count <= 0:
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raise DecompressError(f"Jump table entry count must be greater than 0, not {count}")
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# The second entry's address is stored explicitly.
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current_int, length = _read_variable_length_integer(data, i)
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i += length
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if debug:
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print(f"-> address of second entry: {current_int:#x}")
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entry = current_int.to_bytes(2, "big", signed=False) + entry_tail
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if debug:
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print(f"-> second entry: {entry}")
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decompressed += entry
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for _ in range(1, count):
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# All further entries' addresses are stored as differences relative to the previous entry's address.
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diff, length = _read_variable_length_integer(data, i)
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i += length
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# For some reason, each difference is 6 higher than it should be.
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diff -= 6
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# Simulate 16-bit integer wraparound.
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current_int = (current_int + diff) & 0xffff
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if debug:
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print(f"\t-> difference {diff:#x}: {current_int:#x}")
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entry = current_int.to_bytes(2, "big", signed=False) + entry_tail
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if debug:
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print(f"\t-> {entry}")
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decompressed += entry
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elif kind in (0x02, 0x03):
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# Repeat 1 or 2 bytes a certain number of times.
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if kind == 0x02:
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byte_count = 1
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elif kind == 0x03:
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byte_count = 2
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else:
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raise AssertionError()
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if debug:
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print(f"Repeat {byte_count}-byte value")
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# The byte(s) to repeat, stored as a variable-length integer. The value is treated as unsigned, i. e. the integer is never negative.
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to_repeat_int, length = _read_variable_length_integer(data, i)
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i += length
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try:
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to_repeat = to_repeat_int.to_bytes(byte_count, "big", signed=False)
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except OverflowError:
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raise DecompressError(f"Value to repeat out of range for {byte_count}-byte repeat: {to_repeat_int:#x}")
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count_m1, length = _read_variable_length_integer(data, i)
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i += length
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count = count_m1 + 1
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if count <= 0:
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raise DecompressError(f"Repeat count must be positive: {count}")
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repeated = to_repeat * count
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if debug:
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print(f"\t-> {to_repeat} * {count}: {repeated}")
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decompressed += repeated
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elif kind == 0x04:
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# 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.
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if debug:
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print(f"Difference-encoded 16-bit integers")
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# The first integer is stored explicitly, as a signed value.
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initial_int, length = _read_variable_length_integer(data, i)
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i += length
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try:
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initial = initial_int.to_bytes(2, "big", signed=True)
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except OverflowError:
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raise DecompressError(f"Initial value out of range for 16-bit integer difference encoding: {initial_int:#x}")
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if debug:
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print(f"\t-> initial: {initial}")
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decompressed += initial
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count, length = _read_variable_length_integer(data, i)
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i += length
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if count < 0:
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raise DecompressError(f"Count cannot be negative: {count}")
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# To make the following calculations simpler, the signed initial_int value is converted to unsigned.
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current_int = initial_int & 0xffff
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for _ in range(count):
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# The difference to the previous integer is stored as an 8-bit signed integer.
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# The usual variable-length integer format is *not* used here.
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diff = int.from_bytes(data[i:i+1], "big", signed=True)
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i += 1
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# Simulate 16-bit integer wraparound.
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current_int = (current_int + diff) & 0xffff
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current = current_int.to_bytes(2, "big", signed=False)
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if debug:
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print(f"\t-> difference {diff:#x}: {current}")
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decompressed += current
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elif kind == 0x06:
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# 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.
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if debug:
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print(f"Difference-encoded 16-bit integers")
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# The first integer is stored explicitly, as a signed value.
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initial_int, length = _read_variable_length_integer(data, i)
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i += length
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try:
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initial = initial_int.to_bytes(4, "big", signed=True)
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except OverflowError:
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raise DecompressError(f"Initial value out of range for 32-bit integer difference encoding: {initial_int:#x}")
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if debug:
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print(f"\t-> initial: {initial}")
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decompressed += initial
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count, length = _read_variable_length_integer(data, i)
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i += length
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assert count >= 0
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# To make the following calculations simpler, the signed initial_int value is converted to unsigned.
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current_int = initial_int & 0xffffffff
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for _ in range(count):
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# The difference to the previous integer is stored as a variable-length integer, whose value may be negative.
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diff, length = _read_variable_length_integer(data, i)
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i += length
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# Simulate 32-bit integer wraparound.
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current_int = (current_int + diff) & 0xffffffff
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current = current_int.to_bytes(4, "big", signed=False)
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if debug:
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print(f"\t-> difference {diff:#x}: {current}")
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decompressed += current
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else:
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raise DecompressError(f"Unknown extended code: 0x{kind:>02x}")
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elif byte == 0xff:
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# End of data marker, always occurs exactly once as the last byte of the compressed data.
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if debug:
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print("End marker")
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if i != len(data) - 1:
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raise DecompressError(f"End marker reached at {i}, before the expected end of data at {len(data) - 1}")
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i += 1
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else:
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raise DecompressError(f"Unknown tag byte: 0x{data[i]:>02x}")
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if decompressed_length % 2 != 0 and len(decompressed) == decompressed_length + 1:
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# 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.
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# 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.
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decompressed = decompressed[:-1]
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if len(decompressed) != decompressed_length:
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raise DecompressError(f"Actual length of decompressed data ({len(decompressed)}) does not match length stored in resource ({decompressed_length})")
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return decompressed
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def _decompress_system_untagged(data: bytes, decompressed_length: int, table: typing.Sequence[bytes], *, debug: bool=False) -> bytes:
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