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https://github.com/dgelessus/python-rsrcfork.git
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8904f6e093
Each decompressor now has its own module, since they share almost no code between each other.
98 lines
4.2 KiB
Python
98 lines
4.2 KiB
Python
import struct
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from . import dcmp0
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from . import dcmp1
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from . import dcmp2
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from .common import DecompressError
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__all__ = [
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"DecompressError",
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"decompress",
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]
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# The signature of all compressed resource data, 0xa89f6572 in hex, or "®üer" in MacRoman.
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COMPRESSED_SIGNATURE = b"\xa8\x9fer"
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# The compression type commonly used for application resources.
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COMPRESSED_TYPE_APPLICATION = 0x0801
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# The compression type commonly used for System file resources.
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COMPRESSED_TYPE_SYSTEM = 0x0901
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# Common header for compressed resources of all types.
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# 4 bytes: Signature (see above).
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# 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.)
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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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# 4 bytes: Length of the data after decompression.
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STRUCT_COMPRESSED_HEADER = struct.Struct(">4sHHI")
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# Header continuation part for an "application" compressed resource.
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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(">BBhH")
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# Header continuation part for a "system" compressed resource.
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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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# 4 bytes: Decompressor-specific parameters.
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STRUCT_COMPRESSED_SYSTEM_HEADER = struct.Struct(">h4s")
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def _decompress_application(data: bytes, decompressed_length: int, *, debug: bool=False) -> bytes:
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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"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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decompress_func = dcmp0.decompress
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elif dcmp_id == 1:
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decompress_func = dcmp1.decompress
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else:
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raise DecompressError(f"Unsupported 'dcmp' ID: {dcmp_id}, expected 0 or 1")
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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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return decompress_func(data[STRUCT_COMPRESSED_APPLICATION_HEADER.size:], decompressed_length, debug=debug)
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def _decompress_system(data: bytes, decompressed_length: int, *, debug: bool=False) -> bytes:
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dcmp_id, params = STRUCT_COMPRESSED_SYSTEM_HEADER.unpack_from(data)
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if dcmp_id == 2:
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decompress_func = dcmp2.decompress
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else:
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raise DecompressError(f"Unsupported 'dcmp' ID: {dcmp_id}, expected 2")
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return decompress_func(data[STRUCT_COMPRESSED_SYSTEM_HEADER.size:], decompressed_length, params, debug=debug)
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def decompress(data: bytes, *, debug: bool=False) -> bytes:
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"""Decompress the given compressed resource data."""
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try:
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signature, header_length, compression_type, decompressed_length = STRUCT_COMPRESSED_HEADER.unpack_from(data)
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except struct.error:
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raise DecompressError(f"Invalid header")
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if signature != COMPRESSED_SIGNATURE:
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raise DecompressError(f"Invalid signature: {signature!r}, expected {COMPRESSED_SIGNATURE}")
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if header_length != 0x12:
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raise DecompressError(f"Unsupported header length: 0x{header_length:>04x}, expected 0x12")
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if compression_type == COMPRESSED_TYPE_APPLICATION:
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decompress_func = _decompress_application
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elif compression_type == COMPRESSED_TYPE_SYSTEM:
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decompress_func = _decompress_system
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else:
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raise DecompressError(f"Unsupported compression type: 0x{compression_type:>04x}")
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if debug:
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print(f"Decompressed length: {decompressed_length}")
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decompressed = decompress_func(data[STRUCT_COMPRESSED_HEADER.size:], decompressed_length, debug=debug)
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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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