62 lines
1.8 KiB
Python
62 lines
1.8 KiB
Python
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import hashlib
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import zlib
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from typing import Tuple
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class GSZ3DecompressionError(Exception):
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pass
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class GSZ3Decompressor:
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MAGIC = b'GSZ3'
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VERSION = 1
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@staticmethod
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def decompress(data: bytes) -> str:
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if len(data) < 12:
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raise GSZ3DecompressionError("Data too short for GSZ3 header")
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if data[:4] != GSZ3Decompressor.MAGIC:
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raise GSZ3DecompressionError("Invalid GSZ3 magic number")
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version = int.from_bytes(data[4:5], 'big')
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if version != GSZ3Decompressor.VERSION:
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raise GSZ3DecompressionError(f"Unsupported GSZ3 version: {version}")
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payload_len = int.from_bytes(data[5:9], 'big')
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stored_checksum = data[9:12]
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if len(data) < 12 + payload_len:
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raise GSZ3DecompressionError("Incomplete payload")
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payload = data[12:12 + payload_len]
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computed_checksum = GSZ3Decompressor._compute_checksum(payload)
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if computed_checksum != stored_checksum:
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raise GSZ3DecompressionError("Checksum mismatch")
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try:
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decompressed = zlib.decompress(payload)
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return decompressed.decode('utf-8')
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except (zlib.error, UnicodeDecodeError) as e:
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raise GSZ3DecompressionError(f"Decompression failed: {e}")
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@staticmethod
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def compress(text: str) -> bytes:
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data = text.encode('utf-8')
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compressed = zlib.compress(data, level=9)
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checksum = GSZ3Decompressor._compute_checksum(compressed)
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payload_len = len(compressed)
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header = GSZ3Decompressor.MAGIC
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header += bytes([GSZ3Decompressor.VERSION])
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header += payload_len.to_bytes(4, 'big')
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header += checksum
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return header + compressed
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@staticmethod
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def _compute_checksum(data: bytes) -> bytes:
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h = hashlib.sha256(data).digest()
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return h[:3]
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