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49 lines
1.3 KiB
Python
49 lines
1.3 KiB
Python
"""二进制解析辅助函数。"""
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import struct
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from typing import Any
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from .exceptions import TdxDecodeError
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def require_bytes(
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data: bytes | bytearray,
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pos: int,
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size: int,
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context: str,
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) -> None:
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"""确保从 pos 起至少还能读取 size 字节。"""
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if pos < 0:
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raise TdxDecodeError(f"{context}: 非法偏移 {pos}")
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end = pos + size
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if end > len(data):
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remaining = max(len(data) - pos, 0)
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raise TdxDecodeError(
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f"{context}: 数据不足，需要 {size} 字节，偏移 {pos}，实际剩余 {remaining} 字节"
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)
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def unpack_from(
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fmt: str,
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data: bytes | bytearray,
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pos: int,
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context: str,
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) -> tuple[Any, ...]:
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"""带边界检查的 struct.unpack_from。"""
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require_bytes(data, pos, struct.calcsize(fmt), context)
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try:
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return struct.unpack_from(fmt, data, pos)
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except struct.error as e: # pragma: no cover - require_bytes 已覆盖大部分路径
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raise TdxDecodeError(f"{context}: 解析失败: {e}") from e
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def slice_bytes(
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data: bytes | bytearray,
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pos: int,
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size: int,
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context: str,
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) -> bytes:
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"""带边界检查的切片读取。"""
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require_bytes(data, pos, size, context)
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return bytes(data[pos : pos + size])
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