74 lines
2.4 KiB
Python
74 lines
2.4 KiB
Python
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#!/usr/bin/env python3
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# -*- coding: utf-8 -*-
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import os
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import sys
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import struct
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def calculate_checksum(data):
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"""计算小端序校验和：每4字节相加后取反（32位无符号）"""
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if len(data) % 4 != 0:
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raise ValueError("Data length must be multiple of 4")
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sum_val = 0
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# 遍历所有4字节块（最后4字节除外）
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for i in range(0, len(data)-4, 4):
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chunk = data[i:i+4]
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value = struct.unpack('<I', chunk)[0] # 小端序解析
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sum_val = (sum_val + value) & 0xFFFFFFFF # 32位溢出保护
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return (~sum_val) & 0xFFFFFFFF # 取反并保持32位
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def process_file(filename):
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"""处理文件的主函数"""
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try:
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# 读取文件内容（二进制模式）
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with open(filename, 'rb+') as f:
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original_data = f.read()
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data_len = len(original_data)
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# ========== 验证阶段 ==========
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# 1. 检查文件长度是否为4的倍数
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if data_len % 4 != 0:
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raise ValueError(f"文件长度 {data_len} 不是4的倍数")
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# 2. 检查第二个4字节是否等于文件长度
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if data_len >= 8:
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declared_length = struct.unpack('<I', original_data[4:8])[0]
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if declared_length != data_len:
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raise ValueError(
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f"长度声明不匹配：文件头声明={declared_length}，实际={data_len}"
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)
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# ========== 计算校验和 ==========
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checksum = calculate_checksum(original_data)
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# ========== 写入校验和 ==========
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# 定位到文件最后4字节
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f.seek(-4, os.SEEK_END)
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f.write(struct.pack('<I', checksum)) # 小端序写入
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print(f"[成功] 文件 {filename} 已更新校验码：0x{checksum:08X}")
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return True
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except Exception as e:
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print(f"[错误] 处理文件 {filename} 失败：{str(e)}")
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return False
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if __name__ == "__main__":
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# 参数检查
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if len(sys.argv) != 2:
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print("用法: python checksum.py <文件名>")
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sys.exit(1)
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input_file = sys.argv[1]
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# 文件存在性检查
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if not os.path.isfile(input_file):
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print(f"[错误] 文件不存在: {input_file}")
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sys.exit(1)
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# 执行处理
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if not process_file(input_file):
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sys.exit(1)
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