如何在二进制文件中查找字节序列并修改指定比特位？

Hey there! The issue you're hitting is pretty straightforward: the array.index() method only works for finding single elements in the array, not an entire sub-sequence of bytes like your abc array (which holds the ASCII values for "ABC"). That's why you're getting the ValueError: array.index(x): x not in list error—even if "ABC" exists in your binary file, the method doesn't know how to look for a group of elements at once.

Let's fix this step by step:

1. Implement a function to find the sub-sequence #

First, we'll write a helper function that scans the array to find the starting index of your target byte sequence. This checks each position in the array to see if the following elements match your sub-array:

def find_subarray(main_array, sub_array):
    sub_len = len(sub_array)
    main_len = len(main_array)
    if sub_len > main_len:
        return -1  # Subsequence can't be longer than the main array
    for i in range(main_len - sub_len + 1):
        if main_array[i:i+sub_len] == sub_array:
            return i
    return -1  # Subsequence not found

2. Update your original code #

Now replace the problematic content.index(abc) call with our helper function. We'll also fix a couple of file handling issues you might run into later:

• After reading the entire file, the file pointer is at the end—we need to move it back to the start with file.seek(0) before writing.
• Use file.truncate() after writing to make sure any extra bytes from the original file are removed (in case your modified content is shorter, though it shouldn't be here).

Here's the revised code:

import os
from array import array

def find_subarray(main_array, sub_array):
    sub_len = len(sub_array)
    main_len = len(main_array)
    if sub_len > main_len:
        return -1
    for i in range(main_len - sub_len + 1):
        if main_array[i:i+sub_len] == sub_array:
            return i
    return -1

filename = "your_binary_file.bin"  # Replace with your actual file path
content = array('B')
with open(filename, mode="r+b") as file:
    # Read the entire file into the array
    content.fromfile(file, os.fstat(file.fileno()).st_size)
    
    # Prepare the target byte sequence (ASCII "ABC")
    abc = array('B', [ord(letter) for letter in "ABC"])
    
    # Find the starting index of the sequence
    i = find_subarray(content, abc)
    if i == -1:
        raise ValueError("Byte sequence 'ABC' not found in the file")
    
    # Modify the target bit (set the 0th bit of the byte at i + 0x16)
    content[i + 0x16] |= 1
    
    # Move file pointer to start and write the modified content
    file.seek(0)
    content.tofile(file)
    file.truncate()  # Remove any leftover bytes from the original file

Key Notes: #

• We're using array('B') for both the main content and the target sequence to ensure we're comparing like-for-like (since slicing an array returns another array, not a list).
• The find_subarray function returns -1 if the sequence isn't found—we added a check to raise a clear error in that case, so you know exactly what went wrong.
• The bit modification content[i + 0x16] |= 1 correctly sets the least significant bit of the target byte—if you need to set a different bit, you can adjust the mask (e.g., 0x20 for the 5th bit).

内容的提问来源于stack exchange，提问作者Tar