##用于根据CRC爆破宽和高，修改相应值使图片正常显示，
##宽高错误时，linux下打不开图片，win可以
import sys
import zlib
import struct


def modify_png_dimensions(filename, new_width, new_height):
    with open(filename, 'rb') as f:
        all_b = f.read()

    new_data = bytearray(all_b)
    new_data[16:20] = struct.pack('>i', new_width)
    new_data[20:24] = struct.pack('>i', new_height)


    new_filename = f"modified_{filename}"
    with open(new_filename, 'wb') as f:
        f.write(new_data)

    return new_filename


if __name__ == '__main__':
    if len(sys.argv) < 2:
        print("Usage: python test.py <filename>")
        sys.exit(1)

    filename = sys.argv[1]
    with open(filename, 'rb') as f:
        all_b = f.read()
        crc32key = int(all_b[29:33].hex(),16)
        data = bytearray(all_b[12:29])
        n = 4095               #理论上0xffffffff,但考虑到屏幕实际/cpu，0x0fff就差不多了
        for w in range(n):     #高和宽一起爆破
            width = bytearray(struct.pack('>i', w))      #q为8字节，i为4字节，h为2字节
            for h in range(n):
                height = bytearray(struct.pack('>i', h))
                for x in range(4):
                    data[x+4] = width[x]
                    data[x+8] = height[x]
                crc32result = zlib.crc32(data)
                if crc32result == crc32key:
                    print("宽为：",end="")
                    print(width)
                    print("高为：",end="")
                    print(height)

                    w = int.from_bytes(width, byteorder='big')
                    h = int.from_bytes(height, byteorder='big')

                    print("Width:", w)
                    print("Height:", h)

                    modified_filename = modify_png_dimensions(filename, w, h)
                    print(f"Modified image saved as {modified_filename}")

python3 crc_width_height.py ~/Desktop/test.png
宽为：bytearray(b'\x00\x00\x05H')
高为：bytearray(b'\x00\x00\x03\xbc')
Width: 1352
Height: 956