PHP reads the file header (2 bytes) to determine the file type

If you see this title, you may say whether the file type is correct. if you directly judge whether the extension does not know the file type, but the extension is easy to forge, This bypasses the judgment. Most files store a special number or character in a specific position (2 bytes at the beginning )/*

If you see this title, you may say whether the file type is correct. if you directly judge whether the extension does not know the file type, but the extension is easy to forge, This bypasses the judgment.
Most files store a special number or character in a specific position (2 bytes at the beginning)

/*** @ Author Mckee * @ link http://www.phpddt.com * // use 'B' to force the use of binary mode $ fp = fopen('qq.jpg ', 'RB '); // read-only binary file. The first two bytes can be used to determine the file type $ bin = fread ($ fp, 2); fclose ($ fp ); // Convert a binary string to a formatted string. here it is converted to a decimal integer $ code = unpack ('c2chars', $ bin); // An array is returned here, let's take a look at $ type_code = intval ($ code ['chars1']. $ code ['chars2']); $ type = ''; switch ($ type_code) {case 255216: $ type = 'jpg '; break; case 7173: $ type = 'gif '; break; case 6677: $ type = 'bmp'; break; case 13780: $ type = 'PNG '; break; default: $ type = 'unknown ';} echo $ type;

The above code is just an introduction and is not accurate. readers can study it on their own. even this can be forged. if it is an image type, many people will use getimagesize ($ file) to judge it.