(PHP Extension) How to Tell if a File is .p7m or .p7s

This example explains how to detect if a file is a .p7m or .p7s. It provides as solution to the following problem:

Sometimes people submit P7S/P7M with wrong extensions. Can I check if file is P7S or P7M with Chilkat?

Also see What is a P7M or P7S File?

Chilkat PHP Downloads PHP Extension for Windows, Linux, MacOS, Alpine Linux, Solaris

<?php

include("chilkat.php");
// Use "chilkat_9_5_0.php" for versions of Chilkat < 10.0.0

// A .p7m or .p7s file is binary and contains PKCS7.
// PKCS7 is ASN.1, and always begins with a SEQUENCE tag (a byte equal to 0x30)
// followed by an encoded length.
// If the file is larger than 128 bytes (and it SHOULD be), the encoded length will begin with either 0x80, 0x81, 0x82, or 0x83.
// It can also begin with 0x84, but only for very large files (where the length is too large for 3 bytes).
// See How ASN.1 Encodes Lengths

// Therefore, if we have a file that might be .p7m or .p7s, we can check by
// examining the 1st 2 bytes of the file.

$bd = new CkBinData();

$success = $bd->LoadFile('qa_data/p7m/a.p7m');
if ($success == false) {
    print 'Failed to load the file.' . "\n";
    exit;
}

$sb = new CkStringBuilder();
$sb->Append($bd->getEncodedChunk(0,2,'hex'));

$caseSensitive = true;
if ($sb->ContentsEqual('3080',$caseSensitive) or $sb->ContentsEqual('3081',$caseSensitive) or $sb->ContentsEqual('3082',$caseSensitive) or $sb->ContentsEqual('3083',$caseSensitive)) {
    print 'This is a .p7m or .p7s file.' . "\n";
}
else {
    print 'This is not a .p7m or .p7s file.' . "\n";
}


?>