Perl

How to Tell if a File is .p7m or .p7s

See more Misc Examples

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?

Perl

use chilkat();

$success = 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 = chilkat::CkBinData->new();

$success = $bd->LoadFile("qa_data/p7m/a.p7m");
if ($success == 0) {
    print "Failed to load the file." . "\r\n";
    exit;
}

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

$caseSensitive = 1;
if ($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." . "\r\n";
}
else {
    print "This is not a .p7m or .p7s file." . "\r\n";
}