(Lianja) 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 Lianja Extension Download Chilkat Lianja Extension

// 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.

loBd = createobject("CkBinData")

llSuccess = loBd.LoadFile("qa_data/p7m/a.p7m")
if (llSuccess = .F.) then
    ? "Failed to load the file."
    release loBd
    return
endif

loSb = createobject("CkStringBuilder")
loSb.Append(loBd.GetEncodedChunk(0,2,"hex"))

llCaseSensitive = .T.
if (loSb.ContentsEqual("3080",llCaseSensitive) or loSb.ContentsEqual("3081",llCaseSensitive) or loSb.ContentsEqual("3082",llCaseSensitive) or loSb.ContentsEqual("3083",llCaseSensitive)) then
    ? "This is a .p7m or .p7s file."
else
    ? "This is not a .p7m or .p7s file."
endif



release loBd
release loSb