(Swift 3,4,5...) Extract PKCS7 Signature Digest

Demonstrates how to extract a signature digest from a PKCS7 signature.

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func chilkatTest() {
    // This example requires the Chilkat Crypt API to have been previously unlocked.
    // See Unlock Chilkat Crypt for sample code.

    let crypt = CkoCrypt2()!

    var p7mFile: String? = "qa_data/p7m/test.pdf.p7m"
    var outPath: String? = "qa_output/test.pdf"

    // First let's see if this .p7m signature can be verified, and the original file extracted.
    var verified: Bool = crypt.verifyP7M(p7mFile, destPath: outPath)
    if verified != true {
        print("\(crypt.lastErrorText!)")
        return
    }

    // How many signers?
    // (The NumSignerCerts property is set whenever a signature is verified.)
    print("Num Signers: \(crypt.numSignerCerts.intValue)")

    // Load the .p7m into memory...
    let pkcs7Data = CkoBinData()!
    pkcs7Data.loadFile(p7mFile)

    // Check to see if this .p7m contains the binary bytes, or if it's
    // already base64 encoded.  Get the 1st two bytes.  If the first two 
    // bytes are the us-ascii values "MI", then we have base64.
    let sbBase64 = CkoStringBuilder()!
    var hexStr: String? = pkcs7Data.getEncodedChunk(0, numBytes: 2, encoding: "hex")
    sbBase64.append(hexStr)

    var bHaveBase64: Bool = false
    if sbBase64.contentsEqual("4D49", caseSensitive: true) == true {
        bHaveBase64 = true
        sbBase64.clear()
        sbBase64.appendBd(pkcs7Data, charset: "utf-8", offset: 0, numBytes: 0)
    }

    // Get each signer's signature digest.
    crypt.encodingMode = "base64"
    var i: Int = 0
    var digest: String?
    while i < crypt.numSignerCerts.intValue {
        if bHaveBase64 {
            digest = crypt.pkcs7ExtractDigest(i, pkcs7: sbBase64.getAsString())
        }
        else {
            digest = crypt.pkcs7ExtractDigest(i, pkcs7: pkcs7Data.getEncoded("base64"))
        }

        if crypt.lastMethodSuccess != true {
            print("\(crypt.lastErrorText!)")
            return
        }

        print("Signer \(i + 1) digest = \(digest!)")
        i = i + 1
    }


}