(Go) SII Chile - FRMT Signature Computation and Add to XML

Compute the FRMT signature and add to the XML. This is the RSA signature of the SHA-1 digest of the "flattened" DD element.

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    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // Also see:  Compute the FRMA Signature and Add to XML

    xml := chilkat.NewXml()

    // Load the unsigned XML that contains the following:

    // <DTE version="1.0">
    //   <Documento ID="F60T33">
    //         <TED version="1.0">
    //             <DD>
    // 		...
    //                 <CAF version="1.0">
    //                     <DA>
    // 			...
    //                     </DA>
    //                     <FRMA algoritmo="SHA1withRSA">...</FRMA>
    //                 </CAF>
    //                 ...
    //             </DD>
    //             ... The FRMT will be added here in another example ...
    //         </TED>
    //   </Documento>
    // </DTE>

    success := xml.LoadXmlFile("qa_data/xml_dsig/sii_cl/test_1.xml")
    if success == false {
        fmt.Println("Failed to load initial XML file.")
        xml.DisposeXml()
        return
    }

    // Get a reference to the "DD" element
    ddXml := xml.FindChild("Documento|TED|DD")
    if xml.LastMethodSuccess() == false {
        fmt.Println("Failed to find DD element")
        xml.DisposeXml()
        return
    }

    //  We need to get the "flattened" DD XML where:
    //    - No whitespace between elements.
    //    - The 5 pre-defined entities are converted.
    //    - The text is encoded in the ISO-8859-1 character set (Latin-1), 
    sbFlattened := chilkat.NewStringBuilder()
    ddXml.SetEmitCompact(true)
    ddXml.SetEmitXmlDecl(false)
    ddXml.GetXmlSb(sbFlattened)

    // Compute the SHA-1 message digest of the iso-8859-1 byte representation, 
    // and sign it with our RSA private key, getting the result in base64 format.

    privKey := chilkat.NewPrivateKey()
    success = privKey.LoadAnyFormatFile("qa_data/rsa/rsaPrivKey_pkcs8.pem","")
    if success == false {
        fmt.Println(privKey.LastErrorText())
        xml.DisposeXml()
        sbFlattened.DisposeStringBuilder()
        privKey.DisposePrivateKey()
        return
    }

    rsa := chilkat.NewRsa()
    rsa.ImportPrivateKeyObj(privKey)

    rsa.SetEncodingMode("base64")
    rsa.SetCharset("iso-8859-1")
    sig := rsa.SignStringENC(*sbFlattened.GetAsString(),"sha1")

    // Add the FRMT signature element to the XML.
    xml.UpdateChildContent("Documento|TED|FRMT",*sig)
    xml.UpdateAttrAt("Documento|TED|FRMT",true,"algoritmo","SHA1withRSA")

    ddXml.DisposeXml()

    // See what we have:
    xml.SetEmitCompact(false)
    xml.SetEmitXmlDecl(true)
    fmt.Println(*xml.GetXml())

    xml.DisposeXml()
    sbFlattened.DisposeStringBuilder()
    privKey.DisposePrivateKey()
    rsa.DisposeRsa()