(Go) Extract TSTInfo from RFC3161 Timestamp Reply

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Sends an RFC 3161 timestamp request to a TSA (Timestamp Authority) server and converts the timestamp reply to XML, and then extracts the TSTInfo from the XML and converts it to XML.

For more information, see https://www.ietf.org/rfc/rfc3161.txt

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    // Note: Requires Chilkat v9.5.0.75 or greater.

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

    // First sha-256 hash the data that is to be timestamped.
    // In this example, the data is the string "Hello World"
    var success bool
    crypt := chilkat.NewCrypt2()
    crypt.SetHashAlgorithm("sha256")
    crypt.SetEncodingMode("base64")
    base64Hash := crypt.HashFileENC("qa_data/hamlet.xml")

    http := chilkat.NewHttp()

    requestToken := chilkat.NewBinData()
    optionalPolicyOid := ""
    addNonce := false
    requestTsaCert := true

    // Create a time-stamp request token
    success = http.CreateTimestampRequest("sha256",*base64Hash,optionalPolicyOid,addNonce,requestTsaCert,requestToken)
    if success == false {
        fmt.Println(http.LastErrorText())
        crypt.DisposeCrypt2()
        http.DisposeHttp()
        requestToken.DisposeBinData()
        return
    }

    // Send the time-stamp request token to the TSA.
    // This is the equivalent of the following CURL command:
    // curl -H "Content-Type: application/timestamp-query" --data-binary '@file.tsq' http://timestamp.digicert.com > file.tsr
    tsaUrl := "http://timestamp.digicert.com"
    resp := http.PBinaryBd("POST",tsaUrl,requestToken,"application/timestamp-query",false,false)
    if http.LastMethodSuccess() == false {
        fmt.Println(http.LastErrorText())
        crypt.DisposeCrypt2()
        http.DisposeHttp()
        requestToken.DisposeBinData()
        return
    }

    // Get the timestamp reply from the HTTP response object.
    timestampReply := chilkat.NewBinData()
    resp.GetBodyBd(timestampReply)
    resp.DisposeHttpResponse()

    // Convert the binary timestamp reply to XML
    asn := chilkat.NewAsn()
    success = asn.LoadBd(timestampReply)
    if success == false {
        fmt.Println(asn.LastErrorText())
        crypt.DisposeCrypt2()
        http.DisposeHttp()
        requestToken.DisposeBinData()
        timestampReply.DisposeBinData()
        asn.DisposeAsn()
        return
    }

    xml := chilkat.NewXml()
    success = xml.LoadXml(*asn.AsnToXml())

    // Extract the TSTInfo from the XML.
    // The TSTInfo is this base64 encoded ASN.1 

    // TSTInfo ::= SEQUENCE  {
    //    version                      INTEGER  { v1(1) },
    //    policy                       TSAPolicyId,
    //    messageImprint               MessageImprint,
    //      -- MUST have the same value as the similar field in
    //      -- TimeStampReq
    //    serialNumber                 INTEGER,
    //     -- Time-Stamping users MUST be ready to accommodate integers
    //     -- up to 160 bits.
    //    genTime                      GeneralizedTime,
    //    accuracy                     Accuracy                 OPTIONAL,
    //    ordering                     BOOLEAN             DEFAULT FALSE,
    //    nonce                        INTEGER                  OPTIONAL,
    //      -- MUST be present if the similar field was present
    //      -- in TimeStampReq.  In that case it MUST have the same value.
    //    tsa                          [0] GeneralName          OPTIONAL,
    //    extensions                   [1] IMPLICIT Extensions   OPTIONAL  }

    tstInfoBase64 := xml.GetChildContent("sequence[1]|contextSpecific|sequence|sequence|contextSpecific|octets")

    bdTstInfo := chilkat.NewBinData()
    bdTstInfo.AppendEncoded(*tstInfoBase64,"base64")

    asnTstInfo := chilkat.NewAsn()
    success = asnTstInfo.LoadBd(bdTstInfo)
    if success == false {
        fmt.Println(asnTstInfo.LastErrorText())
        crypt.DisposeCrypt2()
        http.DisposeHttp()
        requestToken.DisposeBinData()
        timestampReply.DisposeBinData()
        asn.DisposeAsn()
        xml.DisposeXml()
        bdTstInfo.DisposeBinData()
        asnTstInfo.DisposeAsn()
        return
    }

    xmlTstInfo := chilkat.NewXml()
    success = xmlTstInfo.LoadXml(*asnTstInfo.AsnToXml())
    fmt.Println(*xmlTstInfo.GetXml())

    // Here's the TSTInfo XML:

    // <?xml version="1.0" encoding="utf-8"?>
    // <sequence>
    //     <int>01</int>
    //     <oid>2.16.840.1.114412.7.1</oid>
    //     <sequence>
    //         <sequence>
    //             <oid>2.16.840.1.101.3.4.2.1</oid>
    //             <null/>
    //         </sequence>
    //         <octets>4sRRyWOzC7EOic4fQ9+Op1pa10DbgoBGjBvkq09LZmE=</octets>
    //     </sequence>
    //     <int>00AD2C86E49872597B60F87D5C54BCFFAE</int>
    //     <universal tag="24" constructed="0">MjAyMzAzMTYxMTQ5NTJa</universal>
    // </sequence>

    //    The genTime (GeneralizedTime) is contained in the final "universal" XML element and is 
    //    in base64. It is the time at which the time-stamp token has been created by
    //    the TSA. After decoding from base64, it is:
    // 
    //    The syntax is: YYYYMMDDhhmmss[.s...]Z
    //    Example: 19990609001326.34352Z

    sbGenTime := chilkat.NewStringBuilder()
    sbGenTime.DecodeAndAppend(*xmlTstInfo.GetChildContent("universal"),"base64","utf-8")
    fmt.Println(*sbGenTime.GetAsString())

    // Result:
    // 20230316115718Z

    crypt.DisposeCrypt2()
    http.DisposeHttp()
    requestToken.DisposeBinData()
    timestampReply.DisposeBinData()
    asn.DisposeAsn()
    xml.DisposeXml()
    bdTstInfo.DisposeBinData()
    asnTstInfo.DisposeAsn()
    xmlTstInfo.DisposeXml()
    sbGenTime.DisposeStringBuilder()