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Index of Chilkat Blog Posts

March 26, 2008

Convert XFDL base64-gzip to XML string

(This example can be provided in all programming languages supported by Chilkat: C#, ASP, VB.NET, C++, Delphi, Perl, Python, Ruby, Java, etc.)

This Visual Basic 6.0 example converts a base64-gzip .xfdl file to a decompressed XML string.

    ' This code converts Gzip'd XFDL to the uncompressed XML document
    ' contained in a string.  The .xfd document to be converted looks like this:
    ' application/vnd.xfdl;content-encoding="base64-gzip"
    ' H4sIAAAAAAAAC x9adOa2Nbod38FN6fq7T5lEgYFoU86pxBQUQRkcLp1K4VMokwyOfz6u9FnftQk
    ' 3Zon6deuTiLszZ7WvPbaa3/67ybwocJOUi8K/3yHfkTeQXZoRpYXun++41XpA0ni1Af03X8/Vz6N
    ' ...
    ' CkString is a freeware String component.  It may be downloaded from:
    ' <a href=\"\"></a>
    ‘ Reference Doc: <a href=\"\"></a>
    Dim ckStr As New CkString
    Dim success As Long
    success = ckStr.LoadFile("test.xfdl", "iso-8859-1")
    If (success = 0) Then
        MsgBox "Failed to load file!"
        Exit Sub
    End If
    ‘ Get rid of the 1st line:
    ckStr.ChopBefore CStr(Chr(10))
    ‘ The Gzip component is included in the Chilkat Zip ActiveX.
    ‘ It requires a "Chilkat Zip" license to use beyond 30-days.
    ‘ Download link: <a href=\"\"></a>
    ‘ GZip reference: <a href=\"\"></a>
    Dim gzip As New gzip
    success = gzip.UnlockComponent("Anything for 30-day trial")
    If (success = 0) Then
        ‘ Failed to unlock component
        MsgBox gzip.LastErrorHtml
        Exit Sub
    End If
    ‘ Decode from base64 to binary (a Variant containing the Gzip bytes)
    Dim binaryData As Variant
    binaryData = gzip.Decode(ckStr.Str, "base64")
    ‘ Ungzip:
    Dim xmlBytes As Variant
    xmlBytes = gzip.UncompressMemory(binaryData)
    ‘ We now have the XML bytes (a Variant containing a byte array)
    ‘ You might be tempted to assign this to a string — but don’t –
    ‘ you don’t yet know the character encoding of the XML.  If it’s non-ANSI,
    ‘ you’d ruin the document.
    ‘ Load the XML document into a CkString object:
    Dim xmlStringObj As New CkString
    ‘ The LoadXmlDoc method parses just enough of the XML bytes to get the charset.
    ‘ It looks for the XML declaration, such as this:
    ‘ <?xml version="1.0" encoding="utf-8"?>
    ‘ If not found, it assumes ANSI.
    ‘ This allows the XML bytes to be interpreted correctly according to the
    ‘ character encoding used.
    xmlStringObj.LoadXmlDoc xmlBytes
    ‘ Now get the XML document as a String:
    Dim xmlString As String
    xmlString = xmlStringObj.Str
    Text1.Text = xmlString

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