How can I encode xml files to xfdl (base64-gzip)?

As far as I know you cannot find the compression level of an already compressed file. When you are compressing the file you can specify the compression level with -# where the # is from 1 to 9 (1 being the fastest compression and 9 being the most compressed file). In practice you should never compare a compressed file with one that has been extracted and recompressed, slight variations can easily crop up. In your case I would compare the base64 encoded versions instead of the gzip'd versions.

Check these out:

http://www.ourada.org/blog/archives/375

http://www.ourada.org/blog/archives/390

They are in Python, not Ruby, but that should get you pretty close.

And the algorithm is actually for files with header 'application/x-xfdl;content-encoding="asc-gzip"' rather than 'application/vnd.xfdl; content-encoding="base64-gzip"'But the good news is that PureEdge (aka IBM Lotus Forms) will open that format with no problem.

Then to top it off, here's a base64-gzip decode (in Python) so you can make the full round-trip:

with open(filename, 'r') as f:  header = f.readline()  if header == 'application/vnd.xfdl; content-encoding="base64-gzip"\n':    decoded = b''    for line in f:      decoded += base64.b64decode(line.encode("ISO-8859-1"))    xml = zlib.decompress(decoded, zlib.MAX_WBITS + 16)

I did this in Java with the help of the Base64 class from http://iharder.net/base64.

I've been working on an application to do form manipulation in Java. I decode the file, create an DOM document from the XML then write it back to file.

My code in Java to read the file looks like this:

public XFDLDocument(String inputFile)         throws IOException,             ParserConfigurationException,            SAXException{    fileLocation = inputFile;    try{        //create file object        File f = new File(inputFile);        if(!f.exists()) {            throw new IOException("Specified File could not be found!");        }        //open file stream from file        FileInputStream fis = new FileInputStream(inputFile);        //Skip past the MIME header        fis.skip(FILE_HEADER_BLOCK.length());           //Decompress from base 64                           Base64.InputStream bis = new Base64.InputStream(fis,                 Base64.DECODE);        //UnZIP the resulting stream        GZIPInputStream gis = new GZIPInputStream(bis);        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();        DocumentBuilder db = dbf.newDocumentBuilder();        doc = db.parse(gis);        gis.close();        bis.close();        fis.close();    }    catch (ParserConfigurationException pce) {        throw new ParserConfigurationException("Error parsing XFDL from file.");    }    catch (SAXException saxe) {        throw new SAXException("Error parsing XFDL into XML Document.");    }}

My code in java looks like this to write the file to disk:

    /**     * Saves the current document to the specified location     * @param destination Desired destination for the file.     * @param asXML True if output needs should be as un-encoded XML not Base64/GZIP     * @throws IOException File cannot be created at specified location     * @throws TransformerConfigurationExample     * @throws TransformerException      */    public void saveFile(String destination, boolean asXML)         throws IOException,             TransformerConfigurationException,             TransformerException          {        BufferedWriter bf = new BufferedWriter(new FileWriter(destination));        bf.write(FILE_HEADER_BLOCK);        bf.newLine();        bf.flush();        bf.close();        OutputStream outStream;        if(!asXML) {            outStream = new GZIPOutputStream(                new Base64.OutputStream(                        new FileOutputStream(destination, true)));        } else {            outStream = new FileOutputStream(destination, true);        }        Transformer t = TransformerFactory.newInstance().newTransformer();        t.transform(new DOMSource(doc), new StreamResult(outStream));        outStream.flush();        outStream.close();          }

Hope that helps.