XSLT: Convert base64 data into image files
base64, evernote, file-io, image-processing, xslt
Solution
I found this entry from the XSL maiing lists that describes how to use the Saxon extension function xs:base64Binary-to-octet to stream it out to a file using the Java FileOutputStream in an XSLT 2.0 stylesheet:
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
version="2.0" xmlns:xs="http://www.w3.org/2001/XMLSchema";
xmlns:saxon="http://saxon.sf.net/";
xmlns:fos="java.io.FileOutputStream">
<xsl:template match="/">
<xsl:variable name="img" select="concat('c:\test\jesper', '.jpg')"/>
<xsl:variable name="fos" select="fos:new(string($img))"/>
<xsl:value-of select="fos:write($fos,
saxon:base64Binary-to-octets(xs:base64Binary(my-base64-encoded-image)))"/>
<xsl:value-of select="fos:close($fos)"/>
</xsl:template>
</xsl:stylesheet>
Problem
I have seen several questions on how to encode an image file in base64, but how about the other way around - how do I reconstitute a picture from a base64 string stored in an XML file? ``` <resource> <data encoding="base64"> R0lGODlhEAAQAPMAMcDAwP/crv/erbigfVdLOyslHQAAAAECAwECAwECAwECAwECAwECAwECAwEC AwECAyH/C01TT0ZGSUNFOS4wGAAAAAxtc09QTVNPRkZJQ0U5LjAHgfNAGQAh/wtNU09GRklDRTku MBUAAAAJcEhZcwAACxMAAAsTAQCanBgAIf8LTVNPRkZJQ0U5LjATAAAAB3RJTUUH1AkWBTYSQXe8 fQAh+QQBAAAAACwAAAAAEAAQAAADSQhgpv7OlDGYstCIMqsZAXYJJEdRQRWRrHk2I9t28CLfX63d ZEXovJ7htwr6dIQB7/hgJGXMzFApOBYgl6n1il0Mv5xuhBEGJAAAOw== </data> <mime>image/gif</mime> <resource-attributes> <file-name>clip_image001.gif</file-name> </resource-attributes> </resource> ``` Given the above XML node `resource`, how do I go about creating `clip_image001.gif`? Please suggest: - XSLT processors and/or extensions enable this, plus - a sample XSLT that triggers the conversion Note that it must be able to handle at least GIF & PNG file formats. Preferably not restricted to any OS. Implemented solution Based around Mads Hansen's solution. Main difference being that I referenced `net.sf.saxon.value.Base64BinaryValue` directly in my namespace rather than using the `saxon` namespace, because I understood the Java APIs more intuitively than the Saxonica website's descriptions of the `base64Binary-to-octets` and `base64Binary` functions. ``` <xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:b64="net.sf.saxon.value.Base64BinaryValue" xmlns:fos="java.io.FileOutputStream" ... exclude-result-prefixes="b64 fos"> ... <xsl:for-each select="resource"> <xsl:variable name="b64" select="b64:new(string(data))"/> ... <xsl:variable name="fos" select="fos:new(string($img))"/> <xsl:value-of select="fos:write($fos, b64:getBinaryValue($b64))"/> <xsl:value-of select="fos:close($fos)"/> </xsl:for-each> ... ``` P.S. See sibling question for my implementation of how to obtain the hashes necessary to identify the image files. This question is a subquestion of another question I have asked previously.