prototype prototype - 18 days ago 12
Node.js Question

Parse XML to JSON and back ... with xml2js and xmlbuilder?

Trying to parse XML into JSON with xml2js and then return the JSON to XML using xmlbuilder (usually after modifying the content programmatically).

I think that the two should be complements, per this post https://github.com/oozcitak/xmlbuilder-js/issues/69. But am having some difficulty, and it's gotta be that I'm not getting the config parameters right.

Here's the code I'm running:

var xml = fs.readFileSync(__dirname + '/../xml/theme.xml', 'utf8');

xml2js.parseString(xml, { attrkey: '@', xmlns: true }, function(err, json) {
var xml2 = xmlbuilder.create(json,
{version: '1.0', encoding: 'UTF-8', standalone: true}
).end({pretty: true, standalone: true})
});


Here's the first bit of the original XML:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<a:theme xmlns:a="http://schemas.openxmlformats.org/drawingml/2006/main" name="Office Theme">
<a:themeElements>
<a:clrScheme name="Office">
<a:dk1>
<a:sysClr val="windowText" lastClr="000000"/>
</a:dk1>
<a:lt1>
<a:sysClr val="window" lastClr="FFFFFF"/>
</a:lt1>
<a:dk2>
<a:srgbClr val="1F497D"/>
</a:dk2>
...
</a:themeElements>
</a:theme>


Here;s how xml2js parses that to JSON, this looks right to me:

{
"a:theme": {
"@": {
"xmlns:a": {
"name": "xmlns:a",
"value": "http://schemas.openxmlformats.org/drawingml/2006/main",
"prefix": "xmlns",
"local": "a",
"uri": "http://www.w3.org/2000/xmlns/"
},
"name": {
"name": "name",
"value": "Office Theme",
"prefix": "",
"local": "name",
"uri": ""
}
},
"@ns": {
"uri": "http://schemas.openxmlformats.org/drawingml/2006/main",
"local": "theme"
},
"a:themeElements": [
{
"@ns": {
"uri": "http://schemas.openxmlformats.org/drawingml/2006/main",
"local": "themeElements"
},
"a:clrScheme": [
{
"@": {
"name": {
"name": "name",
"value": "Office",
"prefix": "",
"local": "name",
"uri": ""
}
},
"@ns": {
"uri": "http://schemas.openxmlformats.org/drawingml/2006/main",
"local": "clrScheme"
},
...


Note that in the JSON above:


  1. the attribute (e.g.
    name=
    ) are turned into keys inside an
    @
    object and

  2. the attribute values are turned into objects



Now here's how it looks when xmlbuilder turns it back into XML:



<a:theme ="[object Object]" ns="[object Object]">
<a:themeElements ns="[object Object]">
<a:clrScheme ="[object Object]" ns="[object Object]">
<a:dk1 ns="[object Object]">
<a:sysClr ="[object Object]" ns="[object Object]"/>
</a:dk1>
<a:lt1 ns="[object Object]">
<a:sysClr ="[object Object]" ns="[object Object]"/>
</a:lt1>
...
</a:themeElements>
</a:theme>


So there are two problems that XML builder is facing:
* it's not recognizing the attribute names within the
@
object and
* it's not recognizing the attribute value within the attribute object

Hacking it appears that xmlbuilder wants attributes names structured like:

`{ "@name": "Office Theme"} `


rather than

`{ "@" : { "name" : { value: "Office Theme" }}}`


Should I configure xml2js differently, xmlbuilder differently, or is there a different pair of libraries that can parse XML -> JSON -> XML?

Answer

The xml2js package comes with its own XML builder, to which the documentation has to say:

Since 0.4.0, objects can be also be used to build XML:

var fs = require('fs'),
    xml2js = require('xml2js');

var obj = {name: "Super", Surname: "Man", age: 23};
var builder = new xml2js.Builder();
var xml = builder.buildObject(obj);

At the moment, a one to one bi-directional conversion is guaranteed only for default configuration, except for attrkey, charkey and explicitArray options you can redefine to your taste.

So, after dropping your custom parser configuration, this works perfectly for me:

var fs = require('fs');
var path = require('path');
var xml2js = require('xml2js');

xmlFileToJs('theme.xml', function (err, obj) {
    if (err) throw (err);
    jsToXmlFile('theme2.xml', obj, function (err) {
        if (err) console.log(err);
    })
});
// -----------------------------------------------------------------------

function xmlFileToJs(filename, cb) {
    var filepath = path.normalize(path.join(__dirname, filename));
    fs.readFile(filepath, 'utf8', function (err, xmlStr) {
        if (err) throw (err);
        xml2js.parseString(xmlStr, {}, cb);
    });    
}

function jsToXmlFile(filename, obj, cb) {
    var filepath = path.normalize(path.join(__dirname, filename));
    var builder = new xml2js.Builder();
    var xml = builder.buildObject(obj);
    fs.writeFile(filepath, xml, cb);
}