Searching for xpath expression with colon in attribute name throws exception (node.js elementtree module)

Question

Searching for xpath expression with colon in attribute name throws exception (node.js elementtree module)

Using the elementtree package in nodejs, I'm trying to verify the existence of a certain xml attribute in an xml file (specifically an android manifest file).

var manifestTxt = fs.readFileSync('AndroidManifest.xml', 'utf-8'),
    manifestDoc = new et.ElementTree(et.XML(manifestTxt)),
    expected = 'application/activity[@android:name="com.whatever.app"]';

test.ok(manifestDoc.find(expected));

I'm getting the following exception:

node_modules/elementtree/lib/elementpath.js:210
      throw new SyntaxError(token, 'Invalid attribute predicate');
        ^
Error: Invalid attribute predicate

It doesn't seem to like the colon in the attribute name, but without it the search doesn't match. I think I'm handling the namespace wrong -- but can't find the proper way.

Edit Here's the sample xml I'm searching:

<?xml version='1.0' encoding='utf-8'?>
<manifest ... xmlns:android="http://schemas.android.com/apk/res/android">
    <application android:debuggable="true" android:icon="@drawable/icon" android:label="@string/app_name">&#xA; 
        <activity android:label="@string/app_name" android:name="com.whatever.app">&#xA;                
            <intent-filter>&#xA;</intent-filter>
        </activity> 
    </application>
    <uses-sdk android:minSdkVersion="5" />
</manifest>

javascript
node.js
xpath
elementtree

Answer 1

In case you don't have the information how to register the namespace and use the associated prefix for it, use:

application/activity
   [@*[local-name()=name' 
     and 
      namespace-uri() = 'http://schemas.android.com/apk/res/android'
      ] 
   = 
    'com.whatever.app'
   ]

Simpler expressions that aren't safe in the general case, but may select the wanted node(s) in this specific case:

application/activity[@*[local-name()='name'] = 'com.whatever.app']

or this expression:

application/activity[@*[name()='android:name'] = 'com.whatever.app']

Answer 2

Elementtree expects namespace URIs, not namespace prefixes.

var manifestTxt = fs.readFileSync('AndroidManifest.xml', 'utf-8'),
    manifestDoc = new et.ElementTree(et.XML(manifestTxt)),
    expected = '//application/activity[@{http://schemas.android.com/apk/res/android}name="com.whatever.app"]';

test.ok( manifestDoc.find(expected) );

See: ElementTree: Working with Qualified Names

Edit The XPath implementation of node-elementtree does not currently seem to have namespace support at all.

Missing that you'd have to do some legwork:

var manifestTxt = fs.readFileSync('AndroidManifest.xml', 'utf-8'),
    manifestDoc = new et.ElementTree(et.XML(manifestTxt)),
    activities = manifestDoc.findall('//application/activity'), i;

for (i=0; i<activities.length; i++) {
  if ( activities[i].attrib['android:name'] === 'com.whatever.app' ) {
    test.ok(true);
  }
}

The line if ( activities[i].attrib['android:name'] === 'com.whatever.app' ) { is largely a guess.

I don't know how the parser handles namespaced attributes. When in doubt, just dump the whole activities[i].attrib to the console and see what the parser did. Adapt the above code accordingly. I'm afraid that's as close as you will get with that kind of limited XPath support.