Querying a Wiki Using Qt

I spent a little time yesterday working on a class that provides a wrapper around the MediaWiki API. It makes quite a nice example of how the QNetworkAccessManager API can be combined with QXmlStreamReader to quickly access web services. The code, as you'll see, is very simple.

First lets take a look at the constructor and the data members. We specify the path to the api.php file of the wiki we want to query, and setup the network access manager.

MediaWiki::MediaWiki( QObject parent ) : QObject( parent ) { d = new MediaWikiPrivate; d->apiUrl = QUrl("http://en.wikipedia.org/w/api.php"); d->manager = new QNetworkAccessManager( this ); d->maxItems = 10; connect( d->manager, SIGNAL(finished(QNetworkReply)), SLOT(finished(QNetworkReply *)) ); }

People using the class can ask us to perform a search by calling the search() method with the term they want to look for. Again, the code is simple.

qDebug() << "Constructed search URL" << url;

d->manager->get( QNetworkRequest(url) );

}

We use the addQueryItem() method of QUrl to construct our search, by specifying each of the options we need. Finally, we launch the request by calling the get() method of QNetworkAccessManager.

Once the network request is completed, our finished() slot is called. We check the status to see if the request succeeded then pass the reply to the processSearchResult() method. Note that QNetworkReply is a subclass of QIODevice which makes it very easy for us to work with.

qDebug() << "Request succeeded";
bool ok = processSearchResult( reply );
emit finished( ok );

QXmlStreamReader reader( source );
while ( !reader.atEnd() ) {
    QXmlStreamReader::TokenType tokenType = reader.readNext();
    // qDebug() << "Token" << int(tokenType);
    if ( tokenType == QXmlStreamReader::StartElement ) {
        if ( reader.name() == QString("p") ) {
            QXmlStreamAttributes attrs = reader.attributes();
            //qDebug() << "Found page" << attrs.value( QString("title") );
            d->results << attrs.value( QString("title") ).toString();
        }
    }
    else if ( tokenType == QXmlStreamReader::Invalid )
        return false;
}

qDebug() << "Results" << d->results;
return true;

}

To parse the XML returned by the wiki, we use QXmlStreamReader. We're only interested in elements that look like this:

   <p ns="0" title="Qt (toolkit)" />

So we locate those when we see a StartElement token, then extract the title attribute. Once this process is complete, we have a list of all the pages matching the query and emit our finished() signal.

To test the code I've written a small wrapper that lets you enter a term, then searches online when you press return. The code queries wikipedia right now, but simply by changing the setApiUrl() call you can tell it to search techbase. I've left that code in place but commented out so people can try it.

In future, this code could be used as a KRunner plugin, as part of an IDE, or more generally anywhere else where someone wants to query a wiki in their application. The full example can be downloaded from http://xmelegance.org/devel/mediawiki/wikiviewer.tar.bz2. Enjoy.