function NodejsStreamOutputAdapter(helper, options, updateCb) {
    Readable.call(this, options);
    this._helper = helper;

    var self = this;
    helper.on("data", function (data, meta) {
        if (!self.push(data)) {
            self._helper.pause();
        }
        if(updateCb) {
            updateCb(meta);
        }
    })
    .on("error", function(e) {
        self.emit('error', e);
    })
    .on("end", function () {
        self.push(null);
    });
}
A nodejs stream using a worker as source.
@see the SourceWrapper in http://nodejs.org/api/stream.html
@constructor
@param {StreamHelper} helper the helper wrapping the worker
@param {Object} options the nodejs stream options
@param {Function} updateCb the update callback.