/**
* Fetches the given USK and returns the new USKRetriever. Does not check whether there is already a fetch for that USK.
*/
private USKRetriever fetch(USK usk) throws MalformedURLException {
FetchContext fetchContext = mClient.getFetchContext();
fetchContext.maxSplitfileBlockRetries = -1; // retry forever
fetchContext.maxNonSplitfileRetries = -1; // retry forever
fetchContext.maxOutputLength = WoTMessageListXML.MAX_XML_SIZE;
if(logDEBUG) Logger.debug(this, "Subscribing to WoTMessageList queue " + usk);
return mUSKManager.subscribeContent(usk, this, true, fetchContext, RequestStarter.UPDATE_PRIORITY_CLASS, mRequestClient);