RequestNavigator wires together Route matching, Filtering of HttpRequests and Handler calling. It manages url addresses and bind them handlers.

class RequestNavigator {
 final Stream<HttpRequest> _incoming;
 final Router _router;

 /**
  * Maps route names to [Stream]
  */
 final Map<String, StreamController<RequestHandlerParameters>> _streams = {};

 /**
  * If no route is matched.
  */
 StreamController<RequestHandlerParameters> _defaultStreamController = null;

 /**
  * Creates new RequestNavigator listening on [_incoming] and routing via [_router].
  */
 RequestNavigator(this._incoming, this._router){
   this._incoming.listen(processHttpRequest);
 }

 StreamController _createStreamControllerWithHandler(dynamic handler){
   var streamController = new StreamController<RequestHandlerParameters>();
   streamController.stream.listen((p) => handler(p.req, p.url_params));
   return streamController;
 }

 /**
  * Registers [Handler] for a [Route] and adds listener to the stream which
  * is also returned.
  */
 void registerHandler(String routeName, dynamic handler){
   if(_streams.containsKey(routeName)){
     throw new ArgumentError("Cannot register handler as route name '$routeName' already in use in RequestNavigator.");
   }

   _streams[routeName] = _createStreamControllerWithHandler(handler);
 }

 /**
  * When [Router] matches nothing then [handler] will be called (through the returned [Stream]).
  */
 void registerDefaultHandler(dynamic handler){
   if(_defaultStreamController != null){
     throw new ArgumentError("Default route already set.");
     _defaultStreamController.close();
   }
   _defaultStreamController = _createStreamControllerWithHandler(handler);
 }

 /**
  * [HttpRequest.uri.path] is matched agains [Router],
  * whole [HttpRequest] is filtered through [Filter] and if passes all then
  * [HttpRequest] is inserted to the correspondig [Stream].
  */
 void processHttpRequest(HttpRequest req){
   var matchInfo = _router.match(req.uri.path);
   if(matchInfo != null){
     if(_streams.containsKey(matchInfo[0])){
       _streams[matchInfo[0]].add(new RequestHandlerParameters(req, matchInfo[1]));
     }
     else{
       throw new ArgumentError("Stream not found for '${matchInfo[0]}'");
     }
   }
   else{
     _defaultStreamController.add(new RequestHandlerParameters(req, {}));
   }
 }
}