async-app.js

exports.app = function myAsyncApp(request){
  return function(responder) {
    responder.init(200, {});
    var i = 0;
    var intervalId = setInterval(function(){
      responder.write("Every second another message");
      if(i++ == 10){
        responder.close();
        clearInterval(intervalId);
      }
    }, 1000);
  };
}

async-middleware.js

exports.middleware = function(app) {
  return function(request) {
    var response = app(request);
    if (typeof response === "function") {
      return function(responder) {
        // create a proxy for the responder
        var proxy = createResponderProxy(responder);
        // ... and overwrite whatever method you want
        proxy.[init|write|close] = ...; 
        response(proxy);
      };
    } else {
      // sync
    }
  }
}