Bayeux Protocol: la nuova frontiera della comunicazione a portata di mano. Relatore Nino Guarnacci

Transcription

1 Bayeux Protocol: la nuova frontiera della comunicazione a portata di mano Relatore Nino Guarnacci

2 to understand the phenomenon of Comet and Reverse AJAX, we need to consider why there is a need for it and why it is so out of the ordinary as to require a label of its own

3 Beginning HTTP HTTP was designed as a protocol for retriving documents from remote servers Communication between the client and the server is always initiated by the client and never by the server Connections between the client and the server are transient and the server do not maintain any long-term state information regarding the client

4 Twist the formula Why, then, should you want the server to be able to contact the client, and mantain persistent connections? - There are several suitable common use case -

5 use cases: AdviceME Monitoring and Data Feeds Client as a Dashboard or Monitor Demand for monitoring applications Market data feeds Security Alerting SLA Violation Advisor

6 use cases: Please Wait Progress Updates Comunicating progress on long-running server-side activities Report progress on long running server task

7 use cases: Share with me Chat and Collaboration Chat System Photo sharing On-Line Gaming Collaborative Tools

8 Actual Approachs Push Using Pooling Collaborative ability by pooling the server with client regular request asking for update. Network wasteful Server resource exhaustion client / browser server Client repeatedly contact the server to check for change. pool Pooling schedule not affected pool update pool

9 Actual Approachs Piggybacking The contents of the response aren t strictly related to the nature of the request client / browser pool server Response wil also contain any changes to the domain model pool Pooling schedule reset Reset timer Update + pool pool

10 <<Comet>> Comet techniques Keep the response stream open for a significantly longer time Server send several pieces of data back in the response client / browser change change server Comet request is held open on the server for a while, multiple discrete changes are communicated Update Long Polling change

11 >>Comet<< Comet techniques Most modern web browser, permit only 2 concurrent HTTP connection to the given domain. client / browser change change Update server If more than one request is being held open against the same server, ordinary request will be blocked (same for different browsertab) blocked Get change

12 >>Comet<< Comet techniques Traditional servers allocate a thread to each incoming request Design work well when serving large volume of short lived request client / browser client / browser client / browser server Long polls are held open request for a considerable length of time. Thread-per-Request model is generally unable to scale to large numbers of clients. Java servlet model itself is inherently a thread-perrequest

13 Java Comet Comet techniques Java servlet model was developed to serve a very different traffic profile. A large number of simultaneous request from Comet clients would exhaust the server s thread pool. (doesn t scale well) client / browser client / browser client / browser server More Comet-Friendly server architectures from the javacommunity: Continuations (Jetty 6) Grizzly Tomcat 6 JSR 315 Servlet 3.0

14 Bayeux provides a very nice abstraction on top of Comet transport, by casting the transfer data in terms of channels, to which clients can publish and subscribe Comet and Reverse Ajax Dave Crane and Phil McCarthy (2008)

15 Bayeux CometD Bayeux Emerging de facto standard for Comet Existing reference implementation: COMETD Provided by the people at Sitepen:» (the same as) Dojo Javascript Toolkit

16 Bayeux CometD Bayeux Adopts exactly the same approach and provides a flexible, scalable API based around a publish-subscribe model Data sent through, is always assigned a notional channel Publishers client / browser server Subscribers Multiple Channels CometD Client Bayeux Server Subscribers HTTP Transport Publishers

17 Bayeux CometD Bayeux Channels allows multiple decoupled conversations on top of a single HTTP connection. The client-side CometD and the server-side Bayeux implementation communicate over several notional channels, all bundled within a single HTTP request-response. Publishers client / browser server Subscribers Multiple Channels CometD Client Bayeux Server Subscribers HTTP Transport Publishers

18 Purpose Cometd is a project by the Dojo Fundation to implement Bayeux specification. Bayeux is a purpose to implement responsive user interaction for web clients using Ajax and server-push technique called Comet The messages are routed via named channels and can be delivered: server2client client2server client2client (via server)

19 JSON Messages Bayeux message are specified in JSON notation [ ] { } "channel": "/some/name", "clientid": "83js73jsh29sjd92", "data": { "myapp" : "specific data", value: 100 } JavaScript Object Notation is a lightweight data-interchange format

20 Channels style Channels are by default broadcast publish subscribe. Channels are identified by names and always starts with / Channel pattern support trailing wildcards of either * or ** : /news/* Valid channels : /news/italy, /news/uk... /news/** Valid channels : /news/italy, /news/italy/lazio...

21 Bayeux approach Bayeux event is sent from the server to the client via HTTP response to a HTTP request sent in anticipation: Polling Transport On receipt of the HTTP response, the bayeux client issues a new bayeux message. Streaming Transport Use streaming technique (forever response), allowing multiple message to be sent over the same response

22 Bi-Direction To solve the issue of bi-directional communications, Bayeux client will use two HTTP connections: Messaging may occur asynchronously client / browser server stream/channels stream/channels stream/channels stream/channels

23 Handshake Connect Bayeux connection are nogotiated between client and server with handshake messages that allow to define: Connection Type Authentication Persistence subscription Identification... client handshake request unsuccessful handshake response handshake request successful handshake response connect request connect response connect request unsucessful connect response handshake request successful handshake response connect request connect response server

24 Interactions Bayeux client may send publish and subscribe messages to register interest in a channel: [ ] { } subscribe "channel": "/meta/subscribe", "clientid": "Un1q31d3nt1f13r", "subscription": "/news/** [ ] { } publish [ recived message "channel": "/news/italy", "clientid": "Un1q31d3nt1f13r", "data": "some application string or JSON object", "id": "some unique message id" { "channel": "/news/italy", "data": some news from italy ", "id": "some unique message id"

25 Server APIs Web application developers can optionally use serverside pub-sub APIs in their servlets or Java classes to get the Bayeux server context, manage channels, and the incoming and outgoing messages pubsubserver = PubSubServerFactory.lookupPubSubServer(serverName); pubsubserver.publishtochannel(localclient, channel, data.tostring()); public void onpublish(deliveredmessageevent event) { Object payload = event.getmessage().getpayload(); if (payload instanceof String) { String command = (String)payLoad; if ("start".equals(command) &&!publishing) { publisher.startup(); publishing = true; } else if ("halt".equals(command) && publishing) { publisher.halt(); publishing = false; WebLogic 10.3 Bayeux Server

26 Stock Demo The demo describes a real-world scenario based on stock trading, and makes extensive use of the Bayeux APIs in both the server and client components The Demo uses :» Dojo as its client-side library» WebLogic Bayeux implementation as server APIs

27 Web XML-Configuration Server dedicated file-based configuration environment <client-timeout-secs>100</client-timeout-secs> <persistent-client-timeout-secs>400</persistent-client-timeout-secs> <interval-millisecs>1000</interval-millisecs> <multi-frame-interval-millisecs>2000</multi-frame-interval-millisecs> server config <channel> <channel-pattern>/chatrooms/**</channel-pattern> </channel> <channel-constraint> <channel-resource-collection> <channel-resource-name>all-permissions</channel-resource-name> <description>grant all permissions for everything by everyone</wlps:description> <channel-pattern>/chatrooms/*</channel-pattern> </channel-resource-collection> </channel-constraint> channels security

28 Security Model JEE security configuration based (ssl support) <channel-constraint> <channel-resource-collection> <channel-resource-name>publish</channel-resource-name> <description>publish channel constraint</description> <channel-pattern>/stock/* *</channel-pattern> <channel-pattern>/management/publisher</channel-pattern> <channel-operation>publish</channel-operation> </channel-resource-collection> <auth-constraint> <description>publisher</description> <role-name>publisher</role-name> </auth-constraint> </channel-constraint> create delete subscribe publish JavaDay demo configuration

29 JMS - Bayeux Durable subscriber and persistence support, based on JMS architecture <jms-handler-mapping> <jms-handler-name>defaultjmshandler</jms-handler-name> <jms-handler> <jms-provider-url>iiop://localhost:7001</jms-provider-url> <connection-factory-jndi-name>connectionfactoryjndi</connection-factory-jndi-name> <topic-jndi-name>topicjndi</topic-jndi-name> </jms-handler> </jms-handler-mapping> <channel> <channel-pattern>/chat/**</channel-pattern> <jms-handler-name>defaultjmshandler</jms-handler-name> </channel> JEE JMS Topic

30 Message Persistence Persistent Channels and session-message failover support <channel> <channel-pattern>/chat/**</channel-pattern> <channel-persistence> <max-persistent-message-duration-secs>3000</max-persistent-message-duration-secs> <persistent-store>filestoredefinition</persistent-store> </channel-persistence> </channel> AJAX Enterprise Solution

31 JS Client APIs Dojo JS Cometd library (Init and Publish) Initialize the Dojo cometd environment. dojo.io.cometd.init({}, "/servletcontextmapping/cometd"); Publish a message to a channel. dojo.io.cometd.publish("/a/channel", "message content"); or JSON message: dojo.io.cometd.publish("/a/channel", {"data": "content"});

32 JS Client APIs Dojo JS Cometd library (Subscribe) Subscribe to a channel dojo.io.cometd.subscribe("/a/channel", null, "onupdate"); function onupdate(message) { if (!message.data) { alert("bad message format "+message); return; } var data = message.data; }

33 JS Dynamic Demo Dynamic Channel sub & unsubscription function subscribe(symbol) { dojo.io.cometd.subscribe("/stock/"+symbol, null, "onupdate"); } function unsubscribe(symbol) { dojo.io.cometd.unsubscribe("/stock/"+symbol, null, "onupdate"); } function subscribeall() { var count = itemsstore.get().length; for (var i=0; i<count; i++) { subscribe(itemsstore.getdatabyindex(i).symbol); } } JavaDay demo configuration

34 Web Publisher Simple web-based client publisher (stock publisher) <html> <head> <title>javaday3 Bayeux Demo</title> <script type="text/javascript" src="dojo/dojo.js"></script> <script type="text/javascript"> dojo.require("dojo.io.cometd"); dojo.io.cometd.init({}, "/stock/cometd"); function startup() { dojo.io.cometd.publish("/management/publisher", "start"); } function halt() { dojo.io.cometd.publish("/management/publisher", "halt"); } </script> </head> <body>... JavaDay demo configuration

35 May be possible DEMO EFFECT Good luck...

36 Some useful link Bayeux specification provides only a protocol definition Cometd is a project by the Dojo Foundation to produce a specification (Bayeux) and a set of implementations of that specification (Cometd)

37 Some useful link Bayeux Java server-side implementation CometdJetty Oracle WebLogic Server p/pubsub.html IBM WebSphere averlock/0802_haverlock.html

38 Some useful link Bayeux others-server side implementation Flash FlexComet Perl CometdPerl Python CometdTwist ed

39 Thanks ;) Happy JavaDay