Server-based Web Programming
(1DV023/1DV523)
Lecture
Real-time web
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Content
- What is real-time web
- Definition
- Examples of real-time web applications
- Examination assignment 3
- Technologies for real-time web applications
- History, problems, today
- Real-time for the Node platform
Definition
Real-time web applications is clients receives data updates in a short time interval after the data is changed/created and without need for additional requests.
- What do we mean by short time? (definitions from wikipedia)
- Hard – missing a deadline is a total system failure.
- Firm – infrequent deadline misses are tolerable, but may degrade the system's quality of service. The usefulness of a result is zero after its deadline.
- Soft – the usefulness of a result degrades after its deadline, thereby degrading the system's quality of service.
- Broadcast to many clients
- Lots of different techniques (and hacks) for web applications
- Not the way the web was intended to work!
What kind of applications...
- Web-based games
- Social communication
- Chat, Live comments, feeds...
- Notifications
- Collaboration tools
What kind of applications...
- 2nd Screen Experience
- Activity streams (live comments)
- Statistics
- Live sport
- Video game extras
- Voting, Peer-instructions
What kind of applications...
- Decision making
- Trading
- Automatic price adjusting
- Monitoring infrastructure and application
- Users, servers...
Change of paradigm?
- Notifications by default
- How do you expect your mobile app to work?
- Web of things?
- Devices communicating in realtime
- Real-time API - Streaming API
- Twitter, Google, Slack
Examination assignment 3
- Create an application that checks issues in your repository/repositories
- Fetching issue information from Git**b Web API
- Read documentation and understand how to authenticate
- Monitoring events From Git**b (issues)
- Registration and using Git**b web hooks
- Sending real-time events to client from "your server"
- Own features? OAuth, communication from client...
- Fetching issue information from Git**b Web API
- Put the application in production
Technologies for real-time web
The problem with HTTP...
...In realtime scenario
History
- JAVA Applets (Netscape 2.0 - 1996)
- Java virtual machine
- Raw TCP socket
- Flash platform
- RTMP servers, Shared Objects
- Flash client
- "Flash Player has been deprecated and has an official end-of-life at the end of 2020"
- Silverlight (.NET)
- Well...(no more development since 2013)
HTML and JavaScript
- Comet (umbrella term)
- Techniques that goes around the HTTP 1.1 spec. and browser implementations
- Persistent HTTP connections, Domain sharding...
- Long-lived hidden iframe
- XHR long polling
- XHR streaming
- Techniques that goes around the HTTP 1.1 spec. and browser implementations
- Server-sent events (HTML5)
- No IE or Edge (https://caniuse.com/#feat=eventsource)
- Just from server, no bi-directional or full duplex (combine with XHR)
- WebSocket
XHR Long polling
XHR Streaming
- "Transfer Encoding: chunked"
- Don´t need to open new connection when data is received
WebSocket
- Socket?
- Connect on HTTP(S), Upgrade to ws:// or wss://
- Firewalls, proxies? Default port 80/443
- Two-way communication, full-duplex
- Text or/and binary data
- IETF Standard, RFC 6455, 2011,
- WebSocket API for browsers, W3C
- Security
- Use Content Security Policy
- Encryption with wss://
WebSocket server on node platform
- Socket.io (https://socket.io/)
- ws (https://www.npmjs.com/package/ws)
- ...
https://blog.bitsrc.io/8-node-js-web-socket-libraries-for-2018-818e7e5b67cf
Challenges with web sockets
- Browser support
- Fallback strategies
- Concurrency
- Synchronization
- Fault-tolerant?
- Offline, Queue-strategies
Other architectures...
- Client-to-Server
- What I just said...
- Client-to-Client
- P2P (peer-to-peer)
- WebRTC
- Server-to-server
- web hooks
Web Hooks, Server to server
Next time
- No more lectures
- Pre-recorded demos
- Bringing the application to production
- A virtual machine on our cloud
- SSH-key and public IP
- A virtual machine on our cloud