There are many solutions to implement online chat technology. The following are the commonly used solutions and their advantages and disadvantages:
1. WebSocket
WebSocket is a two-way communication protocol based on the TCP protocol. It can establish a persistent connection between the browser and the server, so that the server can actively send messages to the browser without requiring the browser to obtain them through polling, etc. renew. Using WebSocket to realize the online chat function can achieve the effect of high real-time performance and fast response speed.
learning url
- MDN Web Docs: https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API
- WebSocket Tutorial: https://www.tutorialspoint.com/websockets/index.htm
advantage:
- Good real-time performance and quick response.
- Supports two-way communication, and can process messages from the client and server at the same time.
- It is very suitable for real-time scenarios such as online chat function.
shortcoming:
- The pressure on the server is relatively high, and issues such as load balancing need to be considered.
- The implementation process is relatively complicated and requires mastering relevant technologies and algorithms.
2. Comet
Comet is an HTTP long-polling technology, also known as "reverse AJAX", which realizes real-time push by keeping the client's HTTP request open and returning it to the client when the server has data updates. Comet is similar to WebSocket, but the implementation mechanism is slightly different.
learning url
- Cometd Project Website: https://cometd.org/
- Comet Programming Guide: http://cometdaily.com/maturity.html
advantage:
- Can use the standard HTTP protocol to communicate and support cross-domain access.
- Compatible with most browsers.
- Server load can be controlled by controlling the interval time of HTTP requests.
shortcoming:
- The real-time performance is slightly worse than WebSocket.
- Comet requires more server resources and network bandwidth than WebSocket.
3. Server-Sent Events (SSE)
Server-Sent Events (SSE) is a one-way communication technology based on the HTTP protocol, which allows the server to send event streams (EventStream) to the client, and supports functions such as disconnection and reconnection. The implementation of SSE is similar to the long polling technology, but it is simpler to use.
learning url
- MDN Web Docs: https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events
- HTML5Rocks SSE Tutorial: https://www.html5rocks.com/en/tutorials/eventsource/basics/
advantage:
- The implementation is simple and easy to use, and does not require a complicated handshake protocol like WebSocket.
- The stability of the connection can be ensured through mechanisms such as disconnection and reconnection.
shortcoming:
- It only supports one-way communication and cannot handle messages sent by clients.
- Poor real-time performance, unable to cope with high-frequency data updates.
4. AJAX polling
AJAX polling is a method of data polling using Ajax technology, which periodically initiates HTTP requests to the server and checks whether there is new data update. Although it is relatively simple to implement, it is not suitable for scenarios with high real-time requirements due to the need to frequently send requests to the server.
Learning website
- AJAX Tutorial: https://www.w3schools.com/xml/ajax_intro.asp
- Detailed explanation of AJAX polling: https://www.cnblogs.com/dolphinX/p/3464058.html
Advantages:
- Simple to implement, easy to understand and maintain.
- Compatible with most browsers.
shortcoming:
- Poor real-time performance, not suitable for fast response scenarios.
- The pressure on the server is relatively high, and issues such as load balancing need to be considered.
Summarize:
WebSocket is the best choice for real-time scenarios such as online chat, but due to its complex implementation and high pressure on the server, specific scenarios and requirements also need to be considered. Other solutions such as Comet, SSE, AJAX polling, etc. have their own advantages and disadvantages, and can be selected according to the specific situation.