What are WebSockets?
The WebSocket protocol was born in 2008 and became an international standard in 2011. All browsers already support it.
WebSockets are a bi-directional, full duplex communications protocol initiated over HTTP. They are commonly used in modern web applications for streaming data and other asynchronous traffic.
Its biggest feature is that the server can actively push information to the client, and the client can also actively send information to the server. It is a true two-way equal dialogue and belongs to a kind of server push technology.
What is the difference between HTTP and WebSockets?
Most communication between web browsers and web sites uses HTTP. With HTTP, the client sends a request and the server returns a response. Typically, the response occurs immediately, and the transaction is complete. Even if the network connection stays open, this will be used for a separate transaction of a request and a response.
Some modern web sites use WebSockets. WebSocket connections are initiated over HTTP and are typically long-lived. Messages can be sent in either direction at any time and are not transactional in nature. The connection will normally stay open and idle until either the client or the server is ready to send a message.
WebSockets are particularly useful in situations where low-latency or server-initiated messages are required, such as real-time feeds of financial data.
features include:
（1）Based on the TCP protocol, the server-side implementation is relatively easy.
（2）It has good compatibility with HTTP protocol. The default ports are also 80 and 443, and the handshake phase uses the HTTP protocol, so it is not easy to shield during the handshake, and can pass through various HTTP proxy servers.
（3）The data format is relatively lightweight, the performance overhead is small, and the communication is efficient.
（4）Either text or binary data can be sent.
（5）There is no same-origin restriction, the client can communicate with any server.
（6）The protocol identifier is ws (or wss if encrypted), and the server address is the URL
How are WebSocket connections established?
WebSocket connections are normally created using client-side JavaScript like the following:
1 | var ws = new WebSocket("wss://surfin-website.com/chat"); |
To establish the connection, the browser and server perform a WebSocket handshake over HTTP. The browser issues a WebSocket handshake request like the following:
1 | GET /chat HTTP/1.1 |
If the server accepts the connection, it returns a WebSocket handshake response like the following:
1 | HTTP/1.1 101 Switching Protocols |
At this point, the network connection remains open and can be used to send WebSocket messages in either direction.
What do WebSocket messages look like?
Once a WebSocket connection has been established, messages can be sent asynchronously in either direction by the client or server.
A simple message could be sent from the browser using client-side JavaScript like the following:
1 | ws.send("Surfin"); |
In principle, WebSocket messages can contain any content or data format. In modern applications, it is common for JSON to be used to send structured data within WebSocket messages.
For example, a chat-bot application using WebSockets might send a message like the following:
1 | {"user":"Surfin","content":"Surfin Cloud welcomes join us!"} |