Revealing the long and short connections of HTTP and the magical effect of keep-alive

HTTP is an integral part of front-end development, and the HTTP connection method has a huge impact on the performance and efficiency of network communication. Today, we will unveil the long and short connections in HTTP, and explain the magical function of keep-alive.

The difference between long connection and short connection

In the HTTP protocol, connections are divided into two methods: long connection (Keep-Alive) and short connection (Non-Keep-Alive).

Short connection: Each HTTP request establishes a new TCP connection and closes the connection immediately after the request is completed. The advantage of this method is that it is simple, but the disadvantage is that each connection needs to go through TCP's three-way handshake and four waves, which increases the communication overhead and affects performance especially in frequent request scenarios.

Long connection: Multiple HTTP requests and responses can be transmitted on a single TCP connection without having to re-establish the connection for each request. This method is achieved by using the keep-alive mechanism, which keeps the connection active and can continue to be used in future HTTP requests. The advantage of a long connection is that it reduces the number of connection establishment and disconnection times and improves performance.

How to enable long connections (Keep-Alive)

In the HTTP request header, we can use Connection: keep-alive to enable long connections, which tells the server not to close the connection after completing the current request so that subsequent requests can continue to use it.

Here is an example showing how to use long connections in JavaScript:

// 代码
const http = require('http');

const server = http.createServer((req, res) => {
  // 启用长连接
  res.setHeader('Connection', 'keep-alive');
  // 其他响应头
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello, World!');
});

server.listen(3000, () => {
  console.log('Server is listening on port 3000');
});

The role of keep-alive

Using keep-alive has the following significant benefits:

1. Reduced latency: Since the connection does not have to be re-established for each request, connection establishment and disconnection delays are reduced and response speed is improved.
2. Reduce resource usage: Each TCP connection needs to occupy system resources. Long connections can reduce this resource usage, which is especially important for servers.
3. Reduce network congestion: Long connections reduce frequent connection establishment and disconnection, helping to alleviate network congestion problems.

Summarize

Long connections (Keep-Alive) and short connections are important connection methods in HTTP, and the use of the keep-alive mechanism can significantly improve performance and reduce network overhead. When developing web applications, rational selection of connection methods and full use of keep-alive will help improve user experience and performance.