How to implement the function of HTTP proxy server using Go and http.Transport?

How to use Go and http.Transport to implement the function of HTTP proxy server?

Introduction:
HTTP proxy server is a powerful intermediary service that allows clients to communicate with target servers through the proxy server. This article will introduce how to use the Go language and the http.Transport library to implement a simple HTTP proxy server, including the establishment and use of the proxy server.

1. Import the required libraries
   First, at the beginning of the code, we need to import the required libraries. In this example, we will use the "net/http" and "net/url" libraries to handle HTTP requests and URL parsing.

import (
    "log"
    "net/http"
    "net/url"
)

2. Create proxy server
   In the main function, we first create an http.Server instance and configure its address and handler. The handler redirects the request to the target server and returns the response to the client.

func main() {
    // 配置代理服务器地址
    proxyURL, err := url.Parse("http://localhost:8080")
    if err != nil {
        log.Fatal("Error parsing proxy URL: ", err)
    }

    // 创建http.Transport实例
    transport := &http.Transport{
        Proxy: http.ProxyURL(proxyURL),
    }

    // 创建http.Client实例
    client := &http.Client{
        Transport: transport,
    }

    // 配置代理服务器的请求处理函数
    http.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
        // 将请求重定向到目标服务器
        resp, err := client.Do(req)
        if err != nil {
            http.Error(w, "Error executing request", http.StatusInternalServerError)
            return
        }
        defer resp.Body.Close()

        // 将目标服务器的响应返回给客户端
        for k, v := range resp.Header {
            w.Header().Set(k, v[0])
        }
        w.WriteHeader(resp.StatusCode)
        io.Copy(w, resp.Body)
    })

    // 启动代理服务器
    log.Fatal(http.ListenAndServe(":8080", nil))
}

3. Test the proxy server
   Save the above code as proxy.go and run the following command in the terminal to start the proxy server:

go run proxy.go

Now , the proxy server is already running on the local port 8080.

Next, we can use any network tool (such as a browser) to test the proxy server. Just replace the URL of your target server with the URL of your proxy server.

For example, if we want to access the website "http://www.example.com", we can enter "http://localhost:8080" in the browser, and then the proxy server will redirect the request to target server and return the response to the browser.

Conclusion:
This article introduces how to use the Go language and the http.Transport library to implement a simple HTTP proxy server. We learned about the principles and configuration of proxy servers and provided complete code examples. Using this example as a starting point, you can extend and customize the proxy server's functionality to your own needs. I wish you success in your practice!

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