How to use golang to implement request forwarding

With the development of web applications, new technologies are constantly emerging. Among them, the golang language has attracted much attention because of its high concurrency, concise and easy-to-understand syntax, and fast compilation speed. In web applications, requests are often forwarded to different APIs. So how to use golang to implement the request forwarding function? This article will introduce how to use golang to implement request forwarding.

1. Principles and methods of implementing request forwarding

Request forwarding refers to the process of sending a request from one server to another server. Under normal circumstances, we will complete the task of request forwarding through an intermediate proxy server. This intermediate proxy server will receive all requests from the client, then forward these requests to different back-end api servers, and finally return the response results to the client.

Since golang comes with its own http library, you can use this library to implement request forwarding. There are two specific implementation methods:

1. The http.Client class of the http package uses the
http.Client class to implement request forwarding. The code is as follows:

package main

import (
    "fmt"
    "io/ioutil"
    "net/http"
)

func main() {
    proxyUrl := "http://localhost:8080/" // 设置代理服务器地址
    client := &http.Client{}
    req, _ := http.NewRequest("GET", "http://www.baidu.com", nil) // 构建请求结构体
    req.Header.Set("Content-Type", "text/html;charset=UTF-8")
    req.Header.Set("User-Agent", "Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:68.0) Gecko/20100101 Firefox/68.0")
    resp, err := client.Do(req) // 发送请求
    if err != nil {
        fmt.Printf("error is %v\n", err)
    }
    defer resp.Body.Close()
    body, err2 := ioutil.ReadAll(resp.Body) // 获取响应结果
    if err2 != nil {
        fmt.Printf("error2 is %v \n", err2)
    }
    fmt.Println(string(body))
}```

上述代码中，我们使用 `http.Client` 类来创建一个代理对象，并设置了代理服务器的地址。然后，构建了一个请求体 `req`，并且设置了请求头信息。最后，使用 `client.Do()` 方法将请求发送给 api 服务器，并通过 `ioutil.ReadAll()` 函数将响应结果转换为字符串类型，最终打印在控制台上。

2、httputil包的`httputil.ReverseProxy`类
利用 `httputil.ReverseProxy` 类实现请求转发，可以比较轻松的搭建出一个反向代理服务器。代码如下：

"log"
"net/http"
"net/http/httputil"
"net/url"

server := http.Server{
    Addr: ":8080",
    Handler: &httputil.ReverseProxy{ // 使用httputil.ReverseProxy搭建代理服务器
        Director: func(req *http.Request) {
            target, _ := url.Parse("https://www.baidu.com/")
            req.URL.Scheme = target.Scheme // 设置请求上下文
            req.URL.Host = target.Host
            req.Header.Set("X-Forwarded-Host", req.Header.Get("Host"))
            req.Host = target.Host
        },
    },
}
log.Fatal(server.ListenAndServe()) // 监听端口并启动代理服务器

`

Director method of the httputil.ReverseProxy class to forward the request passed by the front end to the backend api server. Parse the address of the api server through the url.Parse() function in the Director method, then use the address of the api server as the target address of the request, and set the request context. Finally, call the ListenAndServe method to start the server and listen on the port, waiting for client requests.

http.Client class, manually constructs a request body, and sets the request header information. The second method is to use the httputil.ReverseProxy class to build a reverse proxy server, which is relatively simple and convenient. In short, for developers who need to implement request forwarding tasks, please choose a more suitable implementation method according to your needs.

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