golang forward http

With the rapid development and popularization of the Internet, the importance of network applications continues to rise. And all of this is inseparable from the HTTP protocol, because it is one of the cornerstones of the World Wide Web. In the development process of network applications, we often encounter situations where HTTP request forwarding is required. This article introduces how to use Golang to implement HTTP request forwarding.

1. Principle of HTTP request forwarding

HTTP request forwarding, as the name suggests, is to forward some client requests to other servers for processing. This process requires multiple HTTP protocol interactions, so you need to understand the principle of HTTP request forwarding.

The principle of HTTP request forwarding is mainly divided into the following steps:

1. The client sends an HTTP request to the forwarding server.

2. After the forwarding server receives the request, it determines whether the request needs to be forwarded to other servers for processing according to certain rules. If so, enter the third step, otherwise it directly returns a response to the client.

3. The forwarding server forwards the request to the target server. After multiple HTTP protocol interactions (including requests and responses), the target server finally returns the response result to the forwarding server.

4. The forwarding server returns the response result to the client.

2. Use Golang to implement HTTP request forwarding

In Golang, you can use the ReverseProxy type provided by the net/http package to implement HTTP request forwarding. ReverseProxy is a structure type that can proxy a set of HTTP requests to another server and return the corresponding response results. The main method of ReverseProxy is the ServeHTTP method, which accepts two parameters, one is the Writer type of the response result, and the other is the pointer type of the HTTP request.

The code for using Golang to implement HTTP request forwarding is as follows:

package main

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

func main() {
    targetUrl, _ := url.Parse("http://www.example.com/")
    proxy := httputil.NewSingleHostReverseProxy(targetUrl)
    http.ListenAndServe(":8080", proxy)
}

The above code first defines a target URL and parses it into a URL object; then uses the NewSingleHostReverseProxy method to create a ReverseProxy instance, And pass in the target URL as a parameter; finally use the ListenAndServe method to start an HTTP server and pass in the ReverseProxy instance created above.

3. Optional configuration of ReverseProxy

In addition to using the default configuration, ReverseProxy also supports some optional configurations, such as:

1. Modify the request body or response body: ReverseProxy provides the function of modifying the request body or response body, which can be achieved by modifying the Director and ModifyResponse methods.

2. Modify the requested URL: This can be achieved by modifying the Director method.

3. Custom error handling: Custom error handling can be implemented by modifying the ErrorLog field.

The following are some sample codes:

package main

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

func main() {
    targetUrl, _ := url.Parse("http://www.example.com/")
    proxy := httputil.NewSingleHostReverseProxy(targetUrl)

    // 修改请求体或者响应体
    proxy.Director = func(req *http.Request) {
        req.Header.Set("Content-Type", "application/json")
    }
    proxy.ModifyResponse = func(response *http.Response) error {
        response.Header.Set("Content-Type", "application/json")
        return nil
    }

    // 修改请求的URL
    proxy.Director = func(req *http.Request) {
        req.Host = "www.anotherexample.com"
        req.URL.Scheme = "https"
    }

    // 自定义错误处理
    logFile, _ := os.OpenFile("access.log", os.O_WRONLY|os.O_CREATE, 0755)
    errorLog := log.New(logFile, "proxy error: ", log.LstdFlags)
    proxy.ErrorLog = errorLog

    http.ListenAndServe(":8080", proxy)
}

4. HTTP request forwarding practice case

A common HTTP request forwarding application scenario is load balancing. Load balancing is an important technology in distributed computing systems. Its purpose is to process requests through multiple servers to achieve high availability and high throughput of services. Common load balancing strategies include round robin, weighted round robin, minimum number of connections, etc.

The following is a simple load balancer implemented using Golang:

package main

import (
    "fmt"
    "log"
    "math/rand"
    "net/http"
    "net/http/httputil"
    "net/url"
    "strconv"
    "strings"
    "time"
)

func main() {
    targetUrls := []string{"http://localhost:8001/", "http://localhost:8002/", "http://localhost:8003/"}

    // 随机数生成器
    rand.Seed(time.Now().Unix())

    balancedHandler := func(rw http.ResponseWriter, req *http.Request) {
        // 随机选择一个目标URL
        targetUrl := targetUrls[rand.Intn(len(targetUrls))]

        // 创建ReverseProxy
        target, _ := url.Parse(targetUrl)
        proxy := httputil.NewSingleHostReverseProxy(target)

        // 修改请求的Host
        req.URL.Host = target.Host
        req.URL.Scheme = target.Scheme
        req.Header.Set("X-Forwarded-Host", req.Header.Get("Host"))
        req.Host = target.Host

        // 记录日志
        log.Printf("%s %s %s
", req.RemoteAddr, req.Method, req.URL)
        proxy.ServeHTTP(rw, req)
    }

    http.HandleFunc("/", balancedHandler)
    if err := http.ListenAndServe(":8080", nil); err != nil {
        fmt.Println(err)
    }
}

func getBalance(targetUrls []string) func() string {
    var last int32 = -1
    return func() string {
        if len(targetUrls) == 0 {
            return ""
        }
        if len(targetUrls) == 1 {
            return targetUrls[0]
        }
        next := last
        for next == last {
            next = rand.Int31n(int32(len(targetUrls)))
        }
        last = next
        return targetUrls[last]
    }
}

The above code first defines the target URL array, and then uses the random number generator provided by the rand package to randomly select a target URL. ; Then create a ReverseProxy instance, and use the Director method to modify the Host and other parameters of the request; Finally, record the request log, and call the ServeHTTP method of ReverseProxy to forward the request.

5. Summary

Through the introduction of this article, you have a preliminary understanding of the basic principles of HTTP request forwarding and its implementation in Golang. At the same time, we have given a simple load balancer example, hoping to be helpful to your development work.

Implementing an efficient, flexible and robust HTTP request forwarding program requires consideration of many aspects, including flow control, error handling, security, etc. We can achieve different needs by using the optional configurations provided by ReverseProxy .

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