How to write HTTP proxy requests using Golang

The power of Golang language lies in its high efficiency and powerful network programming capabilities. Among them, HTTP proxy request is one of the problems that developers often encounter.

In this article, we will explore how to write HTTP proxy requests using Golang. We will achieve this through the following steps:

1. Understand how HTTP proxy requests work
2. Write HTTP proxy request code
3. Add proxy authentication function
4. Solve common problems with proxy requests

Understand how HTTP proxy requests work

HTTP proxy requests are a network communication protocol that allow clients to send requests through a proxy server to access a target website . This proxy server blocks direct communication between the client and the target server by forwarding requests and responses. There are two types of proxy servers: forward proxy and reverse proxy.

A forward proxy is a server that sits between the client and the target server. The client sends a request to the proxy server, and the proxy server forwards the request to the target server and returns the target server's response to the client. Using a forward proxy can hide the client IP address and control and monitor data in the network.

A reverse proxy is a server that sits between the target server and the client. Forward requests to the best server to improve system performance, scalability, and security. Reverse proxies are often used for load balancing to ensure efficient network communication.

In this article, we will introduce how to use Golang to write forward proxy request code.

Writing HTTP proxy request code

Next, we will introduce how to use Golang to write HTTP proxy request code:

1. First, we need to import the net/http package and fmt package.

package main

import (
   "fmt"
   "net/http"
)

2. Next, we need to write a processing function that receives two parameters: one is the request request and the other is the response response. The code in the function will send the request and return the response.

 func handler(w http.ResponseWriter, r *http.Request) {
   response, err := http.Get("https://www.google.com")
   if err != nil {
       fmt.Fprintf(w, "Error Occured: %s", err.Error())
   }else {
       fmt.Fprintf(w, "<title>%s</title>", response.Status)
       fmt.Fprintf(w, "<h1 id="Status">Status</h1>")
       fmt.Fprintf(w, "<pre class="brush:php;toolbar:false">%s

", response.Status)        fmt.Fprintf(w, "

Header

")        for k, v := range response.Header {            fmt.Fprintf(w, "

%s: %s

", k, v[0])        }        fmt.Fprintf(w, "

Body

")        body, _ := ioutil.ReadAll(response.Body)        fmt.Fprintf(w, "%s", body)        fmt.Fprintf(w, "")     } }

In the above code, we use the http.Get function to send a request that accesses the google.com website. If the request is successful, we use the fmt.Fprintf function to write the response result into the response. If the request fails, an error message is returned.

3. Now, we need to create an HTTP server. We can use the http.HandleFunc function to pass the handler function we just created to the server so that the server can handle requests from the client.

func main() {
   http.HandleFunc("/", handler)
   http.ListenAndServe(":9090", nil)
}

In the above code, we use the http.HandleFunc function to pass the handler function to the server so that the server can handle the client request. We also created an HTTP server using the http.ListenAndServe function, which listens on port 9090.

After running the above code, when we visit http://localhost:9090, we will see that the program sends a request to google.com and displays the response in our browser.

Add proxy authentication function

Now, we already know how to send HTTP proxy requests. At this time, if we need to use a proxy server to send a request to a website, we need to access the proxy server and authenticate. Below, we will demonstrate how to send an HTTP request to a proxy server through a program.

First, we need to add the HTTP proxy address to our program. We also need to specify the IP address and port number for the proxy server. For example:

proxyUrl, err:= url.Parse("http://proxy-server-address:port")

Next, we need to create an HTTP client that contains the proxy address:

transport := &http.Transport{
   Proxy: http.ProxyURL(proxyUrl),
}

In the above code, we create a transport object that contains our proxy address. We can use this object to send authentication requests to the proxy server.

In the following code example, we will use the http.NewRequest function to send a request and authenticate:

  req, err := http.NewRequest("GET", "https://www.google.com", nil)
  req.Header.Set("Proxy-Authorization", "Basic "+base64.StdEncoding.EncodeToString([]byte("username:password")))
  client := &http.Client{Transport: transport}
  response, err := client.Do(req)
  if err != nil {
     fmt.Fprintf(w, "Error Occured: %s", err.Error())
  } else {}

In the above code, we use the http.NewRequest function to send an HTTP request and authenticate to the proxy The server sends an authentication header. We also create an HTTP client object and use this object to send the request. If an error occurs while sending the request, the handler function will output an error message.

Solution to common problems with proxy requests

When using HTTP proxy requests, we may encounter some common problems.

1. Forward request.Body

Suppose we need to send a POST request and send the file content in file.txt as the request body. We can use the following code:

  file, err := os.Open("file.txt")
  if err != nil {
      fmt.Fprintf(w, "Error Occured: %s", err.Error())
  }
  defer file.Close()
  req, err := http.NewRequest("POST", "http://example.com/upload", file)

In the above code, we provide a File object that reads file.txt data in the third parameter of the http.NewRequest function. We then use this object as the body of the POST request.

However, when using an HTTP proxy to forward the POST request to the target server, the data in the request body will be lost. For this, we can use the ReadAll function in the ioutil library to read all the data of the request body and append it to the new request body.

  body, err := ioutil.ReadAll(r.Body)
  if err != nil {
     fmt.Fprintf(w, "Error Occured while reading body: %s", err.Error())
  }
  req, err := http.NewRequest("POST", "http://example.com/upload", bytes.NewBuffer(body))

In the above code, we read the contents of all request bodies and append them to the body of a new HTTP request.

2. Forward request headers

If we want to include a specific HTTP header in the request, such as "Referer" or "User-Agent", then we can directly Set headers in the HTTP request object.

  req, err := http.NewRequest("GET", "http://example.com/image.jpg", nil)
  req.Header.Set("Referer", "http://www.google.com")

在上述代码中，我们使用http.NewRequest函数创建了一个GET请求，并设置了其中的“Referer”标头。

结论

在本文中，我们探讨了如何使用Golang编写HTTP代理请求代码。通过了解HTTP代理的工作原理，我们能够更好地理解如何使用Golang为代理请求添加身份验证。我们还演示了如何解决常见的代理请求问题，并向您展示了如何在请求中包含特定的HTTP标头。无论您是开发Web应用程序还是使用它来生产工作，这些技巧和技术都将为您的工作带来很大的便利。

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