How do I use a forward proxy in Go (Golang)?

To use a forward proxy in Go (Golang), you'll need to configure an http.Client with a Transport that uses a proxy URL. Here's a step-by-step guide:

1. Import necessary packages:

- You'll need the net/http and net/url packages.

2. Define your proxy URL:

- The proxy URL should be in the format "http://proxy_address:proxy_port" or "socks5://proxy_address:proxy_port".

3. Create a Transport with the proxy configuration:

- Use http.ProxyURL to parse the proxy URL and then set it in the Transport.

4. Create an http.Client with the configured Transport:

- Assign the Transport to the Client's Transport field.

5. Use the Client to make HTTP requests:

- All requests made with this Client will now go through the specified forward proxy.

Here’s an example code:

package main

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

func main() {
    proxyURL, err := url.Parse("http://your_proxy_address:your_proxy_port")
    if err != nil {
        log.Fatal(err)
    }

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

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

    resp, err := client.Get("https://www.example.com")
    if err != nil {
        log.Fatal(err)
    }
    defer resp.Body.Close()

    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Println(string(body))
}

Explanation:

- Replace "http://your_proxy_address:your_proxy_port" with your actual proxy address and port.

- The http.ProxyURL function parses the proxy URL string into a url.URL struct.

- The http.Transport is responsible for handling the actual network connections. We set its Proxy field to use the parsed proxy URL.

- An http.Client is created, and its Transport field is set to the configured Transport.

- The client.Get method makes an HTTP GET request through the proxy.

Handling Proxy Authentication:

If your proxy requires authentication, you can embed the username and password directly in the proxy URL:

proxyURL, err := url.Parse("http://username:password@your_proxy_address:your_proxy_port")

Make sure to replace username and password with the actual credentials.

Important Considerations:

- Ensure the proxy server is running and accessible.

- Handle errors gracefully, especially when parsing the proxy URL or making HTTP requests.

- Be mindful of security implications when using proxies, especially when handling sensitive data.

Learn more about this