Golang : Set up source IP address before making HTTP request

Problem :

There are times that you want to use certain IP address in a machine ( such as the one with permission to connect outside a firewall ) before making a HTTP request to another server. This is similar to the wget binding command :

For example : wget --bind-address=192.168.10.1 \

How to do that in Golang?

NOTE : This is not for masking or spoofing your IP address

Solution :

Build your own custom HTTP transport client and specify the local IP address that has the permission to connect outside a firewall.

For example :

 package main

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

 func main() {
 OKAddr := "<change here>" // local IP address to use

 OKAddress, _ := net.ResolveTCPAddr("tcp", OKAddr)

 transport := &http.Transport{
 Proxy: http.ProxyFromEnvironment,
 Dial: (&net.Dialer{
 Timeout: 30 * time.Second,
 KeepAlive: 30 * time.Second,
 OKAddr: OKAddress}).Dial, TLSHandshakeTimeout: 10 * time.Second}

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

 resp, err := client.Get("http://example.com/filetodown.zip")

 if err != nil {
 panic(err)
 }

 defer resp.Body.Close()

 html, err := ioutil.ReadAll(resp.Body)

 if err != nil {
 panic(err)
 }

 // fmt.Println(os.Stdout, string(html))
 // or save the zip - see https://www.socketloop.com/tutorials/golang-download-file-example
 }

References :

https://www.socketloop.com/tutorials/golang-convert-http-response-body-to-string

https://www.socketloop.com/tutorials/golang-download-file-example