set headers for request using http.Client and http.Transport

I have more than one ip to go to the internet. I am making request choosing interface. In this case how should I set headers?

tcpAddr := &net.TCPAddr{
IP: addrs[3].(*net.IPNet).IP, // Choosing ip address number 3
}
d := net.Dialer{LocalAddr: tcpAddr}
conn, err2 := d.Dial("tcp", "www.whatismyip.com:80")
if err2 != nil {
log.Fatal(err2)
}
defer conn.Close()
transport := &http.Transport{
Proxy:               http.ProxyFromEnvironment,
Dial:                (&net.Dialer{LocalAddr: tcpAddr}).Dial,
TLSHandshakeTimeout: 10 * time.Second,
}
client := &http.Client{
Transport: transport,
}
response, err := client.Get("https://www.whatismyip.com/")

Usually headers are set in this way:

req.Header.Set("name", "value")

But cannot figure out how to set them to my code.

I guess they must be set somewhere in http.Transport or http.Client. But how exactly?

My full code:

package main
import (
"bytes"
"fmt"
"github.com/PuerkitoBio/goquery"
"io/ioutil"
"log"
"net"
"net/http"
"os"
"time"
)
func main() {
ief, err := net.InterfaceByName("eth0")
if err != nil {
log.Fatal(err)
}
addrs, err := ief.Addrs()
if err != nil {
log.Fatal(err)
}
tcpAddr := &net.TCPAddr{
IP: addrs[3].(*net.IPNet).IP, // Choosing ip address number 3
}
d := net.Dialer{LocalAddr: tcpAddr}
conn, err2 := d.Dial("tcp", "www.whatismyip.com:80")
if err2 != nil {
log.Fatal(err2)
}
defer conn.Close()
transport := &http.Transport{
Proxy:               http.ProxyFromEnvironment,
Dial:                (&net.Dialer{LocalAddr: tcpAddr}).Dial,
TLSHandshakeTimeout: 10 * time.Second,
}
client := &http.Client{
Transport: transport,
}
response, err := client.Get("https://www.whatismyip.com/")
if err != nil {
fmt.Printf("%s", err)
os.Exit(1)
} else {
defer response.Body.Close()
contents, err := ioutil.ReadAll(response.Body)
if err != nil {
fmt.Printf("%s", err)
os.Exit(1)
}
var contentsStr = string(contents)
fmt.Printf("%s\n", contentsStr)
var doc = DocByHtmlString(contentsStr)
doc.Find("div").Each(func(i int, s *goquery.Selection) {
attr, exists := s.Attr("class")
if exists {
if attr == "ip" {
fmt.Println(s.Text())
}
}
})
}
}
func DocByHtmlString(html string) *goquery.Document {
doc, err := goquery.NewDocumentFromReader(bytes.NewBufferString(html))
if err != nil {
panic(err)
}
return doc
}

Create a request:

 req, err := http.NewRequest("GET", "https://www.whatismyip.com/", nil)
if err != nil {
// handle error
}

Set the headers:

 req.Header.Set("name", "value")

Run the request using client as configured in the question:

 resp, err := client.Do(req)
if err != nil {
// handle error
}

Handle the response as shown in the question.