How to connect a domain with specific ip address

Sometimes, we might configure multiple ip address to a domain, or sometimes the domain does not work in some places, so I want to know how to specify the ip address when connect to the domain.

Specify ip address when connect with curl

I want to connect to a domain with specify ip address, and I find that we can use the --resolve to do it, I get the help from How to test a HTTPS URL with a given IP address. The command is like below:

curl https://www.google.com --resolve 'www.google.com:443:216.58.199.228'

Implement it in golang

Then I want to know how to implement it in golang, I find the help from golang force http request to specific ip (similar to curl — resolve), the following code is an example.

func main() { 
 dialer := &net.Dialer{ 
  Timeout:   30 * time.Second, 
  KeepAlive: 30 * time.Second, 
  // DualStack: true, // this is deprecated as of go 1.16 
 } 
 // or create your own transport, there's an example on godoc. 
 http.DefaultTransport.(*http.Transport).DialContext = func(ctx context.Context, network, addr string) (net.Conn, error) { 
  if addr == "www.google.com:443" { 
   addr = "216.58.199.228:443" 
  } 
  return dialer.DialContext(ctx, network, addr) 
 } 
 resp, err := http.Get("https://www.google.com") 
 log.Println(resp.Header, err) 
 content, err := ioutil.ReadAll(resp.Body) 
 if err != nil { 
  fmt.Printf("Failed to read content, the error is %v", err) 
 } 
 fmt.Printf("The body is %s\n", string(content)) 
}