HttpTransport

For advanced scenarios, you can provide your own http.Client / http.Transport. You need to create your own http.Client, set its Transport field, then configure the new client with elastic.SetHttpClient(...).

Here is an example that counts requests.

// CountingTransport will count requests.
type CountingTransport struct {
  N    int64              // number of requests passing this transport
  next http.RoundTripper  // next round-tripper or http.DefaultTransport if nil
}

// RoundTrip implements a transport that will count requests.
func (tr *CountingTransport) RoundTrip(r *http.Request) (*http.Response, error) {
  atomic. AddInt64(&tr.N, 1)
  if tr.next != nil {
    return tr.next.RoundTrip(r)
  }
  return http.DefaultTransport.RoundTrip(r)
}

...
myHttpClient := &http.Client{Transport: &CountingTransport{}}
client, err := elastic.NewClient(elastic.SetHttpClient(myHttpClient))

HTTP Basic Authentication

Notice that this is just an example: You can use the SetBasicAuth configuration setting for this now.

Another example of using your own http.Transport is HTTP Basic Authentication. As HTTP Basic Authentication is a common use case, there is a elastic.SetBasicAuth("username", "password") option that you can use when setting up a new Client (see docs). The SetBasicAuth options is available since 2.0.13. Anyway, here's how to do that with your own http.Transport:

// BasicAuthTransport 
type BasicAuthTransport struct {
  username string
  password string
}

func (tr *BasicAuthTransport) RoundTrip(r *http.Request) (*http.Response, error) {
  r.SetBasicAuth(tr.username, tr.password)
  return http.DefaultTransport.RoundTrip(r)
}

...
httpClient = &http.Client{
  Transport: &BasicAuthTransport{
    username:  "me",
    password:  "secret",
  },
}
client, err := elastic.NewClient(elastic.SetHttpClient(httpClient))