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 (see docs).

Another example of using your own http.Transport is e.g. HTTP Basic Authentication. Here's how to do HTTP Basic Authentication 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))