To make an HTTP JSON POST request:

url := "http://example.com"

var jsonStr = []byte(`{"message":"hello!"}`)
req, err := http.NewRequest("POST", url, bytes.NewBuffer(jsonStr))
req.Header.Set("Content-Type", "application/json")

client := &http.Client{}
resp, err := client.Do(req)
if err != nil {
	log.Fatalln(err)
}
defer resp.Body.Close()

body, _ := ioutil.ReadAll(resp.Body)

sb := string(body)
log.Printf(sb)