How to return json on net/http

Question

I have the following code sample and wondering how can I return the proper json?

    package main

import (
    "fmt"
    "net/http"
    "net/url"
    "strings"
)

func main() {
    apiURL := "http://example.com"
    resource := "/sample"
    data := url.Values{}
    data.Add("test", "y")

    u, _ := url.ParseRequestURI(apiURL)
    u.Path = resource
    urlStr := u.String()

    client := &http.Client{}
    r, _ := http.NewRequest("POST", urlStr, strings.NewReader(data.Encode())) // URL-encoded payload

    resp, _ := client.Do(r)
    fmt.Println(resp.Status)
    fmt.Println(resp.ContentLength)
    fmt.Println(resp.Request)
    // fmt.Println(json.NewDecoder(resp.Body.Decode()))
}

Once I get the response, how can I accurately return a JSON response?