一个简单的json请求返回一个奇怪的字符串，而不是json本身

I'm trying to return a simple json in Go. This is a web app and here's a part of a handler:

func JsonTest1(w http.ResponseWriter, r *http.Request) {
  test1 := "something1"
  test2 := 456
  j1 := []byte(fmt.Sprintf(`
    {
      data: {
        "test1": %s,
        "test2": %d
      }
    }
  `, test1, test2))



  j2, _ := json.Marshal(&j1)
  w.Header().Set("Content-Type", "application/json")
  w.Write(j2)
 }

When I'm doing a request via curl, I receive something like:

  CiAgICB7CiAgICAgIGRhdGE6IHsKICAgICAgICAicmVkaXJlY3RfdXJsIjogdGVzdF9yZWRpcl91cmwxLAogICAgICAgICJtZXNzYWdlIjogdGVzdCBtc2cgMQogICAgICB9CiAgICB9CiAg

Why? How to fix that?

When you JSON-encode a []byte, it will be rendered as a base64-encoded string, the most effective way to represent an arbitrary byte slice/array in JSON (the only real alternative being "field": [7, 129, 13, 48, ...] and so on). In your code, however, you're doing a couple of unusual things that may not be what's intended:

• You're manually creating a JSON-ish string using Sprintf, then trying to JSON-encode your JSON. json.Marshal is for taking some arbitrary Go value and rendering it as JSON.
• Your manually-created JSON is invalid; you have a string field value that's unquoted.

What you want is probably one of these options:

// Manually-created *valid* JSON
func JsonTest1(w http.ResponseWriter, r *http.Request) {
    test1 := "something1"
    test2 := 456
    // %q instead of %s gives us a quoted string:
    j1 := []byte(fmt.Sprintf(`
    {
      data: {
        "test1": %q,
        "test2": %d
      }
    }
  `, test1, test2))

    w.Header().Set("Content-Type", "application/json")
    w.Write(j1)
}

// JSON created with json.Marshal
func JsonTest2(w http.ResponseWriter, r *http.Request) {
    test1 := "something1"
    test2 := 456
    data := map[string]interface{}{
        "data": map[string]interface{}{
            "test1": test1,
            "test2": test2,
        },
    }
    j1, _ := json.Marshal(data)
    w.Header().Set("Content-Type", "application/json")
    w.Write(j1)
}