Can you return json in golang http.Error?

Question

Can you return json when http.Error is called?

        myObj := MyObj{
            MyVar: myVar}

        data, err := json.Marshal(myObj)
        if err != nil {
            http.Error(w, err.Error(), http.StatusInternalServerError)
            return 
        }
        w.Write(data)
        w.Header().Set("Content-Type", "application/json")

        http.Error(w, "some error happened", http.StatusInternalServerError)

I see that it returns 200 with no json but the json is embed in text

Answer 1

I've discovered that it's really easy to read the Go source. If you click on the function in the docs, you will be taken to the source for the Error function: https://golang.org/src/net/http/server.go?s=61907:61959#L2006

// Error replies to the request with the specified error message and HTTP code.
// It does not otherwise end the request; the caller should ensure no further
// writes are done to w.
// The error message should be plain text.
func Error(w ResponseWriter, error string, code int) {
    w.Header().Set("Content-Type", "text/plain; charset=utf-8")
    w.Header().Set("X-Content-Type-Options", "nosniff")
    w.WriteHeader(code)
    fmt.Fprintln(w, error)
}

So if you want to return JSON, it's easy enough to write your own Error function.

func JSONError(w http.ResponseWriter, err interface{}, code int) {
    w.Header().Set("Content-Type", "application/json; charset=utf-8")
    w.Header().Set("X-Content-Type-Options", "nosniff")
    w.WriteHeader(code)
    json.NewEncoder(w).Encode(err)
}