[json] How to serve up a JSON response using Go?

Question: Currently I'm printing out my response in the func Index like this fmt.Fprintf(w, string(response)) however, how can I send JSON properly in the request so that it maybe consumed by a view?

package main

import (
    "fmt"
    "github.com/julienschmidt/httprouter"
    "net/http"
    "log"
    "encoding/json"
)

type Payload struct {
    Stuff Data
}
type Data struct {
    Fruit Fruits
    Veggies Vegetables
}
type Fruits map[string]int
type Vegetables map[string]int


func Index(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
    response, err := getJsonResponse();
    if err != nil {
        panic(err)
    }
    fmt.Fprintf(w, string(response))
}


func main() {
    router := httprouter.New()
    router.GET("/", Index)
    log.Fatal(http.ListenAndServe(":8080", router))
}

func getJsonResponse()([]byte, error) {
    fruits := make(map[string]int)
    fruits["Apples"] = 25
    fruits["Oranges"] = 10

    vegetables := make(map[string]int)
    vegetables["Carrats"] = 10
    vegetables["Beets"] = 0

    d := Data{fruits, vegetables}
    p := Payload{d}

    return json.MarshalIndent(p, "", "  ")
}

In gobuffalo.io framework I got it to work like this:

// say we are in some resource Show action
// some code is omitted
user := &models.User{}
if c.Request().Header.Get("Content-type") == "application/json" {
    return c.Render(200, r.JSON(user))
} else {
    // Make user available inside the html template
    c.Set("user", user)
    return c.Render(200, r.HTML("users/show.html"))
}

and then when I want to get JSON response for that resource I have to set "Content-type" to "application/json" and it works.

I think Rails has more convenient way to handle multiple response types, I didn't see the same in gobuffalo so far.

You can do something like this in you getJsonResponse function -

jData, err := json.Marshal(Data)
if err != nil {
    // handle error
}
w.Header().Set("Content-Type", "application/json")
w.Write(jData)

You may use this package renderer, I have written to solve this kind of problem, it's a wrapper to serve JSON, JSONP, XML, HTML etc.

Other users commenting that the Content-Type is plain/text when encoding. You have to set the Content-Type first w.Header().Set, then the HTTP response code w.WriteHeader.

If you call w.WriteHeader first then call w.Header().Set after you will get plain/text.

An example handler might look like this;

func SomeHandler(w http.ResponseWriter, r *http.Request) {
    data := SomeStruct{}
    w.Header().Set("Content-Type", "application/json")
    w.WriteHeader(http.StatusCreated)
    json.NewEncoder(w).Encode(data)
}