how to dynamically render as HTML/JSON/XML in golang with martini?

I am trying to have a simple REST API server in golang site which serves HTML, JSON or XML format of the same date as requested by client. I am not able to figure out. I hope I am not doing something silly.

Code:

package main

import (
	"github.com/go-martini/martini"
	"github.com/martini-contrib/render"
)

type Ticket struct {
	Number      int    `json:"number"`
	Description string `json:"description"`
	State       string `json:"state"`
}

func dummyStatus() Ticket {

	ticket := Ticket{
		Number:      2345,
		Description: "A dummy customer ticket",
		State:       "resolved",
	}
	return ticket
}

// http://localhost:3000/status/id:1
func ReadStatus(r render.Render, params martini.Params) Ticket {

	// read from DB
	return dummyStatus()
}

func WriteStatus(params martini.Params) Ticket {

	// write to DB
	return dummyStatus()
}

func main() {

	m := martini.Classic()
	m.Use(render.Renderer())

	m.Group("/status", func(r martini.Router) {
		r.Get("/:id", ReadStatus)
		r.Post("/:id", WriteStatus)
	})

	m.Run()

}

Result:
I request for JSON and I just receive a string

$ curl -i -H "Accept: application/json" -H "Content-Type:application/json" -X GET http://localhost:3000/status/id:12345
HTTP/1.1 200 OK
Date: Wed, 24 Dec 2014 20:01:32 GMT
Content-Length: 19
Content-Type: text/plain; charset=utf-8

<main.Ticket Value>

With some trial and error, I figured this out, however, I am still struggling to make it work with routing group. If I ever figure that out, I will update this answer. Hope this helps.

package main

import (
	"github.com/go-martini/martini"
	"github.com/martini-contrib/render"
)

type Ticket struct {
	Number      int    `json:"number"`
	Description string `json:"description"`
	State       string `json:"state"`
}

func ReadStatus(p martini.Params) Ticket {

	ticket := Ticket{
		Number:      645,
		Description: "A dummy customer ticket " + p["id"],
		State:       "resolved",
	}
	return ticket
}

func main() {

	m := martini.Classic()
	m.Use(render.Renderer())

	m.Get("/status/:id", func(r render.Render, params martini.Params) { r.JSON(200, ReadStatus(params)) })

	m.Run()

}