package main

import (
    "io"
    "net/http"
)

type myHandler int

func (h myHandler) ServeHTTP(res http.ResponseWriter, req *http.Request) {
    res.Header().Set("Content-Type", "text/html; charset=utf-8")
    switch req.URL.Path {
    case "/cat":
        io.WriteString(res, `<img src="https://upload.wikimedia.org/wikipedia/commons/0/06/Kitten_in_Rizal_Park%2C_Manila.jpg">`)
    case "/dog":
        io.WriteString(res, `<img src="https://upload.wikimedia.org/wikipedia/commons/6/6e/Golde33443.jpg">`)
    }
}

func main() {

    var h myHandler
    http.ListenAndServe(":9000", h)
}