Golang : Read, Write(Create) and Delete Cookie example

Got an email from a reader asking for a more elaborated example of how to read, write(create) and delete a cookie in Golang. Somehow the previous tutorial on dropping a cookie to visitor's browser wasn't detailed enough.

Alright, a fair request.

Below is an example of how to read, write/create and delete a cookie within a simple webserver.

NOTE: IF you are planning to read, write/create and delete multiple cookies. See how to use net/http/cookiejar tutorial at https://www.socketloop.com/tutorials/golang-storing-cookies-in-http-cookiejar-example

Here you go!

 package main

 import (
 "net/http"
 )

 func SayHelloWorld(w http.ResponseWriter, r *http.Request) {
 html := "Hello World! "
 w.Write([]byte(html))
 }

 func ReadCookie(w http.ResponseWriter, r *http.Request) {
 c, err := r.Cookie("ithinkidroppedacookie")
 if err != nil {
 w.Write([]byte("error in reading cookie : " + err.Error() + "\n"))
 } else {
 value := c.Value
 w.Write([]byte("cookie has : " + value + "\n"))
 }
 }

 // see https://golang.org/pkg/net/http/#Cookie
 // Setting MaxAge<0 means delete cookie now.

 func DeleteCookie(w http.ResponseWriter, r *http.Request) {
 c := http.Cookie{
 Name: "ithinkidroppedacookie",
 MaxAge: -1}
 http.SetCookie(w, &c)

 w.Write([]byte("old cookie deleted!\n"))
 }

 func CreateCookie(w http.ResponseWriter, r *http.Request) {
 c := http.Cookie{
 Name: "ithinkidroppedacookie",
 Value:  "thedroppedcookiehasgoldinit",
 MaxAge: 3600}
 http.SetCookie(w, &c)

 w.Write([]byte("new cookie created!\n"))
 }

 func main() {
 mux := http.NewServeMux()
 mux.HandleFunc("/", SayHelloWorld)
 mux.HandleFunc("/readcookie", ReadCookie)
 mux.HandleFunc("/deletecookie", DeleteCookie)
 mux.HandleFunc("/createcookie", CreateCookie)
 http.ListenAndServe(":8080", mux)
 }

Now, to see how the cookie is being created, read and deleted. You need to follow this sequence.

1. Run the program and point your web browser to localhost:8080
2. Change the URL to localhost:8080/createcookie to create new cookie.
3. Read the cookie by changing to localhost:8080/createcookie.
4. Finally, delete the cookie by changing to localhost:8080/deletecookie.

If you happen to view with Chrome browser, open up the inspector to see the cookie value

Hope this helps!

References:

https://www.socketloop.com/tutorials/golang-drop-cookie-to-visitor-s-browser-and-http-setcookie-example

https://www.socketloop.com/tutorials/golang-http-server-example