Read cookie http in Go (Golang)

Overview

net/http Request struct provides a convenient method to read a particular cookie given its name. Below is the signature of that method. https://golang.org/pkg/net/http/#Request.Cookie

func (r *Request) Cookie(name string) (*Cookie, error)

To print all cookies,  we can iterate over the Cookies method of http.Request struct. We can use a range keyword for that.

for _, c := range r.Cookies() {
     fmt.Println(c)
}

Both these functions will return the instance of the Cookie struct. A cookie in golang is represented as below in golang.

https://golang.org/src/net/http/cookie.go

type Cookie struct {
	Name  string
	Value string

	Path       string    // optional
	Domain     string    // optional
	Expires    time.Time // optional
	RawExpires string    // for reading cookies only

	// MaxAge=0 means no 'Max-Age' attribute specified.
	// MaxAge<0 means delete cookie now, equivalently 'Max-Age: 0'
	// MaxAge>0 means Max-Age attribute present and given in seconds
	MaxAge   int
	Secure   bool
	HttpOnly bool
	SameSite SameSite
	Raw      string
	Unparsed []string // Raw text of unparsed attribute-value pairs
}

See https://tools.ietf.org/html/rfc6265 for details of each of the fields of the above cookie.

Program

Below is the program for the same to illustrate the Cookie and Cookies method of the http.Request struct

package main

import (
	"fmt"
	"log"
	"net/http"
)

func main() {
	docHandler := http.HandlerFunc(docHandler)
	http.Handle("/doc", docHandler)

	http.ListenAndServe(":8080", nil)
}

func docHandler(w http.ResponseWriter, r *http.Request) {
	fmt.Println("Cookies in API Call:")

	tokenCookie, err := r.Cookie("token")
	if err != nil {
		log.Fatalf("Error occured while reading cookie")
	}
	fmt.Println("\nPrinting cookie with name as token")
	fmt.Println(tokenCookie)

	fmt.Println("\nPrinting all cookies")
	for _, c := range r.Cookies() {
		fmt.Println(c)
	}
	fmt.Println()
	w.WriteHeader(200)
	w.Write([]byte("Doc Get Successful"))
	return
}

Run the program above and make the below curl call

curl -X GET localhost:8080/doc --cookie "id=abcd; token=some_token"

The curl call is passing two cookie name-value pairs

• id=abcd

• token=some_token

It will give below output

Cookies in API Call:

Printing cookie with name as "token"
token=some_token

Printing all cookies
id=abcd
token=some_token

This is how we print a particular cookie with a given name “token”

tokenCookie, err := r.Cookie("token")

It prints as seen from the output

token=some_token

This is how we print all the cookies

for _, c := range r.Cookies() {
     fmt.Println(c)
}

It outputs both the cookies name-value pairs that we had sent in the curl call

id=abcd
token=some_token

That was all about cookies in golang. Hope you have liked the tutorial. Please share feedback in the comments.

Also, check out our Golang advance tutorial Series – Golang Advance Tutorial