Read cookie in Go

Question

I'm deploying a simple HTTP server and a simple HTTP client in Go. I tried to read the cookie value from the client without success (I receive an empty value) even if on the server the value that I see is set. How can I read the cookie value from the client side (i.e. to send the further requests by including the cookie that I received)?

Server Code

package main

import (
    "log"
    "math/rand"
    "net/http"
    "strconv"
    "strings"
    "time"
)

var SERVER_PORT string = ":8080"

func setCookie(w http.ResponseWriter, username string){
    cookieValue := username + ":" + (username+strconv.Itoa(rand.Intn(100000000)))
    //expiration := time.Now().Add(365 * 24 * time.Hour)
    expiration := time.Now().Add(20 * time.Second)
    cookie := http.Cookie{Name:"SessionID", Value: cookieValue, Expires: expiration}
    http.SetCookie(w, &cookie)
    log.Print(cookie)
}

func sayHello(w http.ResponseWriter, r* http.Request) {
    username := r.URL.Path
    username = strings.TrimPrefix(username, "/")
    setCookie(w,username)
    message := "Hello " + username
    w.Write([]byte(message))
}

func ReadCookieServer(w http.ResponseWriter, req *http.Request) {
    // read cookie
    var cookie,err = req.Cookie("SessionID")
    if err == nil {
        var cookievalue = cookie.Value
        w.Write([]byte(cookievalue))
    }
}

func main() {
    http.HandleFunc("/", sayHello)
    http.HandleFunc("/readcookie", ReadCookieServer)
    if err := http.ListenAndServe(SERVER_PORT, nil); err != nil {
        panic(err)
    }
}

Client Code

package main

import (
    "io/ioutil"
    "log"
    http "net/http"
)

var serverName string = "http://localhost"
var serverPort string = ":8080/"

func MakeRequest() {
    var username string = "blabla"
    resp, err := http.Get(serverName + serverPort + username)
    if err != nil {
        log.Fatalln(err)
    }
    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatalln(err)
    }
    log.Println(string(body))
}

func Readcookie() {
    resp, err := http.Get(serverName + serverPort + "readcookie")
    if err != nil {
        log.Fatalln(err)
    }
    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatalln(err)
    }
    log.Println(string(body))
}

func main() {
    MakeRequest()
    Readcookie()
}

Answer 1

If you want to read the cookie from an HTTP request, you do it with the Cookies method. Example:

func Readcookie() {
    resp, err := http.Get(serverName + serverPort + "readcookie")
    if err != nil {
        log.Fatalln(err)
    }
    for _, cookie := range resp.Cookies() {
        if cookie.Name == "SessionID" {
            log.Println("Cookie: ", cookie.Value)
        }
    }
    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatalln(err)
    }
    log.Println(string(body))
}

To achieve your larger goal, of session management across subsequent HTTP requests, simply instantiate a cookie jar on your HTTP client. Example:

var client *http.Client

func init() {
    jar, err := cookiejar.New(&cookiejar.Options{PublicSuffixList: publicsuffix.List})
    if err != nil {
        panic(err)
    }
    client = &http.Client{Jar: jar}
}

Then use this client (rather than the default) for your subsequent requests:

func Readcookie() {
    resp, err := client.Get(serverName + serverPort + "readcookie")
    if err != nil {
        log.Fatalln(err)
    }
    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatalln(err)
    }
    log.Println(string(body))
}