How to read cookies?

go cookies

14,472

A better way would be to encode your json into base64 for example. I made a working example...

main.go

package main

import (
    "encoding/base64"
    "encoding/json"
    "fmt"
    "io"
    "io/ioutil"
    "net/http"
)

// Contains everything about an appointment
type Appointment struct {
    Date    string `json:"appointmentDate"`    // Contains date as string
    StartMn string `json:"appointmentStartMn"` // Our startMn ?
    ID      int    `json:"appointmentId"`      // AppointmentId
    UserID  int    `json:"appointmentUserId"`  // UserId
}

func main() {
    handler := http.NewServeMux()

    // Main request
    handler.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        fmt.Printf("Requested /\r\n")

        // set typical headers
        w.Header().Set("Content-Type", "text/html")
        w.WriteHeader(http.StatusOK)

        // Read file
        b, _ := ioutil.ReadFile("index.html")
        io.WriteString(w, string(b))
    })

    // booking request
    handler.HandleFunc("/booking/", func(w http.ResponseWriter, r *http.Request) {
        fmt.Printf("Requested /booking/\r\n")

        // set typical headers
        w.Header().Set("Content-Type", "text/html")
        w.WriteHeader(http.StatusOK)

        // Read cookie
        cookie, err := r.Cookie("appointment")
        if err != nil {
            fmt.Printf("Cant find cookie :/\r\n")
            return
        }

        fmt.Printf("%s=%s\r\n", cookie.Name, cookie.Value)

        // Cookie data
        data, err := base64.StdEncoding.DecodeString(cookie.Value)
        if err != nil {
            fmt.Printf("Error:", err)
        }

        var appointment Appointment
        er := json.Unmarshal(data, &appointment)
        if err != nil {
            fmt.Printf("Error: ", er)
        }

        fmt.Printf("%s, %s, %d, %d\r\n", appointment.Date, appointment.StartMn, appointment.ID, appointment.UserID)

        // Read file
        b, _ := ioutil.ReadFile("booking.html")
        io.WriteString(w, string(b))
    })

    // Serve :)
    http.ListenAndServe(":8080", handler)
}

index.html

<html>
    <head>
        <title>Your page</title>
    </head>
<body>
    Setting cookie via Javascript

    <script type="text/javascript">
    window.onload = () => {
        function setCookie(name, value, days) {
            var expires = "";
            if (days) {
                var date = new Date();
                date.setTime(date.getTime() + (days*24*60*60*1000));
                expires = "; expires=" + date.toUTCString();
            }
            document.cookie = name + "=" + btoa((value || ""))  + expires + "; path=/";
        }

        setCookie("appointment", JSON.stringify({
                    appointmentDate: "20-01-2019 13:06",
                    appointmentStartMn: "1-2",
                    appointmentId: 2,
                    appointmentUserId: 3
            })
        );

        document.location = "/booking/";
    }
    </script>
</body>

booking.html

<html>
    <head>
        <title>Your page</title>
    </head>
<body>
    Your booking is okay :)
</body>

14,472

Author by

Ado Ren

Updated on July 06, 2022

Comments

Ado Ren almost 2 years

I set a cookie from javascript such as:

setCookie("appointment", JSON.stringify({
                appointmentDate: selectedDay.date,
                appointmentStartMn: appointment.mnRange[0],
                appointmentId: appointment.id || 0,
                appointmentUserId: appointment.user.id || 0
          })
);

After cookie is set I want to redirect the user to a booking page:

window.location.href = "https://localhost:8080/booking/"

The setCookie function:

function setCookie(cookieName, cookieValue) {
    document.cookie = `${cookieName}=${cookieValue};secure;`;
}

I'd like to retrieve that cookie from my go backend but I can't figure out how to do this. I've read about this question since I've never used cookies before but the answers seems to tell that I don't have to do much aside from setting document.cookie.

In my browser storage I can see the cookie is indeed set as expected.

In my Go back end I want to print the cookie:

r.HandleFunc("/booking/", handler.serveTemplate)

func (handler *templateHandler) serveTemplate(w http.ResponseWriter, r *http.Request) {
    c, err := r.Cookie("appointment")
    if err != nil {
        fmt.Println(err.Error())
    } else {
        fmt.Println(c.Value)
    }
}

//output http: named cookie not present

What is the specific I am missing ? I think I'm confusing local/http cookie but how to achieve the reading of client set cookies?

UPDATE (see answer for more)

It has nothing to do with golang. My:

appointmentDate: selectedDay.date

What formatted as 2019-01-01 and - is not a valid character that can be send to the backend. It worked into my browser, but it needs to be URI encoded to be passed.

So this did the trick:

`${cookieName}=${encodeURIComponent(cookieValue)};secure;` + "path=/";`

And in go (didn't catch err here to save space):

cookie, _ := r.Cookie("appointment")
data, _ := url.QueryUnescape(cookie.Value)

Ado Ren over 5 years

Appreciate the time you've put into your answer. Why do you say base64 is a better way ?
Sebastian Waldbauer over 5 years

As mkopriva already mentioned, there are some "illegal" characters in your cookie instead. You can use any serialisation method like base64 or encode to eliminate those characters.
Ado Ren over 5 years

I validate your answer. You nailed that my data contained illegal characters. The date as a matter of fact. Thanks