Cookies and Sessions

Handle cookies and maintain sessions in k6

VU Cookie Jar

By default, each Virtual User (VU) maintains its own cookie jar that automatically handles cookies:

import http from "k6/http";
import { check, group } from "k6";

export let options = {
    maxRedirects: 3
};

export default function() {
    group("Simple cookies set with VU jar", function() {
        // Since this request redirects the `res.cookies` property won't contain the cookies
        let res = http.get("http://httpbin.org/cookies/set?name3=value3&name4=value4");
        check(res, {
            "status is 200": (r) => r.status === 200
        });

        // Make sure cookies have been added to VU cookie jar
        let vuJar = http.cookieJar();
        let cookiesForURL = vuJar.cookiesForURL(res.url);
        check(null, {
            "vu jar has cookie 'name3'": () => cookiesForURL.name3.length > 0,
            "vu jar has cookie 'name4'": () => cookiesForURL.name4.length > 0
        });
    });
}

Cookies set by the server (via Set-Cookie headers) are automatically stored in the VU’s cookie jar.

Sending Cookies with Requests

Send cookies as part of a request:

import http from "k6/http";
import { check, group } from "k6";

export default function() {
    group("Simple cookies send with VU jar", function() {
        let cookies = {
            name: "value1",
            name2: "value2"
        };
        let res = http.get("http://httpbin.org/cookies", { cookies: cookies });
        check(res, {
            "status is 200": (r) => r.status === 200,
            "has cookie 'name'": (r) => r.json().cookies.name.length > 0,
            "has cookie 'name2'": (r) => r.json().cookies.name2.length > 0
        });

        // Since the cookies are set as "request cookies" they won't be added to VU cookie jar
        let vuJar = http.cookieJar();
        let cookiesForURL = vuJar.cookiesForURL(res.url);
        check(null, {
            "vu jar doesn't have cookie 'name'": () => cookiesForURL.name === undefined,
            "vu jar doesn't have cookie 'name2'": () => cookiesForURL.name2 === undefined
        });
    });
}

Local Cookie Jar

Create a separate cookie jar for specific use cases:

1. Create local jar

   import http from "k6/http";
   
   let jar = new http.CookieJar();
   
2. Send cookies with local jar

   let cookies = {
       name5: "value5",
       name6: "value6"
   };
   let res = http.get("http://httpbin.org/cookies", { 
       cookies: cookies, 
       jar: jar 
   });
   
3. Check cookies in local jar

   let cookiesForURL = jar.cookiesForURL(res.url);
   console.log(cookiesForURL);
   

Advanced Cookie Management

Setting Cookies Manually

import http from "k6/http";
import { check, group } from "k6";

export default function() {
    group("Advanced send with local jar", function() {
        let jar = new http.CookieJar();
        jar.set("http://httpbin.org/cookies", "name7", "value7");
        jar.set("http://httpbin.org/cookies", "name8", "value8");
        let res = http.get("http://httpbin.org/cookies", { jar: jar });
        let cookiesForURL = jar.cookiesForURL(res.url);
        check(res, {
            "status is 200": (r) => r.status === 200,
            "has cookie 'name7'": (r) => r.json().cookies.name7.length > 0,
            "has cookie 'name8'": (r) => r.json().cookies.name8.length > 0
        });

        cookiesForURL = jar.cookiesForURL(res.url);
        check(null, {
            "local jar has cookie 'name7'": () => cookiesForURL.name7.length > 0,
            "local jar has cookie 'name8'": () => cookiesForURL.name8.length > 0
        });

        // Make sure cookies have NOT been added to VU cookie jar
        let vuJar = http.cookieJar();
        cookiesForURL = vuJar.cookiesForURL(res.url);
        check(null, {
            "vu jar doesn't have cookie 'name7'": () => cookiesForURL.name7 === undefined,
            "vu jar doesn't have cookie 'name8'": () => cookiesForURL.name8 === undefined
        });
    });
}

Cookie Attributes

Set cookie attributes like domain and path:

import http from "k6/http";
import { check, group } from "k6";

export default function() {
    group("Advanced cookie attributes", function() {
        let jar = http.cookieJar();
        jar.set("http://httpbin.org/cookies", "name9", "value9", { 
            domain: "httpbin.org", 
            path: "/cookies" 
        });

        let res = http.get("http://httpbin.org/cookies", { jar: jar });
        check(res, {
            "status is 200": (r) => r.status === 200,
            "has cookie 'name9'": (r) => r.json().cookies.name9 === "value9"
        });

        jar.set("http://httpbin.org/cookies", "name10", "value10", { 
            domain: "example.com", 
            path: "/" 
        });
        res = http.get("http://httpbin.org/cookies", { jar: jar });
        check(res, {
            "status is 200": (r) => r.status === 200,
            "doesn't have cookie 'name10'": (r) => r.json().cookies.name10 === undefined
        });
    });
}

Session Persistence

Maintain user sessions across multiple requests:

import http from "k6/http";
import { check, group } from "k6";
import { sleep } from "k6";

export default function() {
    // Login to establish session
    let loginRes = http.post("https://example.com/login", {
        username: "user",
        password: "pass"
    });
    
    check(loginRes, {
        "login successful": (r) => r.status === 200
    });
    
    // Session cookies are automatically maintained
    sleep(1);
    
    // Make authenticated request (cookies sent automatically)
    let dashboardRes = http.get("https://example.com/dashboard");
    
    check(dashboardRes, {
        "dashboard loaded": (r) => r.status === 200
    });
    
    sleep(1);
    
    // Another authenticated request
    let profileRes = http.get("https://example.com/profile");
    
    check(profileRes, {
        "profile loaded": (r) => r.status === 200
    });
}

Each VU maintains its own cookie jar throughout the test iteration, simulating independent user sessions.