Crossing the HTTP Stateless Boundary: Practical Application of Cookie and Session in Django

This article deeply explores Cookie and Session in Django, analyzes how to deal with the stateless problem of HTTP protocol, explains its basic concepts, analyzes the working principle, and discusses when to choose to use Cookie or Session. The advanced part of the article proposes efficient management of Cookies and Sessions, and how to use them for user authentication.

The statelessness of the HTTP protocol

HTTP, Hypertext Transfer Protocol, is an application layer protocol. It is the most widely used network protocol on the Internet. The HTTP protocol is stateless, but why are we talking about this statelessness? What problems will this statelessness bring? Let's dive in together.

Basic introduction to HTTP protocol

HTTP is the most widely used network protocol on the Internet, and all www files must comply with this standard.

# 一个典型的HTTP请求
GET /index.html HTTP/1.1
Host: www.example.com

In this request, GETit is the HTTP method, /index.htmlthe resource to be obtained, HTTP/1.1the protocol version, Hostand an HTTP header indicating the requested domain.

what is statelessness

The HTTP protocol is stateless, which means that the server does not remember the user's information. Specifically, when you browse a webpage and then jump to another webpage on the same website, the server does not know that the two requests are from the same user.

# 第一个HTTP请求
GET /index.html HTTP/1.1
Host: www.example.com

# 第二个HTTP请求
GET /about.html HTTP/1.1
Host: www.example.com

In this example, the server will not know /index.htmlthat /about.htmlthe request and request are from the same user.

Problems with statelessness

The stateless nature of the HTTP protocol means that whenever a client obtains a server resource, the server cannot obtain any information from the previous request. This results in that in a web application with multiple pages and multiple requests, data cannot be shared between different pages.

# 用户在购物车中添加了一件商品
POST /cart/add HTTP/1.1
Host: www.example.com
Content-Type: application/x-www-form-urlencoded

product_id=1&quantity=1

# 用户尝试检查购物车
GET /cart HTTP/1.1
Host: www.example.com

In this example, due to the stateless nature of HTTP, even if the user adds an item to the shopping cart in the first request, the server cannot remember this action in the second request. When the user checks the shopping cart, it may be empty, which is obviously not in line with our expectations.

The basic concept of Cookie and Session

In order to solve the problems caused by the statelessness of the HTTP protocol, web applications usually use cookies and sessions to save the state between multiple user requests. Next, let's dive into both technologies.

what are cookies

A cookie is a piece of data sent by the server to the user's browser and stored on the browser. It will be carried and sent to the server when the browser sends a request to the same server next time.

# 服务器在响应头中设置Cookie
HTTP/1.1 200 OK
Set-Cookie: id=a3fWa; Expires=Wed, 21 Oct 2023 07:28:00 GMT;

# 浏览器下一次请求携带这个Cookie
GET /index.html HTTP/1.1
Host: www.example.com
Cookie: id=a3fWa;

What is Session

Session is another way to maintain state between multiple requests from the user. It is more like a data structure saved on the server side, which can save the user's operation records on the server.

# 用户登录，服务器创建一个Session，并将Session ID发送给浏览器
POST /login HTTP/1.1
Host: www.example.com
Content-Type: application/x-www-form-urlencoded

username=john&password=123456

# 服务器响应
HTTP/1.1 200 OK
Set-Cookie: sessionid=123abc; 

# 用户访问受保护的资源，浏览器发送包含Session ID的请求
GET /dashboard HTTP/1.1
Host: www.example.com
Cookie: sessionid=123abc;

The role and difference between Cookie and Session

• Both Cookie and Session are born to solve the statelessness of the HTTP protocol, and both of them can maintain state between multiple requests of the user.
• Cookie data is stored on the client's browser, and Session data is stored on the server.
• In terms of security, Session is more secure than Cookie, because Cookie information can be tampered with on the browser side, while Session is stored on the server side and cannot be modified by the client.
• From the perspective of storage, Cookie is not very "lightweight". Every HTTP request will carry Cookie to the server. If too many Cookies are used, the performance of the server will be affected. Session is relatively light, but if the number of visits If it is too large, it will put pressure on the server.
• A common practice is to use cookies to store the Session id, which not only solves the problem of storage space, but also better maintains the state.

In-depth understanding of cookies

Next we will explore cookies in more detail, including how they work, their properties, and how to use cookies in Python and Django.

How Cookies Work

When the user visits the website for the first time, the server sends the cookie to the user's browser through the Set-Cookie HTTP response header. The browser saves the cookie, and then sends the cookie back to the server through the Cookie HTTP request header in each subsequent request.

Cookie properties

A cookie has the following main attributes:

• Name: A name that uniquely identifies the cookie.
• Value: String value stored in the cookie.
• Expiration Time: Defines the date and time when the cookie expires.
• Path: Define which web pages can get cookies.
• Domain: Defines which websites can get cookies.
• Secure: Specifies whether the cookie can only be transmitted via HTTPS.
• HttpOnly: Specifies whether the cookie can be accessed through JavaScript.

Working with Cookies in Python and Django

In Python and Django, we can easily set and get cookies.

# 在Django中设置Cookie
def set_cookie(request):
    response = HttpResponse("Setting a cookie")
    response.set_cookie('cookie_name', 'cookie_value')
    return response

# 在Django中获取Cookie
def get_cookie(request):
    value = request.COOKIES.get('cookie_name')
    return HttpResponse(f"The value of cookie 'cookie_name' is {value}")

Cookie security

Although cookies are very useful in web applications, they also pose some security problems. For example, if cookies are used improperly, attackers may steal users' cookies through various methods to obtain users' private information. Therefore, we must always take security into consideration when using cookies.

How to protect your cookies

There are many ways to protect your cookies, including setting the Secure and HttpOnly flags, using the same-origin policy, and regularly updating and deleting cookies that are no longer needed.

In-depth understanding of Session

Before we delve into Session, we first need to understand that HTTP is stateless, each request is independent, and we don't know what the previous request did. This can cause problems in web applications that interact with users, especially when we need to maintain state across multiple requests. This is where Session comes into play.

How sessions work

When the user requests the website for the first time, the server will create a new Session, then set the unique Session ID as part of the cookie, and send it back to the browser. Then, when the browser sends a request to the server again, it will include this Session ID, which the server can use to find and load the Session.

Session life cycle

The life cycle of a session usually starts from the user's first visit to the website until the user ends the session, such as by logging out or closing the browser. During this process, the server will always maintain the Session. If the user is inactive for a period of time, the server may automatically end the Session to free up resources.

Working with Sessions in Python and Django

In Python and Django, we can set and get Session very conveniently.

# 在Django中设置Session
def set_session(request):
    request.session['key'] = 'value'
    return HttpResponse("Setting a session")

# 在Django中获取Session
def get_session(request):
    value = request.session.get('key')
    return HttpResponse(f"The value of session key is {value}")

Session security

Although sessions are very useful in web applications, they also pose some security problems. For example, if an attacker is able to steal a user's Session ID, they can impersonate the user, which is known as session hijacking. Therefore, we must always consider security when using Session.

How to protect your session

There are many ways to protect your sessions, including: using secure cookies to transmit session IDs, periodically regenerating session IDs, using CSRF tokens for all sensitive operations, periodically ending old sessions, etc.

Choice of Cookie and Session

In many cases, choosing to use Cookie or Session mainly depends on your specific needs. The following are some common factors that determine whether to use Cookie or Session.

data storage location

• If you want the data to be stored on the client side, then cookies might be a better choice. Because cookies are stored directly on the user's browser, your app can access this data without doing a server-side lookup. However, sensitive information should not be stored in cookies because they are easily viewed and modified by the user.
• On the other hand, if your application needs to store a lot of data, or you don't want (or can't) store all the data on the user's browser, then you should choose to use Session.

safety

• If you need to store sensitive information, such as user credentials or payment information, then you should choose to use Session. Since session data is stored on the server, they are more secure than cookies stored on the client.
• However, you also need to be aware of session hijacking and session fixation attacks, which are two common security threats you may encounter when using sessions. You can mitigate these threats by periodically changing the Session ID and using secure cookies.

life cycle

• If you need to save data even after the user closes the browser, then you should choose to use cookies. You can set the expiration date of the cookie so that it persists after the user closes the browser.
• However, if you don't want the data to persist after the user session ends, or you want to be able to control when the data expires on the server side, then you should choose to use Session.

Summarize

In general, choosing to use Cookie or Session mainly depends on your application requirements. Ideally, you should use both techniques together in order to maximize their benefits.

Advanced Application of Cookie and Session

Below, we will introduce some more advanced applications of Cookie and Session. This content will help you better understand how these two technologies are used in complex web applications.

Advanced Application of Cookies: Third Party Cookies

In addition to the usual "first-party" cookies, there are also so-called "third-party" cookies. These cookies are often used to track user behavior across websites, for example for advertising targeting. Knowing how this type of cookie works helps us understand and deal with cookie privacy issues.

Advanced application of Session: persistent Session

In some cases, we may want the Session to survive after the user closes the browser. This type of session is called a "persistent session" and is useful when implementing features such as automatic user login.

In Django, you can use SESSION_EXPIRE_AT_BROWSER_CLOSEsettings to control whether the session expires when the browser is closed. For example, you can add the following code to your Django settings to enable persistent sessions:

SESSION_EXPIRE_AT_BROWSER_CLOSE = False

Another storage method of Session: storing Session data in Cookie

Although usually we store Session data on the server, in some cases, we can also choose to store Session data in Cookie. Doing so can reduce the load on the server, but cookies need to be secured as they now contain more sensitive information.

In Django, you can use SESSION_COOKIE_SECUREsettings to control whether session cookies are only transmitted over HTTPS. For example, you can add the following code to your Django settings to enable this feature:

SESSION_COOKIE_SECURE = True

Authentication using JSON Web Tokens (JWT)

In addition to using cookies and sessions, more and more web applications now choose to use JSON Web Tokens (JWT) for authentication. JWT is an open standard that defines a compact and self-contained way for securely transferring information between parties as JSON objects. This information can be verified and trusted because it is digitally signed.

The main advantage of using JWT for authentication is that the server does not need to store Session state, which is especially useful when building scalable large applications. Also, since JWTs are self-contained, they can contain all necessary information without making additional database queries.

Here's a simple example of creating and verifying a JWT using the Python JWT library:

import jwt

# 创建一个新的token
payload = {"user_id": 123}
secret = 'secret'
token = jwt.encode(payload, secret, algorithm='HS256')

# 验证并解码token
decoded_payload = jwt.decode(token, secret, algorithms=['HS256'])
print(decoded_payload)  # 输出: {"user_id": 123}

Note that you need to install the jwt library with pip first:

pip install PyJWT

Summarize

This article mainly discusses Cookie and Session in Django, and how to use them in web development.

• We first understood the statelessness of the HTTP protocol, and how this statelessness leads to the need for cookies and sessions to maintain state in web applications.
• Then, we explored the basic concepts of Cookie and Session respectively, including how they work, their purpose, advantages and disadvantages.
• We took a deep dive into the implementation details of Cookies and Sessions, and how to use them in Django.
• In our discussion, we also explored some more advanced topics, such as third-party cookies, persistent sessions, storing session data in cookies, and using JSON Web Tokens for authentication.

Whether you are an experienced developer or a beginner, I hope this article will help you in your learning. Keep following me for more in-depth knowledge about Django development!

If it is helpful, please pay more attention to the personal WeChat public account: [Python full perspective] TeahLead_KrisChang, 10+ years of experience in the Internet and artificial intelligence industry, 10+ years of experience in technology and business team management, Tongji Software Engineering Bachelor, Fudan Engineering Management Master, Aliyun certified cloud service senior architect, head of AI product business with hundreds of millions of revenue.