Statelessness requirement in Rest API - Step-by-Step Execution

Concept Flow - Statelessness requirement

Client sends request

↓

Server receives request

↓

Server processes request WITHOUT storing client info

↓

Server sends response

↓

Client receives response

↓

Next request treated as new, no memory of previous

Each request from client to server is independent; the server does not remember past requests.

Execution Sample

Rest API

GET /user/123 HTTP/1.1
Host: example.com
Authorization: Bearer token123

Response: {"id":123,"name":"Alice"}

Client sends a request with all needed info; server responds without storing session data.

Execution Table

Step	Action	Server State	Client Info Stored?	Response Sent
1	Client sends GET /user/123 with token	No stored data	No	User data for id 123
2	Server processes request using token	No stored data	No	User data sent
3	Server finishes request	No stored data	No	Response complete
4	Client sends next request GET /user/456 with token	No stored data	No	User data for id 456
5	Server processes new request independently	No stored data	No	User data sent
6	Server finishes second request	No stored data	No	Response complete

💡 Server never stores client info; each request is handled independently.

Variable Tracker

Variable	Start	After Step 1	After Step 4	Final
Server Stored Data	None	None	None	None
Client Request Info	None	Request with token123	Request with token456	Request with token456

Key Moments - 2 Insights

Why doesn't the server remember the client's previous request?

Because the server does not store any client info between requests, as shown in execution_table rows 1-3 and 4-6.

How does the server know who the client is if it doesn't store data?

The client sends all needed info (like tokens) with each request, so the server can authenticate without stored data (see execution_table step 1 and 4).

Visual Quiz - 3 Questions

Look at the execution_table, what is the server's stored data after step 3?

A User session info stored

B No stored data

C Partial client info stored

D Error state

💡 Hint

Check the 'Server State' column at step 3 in execution_table.

At which step does the server process a new request independently?

A Step 2

B Step 4

C Step 5

D Step 3

💡 Hint

Look for 'Server processes new request independently' in execution_table.

If the server started storing client info, which variable in variable_tracker would change?

A Server Stored Data

B Client Request Info

C Response Sent

D None

💡 Hint

Server Stored Data tracks what the server keeps between requests.

Concept Snapshot

Statelessness means each client request is independent.
Server does NOT keep client info between requests.
Client must send all needed info each time.
This makes servers simpler and scalable.
Example: REST APIs follow this rule.

Full Transcript

Statelessness requirement means the server treats every client request as new and independent. The server does not save any information about the client between requests. Instead, the client sends all necessary data, like authentication tokens, with each request. This approach simplifies server design and helps it handle many clients efficiently. The execution table shows the server processing two separate requests without storing any client data. Variables tracking server stored data remain empty throughout. This is the core idea behind REST API statelessness.

Practice

1. What does the statelessness requirement in REST APIs mean?

easy

A. Each request from client to server must contain all information needed to understand and process it.

B. The server must remember all previous requests from the client.

C. The server stores user session data between requests.

D. The client does not need to send any authentication information after the first request.

Solution

1. Step 1: Understand statelessness in REST

   Statelessness means the server does not keep any client context between requests.

2. Step 2: Identify what each request must contain

   Each request must have all data needed to process it, including authentication and parameters.

3. Final Answer:

   Each request from client to server must contain all information needed to understand and process it. -> Option A

4. Quick Check:

   Statelessness = All info in each request [OK]

Hint: Remember: server forgets past requests, all info sent every time [OK]

Common Mistakes:

• Thinking server stores session data
• Assuming client sends partial info only once
• Confusing statelessness with authentication persistence

2. Which of the following HTTP request examples follows the statelessness principle?

easy

A. POST /login HTTP/1.1\nHost: example.com\nCookie: sessionid=abc123

B. GET /profile HTTP/1.1\nHost: example.com

C. GET /profile HTTP/1.1\nHost: example.com\nReferer: /home

D. GET /profile HTTP/1.1\nHost: example.com\nAuthorization: Bearer token123

Solution

1. Step 1: Check if request contains all needed info

   GET /profile HTTP/1.1\nHost: example.com\nAuthorization: Bearer token123 includes Authorization header, so server can authenticate without stored session.

2. Step 2: Compare with other options

   POST /login HTTP/1.1\nHost: example.com\nCookie: sessionid=abc123 relies on cookies, which imply server state. Options B and D lack explicit authentication info.

3. Final Answer:

   GET request with Authorization header carrying token -> Option D

4. Quick Check:

   Auth info in request = stateless [OK]

Hint: Look for Authorization header in request to confirm statelessness [OK]

Common Mistakes:

• Assuming cookies mean statelessness
• Ignoring missing auth info in requests
• Confusing Referer header with authentication

3. Consider this REST API server behavior: It does not store any client session data. A client sends two requests:
1. GET /data?user=123&token=abc
2. GET /data?user=123
What will happen on the second request?

medium

A. The server rejects the request due to missing authentication token.

B. The server processes the request successfully using stored session data.

C. The server processes the request ignoring authentication.

D. The server crashes because of missing parameters.

Solution

1. Step 1: Analyze statelessness and authentication

   Since server is stateless, it does not remember previous tokens; each request must include token.

2. Step 2: Check second request parameters

   Second request lacks token parameter, so server cannot authenticate and must reject it.

3. Final Answer:

   Server rejects request due to missing authentication token. -> Option A

4. Quick Check:

   Missing token means reject request [OK]

Hint: Every request needs auth info; missing it causes rejection [OK]

Common Mistakes:

• Assuming server remembers token from first request
• Thinking server ignores missing token
• Believing server crashes on missing params

4. A developer wrote this REST API code snippet to handle user requests:

def handle_request(request):
    if 'session_id' in server_memory:
        user = server_memory['session_id']
        return f"Hello, {user}!"
    else:
        return "Unauthorized"

What is the main problem related to statelessness here?

medium

A. The code does not check for authentication token in the request.

B. The code correctly implements statelessness by using server memory.

C. The code stores session data on the server, violating statelessness.

D. The code uses request parameters properly for authentication.

Solution

1. Step 1: Identify server memory usage

   The code checks 'session_id' in server_memory, meaning it stores client state on server.

2. Step 2: Compare with statelessness principle

   Statelessness forbids server from storing client session data between requests.

3. Final Answer:

   Code stores session data on server, violating statelessness. -> Option C

4. Quick Check:

   Server storing session = stateful, not stateless [OK]

Hint: Stateless means no server memory of client sessions [OK]

Common Mistakes:

• Thinking server memory use is allowed
• Ignoring missing token checks
• Assuming code is stateless because it returns a string

5. You are designing a REST API for a shopping cart. To keep it stateless, which approach is best to track the user's cart items across requests?

hard

A. Store the cart items in a server-side session linked to the user ID.

B. Require the client to send the full cart data with each request.

C. Save the cart data in a database and keep session ID on server memory.

D. Use cookies to store cart items and rely on server to read them.

Solution

1. Step 1: Understand statelessness in API design

   Statelessness means server does not keep client state; all info must come with each request.

2. Step 2: Evaluate options for cart tracking

   Require the client to send the full cart data with each request. requires the client to send the full cart data with each request, fitting statelessness. Options A, B, and C rely on server or cookies storing state.

3. Final Answer:

   Require client to send full cart data with each request. -> Option B

4. Quick Check:

   Client sends all data = stateless API [OK]

Hint: Keep server stateless by sending all data from client every time [OK]

Common Mistakes:

• Using server sessions to store cart
• Assuming cookies make API stateless
• Relying on server memory for user data