REST constraints and principles in Rest API - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does REST stand for?

REST stands for Representational State Transfer. It is a style for designing networked applications.

intermediate

Name the six main constraints of REST.

The six main REST constraints are:
1. Client-Server
2. Stateless
3. Cacheable
4. Uniform Interface
5. Layered System
6. Code on Demand (optional)

beginner

Explain the Client-Server constraint in REST.

Client and server are separate. The client handles the user interface, and the server manages data and logic. This separation allows each to evolve independently.

beginner

What does it mean that REST is stateless?

Each request from client to server must contain all information needed to understand and process it. The server does not store client context between requests.

intermediate

Why is the Uniform Interface constraint important in REST?

It simplifies and decouples the architecture, allowing each part to evolve independently. It defines a standard way to communicate using resources and HTTP methods.

Which REST constraint requires that each request contains all information needed to process it?

A Cacheable

B Layered System

C Stateless

D Client-Server

The Stateless constraint means the server does not keep client state between requests. Each request must be self-contained.

What is the purpose of the Cacheable constraint in REST?

A To separate client and server

B To allow clients to store responses for reuse

C To allow code to be sent from server to client

D To enforce a uniform interface

Cacheable means responses can be stored by clients or intermediaries to improve performance by reusing data.

Which HTTP method is NOT typically part of the REST uniform interface?

A GET

B POST

C DELETE

D CONNECT

CONNECT is not commonly used in REST APIs. GET, POST, DELETE are standard methods for resource operations.

What does the Layered System constraint allow in REST architecture?

A Clients cannot tell if they are connected directly to the end server or an intermediary

B Servers must store client state

C Clients and servers must be tightly coupled

D Code can be downloaded and executed on the client

Layered System allows intermediaries like proxies or gateways to be used without clients knowing.

Which REST constraint is optional and allows servers to send executable code to clients?

A Code on Demand

B Cacheable

C Stateless

D Uniform Interface

Code on Demand lets servers extend client functionality by sending code like JavaScript, but it is optional.

List and briefly explain the six REST constraints.

Think about how REST organizes communication and data handling.

Why is statelessness important in REST APIs? How does it affect server design?

Consider what happens if the server crashes or handles many clients.

Practice

1. Which of the following is a key constraint of REST that ensures each request from client to server must contain all the information needed to understand and process the request?

easy

A. Cacheability

B. Layered System

C. Statelessness

D. Code on Demand

Solution

1. Step 1: Understand the meaning of statelessness in REST

   Statelessness means the server does not store any client context between requests. Each request must be self-contained.

2. Step 2: Match the constraint to the description

   The description says each request must have all needed info, which matches statelessness.

3. Final Answer:

   Statelessness -> Option C

4. Quick Check:

   Request self-contained = Statelessness [OK]

Hint: Requests must be independent and self-contained [OK]

Common Mistakes:

• Confusing cacheability with statelessness
• Thinking layered system means stateless
• Assuming code on demand is required

2. Which HTTP method is NOT considered safe and idempotent according to REST principles?

easy

A. POST

B. PUT

C. GET

D. DELETE

Solution

1. Step 1: Recall safe and idempotent HTTP methods

   GET, PUT, and DELETE are idempotent; GET is safe. POST is neither safe nor idempotent.

2. Step 2: Identify the method that is not safe and idempotent

   POST changes server state and can create multiple resources, so it is not idempotent or safe.

3. Final Answer:

   POST -> Option A

4. Quick Check:

   POST is not safe or idempotent [OK]

Hint: POST changes data and is not idempotent [OK]

Common Mistakes:

• Thinking PUT is unsafe
• Confusing DELETE as unsafe
• Assuming GET modifies data

3. Given the following REST API response headers, which constraint is being applied?

Cache-Control: max-age=3600
ETag: "abc123"

medium

A. Cacheability

B. Uniform Interface

C. Statelessness

D. Client-Server

Solution

1. Step 1: Analyze the headers Cache-Control and ETag

   Cache-Control and ETag headers control how responses are cached by clients or intermediaries.

2. Step 2: Identify the REST constraint related to caching

   Cacheability means responses can be stored and reused to improve performance.

3. Final Answer:

   Cacheability -> Option A

4. Quick Check:

   Cache headers = Cacheability [OK]

Hint: Cache headers indicate cacheability constraint [OK]

Common Mistakes:

• Confusing cache headers with statelessness
• Thinking uniform interface relates to headers
• Assuming client-server means caching

4. You have a REST API that stores user sessions on the server between requests. Which REST constraint is violated and how can you fix it?

medium

A. Uniform Interface; change URL structure

B. Cacheability; disable caching on responses

C. Layered System; remove intermediaries

D. Statelessness; move session data to client or include in each request

Solution

1. Step 1: Identify the violated constraint

   Storing session data on server between requests breaks statelessness because server keeps client state.

2. Step 2: Suggest a fix to restore statelessness

   Move session info to client (like tokens) or send all needed info in each request.

3. Final Answer:

   Statelessness; move session data to client or include in each request -> Option D

4. Quick Check:

   Server session storage breaks statelessness [OK]

Hint: No server session storage means statelessness [OK]

Common Mistakes:

• Confusing cacheability with session storage
• Thinking layered system relates to sessions
• Trying to fix by changing URLs

5. You want to design a REST API that allows clients to update user profiles partially without sending the entire profile data. Which HTTP method and REST principle best support this requirement?

hard

A. PUT method and Uniform Interface constraint

B. PATCH method and Uniform Interface constraint

C. POST method and Statelessness constraint

D. DELETE method and Cacheability constraint

Solution

1. Step 1: Identify the HTTP method for partial updates

   PATCH is designed for partial updates, unlike PUT which replaces entire resource.

2. Step 2: Connect the method to the REST principle

   Uniform Interface means using standard methods consistently; PATCH fits this principle for partial updates.

3. Final Answer:

   PATCH method and Uniform Interface constraint -> Option B

4. Quick Check:

   Partial update = PATCH + Uniform Interface [OK]

Hint: Partial update uses PATCH and uniform interface [OK]

Common Mistakes:

• Using PUT for partial updates
• Confusing POST with PATCH
• Linking DELETE to updates