REST constraints and principles in Rest API

Introduction

REST helps computers talk to each other in a simple and clear way. It makes web services easy to use and understand.

When building a web service that needs to be easy to use by many different apps.

When you want your service to be fast and reliable by using simple rules.

When you want to organize your data and actions clearly using web addresses.

When you want your service to work well on the internet with many users.

When you want to make your service easy to update and maintain over time.

Syntax

Rest API

REST uses these main rules:
1. Client-Server: Separate user interface and data storage.
2. Stateless: Each request has all info needed.
3. Cacheable: Responses can be stored to speed up.
4. Uniform Interface: Use standard ways to access resources.
5. Layered System: Use layers to organize the system.
6. Code on Demand (optional): Servers can send code to clients.

These rules help make web services simple and scalable.

Not all rules are always used, but most REST services follow many of them.

Examples

This shows the Uniform Interface and Stateless rules in action.

Rest API

GET /books/123

// Client asks server for book with ID 123 using a simple URL.

Shows how client-server and uniform interface work together.

Rest API

POST /books
{
  "title": "Learn REST",
  "author": "Jane"
}

// Client sends new book data to server to add it.

This is the Cacheable constraint helping speed up responses.

Rest API

Cache-Control: max-age=3600

// Server tells client it can save response for 1 hour.

Sample Program

This program asks a web service for a post using a simple URL. It shows stateless and uniform interface principles.

Rest API

import requests

# Simple example showing REST principles

# Stateless request: all info in URL
response = requests.get('https://jsonplaceholder.typicode.com/posts/1')

# Print response data
print(response.json())

Important Notes

Stateless means the server does not remember past requests from the client.

Uniform Interface means using standard HTTP methods like GET, POST, PUT, DELETE.

Cacheable responses help reduce network traffic and speed up apps.

Summary

REST uses simple rules to make web services easy and fast.

Key rules include statelessness, uniform interface, and caching.

Following REST helps apps work well on the internet and stay easy to maintain.

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