REST constraints and principles in Rest API - Step-by-Step Execution

Concept Flow - REST constraints and principles

Client sends request

↓

Stateless interaction

↓

Cacheable response

↓

Uniform interface

↓

Layered system

↓

Code on demand (optional)

↓

Server processes request and sends response

↓

Client receives response

This flow shows how REST principles guide the interaction between client and server step-by-step.

Execution Sample

Rest API

GET /books/123 HTTP/1.1
Host: example.com
Accept: application/json

A client requests a book resource using a stateless GET request with a uniform interface.

Execution Table

Step	Action	Description	Result
1	Client sends GET request	Client requests /books/123 with headers	Request sent statelessly
2	Server receives request	Server processes request without session info	Stateless processing
3	Server checks cache	Server looks for cached response	Cache hit or miss
4	Server generates response	Server creates JSON response for book 123	Response ready
5	Server sends response	Response sent with cache headers	Client receives response
6	Client processes response	Client uses uniform interface to parse JSON	Resource data available
7	Optional: Code on demand	Server may send executable code (e.g., JavaScript)	Client may execute code
8	End	Request-response cycle complete	Interaction finished

💡 Request-response cycle ends after client receives and processes response.

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 5	Final
Request	Not sent	Received by server	Processed	Sent response	Complete
Response	None	None	Generated	Sent to client	Received by client
Cache status	Unknown	Checked	Hit or Miss	Used if hit	Finalized

Key Moments - 3 Insights

Why is REST called stateless?

Because each request from client to server contains all information needed, the server does not store client session data between requests, as shown in execution_table step 2.

What does 'uniform interface' mean in REST?

It means the client and server communicate using a standard way like HTTP methods and resource URIs, so clients can understand responses consistently, as seen in step 6.

How does caching improve REST performance?

Caching lets servers or clients reuse previous responses to avoid repeated processing, shown in step 3 where cache is checked before generating a new response.

Visual Quiz - 3 Questions

Look at the execution_table, at which step does the server check for cached data?

A Step 3

B Step 2

C Step 5

D Step 6

💡 Hint

Refer to the 'Action' column in execution_table row 3.

According to variable_tracker, what is the state of 'Response' after Step 4?

A Received by client

B None

C Generated

D Sent to client

💡 Hint

Check the 'Response' row under 'After Step 4' in variable_tracker.

If the server stored client session data, which REST constraint would be violated?

A Cacheable

B Stateless

C Layered system

D Uniform interface

💡 Hint

See key_moments about statelessness and execution_table step 2.

Concept Snapshot

REST constraints guide client-server communication:
- Stateless: no client context stored on server
- Cacheable: responses can be cached
- Uniform interface: standard methods and URIs
- Layered system: intermediaries possible
- Code on demand: optional executable code
These principles make APIs scalable and simple.

Full Transcript

REST constraints and principles define how clients and servers communicate over the web. The client sends a request with all needed info (stateless). The server processes it without remembering past requests. It may check cache to reuse responses. The communication uses a uniform interface like HTTP methods and URIs. Responses can be cached to improve speed. Servers can be layered with intermediaries. Optionally, servers can send executable code to clients. This flow ensures simple, scalable, and reliable web APIs.

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