Client-server architecture in Rest API - Step-by-Step Execution

Concept Flow - Client-server architecture

Client sends request

↓

Server receives request

↓

Server processes request

↓

Server sends response

↓

Client receives response

↓

Client uses data

The client sends a request to the server, the server processes it and sends back a response, which the client then uses.

Execution Sample

Rest API

GET /api/data HTTP/1.1
Host: example.com

--- Server processes request ---
HTTP/1.1 200 OK
Content-Type: application/json

{"message": "Hello, client!"}

This shows a client sending a GET request and the server responding with a JSON message.

Execution Table

Step	Action	Details	Result
1	Client sends request	GET /api/data to server	Request sent over network
2	Server receives request	Server listens on port	Request accepted
3	Server processes request	Reads GET /api/data	Prepares JSON response
4	Server sends response	HTTP 200 OK with JSON	Response sent over network
5	Client receives response	Reads HTTP status and body	Data available to client
6	Client uses data	Parses JSON message	Displays or uses message
7	End	No more actions	Communication complete

💡 Communication ends after client receives and uses server response

Variable Tracker

Variable	Start	After Step 1	After Step 3	After Step 5	Final
request	None	GET /api/data	GET /api/data	GET /api/data	None (processed)
response	None	None	{"message": "Hello, client!"}	{"message": "Hello, client!"}	Used by client
client_data	None	None	None	{"message": "Hello, client!"}	Displayed or used

Key Moments - 3 Insights

Why does the client wait after sending the request?

The client waits because it needs the server's response to continue. See execution_table step 5 where the client receives the response.

What happens if the server does not send a response?

The client will keep waiting or timeout. The flow stops before step 5 in the execution_table, so no data is available to the client.

Is the server always running to receive requests?

Yes, the server listens continuously for requests as shown in step 2 of the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the server doing at step 3?

A Processing the request

B Receiving the request

C Sending the response

D Client parsing data

💡 Hint

Check the 'Action' and 'Details' columns at step 3 in the execution_table.

At which step does the client receive the server's response?

A Step 2

B Step 5

C Step 4

D Step 6

💡 Hint

Look for 'Client receives response' in the 'Action' column of the execution_table.

If the server sends a different JSON message, which variable in variable_tracker changes?

A request

B client_data

C response

D None

💡 Hint

The 'response' variable holds the server's message as shown in variable_tracker.

Concept Snapshot

Client-server architecture:
- Client sends request to server
- Server listens and processes request
- Server sends response back
- Client receives and uses response
- Communication happens over network
- Server runs continuously to serve clients

Full Transcript

Client-server architecture works by the client sending a request to the server. The server listens for requests and when it receives one, it processes it. Then the server sends back a response. The client waits for this response and uses the data it receives. This communication happens over a network. The server is always running to handle incoming requests. This flow ensures that clients can get data or services from servers anytime they ask.

Practice

1. In a client-server architecture, what is the main role of the client?

easy

A. To request data or services from the server

B. To store and manage data permanently

C. To control the network hardware

D. To provide power to the server

Solution

1. Step 1: Understand client role

   The client is the part of the system that asks for information or services.

2. Step 2: Differentiate from server role

   The server responds to client requests by sending data or services.

3. Final Answer:

   To request data or services from the server -> Option A

4. Quick Check:

   Client requests, server responds [OK]

Hint: Clients always ask; servers always answer [OK]

Common Mistakes:

• Confusing client with server
• Thinking client stores data permanently
• Assuming client controls network hardware

2. Which of the following is the correct way a client sends a request to a server in REST API?

easy

A. Using a SQL SELECT statement

B. Using an HTTP GET method

C. Using a FTP upload command

D. Using a local file read operation

Solution

1. Step 1: Identify REST API request methods

   REST APIs use HTTP methods like GET, POST, PUT, DELETE to communicate.

2. Step 2: Match method to client request

   GET is used by clients to request data from servers.

3. Final Answer:

   Using an HTTP GET method -> Option B

4. Quick Check:

   REST client requests use HTTP methods [OK]

Hint: REST clients use HTTP verbs like GET to ask [OK]

Common Mistakes:

• Confusing SQL with REST API
• Using FTP commands for REST requests
• Thinking local file reads send requests

3. What will the server respond with if a client sends a GET request to /users/123 and the user exists?

medium

A. A JSON object with user details

B. An error message saying 'User not found'

C. A redirect to the homepage

D. A blank page with no content

Solution

1. Step 1: Understand GET request to resource

   A GET request to /users/123 asks for user data with ID 123.

2. Step 2: Server response when user exists

   If user exists, server sends back user details, usually as JSON.

3. Final Answer:

   A JSON object with user details -> Option A

4. Quick Check:

   GET existing resource returns data [OK]

Hint: GET returns data if resource exists, else error [OK]

Common Mistakes:

• Assuming error if user exists
• Thinking GET causes redirect
• Expecting blank page on success

4. A client sends a POST request to create a new user, but the server responds with a 404 error. What is the most likely cause?

medium

A. The client sent too much data

B. The client used the wrong HTTP method

C. The server successfully created the user

D. The server URL endpoint is incorrect or missing

Solution

1. Step 1: Understand 404 error meaning

   404 means the requested URL or endpoint was not found on the server.

2. Step 2: Link error to cause

   If POST returns 404, likely the client sent request to wrong or missing URL.

3. Final Answer:

   The server URL endpoint is incorrect or missing -> Option D

4. Quick Check:

   404 means URL not found [OK]

Hint: 404 means wrong or missing URL endpoint [OK]

Common Mistakes:

• Confusing 404 with method error
• Assuming success on 404
• Thinking data size causes 404

5. You want to design a REST API where clients can update user info only if they provide a valid token. Which client-server architecture concept helps enforce this?

hard

A. Client directly modifying server database

B. Client caching data locally

C. Authentication and authorization on the server

D. Server sending data without checks

Solution

1. Step 1: Identify security need

   Allowing updates only with valid token means controlling access.

2. Step 2: Apply client-server security concept

   Authentication verifies identity; authorization controls permissions on server side.

3. Final Answer:

   Authentication and authorization on the server -> Option C

4. Quick Check:

   Access control = Authentication + Authorization [OK]

Hint: Use server-side auth to control client access [OK]

Common Mistakes:

• Thinking client caches control access
• Assuming server sends data without checks
• Believing client can modify database directly