404 Not Found in Rest API - Step-by-Step Execution

Concept Flow - 404 Not Found

Client sends HTTP request

↓

Server receives request

↓

Check if resource exists

↓

Return resource

↓

Client receives response

The client sends a request; the server checks if the resource exists. If not, it returns a 404 Not Found response.

Execution Sample

Rest API

GET /api/users/123 HTTP/1.1
Host: example.com

Response:
HTTP/1.1 404 Not Found
Content-Type: application/json

{"error":"User not found"}

A client requests a user that does not exist; the server responds with 404 Not Found and an error message.

Execution Table

Step	Action	Resource Exists?	Response Status	Response Body
1	Client sends GET /api/users/123	Unknown	Waiting	None
2	Server checks resource	No	Determined	None
3	Server sends response	No	404 Not Found	{"error":"User not found"}
4	Client receives response	No	404 Not Found	{"error":"User not found"}

💡 Resource does not exist, so server returns 404 Not Found response.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
resource_exists	Unknown	Unknown	No	No	No
response_status	None	Waiting	Determined	404 Not Found	404 Not Found
response_body	None	None	None	{"error":"User not found"}	{"error":"User not found"}

Key Moments - 2 Insights

Why does the server return 404 Not Found instead of the requested data?

Because the server checked and found that the requested resource does not exist, as shown in step 2 and 3 of the execution table.

Is 404 Not Found an error in the client request or server problem?

404 Not Found means the client requested something that isn't there; it's not a server error but a missing resource, as seen in the response status in step 3.

Visual Quiz - 3 Questions

Look at the execution table, what is the response status at step 3?

A 200 OK

B 404 Not Found

C 500 Internal Server Error

D 301 Moved Permanently

💡 Hint

Check the 'Response Status' column at step 3 in the execution table.

At which step does the server determine the resource does not exist?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Resource Exists?' column in the execution table.

If the resource existed, how would the response status change in the table?

A It would change to 200 OK

B It would change to 500 Internal Server Error

C It would stay 404 Not Found

D It would be 301 Moved Permanently

💡 Hint

Think about what status code means success versus not found.

Concept Snapshot

404 Not Found:
- HTTP status code meaning resource not found
- Server checks if resource exists
- If missing, returns 404 with error message
- Client receives 404 and knows resource is missing
- Common in REST APIs for invalid URLs or IDs

Full Transcript

When a client sends a request to a server, the server checks if the requested resource exists. If it does not, the server responds with a 404 Not Found status code and an error message. This tells the client that the resource is missing, not that the server failed. The client can then handle this response appropriately, such as showing a 'not found' message to the user.