If-None-Match and 304 responses in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What does the If-None-Match header do in an HTTP request?

Choose the best description of the purpose of the If-None-Match header in an HTTP request.

A It tells the server to send the resource only if the ETag does not match the given value.

B It forces the server to ignore caching and always send the full resource.

C It instructs the server to send a 500 Internal Server Error if the ETag matches.

D It requests the server to delete the resource if the ETag matches the given value.

💡 Hint

Think about how caching works and when a server decides to send a full response or not.

The If-None-Match header is used to make a request conditional. It contains an ETag value, and the server compares it with the current ETag of the resource. If they match, the server responds with 304 Not Modified to save bandwidth by not sending the resource again.

❓ Predict Output

intermediate

What is the HTTP status code returned when If-None-Match matches the resource ETag?

Given a client sends a request with If-None-Match header matching the current ETag of the resource, what status code does the server respond with?

A 200 OK

B 412 Precondition Failed

C 404 Not Found

D 304 Not Modified

💡 Hint

This status code means the resource has not changed since last fetched.

When the ETag in If-None-Match matches the current resource ETag, the server returns 304 Not Modified to indicate the cached version is still valid.

🔧 Debug

advanced

Why does this server code always return 200 OK even when ETags match?

Consider this pseudocode for handling If-None-Match:

if request.headers['If-None-Match'] == resource.etag:
    return 200, resource.data
else:
    return 304, None

Why is this incorrect?

A Because it returns 200 OK when ETags match instead of 304 Not Modified.

B Because it does not check if the resource exists before comparing ETags.

C Because it compares the wrong headers; should use If-Match instead.

D Because it returns 304 Not Modified with resource data, which is invalid.

💡 Hint

Think about what status code means the resource has not changed.

The code returns 200 OK with the resource data when the ETags match, but it should return 304 Not Modified with no body to save bandwidth.

📝 Syntax

advanced

Which HTTP response header is required with a 304 Not Modified response?

When a server responds with 304 Not Modified, which header must it include to comply with HTTP standards?

A Content-Length

B ETag

C Content-Type

D Authorization

💡 Hint

This header helps the client validate the cached resource.

The ETag header must be included in a 304 response to indicate the current version of the resource.

🚀 Application

expert

How many bytes are sent in the response body when a 304 Not Modified is returned?

A client sends a GET request with an If-None-Match header matching the resource's ETag. The server responds with 304 Not Modified. How many bytes are sent in the response body?

A Only the ETag string bytes

B The full size of the resource in bytes

C Zero bytes (empty body)

D A small JSON message explaining the status

💡 Hint

304 means the client should use its cached copy without new data.

A 304 Not Modified response has no body. The server sends headers only, so zero bytes are sent in the body.