Response headers (Cache-Control, ETag) in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this HTTP response header?

Consider a REST API response with the following headers:

Cache-Control: max-age=3600, must-revalidate
ETag: "abc123"

If a client sends a request with header If-None-Match: "abc123", what will the server most likely respond with?

A HTTP 304 Not Modified with no body

B HTTP 200 OK with full response body

C HTTP 500 Internal Server Error

D HTTP 403 Forbidden

💡 Hint

ETag helps the server decide if the resource has changed.

If the If-None-Match header matches the current ETag, the server returns 304 Not Modified without the body to save bandwidth.

🧠 Conceptual

intermediate

Which Cache-Control directive forces revalidation every time?

Which Cache-Control directive ensures that the client must check with the server before using a cached response?

A public

B max-age=3600

C no-cache

D private

💡 Hint

Think about which directive means 'always check before use'.

no-cache means the client must revalidate with the server before using the cached response, even if it is fresh.

❓ Predict Output

advanced

What is the effect of this Cache-Control header?

Given this response header:

Cache-Control: private, max-age=0, must-revalidate

What does this mean for caching behavior?

A The response is not cached anywhere

B The response is cached by any cache and never revalidated

C The response is publicly cached and served without revalidation for 1 hour

D The response is cached only by the browser and must be revalidated before each use

💡 Hint

Consider what private and max-age=0 imply together.

private means only the browser caches it, max-age=0 means it is immediately stale, and must-revalidate forces revalidation before reuse.

❓ Predict Output

advanced

What error occurs with this ETag usage?

Consider this server code snippet that sets ETag header incorrectly:

response.headers['ETag'] = 12345

What error or behavior will this cause?

A TypeError because header value must be a string

B SyntaxError due to invalid header format

C The ETag header is ignored silently

D The server sends ETag as a string "12345" without error

💡 Hint

HTTP headers must be strings.

Setting a non-string value for a header usually raises a TypeError in most server frameworks.

🧠 Conceptual

expert

How does ETag improve REST API efficiency?

Which statement best explains how ETag headers improve REST API efficiency?

A ETag forces servers to always send full responses to clients

B ETag enables clients to send conditional requests to avoid downloading unchanged resources

C ETag allows clients to cache responses indefinitely without revalidation

D ETag disables caching and forces fresh data every time

💡 Hint

Think about how clients can save bandwidth using ETag.

ETag lets clients send If-None-Match headers so servers can respond with 304 Not Modified if the resource is unchanged, saving bandwidth.