Response headers (Cache-Control, ETag) in Rest API - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the Cache-Control header in HTTP responses?

The Cache-Control header tells browsers and other clients how to store and reuse the response. It controls caching behavior like how long to keep the data or whether to cache it at all.

beginner

Explain what an ETag header does in HTTP responses.

An ETag is a unique identifier for a specific version of a resource. It helps clients check if the resource has changed since the last request, enabling efficient caching and conditional requests.

intermediate

What does the directive Cache-Control: no-cache mean?

It means the client must revalidate with the server before using a cached copy. The cached response can be stored but must be checked for freshness before reuse.

intermediate

How does the client use the If-None-Match header with ETag?

The client sends If-None-Match with the ETag value it has. The server compares it to the current ETag. If they match, the server replies with 304 Not Modified, saving bandwidth.

beginner

Why are Cache-Control and ETag headers important for REST APIs?

They improve performance by reducing unnecessary data transfer and server load. Cache-Control manages how responses are cached, and ETag helps detect changes to resources efficiently.

What does the Cache-Control: max-age=3600 header instruct the client to do?

A Immediately revalidate the response

B Never cache the response

C Cache the response forever

D Cache the response for 3600 seconds before revalidating

The max-age=3600 directive tells the client to consider the cached response fresh for 3600 seconds (1 hour) before checking with the server again.

Which header is used by the client to tell the server the version of the resource it has cached?

A Cache-Control

B If-None-Match

C ETag

D Last-Modified

If-None-Match is sent by the client with the ETag value to ask the server if the resource has changed.

What response status code does the server send if the resource has not changed when using ETag validation?

A 200 OK

B 404 Not Found

C 304 Not Modified

D 500 Internal Server Error

The server sends 304 Not Modified to tell the client the cached version is still valid.

If a response has Cache-Control: no-store, what does it mean?

A The response must not be cached anywhere

B The response can be cached indefinitely

C The response can be cached but must be revalidated

D The response is private

no-store means the response must not be stored in any cache.

Which header helps reduce bandwidth by avoiding sending unchanged resources?

A ETag

B Cache-Control

C Content-Type

D Authorization

ETag allows the server to tell the client if the resource has changed, avoiding resending unchanged data.

Describe how Cache-Control and ETag headers work together to improve API performance.

Think about caching rules and how the client checks if data changed.

Explain the difference between Cache-Control: no-cache and Cache-Control: no-store.

Focus on whether caching is allowed or not.