If-None-Match and 304 responses in Rest API - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the If-None-Match HTTP header?

The If-None-Match header is used by clients to make a conditional request. It sends an ETag value to the server, asking to return the resource only if it has changed. If the resource's ETag matches the value, the server can respond with a 304 Not Modified status, saving bandwidth.

beginner

What does a 304 Not Modified response mean?

A 304 Not Modified response means the requested resource has not changed since the last time the client requested it. The server tells the client to use its cached version, so no new data is sent.

intermediate

How does the server decide to send a 304 response when it receives an If-None-Match header?

The server compares the ETag value sent in the If-None-Match header with the current ETag of the resource. If they match, it means the resource has not changed, so the server sends a 304 Not Modified response without the resource body.

beginner

Why is using If-None-Match and 304 responses beneficial?

They reduce data transfer and improve performance by avoiding sending the full resource when it hasn't changed. This saves bandwidth and speeds up loading times for users.

beginner

What is an ETag in the context of HTTP caching?

An ETag (Entity Tag) is a unique identifier assigned by the server to a specific version of a resource. It helps clients and servers determine if the resource has changed since the last request.

What does the If-None-Match header contain?

A The server's status code

B The full content of the resource

C An ETag value from a previous response

D The client's IP address

The If-None-Match header contains an ETag value that the client received earlier to check if the resource has changed.

What status code does the server send if the resource has NOT changed?

A 304 Not Modified

B 404 Not Found

C 200 OK

D 500 Internal Server Error

The server sends a 304 Not Modified status to tell the client to use its cached copy.

Why is a 304 response useful?

A It forces the client to reload the page

B It reduces bandwidth by not sending the resource again

C It deletes the cached resource

D It indicates a server error

A 304 response saves bandwidth by telling the client the resource hasn't changed, so no need to resend it.

What happens if the ETag in If-None-Match does NOT match the current resource ETag?

A Server sends 200 OK with the new resource

B Server sends 304 Not Modified

C Server sends 404 Not Found

D Server closes the connection

If the ETags don't match, the server sends the updated resource with a 200 OK status.

Which header does the server include in the response to identify the resource version?

A Content-Type

B Cache-Control

C Authorization

D ETag

The server includes the ETag header to identify the current version of the resource.

Explain how the If-None-Match header and 304 Not Modified response work together to optimize web requests.

Think about how the client checks if the resource changed before downloading it again.

Describe what an ETag is and why it is important in HTTP caching.

Consider how the server and client know if the resource has changed.