ETag for conditional requests in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the HTTP status code returned when the ETag matches?

Consider a REST API endpoint that returns a resource with an ETag header. A client sends a GET request with the header If-None-Match set to the current ETag value of the resource.

What HTTP status code will the server return if the resource has not changed?

Rest API

GET /resource HTTP/1.1
Host: example.com
If-None-Match: "abc123etag"

A 404 Not Found

B 200 OK with the full resource body

C 304 Not Modified with no body

D 500 Internal Server Error

💡 Hint

Think about what the server does when the resource has not changed since the client last fetched it.

If the ETag sent by the client matches the current ETag of the resource, the server responds with 304 Not Modified and does not send the resource body again. This saves bandwidth.

🧠 Conceptual

intermediate

What is the purpose of the ETag header in HTTP?

Choose the best description of what the ETag header does in HTTP responses.

A It provides a unique identifier for a specific version of a resource.

B It specifies the content type of the response body.

C It indicates the server's IP address.

D It sets the cache expiration time.

💡 Hint

ETag helps clients know if the resource has changed or not.

The ETag header is a unique string that identifies a specific version of a resource. Clients use it to check if the resource has changed since last fetched.

🔧 Debug

advanced

Why does this conditional GET request always return 200 OK instead of 304 Not Modified?

Given the following server code snippet handling ETag conditional requests, identify the bug causing the server to always return 200 OK even when the resource is unchanged.

Rest API

etag = get_current_etag(resource)
if request.headers.get('If-None-Match') == etag:
    return resource, 304, {'ETag': etag}
else:
    return resource, 200, {'ETag': etag}

A The server should return 304 status code when ETags match, not 200.

B The server is missing the ETag header in the response.

C The server should compare If-Match header instead of If-None-Match.

D The server should always return 404 if ETags don't match.

💡 Hint

Check the status code returned when the ETags match.

When the client's If-None-Match header matches the current ETag, the server must return 304 Not Modified status code without the resource body. Returning 200 always sends the full resource.

📝 Syntax

advanced

Which HTTP header syntax is correct for sending an ETag in a response?

Choose the correct syntax for the ETag header in an HTTP response.

A ETag: abc123etag

B ETag: 'abc123etag'

C ETag = "abc123etag"

D ETag: "abc123etag"

💡 Hint

ETag values are usually quoted strings.

The ETag header value must be enclosed in double quotes to be valid according to HTTP standards.

🚀 Application

expert

How many items are in the cache after these conditional requests with ETags?

A client makes three GET requests to a REST API for the same resource with ETag "v1". The server responds:

• First request: 200 OK with ETag "v1"
• Second request: If-None-Match: "v1" → 304 Not Modified
• Third request: If-None-Match: "v1" → 304 Not Modified

How many copies of the resource are stored in the client's cache after these requests?

A 2 copies

B 1 copy

C 0 copies

D 3 copies

💡 Hint

Think about how caching works with 304 responses.

The client caches one copy of the resource after the first 200 OK response. Subsequent 304 responses mean the cached copy is still valid, so no new copies are stored.