Validation-based caching in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this HTTP cache validation example?

Consider a REST API that uses ETag headers for validation-based caching. The server responds with an ETag value "abc123" for a resource. A client sends a GET request with header If-None-Match: "abc123". What will the server respond?

Rest API

HTTP/1.1 304 Not Modified
ETag: "abc123"

A HTTP 404 Not Found

B HTTP 500 Internal Server Error

C HTTP 304 Not Modified with no body

D HTTP 200 OK with full resource body

💡 Hint

Think about what the server does when the client's ETag matches the current resource's ETag.

When the client's If-None-Match header matches the server's current ETag, the server responds with 304 Not Modified and no body, telling the client to use its cached copy.

🧠 Conceptual

intermediate

Which HTTP header is used by clients to validate cached resources?

In validation-based caching, clients send a header to check if their cached resource is still valid. Which header is it?

A If-Modified-Since

B Cache-Control

C Authorization

D Content-Type

💡 Hint

It is a header that asks the server if the resource has changed since a certain date.

The If-Modified-Since header is sent by clients to ask the server if the resource has changed since the given date. If not, the server can respond with 304 Not Modified.

🔧 Debug

advanced

Why does this validation-based caching code always return full data instead of 304?

Given this simplified server code snippet in Python Flask, why does the server never return 304 Not Modified?

Rest API

from flask import Flask, request, jsonify, make_response
app = Flask(__name__)

@app.route('/data')
def data():
    etag = '"xyz789"'
    if request.headers.get('If-None-Match') == etag:
        return make_response('', 304)
    response = make_response(jsonify({'value': 42}))
    response.headers['ETag'] = etag
    return response

A The response body is always sent regardless of ETag

B The server does not check the If-Modified-Since header

C The ETag header is not set in the response

D The If-None-Match header is compared incorrectly (missing quotes)

💡 Hint

Check how the ETag value is formatted and compared with the header.

The ETag header value is usually quoted (e.g., "xyz789"), but the code compares the raw string without quotes to the header value which includes quotes. This causes the comparison to fail and the server always sends full data.

📝 Syntax

advanced

Which option correctly sets the ETag header in this Node.js Express code?

Choose the correct way to set the ETag header in an Express.js response.

Rest API

app.get('/resource', (req, res) => {
  const etagValue = 'abc123';
  // Set ETag header here
  res.send('Hello World');
});

A res.set('ETag', etagValue);

B res.setHeader('etag', etagValue);

C res.header('ETag', etagValue);

D res.etag = etagValue;

💡 Hint

Express response objects have a method to set headers with case-insensitive names.

The res.set() method is the correct way to set headers in Express. It is case-insensitive and sets the header properly. res.header() is an alias but less recommended. res.setHeader() is not a method on Express response. res.etag is not a valid property.

🚀 Application

expert

How many items are cached when using validation-based caching with ETag and If-None-Match?

A REST API serves 3 different resources, each with unique ETags. A client caches all 3 resources and sends requests with If-None-Match headers for each. How many resources will the client avoid downloading if all ETags match?

A 0

B 3

C 2

D 1

💡 Hint

If the client's ETag matches the server's, the server responds with 304 Not Modified.

If all 3 ETags match, the server responds with 304 Not Modified for all 3 resources, so the client avoids downloading all 3 again.