Response headers (Cache-Control, ETag) in Rest API - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the Cache-Control header to no-cache.

Rest API

response.headers['Cache-Control'] = '[1]'

Drag options to blanks, or click blank then click option'

Ano-cache

Bmax-age=3600

Cprivate

Dpublic

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'max-age=3600' which allows caching for 1 hour.

Using 'public' which allows caching by any cache.

The Cache-Control header value no-cache tells browsers not to cache the response.

2fill in blank

medium

Complete the code to set the ETag header with a unique identifier.

Rest API

response.headers['ETag'] = '[1]'

Drag options to blanks, or click blank then click option'

A12345

B"12345"

Cetag_value

D'12345'

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting the ETag value.

Using single quotes instead of double quotes.

The ETag value must be a quoted string, so "12345" is correct.

3fill in blank

hard

Fix the error in setting Cache-Control to allow caching for 10 minutes.

Rest API

response.headers['Cache-Control'] = '[1]'

Drag options to blanks, or click blank then click option'

Amax-age=600

Bmax_age=600

Cmaxage=600

Dmax-age:600

Attempts:

3 left

💡 Hint

Common Mistakes

Using underscore instead of dash.

Using colon instead of equals sign.

The correct syntax for Cache-Control max age is max-age=600 (600 seconds = 10 minutes).

4fill in blank

hard

Fill both blanks to set Cache-Control to private and ETag to "abc123".

Rest API

response.headers['Cache-Control'] = '[1]'
response.headers['ETag'] = '[2]'

Drag options to blanks, or click blank then click option'

Aprivate

B"abc123"

Cpublic

Dabc123

Attempts:

3 left

💡 Hint

Common Mistakes

Setting ETag without quotes.

Using 'public' instead of 'private' for Cache-Control.

Cache-Control should be set to private to restrict caching to a single user.
ETag must be a quoted string like "abc123".

5fill in blank

hard

Fill all three blanks to set Cache-Control to no-store, ETag to "xyz789", and add a custom header X-Custom.

Rest API

response.headers['Cache-Control'] = '[1]'
response.headers['ETag'] = '[2]'
response.headers['X-Custom'] = '[3]'

Drag options to blanks, or click blank then click option'

Ano-store

B"xyz789"

Ccustom-value

Dno-cache

Attempts:

3 left

💡 Hint

Common Mistakes

Using no-cache instead of no-store.

Not quoting the ETag value.

Leaving custom header value empty.

no-store tells browsers not to store any cache.
ETag must be quoted like "xyz789".
Custom headers can have any string value like custom-value.

Practice

1. What is the main purpose of the Cache-Control header in an HTTP response?

easy

A. To indicate the response content type

B. To encrypt the response data for security

C. To specify the server's IP address

D. To tell browsers how long to keep the response data

Solution

1. Step 1: Understand the role of Cache-Control

   The Cache-Control header instructs browsers and caches how long they can store the response data before requesting it again.

2. Step 2: Compare options with Cache-Control purpose

   Only To tell browsers how long to keep the response data correctly describes this behavior. Other options describe unrelated functions.

3. Final Answer:

   To tell browsers how long to keep the response data -> Option D

4. Quick Check:

   Cache-Control = Duration for caching [OK]

Hint: Cache-Control controls data storage time in browsers [OK]

Common Mistakes:

• Confusing Cache-Control with security headers
• Thinking Cache-Control sets content type
• Assuming Cache-Control reveals server info

2. Which of the following is the correct syntax to set a Cache-Control header to cache content for 3600 seconds?

easy

A. "Cache-Control: max-age=3600"

B. "Cache-Control: timeout=3600"

C. "Cache-Control: expires=3600"

D. "Cache-Control: duration=3600"

Solution

1. Step 1: Recall Cache-Control max-age syntax

   The correct way to specify caching time in seconds is using max-age=seconds.

2. Step 2: Check each option's correctness

   Only "Cache-Control: max-age=3600" uses max-age=3600, which is valid. Others use invalid directives.

3. Final Answer:

   "Cache-Control: max-age=3600" -> Option A

4. Quick Check:

   max-age sets cache time [OK]

Hint: Use max-age to set cache time in seconds [OK]

Common Mistakes:

• Using 'timeout' instead of 'max-age'
• Confusing Cache-Control with Expires header syntax
• Using unsupported directives like 'duration'

3. Given this HTTP response header snippet:

Cache-Control: max-age=0, must-revalidate
ETag: "abc123"

What happens when the browser sends a request with header If-None-Match: "abc123"?

medium

A. Server returns 304 Not Modified if content unchanged

B. Server returns full content ignoring ETag

C. Server returns 500 Internal Server Error

D. Server always returns 200 OK with new ETag

Solution

1. Step 1: Understand ETag and If-None-Match interaction

   The ETag header is a unique identifier for the content version. The browser sends If-None-Match with the ETag value to check if content changed.

2. Step 2: Interpret Cache-Control and server response

   With max-age=0 and must-revalidate, the browser asks server to validate content. If ETag matches, server responds with 304 Not Modified, saving bandwidth.

3. Final Answer:

   Server returns 304 Not Modified if content unchanged -> Option A

4. Quick Check:

   ETag + If-None-Match = 304 if unchanged [OK]

Hint: ETag + If-None-Match = 304 Not Modified if same [OK]

Common Mistakes:

• Assuming server always sends full content
• Confusing 304 with error codes
• Ignoring Cache-Control directives

4. A developer sets the response header as Cache-Control: max-age=abc. What is the likely result?

medium

A. The browser caches the response for 'abc' seconds

B. The server returns a syntax error

C. The browser ignores the Cache-Control header and does not cache

D. The browser caches the response indefinitely

Solution

1. Step 1: Analyze max-age value validity

   The max-age directive requires a numeric value in seconds. 'abc' is invalid.

2. Step 2: Understand browser behavior on invalid Cache-Control

   Browsers typically ignore invalid Cache-Control headers and treat the response as non-cacheable.

3. Final Answer:

   The browser ignores the Cache-Control header and does not cache -> Option C

4. Quick Check:

   Invalid max-age causes no caching [OK]

Hint: max-age must be a number, else ignored [OK]

Common Mistakes:

• Thinking server returns error for header syntax
• Assuming browser caches with invalid value
• Confusing max-age with other headers

5. You want to optimize a REST API to reduce bandwidth by sending full data only when it changes. Which combination of headers should you use in the response?

hard

A. Cache-Control: max-age=0 and no ETag

B. Cache-Control: no-cache and ETag with unique value

C. Cache-Control: no-store and no ETag

D. Cache-Control: max-age=3600 and no ETag

Solution

1. Step 1: Identify headers that enable conditional requests

   ETag provides a unique identifier for content versions, allowing clients to ask if content changed.

2. Step 2: Understand Cache-Control no-cache directive

   no-cache forces the browser to validate with the server before using cached data, ensuring fresh content without unnecessary full data transfer.

3. Step 3: Evaluate other options

   Options without ETag cannot validate changes efficiently; no-store disables caching; max-age=0 without ETag disables validation.

4. Final Answer:

   Cache-Control: no-cache and ETag with unique value -> Option B

5. Quick Check:

   no-cache + ETag = bandwidth saving [OK]

Hint: Use no-cache with ETag for efficient validation [OK]

Common Mistakes:

• Omitting ETag disables change detection
• Using no-store disables caching entirely
• Assuming max-age alone reduces bandwidth