Content negotiation in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this HTTP Accept header handling code?

Consider a REST API server that supports JSON and XML responses. The server code snippet below processes the Accept header to decide the response format.

accept_header = 'application/xml,application/json;q=0.9'

if 'application/json' in accept_header:
    response = 'JSON response'
elif 'application/xml' in accept_header:
    response = 'XML response'
else:
    response = 'Default response'

What will be the value of response after running this code?

Rest API

accept_header = 'application/xml,application/json;q=0.9'

if 'application/json' in accept_header:
    response = 'JSON response'
elif 'application/xml' in accept_header:
    response = 'XML response'
else:
    response = 'Default response'

A JSON response

B XML response

C Default response

D Error: header parsing failed

💡 Hint

Check the order of if and elif conditions and how substring matching works.

The code checks if the string 'application/json' is anywhere in the accept_header. Since it is present (after the comma), the first if condition is true, so response is set to 'JSON response'. The elif is not checked after that.

🧠 Conceptual

intermediate

Which HTTP header is primarily used for content negotiation?

In REST APIs, clients specify the desired response format using a specific HTTP header. Which header is this?

A User-Agent

B Authorization

C Content-Type

D Accept

💡 Hint

It tells the server what media types the client can handle.

The Accept header is used by clients to tell the server which content types they prefer. The server uses this to perform content negotiation and respond accordingly.

❓ Predict Output

advanced

What is the output of this server content negotiation snippet?

Given the following Python code snippet simulating content negotiation, what will be printed?

accept_header = 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8'

if 'application/json' in accept_header:
    print('Send JSON')
elif 'application/xml' in accept_header:
    print('Send XML')
elif 'text/html' in accept_header:
    print('Send HTML')
else:
    print('Send default')

Rest API

accept_header = 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8'

if 'application/json' in accept_header:
    print('Send JSON')
elif 'application/xml' in accept_header:
    print('Send XML')
elif 'text/html' in accept_header:
    print('Send HTML')
else:
    print('Send default')

A Send XML

B Send HTML

C Send JSON

D Send default

💡 Hint

Check the order of conditions and presence of substrings in the header string.

The string 'application/json' is not present, so first if fails. The string 'application/xml' is present (with quality factor), so the second elif is true and prints 'Send XML'. The later conditions are not checked.

🔧 Debug

advanced

Why does this content negotiation code always return JSON?

Look at this Python code snippet:

accept_header = 'application/xml'

if accept_header == 'application/json' or 'application/xml':
    response = 'JSON response'
else:
    response = 'Default response'

Why does response always become 'JSON response' even when accept_header is 'application/xml'?

Rest API

accept_header = 'application/xml'

if accept_header == 'application/json' or 'application/xml':
    response = 'JSON response'
else:
    response = 'Default response'

A Because accept_header is overwritten before the if statement

B Because the code compares accept_header to both strings correctly

C Because 'application/xml' is always truthy, so the condition is always true

D Because the else block is never reached due to syntax error

💡 Hint

Look carefully at how the or operator is used in the condition.

The condition accept_header == 'application/json' or 'application/xml' is evaluated as (accept_header == 'application/json') or ('application/xml'). Since non-empty strings are always true in Python, the condition always evaluates to true, so response is always 'JSON response'.

🚀 Application

expert

How many media types will this content negotiation dictionary contain?

Given this Python dictionary comprehension that parses an Accept header string into media types and their quality factors:

accept_header = 'text/html,application/json;q=0.8,application/xml;q=0.9'

media_types = {part.split(';')[0]: float(part.split('q=')[1]) if 'q=' in part else 1.0 for part in accept_header.split(',')}

print(len(media_types))

What is the output of the print statement?

Rest API

accept_header = 'text/html,application/json;q=0.8,application/xml;q=0.9'

media_types = {part.split(';')[0]: float(part.split('q=')[1]) if 'q=' in part else 1.0 for part in accept_header.split(',')}

print(len(media_types))

A 2

B 3

C 1

D Raises ValueError

💡 Hint

Count how many unique media types are extracted from the header string.

The dictionary comprehension splits the header by commas, then for each part extracts the media type before any semicolon and assigns a quality factor (default 1.0 if missing). The header has three media types: 'text/html', 'application/json', and 'application/xml'. So the dictionary has 3 keys, and len(media_types) is 3.

Practice

1. What is the main purpose of content negotiation in REST APIs?

easy

A. To allow clients to specify the data format they want using the Accept header

B. To encrypt data between client and server

C. To authenticate users before sending data

D. To compress data for faster transfer

Solution

1. Step 1: Understand content negotiation role

   Content negotiation lets clients tell servers what data format they prefer.

2. Step 2: Identify how clients specify format

   Clients use the Accept header to communicate their preferred format.

3. Final Answer:

   To allow clients to specify the data format they want using the Accept header -> Option A

4. Quick Check:

   Content negotiation = Accept header usage [OK]

Hint: Remember: Accept header tells server your preferred format [OK]

Common Mistakes:

• Confusing content negotiation with authentication
• Thinking it compresses data
• Believing it encrypts data

2. Which of the following is the correct way to specify JSON format in the Accept header?

easy

A. Accept: application/xml

B. Accept: text/html

C. Accept: image/png

D. Accept: application/json

Solution

1. Step 1: Recall MIME types for common formats

   JSON format uses the MIME type 'application/json'.

2. Step 2: Match Accept header to JSON

   The correct Accept header for JSON is 'Accept: application/json'.

3. Final Answer:

   Accept: application/json -> Option D

4. Quick Check:

   JSON MIME type = application/json [OK]

Hint: JSON MIME type always is application/json in Accept header [OK]

Common Mistakes:

• Using text/html for JSON
• Confusing image/png with data formats
• Using application/xml instead of JSON

3. Given this HTTP request header:
Accept: application/xml, application/json;q=0.8
Which content type will the server most likely respond with?

medium

A. application/xml

B. application/pdf

C. text/html

D. application/json

Solution

1. Step 1: Understand quality values (q) in Accept header

   The q value shows preference; higher q means higher priority.

2. Step 2: Compare q values for application/xml and application/json

   application/xml has no q value, so defaults to 1. application/json has q=0.8, lower priority.

3. Final Answer:

   application/xml -> Option A

4. Quick Check:

   Higher q or default 1 wins = application/xml [OK]

Hint: No q means 1.0, highest priority wins [OK]

Common Mistakes:

• Ignoring q values and picking lower priority
• Choosing JSON because it appears second
• Selecting unrelated content types

4. A server returns a 406 Not Acceptable error. What is the most likely cause related to content negotiation?

medium

A. Server failed to authenticate the client

B. Client requested a format the server cannot provide

C. Client sent an invalid HTTP method

D. Server ran out of memory

Solution

1. Step 1: Understand HTTP 406 status meaning

   406 means server cannot provide a response matching the Accept header.

2. Step 2: Link 406 to content negotiation failure

   If client requests unsupported format, server responds 406 Not Acceptable.

3. Final Answer:

   Client requested a format the server cannot provide -> Option B

4. Quick Check:

   406 = unsupported requested format [OK]

Hint: 406 means no matching format found for Accept header [OK]

Common Mistakes:

• Confusing 406 with authentication errors
• Thinking 406 means server error
• Assuming 406 is about HTTP methods

5. You want your REST API to support both JSON and XML responses. Which server-side approach correctly implements content negotiation?

hard

A. Ignore the Accept header and always send JSON

B. Send both JSON and XML in the same response body

C. Check the Accept header and respond with JSON or XML accordingly

D. Respond with XML only if the client sends a custom header

Solution

1. Step 1: Understand content negotiation best practice

   The server should read the Accept header to decide response format.

2. Step 2: Choose approach matching client preference

   Responding with JSON or XML based on Accept header is correct behavior.

3. Final Answer:

   Check the Accept header and respond with JSON or XML accordingly -> Option C

4. Quick Check:

   Content negotiation = respond per Accept header [OK]

Hint: Always respect Accept header to choose response format [OK]

Common Mistakes:

• Ignoring Accept header and hardcoding response
• Sending multiple formats in one response
• Using unrelated custom headers for format choice