Link headers for navigation in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this HTTP Link header parsing?

Given the HTTP Link header below, what is the value of the 'next' URL extracted?

Rest API

Link: <https://api.example.com/items?page=2>; rel="next", <https://api.example.com/items?page=5>; rel="last"

A https://api.example.com/items?page=1

B https://api.example.com/items?page=5

C https://api.example.com/items?page=2

D https://api.example.com/items?page=3

💡 Hint

Look for the rel="next" link in the header.

The Link header contains multiple URLs with rel attributes. The URL with rel="next" is the one for the next page, which is page=2.

🧠 Conceptual

intermediate

What is the purpose of the 'rel' attribute in Link headers?

In HTTP Link headers used for navigation, what does the 'rel' attribute specify?

A It sets the cache expiration time for the link.

B It specifies the HTTP method to use for the link.

C It indicates the content type of the linked resource.

D It defines the relationship type of the linked resource to the current resource.

💡 Hint

Think about how the client knows what the link means.

The 'rel' attribute describes the relationship between the current resource and the linked resource, such as 'next', 'prev', or 'last'.

🔧 Debug

advanced

Why does this Link header cause a parsing error?

Consider this Link header: Link: rel="next", ; rel="last" Why does it cause a parsing error?

A Because the first link is missing a semicolon before rel attribute.

B Because the rel attribute value is not capitalized.

C Because the URLs are not enclosed in quotes.

D Because the Link header must have only one URL.

💡 Hint

Check the syntax between the URL and the rel attribute.

Each link must separate the URL and its parameters with a semicolon. The first link misses the semicolon before rel="next".

🚀 Application

advanced

How to include multiple navigation links in a single Link header?

You want to provide 'first', 'prev', 'next', and 'last' navigation links in one HTTP Link header. Which is the correct format?

A Link: <url1>; rel="first", <url2>; rel="prev", <url3>; rel="next", <url4>; rel="last"

B Link: <url1> rel=first, <url2> rel=prev, <url3> rel=next, <url4> rel=last

C Link: <url1>; rel="first" <url2>; rel="prev" <url3>; rel="next" <url4>; rel="last"

D Link: rel="first" <url1>, rel="prev" <url2>, rel="next" <url3>, rel="last" <url4>

💡 Hint

Look for correct separators and syntax between links.

Multiple links in a Link header are separated by commas, and each link's parameters follow a semicolon after the URL.

❓ Predict Output

expert

What is the output of this Python code parsing Link headers?

Given the Python code below that parses an HTTP Link header, what is the output printed?

Rest API

link_header = '<https://api.example.com/items?page=3>; rel="next", <https://api.example.com/items?page=1>; rel="prev"'

links = {}
for part in link_header.split(','):
    url_part, rel_part = part.strip().split(';')
    url = url_part.strip()[1:-1]
    rel = rel_part.strip().split('=')[1].strip('"')
    links[rel] = url

print(links.get('prev'))

A https://api.example.com/items?page=3

B https://api.example.com/items?page=1

C None

D KeyError

💡 Hint

Check how the dictionary keys are assigned and what is printed.

The code splits the header by commas, extracts URLs and rel values, stores them in a dictionary, then prints the URL for 'prev'.

Practice

1. What is the main purpose of using Link headers in REST APIs?

easy

A. To provide URLs for navigating between related API pages or resources

B. To send authentication tokens securely

C. To specify the content type of the response

D. To compress the API response data

Solution

1. Step 1: Understand the role of Link headers

   Link headers are used to provide URLs that help clients navigate between related pages or resources in an API.

2. Step 2: Compare with other header uses

   Authentication tokens, content types, and compression are handled by other headers, not Link headers.

3. Final Answer:

   To provide URLs for navigating between related API pages or resources -> Option A

4. Quick Check:

   Link headers = navigation URLs [OK]

Hint: Link headers always give navigation URLs, not data or tokens [OK]

Common Mistakes:

• Confusing Link headers with authentication headers
• Thinking Link headers specify content type
• Assuming Link headers compress data

2. Which of the following is the correct syntax for a Link header indicating the next page URL?

easy

A. Link: next=

B. Link: ; rel="next"

C. Link: rel="next"

D. Link: next

Solution

1. Step 1: Recall Link header format

   The correct format is: Link: <URL>; rel="relation" where URL is in angle brackets and rel specifies the link role.

2. Step 2: Check each option

   Link: ; rel="next" matches the correct syntax with URL in <> and rel="next". Others have incorrect order or missing punctuation.

3. Final Answer:

   Link: <https://api.example.com/items?page=2>; rel="next" -> Option B

4. Quick Check:

   Link header syntax = <URL>; rel="next" [OK]

Hint: Link header always uses angle brackets for URLs and rel="next" [OK]

Common Mistakes:

• Placing rel before the URL
• Omitting angle brackets around URL
• Using incorrect separators or missing semicolons

3. Given the following HTTP response header:

Link: ; rel="next", ; rel="prev"

What URL should the client use to get the previous page?

medium

A. https://api.example.com/items?page=3

B. https://api.example.com/items?page=4

C. https://api.example.com/items?page=1

D. https://api.example.com/items?page=2

Solution

1. Step 1: Identify the rel attribute for previous page

   The Link header with rel="prev" indicates the URL for the previous page, which is https://api.example.com/items?page=1.

2. Step 2: Match the URL to the correct option

   https://api.example.com/items?page=1 matches the URL with rel="prev" exactly.

3. Final Answer:

   https://api.example.com/items?page=1 -> Option C

4. Quick Check:

   rel="prev" URL = page=1 [OK]

Hint: Look for rel="prev" to find previous page URL [OK]

Common Mistakes:

• Confusing rel="next" with rel="prev"
• Choosing a page number not in the Link header
• Ignoring the rel attribute

4. You receive this Link header:

Link: https://api.example.com/items?page=2; rel="next"

What is wrong with this header?

medium

A. The URL should not contain query parameters

B. The rel attribute should be capitalized

C. The semicolon should be a comma

D. The URL is missing angle brackets <>

Solution

1. Step 1: Check URL formatting in Link header

   URLs in Link headers must be enclosed in angle brackets <> to be valid.

2. Step 2: Verify other parts

   rel attribute is case-insensitive and semicolon is correct separator; query parameters are allowed.

3. Final Answer:

   The URL is missing angle brackets <> -> Option D

4. Quick Check:

   URL must be inside <> in Link header [OK]

Hint: Always put URLs in angle brackets in Link headers [OK]

Common Mistakes:

• Omitting angle brackets around URLs
• Changing semicolon to comma incorrectly
• Thinking rel attribute is case sensitive

5. You want to provide navigation links for first, previous, next, and last pages in your API response. Which of the following Link header values correctly includes all these relations?

hard

A. Link: ; rel="first", ; rel="prev", ; rel="next", ; rel="last"

B. Link: ; rel first, ; rel=prev, ; rel=next, ; rel=last

C. Link: first, prev, next, last

D. Link: rel="first" , rel="prev" , rel="next" , rel="last"

Solution

1. Step 1: Confirm correct Link header syntax

   The correct format is Link: <URL>; rel="relation", <URL>; rel="relation" etc., with URL in <>, semicolon, rel= with value in quotes.

2. Step 2: Evaluate each option

   Link: <https://api.example.com/items?page=1>; rel="first", <https://api.example.com/items?page=2>; rel="prev" etc. matches exactly. The similar one has 'rel first' (missing = after rel). Others miss semicolons, have rel before URL, or wrong separators.

3. Final Answer:

   Link: <https://api.example.com/items?page=1>; rel="first", <https://api.example.com/items?page=2>; rel="prev", <https://api.example.com/items?page=4>; rel="next", <https://api.example.com/items?page=10>; rel="last" -> Option A

4. Quick Check:

   All links with <> and rel="relation" separated by commas [OK]

Hint: Use <URL>; rel="relation" for each link, separated by commas [OK]

Common Mistakes:

• Placing rel before URL
• Missing semicolons between URL and rel
• Not separating links with commas