Header-based versioning in Rest API

Introduction

Header-based versioning helps servers know which version of an API a client wants by checking special information in the request headers. This keeps URLs clean and lets clients choose versions easily.

When you want to keep your API URLs simple and not cluttered with version numbers.

When clients need to switch between different API versions without changing the URL.

When you want to separate version information from the resource path for better organization.

When you want to support multiple API versions at the same time without confusing URLs.

Syntax

Rest API

GET /resource HTTP/1.1
Host: api.example.com
Accept: application/vnd.example.v1+json

The version is specified in the Accept header or a custom header like X-API-Version.

The server reads this header to decide which version of the API to send back.

Examples

This request asks for version 1 of the API using the Accept header.

Rest API

GET /users HTTP/1.1
Host: api.example.com
Accept: application/vnd.example.v1+json

This request uses a custom header X-API-Version to ask for version 2.

Rest API

GET /users HTTP/1.1
Host: api.example.com
X-API-Version: 2

Sample Program

This simple Flask app shows how to read a custom header X-API-Version to return different data formats for different API versions.

Rest API

from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route('/users')
def users():
    version = request.headers.get('X-API-Version', '1')
    if version == '1':
        return jsonify({'users': ['Alice', 'Bob']})
    elif version == '2':
        return jsonify({'users': [{'name': 'Alice', 'age': 30}, {'name': 'Bob', 'age': 25}]})
    else:
        return jsonify({'error': 'Unsupported API version'}), 400

if __name__ == '__main__':
    app.run(debug=True)

Important Notes

Clients must include the correct header to get the right API version.

Servers should handle missing or unknown versions gracefully.

Header-based versioning keeps URLs clean but requires clients to set headers properly.

Summary

Header-based versioning uses HTTP headers to specify API versions.

This method keeps URLs simple and separates version info from resource paths.

Servers read headers like Accept or custom headers to decide response format.

Practice

1. What is the main purpose of header-based versioning in REST APIs?

easy

A. To change the API URL structure for each version

B. To specify the API version using HTTP headers instead of URLs

C. To embed version info inside the request body

D. To use query parameters for version control

Solution

1. Step 1: Understand header-based versioning concept

   Header-based versioning uses HTTP headers to indicate which API version the client wants.

2. Step 2: Compare with other versioning methods

   Unlike URL or query parameter versioning, header-based keeps URLs clean and uses headers instead.

3. Final Answer:

   To specify the API version using HTTP headers instead of URLs -> Option B

4. Quick Check:

   Header versioning = version in HTTP headers [OK]

Hint: Remember: header versioning hides version in HTTP headers [OK]

Common Mistakes:

• Confusing header versioning with URL versioning
• Thinking version is in request body
• Assuming query parameters are used

2. Which HTTP header is commonly used to specify API version in header-based versioning?

easy

A. Content-Type

B. User-Agent

C. Accept

D. Authorization

Solution

1. Step 1: Identify common headers for versioning

   The Accept header is often used to specify the desired API version by content negotiation.

2. Step 2: Exclude unrelated headers

   Content-Type specifies data format sent, Authorization is for credentials, and User-Agent identifies client software.

3. Final Answer:

   Accept -> Option C

4. Quick Check:

   Version in Accept header = D [OK]

Hint: Version info usually goes in the Accept header [OK]

Common Mistakes:

• Using Content-Type instead of Accept for versioning
• Confusing Authorization with version header
• Thinking User-Agent controls version

3. Given this HTTP request header:
Accept: application/vnd.example.v2+json
Which API version is the client requesting?

medium

A. Version 2

B. Version 1

C. Version 3

D. No version specified

Solution

1. Step 1: Parse the Accept header value

   The value application/vnd.example.v2+json includes v2, indicating version 2.

2. Step 2: Confirm version number meaning

   The v2 part is a common pattern to specify version 2 of the API.

3. Final Answer:

   Version 2 -> Option A

4. Quick Check:

   v2 in Accept header means version 2 [OK]

Hint: Look for 'v' followed by number in Accept header [OK]

Common Mistakes:

• Ignoring the 'v2' part and guessing version 1
• Assuming no version if not in URL
• Confusing +json suffix with version

4. A developer wrote this code snippet to check API version from headers:

version = request.headers.get('Content-Type')
if version == 'application/vnd.example.v1+json':
    return 'Version 1'
else:
    return 'Unknown version'

What is the main issue here?

medium

A. Using request.headers.get instead of request.get_header

B. Comparing version string incorrectly

C. Missing else condition

D. Using Content-Type header instead of Accept header for versioning

Solution

1. Step 1: Identify header used for versioning

   Header-based versioning typically uses the Accept header, not Content-Type.

2. Step 2: Explain why Content-Type is wrong here

   Content-Type describes the data format sent by the client, not the requested API version.

3. Final Answer:

   Using Content-Type header instead of Accept header for versioning -> Option D

4. Quick Check:

   Version header should be Accept, not Content-Type [OK]

Hint: Version info is in Accept header, not Content-Type [OK]

Common Mistakes:

• Checking Content-Type for version info
• Assuming request.headers.get is invalid
• Ignoring else branch

5. You want to support two API versions (v1 and v2) simultaneously using header-based versioning. Which approach correctly handles this in your server code?

hard

A. Check the Accept header for 'application/vnd.example.v1+json' or 'application/vnd.example.v2+json' and route accordingly

B. Use URL paths like /v1/resource and /v2/resource to separate versions

C. Ignore headers and always serve the latest version

D. Use query parameters like ?version=1 or ?version=2 to select version

Solution

1. Step 1: Understand header-based versioning goal

   It requires checking the HTTP headers to determine which API version to serve.

2. Step 2: Identify correct version detection method

   Checking the Accept header for specific version strings and routing requests accordingly is the right approach.

3. Final Answer:

   Check the Accept header for 'application/vnd.example.v1+json' or 'application/vnd.example.v2+json' and route accordingly -> Option A

4. Quick Check:

   Route by Accept header version strings [OK]

Hint: Route requests by Accept header version values [OK]

Common Mistakes:

• Mixing header versioning with URL or query parameter versioning
• Ignoring version headers and serving one version only
• Using wrong headers for version detection