Reader's challenge – an API for URL shortening

With all the basics you have learned up to now, try to implement a URL shortening service. A URL shortener takes a very long URL and returns a shortened, crisp, and memorable URL back to the user. At first sight, it looks like magic, but it is a simple math trick.

In a single statement, URL shortening services are built upon two things:

• A string mapping algorithm to map long strings to short strings (Base 62)
• A simple web server that redirects a short URL to the original URL

There are a few obvious advantages of URL shortening:

• Users can remember the URL; easy to maintain
• Users can use the links where there are restrictions on text length, for example, Twitter
• Predictable shortened URL length

Take a look at the following diagram:

Under the hood, the following things happen in a URL shortening service:

1. Take the original URL
2. Apply BASE62 encoding on it; it generates a Shortened URL
3. Store that URL in the database. Map it to the original URL ([shortened_url: original_url])
4. Whenever a request comes to the shortened URL, just do an HTTP redirect to the original URL

We will implement a full example in upcoming chapters when we integrate databases to our API server, but before that, though, we should specify the API design documentation.

Take a look at the following table: