shortlink

By Winston Hsiao

April/May 2023

Yello.co Software Engineer Intern - Take Home

Built and Tested with Ruby v3.2.2 and Rails v7.0.4.3

Setup/How to Run

Instructions for Mac

1. Ensure that compatible versions of Ruby and Rails are installed on local device.
   • run ruby -v and rails -v in terminal to check versions.
   • Link to Ruby on Rails Setup
2. Clone the repository
3. Navigate to shortlink directory
4. run rails server to run shortlink on http://localhost:3000
5. Post requests can then be made via an API testing platform like Postman

Testing/Running

While application is running on http://localhost:3000 by running rails server, open Postman's Desktop Agent and test by sending post requests to encode and decode endpoints.

Testing Encode:

Send a POST request to encode endpoint http://localhost:3000/encode with a JSON body containing a link to be shortened. Example below:

{
	"original_url": "https://www.youtube.com/watch?v=dQw4w9WgXcQ&ab_channel=RickAstley",
}

A JSON response containing the shortened URL is returned. Example below:

{
	short_url": "https://short.li/S3IoLi""
}

Testing Decode:

Send a POST request to decode endpoint http://localhost:3000/decode with a JSON body containing shortened URL. Example below:

{
	"short_url": "https://short.li/S3IoLi"
}

Tests performed/Design Choices

Existing Original URL

Expected behavior:

• When making a POST request using an original url identical to one existing in the database, a new short link will be returned every time.

Reasoning:

• If a user wants to create a shortened link they might want to track the number of clicks on that link. This value would be stored with the ShortenedURL object containing the original_url and the unique short_url. It would not make sense to prevent a user from creating a new short link for an original link that has already been shortened (would cause overlap and issues with analytics tracking if implemented)

Short Original URL

Original URL has less than 24 characters.

Expected behavior:

• ShortenedURL object containing original_url and short_url is not saved/persisted into database. Error is thrown requesting longer original URL.

Reasoning:

• If original URL has less than 24 characters, the short link generated is obsolete, as short links are 23 characters long. This is because the service currently acts purely as a link shortener. If the aim of the service is to produce unique links (that happen to be short) and track clicks/analytics then this restriction is not as important, as data might want to be recorded on a link that is short, and generating the short link is helpful for rerouting and tracking traffic.

Path Generation

Implementation:

• The unique 6 character path is generated from characters (a-z), (A-Z), (0-9), (26 + 26 + 10 = 62 characters), we allow duplicates so 62 possible character for each spot in the 6 character path, so there are 62^6 = 56,800,235,584 possible unique URL paths.

Design Choices/Trade-offs:

• A path with 6 character length provides ~56 billion unique short link combinations. This amount of possible combinations reduces potential collisions when generating URLs, and provides current users and future users the ability to generate URLs without worry of running out of links that can be made.
• Having a shorter character length of 4 or 5 would help make the link shorter overall helping achieve one of the primary purposes of having a shortened link (convenience, easy to share/remember).
• In terms of data/storage each character takes up 1 byte assuming standard 8 bit ASCII character encoding. Assuming a 5 character path instead of 6, saving 1 byte (1 less character) for 10 million short links, saves 10 million bytes equivalent to (10MB / 0.01GB) in saved storage making the storage saved essentially negligble. While saving a minimal amount of storage, a 5 character path would result in a significantly smaller amount of unique URL paths. 62^5 = 916,132,832 possible unique URL paths. ~56 billion vs ~916 million.
• Additionally, storage of the original long URL would have a much large impact relatively speaking as these original links are likely to have many more characters on average.
• Another option would be to allow for shorter path sizes, ranging from combinations of 3-6 characters rather than only combinations of 6 characters. This would allow for more total possible combinations, and save space relatively speaking (still negligble).

Duplicate Short Url Generation

Expected behavior:

• Implementation will not allow for duplicate short URL's to be generated. If by chance during function runtime a short link is generated that matches an existing short link in the database, it will not be returned, and a new link will be generated with a different path.

Reasoning:

• short_url's act as a key for searching the database for the original_url value that is associated with it. Duplicate short_url's would cause issues and if tracking/analytics were added, it would not be possible to distinguish objects (links) apart from eachother amongst other duplicate entry issues.

Invalid Short Url to be decoded

Expected behavior:

• POST requests sent to the decode endpoint with a short link that does not exist in the database will return the below error.

{
	"error": "Invalid short link, no entry with that short link was found in the database."
}

Example URL's tested:

{
	"short_url": "http://short.li/ABCDEF"
}

{
	"short_url": "ABCDEF"
}

If the "short_url": label/field is not present in the JSON body, a standard bad request error is thrown. Example:

{
	"http://short.li/ABCDEF"
}

Reasoning:

• There is no ShortenedURL object in the database with the invalid short link as a key, so it can not be retrieved.

Database

Database is hosted locally using SQLite3 but is interchangeable with other database options such as MySQL, PostgreSQL, etc.

The database consists of ShortenedURL objects containing 2 string entries "original_url" and "short_url".

To view URL's stored in the database:

1. run rails console
2. once in the Rails console run ShortenedURL.all to return all ShortenedURL objects
3. run exit to exit the rails console.

Below is an example entry in the database.

  id: 1,                                                                
  original_url: "https://www.youtube.com",                              
  short_url: "https://short.li/IcRLmw",                                  
  created_at: Thu, 27 Apr 2023 20:13:58.166492000 UTC +00:00,           
  updated_at: Thu, 27 Apr 2023 20:13:58.166492000 UTC +00:00

Notes/Changes

In commit 4, changed prefix to "https://" from "http://"