URL SHORTENER

A URL shortener service creates a short url/aliases/tiny url against a long url.When a user click on the tiny url, he/she gets redirected to original url.

Project Directory Structure

│
├── src
|   ├── api
|   |   ├── private
|   |   |   └── url.js
|   |   └── public
|   |       ├── url.js
|   |       └── user.js
|   ├── auth
|   |   └── auth.js
│   ├── config
│   │   └── index.js
│   ├── ErrorHandeler
│   │   ├── ApiErrorHandeler.js
│   │   ├── BaseError.js
│   │   └── httpStatusCode.js
|   ├── database
|   |   └── models
|   |       ├── url.js
│   │       └── users.js
│   ├── data-access
|   |   ├── user.js
│   │   └── url.js
│   ├── helpers
|   |   ├── rate-limit.js
|   |   ├── schema-validator.js
│   │   └── validator.js
│   ├── service
|   |   ├── user.js
│   │   └── url.js
├── app.js
├── package.json
├── Readme.md
├── package-lock.json

System Design

System APIs Examples

• createURL(long_url,alias=None,user_id)

  • Response Body:201

  {
    "message": "success",
    "data": {
      "shorturl": "http://localhost:8080/FwcE4IV",
      "longurl": "https://www.educative.io/courses/grokking-the-system-design-interview/m2ygV4E81AR",
      "clickcount": 0,
      "createdby": "613903e4fc682fd9c47186f9",
      "_id": "6139182b59b234b4ea0d20f0"
    }
  }

• getURL(short_url):301(Redirect)

• listURLs(user_id)

  • Response Body:200

  {
    "data": [
      {
        "_id": "613903f8fc682fd9c47186fc",
        "shorturl": "http://localhost:8080/0WKmRFT",
        "longurl": "https://www.youtube.com/watch?v=ZE5zXLOyEOQ",
        "clickcount": 1
      },
      {
        "_id": "6139182b59b234b4ea0d20f0",
        "shorturl": "http://localhost:8080/FwcE4IV",
        "longurl": "https://stackoverflow.com/questions/14597241/setting-expiry-time-for-a-collection-in-mongodb-using-mongoose",
        "clickcount": 0
      }
    ]
  }

Database Design

URL
_id:ObjectId
shorturl:string
longurl:string
clickcount:Number
createdby:ObjectId

USERS
_id:ObjectId
name:String
email:String
password:String

High Level Design

Assumptions

• Base 62 is chosen as the Base encoding scheme
• 7 character is the length of generated short URL
• 62^7=3.5 trillion unique URLs can be generated

Technique

1. Short URLs from base conversion of random numbers (In use)

   • 7 char Random Id is generated as short URL
   • The collision probability increases if the size of the random Id is decreased
   • After generating, the service makes a findURL call to the database to check for duplicates which is an overhead

2. Short URLs from base conversion of COUNTER (Implemented but not in use)

   • A COUNTER variable is mainted and is passed to a custom function that returns a unique 7 char string by converting COUNTER to its BASE_62 representation and COUNTER is incremented
   • Every generated string is unique so there is no need to check for duplicates
   • Adding a large number might lead to INTEGER_OVERFLOW

Features

• Alias - Users can provide thier custom URLs
• Clickcount - Users can check no of clicks on thier shortURLs

Future enhancements

• Cache layer can be introduced to cache URLs that are frequently accessed which can reduces load on the server.