Problem Description

Design a URL shortening service like bit.ly or goo.gl.

Requirements

• Given a long URL, return a unique short URL.
• When a user accesses the short URL, redirect them to the original long URL.
• Users can optionally pick a custom alias for their URL.
• Links expire after a standard default timespan (e.g., 5 years).

High-Level Design

1. API Endpoints:
   • POST /api/v1/data/shorten: Takes longUrl, returns shortUrl.
   • GET /{shortUrl}: Redirects to longUrl.
2. Database Schema:
   • URLMapping Table:
     • Hash (PK): varchar(6-7)
     • OriginalURL: varchar(2048)
     • CreationDate: datetime
     • ExpirationDate: datetime
     • UserID: int (optional)
3. URL Encoding:
   • Use Base62 encoding ([a-z, A-Z, 0-9]) for the hash.
   • A 7-character Base62 string offers ~3.5 trillion combinations ($62^7$).
4. Key Generation Service (KGS):
   • To avoid collision checks on every insertion, pre-generate keys and store them in a separate DB or use a standalone service (KGS) to hand out unique keys.