ShortTree

ShortTree is a compact URL shortener service built with ASP.NET Core, Entity Framework Core, and SQLite. It focuses on fast redirects and reliable click tracking, using background processing and caching to keep latency low while still capturing analytics.

Overview

ShortTree lets you register custom, human-friendly slugs for long URLs and then redirect users to the original destination. Redirects are optimized by caching link lookups in memory, while click logs are queued in an unbounded channel and persisted by a background worker to avoid slowing the redirect path.

Key goals:

• Low-latency redirects with minimal database hits.
• Simple API-first design (JSON over HTTP).
• Durable analytics via click logs stored in SQLite.
• Clean separation of concerns using DI and hosted services.

Architecture

Request flow (redirect)

1. Client requests GET /r/{username}/{slug}.
2. The controller checks IMemoryCache for {username}:{slug}.
3. On cache miss, the link is loaded from SQLite and cached with sliding expiration.
4. The redirect is returned immediately.
5. A click log entry is queued to a Channel and written asynchronously by a background service.

This pattern ensures user-perceived latency is low while analytics remain reliable.

Data model

• User: Owner of links. Unique username and email.
• Link: Custom slug for a real URL. Tracks total clicks.
• ClickLog: Individual click events (timestamp, IP, user agent, referrer).

Background processing

• ClickLogBackgroundService reads from a channel and writes click logs to the database.
• The link's click counter is updated in the same transaction.

Caching

• IMemoryCache stores {username}:{slug} -> {linkId, longUrl}.
• Sliding expiration keeps frequently used links hot and evicts inactive ones.

API Endpoints

Links

• POST /api/links - Create a link
• GET /api/links/{username}/{slug} - Get a single link
• GET /api/links/{username} - List all links for a user

Redirect

• GET /r/{username}/{slug} - Redirect to the long URL and record a click

Users

• POST /api/user - Create a user
• GET /api/user/{username} - Get a user
• GET /api/user - List users

Stats

• GET /api/stats/users - Aggregate stats per user
• GET /api/stats/users/{username} - Stats for a specific user
• GET /api/stats/clicks?username={u}&slug={s}&take={n} - Click logs with filters

Link Stats

• GET /api/link-stats/{username} - Click totals per link for a user
• GET /api/link-stats/{username}/{slug} - Click stats for a specific link

Request examples

Create a user

POST /api/user
Content-Type: application/json

{
  "username": "ana",
  "email": "ana@example.com"
}

Create a link

POST /api/links
Content-Type: application/json

{
  "username": "ana",
  "title": "My blog",
  "longUrl": "https://example.com/blog",
  "slug": "blog",
  "visibleInProfile": true,
  "email": "ana@example.com"
}

Redirect

GET /r/ana/blog

User stats

GET /api/stats/users/ana

Link stats

GET /api/link-stats/ana

Configuration

Connection string

SQLite uses a local file named shorttree.db by default:

"ConnectionStrings": {
  "DefaultConnection": "Data Source=shorttree.db"
}

Cache settings

• Sliding expiration is currently set to 10 minutes in RedirectController.
• You can adjust this by changing the CacheSlidingExpiration value.

Running locally

1. Restore and run:
   • dotnet restore
   • dotnet run
2. The database is created automatically on startup (EnsureCreated).
3. Use Postman or curl to test the endpoints.

License

MIT