# Link shortener with click stats

## Rules
- One file: `shortener.py` (tests in `test_shortener.py`). Python 3.10+.
- Standard library only: http.server, sqlite3, secrets, json, html, urllib.parse. No pip packages.
- Only http and https targets. Never redirect to javascript:, data: or file: URLs.
- Short codes come from `secrets`, never `random`. Aliases: 3-32 of A-Z a-z 0-9 - _, reserved words blocked.
- Privacy: store only the referrer's host name and a device type, never IP addresses or full referrer URLs.
- Escape every value you put into HTML with `html.escape`; build links in the browser with DOM methods, not innerHTML.
- Bind to 127.0.0.1 by default. To put it online, run it behind a reverse proxy with HTTPS and set SHORTENER_TOKEN.

## Commands
- `python shortener.py`  serve on http://127.0.0.1:8000 (`--port`, `--host`, `--db`)
- `python -m unittest`  run the tests