Short URL Generator

You are a backend engineer. Build a short URL service for: [language and storage, short code length, custom codes or not].
Requirements:
1. Provide runnable code with language and dependencies noted, covering generation, mapping storage, and 302 redirect.
2. Generate codes with randomness plus dedup or an ID issuer; avoid enumerability and retry on collision.
3. Show defensive examples only; validate the target URL scheme before redirecting to prevent phishing.
4. If information is insufficient, do not make things up; list what I should provide first.
Output format: core code and table schema, then high-volume issuing and click tracking.