Short answer: approach a compressed URL by understanding how URL shorteners map long URLs to short keys, plus how to verify, store, and safely redirect, while staying mindful of security and risks.

Core concepts

• Purpose and mechanism
  • URL shorteners create a compact key that maps to a full destination URL. The short URL redirects the user to the original long URL using HTTP redirects (301/302/307/308) after looking up the mapping. This is the foundational pattern behind TinyURL and similar services.

• Key generation strategies
  • Simple incremental IDs: assign a new, unique numeric ID and encode it in a short alphabet (base62) to form the key. This yields predictable, scalable short URLs but requires coordination to avoid collisions.

* Hash-based keys: generate a hash (MD5, SHA-256, etc.) of the long URL and encode a portion of it. This can deduplicate identical long URLs but may produce collisions, requiring a collision-handling step.

* Custom or user-provided keys: allow users to specify their own alias when available, trading off flexibility for potential collisions and misuse.

• Data model and storage
  • Maintain a durable mapping between short key and long URL, plus metadata such as creation time, usage stats, and expiration if needed. Use a central datastore (e.g., key-value store) to ensure fast lookups across distributed systems.

• Redirection behavior
  • HTTP 301 (permanent) or 302/307 (temporary) redirects are standard. Services may also implement analytics tracking before redirecting.

• Security and safety considerations
  • Shortened URLs can mask dangerous destinations. Validate or pre-scan destinations when feasible, implement warnings for suspicious domains, and consider blocking known malicious targets. Provide users with visibility into the final destination when possible.

Practical design considerations

• Collision handling
  • If a generated short key already exists for a different long URL, retry with another key or append/alter to resolve collisions. Ensure atomicity in the write path to avoid race conditions in distributed deployments.

• Scalability
  • Separate the write path (short URL creation) from the read path (redirection). Use caching for hot keys and a scalable datastore capable of high-throughput lookups. Consider sharding by key space to distribute load.

• Metadata and lifecycle
  • Track creation time, last access time, and analytics. Implement expiration or renewal policies if temporary links are desired.

• Security practices
  • Consider domain whitelisting, URL validation on input, and caution for redirection loops. Use safe URL parsing to prevent injection or open redirect vulnerabilities.

Common implementation patterns

• Encoding-based short URLs
  • Create a numeric ID for each new long URL, encode in base62 (digits + uppercase + lowercase) to form the short key, and store the mapping. On access, look up the key and redirect accordingly.

• Hash-based deduplication
  • Compute a hash of the long URL, take a prefix as the key, check for existing mappings, and if collision occurs, resolve by extending the key or using a secondary index. This can reduce storage when identical URLs are shortened multiple times.

• Hybrid approaches
  • Use a hash-derived key with a fallback to a traditional incremental key if a collision or non-unique mapping is detected. This balances deduplication with simplicity.

Security tips for users and operators

• Be cautious with compressed URLs from untrusted sources; they can lead to phishing or malware. Prefer preview pages or safety checks when available.

• Provide users with a sense of the destination, such as a tooltip or a preview page, to reduce surprise redirections.

• Monitor for abuse (spam, malware, phishing) and implement rate limiting and domain reputation checks to protect the service and end users.

If you’d like, I can tailor this into a concrete microservice design (API endpoints, data models, and a simple flow) for a URL-shortening feature, and include example code sketches.