In a Ruby on Rails monolith serving 10M+ daily requests for an e-commerce marketplace, the router sits on the critical path for every request. A small regression in route matching can increase P99 latency, cause incorrect controller dispatch (user-facing 404s), or accidentally expose admin endpoints if precedence is wrong.
You’re asked to explain, at an implementation level, how a Rails-style router could work.
GET /users/42/orders/9 when you have static routes (e.g., /users/new), dynamic segments (e.g., /users/:id), and wildcards (e.g., /assets/*path)? What precedence rules prevent /users/new from being captured by /users/:id?:id) and wildcard captures extracted efficiently and safely?Discuss internal representation (e.g., tries/DFAs/compiled regex), trade-offs (memory vs speed), complexity, and common pitfalls (route shadowing, ambiguous matches, and pathological patterns). You don’t need to write Ruby, but your explanation should be concrete enough to implement in any language.