go-router

What it is

A router in the spirit of chi: static routes and {param} captures, groups, mounting and middleware chains, on top of the standard library only. It started in 2023 as a way to learn how routers actually match paths, and grew into something I would be comfortable depending on.

r := router.NewRouter()
r.Get("/users/{id}", func(w http.ResponseWriter, r *http.Request) {
    w.Write([]byte("user " + context.Param(r, "id")))
})
r.Group("/admin", func(r *router.Router) {
    r.Use(requireAuth)
    r.Get("/stats", stats)
})
http.ListenAndServe(":3333", r)

Design

• Patricia trie matching. A shared literal prefix, even across a /, collapses into one edge instead of one node per segment. The tree splits only at the byte where two routes first diverge.
• Atomic tree swaps. Registration builds a new tree and swaps it in atomically, so adding or mounting routes while serving traffic never exposes a half-built tree, and lookups never take a lock.
• HTTP semantics done properly. HEAD falls back to GET; OPTIONS on a known path answers 204 with a computed Allow header. Registering either explicitly always wins.
• Groups and mounting. Group shares a prefix and middleware; Mount grafts another router’s routes, handlers and middleware intact, under a prefix.

Verification

Beyond unit tests, the routing tree carries three layers:

1. Fuzz tests for route registration and lookup against arbitrary input.
2. Benchmarks for static, parameter, escaped and miss lookups, including parallel and large-fanout cases.
3. Load tests driven by vegeta that check correctness under concurrent load, including registering and mounting routes while traffic is in flight.

The last one is the point: “concurrency-safe” is a claim, and the load test is what makes it a fact.