//...
func main() {
  r := chi.NewRouter()
  r.Use(middleware.RequestID)
  r.Use(middleware.RealIP)
  r.Use(middleware.Logger)
  r.Use(middleware.Recoverer)
  hr := hostrouter.New()
  // Requests to api.domain.com
  hr.Map("", apiRouter()) // default
  hr.Map("api.domain.com", apiRouter())
  // Requests to doma.in
  hr.Map("doma.in", shortUrlRouter())
  // Requests to *.doma.in
  hr.Map("*.doma.in", shortUrlRouter())
  // Requests to host that isn't defined above
  hr.Map("*", everythingElseRouter())
  // Mount the host router
  r.Mount("/", hr)
  http.ListenAndServe(":3333", r)
}
// Router for the API service
func apiRouter() chi.Router {
  r := chi.NewRouter()
  r.Get("/", apiIndexHandler)
  // ...
  return r
}
// Router for the Short URL service
func shortUrlRouter() chi.Router {
  r := chi.NewRouter()
  r.Get("/", shortIndexHandler)
  // ...
  return r
}