Handle double service registration gracefully

pkg/api/router.go

@@ -89,11 +89,19 @@ func NewRouter(options ...RouterOption) *Router {
 // RegisterService registers a service with the router.
 // The service config must have a Name field set.
 // The service will be registered at the route "/{cfg.Name}".
+// If a service with the same Name is already registered, the call is
+// ignored with a warning - without this guard, chi.Mount would panic
+// and crash the process.
 func (r *Router) RegisterService(
 	cfg *config.ServiceConfig,
 	handler Handler,
 	opts ...HandlerOption,
 ) {
+	if r.isServiceRegistered(cfg.Name) {
+		slog.Warn("Service already registered, skipping", "name", cfg.Name)
+		return
+	}
+
 	options := &handlerOptions{}
 	for _, opt := range opts {
 		opt(options)
@@ -162,11 +170,19 @@ func WithMiddleware(mw []func(*middleware.Params) func(http.Handler) http.Handle
 // RegisterHTTPHandler registers a Handler as a service.
 // The handlerFactory receives the service DB and returns the handler.
 // The service will be registered at the route "/{cfg.Name}".
+// If a service with the same Name is already registered, the call is
+// ignored with a warning - without this guard, chi.Mount would panic
+// and crash the process.
 func (r *Router) RegisterHTTPHandler(
 	cfg *config.ServiceConfig,
 	handlerFactory func(db.DB) Handler,
 	opts ...HandlerOption,
 ) {
+	if r.isServiceRegistered(cfg.Name) {
+		slog.Warn("Service already registered, skipping", "name", cfg.Name)
+		return
+	}
+
 	options := &handlerOptions{}
 	for _, opt := range opts {
 		opt(options)
@@ -239,6 +255,13 @@ func (r *Router) GetServices() map[string]*ServiceItem {
 	return res
 }
 
+func (r *Router) isServiceRegistered(name string) bool {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	_, ok := r.services[name]
+	return ok
+}
+
 // GetDB returns the database for a specific service.
 // Returns nil if the service is not registered.
 func (r *Router) GetDB(serviceName string) db.DB {

pkg/api/router_test.go

@@ -215,6 +215,60 @@ func TestRouter_RegisterService(t *testing.T) {
 	})
 }
 
+func TestRouter_RegisterService_DuplicateNameIsIgnored(t *testing.T) {
+	router := newTestRouter(t)
+
+	cfg := config.NewServiceConfig()
+	cfg.Name = "petstore"
+	first := &mockService{
+		name:   "petstore",
+		config: cfg,
+		routes: func(r chi.Router) {
+			r.Get("/ping", func(w http.ResponseWriter, req *http.Request) {
+				_, _ = w.Write([]byte("first"))
+			})
+		},
+	}
+	second := &mockService{
+		name:   "petstore",
+		config: cfg,
+		routes: func(r chi.Router) {
+			r.Get("/ping", func(w http.ResponseWriter, req *http.Request) {
+				_, _ = w.Write([]byte("second"))
+			})
+		},
+	}
+
+	router.RegisterService(cfg, first)
+	assert.NotPanics(t, func() { router.RegisterService(cfg, second) })
+
+	req := httptest.NewRequest(http.MethodGet, "/petstore/ping", nil)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, req)
+	assert.Equal(t, "first", w.Body.String())
+}
+
+func TestRouter_RegisterHTTPHandler_DuplicateNameIsIgnored(t *testing.T) {
+	router := newTestRouter(t)
+
+	cfg := config.NewServiceConfig()
+	cfg.Name = "petstore"
+	factory := func(_ db.DB) Handler {
+		return &mockService{
+			name:   "petstore",
+			config: cfg,
+			routes: func(r chi.Router) {
+				r.Get("/ping", func(w http.ResponseWriter, req *http.Request) {
+					_, _ = w.Write([]byte("ok"))
+				})
+			},
+		}
+	}
+
+	router.RegisterHTTPHandler(cfg, factory)
+	assert.NotPanics(t, func() { router.RegisterHTTPHandler(cfg, factory) })
+}
+
 func TestRouter_MiddlewareOrder(t *testing.T) {
 	t.Run("Middleware executes in correct order", func(t *testing.T) {
 		router := newTestRouter(t)