Does gorilla mux subrouters inherit the middlewares of their parent router? - go

Question

The whole question is in the title.
I was searching on SO if a subrouter will use a middleware of its parent, in the case the middleware is applied to the parent router with the method Use(), but I couldn't find a clear concise answer.
I couldn't find that information in the package documentation either, so I decided to test it and post a question and an answer here for everyone in the same case.
In the following code sample, does requesting on /john will trigger the logMiddleware ?
mainRouter := mux.NewRouter()
mainRouter.Use(logMiddleware)
subRouter := mainRouter.PathPrefix("/users/").Subrouter()
subRouter.Handle("/john", johnHandler())

Answer 1

Yes, mux subrouters inherit their parent's middlewares when applied with Use() method.
Here is the test I created in case you want to try in your favorite IDE :
router code
package so
import (
"context"
"net/http"
"github.com/gorilla/mux"
)
func newRouter(useMainMiddleware bool) mux.Router {
mainRouter := mux.NewRouter()
if useMainMiddleware {
mainRouter.Use(middleware)
}
subRouter := mainRouter.PathPrefix("/users/").Subrouter()
subRouter.Handle("/test", testHandler())
return *mainRouter
}
func middleware(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
r = r.WithContext(context.WithValue(r.Context(), "is_using_middleware", true))
next.ServeHTTP(w, r)
})
}
func testHandler() http.Handler {
return http.HandlerFunc(
func(w http.ResponseWriter, r *http.Request) {
if using, castOk := r.Context().Value("is_using_middleware").(bool); castOk && using {
w.WriteHeader(http.StatusOK)
return
}
w.WriteHeader(http.StatusInternalServerError)
return
},
)
}
test file
package so
import (
"net/http"
"net/http/httptest"
"testing"
"github.com/stretchr/testify/assert"
)
func TestSubrouterWithMiddleware(t *testing.T) {
// GIVEN
request := httptest.NewRequest(http.MethodGet, "/users/test", nil)
recorder := httptest.NewRecorder()
router := newRouter(true) // using a middleware
// WHEN
router.ServeHTTP(recorder, request)
// THEN
assert.Equal(t, http.StatusOK, recorder.Result().StatusCode)
}
func TestSubrouterWithoutMiddleware(t *testing.T) {
// GIVEN
request := httptest.NewRequest(http.MethodGet, "/users/test", nil)
recorder := httptest.NewRecorder()
router := newRouter(false) // not using a middleware
// WHEN
router.ServeHTTP(recorder, request)
// THEN
assert.Equal(t, http.StatusInternalServerError, recorder.Result().StatusCode)
}