golang unit test for http handler with custom ServeHTTP implementation - unit-testing

Question

I am trying to write unit test for my http file server.
I have implemented the ServeHTTP function so that it'd replace "//" with "/" in the URL:
type slashFix struct {
mux http.Handler
}
func (h *slashFix) ServeHTTP(w http.ResponseWriter, r *http.Request) {
r.URL.Path = strings.Replace(r.URL.Path, "//", "/", -1)
h.mux.ServeHTTP(w, r)
}
The bare-minimum code would look like this:
func StartFileServer() {
httpMux := http.NewServeMux()
httpMux.HandleFunc("/abc/", basicAuth(handle))
http.ListenAndServe(":8000", &slashFix{httpMux})
}
func handle(writer http.ResponseWriter, r *http.Request) {
dirName := "C:\\Users\\gayr\\GolandProjects\\src\\NDAC\\download\\"
http.StripPrefix("/abc",
http.FileServer(http.Dir(dirName))).ServeHTTP(writer, r)
}
func basicAuth(handler http.HandlerFunc) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
user, pass, ok := r.BasicAuth()
if user != "UserName" || pass != "Password" {
w.WriteHeader(401)
w.Write([]byte("Unauthorised.\n"))
return
}
handler(w, r)
}
}
I came across instances like the following to test http handlers:
req, err := http.NewRequest("GET", "/abc/testfile.txt", nil)
if err != nil {
t.Fatal(err)
}
req.SetBasicAuth("UserName", "Password")
rr := httptest.NewRecorder()
handler := http.HandlerFunc(basicAuth(handle))
handler.ServeHTTP(rr, req)
Doing so would invoke the ServeHTTP function implemented using http.HandleFunc, but I want ServeHTTP implemented in my code to be invoked. How can this be achieved? Also, is there a way for me to directly test StartFileServer()?
Edit: I checked the link provided in the comments; my question does not appear to be a duplicate. I have a specific question: instead of invoking the ServeHTTP function implemented using http.HandleFunc, I want ServeHTTP implemented in my code to be invoked. I do not see this addressed in the provided link.

Answer 1

http.HandlerFunc implements http.Handler. As Flimzy pointed out in the comments, there is no need for basicAuth to require a HandlerFunc; any http.Handler will do. Sticking to the http.Handler interface instead of the concrete HandlerFunc type will make everything easily composable:
func basicAuth(handler http.Handler) http.Handler { // Note: http.Handler, not http.HandlerFunc
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
user, pass, ok := r.BasicAuth()
if !ok {
// TODO
}
if user != "UserName" || pass != "Password" {
w.WriteHeader(401)
w.Write([]byte("Unauthorised.\n"))
return
}
handler.ServeHTTP(w, r)
})
}
func TestFoo(t *testing.T) {
req, err := http.NewRequest("GET", "/abc/testfile.txt", nil)
if err != nil {
t.Fatal(err)
}
req.SetBasicAuth("UserName", "Password")
rr := httptest.NewRecorder()
// composition is trivial now
sf := &slashFix{
mux: http.HandlerFunc(handle),
}
handler := basicAuth(sf)
handler.ServeHTTP(rr, req)
// assert correct rr
}