golang unit test for http handler with custom ServeHTTP implementation

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.

Possible duplicate of How to test http calls in go using httptest — Jonathan Hall
– Jonathan Hall, Commented Jun 21, 2018 at 9:27
I checked the link provided above; my question does not appear to be a duplicate. I have specific question: instead of invoking the ServeHTTP function implemented using http.HandleFunc, I want ServeHTTP implemented in my code to be invoked. — gvij
– gvij, Commented Jun 21, 2018 at 9:40
That is answered. Just pass an instance of your slashFix type, as it's already an http.Handler. — Jonathan Hall
– Jonathan Hall, Commented Jun 21, 2018 at 9:42
Passing the instance of slashFix (following this answer: stackoverflow.com/a/37549527/5772695) calls ServeHTTP implemented by me, but how do I incorporate it with basicAuth(handle) which basically does the file serving part? Without this, I get "panic: runtime error: invalid memory address or nil pointer dereference" — gvij
– gvij, Commented Jun 21, 2018 at 9:58
basicAuth should take an http.Handler rather than http.HandlerFunc, then it will be easy. — Jonathan Hall
– Jonathan Hall, Commented Jun 21, 2018 at 10:23

Peter · Accepted Answer · 2018-06-21 10:37:19Z

2

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
}

answered Jun 21, 2018 at 10:37

Peter

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2 Comments

Peter Over a year ago

I'm not sure that I understood your intended test case, but since everything is an http.Handler now you can plug the handlers together however you like.

gvij Over a year ago

This is helpful, thanks! When there were both http.Handler and http.HandleFunc, it was confusing for me. Now, it is clear.

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