Fix SkipUrlClean by not using DefaultServeMux

The issue itself happen because we wrap `gorilla.Mux` router through
`http.ServeMux`, which is kinda wrong, because `Mux` is already a
`ServeMux` implementation. So we processing routes twice.

Default `ServeMux` implementation have own route sanitization logic, and
can’t be configured with `SkipClean` option, like gorilla
implementation.

The solution here is to stop using ServeMux and use Gorilla directly.

Problem with this approach is that we need to reload, eg. replace, the
router inside `doReload` function. Neither gorilla or ServeMux support
replacing the routes, so replacing the whole router object is the only
solution. When we pass raw Gorilla Router object to the
`Server.Handler`, and replace `mainRouter` in `doReload`, server do not
see the changes: thats why we had issues when API reloads was not
working.

There are 2 ways to solve this issue: expose server object as a global
variable, and dynamically replace `Handler` attribute, or write simple
`http.Handler` wrapper around `mainRouter`, which always calls the
current router.

I’m not sure about safety of this approach but since previously we
replaced `DefaultServeMux` directly, and had no any issues, I may assume
that it should be thread safe.

Should fix #1093

gateway_test.go

@@ -22,6 +22,7 @@ import (
 	"github.com/gorilla/mux"
 	"github.com/justinas/alice"
 
+	"github.com/TykTechnologies/tyk/apidef"
 	"github.com/TykTechnologies/tyk/config"
 )
 
@@ -1029,3 +1030,55 @@ func TestProxyUserAgent(t *testing.T) {
 		}
 	}
 }
+
+func buildAndLoadAPI(apiGens ...func(spec *APISpec)) {
+	globalConf.AppPath, _ = ioutil.TempDir("", "apps")
+	defer func() {
+		os.RemoveAll(globalConf.AppPath)
+		globalConf.AppPath = "apps/"
+	}()
+
+	for i, gen := range apiGens {
+		spec := &APISpec{APIDefinition: &apidef.APIDefinition{}}
+		json.Unmarshal([]byte(sampleAPI), spec.APIDefinition)
+		gen(spec)
+		specBytes, _ := json.Marshal(spec)
+		specFilePath := filepath.Join(globalConf.AppPath, spec.APIID+strconv.Itoa(i)+".json")
+		if err := ioutil.WriteFile(specFilePath, specBytes, 0644); err != nil {
+			panic(err)
+		}
+	}
+
+	doReload()
+}
+
+func TestSkipUrlCleaning(t *testing.T) {
+	globalConf.HttpServerOptions.OverrideDefaults = true
+	globalConf.HttpServerOptions.SkipURLCleaning = true
+
+	ln, _ := generateListener(0)
+	baseURL := "http://" + ln.Addr().String()
+	listen(ln, nil, nil)
+
+	defer func() {
+		globalConf.HttpServerOptions.OverrideDefaults = false
+		globalConf.HttpServerOptions.SkipURLCleaning = false
+		ln.Close()
+	}()
+
+	s := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte(r.URL.Path))
+	}))
+
+	buildAndLoadAPI(func(spec *APISpec) {
+		spec.Proxy.ListenPath = "/"
+		spec.Proxy.TargetURL = s.URL
+	})
+
+	resp, _ := http.Get(baseURL + "/http://example.com")
+	body, _ := ioutil.ReadAll(resp.Body)
+
+	if string(body) != "/http://example.com" {
+		t.Error("Should not strip URL", string(body))
+	}
+}

main.go

@@ -563,18 +563,15 @@ func doReload() {
 	log.WithFields(logrus.Fields{
 		"prefix": "main",
 	}).Info("Preparing new router")
-	newRouter := mux.NewRouter()
-	mainRouter = newRouter
+	mainRouter = mux.NewRouter()
+	if globalConf.HttpServerOptions.OverrideDefaults {
+		mainRouter.SkipClean(globalConf.HttpServerOptions.SkipURLCleaning)
+	}
 
 	if globalConf.ControlAPIPort == 0 {
-		loadAPIEndpoints(newRouter)
+		loadAPIEndpoints(mainRouter)
 	}
-	loadApps(specs, newRouter)
-
-	newServeMux := http.NewServeMux()
-	newServeMux.Handle("/", mainRouter)
-
-	http.DefaultServeMux = newServeMux
+	loadApps(specs, mainRouter)
 
 	log.WithFields(logrus.Fields{
 		"prefix": "main",
@@ -1190,6 +1187,13 @@ func startDRL() {
 	startRateLimitNotifications()
 }
 
+// mainHandler's only purpose is to allow mainRouter to be dynamically replaced
+type mainHandler struct{}
+
+func (_ mainHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	mainRouter.ServeHTTP(w, r)
+}
+
 func listen(l, controlListener net.Listener, err error) {
 	readTimeout := 120
 	writeTimeout := 120
@@ -1240,12 +1244,9 @@ func listen(l, controlListener net.Listener, err error) {
 				Addr:         ":" + targetPort,
 				ReadTimeout:  time.Duration(readTimeout) * time.Second,
 				WriteTimeout: time.Duration(writeTimeout) * time.Second,
+				Handler:      mainHandler{},
 			}
 
-			newServeMux := http.NewServeMux()
-			newServeMux.Handle("/", defaultRouter)
-			http.DefaultServeMux = newServeMux
-
 			// Accept connections in a new goroutine.
 			go s.Serve(l)
 
@@ -1262,13 +1263,9 @@ func listen(l, controlListener net.Listener, err error) {
 				"prefix": "main",
 			}).Printf("Gateway started (%s)", VERSION)
 
-			go http.Serve(l, nil)
+			go http.Serve(l, mainHandler{})
 
 			if !rpcEmergencyMode {
-				newServeMux := http.NewServeMux()
-				newServeMux.Handle("/", mainRouter)
-				http.DefaultServeMux = newServeMux
-
 				if controlListener != nil {
 					go http.Serve(controlListener, controlRouter)
 				}
@@ -1312,19 +1309,18 @@ func listen(l, controlListener net.Listener, err error) {
 		}
 
 		if globalConf.HttpServerOptions.OverrideDefaults {
+			defaultRouter.SkipClean(globalConf.HttpServerOptions.SkipURLCleaning)
+
 			log.WithFields(logrus.Fields{
 				"prefix": "main",
 			}).Warning("HTTP Server Overrides detected, this could destabilise long-running http-requests")
 			s := &http.Server{
 				Addr:         ":" + targetPort,
 				ReadTimeout:  time.Duration(readTimeout) * time.Second,
 				WriteTimeout: time.Duration(writeTimeout) * time.Second,
+				Handler:      mainHandler{},
 			}
 
-			newServeMux := http.NewServeMux()
-			newServeMux.Handle("/", defaultRouter)
-			http.DefaultServeMux = newServeMux
-
 			log.WithFields(logrus.Fields{
 				"prefix": "main",
 			}).Info("Custom gateway started")
@@ -1343,13 +1339,9 @@ func listen(l, controlListener net.Listener, err error) {
 				"prefix": "main",
 			}).Printf("Gateway resumed (%s)", VERSION)
 
-			go http.Serve(l, nil)
+			go http.Serve(l, mainHandler{})
 
 			if !rpcEmergencyMode {
-				newServeMux := http.NewServeMux()
-				newServeMux.Handle("/", mainRouter)
-				http.DefaultServeMux = newServeMux
-
 				if controlListener != nil {
 					go http.Serve(controlListener, controlRouter)
 				}