Fix rooms v3 url paths for good - with tests (#1130)

* Fix rooms v3 url paths for good - with tests

- Add a test rig around `federationapi` to test routing.
- Use `JSONVerifier` over `KeyRing` so we can stub things out more easily.
- Add `test.NopJSONVerifier` which verifies nothing.
- Add `base.BaseMux` which is the original `mux.Router` used to spawn public/internal routers.
- Listen on `base.BaseMux` and not the default serve mux as it cleans paths which we don't want.
- Factor out `ListenAndServe` to `test.ListenAndServe` and add flag for listening on TLS.

* Fix comments

* Linting

cmd/dendritejs/jsServer.go

@@ -28,7 +28,7 @@ import (
 // JSServer exposes an HTTP-like server interface which allows JS to 'send' requests to it.
 type JSServer struct {
 	// The router which will service requests
-	Mux *http.ServeMux
+	Mux http.Handler
 }
 
 // OnRequestFromJS is the function that JS will invoke when there is a new request.

cmd/dendritejs/main.go

@@ -19,7 +19,6 @@ package main
 import (
 	"crypto/ed25519"
 	"fmt"
-	"net/http"
 	"syscall/js"
 
 	"github.com/matrix-org/dendrite/appservice"
@@ -233,7 +232,7 @@ func main() {
 	monolith.AddAllPublicRoutes(base.PublicAPIMux)
 
 	httputil.SetupHTTPAPI(
-		http.DefaultServeMux,
+		base.BaseMux,
 		base.PublicAPIMux,
 		base.InternalAPIMux,
 		cfg,
@@ -245,7 +244,7 @@ func main() {
 		go func() {
 			logrus.Info("Listening on libp2p-js host ID ", node.Id)
 			s := JSServer{
-				Mux: http.DefaultServeMux,
+				Mux: base.BaseMux,
 			}
 			s.ListenAndServe("p2p")
 		}()
@@ -255,7 +254,7 @@ func main() {
 	go func() {
 		logrus.Info("Listening for service-worker fetch traffic")
 		s := JSServer{
-			Mux: http.DefaultServeMux,
+			Mux: base.BaseMux,
 		}
 		s.ListenAndServe("fetch")
 	}()