Implement APIv4 infrastructure (#5191)

* Implement APIv4 infrastructure

* Update parameter requirement functions per feedback

vendor/github.com/gorilla/mux/mux_test.go

@@ -1017,6 +1017,9 @@ func TestBuildVarsFunc(t *testing.T) {
 func TestSubRouter(t *testing.T) {
 	subrouter1 := new(Route).Host("{v1:[a-z]+}.google.com").Subrouter()
 	subrouter2 := new(Route).PathPrefix("/foo/{v1}").Subrouter()
+	subrouter3 := new(Route).PathPrefix("/foo").Subrouter()
+	subrouter4 := new(Route).PathPrefix("/foo/bar").Subrouter()
+	subrouter5 := new(Route).PathPrefix("/{category}").Subrouter()
 
 	tests := []routeTest{
 		{
@@ -1057,6 +1060,61 @@ func TestSubRouter(t *testing.T) {
 			pathTemplate: `/foo/{v1}/baz/{v2}`,
 			shouldMatch:  false,
 		},
+		{
+			route:        subrouter3.Path("/"),
+			request:      newRequest("GET", "http://localhost/foo/"),
+			vars:         map[string]string{},
+			host:         "",
+			path:         "/foo/",
+			pathTemplate: `/foo/`,
+			shouldMatch:  true,
+		},
+		{
+			route:        subrouter3.Path(""),
+			request:      newRequest("GET", "http://localhost/foo"),
+			vars:         map[string]string{},
+			host:         "",
+			path:         "/foo",
+			pathTemplate: `/foo`,
+			shouldMatch:  true,
+		},
+
+		{
+			route:        subrouter4.Path("/"),
+			request:      newRequest("GET", "http://localhost/foo/bar/"),
+			vars:         map[string]string{},
+			host:         "",
+			path:         "/foo/bar/",
+			pathTemplate: `/foo/bar/`,
+			shouldMatch:  true,
+		},
+		{
+			route:        subrouter4.Path(""),
+			request:      newRequest("GET", "http://localhost/foo/bar"),
+			vars:         map[string]string{},
+			host:         "",
+			path:         "/foo/bar",
+			pathTemplate: `/foo/bar`,
+			shouldMatch:  true,
+		},
+		{
+			route:        subrouter5.Path("/"),
+			request:      newRequest("GET", "http://localhost/baz/"),
+			vars:         map[string]string{"category": "baz"},
+			host:         "",
+			path:         "/baz/",
+			pathTemplate: `/{category}/`,
+			shouldMatch:  true,
+		},
+		{
+			route:        subrouter5.Path(""),
+			request:      newRequest("GET", "http://localhost/baz"),
+			vars:         map[string]string{"category": "baz"},
+			host:         "",
+			path:         "/baz",
+			pathTemplate: `/{category}`,
+			shouldMatch:  true,
+		},
 	}
 
 	for _, test := range tests {

vendor/github.com/gorilla/mux/route.go

@@ -153,7 +153,7 @@ func (r *Route) addRegexpMatcher(tpl string, matchHost, matchPrefix, matchQuery
 	}
 	r.regexp = r.getRegexpGroup()
 	if !matchHost && !matchQuery {
-		if len(tpl) == 0 || tpl[0] != '/' {
+		if tpl == "/" && (len(tpl) == 0 || tpl[0] != '/') {
 			return fmt.Errorf("mux: path must start with a slash, got %q", tpl)
 		}
 		if r.regexp.path != nil {