vault: Router can check for matching mounts

vault/router.go

@@ -91,6 +91,17 @@ func (r *Router) Remount(src, dst string) error {
 	return nil
 }
 
+// MatchingMOunt returns the mount prefix that would be used for a path
+func (r *Router) MatchingMount(path string) string {
+	r.l.RLock()
+	mount, _, ok := r.root.LongestPrefix(path)
+	r.l.RUnlock()
+	if !ok {
+		return ""
+	}
+	return mount
+}
+
 // Route is used to route a given request
 func (r *Router) Route(req *Request) (*Response, error) {
 	// Find the mount point

vault/router_test.go

@@ -39,6 +39,14 @@ func TestRouter_Mount(t *testing.T) {
 		t.Fatalf("err: %v", err)
 	}
 
+	if path := r.MatchingMount("prod/aws/foo"); path != "prod/aws/" {
+		t.Fatalf("bad: %s", path)
+	}
+
+	if path := r.MatchingMount("stage/aws/foo"); path != "" {
+		t.Fatalf("bad: %s", path)
+	}
+
 	req := &Request{
 		Path: "prod/aws/foo",
 	}