Rewrite: Use middleware.Replacer for simple rule.

middleware/rewrite/rewrite.go

@@ -52,7 +52,11 @@ func (s SimpleRule) Rewrite(r *http.Request) bool {
 		// take note of this rewrite for internal use by fastcgi
 		// all we need is the URI, not full URL
 		r.Header.Set(headerFieldName, r.URL.RequestURI())
-		r.URL.Path = s.To
+
+		// replace variables
+		to := path.Clean(middleware.NewReplacer(r, nil, "").Replace(s.To))
+
+		r.URL.Path = to
 		return true
 	}
 	return false

middleware/rewrite/rewrite_test.go

@@ -17,6 +17,7 @@ func TestRewrite(t *testing.T) {
 		Rules: []Rule{
 			NewSimpleRule("/from", "/to"),
 			NewSimpleRule("/a", "/b"),
+			NewSimpleRule("/b", "/b{uri}"),
 		},
 	}
 
@@ -50,6 +51,7 @@ func TestRewrite(t *testing.T) {
 	}{
 		{"/from", "/to"},
 		{"/a", "/b"},
+		{"/b", "/b/b"},
 		{"/aa", "/aa"},
 		{"/", "/"},
 		{"/a?foo=bar", "/b?foo=bar"},