From d8d3466de53ddfd577f39e0a36ee686032b397e1 Mon Sep 17 00:00:00 2001
From: gVisor bot <gvisor-bot@google.com>
Date: Wed, 6 Jul 2022 21:25:25 +0800
Subject: [PATCH] fix: h3 of doh fall back logic

---
 dns/doh.go | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/dns/doh.go b/dns/doh.go
index c79e7ba2..2e3f685a 100644
--- a/dns/doh.go
+++ b/dns/doh.go
@@ -70,9 +70,7 @@ func (dc *dohClient) doRequest(req *http.Request) (msg *D.Msg, err error) {
 	client := &http.Client{Transport: dc.transport}
 	resp, err := client.Do(req)
 	if err != nil {
-		if err != nil {
-			return nil, err
-		}
+		return nil, err
 	}
 
 	defer resp.Body.Close()
@@ -168,6 +166,14 @@ func (doh *dohTransport) RoundTrip(req *http.Request) (*http.Response, error) {
 	var resp *http.Response
 	var err error
 	var bodyBytes []byte
+	var h3Err bool
+	var fallbackErr bool
+	defer func() {
+		if doh.preferH3 && h3Err {
+			doh.canUseH3.Store(doh.preferH3 && fallbackErr)
+		}
+	}()
+
 	if req.Body != nil {
 		bodyBytes, err = ioutil.ReadAll(req.Body)
 	}
@@ -175,20 +181,17 @@ func (doh *dohTransport) RoundTrip(req *http.Request) (*http.Response, error) {
 	req.Body = ioutil.NopCloser(bytes.NewReader(bodyBytes))
 	if doh.preferH3 && doh.canUseH3.Load() {
 		resp, err = doh.h3.RoundTrip(req)
-		if err == nil {
+		h3Err = err != nil
+		if !h3Err {
 			return resp, err
 		} else {
-			doh.canUseH3.Store(false)
 			req.Body = ioutil.NopCloser(bytes.NewReader(bodyBytes))
 		}
 	}
 
 	resp, err = doh.Transport.RoundTrip(req)
-	if err != nil {
-		if doh.preferH3 {
-			doh.canUseH3.Store(true)
-		}
-
+	fallbackErr = err != nil
+	if fallbackErr {
 		return resp, err
 	}