From 2d9c9eba502376fc283eb96a789ecc71d77b1cf0 Mon Sep 17 00:00:00 2001
From: Star Brilliant <coder@poorlab.com>
Date: Wed, 7 Nov 2018 19:41:55 +0800
Subject: [PATCH] Detect context.DeadlineExceeded

---
 doh-client/google.go |  7 +++++++
 doh-client/ietf.go   | 15 +++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/doh-client/google.go b/doh-client/google.go
index b02feb0..506f519 100644
--- a/doh-client/google.go
+++ b/doh-client/google.go
@@ -92,6 +92,13 @@ func (c *Client) generateRequestGoogle(ctx context.Context, w dns.ResponseWriter
 	c.httpClientMux.RLock()
 	resp, err := c.httpClient.Do(req)
 	c.httpClientMux.RUnlock()
+	if err == context.DeadlineExceeded {
+		// Do not respond, silently fail to prevent caching of SERVFAIL
+		log.Println(err)
+		return &DNSRequest{
+			err: err,
+		}
+	}
 	if err != nil {
 		log.Println(err)
 		reply := jsonDNS.PrepareReply(r)
diff --git a/doh-client/ietf.go b/doh-client/ietf.go
index b8e2816..85a9a34 100644
--- a/doh-client/ietf.go
+++ b/doh-client/ietf.go
@@ -108,8 +108,10 @@ func (c *Client) generateRequestIETF(ctx context.Context, w dns.ResponseWriter,
 	if len(requestURL) < 2048 {
 		req, err = http.NewRequest("GET", requestURL, nil)
 		if err != nil {
-			// Do not respond, silently fail to prevent caching of SERVFAIL
 			log.Println(err)
+			reply := jsonDNS.PrepareReply(r)
+			reply.Rcode = dns.RcodeServerFailure
+			w.WriteMsg(reply)
 			return &DNSRequest{
 				err: err,
 			}
@@ -117,8 +119,10 @@ func (c *Client) generateRequestIETF(ctx context.Context, w dns.ResponseWriter,
 	} else {
 		req, err = http.NewRequest("POST", upstream, bytes.NewReader(requestBinary))
 		if err != nil {
-			// Do not respond, silently fail to prevent caching of SERVFAIL
 			log.Println(err)
+			reply := jsonDNS.PrepareReply(r)
+			reply.Rcode = dns.RcodeServerFailure
+			w.WriteMsg(reply)
 			return &DNSRequest{
 				err: err,
 			}
@@ -131,6 +135,13 @@ func (c *Client) generateRequestIETF(ctx context.Context, w dns.ResponseWriter,
 	c.httpClientMux.RLock()
 	resp, err := c.httpClient.Do(req)
 	c.httpClientMux.RUnlock()
+	if err == context.DeadlineExceeded {
+		// Do not respond, silently fail to prevent caching of SERVFAIL
+		log.Println(err)
+		return &DNSRequest{
+			err: err,
+		}
+	}
 	if err != nil {
 		log.Println(err)
 		reply := jsonDNS.PrepareReply(r)