From 07d75d52e60a99e0d9cee35db406968e8218c3ac Mon Sep 17 00:00:00 2001
From: gVisor bot <gvisor-bot@google.com>
Date: Sun, 11 Jun 2023 20:58:51 +0800
Subject: [PATCH] chore: Disable cache for RCode client

---
 dns/dhcp.go     |  3 ++-
 dns/resolver.go | 15 ++++++++++-----
 dns/util.go     | 11 +++++++----
 3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/dns/dhcp.go b/dns/dhcp.go
index a6c1df76..7d420d89 100644
--- a/dns/dhcp.go
+++ b/dns/dhcp.go
@@ -59,7 +59,8 @@ func (d *dhcpClient) ExchangeContext(ctx context.Context, m *D.Msg) (msg *D.Msg,
 		return nil, err
 	}
 
-	return batchExchange(ctx, clients, m)
+	msg, _, err = batchExchange(ctx, clients, m)
+	return
 }
 
 func (d *dhcpClient) resolve(ctx context.Context) ([]dnsClient, error) {
diff --git a/dns/resolver.go b/dns/resolver.go
index 5ae7ba33..8f41a44e 100644
--- a/dns/resolver.go
+++ b/dns/resolver.go
@@ -182,6 +182,7 @@ func (r *Resolver) exchangeWithoutCache(ctx context.Context, m *D.Msg) (msg *D.M
 	fn := func() (result any, err error) {
 		ctx, cancel := context.WithTimeout(context.Background(), resolver.DefaultDNSTimeout) // reset timeout in singleflight
 		defer cancel()
+		cache := false
 
 		defer func() {
 			if err != nil {
@@ -192,7 +193,9 @@ func (r *Resolver) exchangeWithoutCache(ctx context.Context, m *D.Msg) (msg *D.M
 
 			msg := result.(*D.Msg)
 
-			putMsgToCache(r.lruCache, q.String(), msg)
+			if cache {
+				putMsgToCache(r.lruCache, q.String(), msg)
+			}
 		}()
 
 		isIPReq := isIPRequest(q)
@@ -201,9 +204,11 @@ func (r *Resolver) exchangeWithoutCache(ctx context.Context, m *D.Msg) (msg *D.M
 		}
 
 		if matched := r.matchPolicy(m); len(matched) != 0 {
-			return r.batchExchange(ctx, matched, m)
+			result, cache, err = r.batchExchange(ctx, matched, m)
+			return
 		}
-		return r.batchExchange(ctx, r.main, m)
+		result, cache, err = r.batchExchange(ctx, r.main, m)
+		return
 	}
 
 	ch := r.group.DoChan(q.String(), fn)
@@ -244,7 +249,7 @@ func (r *Resolver) exchangeWithoutCache(ctx context.Context, m *D.Msg) (msg *D.M
 	return
 }
 
-func (r *Resolver) batchExchange(ctx context.Context, clients []dnsClient, m *D.Msg) (msg *D.Msg, err error) {
+func (r *Resolver) batchExchange(ctx context.Context, clients []dnsClient, m *D.Msg) (msg *D.Msg, cache bool, err error) {
 	ctx, cancel := context.WithTimeout(ctx, resolver.DefaultDNSTimeout)
 	defer cancel()
 
@@ -371,7 +376,7 @@ func (r *Resolver) lookupIP(ctx context.Context, host string, dnsType uint16) (i
 func (r *Resolver) asyncExchange(ctx context.Context, client []dnsClient, msg *D.Msg) <-chan *result {
 	ch := make(chan *result, 1)
 	go func() {
-		res, err := r.batchExchange(ctx, client, msg)
+		res, _, err := r.batchExchange(ctx, client, msg)
 		ch <- &result{Msg: res, Error: err}
 	}()
 	return ch
diff --git a/dns/util.go b/dns/util.go
index a409d679..2ba4d426 100644
--- a/dns/util.go
+++ b/dns/util.go
@@ -287,17 +287,20 @@ func listenPacket(ctx context.Context, proxyAdapter C.ProxyAdapter, proxyName st
 	return proxyAdapter.ListenPacketContext(ctx, metadata, opts...)
 }
 
-func batchExchange(ctx context.Context, clients []dnsClient, m *D.Msg) (msg *D.Msg, err error) {
+func batchExchange(ctx context.Context, clients []dnsClient, m *D.Msg) (msg *D.Msg, cache bool, err error) {
 	fast, ctx := picker.WithTimeout[*D.Msg](ctx, resolver.DefaultDNSTimeout)
 	domain := msgToDomain(m)
 	for _, client := range clients {
-		_, ignoreRCodeError := client.(rcodeClient)
+		_, cache = client.(rcodeClient)
+		cache = !cache
 		fast.Go(func() (*D.Msg, error) {
 			log.Debugln("[DNS] resolve %s from %s", domain, client.Address())
 			m, err := client.ExchangeContext(ctx, m)
 			if err != nil {
 				return nil, err
-			} else if !ignoreRCodeError && (m.Rcode == D.RcodeServerFailure || m.Rcode == D.RcodeRefused) {
+			} else if cache && (m.Rcode == D.RcodeServerFailure || m.Rcode == D.RcodeRefused) {
+				// currently, cache indicates whether this msg was from a RCode client,
+				// so we would ignore RCode errors from RCode clients.
 				return nil, errors.New("server failure")
 			}
 			log.Debugln("[DNS] %s --> %s, from %s", domain, msgToIP(m), client.Address())
@@ -311,7 +314,7 @@ func batchExchange(ctx context.Context, clients []dnsClient, m *D.Msg) (msg *D.M
 		if fErr := fast.Error(); fErr != nil {
 			err = fmt.Errorf("%w, first error: %s", err, fErr.Error())
 		}
-		return nil, err
+		return nil, true, err
 	}
 	msg = elm
 	return