From 81dd0ed2db1426fe08eafd68a80ade6d6b8e03bf Mon Sep 17 00:00:00 2001
From: gVisor bot <gvisor-bot@google.com>
Date: Wed, 24 Aug 2022 21:36:19 +0800
Subject: [PATCH] Chore: reduce dhcp dns client cost

---
 dns/dhcp.go     | 19 +++++++++----------
 dns/resolver.go | 28 +++-------------------------
 dns/util.go     | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 44 insertions(+), 35 deletions(-)

diff --git a/dns/dhcp.go b/dns/dhcp.go
index f964cec8..8e0d5d4c 100644
--- a/dns/dhcp.go
+++ b/dns/dhcp.go
@@ -29,7 +29,7 @@ type dhcpClient struct {
 
 	ifaceAddr *net.IPNet
 	done      chan struct{}
-	resolver  *Resolver
+	clients   []dnsClient
 	err       error
 }
 
@@ -41,15 +41,15 @@ func (d *dhcpClient) Exchange(m *D.Msg) (msg *D.Msg, err error) {
 }
 
 func (d *dhcpClient) ExchangeContext(ctx context.Context, m *D.Msg) (msg *D.Msg, err error) {
-	res, err := d.resolve(ctx)
+	clients, err := d.resolve(ctx)
 	if err != nil {
 		return nil, err
 	}
 
-	return res.ExchangeContext(ctx, m)
+	return batchExchange(ctx, clients, m)
 }
 
-func (d *dhcpClient) resolve(ctx context.Context) (*Resolver, error) {
+func (d *dhcpClient) resolve(ctx context.Context) ([]dnsClient, error) {
 	d.lock.Lock()
 
 	invalidated, err := d.invalidate()
@@ -64,8 +64,9 @@ func (d *dhcpClient) resolve(ctx context.Context) (*Resolver, error) {
 			ctx, cancel := context.WithTimeout(context.Background(), DHCPTimeout)
 			defer cancel()
 
-			var res *Resolver
+			var res []dnsClient
 			dns, err := dhcp.ResolveDNSFromDHCP(ctx, d.ifaceName)
+			// dns never empty if err is nil
 			if err == nil {
 				nameserver := make([]NameServer, 0, len(dns))
 				for _, item := range dns {
@@ -75,9 +76,7 @@ func (d *dhcpClient) resolve(ctx context.Context) (*Resolver, error) {
 					})
 				}
 
-				res = NewResolver(Config{
-					Main: nameserver,
-				})
+				res = transform(nameserver, nil)
 			}
 
 			d.lock.Lock()
@@ -86,7 +85,7 @@ func (d *dhcpClient) resolve(ctx context.Context) (*Resolver, error) {
 			close(done)
 
 			d.done = nil
-			d.resolver = res
+			d.clients = res
 			d.err = err
 		}()
 	}
@@ -96,7 +95,7 @@ func (d *dhcpClient) resolve(ctx context.Context) (*Resolver, error) {
 	for {
 		d.lock.Lock()
 
-		res, err, done := d.resolver, d.err, d.done
+		res, err, done := d.clients, d.err, d.done
 
 		d.lock.Unlock()
 
diff --git a/dns/resolver.go b/dns/resolver.go
index 2f993600..4d3634a4 100644
--- a/dns/resolver.go
+++ b/dns/resolver.go
@@ -10,7 +10,6 @@ import (
 	"time"
 
 	"github.com/Dreamacro/clash/common/cache"
-	"github.com/Dreamacro/clash/common/picker"
 	"github.com/Dreamacro/clash/component/fakeip"
 	"github.com/Dreamacro/clash/component/resolver"
 	"github.com/Dreamacro/clash/component/trie"
@@ -187,31 +186,10 @@ func (r *Resolver) exchangeWithoutCache(ctx context.Context, m *D.Msg) (msg *D.M
 }
 
 func (r *Resolver) batchExchange(ctx context.Context, clients []dnsClient, m *D.Msg) (msg *D.Msg, err error) {
-	fast, ctx := picker.WithTimeout(ctx, resolver.DefaultDNSTimeout)
-	for _, client := range clients {
-		r := client
-		fast.Go(func() (any, error) {
-			m, err := r.ExchangeContext(ctx, m)
-			if err != nil {
-				return nil, err
-			} else if m.Rcode == D.RcodeServerFailure || m.Rcode == D.RcodeRefused {
-				return nil, errors.New("server failure")
-			}
-			return m, nil
-		})
-	}
+	ctx, cancel := context.WithTimeout(ctx, resolver.DefaultDNSTimeout)
+	defer cancel()
 
-	elm := fast.Wait()
-	if elm == nil {
-		err := errors.New("all DNS requests failed")
-		if fErr := fast.Error(); fErr != nil {
-			err = fmt.Errorf("%w, first error: %s", err, fErr.Error())
-		}
-		return nil, err
-	}
-
-	msg = elm.(*D.Msg)
-	return
+	return batchExchange(ctx, clients, m)
 }
 
 func (r *Resolver) matchPolicy(m *D.Msg) []dnsClient {
diff --git a/dns/util.go b/dns/util.go
index 99590d63..df3a3331 100644
--- a/dns/util.go
+++ b/dns/util.go
@@ -1,11 +1,15 @@
 package dns
 
 import (
+	"context"
 	"crypto/tls"
+	"errors"
+	"fmt"
 	"net"
 	"time"
 
 	"github.com/Dreamacro/clash/common/cache"
+	"github.com/Dreamacro/clash/common/picker"
 	"github.com/Dreamacro/clash/log"
 
 	D "github.com/miekg/dns"
@@ -102,3 +106,31 @@ func msgToIP(msg *D.Msg) []net.IP {
 
 	return ips
 }
+
+func batchExchange(ctx context.Context, clients []dnsClient, m *D.Msg) (msg *D.Msg, err error) {
+	fast, ctx := picker.WithContext(ctx)
+	for _, client := range clients {
+		r := client
+		fast.Go(func() (any, error) {
+			m, err := r.ExchangeContext(ctx, m)
+			if err != nil {
+				return nil, err
+			} else if m.Rcode == D.RcodeServerFailure || m.Rcode == D.RcodeRefused {
+				return nil, errors.New("server failure")
+			}
+			return m, nil
+		})
+	}
+
+	elm := fast.Wait()
+	if elm == nil {
+		err := errors.New("all DNS requests failed")
+		if fErr := fast.Error(); fErr != nil {
+			err = fmt.Errorf("%w, first error: %s", err, fErr.Error())
+		}
+		return nil, err
+	}
+
+	msg = elm.(*D.Msg)
+	return
+}