From c4e67690f4fcceb055cbea73610b5974855db96f Mon Sep 17 00:00:00 2001
From: Simon Zolin <s.zolin@adguard.com>
Date: Wed, 24 Apr 2019 12:49:12 +0300
Subject: [PATCH] * dnsfilter: don't use global variable for custom resolver
 function

---
 dnsfilter/dnsfilter.go | 77 +++++++++++++++++++++---------------------
 1 file changed, 39 insertions(+), 38 deletions(-)

diff --git a/dnsfilter/dnsfilter.go b/dnsfilter/dnsfilter.go
index 1b12d8b5..c46c3e97 100644
--- a/dnsfilter/dnsfilter.go
+++ b/dnsfilter/dnsfilter.go
@@ -162,8 +162,6 @@ var (
 	safeSearchCache   gcache.Cache
 )
 
-var resolverAddr string // DNS server address
-
 // Result holds state of hostname check
 type Result struct {
 	IsFiltered bool   `json:",omitempty"` // True if the host name is filtered
@@ -974,45 +972,49 @@ func (d *Dnsfilter) matchHost(host string) (Result, error) {
 // lifecycle helper functions
 //
 
+type dialFunctionType func(ctx context.Context, network, addr string) (net.Conn, error)
+
 // Connect to a remote server resolving hostname using our own DNS server
-func customDialContext(ctx context.Context, network, addr string) (net.Conn, error) {
-	log.Tracef("network:%v  addr:%v", network, addr)
+func createCustomDialContext(resolverAddr string) dialFunctionType {
+	return func(ctx context.Context, network, addr string) (net.Conn, error) {
+		log.Tracef("network:%v  addr:%v", network, addr)
 
-	host, port, err := net.SplitHostPort(addr)
-	if err != nil {
-		return nil, err
-	}
-
-	dialer := &net.Dialer{
-		Timeout: time.Minute * 5,
-	}
-
-	if net.ParseIP(host) != nil {
-		con, err := dialer.DialContext(ctx, network, addr)
-		return con, err
-	}
-
-	r := upstream.NewResolver(resolverAddr, 30*time.Second)
-	addrs, e := r.LookupIPAddr(ctx, host)
-	log.Tracef("LookupIPAddr: %s: %v", host, addrs)
-	if e != nil {
-		return nil, e
-	}
-
-	var firstErr error
-	firstErr = nil
-	for _, a := range addrs {
-		addr = fmt.Sprintf("%s:%s", a.String(), port)
-		con, err := dialer.DialContext(ctx, network, addr)
+		host, port, err := net.SplitHostPort(addr)
 		if err != nil {
-			if firstErr == nil {
-				firstErr = err
-			}
-			continue
+			return nil, err
 		}
-		return con, err
+
+		dialer := &net.Dialer{
+			Timeout: time.Minute * 5,
+		}
+
+		if net.ParseIP(host) != nil {
+			con, err := dialer.DialContext(ctx, network, addr)
+			return con, err
+		}
+
+		r := upstream.NewResolver(resolverAddr, 30*time.Second)
+		addrs, e := r.LookupIPAddr(ctx, host)
+		log.Tracef("LookupIPAddr: %s: %v", host, addrs)
+		if e != nil {
+			return nil, e
+		}
+
+		var firstErr error
+		firstErr = nil
+		for _, a := range addrs {
+			addr = fmt.Sprintf("%s:%s", a.String(), port)
+			con, err := dialer.DialContext(ctx, network, addr)
+			if err != nil {
+				if firstErr == nil {
+					firstErr = err
+				}
+				continue
+			}
+			return con, err
+		}
+		return nil, firstErr
 	}
-	return nil, firstErr
 }
 
 // New creates properly initialized DNS Filter that is ready to be used
@@ -1035,8 +1037,7 @@ func New(c *Config) *Dnsfilter {
 		ExpectContinueTimeout: 1 * time.Second,
 	}
 	if c != nil && len(c.ResolverAddress) != 0 {
-		resolverAddr = c.ResolverAddress
-		d.transport.DialContext = customDialContext
+		d.transport.DialContext = createCustomDialContext(c.ResolverAddress)
 	}
 	d.client = http.Client{
 		Transport: d.transport,