downloader: Number of DNS requests seem excessive (#5145) (#10739)

cherry-pick #10693 to release

erigon-lib/downloader/downloader.go

@@ -2591,10 +2591,17 @@ func openClient(ctx context.Context, dbDir, snapDir string, cfg *torrent.ClientC
 	//})
 	cfg.DefaultStorage = m
 
+	dnsResolver := &downloadercfg.DnsCacheResolver{RefreshTimeout: 24 * time.Hour}
+	cfg.TrackerDialContext = dnsResolver.DialContext
+
 	torrentClient, err = torrent.NewClient(cfg)
 	if err != nil {
 		return nil, nil, nil, nil, fmt.Errorf("torrent.NewClient: %w", err)
 	}
 
+	go func() {
+		dnsResolver.Run(ctx)
+	}()
+
 	return db, c, m, torrentClient, nil
 }

erigon-lib/downloader/downloadercfg/dns_cache_resolver.go

@@ -0,0 +1,49 @@
+package downloadercfg
+
+import (
+	"context"
+	"net"
+	"time"
+
+	"github.com/rs/dnscache"
+)
+
+// DnsCacheResolver resolves DNS requests for an HTTP client using an in-memory cache.
+type DnsCacheResolver struct {
+	RefreshTimeout time.Duration
+
+	resolver dnscache.Resolver
+}
+
+func (r *DnsCacheResolver) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
+	host, port, err := net.SplitHostPort(address)
+	if err != nil {
+		return nil, err
+	}
+	ips, err := r.resolver.LookupHost(ctx, host)
+	if err != nil {
+		return nil, err
+	}
+	var conn net.Conn
+	for _, ip := range ips {
+		var dialer net.Dialer
+		conn, err = dialer.DialContext(ctx, network, net.JoinHostPort(ip, port))
+		if err == nil {
+			break
+		}
+	}
+	return conn, err
+}
+
+func (r *DnsCacheResolver) Run(ctx context.Context) {
+	ticker := time.NewTicker(r.RefreshTimeout)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			r.resolver.Refresh(true)
+		}
+	}
+}

erigon-lib/go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/ledgerwatch/interfaces v0.0.0-20240320062914-b57f05746087
 	github.com/ledgerwatch/log/v3 v3.9.0
 	github.com/ledgerwatch/secp256k1 v1.0.0
+	github.com/rs/dnscache v0.0.0-20211102005908-e0241e321417
 )
 
 require (
@@ -125,7 +126,6 @@ require (
 	github.com/prometheus/common v0.48.0 // indirect
 	github.com/prometheus/procfs v0.12.0 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
-	github.com/rs/dnscache v0.0.0-20211102005908-e0241e321417 // indirect
 	github.com/shoenig/go-m1cpu v0.1.6 // indirect
 	github.com/showwin/speedtest-go v1.6.12
 	github.com/sirupsen/logrus v1.9.3 // indirect