net: shuffle resolved addrs before sort by RFC6724 for connection load-balancing

src/net/dnsclient_unix.go

@@ -595,7 +595,6 @@ func goLookupIPFiles(name string) (addrs []IPAddr, canonical string) {
 			addrs = append(addrs, addr)
 		}
 	}
-	sortByRFC6724(addrs)
 	return addrs, canonical
 }
 
@@ -607,6 +606,12 @@ func (r *Resolver) goLookupIP(ctx context.Context, network, host string, order h
 }
 
 func (r *Resolver) goLookupIPCNAMEOrder(ctx context.Context, network, name string, order hostLookupOrder, conf *dnsConfig) (addrs []IPAddr, cname dnsmessage.Name, err error) {
+	addrs, cname, err = r.goLookupIPCNAME(ctx, network, name, order, conf)
+	sortByRFC6724(addrs)
+	return addrs, cname, err
+}
+
+func (r *Resolver) goLookupIPCNAME(ctx context.Context, network, name string, order hostLookupOrder, conf *dnsConfig) (addrs []IPAddr, cname dnsmessage.Name, err error) {
 	if order == hostLookupFilesDNS || order == hostLookupFiles {
 		var canonical string
 		addrs, canonical = goLookupIPFiles(name)
@@ -796,7 +801,6 @@ func (r *Resolver) goLookupIPCNAMEOrder(ctx context.Context, network, name strin
 		// just one is misleading. See also golang.org/issue/6324.
 		lastErr.Name = name
 	}
-	sortByRFC6724(addrs)
 	if len(addrs) == 0 && !(network == "CNAME" && cname.Length > 0) {
 		if order == hostLookupDNSFiles {
 			var canonical string

src/net/lookup.go

@@ -10,6 +10,7 @@ import (
 	"internal/nettrace"
 	"internal/singleflight"
 	"internal/stringslite"
+	"math/rand/v2"
 	"net/netip"
 	"sync"
 
@@ -373,7 +374,18 @@ func (r *Resolver) lookupIPAddr(ctx context.Context, network, host string) ([]IP
 			addrs, _ := r.Val.([]IPAddr)
 			trace.DNSDone(ipAddrsEface(addrs), r.Shared, err)
 		}
-		return lookupIPReturn(r.Val, err, r.Shared)
+		// shuffle resolved addrs before sort by RFC6724 for connection load-balancing
+		// See https://github.com/golang/go/issues/34511
+		// See https://github.com/grafana/loki/issues/3301
+		// See https://github.com/grafana/loki/issues/9239
+		// See https://github.com/restic/restic/issues/4444
+		// See https://github.com/golang/go/issues/31698
+		addrs, err := lookupIPReturn(r.Val, err, r.Shared)
+		rand.Shuffle(len(addrs), func(i, j int) {
+			addrs[i], addrs[j] = addrs[j], addrs[i]
+		})
+		sortByRFC6724(addrs)
+		return addrs, err
 	}
 }
 

src/net/lookup_test.go

@@ -505,7 +505,7 @@ func TestDNSFlood(t *testing.T) {
 
 	defer dnsWaitGroup.Wait()
 
-	var N = 5000
+	N := 5000
 	if runtime.GOOS == "darwin" || runtime.GOOS == "ios" {
 		// On Darwin this test consumes kernel threads much
 		// than other platforms for some reason.
@@ -757,7 +757,7 @@ func TestLookupPort(t *testing.T) {
 		port    int
 		ok      bool
 	}
-	var tests = []test{
+	tests := []test{
 		{"tcp", "0", 0, true},
 		{"udp", "0", 0, true},
 		{"udp", "domain", 53, true},
@@ -809,7 +809,7 @@ func TestLookupPort_Minimal(t *testing.T) {
 		name    string
 		port    int
 	}
-	var tests = []test{
+	tests := []test{
 		{"tcp", "http", 80},
 		{"tcp", "HTTP", 80}, // case shouldn't matter
 		{"tcp", "https", 443},
@@ -832,7 +832,7 @@ func TestLookupProtocol_Minimal(t *testing.T) {
 		name string
 		want int
 	}
-	var tests = []test{
+	tests := []test{
 		{"tcp", 6},
 		{"TcP", 6}, // case shouldn't matter
 		{"icmp", 1},
@@ -847,7 +847,6 @@ func TestLookupProtocol_Minimal(t *testing.T) {
 			t.Errorf("LookupProtocol(%q) = %d, %v; want %d, error=nil", tt.name, got, err, tt.want)
 		}
 	}
-
 }
 
 func TestLookupNonLDH(t *testing.T) {
@@ -1192,14 +1191,24 @@ func TestLookupIPAddrConcurrentCallsForNetworks(t *testing.T) {
 				t.Errorf("lookupIPAddr(%v, %v): unexpected error: %v", network, host, err)
 			}
 			wantIPs := results[[2]string{network, host}]
-			if !reflect.DeepEqual(gotIPs, wantIPs) {
+			// ingore order
+			if !reflect.DeepEqual(sortedIPAddrStrings(gotIPs), sortedIPAddrStrings(wantIPs)) {
 				t.Errorf("lookupIPAddr(%v, %v): mismatched IPAddr results\n\tGot: %v\n\tWant: %v", network, host, gotIPs, wantIPs)
 			}
 		}()
 	}
 	wg.Wait()
 }
 
+func sortedIPAddrStrings(ipAddrs []IPAddr) []string {
+	ret := make([]string, len(ipAddrs))
+	for i, ipAddr := range ipAddrs {
+		ret[i] = ipAddr.String() + "\000" + ipAddr.Zone
+	}
+	slices.Sort(ret)
+	return ret
+}
+
 // Issue 53995: Resolver.LookupIP should return error for empty host name.
 func TestResolverLookupIPWithEmptyHost(t *testing.T) {
 	_, err := DefaultResolver.LookupIP(context.Background(), "ip", "")

src/net/lookup_unix.go

@@ -63,7 +63,7 @@ func (r *Resolver) lookupIP(ctx context.Context, network, host string) (addrs []
 	if order == hostLookupCgo {
 		return cgoLookupIP(ctx, network, host)
 	}
-	ips, _, err := r.goLookupIPCNAMEOrder(ctx, network, host, order, conf)
+	ips, _, err := r.goLookupIPCNAME(ctx, network, host, order, conf)
 	return ips, err
 }