fix: harden DynDNS recovery and publish v1.5.1

internal/netresolve/resolver_test.go

@@ -0,0 +1,120 @@
+package netresolve
+
+import (
+	"context"
+	"errors"
+	"net"
+	"net/netip"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+type lookupFunc func(context.Context, string, string) ([]netip.Addr, error)
+
+func (f lookupFunc) LookupNetIP(ctx context.Context, network, host string) ([]netip.Addr, error) {
+	return f(ctx, network, host)
+}
+
+func TestDNSOutageFallbackAndReturnToSystem(t *testing.T) {
+	t.Parallel()
+	var healthy atomic.Bool
+	var fallbacks atomic.Int32
+	r := &Resolver{timeout: time.Second}
+	r.system = lookupFunc(func(_ context.Context, network, host string) ([]netip.Addr, error) {
+		if network != "ip4" || host != "api.ipify.org" {
+			t.Errorf("unexpected query %s %s", network, host)
+		}
+		if healthy.Load() {
+			return []netip.Addr{netip.MustParseAddr("1.0.0.1")}, nil
+		}
+		return nil, &net.DNSError{Err: "server misbehaving", IsTemporary: true}
+	})
+	r.fallbacks = []lookup{lookupFunc(func(_ context.Context, network, host string) ([]netip.Addr, error) {
+		fallbacks.Add(1)
+		if network != "ip4" || host != "api.ipify.org." {
+			t.Errorf("fallback must use absolute family-specific query: %s %s", network, host)
+		}
+		return []netip.Addr{netip.MustParseAddr("1.1.1.1")}, nil
+	})}
+	for _, recovered := range []bool{false, true} {
+		healthy.Store(recovered)
+		ips, err := r.LookupNetIP(context.Background(), "ip4", "api.ipify.org")
+		want := "1.1.1.1"
+		if recovered {
+			want = "1.0.0.1"
+		}
+		if err != nil || len(ips) != 1 || ips[0].String() != want {
+			t.Fatalf("DNS recovery: %v %v", ips, err)
+		}
+	}
+	if fallbacks.Load() != 1 {
+		t.Fatal("system recovery did not stop fallback use")
+	}
+}
+
+func TestSlowDNSCannotBlockWorkingFallback(t *testing.T) {
+	t.Parallel()
+	slow := lookupFunc(func(ctx context.Context, _, _ string) ([]netip.Addr, error) { <-ctx.Done(); return nil, ctx.Err() })
+	r := &Resolver{system: slow, timeout: 20 * time.Millisecond, fallbacks: []lookup{slow, lookupFunc(func(context.Context, string, string) ([]netip.Addr, error) {
+		return []netip.Addr{netip.MustParseAddr("1.1.1.1")}, nil
+	})}}
+	started := time.Now()
+	ips, err := r.LookupNetIP(context.Background(), "ip4", "api.ipify.org")
+	if err != nil || len(ips) != 1 || time.Since(started) > time.Second {
+		t.Fatalf("blocked fallback: %v %v", ips, err)
+	}
+	r.fallbacks = []lookup{slow}
+	if _, err = r.LookupNetIP(context.Background(), "ip4", "api.ipify.org"); err == nil {
+		t.Fatal("total outage was hidden")
+	}
+}
+
+func TestDNSFallbackDoesNotOverrideNegativeAnswersOrLocalNames(t *testing.T) {
+	t.Parallel()
+	for _, test := range []struct {
+		host string
+		err  error
+	}{
+		{"api.ipify.org", &net.DNSError{IsNotFound: true}},
+		{"api.ipify.org", errors.New("permanent DNS error")},
+		{"pi.hole", &net.DNSError{IsTemporary: true}},
+		{"private.example", &net.DNSError{IsTemporary: true}},
+	} {
+		r := &Resolver{timeout: time.Second, system: lookupFunc(func(context.Context, string, string) ([]netip.Addr, error) { return nil, test.err }), fallbacks: []lookup{lookupFunc(func(context.Context, string, string) ([]netip.Addr, error) {
+			t.Error("unexpected external query")
+			return nil, nil
+		})}}
+		if _, err := r.LookupNetIP(context.Background(), "ip4", test.host); !errors.Is(err, test.err) {
+			t.Fatalf("original error lost: %v", err)
+		}
+	}
+}
+
+func TestCanceledDNSDoesNotStartFallback(t *testing.T) {
+	t.Parallel()
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	r := &Resolver{timeout: time.Second, system: lookupFunc(func(ctx context.Context, _, _ string) ([]netip.Addr, error) { return nil, ctx.Err() }), fallbacks: []lookup{lookupFunc(func(context.Context, string, string) ([]netip.Addr, error) {
+		t.Error("fallback after cancellation")
+		return nil, nil
+	})}}
+	if _, err := r.LookupNetIP(ctx, "ip6", "api6.ipify.org"); !errors.Is(err, context.Canceled) {
+		t.Fatal(err)
+	}
+}
+
+func TestDialAddressesTriesNextAddress(t *testing.T) {
+	t.Parallel()
+	listener, err := net.Listen("tcp4", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listener.Close()
+	_, port, _ := net.SplitHostPort(listener.Addr().String())
+	conn, err := DialAddresses(context.Background(), "tcp4", []netip.Addr{netip.MustParseAddr("127.0.0.2"), netip.MustParseAddr("127.0.0.1")}, port)
+	if err != nil {
+		t.Fatal(err)
+	}
+	conn.Close()
+}