refactor(netxlite): use *Netx for the system dialer

This diff is like 7224984
except that we are converting the system dialer constructors to
use *Netx rather than converting the system resolver.

While there, realize that DialerSystem could become private.

Part of ooni/probe#2531

internal/netxlite/dialer.go

@@ -22,10 +22,17 @@ func NewDialerWithStdlibResolver(dl model.DebugLogger) model.Dialer {
 	return NewDialerWithResolver(dl, reso)
 }
 
-// NewDialerWithResolver is equivalent to calling WrapDialer with
-// the dialer argument being equal to &DialerSystem{}.
+// NewDialerWithResolver is equivalent to calling WrapDialer with a dialer using the stdlib
+// where the underlying dialer uses the [*Netx] UnderlyingNetwork for dialing.
+func (netx *Netx) NewDialerWithResolver(dl model.DebugLogger, r model.Resolver, w ...model.DialerWrapper) model.Dialer {
+	return WrapDialer(dl, r, &dialerSystem{provider: netx.maybeCustomUnderlyingNetwork()}, w...)
+}
+
+// NewDialerWithResolver is equivalent to creating an empty [*Netx]
+// and callings its NewDialerWithResolver method.
 func NewDialerWithResolver(dl model.DebugLogger, r model.Resolver, w ...model.DialerWrapper) model.Dialer {
-	return WrapDialer(dl, r, &DialerSystem{}, w...)
+	netx := &Netx{Underlying: nil}
+	return netx.NewDialerWithResolver(dl, r, w...)
 }
 
 // WrapDialer wraps an existing Dialer to add extra functionality
@@ -142,24 +149,24 @@ func NewDialerWithoutResolver(dl model.DebugLogger, w ...model.DialerWrapper) mo
 	return NewDialerWithResolver(dl, &NullResolver{}, w...)
 }
 
-// DialerSystem is a model.Dialer that uses the stdlib's net.Dialer
+// dialerSystem is a model.Dialer that uses the stdlib's net.Dialer
 // to construct the new SimpleDialer used for dialing. This dialer has
 // a fixed timeout for each connect operation equal to 15 seconds.
-type DialerSystem struct {
+type dialerSystem struct {
 	// provider is the OPTIONAL nil-safe [model.UnderlyingNetwork] provider.
 	provider *MaybeCustomUnderlyingNetwork
 }
 
-var _ model.Dialer = &DialerSystem{}
+var _ model.Dialer = &dialerSystem{}
 
-func (d *DialerSystem) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
+func (d *dialerSystem) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
 	p := d.provider.Get()
 	ctx, cancel := context.WithTimeout(ctx, p.DialTimeout())
 	defer cancel()
 	return p.DialContext(ctx, network, address)
 }
 
-func (d *DialerSystem) CloseIdleConnections() {
+func (d *dialerSystem) CloseIdleConnections() {
 	// nothing to do here
 }
 

internal/netxlite/dialer_test.go

@@ -31,7 +31,7 @@ func TestNewDialerWithStdlibResolver(t *testing.T) {
 		t.Fatal("invalid logger")
 	}
 	errWrapper := logger.Dialer.(*dialerErrWrapper)
-	_ = errWrapper.Dialer.(*DialerSystem)
+	_ = errWrapper.Dialer.(*dialerSystem)
 }
 
 type extensionDialerFirst struct {
@@ -76,19 +76,19 @@ func TestNewDialer(t *testing.T) {
 		ext2 := logger.Dialer.(*extensionDialerSecond)
 		ext1 := ext2.Dialer.(*extensionDialerFirst)
 		errWrapper := ext1.Dialer.(*dialerErrWrapper)
-		_ = errWrapper.Dialer.(*DialerSystem)
+		_ = errWrapper.Dialer.(*dialerSystem)
 	})
 }
 
 func TestDialerSystem(t *testing.T) {
 	t.Run("CloseIdleConnections", func(t *testing.T) {
-		d := &DialerSystem{}
+		d := &dialerSystem{}
 		d.CloseIdleConnections() // to avoid missing coverage
 	})
 
 	t.Run("DialContext", func(t *testing.T) {
 		t.Run("with canceled context", func(t *testing.T) {
-			d := &DialerSystem{}
+			d := &dialerSystem{}
 			ctx, cancel := context.WithCancel(context.Background())
 			cancel() // immediately!
 			conn, err := d.DialContext(ctx, "tcp", "8.8.8.8:443")
@@ -108,7 +108,7 @@ func TestDialerSystem(t *testing.T) {
 				},
 				MockDialContext: defaultTp.DialContext,
 			}
-			d := &DialerSystem{provider: &MaybeCustomUnderlyingNetwork{tp}}
+			d := &dialerSystem{provider: &MaybeCustomUnderlyingNetwork{tp}}
 			ctx := context.Background()
 			start := time.Now()
 			conn, err := d.DialContext(ctx, "tcp", "dns.google:443")
@@ -134,7 +134,7 @@ func TestDialerSystem(t *testing.T) {
 					return nil, expected
 				},
 			}
-			d := &DialerSystem{provider: &MaybeCustomUnderlyingNetwork{proxy}}
+			d := &dialerSystem{provider: &MaybeCustomUnderlyingNetwork{proxy}}
 			conn, err := d.DialContext(context.Background(), "tcp", "dns.google:443")
 			if conn != nil {
 				t.Fatal("unexpected conn")
@@ -150,7 +150,7 @@ func TestDialerResolverWithTracing(t *testing.T) {
 	t.Run("DialContext", func(t *testing.T) {
 		t.Run("fails without a port", func(t *testing.T) {
 			d := &dialerResolverWithTracing{
-				Dialer:   &DialerSystem{},
+				Dialer:   &dialerSystem{},
 				Resolver: NewUnwrappedStdlibResolver(),
 			}
 			const missingPort = "ooni.nu"
@@ -497,7 +497,7 @@ func TestDialerResolverWithTracing(t *testing.T) {
 	t.Run("lookupHost", func(t *testing.T) {
 		t.Run("handles addresses correctly", func(t *testing.T) {
 			dialer := &dialerResolverWithTracing{
-				Dialer:   &DialerSystem{},
+				Dialer:   &dialerSystem{},
 				Resolver: &NullResolver{},
 			}
 			addrs, err := dialer.lookupHost(context.Background(), "1.1.1.1")
@@ -511,7 +511,7 @@ func TestDialerResolverWithTracing(t *testing.T) {
 
 		t.Run("fails correctly on lookup error", func(t *testing.T) {
 			dialer := &dialerResolverWithTracing{
-				Dialer:   &DialerSystem{},
+				Dialer:   &dialerSystem{},
 				Resolver: &NullResolver{},
 			}
 			ctx := context.Background()

internal/netxlite/netx.go

@@ -22,12 +22,6 @@ func (netx *Netx) maybeCustomUnderlyingNetwork() *MaybeCustomUnderlyingNetwork {
 	return &MaybeCustomUnderlyingNetwork{netx.Underlying}
 }
 
-// NewDialerWithResolver is like [netxlite.NewDialerWithResolver] but the constructed [model.Dialer]
-// uses the [model.UnderlyingNetwork] configured inside the [Netx] structure.
-func (n *Netx) NewDialerWithResolver(dl model.DebugLogger, r model.Resolver, w ...model.DialerWrapper) model.Dialer {
-	return WrapDialer(dl, r, &DialerSystem{provider: n.maybeCustomUnderlyingNetwork()}, w...)
-}
-
 // NewUDPListener is like [netxlite.NewUDPListener] but the constructed [model.UDPListener]
 // uses the [model.UnderlyingNetwork] configured inside the [Netx] structure.
 func (n *Netx) NewUDPListener() model.UDPListener {

internal/netxlite/tls_test.go

@@ -711,7 +711,7 @@ func TestTLSDialer(t *testing.T) {
 		t.Run("failure dialing", func(t *testing.T) {
 			ctx, cancel := context.WithCancel(context.Background())
 			cancel() // immediately fail
-			dialer := tlsDialer{Dialer: &DialerSystem{}}
+			dialer := tlsDialer{Dialer: &dialerSystem{}}
 			conn, err := dialer.DialTLSContext(ctx, "tcp", "www.google.com:443")
 			if err == nil || !strings.HasSuffix(err.Error(), "operation was canceled") {
 				t.Fatal("not the error we expected", err)