feat(netxlite): implement single use {,tls} dialer (#464)

This basically adapts already existing code inside websteps to
instead be into the netxlite package, where it belongs.

In the process, abstract the TLSDialer but keep a reference to the
previous name to avoid refactoring existing code (just for now).

While there, notice that the right name is CloseIdleConnections (i.e.,
plural not singular) and change the name.

While there, since we abstracted TLSDialer to be an interface, create
suitable factories for making a TLSDialer type from a Dialer and a
TLSHandshaker.

See https://github.com/ooni/probe/issues/1591

internal/netxlite/tls_test.go

@@ -280,21 +280,21 @@ func TestTLSHandshakerLoggerFailure(t *testing.T) {
 
 func TestTLSDialerCloseIdleConnections(t *testing.T) {
 	var called bool
-	dialer := &TLSDialer{
+	dialer := &tlsDialer{
 		Dialer: &mocks.Dialer{
 			MockCloseIdleConnections: func() {
 				called = true
 			},
 		},
 	}
-	dialer.CloseIdleConnection()
+	dialer.CloseIdleConnections()
 	if !called {
 		t.Fatal("not called")
 	}
 }
 
 func TestTLSDialerDialTLSContextFailureSplitHostPort(t *testing.T) {
-	dialer := &TLSDialer{}
+	dialer := &tlsDialer{}
 	ctx := context.Background()
 	const address = "www.google.com" // missing port
 	conn, err := dialer.DialTLSContext(ctx, "tcp", address)
@@ -309,7 +309,7 @@ func TestTLSDialerDialTLSContextFailureSplitHostPort(t *testing.T) {
 func TestTLSDialerDialTLSContextFailureDialing(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	cancel() // immediately fail
-	dialer := TLSDialer{Dialer: defaultDialer}
+	dialer := tlsDialer{Dialer: defaultDialer}
 	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)
@@ -321,7 +321,7 @@ func TestTLSDialerDialTLSContextFailureDialing(t *testing.T) {
 
 func TestTLSDialerDialTLSContextFailureHandshaking(t *testing.T) {
 	ctx := context.Background()
-	dialer := TLSDialer{
+	dialer := tlsDialer{
 		Config: &tls.Config{},
 		Dialer: &mocks.Dialer{MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
 			return &mocks.Conn{MockWrite: func(b []byte) (int, error) {
@@ -345,7 +345,7 @@ func TestTLSDialerDialTLSContextFailureHandshaking(t *testing.T) {
 
 func TestTLSDialerDialTLSContextSuccessHandshaking(t *testing.T) {
 	ctx := context.Background()
-	dialer := TLSDialer{
+	dialer := tlsDialer{
 		Dialer: &mocks.Dialer{MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
 			return &mocks.Conn{MockWrite: func(b []byte) (int, error) {
 				return 0, io.EOF
@@ -372,7 +372,7 @@ func TestTLSDialerDialTLSContextSuccessHandshaking(t *testing.T) {
 }
 
 func TestTLSDialerConfigFromEmptyConfigForWeb(t *testing.T) {
-	d := &TLSDialer{}
+	d := &tlsDialer{}
 	config := d.config("www.google.com", "443")
 	if config.ServerName != "www.google.com" {
 		t.Fatal("invalid server name")
@@ -383,7 +383,7 @@ func TestTLSDialerConfigFromEmptyConfigForWeb(t *testing.T) {
 }
 
 func TestTLSDialerConfigFromEmptyConfigForDoT(t *testing.T) {
-	d := &TLSDialer{}
+	d := &tlsDialer{}
 	config := d.config("dns.google", "853")
 	if config.ServerName != "dns.google" {
 		t.Fatal("invalid server name")
@@ -394,7 +394,7 @@ func TestTLSDialerConfigFromEmptyConfigForDoT(t *testing.T) {
 }
 
 func TestTLSDialerConfigWithServerName(t *testing.T) {
-	d := &TLSDialer{
+	d := &tlsDialer{
 		Config: &tls.Config{
 			ServerName: "example.com",
 		},
@@ -409,7 +409,7 @@ func TestTLSDialerConfigWithServerName(t *testing.T) {
 }
 
 func TestTLSDialerConfigWithALPN(t *testing.T) {
-	d := &TLSDialer{
+	d := &tlsDialer{
 		Config: &tls.Config{
 			NextProtos: []string{"h2"},
 		},
@@ -440,3 +440,43 @@ func TestNewTLSHandshakerStdlibTypes(t *testing.T) {
 		t.Fatal("expected nil NewConn")
 	}
 }
+
+func TestNewTLSDialerWorksAsIntended(t *testing.T) {
+	d := &mocks.Dialer{}
+	tlsh := &mocks.TLSHandshaker{}
+	td := NewTLSDialer(d, tlsh)
+	tdut, okay := td.(*tlsDialer)
+	if !okay {
+		t.Fatal("invalid type")
+	}
+	if tdut.Config == nil {
+		t.Fatal("unexpected config")
+	}
+	if tdut.Dialer != d {
+		t.Fatal("unexpected dialer")
+	}
+	if tdut.TLSHandshaker != tlsh {
+		t.Fatal("invalid handshaker")
+	}
+}
+
+func TestNewSingleUseTLSDialerWorksAsIntended(t *testing.T) {
+	conn := &mocks.TLSConn{}
+	d := NewSingleUseTLSDialer(conn)
+	outconn, err := d.DialTLSContext(context.Background(), "", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if conn != outconn {
+		t.Fatal("invalid outconn")
+	}
+	for i := 0; i < 4; i++ {
+		outconn, err = d.DialTLSContext(context.Background(), "", "")
+		if !errors.Is(err, ErrNoConnReuse) {
+			t.Fatal("not the error we expected", err)
+		}
+		if outconn != nil {
+			t.Fatal("expected nil outconn here")
+		}
+	}
+}