fix(netxlite): improve TLS auto-configuration (#409)

Auto-configure every relevant TLS field as close as possible to
where it's actually used.

As a side effect, add support for mocking the creation of a TLS
connection, which should possibly be useful for uTLS?

Work that is part of https://github.com/ooni/probe/issues/1505

internal/netxmocks/quic.go

@@ -1,6 +1,12 @@
 package netxmocks
 
-import "net"
+import (
+	"context"
+	"crypto/tls"
+	"net"
+
+	"github.com/lucas-clemente/quic-go"
+)
 
 // QUICListener is a mockable netxlite.QUICListener.
 type QUICListener struct {
@@ -11,3 +17,15 @@ type QUICListener struct {
 func (ql *QUICListener) Listen(addr *net.UDPAddr) (net.PacketConn, error) {
 	return ql.MockListen(addr)
 }
+
+// QUICContextDialer is a mockable netxlite.QUICContextDialer.
+type QUICContextDialer struct {
+	MockDialContext func(ctx context.Context, network, address string,
+		tlsConfig *tls.Config, quicConfig *quic.Config) (quic.EarlySession, error)
+}
+
+// DialContext calls MockDialContext.
+func (qcd *QUICContextDialer) DialContext(ctx context.Context, network, address string,
+	tlsConfig *tls.Config, quicConfig *quic.Config) (quic.EarlySession, error) {
+	return qcd.MockDialContext(ctx, network, address, tlsConfig, quicConfig)
+}

internal/netxmocks/quic_test.go

@@ -1,9 +1,13 @@
 package netxmocks
 
 import (
+	"context"
+	"crypto/tls"
 	"errors"
 	"net"
 	"testing"
+
+	"github.com/lucas-clemente/quic-go"
 )
 
 func TestQUICListenerListen(t *testing.T) {
@@ -21,3 +25,22 @@ func TestQUICListenerListen(t *testing.T) {
 		t.Fatal("expected nil conn here")
 	}
 }
+
+func TestQUICContextDialerDialContext(t *testing.T) {
+	expected := errors.New("mocked error")
+	qcd := &QUICContextDialer{
+		MockDialContext: func(ctx context.Context, network string, address string, tlsConfig *tls.Config, quicConfig *quic.Config) (quic.EarlySession, error) {
+			return nil, expected
+		},
+	}
+	ctx := context.Background()
+	tlsConfig := &tls.Config{}
+	quicConfig := &quic.Config{}
+	sess, err := qcd.DialContext(ctx, "udp", "dns.google:443", tlsConfig, quicConfig)
+	if !errors.Is(err, expected) {
+		t.Fatal("not the error we expected")
+	}
+	if sess != nil {
+		t.Fatal("expected nil session")
+	}
+}

internal/netxmocks/tlsconn.go

@@ -0,0 +1,25 @@
+package netxmocks
+
+import "crypto/tls"
+
+// TLSConn allows to mock netxlite.TLSConn.
+type TLSConn struct {
+	// Conn is the embedded mockable Conn.
+	Conn
+
+	// MockConnectionState allows to mock the ConnectionState method.
+	MockConnectionState func() tls.ConnectionState
+
+	// MockHandshake allows to mock the Handshake method.
+	MockHandshake func() error
+}
+
+// ConnectionState calls MockConnectionState.
+func (c *TLSConn) ConnectionState() tls.ConnectionState {
+	return c.MockConnectionState()
+}
+
+// Handshake calls MockHandshake.
+func (c *TLSConn) Handshake() error {
+	return c.MockHandshake()
+}