feat: tlsmiddlebox experiment (#817)

See https://github.com/ooni/probe/issues/2124

internal/engine/experiment/tlsmiddlebox/dialer.go

@@ -0,0 +1,45 @@
+package tlsmiddlebox
+
+//
+// Custom TTL dialer
+//
+
+import (
+	"context"
+	"net"
+	"time"
+
+	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/netxlite"
+)
+
+const timeout time.Duration = 15 * time.Second
+
+func NewDialerTTLWrapper() model.Dialer {
+	return &dialerTTLWrapper{
+		Dialer: &net.Dialer{Timeout: timeout},
+	}
+}
+
+// dialerTTLWrapper wraps errors and also returns a TTL wrapped conn
+type dialerTTLWrapper struct {
+	Dialer model.SimpleDialer
+}
+
+var _ model.Dialer = &dialerTTLWrapper{}
+
+// DialContext implements model.Dialer.DialContext
+func (d *dialerTTLWrapper) DialContext(ctx context.Context, network string, address string) (net.Conn, error) {
+	conn, err := d.Dialer.DialContext(ctx, network, address)
+	if err != nil {
+		return nil, netxlite.NewErrWrapper(netxlite.ClassifyGenericError, netxlite.ConnectOperation, err)
+	}
+	return &dialerTTLWrapperConn{
+		Conn: conn,
+	}, nil
+}
+
+// CloseIdleConnections implements model.Dialer.CloseIdleConnections
+func (d *dialerTTLWrapper) CloseIdleConnections() {
+	// nothing to do here
+}