refactor: move tls handshaker to netxlite (#400)

Part of https://github.com/ooni/probe/issues/1505

internal/netxlite/tlshandshaker.go

@@ -0,0 +1,46 @@
+package netxlite
+
+import (
+	"context"
+	"crypto/tls"
+	"net"
+	"time"
+)
+
+// TLSHandshaker is the generic TLS handshaker.
+type TLSHandshaker interface {
+	// Handshake creates a new TLS connection from the given connection and
+	// the given config. This function DOES NOT take ownership of the connection
+	// and it's your responsibility to close it on failure.
+	Handshake(ctx context.Context, conn net.Conn, config *tls.Config) (
+		net.Conn, tls.ConnectionState, error)
+}
+
+// TLSHandshakerStdlib is the stdlib's TLS handshaker.
+type TLSHandshakerStdlib struct {
+	// Timeout is the timeout imposed on the TLS handshake. If zero
+	// or negative, we will use default timeout of 10 seconds.
+	Timeout time.Duration
+}
+
+var _ TLSHandshaker = &TLSHandshakerStdlib{}
+
+// Handshake implements Handshaker.Handshake
+func (h *TLSHandshakerStdlib) Handshake(
+	ctx context.Context, conn net.Conn, config *tls.Config,
+) (net.Conn, tls.ConnectionState, error) {
+	timeout := h.Timeout
+	if timeout <= 0 {
+		timeout = 10 * time.Second
+	}
+	defer conn.SetDeadline(time.Time{})
+	conn.SetDeadline(time.Now().Add(timeout))
+	tlsconn := tls.Client(conn, config)
+	if err := tlsconn.Handshake(); err != nil {
+		return nil, tls.ConnectionState{}, err
+	}
+	return tlsconn, tlsconn.ConnectionState(), nil
+}
+
+// DefaultTLSHandshaker is the default TLS handshaker.
+var DefaultTLSHandshaker = &TLSHandshakerStdlib{}