feat(tsconnect/wasm): add upgradeTLS to wrapped conns

Adds an upgradeTLS method to the conn objects returned by dial/accept,
wrapping the existing net.Conn with crypto/tls in place (STARTTLS /
FTPS AUTH TLS style). Client mode reuses the dialTLS options
(serverName, insecureSkipVerify, caCerts), now factored into
tlsClientConfigFromJS; server mode takes isServer with certPem/keyPem.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XfRgMke8p7QDxD5QM5thxH

cmd/tsconnect/wasm/wasm_js.go

@@ -889,6 +889,41 @@ func (i *jsIPN) listen(network, addr string) js.Value {
 	})
 }
 
+// tlsClientConfigFromJS builds a client tls.Config from optional JS options
+// (serverName, insecureSkipVerify, caCerts). defaultServerName may be empty
+// (STARTTLS upgrade case), in which case serverName must be provided unless
+// insecureSkipVerify is set.
+//
+// On wasm there's no system root pool, so default to the baked-in
+// LetsEncrypt roots (which is what `tailscale cert` uses for tailnet
+// HTTPS endpoints). Callers can override with caCerts (PEM) or bypass
+// entirely with insecureSkipVerify.
+func tlsClientConfigFromJS(defaultServerName string, opts js.Value) (*tls.Config, error) {
+	cfg := &tls.Config{
+		ServerName: defaultServerName,
+		RootCAs:    bakedroots.Get(),
+	}
+	if !opts.IsUndefined() && !opts.IsNull() {
+		if sn := opts.Get("serverName"); sn.Type() == js.TypeString {
+			cfg.ServerName = sn.String()
+		}
+		if iv := opts.Get("insecureSkipVerify"); iv.Type() == js.TypeBoolean {
+			cfg.InsecureSkipVerify = iv.Bool()
+		}
+		if ca := opts.Get("caCerts"); ca.Type() == js.TypeString {
+			pool := x509.NewCertPool()
+			if !pool.AppendCertsFromPEM([]byte(ca.String())) {
+				return nil, fmt.Errorf("caCerts: no valid PEM certificates found")
+			}
+			cfg.RootCAs = pool
+		}
+	}
+	if cfg.ServerName == "" && !cfg.InsecureSkipVerify {
+		return nil, fmt.Errorf("serverName is required unless insecureSkipVerify is set")
+	}
+	return cfg, nil
+}
+
 func (i *jsIPN) dialTLS(addr string, opts js.Value) js.Value {
 	return makePromise(func() (any, error) {
 		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
@@ -899,28 +934,9 @@ func (i *jsIPN) dialTLS(addr string, opts js.Value) js.Value {
 			return nil, fmt.Errorf("invalid address %q: %w", addr, err)
 		}
 
-		// On wasm there's no system root pool, so default to the
-		// baked-in LetsEncrypt roots (which is what `tailscale cert`
-		// uses for tailnet HTTPS endpoints). Callers can override with
-		// caCerts (PEM) or bypass entirely with insecureSkipVerify.
-		cfg := &tls.Config{
-			ServerName: host,
-			RootCAs:    bakedroots.Get(),
-		}
-		if !opts.IsUndefined() && !opts.IsNull() {
-			if sn := opts.Get("serverName"); sn.Type() == js.TypeString {
-				cfg.ServerName = sn.String()
-			}
-			if iv := opts.Get("insecureSkipVerify"); iv.Type() == js.TypeBoolean {
-				cfg.InsecureSkipVerify = iv.Bool()
-			}
-			if ca := opts.Get("caCerts"); ca.Type() == js.TypeString {
-				pool := x509.NewCertPool()
-				if !pool.AppendCertsFromPEM([]byte(ca.String())) {
-					return nil, fmt.Errorf("caCerts: no valid PEM certificates found")
-				}
-				cfg.RootCAs = pool
-			}
+		cfg, err := tlsClientConfigFromJS(host, opts)
+		if err != nil {
+			return nil, err
 		}
 
 		rawConn, err := i.dialer.UserDial(ctx, "tcp", addr)
@@ -1464,6 +1480,46 @@ func wrapConn(conn net.Conn) map[string]any {
 		"remoteAddr": js.FuncOf(func(this js.Value, args []js.Value) any {
 			return conn.RemoteAddr().String()
 		}),
+		// upgradeTLS wraps the conn in TLS in place (STARTTLS-style) and
+		// returns a new wrapped conn sharing the same underlying net.Conn;
+		// the old handle must not be used afterward. On handshake failure
+		// the underlying conn is closed. With isServer, certPem and keyPem
+		// are required; otherwise client options as in dialTLS apply.
+		"upgradeTLS": js.FuncOf(func(this js.Value, args []js.Value) any {
+			opts := js.Undefined()
+			if len(args) > 0 {
+				opts = args[0]
+			}
+			return makePromise(func() (any, error) {
+				var tlsConn *tls.Conn
+				hasOpts := !opts.IsUndefined() && !opts.IsNull()
+				if hasOpts && opts.Get("isServer").Type() == js.TypeBoolean && opts.Get("isServer").Bool() {
+					certPem := opts.Get("certPem")
+					keyPem := opts.Get("keyPem")
+					if certPem.Type() != js.TypeString || keyPem.Type() != js.TypeString {
+						return nil, fmt.Errorf("upgradeTLS: certPem and keyPem are required when isServer is set")
+					}
+					cert, err := tls.X509KeyPair([]byte(certPem.String()), []byte(keyPem.String()))
+					if err != nil {
+						return nil, fmt.Errorf("upgradeTLS: parsing cert/key: %w", err)
+					}
+					tlsConn = tls.Server(conn, &tls.Config{Certificates: []tls.Certificate{cert}})
+				} else {
+					cfg, err := tlsClientConfigFromJS("", opts)
+					if err != nil {
+						return nil, err
+					}
+					tlsConn = tls.Client(conn, cfg)
+				}
+				ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+				defer cancel()
+				if err := tlsConn.HandshakeContext(ctx); err != nil {
+					conn.Close()
+					return nil, err
+				}
+				return wrapConn(tlsConn), nil
+			})
+		}),
 	}
 }