Add shadowtls (#49)

* Add shadowtls outbound

* Add shadowtls inbound

* Add shadowtls example

* Add shadowtls documentation

outbound/shadowtls.go

@@ -0,0 +1,84 @@
+package outbound
+
+import (
+	"context"
+	"crypto/tls"
+	"net"
+	"os"
+
+	"github.com/sagernet/sing-box/adapter"
+	"github.com/sagernet/sing-box/common/dialer"
+	C "github.com/sagernet/sing-box/constant"
+	"github.com/sagernet/sing-box/log"
+	"github.com/sagernet/sing-box/option"
+	"github.com/sagernet/sing/common"
+	M "github.com/sagernet/sing/common/metadata"
+	N "github.com/sagernet/sing/common/network"
+)
+
+var _ adapter.Outbound = (*ShadowTLS)(nil)
+
+type ShadowTLS struct {
+	myOutboundAdapter
+	dialer     N.Dialer
+	serverAddr M.Socksaddr
+	tlsConfig  *tls.Config
+}
+
+func NewShadowTLS(ctx context.Context, router adapter.Router, logger log.ContextLogger, tag string, options option.ShadowTLSOutboundOptions) (*ShadowTLS, error) {
+	outbound := &ShadowTLS{
+		myOutboundAdapter: myOutboundAdapter{
+			protocol: C.TypeShadowTLS,
+			network:  []string{N.NetworkTCP},
+			router:   router,
+			logger:   logger,
+			tag:      tag,
+		},
+		dialer:     dialer.NewOutbound(router, options.OutboundDialerOptions),
+		serverAddr: options.ServerOptions.Build(),
+	}
+	if options.TLS == nil || !options.TLS.Enabled {
+		return nil, C.ErrTLSRequired
+	}
+	options.TLS.MinVersion = "1.2"
+	options.TLS.MaxVersion = "1.2"
+	var err error
+	outbound.tlsConfig, err = dialer.TLSConfig(options.Server, common.PtrValueOrDefault(options.TLS))
+	if err != nil {
+		return nil, err
+	}
+	return outbound, nil
+}
+
+func (s *ShadowTLS) DialContext(ctx context.Context, network string, destination M.Socksaddr) (net.Conn, error) {
+	switch N.NetworkName(network) {
+	case N.NetworkTCP:
+	default:
+		return nil, os.ErrInvalid
+	}
+	conn, err := s.dialer.DialContext(ctx, N.NetworkTCP, s.serverAddr)
+	if err != nil {
+		return nil, err
+	}
+	tlsConn, err := dialer.TLSClient(ctx, conn, s.tlsConfig)
+	if err != nil {
+		return nil, err
+	}
+	err = tlsConn.HandshakeContext(ctx)
+	if err != nil {
+		return nil, err
+	}
+	return conn, nil
+}
+
+func (s *ShadowTLS) ListenPacket(ctx context.Context, destination M.Socksaddr) (net.PacketConn, error) {
+	return nil, os.ErrInvalid
+}
+
+func (s *ShadowTLS) NewConnection(ctx context.Context, conn net.Conn, metadata adapter.InboundContext) error {
+	return NewConnection(ctx, s, conn, metadata)
+}
+
+func (s *ShadowTLS) NewPacketConnection(ctx context.Context, conn N.PacketConn, metadata adapter.InboundContext) error {
+	return os.ErrInvalid
+}