Add shadow-tls support

transport/internet/tls/custom.go

@@ -0,0 +1,21 @@
+package tls
+
+import (
+	"context"
+	"crypto/tls"
+
+	"github.com/xtls/xray-core/common/net"
+)
+
+type customClientKey struct{}
+
+type CustomClientFunc func(conn net.Conn, config *tls.Config) net.Conn
+
+func CustomClientFromContext(ctx context.Context) (CustomClientFunc, bool) {
+	client, loaded := ctx.Value(customClientKey{}).(CustomClientFunc)
+	return client, loaded
+}
+
+func ContextWithCustomClient(ctx context.Context, customClient CustomClientFunc) context.Context {
+	return context.WithValue(ctx, customClientKey{}, customClient)
+}