package sniff

import (
	"context"
	"os"

	"github.com/sagernet/sing-box/adapter"
	C "github.com/sagernet/sing-box/constant"
)

func DTLSRecord(ctx context.Context, packet []byte) (*adapter.InboundContext, error) {
	const fixedHeaderSize = 13
	if len(packet) < fixedHeaderSize {
		return nil, os.ErrInvalid
	}
	contentType := packet[0]
	switch contentType {
	case 20, 21, 22, 23, 25:
	default:
		return nil, os.ErrInvalid
	}
	versionMajor := packet[1]
	if versionMajor != 0xfe {
		return nil, os.ErrInvalid
	}
	versionMinor := packet[2]
	if versionMinor != 0xff && versionMinor != 0xfd {
		return nil, os.ErrInvalid
	}
	return &adapter.InboundContext{Protocol: C.ProtocolDTLS}, nil
}