package classifiers

import (
	"bytes"
	"encoding/binary"
	"github.com/google/gopacket"
	"github.com/google/gopacket/layers"
	"gitee.com/tingkle/godpi/types"
)

// RPCClassifier struct
type RPCClassifier struct{}

// HeuristicClassify for RPCClassifier
func (classifier RPCClassifier) HeuristicClassify(flow *types.Flow) bool {
	return checkFirstPayload(flow.GetPackets(), layers.LayerTypeTCP,
		func(payload []byte, packetsRest []gopacket.Packet) bool {
			if len(payload) < 24 {
				return false
			}
			// check first bytes for version 5.0 bind request
			firstBytes := []byte{5, 0, 11, 3, 16, 0, 0, 0}
			// check if lengths match
			frameLen := int(binary.LittleEndian.Uint16(payload[8:10]))
			return bytes.HasPrefix(payload, firstBytes) && len(payload) == frameLen
		})
}

// GetProtocol returns the corresponding protocol
func (classifier RPCClassifier) GetProtocol() types.Protocol {
	return types.RPC
}