/
packet.go
339 lines (295 loc) · 9.88 KB
/
packet.go
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package packet
import (
"bytes"
"encoding/binary"
"fmt"
"strconv"
"github.com/LdDl/go-egts/egts/subrecord"
"github.com/LdDl/go-egts/crc"
)
// Packet EGTS packet
type Packet struct {
/* Header section */
ProtocolVersion uint8 `json:"PRV"` // PRV (Protocol Version)
SecurityKeyID uint8 `json:"SKID"` // SKID (Security Key ID)
/* Flags section */
PRF string `json:"PRF"` // PRF (Prefix)
PR string `json:"PR"` // PR (Priority)
CMP string `json:"CMP"` // CMP (Compression)
ENA string `json:"ENA"` // ENA (Encryption Algorithm)
RTE string `json:"RTE"` // RTE (Route)
/* Data section */
HeaderLength uint8 `json:"HL"` // HL (Header Length)
HeaderEncoding uint8 `json:"HE"` // HE (Header Encoding)
FrameDataLength uint16 `json:"FDL"` // FDL (Frame Data Length)
PacketID uint16 `json:"PID"` // PID (Packet Identifier)
PacketType uint8 `json:"PT"` // PT (Packet Type)
PeerAddress uint16 `json:"PRA"` // PRA (Peer Address)
RecipientAddress uint16 `json:"RCA"` // RCA (Recipient Address)
TimeToLive uint8 `json:"TTL"` // TTL (Time To Live)
HeaderCheckSum uint8 `json:"HCS"` // HCS (Header Check Sum)
ServicesFrameData BytesData `json:"SFRD"` // SFRD (Services Frame Data)
ServicesFrameDataCheckSum uint16 `json:"SFRCS"` // SFRCS
ErrorCode uint8 `json:"-"`
}
// ReadPacket Parse slice of bytes as EGTS packet
func ReadPacket(b []byte) (p Packet, err error) {
buffer := bytes.NewBuffer(b)
// PR Processing Result
if p.ProtocolVersion, err = buffer.ReadByte(); err != nil {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_INC_HEADERFORM;" + err.Error())
}
if p.SecurityKeyID, err = buffer.ReadByte(); err != nil {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_INC_HEADERFORM;" + err.Error())
}
flagByte := byte(0)
if flagByte, err = buffer.ReadByte(); err != nil {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_INC_HEADERFORM;" + err.Error())
}
flagByteAsBits := fmt.Sprintf("%08b", flagByte)
p.PRF = flagByteAsBits[:2] // flags << 7, flags << 6
p.RTE = flagByteAsBits[2:3] // flags << 5
p.ENA = flagByteAsBits[3:5] // flags << 4, flags << 3
p.CMP = flagByteAsBits[5:6] // flags << 2
p.PR = flagByteAsBits[6:] // flags << 1, flags << 0
if p.HeaderLength, err = buffer.ReadByte(); err != nil {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_INC_HEADERFORM;" + err.Error())
}
if p.HeaderEncoding, err = buffer.ReadByte(); err != nil {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_INC_HEADERFORM;" + err.Error())
}
tmpFDL := make([]byte, 2)
if _, err = buffer.Read(tmpFDL); err != nil {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_INC_HEADERFORM;" + err.Error())
}
p.FrameDataLength = binary.LittleEndian.Uint16(tmpFDL)
tmpPID := make([]byte, 2)
if _, err = buffer.Read(tmpPID); err != nil {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_INC_HEADERFORM;" + err.Error())
}
p.PacketID = binary.LittleEndian.Uint16(tmpPID)
if p.PacketType, err = buffer.ReadByte(); err != nil {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_INC_HEADERFORM;" + err.Error())
}
if p.RTE == "1" {
tmpPeer := make([]byte, 2)
if _, err = buffer.Read(tmpPeer); err != nil {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_INC_HEADERFORM;" + err.Error())
}
p.PeerAddress = binary.LittleEndian.Uint16(tmpPeer)
tmpRecipient := make([]byte, 2)
if _, err = buffer.Read(tmpRecipient); err != nil {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_INC_HEADERFORM;" + err.Error())
}
p.RecipientAddress = binary.LittleEndian.Uint16(tmpRecipient)
if p.TimeToLive, err = buffer.ReadByte(); err != nil {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_INC_HEADERFORM;" + err.Error())
}
}
if p.HeaderCheckSum, err = buffer.ReadByte(); err != nil {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_INC_HEADERFORM;" + err.Error())
}
// Evaluate crc-8
if len(b) < int(p.HeaderLength) {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_HEADERCRC_ERROR")
}
if p.HeaderLength-1 > uint8(len(b)) {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_HEADERCRC_ERROR")
}
if int(p.HeaderCheckSum) != crc.Crc(8, b[:p.HeaderLength-1]) {
p.ErrorCode = EGTS_PC_HEADERCRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_HEADERCRC_ERROR")
}
dataFrameBytes := make([]byte, p.FrameDataLength)
if _, err = buffer.Read(dataFrameBytes); err != nil {
p.ErrorCode = EGTS_PC_INC_DATAFORM
return p, fmt.Errorf("Packet; EGTS_PC_INC_DATAFORM;" + err.Error())
}
// Check type of packet
switch p.PacketType {
case EGTS_PT_RESPONSE:
p.ServicesFrameData = &PTResponse{}
break
case EGTS_PT_APPDATA:
p.ServicesFrameData = &ServicesFrameData{}
break
case EGTS_PT_SIGNED_APPDATA:
// @TODO (not implemented yet)
break
default:
// nothing
break
}
if err = p.ServicesFrameData.Decode(dataFrameBytes); err != nil {
p.ErrorCode = EGTS_PC_INC_DATAFORM
return p, fmt.Errorf("Packet dataFrame; EGTS_PC_INC_DATAFORM;" + err.Error())
}
crc16Bytes := make([]byte, 2)
if _, err = buffer.Read(crc16Bytes); err != nil {
p.ErrorCode = EGTS_PC_DECRYPT_ERROR
return p, fmt.Errorf("Packet crc16; EGTS_PC_DECRYPT_ERROR;" + err.Error())
}
p.ServicesFrameDataCheckSum = binary.LittleEndian.Uint16(crc16Bytes)
if int(p.ServicesFrameDataCheckSum) != crc.Crc(16, b[p.HeaderLength:uint16(p.HeaderLength)+p.FrameDataLength]) {
p.ErrorCode = EGTS_PC_DATACRC_ERROR
return p, fmt.Errorf("Packet; EGTS_PC_DATACRC_ERROR")
}
return p, nil
}
// Encode Parse EGTS_PT_RESPONSE to slice of bytes
func (p *Packet) Encode() (b []byte) {
b = append(b, p.ProtocolVersion)
b = append(b, p.SecurityKeyID)
flagsBits := p.PRF + p.RTE + p.ENA + p.CMP + p.PR
flags := uint64(0)
flags, _ = strconv.ParseUint(flagsBits, 2, 8)
b = append(b, uint8(flags))
b = append(b, p.HeaderLength)
b = append(b, p.HeaderEncoding)
fdl := make([]byte, 2)
binary.LittleEndian.PutUint16(fdl, p.FrameDataLength)
b = append(b, fdl...)
pid := make([]byte, 2)
binary.LittleEndian.PutUint16(pid, p.PacketID)
b = append(b, pid...)
b = append(b, p.PacketType)
if p.RTE == "1" {
peerA := make([]byte, 2)
binary.LittleEndian.PutUint16(peerA, p.PeerAddress)
b = append(b, peerA...)
recepientA := make([]byte, 2)
binary.LittleEndian.PutUint16(recepientA, p.RecipientAddress)
b = append(b, recepientA...)
b = append(b, p.TimeToLive)
}
crc8 := uint8(crc.Crc(8, b))
b = append(b, crc8)
if p.ServicesFrameData != nil {
sfrd, _ := p.ServicesFrameData.Encode()
if len(sfrd) > 1 {
b = append(b, sfrd...)
crc16 := uint16(crc.Crc(16, sfrd))
crc16hash := make([]byte, 2)
binary.LittleEndian.PutUint16(crc16hash, crc16)
b = append(b, crc16hash...)
}
}
return b
}
// PrepareAnswer Prepare answer for incoming packet
func (p *Packet) PrepareAnswer(recordNum, pid uint16) Packet {
if p.PacketType == EGTS_PT_APPDATA {
records := RecordsData{}
serviceType := uint8(0)
if p.ServicesFrameData != nil {
for _, r := range *p.ServicesFrameData.(*ServicesFrameData) {
records = append(records, &RecordData{
SubrecordType: RecordResponse,
SubrecordLength: 3,
SubrecordData: &subrecord.SRRecordResponse{
ConfirmedRecordNumber: r.RecordNumber,
RecordStatus: EGTS_PC_OK,
},
})
serviceType = r.SourceServiceType
}
resp := PTResponse{
ResponsePacketID: p.PacketID,
ProcessingResult: p.ErrorCode,
}
if records != nil {
resp.SDR = &ServicesFrameData{
&ServiceDataRecord{
RecordLength: records.Len(),
RecordNumber: recordNum,
SSOD: "0",
RSOD: "1",
GRP: "0",
RPP: "11",
TMFE: "0",
EVFE: "0",
OBFE: "0",
SourceServiceType: serviceType,
RecipientServiceType: serviceType,
RecordsData: records,
},
}
}
ans := Packet{
ProtocolVersion: 1,
SecurityKeyID: 0,
PRF: "00",
RTE: "0",
ENA: "00",
CMP: "0",
PR: "11",
HeaderLength: 11,
HeaderEncoding: 0,
FrameDataLength: resp.Len(),
PacketID: pid,
PacketType: EGTS_PT_RESPONSE,
ServicesFrameData: &resp,
}
return ans
}
}
return Packet{}
}
// PrepareSRResultCode Prepare result code (SR_Result_Code) for incoming packet
func (p *Packet) PrepareSRResultCode(c uint8, recordNum, pid uint16) Packet {
data := RecordsData{
&RecordData{
SubrecordType: ResultCode,
SubrecordLength: 1,
SubrecordData: &subrecord.SRResultCode{
RCD: c,
},
},
}
sfrd := ServicesFrameData{
&ServiceDataRecord{
RecordLength: data.Len(),
RecordNumber: recordNum,
SSOD: "0",
RSOD: "0",
GRP: "1",
RPP: "00",
TMFE: "0",
EVFE: "0",
OBFE: "0",
SourceServiceType: SERVICE_AUTH,
RecipientServiceType: SERVICE_AUTH,
RecordsData: data,
},
}
resp := Packet{
ProtocolVersion: 1,
SecurityKeyID: 0,
PRF: "00",
RTE: "0",
ENA: "00",
CMP: "0",
PR: "00",
HeaderLength: 11,
HeaderEncoding: 0,
FrameDataLength: sfrd.Len(),
PacketID: pid,
PacketType: RecordResponse,
ServicesFrameData: &sfrd,
}
return resp
}