詳解S7源碼3-COTP and TPKT

連接 S7COMM簡介 https://www.anquanke.com/post/id/186099

OSI layer    Protocol
Application Layer    S7 communication
Presentation Layer    S7 communication(COTP)
Session Layer    S7 communication(TPKT)
Transport Layer    ISO-on-TCP (RFC 1006)
Network Layer    IP
Data Link Layer    Ethernet
Physical Layer    Ethernet

1,TPKT(默認端口號102)

tpkt主要為

version	1byte	0x03	3
resrved	1byte	0x00	0
length	2byte	0x16	22

length為包括這4字節+Payload在內的字節數.(Payload)為data包裝后數據.

1,TPKT類,返回TPKT信息和數據包.根據length-4求得data.就是Payload的數據.(解封).

internal class TPKT
    {
        public byte Version;
        public byte Reserved1;
        public int Length;
        public byte[] Data;

        /// <summary>
        /// Reads a TPKT from the socket
        /// </summary>
        /// <param name="stream">The stream to read from</param>
        /// <returns>TPKT Instance</returns>
        public static TPKT Read(Stream stream)
        {
            var buf = new byte[4];
            int len = stream.Read(buf, 0, 4);
            if (len < 4) throw new TPKTInvalidException("TPKT is incomplete / invalid");
            var pkt = new TPKT
            {
                Version = buf[0],
                Reserved1 = buf[1],
                Length = buf[2] * 256 + buf[3] //BigEndian
            };
            if (pkt.Length > 0)
            {
                pkt.Data = new byte[pkt.Length - 4];
                len = stream.Read(pkt.Data, 0, pkt.Length - 4);
                if (len < pkt.Length - 4)
                    throw new TPKTInvalidException("TPKT is incomplete / invalid");
            }
            return pkt;
        }

        /// <summary>
        /// Reads a TPKT from the socket Async
        /// </summary>
        /// <param name="stream">The stream to read from</param>
        /// <returns>Task TPKT Instace</returns>
        public static async Task<TPKT> ReadAsync(Stream stream)
        {
            var buf = new byte[4];
            int len = await stream.ReadAsync(buf, 0, 4);
            if (len < 4) throw new TPKTInvalidException("TPKT is incomplete / invalid");
            var pkt = new TPKT
            {
                Version = buf[0],
                Reserved1 = buf[1],
                Length = buf[2] * 256 + buf[3] //BigEndian
            };
            if (pkt.Length > 0)
            {
                pkt.Data = new byte[pkt.Length - 4];
                len = await stream.ReadAsync(pkt.Data, 0, pkt.Length - 4);
                if (len < pkt.Length - 4) throw new TPKTInvalidException("TPKT is incomplete / invalid");
            }
            return pkt;
        }

        public override string ToString()
        {
            return string.Format("Version: {0} Length: {1} Data: {2}",
                Version,
                Length,
                BitConverter.ToString(Data)
                );
        }
    }

2,TPDU-----Transport protocol data unit---一個基本數據傳輸單元(COTP)

第一個byte--標識為length---不包括本身.標識

第二給byte---標識為PDUType--分為以下幾種

0x0d	連接確認	0x05	拒絕
0x0e	連接請求	0xf0	數據包
0x08	斷開請求
0x0c	斷開確認

當其為0xf0的時候:

第三個byte---flags:其位7標志是否為最后的TPDU,位0-6標識塊NUMBER---TPDU NUMBER.

從stream---->TPKT---->TPDU---->再從TPDU中讀取數據TSDU.(減去4個字節的TPKT包裹+headerLength).

 public class TPDU
        {
            public byte HeaderLength;
            public byte PDUType;
            public int TPDUNumber;
            public byte[] Data;
            public bool LastDataUnit;

            public TPDU(TPKT tPKT)
            {
                var br = new BinaryReader(new MemoryStream(tPKT.Data));

                  
                HeaderLength = br.ReadByte();
                if (HeaderLength >= 2)
                {
                    PDUType = br.ReadByte();
                    if (PDUType == 0xf0) //DT Data
                    {
                        var flags = br.ReadByte();
                        TPDUNumber = flags & 0x7F;
                        LastDataUnit = (flags & 0x80) > 0;
                        Data = br.ReadBytes(tPKT.Length - HeaderLength - 4); //4 = TPKT Size
                        return;
                    }
                    //TODO: Handle other PDUTypes
                }
                Data = new byte[0];
            }

            /// <summary>
            /// Reads COTP TPDU (Transport protocol data unit) from the network stream
            /// See: https://tools.ietf.org/html/rfc905
            /// </summary>
            /// <param name="stream">The socket to read from</param>
            /// <returns>COTP DPDU instance</returns>
            public static TPDU Read(Stream stream)
            {
                var tpkt = TPKT.Read(stream);
                if (tpkt.Length > 0) return new TPDU(tpkt);
                return null;
            }

            /// <summary>
            /// Reads COTP TPDU (Transport protocol data unit) from the network stream
            /// See: https://tools.ietf.org/html/rfc905
            /// </summary>
            /// <param name="stream">The socket to read from</param>
            /// <returns>COTP DPDU instance</returns>
            public static async Task<TPDU> ReadAsync(Stream stream)
            {
                var tpkt = await TPKT.ReadAsync(stream);
                if (tpkt.Length > 0) return new TPDU(tpkt);
                return null;
            }

            public override string ToString()
            {
                return string.Format("Length: {0} PDUType: {1} TPDUNumber: {2} Last: {3} Segment Data: {4}",
                    HeaderLength,
                    PDUType,
                    TPDUNumber,
                    LastDataUnit,
                    BitConverter.ToString(Data)
                    );
            }

        }

3,TSDU---服務數據單元---定義了將連續的TPDU轉換為一個TSDU單元.

 public class TSDU
        {
            /// <summary>
            /// Reads the full COTP TSDU (Transport service data unit)
            /// See: https://tools.ietf.org/html/rfc905
            /// </summary>
            /// <param name="stream">The stream to read from</param>
            /// <returns>Data in TSDU</returns>
            public static byte[] Read(Stream stream)
            {
                var segment = TPDU.Read(stream);
                if (segment == null) return null;

                var output = new MemoryStream(segment.Data.Length);
                output.Write(segment.Data, 0, segment.Data.Length);

                while (!segment.LastDataUnit)
                {
                    segment = TPDU.Read(stream);
                    output.Write(segment.Data, (int)output.Position, segment.Data.Length);
                }
                return output.GetBuffer().Take((int)output.Position).ToArray();
            }

            /// <summary>
            /// Reads the full COTP TSDU (Transport service data unit)
            /// See: https://tools.ietf.org/html/rfc905
            /// </summary>
            /// <param name="stream">The stream to read from</param>
            /// <returns>Data in TSDU</returns>
            public static async Task<byte[]> ReadAsync(Stream stream)
            {
                var segment = await TPDU.ReadAsync(stream);
                if (segment == null) return null;

                var output = new MemoryStream(segment.Data.Length);
                output.Write(segment.Data, 0, segment.Data.Length);

                while (!segment.LastDataUnit)
                {
                    segment = await TPDU.ReadAsync(stream);
                    output.Write(segment.Data, (int)output.Position, segment.Data.Length);
                }
                return output.GetBuffer().Take((int)output.Position).ToArray();
            }
        }