NatTypeTester/STUN/Message/StunMessage.cs

using STUN.Message.Enums;
using System;
using System.Collections.Generic;
using System.Net;
using System.Text;

namespace STUN.Message
{
    /// <summary>
    /// Implements STUN message. Defined in RFC 5389.
    /// </summary>
    /// <remarks>
    /// https://tools.ietf.org/html/rfc5389#section-6
    /// </remarks>
    public class StunMessage
    {
        #region Properties Implementation

        /// <summary>
        /// Gets STUN message type.
        /// </summary>
        public StunMessageType Type { get; set; } = StunMessageType.BindingRequest;

        /// <summary>
        /// Gets magic cookie value. This is always 0x2112A442.
        /// </summary>
        public int MagicCookie { get; private set; }

        /// <summary>
        /// Gets transaction ID.
        /// </summary>
        public byte[] TransactionId { get; private set; }

        /// <summary>
        /// Gets or sets IP end point what was actually connected to STUN server. Returns null if not specified.
        /// </summary>
        public IPEndPoint MappedAddress { get; set; }

        /// <summary>
        /// Gets or sets IP end point where to STUN client likes to receive response.
        /// Value null means not specified.
        /// </summary>
        public IPEndPoint ResponseAddress { get; set; }

        /// <summary>
        /// Gets or sets how and where STUN server must send response back to STUN client.
        /// Value null means not specified.
        /// </summary>
        public StunChangeRequest ChangeRequest { get; set; }

        /// <summary>
        /// Gets or sets STUN server IP end point what sent response to STUN client. Value null
        /// means not specified.
        /// </summary>
        public IPEndPoint SourceAddress { get; set; }

        /// <summary>
        /// Gets or sets IP end point where STUN server will send response back to STUN client 
        /// if the "change IP" and "change port" flags had been set in the ChangeRequest.
        /// </summary>
        public IPEndPoint ChangedAddress { get; set; }

        /// <summary>
        /// Gets or sets user name. Value null means not specified.
        /// </summary>          
        public string UserName { get; set; }

        /// <summary>
        /// Gets or sets password. Value null means not specified.
        /// </summary>
        public string Password { get; set; }

        //public MessageIntegrity

        /// <summary>
        /// Gets or sets error info. Returns null if not specified.
        /// </summary>
        public StunErrorCode ErrorCode { get; set; }


        /// <summary>
        /// Gets or sets IP endpoint from which IP end point STUN server got STUN client request.
        /// Value null means not specified.
        /// </summary>
        public IPEndPoint ReflectedFrom { get; set; }

        /// <summary>
        /// Gets or sets server name.
        /// </summary>
        public string ServerName { get; set; }

        #endregion

        public StunMessage()
        {
            TransactionId = new byte[12];
            new Random().NextBytes(TransactionId);
        }

        #region method Parse

        /// <summary>
        /// Parses STUN message from raw data packet.
        /// </summary>
        /// <param name="data">Raw STUN message.</param>
        /// <exception cref="ArgumentNullException">Is raised when <b>data</b> is null reference.</exception>
        public void Parse(byte[] data)
        {
            if (data == null)
            {
                throw new ArgumentNullException(nameof(data));
            }

            /* RFC 5389 6.             
                All STUN messages MUST start with a 20-byte header followed by zero
                or more Attributes.  The STUN header contains a STUN message type,
                magic cookie, transaction ID, and message length.

                 0                   1                   2                   3
                 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 |0 0|     STUN Message Type     |         Message Length        |
                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 |                         Magic Cookie                          |
                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 |                                                               |
                 |                     Transaction ID (96 bits)                  |
                 |                                                               |
                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              
               The message length is the count, in bytes, of the size of the
               message, not including the 20 byte header.
            */

            if (data.Length < 20)
            {
                throw new ArgumentException(@"Invalid STUN message value !");
            }

            var offset = 0;

            //--- message header --------------------------------------------------

            // STUN Message Type
            var messageType = data[offset++] << 8 | data[offset++];
            if (messageType == (int)StunMessageType.BindingErrorResponse)
            {
                Type = StunMessageType.BindingErrorResponse;
            }
            else if (messageType == (int)StunMessageType.BindingRequest)
            {
                Type = StunMessageType.BindingRequest;
            }
            else if (messageType == (int)StunMessageType.BindingResponse)
            {
                Type = StunMessageType.BindingResponse;
            }
            else if (messageType == (int)StunMessageType.SharedSecretErrorResponse)
            {
                Type = StunMessageType.SharedSecretErrorResponse;
            }
            else if (messageType == (int)StunMessageType.SharedSecretRequest)
            {
                Type = StunMessageType.SharedSecretRequest;
            }
            else if (messageType == (int)StunMessageType.SharedSecretResponse)
            {
                Type = StunMessageType.SharedSecretResponse;
            }
            else
            {
                throw new ArgumentException(@"Invalid STUN message type value !");
            }

            // Message Length
            var messageLength = data[offset++] << 8 | data[offset++];

            // Magic Cookie
            MagicCookie = data[offset++] << 24 | data[offset++] << 16 | data[offset++] << 8 | data[offset++];

            // Transaction ID
            TransactionId = new byte[12];
            Array.Copy(data, offset, TransactionId, 0, 12);
            offset += 12;

            //--- Message attributes ---------------------------------------------
            while (offset - 20 < messageLength)
            {
                ParseAttribute(data, ref offset);
            }
        }

        #endregion

        #region method ToByteData

        /// <summary>
        /// Converts this to raw STUN packet.
        /// </summary>
        /// <returns>Returns raw STUN packet.</returns>
        public byte[] ToByteData()
        {
            /* RFC 5389 6.             
                All STUN messages MUST start with a 20-byte header followed by zero
                or more Attributes.  The STUN header contains a STUN message type,
                magic cookie, transaction ID, and message length.

                 0                   1                   2                   3
                 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 |0 0|     STUN Message Type     |         Message Length        |
                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 |                         Magic Cookie                          |
                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 |                                                               |
                 |                     Transaction ID (96 bits)                  |
                 |                                                               |
                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              
               The message length is the count, in bytes, of the size of the
               message, not including the 20 byte header.
            */

            // We allocate 512 for header, that should be more than enough.
            var msg = new byte[512];

            var offset = 0;

            //--- message header -------------------------------------

            // STUN Message Type (2 bytes)
            msg[offset++] = (byte)(((int)Type >> 8) & 0x3F);
            msg[offset++] = (byte)((int)Type & 0xFF);

            // Message Length (2 bytes) will be assigned at last.
            msg[offset++] = 0;
            msg[offset++] = 0;

            // Magic Cookie           
            msg[offset++] = (byte)((MagicCookie >> 24) & 0xFF);
            msg[offset++] = (byte)((MagicCookie >> 16) & 0xFF);
            msg[offset++] = (byte)((MagicCookie >> 8) & 0xFF);
            msg[offset++] = (byte)(MagicCookie & 0xFF);

            // Transaction ID (16 bytes)
            Array.Copy(TransactionId, 0, msg, offset, 12);
            offset += 12;

            //--- Message attributes ------------------------------------

            /* RFC 3489 11.2.
                After the header are 0 or more attributes.  Each attribute is TLV
                encoded, with a 16 bit type, 16 bit length, and variable value:

                0                   1                   2                   3
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               |         Type                  |            Length             |
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               |                             Value                             ....
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            */

            if (MappedAddress != null)
            {
                StoreEndPoint(AttributeType.MappedAddress, MappedAddress, msg, ref offset);
            }
            else if (ResponseAddress != null)
            {
                StoreEndPoint(AttributeType.ResponseAddress, ResponseAddress, msg, ref offset);
            }
            else if (ChangeRequest != null)
            {
                /*
                    The CHANGE-REQUEST attribute is used by the client to request that
                    the server use a different address and/or port when sending the
                    response.  The attribute is 32 bits long, although only two bits (A
                    and B) are used:

                     0                   1                   2                   3
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 A B 0|
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    The meaning of the flags is:

                    A: This is the "change IP" flag.  If true, it requests the server
                       to send the Binding Response with a different IP address than the
                       one the Binding Request was received on.

                    B: This is the "change port" flag.  If true, it requests the
                       server to send the Binding Response with a different port than the
                       one the Binding Request was received on.
                */

                // Attribute header
                msg[offset++] = 0;
                msg[offset++] = (int)AttributeType.ChangeRequest & 0xFF;
                msg[offset++] = 0;
                msg[offset++] = 4;

                msg[offset++] = 0;
                msg[offset++] = 0;
                msg[offset++] = 0;
                msg[offset++] = (byte)(Convert.ToInt32(ChangeRequest.ChangeIp) << 2 | Convert.ToInt32(ChangeRequest.ChangePort) << 1);
            }
            else if (SourceAddress != null)
            {
                StoreEndPoint(AttributeType.SourceAddress, SourceAddress, msg, ref offset);
            }
            else if (ChangedAddress != null)
            {
                StoreEndPoint(AttributeType.ChangedAddress, ChangedAddress, msg, ref offset);
            }
            else if (UserName != null)
            {
                var userBytes = Encoding.ASCII.GetBytes(UserName);

                // Attribute header
                msg[offset++] = (int)AttributeType.Username >> 8;
                msg[offset++] = (int)AttributeType.Username & 0xFF;
                msg[offset++] = (byte)(userBytes.Length >> 8);
                msg[offset++] = (byte)(userBytes.Length & 0xFF);

                Array.Copy(userBytes, 0, msg, offset, userBytes.Length);
                offset += userBytes.Length;
            }
            else if (Password != null)
            {
                var userBytes = Encoding.ASCII.GetBytes(UserName);

                // Attribute header
                msg[offset++] = (int)AttributeType.Password >> 8;
                msg[offset++] = (int)AttributeType.Password & 0xFF;
                msg[offset++] = (byte)(userBytes.Length >> 8);
                msg[offset++] = (byte)(userBytes.Length & 0xFF);

                Array.Copy(userBytes, 0, msg, offset, userBytes.Length);
                offset += userBytes.Length;
            }
            else if (ErrorCode != null)
            {
                /* 3489 11.2.9.
                    0                   1                   2                   3
                    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    |                   0                     |Class|     Number    |
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    |      Reason Phrase (variable)                                ..
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                */

                var reasonBytes = Encoding.ASCII.GetBytes(ErrorCode.ReasonText);

                // Header
                msg[offset++] = 0;
                msg[offset++] = (int)AttributeType.ErrorCode;
                msg[offset++] = 0;
                msg[offset++] = (byte)(4 + reasonBytes.Length);

                // Empty
                msg[offset++] = 0;
                msg[offset++] = 0;
                // Class
                msg[offset++] = (byte)Math.Floor(ErrorCode.Code / 100.0);
                // Number
                msg[offset++] = (byte)(ErrorCode.Code & 0xFF);
                // ReasonPhrase
                Array.Copy(reasonBytes, msg, reasonBytes.Length);
                offset += reasonBytes.Length;
            }
            else if (ReflectedFrom != null)
            {
                StoreEndPoint(AttributeType.ReflectedFrom, ReflectedFrom, msg, ref offset);
            }

            // Update Message Length. NOTE: 20 bytes header not included.
            msg[2] = (byte)((offset - 20) >> 8);
            msg[3] = (byte)((offset - 20) & 0xFF);

            // Make retVal with actual size.
            var retVal = new byte[offset];
            Array.Copy(msg, retVal, retVal.Length);

            return retVal;
        }

        #endregion


        #region method ParseAttribute

        /// <summary>
        /// Parses attribute from data.
        /// </summary>
        /// <param name="data">SIP message data.</param>
        /// <param name="offset">Offset in data.</param>
        private void ParseAttribute(byte[] data, ref int offset)
        {
            /* RFC 3489 11.2.
                Each attribute is TLV encoded, with a 16 bit type, 16 bit length, and variable value:

                0                   1                   2                   3
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               |         Type                  |            Length             |
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               |                             Value                             ....
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                            
            */

            // Type
            var type = (AttributeType)(data[offset++] << 8 | data[offset++]);

            // Length
            var length = data[offset++] << 8 | data[offset++];

            // MAPPED-ADDRESS
            if (type == AttributeType.MappedAddress)
            {
                MappedAddress = ParseEndPoint(data, ref offset);
            }
            // RESPONSE-ADDRESS
            else if (type == AttributeType.ResponseAddress)
            {
                ResponseAddress = ParseEndPoint(data, ref offset);
            }
            // CHANGE-REQUEST
            else if (type == AttributeType.ChangeRequest)
            {
                /*
                    The CHANGE-REQUEST attribute is used by the client to request that
                    the server use a different address and/or port when sending the
                    response.  The attribute is 32 bits long, although only two bits (A
                    and B) are used:

                     0                   1                   2                   3
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 A B 0|
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    The meaning of the flags is:

                    A: This is the "change IP" flag.  If true, it requests the server
                       to send the Binding Response with a different IP address than the
                       one the Binding Request was received on.

                    B: This is the "change port" flag.  If true, it requests the
                       server to send the Binding Response with a different port than the
                       one the Binding Request was received on.
                */

                // Skip 3 bytes
                offset += 3;

                ChangeRequest = new StunChangeRequest((data[offset] & 4) != 0, (data[offset] & 2) != 0);
                offset++;
            }
            // SOURCE-ADDRESS
            else if (type == AttributeType.SourceAddress)
            {
                SourceAddress = ParseEndPoint(data, ref offset);
            }
            // CHANGED-ADDRESS
            else if (type == AttributeType.ChangedAddress)
            {
                ChangedAddress = ParseEndPoint(data, ref offset);
            }
            // USERNAME
            else if (type == AttributeType.Username)
            {
                UserName = Encoding.Default.GetString(data, offset, length);
                offset += length;
            }
            // PASSWORD
            else if (type == AttributeType.Password)
            {
                Password = Encoding.Default.GetString(data, offset, length);
                offset += length;
            }
            // MESSAGE-INTEGRITY
            else if (type == AttributeType.MessageIntegrity)
            {
                offset += length;
            }
            // ERROR-CODE
            else if (type == AttributeType.ErrorCode)
            {
                /* 3489 11.2.9.
                    0                   1                   2                   3
                    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    |                   0                     |Class|     Number    |
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    |      Reason Phrase (variable)                                ..
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                */

                var errorCode = (data[offset + 2] & 0x7) * 100 + (data[offset + 3] & 0xFF);

                ErrorCode = new StunErrorCode(errorCode, Encoding.Default.GetString(data, offset + 4, length - 4));
                offset += length;
            }
            // UNKNOWN-ATTRIBUTES
            else if (type == AttributeType.UnknownAttribute)
            {
                offset += length;
            }
            // REFLECTED-FROM
            else if (type == AttributeType.ReflectedFrom)
            {
                ReflectedFrom = ParseEndPoint(data, ref offset);
            }
            // XorMappedAddress
            // XorOnly
            // Software
            else if (type == AttributeType.Software)
            {
                ServerName = Encoding.Default.GetString(data, offset, length);
                offset += length;
            }
            // Unknown
            else
            {
                offset += length;
            }
        }

        #endregion

        #region method ParseEndPoint

        /// <summary>
        /// Parses IP endpoint attribute.
        /// </summary>
        /// <param name="data">STUN message data.</param>
        /// <param name="offset">Offset in data.</param>
        /// <returns>Returns parsed IP end point.</returns>
        private static IPEndPoint ParseEndPoint(IReadOnlyList<byte> data, ref int offset)
        {
            /*
                It consists of an eight bit address family, and a sixteen bit
                port, followed by a fixed length value representing the IP address.

                0                   1                   2                   3
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                |x x x x x x x x|    Family     |           Port                |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                |                             Address                           |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            */

            // Skip family
            offset++;
            offset++;

            // Port
            var port = data[offset++] << 8 | data[offset++];

            // Address
            var ip = new byte[4];
            ip[0] = data[offset++];
            ip[1] = data[offset++];
            ip[2] = data[offset++];
            ip[3] = data[offset++];

            return new IPEndPoint(new IPAddress(ip), port);
        }

        #endregion

        #region method StoreEndPoint

        /// <summary>
        /// Stores ip end point attribute to buffer.
        /// </summary>
        /// <param name="type">Attribute type.</param>
        /// <param name="endPoint">IP end point.</param>
        /// <param name="message">Buffer where to store.</param>
        /// <param name="offset">Offset in buffer.</param>
        private static void StoreEndPoint(AttributeType type, IPEndPoint endPoint, IList<byte> message, ref int offset)
        {
            /*
                It consists of an eight bit address family, and a sixteen bit
                port, followed by a fixed length value representing the IP address.

                0                   1                   2                   3
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                |x x x x x x x x|    Family     |           Port                |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                |                             Address                           |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+             
            */

            // Header
            message[offset++] = (byte)((int)type >> 8);
            message[offset++] = (byte)((int)type & 0xFF);
            message[offset++] = 0;
            message[offset++] = 8;

            // Unused
            message[offset++] = 0;
            // Family
            message[offset++] = (byte)IpFamily.IPv4;
            // Port
            message[offset++] = (byte)(endPoint.Port >> 8);
            message[offset++] = (byte)(endPoint.Port & 0xFF);
            // Address
            var ipBytes = endPoint.Address.GetAddressBytes();
            message[offset++] = ipBytes[0];
            message[offset++] = ipBytes[1];
            message[offset++] = ipBytes[2];
            message[offset++] = ipBytes[3];
        }

        #endregion


    }
}