UdpHeader.GetProtocolPacketBytes C# (CSharp) Method

    public override byte[] GetProtocolPacketBytes(byte[] payLoad)
    {
        byte[] udpPacket = new byte[UdpHeaderLength + payLoad.Length], pseudoHeader = null, byteValue = null;
        int offset = 0;

        // Build the UDP packet first
        byteValue = BitConverter.GetBytes(srcPort);
        Array.Copy(byteValue, 0, udpPacket, offset, byteValue.Length);
        offset += byteValue.Length;

        byteValue = BitConverter.GetBytes(destPort);
        Array.Copy(byteValue, 0, udpPacket, offset, byteValue.Length);
        offset += byteValue.Length;

        byteValue = BitConverter.GetBytes(udpLength);
        Array.Copy(byteValue, 0, udpPacket, offset, byteValue.Length);
        offset += byteValue.Length;

        udpPacket[offset++] = 0;      // Checksum is initially zero
        udpPacket[offset++] = 0;

        // Copy payload to end of packet
        Array.Copy(payLoad, 0, udpPacket, offset, payLoad.Length);

        if (ipv4PacketHeader != null)
        {
            pseudoHeader = new byte[UdpHeaderLength + 12 + payLoad.Length];

            // Build the IPv4 pseudo header
            offset = 0;

            // Source address
            byteValue = ipv4PacketHeader.SourceAddress.GetBytes();
            Array.Copy(byteValue, 0, pseudoHeader, offset, byteValue.Length);
            offset += byteValue.Length;

            // Destination address
            byteValue = ipv4PacketHeader.DestinationAddress.GetBytes();
            Array.Copy(byteValue, 0, pseudoHeader, offset, byteValue.Length);
            offset += byteValue.Length;

            // 1 byte zero pad plus next header protocol value
            pseudoHeader[offset++] = 0;
            pseudoHeader[offset++] = ipv4PacketHeader.Protocol;

            // Packet length
            byteValue = BitConverter.GetBytes(udpLength);
            Array.Copy(byteValue, 0, pseudoHeader, offset, byteValue.Length);
            offset += byteValue.Length;

            // Copy the UDP packet to the end of this
            Array.Copy(udpPacket, 0, pseudoHeader, offset, udpPacket.Length);
        }

        else if (ipv6PacketHeader != null)
        {
            uint ipv6PayloadLength;

            pseudoHeader = new byte[UdpHeaderLength + 40 + payLoad.Length];

            // Build the IPv6 pseudo header
            offset = 0;

            // Source address
            byteValue = ipv6PacketHeader.SourceAddress.GetBytes();
            Array.Copy(byteValue, 0, pseudoHeader, offset, byteValue.Length);
            offset += byteValue.Length;

            // Destination address
            byteValue = ipv6PacketHeader.DestinationAddress.GetBytes();
            Array.Copy(byteValue, 0, pseudoHeader, offset, byteValue.Length);
            offset += byteValue.Length;

            ipv6PayloadLength = (uint)NetworkingHelpers.HostToNetworkOrder((int)(payLoad.Length + UdpHeaderLength));

            // Packet payload: ICMPv6 headers plus payload
            byteValue = BitConverter.GetBytes(ipv6PayloadLength);
            Array.Copy(byteValue, 0, pseudoHeader, offset, byteValue.Length);
            offset += byteValue.Length;

            // 3 bytes zero pad plus next header protocol value
            pseudoHeader[offset++] = 0;
            pseudoHeader[offset++] = 0;
            pseudoHeader[offset++] = 0;
            pseudoHeader[offset++] = ipv6PacketHeader.NextHeader;

            // Copy the UDP packet to the end of this
            Array.Copy(udpPacket, 0, pseudoHeader, offset, udpPacket.Length);
        }

        if (pseudoHeader != null)
        {
            Checksum = ComputeChecksum(pseudoHeader);
        }

        // Put checksum back into packet
        byteValue = BitConverter.GetBytes(udpChecksum);
        Array.Copy(byteValue, 0, udpPacket, 6, byteValue.Length);

        return udpPacket;
    }