OmronFinsTcpPacket.cs

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using System.Text;
 
namespace Dreamine.PLC.Omron.Fins.Protocol;

public static class OmronFinsTcpPacket
{
    private static readonly byte[] Signature = Encoding.ASCII.GetBytes("FINS");

    public static byte[] Wrap(IReadOnlyList<byte> finsFrame)
    {
        ArgumentNullException.ThrowIfNull(finsFrame);
 
        var packet = new byte[16 + finsFrame.Count];
        Buffer.BlockCopy(Signature, 0, packet, 0, Signature.Length);
        OmronFinsEndian.WriteInt32(packet, 4, 8 + finsFrame.Count);
        OmronFinsEndian.WriteInt32(packet, 8, 2);
        OmronFinsEndian.WriteInt32(packet, 12, 0);
 
        for (var index = 0; index < finsFrame.Count; index++)
        {
            packet[16 + index] = finsFrame[index];
        }
 
        return packet;
    }

    public static byte[] Extract(ReadOnlySpan<byte> packet)
    {
        if (packet.Length < 16)
        {
            throw new InvalidOperationException($"FINS/TCP packet is too short. Length={packet.Length}.");
        }
 
        if (packet[0] != Signature[0] || packet[1] != Signature[1] || packet[2] != Signature[2] || packet[3] != Signature[3])
        {
            throw new InvalidOperationException("Invalid FINS/TCP signature.");
        }
 
        var errorCode = OmronFinsEndian.ReadInt32(packet, 12);
        if (errorCode != 0)
        {
            throw new InvalidOperationException($"FINS/TCP error: 0x{errorCode:X8}.");
        }
 
        return packet[16..].ToArray();
    }
}