EchoRequest.cs

using System;
using OSDP.Net.Messages;
using OSDP.Net.Messages.SecureChannel;
using OSDP.Net.Model.CommandData;
 
namespace OSDP.Net.LineQuality
{
    public class EchoRequest : CommandData
    {
        public EchoRequest(byte sequenceNumber, TestPattern pattern, int payloadLength)
            : this(sequenceNumber, pattern, LineQualityProtocol.GeneratePattern(pattern, payloadLength),
                payloadLength)
        {
        }
 
        private EchoRequest(byte sequenceNumber, TestPattern pattern, byte[] data, int declaredPayloadLength)
        {
            SequenceNumber = sequenceNumber;
            Pattern = pattern;
            Data = data ?? throw new ArgumentNullException(nameof(data));
            DeclaredPayloadLength = declaredPayloadLength;
        }

        public byte SequenceNumber { get; }

        public TestPattern Pattern { get; }

        public byte[] Data { get; }

        public int DeclaredPayloadLength { get; }

        public bool IsLengthConsistent => DeclaredPayloadLength == Data.Length;

        public override CommandType CommandType => CommandType.ManufacturerSpecific;

        public override byte Code => (byte)CommandType;

        public override ReadOnlySpan<byte> SecurityControlBlock() => SecurityBlock.CommandMessageWithDataSecurity;

        public override byte[] BuildData()
        {
            var data = new byte[LineQualityProtocol.EchoHeaderLength + Data.Length];
            LineQualityProtocol.VendorCodeBytes.CopyTo(data, 0);
            data[3] = LineQualityProtocol.EchoCommandId;
            data[4] = SequenceNumber;
            data[5] = (byte)Pattern;
            data[6] = (byte)DeclaredPayloadLength;
            Data.CopyTo(data, LineQualityProtocol.EchoHeaderLength);
            return data;
        }

        public static bool TryParse(ReadOnlySpan<byte> payload, out EchoRequest request)
        {
            request = null;
 
            if (payload.Length < LineQualityProtocol.EchoHeaderLength) return false;
            if (!LineQualityProtocol.IsLineQualityVendorCode(payload)) return false;
            if (payload[3] != LineQualityProtocol.EchoCommandId) return false;
 
            int available = payload.Length - LineQualityProtocol.EchoHeaderLength;
            int declared = payload[6];
            var data = payload.Slice(LineQualityProtocol.EchoHeaderLength,
                Math.Min(declared, available)).ToArray();
 
            request = new EchoRequest(payload[4], (TestPattern)payload[5], data, declared);
            return true;
        }
    }
}