MQTTnet/MQTTnet.Core/Packets/MqttSubscribePacket.cs

using System.Collections.Generic;
using System.Linq;

namespace MQTTnet.Core.Packets
{
    public sealed class MqttSubscribePacket : MqttBasePacket, IPacketWithIdentifier
    {
        public ushort PacketIdentifier { get; set; }
        
        public IList<TopicFilter> TopicFilters { get; set; } = new List<TopicFilter>();

        public override string ToString()
        {
            var topicFiltersText = string.Join(",", TopicFilters.Select(f => $"{f.Topic}@{f.QualityOfServiceLevel}"));
            return
                $"{nameof(MqttSubscribePacket)} [PacketIdentifier={PacketIdentifier}] [TopicFilters={topicFiltersText}]";
        }
    }
}