MQTTnet MessagePack helper that supports mqtt 5 topic alias

PublishMsgPack.cs

using MessagePack;
using MQTTnet;
using MQTTnet.Client;

public static class MqttExtensions
{
    static readonly HashSet<ushort> topicAliases = new();

    /// <summary>
    /// Publish a message pack serialized message with optional topic alias.
    /// </summary>
    /// <remarks>
    /// The implementation will stop using the topic once the alias is successfully published once and could result
    /// in the topic to be use more than once but this is the safe approach compared to only using the topic for
    /// the 1st message
    /// </remarks>
    public static async ValueTask PublishMsgPack<T>(
        this IMqttClient client,
        string topic,
        T value,
        ushort alias = 0,
        CancellationToken cancellationToken = default
    ) where T : struct
    {
        var useAliasOnly = alias != 0 && topicAliases.Contains(alias); // Safe without lock
        var payload = MessagePackSerializer.Serialize(value);

        var message = new MqttApplicationMessage
        {
            TopicAlias = alias, PayloadSegment = payload
        };

        if (!useAliasOnly) message.Topic = topic;

        await client.PublishAsync(message, cancellationToken);

        if (useAliasOnly) return;

        lock (topicAliases) topicAliases.Add(alias);
    }
}