Akka.Cluster.Metrics mis-uses code-genned Protobuf objects for internal business logic

[Aaronontheweb]

Per the blockers we ran into on #7063

akka.net/src/contrib/cluster/Akka.Cluster.Metrics/Serialization/NodeMetrics.cs

Lines 23 to 110 in 0782c7d

	public sealed partial class NodeMetrics
	{
	public Actor.Address Address { get; private set; }
	/// <summary>
	/// Creates new instance of <see cref="NodeMetrics"/>
	/// </summary>
	/// <param name="address">Address of the node the metrics are gathered at</param>
	/// <param name="timestamp">the time of sampling, in milliseconds since midnight, January 1, 1970 UTC</param>
	/// <param name="metrics">The set of sampled <see cref="Types.Metric"/></param>
	public NodeMetrics(Actor.Address address, long timestamp, IEnumerable<Types.Metric> metrics)
	{
	Address = address;
	timestamp_ = timestamp;
	metrics_ = new RepeatedField<Types.Metric>();
	metrics_.AddRange(metrics);
	}
	/// <summary>
	/// Returns the most recent data.
	/// </summary>
	public NodeMetrics Merge(NodeMetrics that)
	{
	if (!Address.Equals(that.Address))
	throw new ArgumentException(nameof(that), $"merge only allowed for same address, {Address} != {that.Address}");
	if (Timestamp >= that.Timestamp)
	return this; // that is order
	return new NodeMetrics(Address, that.Timestamp, that.Metrics.Union(Metrics));
	}
	/// <summary>
	/// Returns the most recent data with <see cref="Types.EWMA"/> averaging.
	/// </summary>
	public NodeMetrics Update(NodeMetrics that)
	{
	if (!Address.Equals(that.Address))
	throw new ArgumentException(nameof(that), $"merge only allowed for same address, {Address} != {that.Address}");
	// Apply sample ordering
	var (latestNode, currentNode) = Timestamp >= that.Timestamp ? (this, that) : (that, this);
	// Average metrics present in both latest and current.
	var updated = latestNode.Metrics
	.SelectMany(latest => currentNode.Metrics.Select(current => (Latest: latest, Current: current)))
	.Where(pair => pair.Latest.SameAs(pair.Current))
	.Select(pair => pair.Current + pair.Latest)
	.ToList();
	// Append metrics missing from either latest or current.
	// Equality is based on the metric's name
	var merged = updated.Union(latestNode.Metrics).Union(currentNode.Metrics);
	return new NodeMetrics(Address, latestNode.Timestamp, merged);
	}
	/// <summary>
	/// Gets metric by key
	/// </summary>
	public Option<Types.Metric> Metric(string name) => Metrics.FirstOrDefault(m => m.Name == name) ?? Option<Types.Metric>.None;
	/// <summary>
	/// Returns true if <code>that</code> address is the same as this
	/// </summary>
	public bool SameAs(NodeMetrics that) => Address.Equals(that.Address);
	/*
	* Two methods below, Equals and GetHashCode, should be used instead of generated in ClusterMetrics.Messages.g.cs
	* file. Since we do not have an option to not generate those methods for this particular class,
	* just stip them from generated code and paste here, with adding Address property check
	*/
	public bool Equals(NodeMetrics other)
	{
	if (ReferenceEquals(null, other)) return false;
	if (ReferenceEquals(this, other)) return true;
	return Equals(Address, other.Address);
	}
	public override int GetHashCode()
	{
	return (Address != null ? Address.GetHashCode() : 0);
	}
	}

Indeed, we are abusing the Protobuf objects inside our internal usages within Akka.Cluster.Metrics. That's a separate issue that I think will need to be solved in a different PR.

Originally posted by @Aaronontheweb in #7063 (comment)

[Aaronontheweb]

I think the solution that is required here is decoupling the wire types from the public API and creating some structs that are actually returned by the NodeMetrics APIs et al.