feat: add ServerStats counters and NatsClient metadata for monitoring

src/NATS.Server/NatsServer.cs

@@ -16,11 +16,19 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
     private readonly ServerInfo _serverInfo;
     private readonly ILogger<NatsServer> _logger;
     private readonly ILoggerFactory _loggerFactory;
+    private readonly ServerStats _stats = new();
     private readonly TaskCompletionSource _listeningStarted = new(TaskCreationOptions.RunContinuationsAsynchronously);
     private Socket? _listener;
     private ulong _nextClientId;
+    private long _startTimeTicks;
 
     public SubList SubList => _subList;
+    public ServerStats Stats => _stats;
+    public DateTime StartTime => new(Interlocked.Read(ref _startTimeTicks), DateTimeKind.Utc);
+    public string ServerId => _serverInfo.ServerId;
+    public string ServerName => _serverInfo.ServerName;
+    public int ClientCount => _clients.Count;
+    public IEnumerable<NatsClient> GetClients() => _clients.Values;
 
     public Task WaitForReadyAsync() => _listeningStarted.Task;
 
@@ -47,6 +55,7 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
         _listener.Bind(new IPEndPoint(
             _options.Host == "0.0.0.0" ? IPAddress.Any : IPAddress.Parse(_options.Host),
             _options.Port));
+        Interlocked.Exchange(ref _startTimeTicks, DateTime.UtcNow.Ticks);
         _listener.Listen(128);
         _listeningStarted.TrySetResult();
 
@@ -84,11 +93,12 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
                 }
 
                 var clientId = Interlocked.Increment(ref _nextClientId);
+                Interlocked.Increment(ref _stats.TotalConnections);
 
                 _logger.LogDebug("Client {ClientId} connected from {RemoteEndpoint}", clientId, socket.RemoteEndPoint);
 
                 var clientLogger = _loggerFactory.CreateLogger($"NATS.Server.NatsClient[{clientId}]");
-                var client = new NatsClient(clientId, socket, _options, _serverInfo, clientLogger);
+                var client = new NatsClient(clientId, socket, _options, _serverInfo, clientLogger, _stats);
                 client.Router = this;
                 _clients[clientId] = client;