feat: implement jsz and live jetstream monitoring

src/NATS.Server/Monitoring/JszHandler.cs

@@ -0,0 +1,62 @@
+using System.Text.Json.Serialization;
+
+namespace NATS.Server.Monitoring;
+
+public sealed class JszHandler
+{
+    private readonly NatsServer _server;
+    private readonly NatsOptions _options;
+
+    public JszHandler(NatsServer server, NatsOptions options)
+    {
+        _server = server;
+        _options = options;
+    }
+
+    public JszResponse Build()
+    {
+        return new JszResponse
+        {
+            ServerId = _server.ServerId,
+            Now = DateTime.UtcNow,
+            Enabled = _server.Stats.JetStreamEnabled,
+            Memory = 0,
+            Storage = 0,
+            Streams = _server.JetStreamStreams,
+            Consumers = _server.JetStreamConsumers,
+            Config = new JetStreamConfig
+            {
+                MaxMemory = _options.JetStream?.MaxMemoryStore ?? 0,
+                MaxStorage = _options.JetStream?.MaxFileStore ?? 0,
+                StoreDir = _options.JetStream?.StoreDir ?? string.Empty,
+            },
+        };
+    }
+}
+
+public sealed class JszResponse
+{
+    [JsonPropertyName("server_id")]
+    public string ServerId { get; set; } = string.Empty;
+
+    [JsonPropertyName("now")]
+    public DateTime Now { get; set; }
+
+    [JsonPropertyName("enabled")]
+    public bool Enabled { get; set; }
+
+    [JsonPropertyName("memory")]
+    public ulong Memory { get; set; }
+
+    [JsonPropertyName("storage")]
+    public ulong Storage { get; set; }
+
+    [JsonPropertyName("streams")]
+    public int Streams { get; set; }
+
+    [JsonPropertyName("consumers")]
+    public int Consumers { get; set; }
+
+    [JsonPropertyName("config")]
+    public JetStreamConfig Config { get; set; } = new();
+}

src/NATS.Server/Monitoring/MonitorServer.cs

@@ -16,6 +16,7 @@ public sealed class MonitorServer : IAsyncDisposable
     private readonly VarzHandler _varzHandler;
     private readonly ConnzHandler _connzHandler;
     private readonly SubszHandler _subszHandler;
+    private readonly JszHandler _jszHandler;
 
     public MonitorServer(NatsServer server, NatsOptions options, ServerStats stats, ILoggerFactory loggerFactory)
     {
@@ -31,6 +32,7 @@ public sealed class MonitorServer : IAsyncDisposable
         _varzHandler = new VarzHandler(server, options);
         _connzHandler = new ConnzHandler(server);
         _subszHandler = new SubszHandler(server);
+        _jszHandler = new JszHandler(server, options);
 
         _app.MapGet(basePath + "/", () =>
         {
@@ -100,7 +102,7 @@ public sealed class MonitorServer : IAsyncDisposable
         _app.MapGet(basePath + "/jsz", () =>
         {
             stats.HttpReqStats.AddOrUpdate("/jsz", 1, (_, v) => v + 1);
-            return Results.Ok(new { });
+            return Results.Ok(_jszHandler.Build());
         });
     }
 

src/NATS.Server/Monitoring/Varz.cs

@@ -422,6 +422,12 @@ public sealed class JetStreamStats
     [JsonPropertyName("ha_assets")]
     public int HaAssets { get; set; }
 
+    [JsonPropertyName("streams")]
+    public int Streams { get; set; }
+
+    [JsonPropertyName("consumers")]
+    public int Consumers { get; set; }
+
     [JsonPropertyName("api")]
     public JetStreamApiStats Api { get; set; } = new();
 }

src/NATS.Server/Monitoring/VarzHandler.cs

@@ -121,6 +121,22 @@ public sealed class VarzHandler : IDisposable
                 Subscriptions = _server.SubList.Count,
                 ConfigLoadTime = _server.StartTime,
                 HttpReqStats = stats.HttpReqStats.ToDictionary(kv => kv.Key, kv => (ulong)kv.Value),
+                JetStream = new JetStreamVarz
+                {
+                    Config = new JetStreamConfig
+                    {
+                        MaxMemory = _options.JetStream?.MaxMemoryStore ?? 0,
+                        MaxStorage = _options.JetStream?.MaxFileStore ?? 0,
+                        StoreDir = _options.JetStream?.StoreDir ?? string.Empty,
+                    },
+                    Stats = new JetStreamStats
+                    {
+                        Accounts = _options.JetStream is null ? 0 : 1,
+                        HaAssets = _server.JetStreamStreams,
+                        Streams = _server.JetStreamStreams,
+                        Consumers = _server.JetStreamConsumers,
+                    },
+                },
             };
         }
         finally