feat: enforce jetstream retention and limits

src/NATS.Server/JetStream/StreamManager.cs

@@ -1,6 +1,7 @@
 using System.Collections.Concurrent;
 using NATS.Server.JetStream.Api;
 using NATS.Server.JetStream.Models;
+using NATS.Server.JetStream.Publish;
 using NATS.Server.JetStream.Storage;
 using NATS.Server.Subscriptions;
 
@@ -37,6 +38,14 @@ public sealed class StreamManager
 
     public bool TryGet(string name, out StreamHandle handle) => _streams.TryGetValue(name, out handle!);
 
+    public ValueTask<StreamState> GetStateAsync(string name, CancellationToken ct)
+    {
+        if (_streams.TryGetValue(name, out var stream))
+            return stream.Store.GetStateAsync(ct);
+
+        return ValueTask.FromResult(new StreamState());
+    }
+
     public StreamHandle? FindBySubject(string subject)
     {
         foreach (var stream in _streams.Values)
@@ -48,6 +57,22 @@ public sealed class StreamManager
         return null;
     }
 
+    public PubAck? Capture(string subject, ReadOnlyMemory<byte> payload)
+    {
+        var stream = FindBySubject(subject);
+        if (stream == null)
+            return null;
+
+        var seq = stream.Store.AppendAsync(subject, payload, default).GetAwaiter().GetResult();
+        EnforceLimits(stream);
+
+        return new PubAck
+        {
+            Stream = stream.Config.Name,
+            Seq = seq,
+        };
+    }
+
     private static StreamConfig NormalizeConfig(StreamConfig config)
     {
         var copy = new StreamConfig
@@ -73,6 +98,22 @@ public sealed class StreamManager
             },
         };
     }
+
+    private static void EnforceLimits(StreamHandle stream)
+    {
+        if (stream.Config.MaxMsgs <= 0)
+            return;
+
+        var maxMessages = (ulong)stream.Config.MaxMsgs;
+        if (stream.Store is MemStore memStore)
+        {
+            memStore.TrimToMaxMessages(maxMessages);
+            return;
+        }
+
+        if (stream.Store is FileStore fileStore)
+            fileStore.TrimToMaxMessages(maxMessages);
+    }
 }
 
 public sealed record StreamHandle(StreamConfig Config, IStreamStore Store);