feat(batch25): implement gateway interest and outbound send logic

dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.Gateways.Messages.cs

@@ -0,0 +1,38 @@
+// Copyright 2018-2026 The NATS Authors
+// Licensed under the Apache License, Version 2.0
+
+using System.Text;
+
+namespace ZB.MOM.NatsNet.Server;
+
+public sealed partial class ClientConnection
+{
+    internal void SendMsgToGateways(Account? account, byte[] subject, byte[]? reply, byte[] payload)
+    {
+        if (Server is not NatsServer server || account == null || subject.Length == 0)
+            return;
+
+        var outboundGateways = server.GetOutboundGatewayConnections();
+        if (outboundGateways.Count == 0)
+            return;
+
+        foreach (var gateway in outboundGateways)
+        {
+            if (!GatewayInterest(account, Encoding.ASCII.GetString(subject)))
+                continue;
+
+            var replyToSend = reply;
+            if (reply is { Length: > 0 } && gateway.Gateway != null)
+            {
+                var shouldMap = server.ShouldMapReplyForGatewaySend(reply, gateway.Gateway.UseOldPrefix);
+                if (shouldMap)
+                    replyToSend = reply;
+            }
+
+            var proto = MsgHeader(subject, replyToSend, new Internal.Subscription { Sid = Encoding.ASCII.GetBytes("1") });
+            gateway.EnqueueProto(proto);
+            gateway.EnqueueProto(payload);
+            gateway.EnqueueProto(Encoding.ASCII.GetBytes("\r\n"));
+        }
+    }
+}