Prevent infinite loops in device linking (#16856)

Content.Server/DeviceNetwork/Systems/DeviceNetworkSystem.cs

@@ -3,11 +3,9 @@ using Content.Shared.DeviceNetwork;
 using JetBrains.Annotations;
 using Robust.Shared.Prototypes;
 using Robust.Shared.Random;
-using Robust.Shared.Utility;
 using System.Buffers;
 using System.Diagnostics.CodeAnalysis;
 using Content.Shared.Examine;
-using static Content.Server.DeviceNetwork.Components.DeviceNetworkComponent;
 
 namespace Content.Server.DeviceNetwork.Systems
 {
@@ -23,21 +21,39 @@ namespace Content.Server.DeviceNetwork.Systems
         [Dependency] private readonly SharedTransformSystem _transformSystem = default!;
 
         private readonly Dictionary<int, DeviceNet> _networks = new(4);
-        private readonly Queue<DeviceNetworkPacketEvent> _packets = new();
+        private readonly Queue<DeviceNetworkPacketEvent> _queueA = new();
+        private readonly Queue<DeviceNetworkPacketEvent> _queueB = new();
+
+        /// <summary>
+        /// The queue being processed in the current tick
+        /// </summary>
+        private Queue<DeviceNetworkPacketEvent> _activeQueue = null!;
+
+        /// <summary>
+        /// The queue that will be processed in the next tick
+        /// </summary>
+        private Queue<DeviceNetworkPacketEvent> _nextQueue = null!;
+
 
         public override void Initialize()
         {
             SubscribeLocalEvent<DeviceNetworkComponent, MapInitEvent>(OnMapInit);
             SubscribeLocalEvent<DeviceNetworkComponent, ComponentShutdown>(OnNetworkShutdown);
             SubscribeLocalEvent<DeviceNetworkComponent, ExaminedEvent>(OnExamine);
+
+            _activeQueue = _queueA;
+            _nextQueue = _queueB;
         }
 
         public override void Update(float frameTime)
         {
-            while (_packets.TryDequeue(out var packet))
+
+            while (_activeQueue.TryDequeue(out var packet))
             {
                 SendPacket(packet);
             }
+
+            SwapQueues();
         }
 
         /// <summary>
@@ -62,10 +78,23 @@ namespace Content.Server.DeviceNetwork.Systems
             if (frequency == null)
                 return false;
 
-            _packets.Enqueue(new DeviceNetworkPacketEvent(device.DeviceNetId, address, frequency.Value, device.Address, uid, data));
+            _nextQueue.Enqueue(new DeviceNetworkPacketEvent(device.DeviceNetId, address, frequency.Value, device.Address, uid, data));
             return true;
         }
 
+        /// <summary>
+        /// Swaps the active queue.
+        /// Queues are swapped so that packets being sent in the current tick get processed in the next tick.
+        /// </summary>
+        /// <remarks>
+        /// This prevents infinite loops while sending packets
+        /// </remarks>
+        private void SwapQueues()
+        {
+            _nextQueue = _activeQueue;
+            _activeQueue = _activeQueue == _queueA ? _queueB : _queueA;
+        }
+
         private void OnExamine(EntityUid uid, DeviceNetworkComponent device, ExaminedEvent args)
         {
             if (device.ExaminableAddress)