Add system to kick people if they connect to multiple servers at once. (#34563)

Content.Server/Database/ServerDbManagerExt.cs

@@ -0,0 +1,76 @@
+using System.Text.Json;
+using Robust.Shared.Asynchronous;
+
+namespace Content.Server.Database;
+
+public static class ServerDbManagerExt
+{
+    /// <summary>
+    /// Subscribe to a database notification on a specific channel, formatted as JSON.
+    /// </summary>
+    /// <param name="dbManager">The database manager to subscribe on.</param>
+    /// <param name="taskManager">The task manager used to run the main callback on the main thread.</param>
+    /// <param name="sawmill">Sawmill to log any errors to.</param>
+    /// <param name="channel">
+    /// The notification channel to listen on. Only notifications on this channel will be handled.
+    /// </param>
+    /// <param name="action">
+    /// The action to run on the notification data.
+    /// This runs on the main thread.
+    /// </param>
+    /// <param name="earlyFilter">
+    /// An early filter callback that runs before the JSON message is deserialized.
+    /// Return false to not handle the notification.
+    /// This does not run on the main thread.
+    /// </param>
+    /// <param name="filter">
+    /// A filter callback that runs after the JSON message is deserialized.
+    /// Return false to not handle the notification.
+    /// This does not run on the main thread.
+    /// </param>
+    /// <typeparam name="TData">The type of JSON data to deserialize.</typeparam>
+    public static void SubscribeToJsonNotification<TData>(
+        this IServerDbManager dbManager,
+        ITaskManager taskManager,
+        ISawmill sawmill,
+        string channel,
+        Action<TData> action,
+        Func<bool>? earlyFilter = null,
+        Func<TData, bool>? filter = null)
+    {
+        dbManager.SubscribeToNotifications(notification =>
+        {
+            if (notification.Channel != channel)
+                return;
+
+            if (notification.Payload == null)
+            {
+                sawmill.Error($"Got {channel} notification with null payload!");
+                return;
+            }
+
+            if (earlyFilter != null && !earlyFilter())
+                return;
+
+            TData data;
+            try
+            {
+                data = JsonSerializer.Deserialize<TData>(notification.Payload)
+                       ?? throw new JsonException("Content is null");
+            }
+            catch (JsonException e)
+            {
+                sawmill.Error($"Got invalid JSON in {channel} notification: {e}");
+                return;
+            }
+
+            if (filter != null && !filter(data))
+                return;
+
+            taskManager.RunOnMainThread(() =>
+            {
+                action(data);
+            });
+        });
+    }
+}