Use IPC via TCP

osu.Desktop/LegacyIpc/LegacyIpcMessage.cs

@@ -0,0 +1,40 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Platform;
+
+namespace osu.Desktop.LegacyIpc
+{
+    /// <summary>
+    /// An <see cref="IpcMessage"/> that can be used to communicate to and from legacy clients.
+    /// </summary>
+    /// <remarks>
+    /// Synchronise any changes with osu-stable.
+    /// </remarks>
+    public class LegacyIpcMessage : IpcMessage
+    {
+        public LegacyIpcMessage()
+        {
+            // Types/assemblies are not inter-compatible, so always serialise/deserialise into objects.
+            base.Type = typeof(object).FullName;
+        }
+
+        public new string Type => base.Type; // Hide setter.
+
+        public new object Value
+        {
+            get => base.Value;
+            set => base.Value = new Data
+            {
+                MessageType = value.GetType().Name,
+                MessageData = value
+            };
+        }
+
+        public class Data
+        {
+            public string MessageType { get; set; }
+            public object MessageData { get; set; }
+        }
+    }
+}