Use IPC via TCP

osu.Desktop/LegacyIpc/LegacyIpcDifficultyCalculationRequest.cs

@@ -0,0 +1,18 @@
+// 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.
+
+namespace osu.Desktop.LegacyIpc
+{
+    /// <summary>
+    /// A difficulty calculation request from the legacy client.
+    /// </summary>
+    /// <remarks>
+    /// Synchronise any changes with osu!stable.
+    /// </remarks>
+    public class LegacyIpcDifficultyCalculationRequest
+    {
+        public string BeatmapFile { get; set; }
+        public int RulesetId { get; set; }
+        public int Mods { get; set; }
+    }
+}