XivCommon/XivCommon/Functions/Chat.cs

using System;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.InteropServices;
using System.Text;
using Dalamud.Game;

namespace XivCommon.Functions {
    public class Chat {
        private GameFunctions Functions { get; }

        private delegate void ProcessChatBoxDelegate(IntPtr uiModule, IntPtr message, IntPtr unused, byte a4);

        private ProcessChatBoxDelegate ProcessChatBox { get; }

        internal Chat(GameFunctions functions, SigScanner scanner) {
            this.Functions = functions;

            var processChatBoxPtr = scanner.ScanText("48 89 5C 24 ?? 57 48 83 EC 20 48 8B FA 48 8B D9 45 84 C9");
            this.ProcessChatBox = Marshal.GetDelegateForFunctionPointer<ProcessChatBoxDelegate>(processChatBoxPtr);
        }

        public void SendMessage(string message) {
            var uiModule = this.Functions.GetUiModule();

            using var payload = new ChatPayload(message);
            var mem1 = Marshal.AllocHGlobal(400);
            Marshal.StructureToPtr(payload, mem1, false);

            this.ProcessChatBox(uiModule, mem1, IntPtr.Zero, 0);

            Marshal.FreeHGlobal(mem1);
        }

        [StructLayout(LayoutKind.Explicit)]
        [SuppressMessage("ReSharper", "PrivateFieldCanBeConvertedToLocalVariable")]
        private readonly struct ChatPayload : IDisposable {
            [FieldOffset(0)]
            private readonly IntPtr textPtr;

            [FieldOffset(16)]
            private readonly ulong textLen;

            [FieldOffset(8)]
            private readonly ulong unk1;

            [FieldOffset(24)]
            private readonly ulong unk2;

            internal ChatPayload(string text) {
                var stringBytes = Encoding.UTF8.GetBytes(text);
                this.textPtr = Marshal.AllocHGlobal(stringBytes.Length + 30);
                Marshal.Copy(stringBytes, 0, this.textPtr, stringBytes.Length);
                Marshal.WriteByte(this.textPtr + stringBytes.Length, 0);

                this.textLen = (ulong) (stringBytes.Length + 1);

                this.unk1 = 64;
                this.unk2 = 0;
            }

            public void Dispose() {
                Marshal.FreeHGlobal(this.textPtr);
            }
        }
    }
}