HellionChat/ChatTwo/GameFunctions/ChatBox.cs

using System.Diagnostics.CodeAnalysis;
using System.Runtime.InteropServices;
using System.Text;
using Dalamud.Game;
using FFXIVClientStructs.FFXIV.Client.System.String;
using FFXIVClientStructs.FFXIV.Client.UI;

namespace ChatTwo.GameFunctions;

// From: https://git.anna.lgbt/anna/XivCommon/src/branch/main/XivCommon/Functions/Chat.cs
public class ChatCommon
{
    private static class Signatures
    {
        internal const string SendChat = "48 89 5C 24 ?? 57 48 83 EC 20 48 8B FA 48 8B D9 45 84 C9";
    }

    private delegate void ProcessChatBoxDelegate(IntPtr uiModule, IntPtr message, IntPtr unused, byte a4);
    private ProcessChatBoxDelegate? ProcessChatBox { get; }

    internal ChatCommon(ISigScanner scanner)
    {
        if (scanner.TryScanText(Signatures.SendChat, out var processChatBoxPtr))
        {
            ProcessChatBox = Marshal.GetDelegateForFunctionPointer<ProcessChatBoxDelegate>(processChatBoxPtr);
        }
    }

    public unsafe void SendMessageUnsafe(byte[] message)
    {
        if (ProcessChatBox == null)
            throw new InvalidOperationException("Could not find signature for chat sending");

        var uiModule = (IntPtr)UIModule.Instance();

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

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

        Marshal.FreeHGlobal(mem1);
    }

    public void SendMessage(string message)
    {
        var bytes = Encoding.UTF8.GetBytes(message);
        if (bytes.Length == 0)
            throw new ArgumentException("message is empty", nameof(message));

        if (bytes.Length > 500)
            throw new ArgumentException("message is longer than 500 bytes", nameof(message));

        if (message.Length != SanitiseText(message).Length)
            throw new ArgumentException("message contained invalid characters", nameof(message));

        SendMessageUnsafe(bytes);
    }

    private static unsafe string SanitiseText(string text)
    {
        var uText = Utf8String.FromString(text);

        uText->SanitizeString( 0x27F, Utf8String.CreateEmpty());

        var sanitised = uText->ToString();
        uText->Dtor();

        return sanitised;
    }

    [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(byte[] stringBytes)
        {
            textPtr = Marshal.AllocHGlobal(stringBytes.Length + 30);
            Marshal.Copy(stringBytes, 0, textPtr, stringBytes.Length);
            Marshal.WriteByte(textPtr + stringBytes.Length, 0);

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

            unk1 = 64;
            unk2 = 0;
        }

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