LuaJIT script to receive a message sent with OutputDebugMessage() from LGS/GHUB

LGS_OutputDebugMessage_Receiver.lua

-- This LuaJIT script receives first OutputDebugMessage() from LGS/GHUB, prints the message to stdout and exits
-- Waiting is limited to 2 seconds

local timeout_msec = 2000  -- set 2^32-1 for infinite waiting

local ffi = require"ffi"
local psapi = ffi.load"psapi"

ffi.cdef[[
uint32_t EnumProcesses(uint32_t *, uint32_t, uint32_t *);
void ** OpenProcess(uint32_t, uint32_t, uint32_t);
uint32_t CloseHandle(void **);
uint32_t GetModuleBaseNameA(void **, void **, void *, uint32_t);
uint32_t DebugActiveProcess(uint32_t);
uint32_t DebugActiveProcessStop(uint32_t);
uint32_t DebugSetProcessKillOnExit(uint32_t);
typedef struct {
   uint32_t dwDebugEventCode;
   uint32_t dwProcessId;
   uint32_t dwThreadId;
   union {
      struct {
         void **  hFile;
         void **  hProcess;
      } CreateProcessInfo;
      struct {
         void *   lpDebugStringData;
         uint16_t fUnicode;
         uint16_t nDebugStringLength;
      } DebugString;
   } u;
} *LPDEBUG_EVENT;
uint32_t WaitForDebugEvent(LPDEBUG_EVENT, uint32_t);
uint32_t ContinueDebugEvent(uint32_t, uint32_t, uint32_t);
uint32_t ReadProcessMemory(void **, void *, void *, size_t, size_t *);
]]

local DWORDS = ffi.typeof"uint32_t[?]"
local block64K = DWORDS(16384)
local DebugEvent = ffi.cast("LPDEBUG_EVENT", block64K)
local block20 = DWORDS(5)
local PID

if psapi.EnumProcesses(block64K, ffi.sizeof(block64K), block20) ~= 0 then
   for j = 0, block20[0]/4 - 1 do
      local next_PID = block64K[j]
      local ProcessHandle = ffi.C.OpenProcess(0x0410, 0, next_PID) -- PROCESS_VM_READ | PROCESS_QUERY_INFORMATION
      if ProcessHandle ~= nil then
         local name_len = psapi.GetModuleBaseNameA(ProcessHandle, nil, block20, ffi.sizeof(block20))
         ffi.C.CloseHandle(ProcessHandle)
         local ProcessName = ffi.string(block20, name_len)
         if ProcessName == "LCore.exe" or ProcessName == "lghub_agent.exe" then
            PID = next_PID
            break
         end
      end
   end
end

if PID and ffi.C.DebugActiveProcess(PID) ~= 0 then
   ffi.C.DebugSetProcessKillOnExit(0)
   local ProcessHandle
   repeat
      local exit = ffi.C.WaitForDebugEvent(DebugEvent, timeout_msec) == 0
      if not exit then
         local ThreadId = DebugEvent.dwThreadId
         local info = DebugEvent.u.CreateProcessInfo
         local DebugEventCode = DebugEvent.dwDebugEventCode
         if DebugEventCode == 3 then      -- CREATE_PROCESS_DEBUG_EVENT
            ProcessHandle = info.hProcess
            ffi.C.CloseHandle(info.hFile)
         elseif DebugEventCode == 6 then  -- LOAD_DLL_DEBUG_EVENT
            ffi.C.CloseHandle(info.hFile)
         elseif DebugEventCode == 8 then  -- OUTPUT_DEBUG_STRING_EVENT
            exit = true
            info = DebugEvent.u.DebugString
            local len = info.nDebugStringLength
            if len ~= 0 and info.fUnicode == 0
               and ffi.C.ReadProcessMemory(ProcessHandle, info.lpDebugStringData, block64K, len, nil) ~= 0
            then
               local str = ffi.string(block64K, len - 1)
               print(str)
            end
         end
         ffi.C.ContinueDebugEvent(PID, ThreadId, 0x10002)  -- DBG_CONTINUE
      end
   until exit
   ffi.C.DebugActiveProcessStop(PID)
   ffi.C.CloseHandle(ProcessHandle)
end