Is possible hook EnumWindowsProc callback function? - delphi

Question

I want know if is possible hook a callback function for example like EnumWindowsProc() using inline hook approach? and if yes, could provide a code snippet (example) please?
Thank you.
EDITION:
EnumWindowsProc is a callback implemented in other app. I not call it inside my app.
And i want hook EnumWindowsProc in this other app, by dll injection.

Answer 1

You have to handle EnumWindows at first, then you have to replace pointer to original EnumWindowsProc to yourself.
My example is valid fow win32
unit Patch;
interface
procedure PatchEnumWindows(Patch: Boolean);
implementation
uses SysUtils, SyncObjs, Windows;
const
INSTR_SIZE = 6;
var
OldEnumWindows: array [0..INSTR_SIZE-1] of Byte;
EnumWindowsPatched: Boolean = False;
function PatchedEnumWindows(EnumWindowsProc: Pointer; Param: Pointer); stdcall;
begin
// You have to replace original EnumWindowsProc to yourself
end;
procedure ApiRedirect(OrigFunction, NewFunction: Pointer; var Old);
const
TEMP_JMP: array[0..INSTR_SIZE-1] of Byte = ($E9,$90,$90,$90,$90,$C3);
var
JmpSize: DWORD;
JMP: array [0..INSTR_SIZE-1] of Byte;
OldProtect: DWORD;
begin
Move(TEMP_JMP, JMP, INSTR_SIZE);
JmpSize := DWORD(NewFunction) - DWORD(OrigFunction) - 5;
if not VirtualProtect(LPVOID(OrigFunction), INSTR_SIZE, PAGE_EXECUTE_READWRITE, OldProtect) then
raise Exception.CreateFmt('%s', [SysErrorMessage(GetLastError)]);
Move(OrigFunction^, Old, INSTR_SIZE);
Move(JmpSize, JMP[1], 4);
Move(JMP, OrigFunction^, INSTR_SIZE);
VirtualProtect(LPVOID(OrigFunction), INSTR_SIZE, OldProtect, nil);
end;
procedure PatchEnumWindows(Patch: Boolean);
var
OrigEnumWindows: Pointer;
begin
if Patch <> EnumWindowsProcPatched then begin
OrigEnumWindows := GetProcAddress(GetModuleHandle('user32.dll'), 'EnumWindows');
if Patch then begin
ApiRedirect(OrigEnumWindows, #PatchedEnumWindows, OldEnumWindows);
end
else begin
Move(OldEnumWindows, OrigEnumWindows, INSTR_SIZE);
end;
EnumWindowsPatched := Patch;
end;
end;
end.