Hook example

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Hook example

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ricnogueira
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Post: #1

Hook example

I am trying to build a simple program that hooks the Windows function MessageBox

I ve analysed the sample that comes with codehook, but I didnt understand how I can do that

Could you supply an exemple for hooking MessageBox?

Tks

Ricardo Nogueira

02-22-2008 06:47 AM

Qi
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Post: #2

RE: Hook example

Hello,

I have no Delphi in hand now. I will post complete code hooking MessageBox when I back to home.

The document tutorial.html in "help" directry may give you some hints.

Now here is a brief instructions to make a hook.

1, Get the interfaces.
InitCodeHookDLL('..\..\..\CHook.dll');
GetCodeHook(GCodeHook);
//if you don't need advanced hook, no need following line
GCodeHook.GetCodeHookHelper(GCodeHookHelper);

2, Get the address of MessageBoxA or MessageBoxW (unicode version). There is no API names MessageBox.
TheAddress := GetProcAddress(GetModuleHandle('user32.dll'), 'MessageBoxA');

3, Write your hook function such like,

function NewMessageBoxA(hWnd: HWND; lpText, lpCaption: PAnsiChar; uType: UINT): Integer; stdcall;
begin
Do something here
end;

4, Now do the hook,
GCodeHook.Hook(TheAddress, @NewMessageBoxA);

Finished.

Here is the raw mode hook. The sample code in the package is the advanced mode which I must admit is not a good start. Smile

This post was last modified: 02-22-2008 11:00 AM by Qi.

02-22-2008 11:00 AM

ricnogueira
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Post: #3

RE: Hook example

Thanks

I will try it

Qi Wrote:

02-22-2008 10:43 PM

Qi
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Post: #4

RE: Hook example

Following is a complete source code of a demo .dpr file.
You can copy and save it as a .dpr to try it.

More detailed simple demo code will come soon.

Note the line InitCodeHookDLL('..\..\..\CHook.dll');
You need to change the path to where CHook.dll is in.

Code:

program CodeHookDemo1;

uses

  SysUtils, Windows,

  CodeHookIntf;

var

  GCodeHook: ICodeHook;

  OldMessageBoxA: function(hWnd: HWND; lpText, lpCaption: PAnsiChar; uType: UINT): Integer; stdcall;

function NewMessageBoxA(hWnd: HWND; lpText, lpCaption: PAnsiChar; uType: UINT): Integer; stdcall;

var

  lMsg: string;

begin

  lMsg := 'The text passed to MessageBox is:'#13#10

    + '"' + StrPas(lpText) + '"'#13#10

    + #13#10

    + 'Now here is some other text appended by the hook function.';

  Result := OldMessageBoxA(hWnd, PChar(lMsg), lpCaption, uType);

end;

procedure ShowMsg(const AMsg: string);

begin

  MessageBoxA(0, PChar(AMsg + #13#10 + 'This is the demo message'), 'Demo title', MB_OK);

end;

procedure ExecuteDemo;

var

  lHookInfo: TCodeHookInfo;

  lHandle: TCodeHookHandle;

  lMessageBoxA: Pointer;

begin

  InitCodeHookDLL('..\..\..\CHook.dll');

  GetCodeHook(GCodeHook);

  ShowMsg('Before hooked');

  lMessageBoxA := GetProcAddress(GetModuleHandle('user32.dll'), 'MessageBoxA');

  lHandle := GCodeHook.Hook(lMessageBoxA, @NewMessageBoxA);

  GCodeHook.GetHookInfo(lHandle, @lHookInfo);

  @OldMessageBoxA := lHookInfo.PreviousMethod;

  ShowMsg('After hooked');

  GCodeHook.Unhook(lHandle);

end;

begin

  ExecuteDemo;

end.

02-22-2008 11:37 PM

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