拦截网络数据封包的方法有三种,一是将网卡设为混杂模式,这次就可以监视到局域网上所有的数据包,二是HOOK目标进程的发送和接收的API函数,第三种方法是自己实现一个代理的DLL.在这里我们使用HOOK API的方法,这样易于实现,而且也不会得到大量的无用数据(如第一种方法就会监视到所有的网络数据).

下面是一个尽量简化了的API HOOK的模版,原理是利用消息钩子将DLL中的代码注入到目标进程中,再用GetProcAddress得到API函数入口地址,将函数入口址改为自己定义的函数入口,这样就得到了API函数的相应参数,处理完后,再改回真实API函数入口地址,并调用它.

HOOK.DLL的代码:
library Hook;

uses
SysUtils,
windows,
Messages,
APIHook in 'APIHook.pas';

type
PData = ^TData;
TData = record
Hook: THandle;
Hooked: Boolean;
end;

var
DLLData: PData;

{------------------------------------}
{过程名:HookProc
{过程功能:HOOK过程
{过程参数:nCode, wParam, lParam消息的相
{ 关参数
{------------------------------------}
procedure HookProc(nCode, wParam, lParam: LongWORD);stdcall;
begin
if not DLLData^.Hooked then
begin
HookAPI;
DLLData^.Hooked := True;
end;
//调用下一个Hook
CallNextHookEx(DLLData^.Hook, nCode, wParam, lParam);
end;

{------------------------------------}
{函数名:InstallHook
{函数功能:在指定窗口上安装HOOK
{函数参数:sWindow:要安装HOOK的窗口
{返回值:成功返回TRUE,失败返回FALSE
{------------------------------------}
function InstallHook(SWindow: LongWORD):Boolean;stdcall;
var
ThreadID: LongWORD;
begin
Result := False;
DLLData^.Hook := 0;
ThreadID := GetWindowThreadProcessId(sWindow, nil);
//给指定窗口挂上钩子
DLLData^.Hook := SetWindowsHookEx(WH_GETMESSAGE, @HookProc, Hinstance, ThreadID);
if DLLData^.Hook > 0 then
Result := True //是否成功HOOK
else
exit;
end;

{------------------------------------}
{过程名:UnHook
{过程功能:卸载HOOK
{过程参数:无
{------------------------------------}
procedure UnHook;stdcall;
begin
UnHookAPI;
//卸载Hook
UnhookWindowsHookEx(DLLData^.Hook);
end;

{------------------------------------}
{过程名:DLL入口函数
{过程功能:进行DLL初始化,释放等
{过程参数:DLL状态
{------------------------------------}
procedure MyDLLHandler(Reason: Integer);
var
FHandle: LongWORD;
begin
case Reason of
DLL_PROCESS_ATTACH:
begin //建立文件映射,以实现DLL中的全局变量
FHandle := CreateFileMapping($FFFFFFFF, nil, PAGE_READWRITE, 0, $ffff, 'MYDLLDATA');
if FHandle = 0 then
if GetLastError = ERROR_ALREADY_EXISTS then
begin
FHandle := OpenFileMapping(FILE_MAP_ALL_ACCESS, False, 'MYDLLDATA');
if FHandle = 0 then Exit;
end else Exit;
DLLData := MapViewOfFile(FHandle, FILE_MAP_ALL_ACCESS, 0, 0, 0);
if DLLData = nil then
CloseHandle(FHandle);
end;
DLL_PROCESS_DETACH:
begin
if Assigned(DLLData) then
begin
UnmapViewOfFile(DLLData);
DLLData := nil;
end;
end;
end;
end;

{$R *.res}
exports
InstallHook, UnHook, HookProc;

begin
DLLProc := @MyDLLHandler;
MyDLLhandler(DLL_PROCESS_ATTACH);
DLLData^.Hooked := False;
end.

----------------------------------------------------------------------------------------
APIHook.Pas的代码:

unit APIHook;

interface

uses
SysUtils,
Windows, WinSock;

type
//要HOOK的API函数定义
TSockProc = function (s: TSocket; var Buf; len, flags: Integer): Integer; stdcall;

PJmpCode = ^TJmpCode;
TJmpCode = packed record
JmpCode: BYTE;
Address: TSockProc;
MovEAX: Array [0..2] of BYTE;
end;

//--------------------函数声明---------------------------
procedure HookAPI;
procedure UnHookAPI;

var
OldSend, OldRecv: TSockProc; //原来的API地址
JmpCode: TJmpCode;
OldProc: array [0..1] of TJmpCode;
AddSend, AddRecv: pointer; //API地址
TmpJmp: TJmpCode;
ProcessHandle: THandle;
implementation

{---------------------------------------}
{函数功能:Send函数的HOOK
{函数参数:同Send
{函数返回值:integer
{---------------------------------------}
function MySend(s: TSocket; var Buf; len, flags: Integer): Integer; stdcall;
var
dwSize: cardinal;
begin
//这儿进行发送的数据处理
MessageBeep(1000); //简单的响一声
//调用直正的Send函数
WriteProcessMemory(ProcessHandle, AddSend, @OldProc[0], 8, dwSize);
Result := OldSend(S, Buf, len, flags);
JmpCode.Address := @MySend;
WriteProcessMemory(ProcessHandle, AddSend, @JmpCode, 8, dwSize);
end;

{---------------------------------------}
{函数功能:Recv函数的HOOK
{函数参数:同Recv
{函数返回值:integer
{---------------------------------------}
function MyRecv(s: TSocket; var Buf; len, flags: Integer): Integer; stdcall;
var
dwSize: cardinal;
begin
//这儿进行接收的数据处理
MessageBeep(1000); //简单的响一声
//调用直正的Recv函数
WriteProcessMemory(ProcessHandle, AddRecv, @OldProc[1], 8, dwSize);
Result := OldRecv(S, Buf, len, flags);
JmpCode.Address := @MyRecv;
WriteProcessMemory(ProcessHandle, AddRecv, @JmpCode, 8, dwSize);
end;

{------------------------------------}
{过程功能:HookAPI
{过程参数:无
{------------------------------------}
procedure HookAPI;
var
DLLModule: THandle;
dwSize: cardinal;
begin
ProcessHandle := GetCurrentProcess;
DLLModule := LoadLibrary('ws2_32.dll');
AddSend := GetProcAddress(DLLModule, 'send'); //取得API地址
AddRecv := GetProcAddress(DLLModule, 'recv');
JmpCode.JmpCode := $B8;
JmpCode.MovEAX[0] := $FF;
JmpCode.MovEAX[1] := $E0;
JmpCode.MovEAX[2] := 0;
ReadProcessMemory(ProcessHandle, AddSend, @OldProc[0], 8, dwSize);
JmpCode.Address := @MySend;
WriteProcessMemory(ProcessHandle, AddSend, @JmpCode, 8, dwSize); //修改Send入口
ReadProcessMemory(ProcessHandle, AddRecv, @OldProc[1], 8, dwSize);
JmpCode.Address := @MyRecv;
WriteProcessMemory(ProcessHandle, AddRecv, @JmpCode, 8, dwSize); //修改Recv入口
OldSend := AddSend;
OldRecv := AddRecv;
end;

{------------------------------------}
{过程功能:取消HOOKAPI
{过程参数:无
{------------------------------------}
procedure UnHookAPI;
var
dwSize: Cardinal;
begin
WriteProcessMemory(ProcessHandle, AddSend, @OldProc[0], 8, dwSize);
WriteProcessMemory(ProcessHandle, AddRecv, @OldProc[1], 8, dwSize);
end;

end.

---------------------------------------------------------------------------------------------
编译这个DLL后,再新建一个程序调用这个DLL的InstallHook并传入目标进程的主窗口句柄就可:
unit fmMain;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;

type
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
Edit1: TEdit;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;
InstallHook: function (SWindow: THandle):Boolean;stdcall;
UnHook: procedure;stdcall;
implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
ModuleHandle: THandle;
TmpWndHandle: THandle;
begin
TmpWndHandle := 0;
TmpWndHandle := FindWindow(nil, '目标窗口的标题');
if not isWindow(TmpWndHandle) then
begin
MessageBox(self.Handle, '没有找到窗口', '!!!', MB_OK);
exit;
end;
ModuleHandle := LoadLibrary('Hook.dll');
@InstallHook := GetProcAddress(ModuleHandle, 'InstallHook');
@UnHook := GetProcAddress(ModuleHandle, 'UnHook');
if InstallHook(FindWindow(nil, 'Untitled')) then
ShowMessage('Hook OK');
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
UnHook
end;

end.