API Function

#include <cstdlib>
#include <cstring>

#include <winsock2.h>
#include <Ws2tcpip.h>

#include <windows.h>

class ApiCave
{
    public:
    void GenerateBytes();
    void RestoreBytes();
    void PlaceJump();
    void GetOriginalFuncAddress(char * moduleName, char * functionName);
    ApiCave(LPVOID DetourFunction, int iSize);
    ~ApiCave();
    private:
    int iInstructionSize;
    BYTE *originalBytes, *hookBytes, *tempBytes;
    DWORD OriginalFunctionAddress, DetourFunctionAddress, oldprotect;
    DWORD myprotect;
};
void ApiCave::GenerateBytes()
{
    tempBytes[0] = 0xE9;
    tempBytes[5] = 0xC3;                                    // 0xE9 = JMP 0x90 = NOP oxC3 = RET
    memcpy(hookBytes, tempBytes, iInstructionSize);                                         // store jmp instruction to JMP
    DWORD JMPSize = ((DWORD)DetourFunctionAddress - (DWORD)OriginalFunctionAddress - 5);    // calculate jump distance
    VirtualProtect((LPVOID)OriginalFunctionAddress, iInstructionSize,                                   // assign read write protection
                   myprotect, &oldprotect);
    memcpy((LPVOID)originalBytes, (LPVOID)OriginalFunctionAddress, iInstructionSize);                                   // make backup
    memcpy(&hookBytes[1], &JMPSize, 4);                                                     // fill the nop's with the jump distance (JMP,distance(4bytes),RET)
    VirtualProtect((LPVOID)OriginalFunctionAddress, iInstructionSize, oldprotect, NULL);
}
void ApiCave::RestoreBytes()
{
    VirtualProtect((LPVOID)OriginalFunctionAddress, iInstructionSize, myprotect, &oldprotect);
    memcpy((LPVOID)OriginalFunctionAddress, originalBytes, iInstructionSize);
    VirtualProtect((LPVOID)OriginalFunctionAddress, iInstructionSize, oldprotect, NULL);
}
void ApiCave::PlaceJump()
{
    VirtualProtect((LPVOID)OriginalFunctionAddress, iInstructionSize, myprotect, &oldprotect);
    memcpy((LPVOID)OriginalFunctionAddress, hookBytes, iInstructionSize);
    VirtualProtect((LPVOID)OriginalFunctionAddress, iInstructionSize, oldprotect, NULL);
}
void ApiCave::GetOriginalFuncAddress(char * moduleName, char * functionName)
{
    OriginalFunctionAddress = (DWORD)GetProcAddress(GetModuleHandle(moduleName), functionName);
}
ApiCave::ApiCave(LPVOID DetourFunction, int iSize)
{
    iInstructionSize = iSize;
    myprotect = PAGE_EXECUTE_READWRITE;
    DetourFunctionAddress = (DWORD)DetourFunction;
    tempBytes = new BYTE[iSize];
    originalBytes = new BYTE[iSize];
    hookBytes = new BYTE[iSize];
}
ApiCave::~ApiCave()
{
    delete[] tempBytes;
    delete[] originalBytes;
    delete[] hookBytes;
}

#include "hook.h"

BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)
{
    switch (fdwReason)
    {
        case DLL_PROCESS_ATTACH:
            DoTheHook();
            break;
    }
    return TRUE; 
}

#include "hkClass.h"

int WINAPI MySend(SOCKET, const char *, int, int);  
int WINAPI MyMessageBoxA(HWND, LPCTSTR, LPCTSTR, UINT);

ApiCave sendCave((LPVOID)MySend, 6);
ApiCave mbCave((LPVOID)MyMessageBoxA, 6);

int WINAPI MySend (SOCKET s, const char * buf, int len, int flags)
{
    sendCave.RestoreBytes();
    int retVal = send(s, buf, len, flags);
    sendCave.PlaceJump();
    return retVal;
}

int WINAPI MyMessageBoxA(HWND hWnd, LPCTSTR text, LPCTSTR title, UINT type)
{
   mbCave.RestoreBytes();
   int retVal = MessageBoxA(hWnd, text, title, type);
   mbCave.PlaceJump();
   return retVal;
}

void DoTheHook()
{
   sendCave.GetOriginalFuncAddress("ws2_32.dll", "send");
   mbCave.GetOriginalFuncAddress("user32.dll", "MessageBoxA");
   
   sendCave.GenerateBytes();
   mbCave.GenerateBytes();
   
   sendCave.PlaceJump();
   mbCave.PlaceJump();
}