运行WinNT和Win2000的系统上,这些APIs在Microsoft提供的DLL(mswsock.dll)里实现,可以通过链接mswsock.lib或者通过WSAioctl的SIO_GET_EXTENSION_FUNCTION_POINTER操作动态调用这些扩展APIs.
未获取函数指针就调用函数(如直接连接mswsock.lib并直接调用AcceptEx)的消耗是很大的,因为AcceptEx 实际上是存在于Winsock2结构体系之外的。每次应用程序常试在服务提供层上(mswsock之上)调用AcceptEx时,都要先通过WSAIoctl获取该函数指针。如果要避免这个很影响性能的操作,应用程序最好是直接从服务提供层通过WSAIoctl先获取这些APIs的指针。
需要注意的是,通过WSAIoctl获取AcceptEx函数指针时,只需要传递给WSAIoctl一个有效的SOCKET即可,该Socket的类型不会影响获取的AcceptEx函数指针。
同理可以获取Connectex与GetAcceptExSockaddrs函数指针。
代码如下:
typedef BOOL (WINAPI *AcceptExPtr)(SOCKET, SOCKET, PVOID, DWORD, DWORD, DWORD, LPDWORD, LPOVERLAPPED);
typedef BOOL (WINAPI *ConnectExPtr)(SOCKET, const struct sockaddr *, int, PVOID, DWORD, LPDWORD, LPOVERLAPPED);
typedef void (WINAPI *GetAcceptExSockaddrsPtr)(PVOID, DWORD, DWORD, DWORD, LPSOCKADDR *, LPINT, LPSOCKADDR *, LPINT);
struct win32_extension_fns {
AcceptExPtr AcceptEx;
ConnectExPtr ConnectEx;
GetAcceptExSockaddrsPtr GetAcceptExSockaddrs;
};
#ifndef WSAID_ACCEPTEX
#define WSAID_ACCEPTEX \
{0xb5367df1,0xcbac,0x11cf,{0x95,0xca,0x00,0x80,0x5f,0x48,0xa1,0x92}}
#endif
#ifndef WSAID_CONNECTEX
#define WSAID_CONNECTEX \
{0x25a207b9,0xddf3,0x4660,{0x8e,0xe9,0x76,0xe5,0x8c,0x74,0x06,0x3e}}
#endif
#ifndef WSAID_GETACCEPTEXSOCKADDRS
#define WSAID_GETACCEPTEXSOCKADDRS \
{0xb5367df2,0xcbac,0x11cf,{0x95,0xca,0x00,0x80,0x5f,0x48,0xa1,0x92}}
#endif
void * get_extension_function(SOCKET s, const GUID *which_fn)
{
void *ptr = NULL;
DWORD bytes=0;
WSAIoctl(s, SIO_GET_EXTENSION_FUNCTION_POINTER,
(GUID*)which_fn, sizeof(*which_fn),
&ptr, sizeof(ptr),
&bytes, NULL, NULL);
return ptr;
}
调用:
const GUID acceptex = WSAID_ACCEPTEX;
const GUID connectex = WSAID_CONNECTEX;
const GUID getacceptexsockaddrs = WSAID_GETACCEPTEXSOCKADDRS;
SOCKET s = socket(AF_INET, SOCK_STREAM, 0);
if (s == INVALID_SOCKET)
return;
ext->AcceptEx = (AcceptExPtr)get_extension_function(s, &acceptex);
ext->ConnectEx = (ConnectExPtr)get_extension_function(s, &connectex);
ext->GetAcceptExSockaddrs = (GetAcceptExSockaddrsPtr)get_extension_function(s,&getacceptexsockaddrs);
closesocket(s);