使用WSAIoctl获取AcceptEx，Connectex,Getacceptexsockaddrs函数指针

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);