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<div align="center"><b><font color="#000099">3.3 Windows Sockets與UNIX套接口編程實例</font></b></div>
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<td height="46">下面是一個簡單的基于連接的點對點實時通信程序.它由兩部分組成,服務器在主機UNIX下直接運行, 客戶機在Windows下運行.</td>
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<td height="36">3.3.1 SERVER介紹</td>
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<td height="55">由于SERVER是在UNIX下運行的,它對套接口的使用都是BSD的標準函數,程序也比較簡單, 只有一段程序,下面簡要解釋一下</td>
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<td height="64">首先,建立自己的套接口.在互連網的進程通信中,全局標識一個進程需要一個被稱為"半相關"的三元組(協議,本地主機地址,本地端口號)來描述,而一個完整的進程通信實例則需要一個被稱為"相關"的五元組(協議,
本地主機地址,本地端口號,遠端主機地址,遠端端口號)來描述</td>
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<td height="34">s=socket(AF_INET, SOCK_STREAM, 0)</td>
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<td height="49">該函數建立指定地址格式,數據類型和協議下的套接口,地址格式為AF_INET(唯一支持的格式),數據類型SOCK_STREAM表示建立流式套接口,參數三為0,即協議缺省</td>
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<td height="32">bind(s, (struct sockaddr *)&server, sizeof(server))</td>
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<td height="42">該函數將建立服務器本地的半相關,其中,server是sockaddr_in結構,其成員描述了本地端口號和本地主機地址,經過bind()將服務器進程在網上標識出來.</td>
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<td height="30">然后,建立連接.先是調用listen()函數表示開始偵聽.再通過accept()調用等待接收連接.</td>
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<td height="52">listen(s,1)表示連接請求隊列長度為1,即只允許有一個請求,若有多個請求,則出現錯誤,給出錯誤代碼WSAECONNREFUSED.</td>
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<td>ns = accept(s, (struct sockaddr *)&client, &namelen)) </td>
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<td height="49">accept()阻塞(缺省)等待請求隊列中的請求,一旦有連接請求來,該函數就建立一個和s有相同屬性的新的套接口.client也是一個sockaddr_in結構,連接建立時填入請求連接的套接口的半相關信息.</td>
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<td height="25">接下來,就可以接收和發送數據了</td>
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<p>recv(ns,buf,1024,0) </p>
<p>send(ns,buf,pktlen,0) </p>
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<td height="44">上面兩個函數分別負責接收和發送數據,recv從ns(建立連接的套接口)接收數據放入buf中,send則將buf中數據發送給ns.至于第四個參數,表示該函數調用方式,可選擇MSG_DONTROUTE和MSG_OOB,
0表示缺省</td>
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<td height="31">最后,關閉套接口.</td>
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<p>close(ns); </p>
<p>close(s); </p>
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<td height="28">3.3.2 CLIENT介紹</td>
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<td height="53">客戶端是在Windows上運行的,使用了一些Windows Sockets的擴展函數,稍微復雜一些.包括了.RC和.C兩個文件,其中的主窗口函數ClientProc()是程序的主要部分,下面簡單解釋一下.</td>
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<td height="53">首先,是在WinMain()中建立好窗口后,即向主窗口函數發一條自定義的WM_USER消息, 做相關的準備工作.在主窗口函數中,一接收到WM_USER消息,首先調用WSAStartup()函數初始化Windows
Sockets DLL,并檢查版本號.如下:</td>
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<td height="36">Status = WSAStartup(VersionReqd, lpmyWSAData);</td>
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<td height="53">其中,VersionReqd描述了WINSOCK的版本(這里為1.1版),lpmyWSAData指向一個WSADATA結構,該結構描述了Windows
Sockets的實現細節.</td>
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<td height="53">WSAStartup()之后,進程通過主機名(運行時命令行參數傳入)獲取主機地址,如下:</td>
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<td height="53">hostaddr = gethostbyname(server_address);</td>
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<td height="53">hostaddr指向hostent結構,內容參見5.2.1.</td>
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<td height="53">然后,進程就不斷地消息循環,等待用戶通過菜單選擇"啟動".這時,通過調用Client()來啟動套接口.在Client()中,首先也是調用socket()來建立套接口.如下:</td>
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<p>if ((s = socket(AF_INET, SOCK_STREAM, 0)) == INVALID_SOCKET) </p>
<p>{ AlertUser(hWnd, "Socket Failed"); </p>
<p>return (FALSE); } </p>
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<td height="53">緊接著,調用WSAAsyncSelect()函數提名FD_CONNECT網絡事件,如下: </td>
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<td height="34">if (!SetSelect(hWnd, FD_CONNECT)) return (FALSE); </td>
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<td height="53">SetSelect()主要就是調用WSAASyncSelect(),讓Windows Sockets DLL在偵測到連接建立時,就發送一條UM_SOCK的自定義消息,使消息循環繼續下去.如下:</td>
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<td height="47">BOOL SetSelect(HWND hWnd, long lEvent) { if (WSAAsyncSelect(s,
hWnd, UM_SOCK, lEvent) == SOCKET_ERROR) { AlertUser(hWnd, "WSAAsyncSelect
Failure."); return (FALSE); } return (TRUE); } </td>
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<td height="41">為建立連接,必須馬上調用connect()如下,由于先調用了WSAASyncSelect(),connect()便是非阻塞調用.進程發出連接請求后就不管了,當連接建立好后,WINSOCK
DLL自動發一條消息給主窗口函數,以使程序運行下去.</td>
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<td height="32">connect(s, (struct sockaddr FAR *)&dst_addr, sizeof(dst_addr));</td>
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<td height="53">窗口函數在收到UM_SOCK消息后,判斷是由哪個網絡事件引起的,第一次,必然是由連接事件引起的,這樣,就會執行相應的程序段,同樣調用SetSelect()來提名FD_WRITE事件.希望在套接口可發送數據時接到消息.在收到FD_WRITE消息時,先調用send()發送數據,再調用SetSelect()來提名FD_READ事件,
希望在套接口可接收數據是接到消息.在收到FD_READ消息時,先調用recv()來接收數據再提名FD_WRITE事件,如此循環下去.直到發生連接關閉的事件FD_CLOSE,這時就調用WSAAsyncSelect(s,hWnd,0,0)來停止異步選擇.在窗口函數接到WM_DESTROY消息時(即關閉窗口之前),先調用closesocket()(作用同UNIX
中的close())來關閉套接口,再調用WSACleanup()終止Windows Sockets DLL,并釋放資源.</td>
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<td height="28">3.3.3 源程序清單</td>
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<p>程序1:</p>
<p>CLIENT.RC </p>
<p>ClientMenu </p>
<p>MENU </p>
<p>BEGIN </p>
<p>POPUP "&Server" </p>
<p>BEGIN </p>
<p>MENUITEM "&Start...", 101 </p>
<p>MENUITEM "&Exit", 102 </p>
<p>END END </p>
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<p><font face="宋體" lang="ZH-CN" size=3>程序</font><font size=3>2:CLIENT.C</font></p>
<font size=3>
<p>#define USERPORT 10001</p>
<p>#define IDM_START 101</p>
<p>#define IDM_EXIT 102</p>
<p>#define UM_SOCK WM_USER + 0X100</p>
<p>#include <alloc.h></p>
<p>#include <mem.h></p>
<p>#include <windows.h></p>
<p>#include <winsock.h></p>
<p>#define MAJOR_VERSION 1</p>
<p>#define MINOR_VERSION 2</p>
<p>#define WSA_MAKEWORD(x,y) ((y)*256+(x))</p>
<p>HANDLE hInst;</p>
<p>char server_address[256] = {0};</p>
<p>char buffer[1024];</p>
<p>char FAR * lpBuffer = &buffer[0];</p>
<p>SOCKET s = 0;</p>
<p>struct sockaddr_in dst_addr;</p>
<p>struct hostent far *hostaddr;</p>
<p>struct hostent hostnm;</p>
<p>struct servent far *sp;</p>
<p>int count = 0;</p>
<p>BOOL InitApplication(HINSTANCE hInstance);</p>
<p>long FAR PASCAL ClientProc(HWND hWnd, unsigned message, UINT wParam,
LONG lParam);</p>
<p>void AlertUser(HWND hWnd, char *message);</p>
<p>BOOL Client(HWND hWnd);</p>
<p>BOOL ReceivePacket(HWND hWnd);</p>
<p>BOOL SetSelect(HWND hWnd, long lEvent);</p>
<p>BOOL SendPacket(HWND hWnd, int len);</p>
<p>int PASCAL WinMain(HANDLE hInstance, HANDLE hPrevInstance, LPSTR lpCmdLine,
int nCmdShow)</p>
<p>{</p>
<p>	HWND hWnd;</p>
<p>	MSG msg;</p>
<p>	lstrcpy((LPSTR)server_address, lpCmdLine);</p>
<p>	if (!hPrevInstance)</p>
<p>		if (!InitApplication(hInstance))</p>
<p>			return (FALSE);</p>
<p>	hInst = hInstance;</p>
<p>	hWnd = CreateWindow("ClientClass", "Windows ECHO Client", WS_OVERLAPPEDWINDOW,\</p>
<p>		CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL,
NULL,\</p>
<p>		hInstance, NULL);</p>
<p>	if (!hWnd)</p>
<p>		return (FALSE);</p>
<p>	ShowWindow(hWnd, nCmdShow);</p>
<p>	UpdateWindow(hWnd);</p>
<p>	PostMessage(hWnd, WM_USER, (WPARAM)0, (LPARAM)0);</p>
<p>	while (GetMessage(&msg, NULL, NULL, NULL))</p>
<p>	{</p>
<p>		TranslateMessage(&msg);</p>
<p>		DispatchMessage(&msg);</p>
<p>	}</p>
<p>	return (msg.wParam);</p>
<p>}</p>
<p>BOOL InitApplication(HINSTANCE hInstance)</p>
<p>{</p>
<p> WNDCLASS WndClass;</p>
</font>
<p> <font face="宋體" lang="ZH-CN" size=3>	</font><font size=3>char *szAppName
= "ClientClass";</font></p>
<font size=3>
<p> // fill in window class information</p>
<p>	WndClass.lpszClassName = (LPSTR)szAppName;</p>
<p>	WndClass.hInstance = hInstance;</p>
</font>
<p><font face="宋體" lang="ZH-CN" size=3>	</font><font size=3>WndClass.lpfnWndProc
= ClientProc;</font></p>
<p><font face="宋體" lang="ZH-CN" size=3>	</font><font size=3>WndClass.hCursor
= LoadCursor(NULL, IDC_ARROW);</font></p>
<font size=3>
<p>	WndClass.hIcon = LoadIcon(hInstance, NULL);</p>
<p>	WndClass.lpszMenuName = "ClientMenu";</p>
<p>	WndClass.hbrBackground = GetStockObject(WHITE_BRUSH);</p>
<p>	WndClass.style = CS_HREDRAW | CS_VREDRAW;</p>
<p>	WndClass.cbClsExtra = 0;</p>
<p>	WndClass.cbWndExtra = 0;</p>
<p> // register the class</p>
<p> if (!RegisterClass(&WndClass))</p>
<p>		return(FALSE);</p>
<p> return(TRUE);</p>
<p>}</p>
<p>long FAR PASCAL ClientProc(HWND hWnd, unsigned message, UINT wParam,
LONG lParam)</p>
<p>{</p>
<p>	int length, i;</p>
<p>	WSADATA wsaData;</p>
<p>	int Status;</p>
<p>	switch (message)</p>
<p>	{</p>
<p>		case WM_USER:</p>
<p>		{</p>
<p>			WORD	wMajorVersion, wMinorVersion;</p>
<p>			LPWSADATA	lpmyWSAData;</p>
<p>			WORD 		VersionReqd;</p>
<p>			int			ret;</p>
<p>			wMajorVersion = MAJOR_VERSION;</p>
<p>			wMinorVersion = MINOR_VERSION;</p>
<p>			VersionReqd = WSA_MAKEWORD(wMajorVersion,wMinorVersion);</p>
<p>		</p>
<p>			lpmyWSAData = (LPWSADATA)malloc(sizeof(WSADATA));</p>
<p>			Status = WSAStartup(VersionReqd, lpmyWSAData);</p>
<p>			if (Status != 0)</p>
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