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Windows Sockets Network Programming (three) - WINDOWS SOCKETS 1.1 programming Author: freezing studio Kitty I. Introduction WINDOWS SOCKETS from Berkeley Sockets expansion comes, on the basis of their inheritance on the Berkeley Sockets, we have conducted a new expansion . These expansion mainly provide some asynchronous functions and add a network event asynchronous selection mechanism that meets Windows message driver characteristics. Windows sockets consists of two parts: development components and runtime components. Developing Components: Windows Sockets Implement Document, Application Interface (API) Introduces Library and Some headers. Run Components: Windows Sockets Application Dynamic Link Library (Winsock.dll). Second, the main expansion note 1. Asynchronous selection mechanism: Windows sockets's asynchronous selection function provides a network event selection of message mechanisms. When using it to register network events, the application corresponding window function will receive a message, indicated in the message. An occurrence of online events, as well as some information related to events. Windows Sockets provides an asynchronous selection function WSaasyncSelect () that uses it to register a network event interested in the application. When these events occur, the application corresponding window function will receive a message. The function structure is as follows: Int Pascal far wsaasyncselect (socket s, hwnd, unsigned INT WMSG, Long LEVENT); Parameter Description: HWND: Window Handle WMSG: Message for Send LEVENT: Event (The content of the event) value: meaning: FD_READ expects to receive data (ie read ready) on the socket (ie read ready), you can receive the notification of data (ie, write ready) on the socket (ie, write preparation) is expected to have an outside of the socket. When the data arrives, the notification fd_accept is expected to receive a notification fd_connect when there are external connections on the socket, which is expected to receive the notification fd_close expect to receive notifications when the socket is closed, for example: we are in a set The read read is ready or write to the notification, the statement is as follows: rc = wsaasyncselect (s, hwnd, wmsg, fd_read | fd_write); if we need to cancel the message to the socket network event, just set the Levent setting To 0 2, the asynchronous request function requesting service in Berkeley Sockets is blocked, in addition to supporting this type of function (WSAAsyncGetxByy ();). 3, Blocking Processing WINDOWS Sockets In order to implement when an application's socket call is blocked, the CPU is abandoned to allow other applications to run, which enters a routine called "hook" when the call is blocked, this example The process is responsible for receiving and distributing Windows messages so that other applications can still receive their own messages and achieve control. Windows is a non-predetermined multitasking environment, that is, if a program does not actively give it to give control, other programs cannot be executed. Therefore, when designing the Windows Sockets program, although the system supports blocking operations, it is still opposed to programmers. However, due to the SUN's Berkeley Sockets socket default operations are blocking, Windows is also intended to support this operation as porting SOCKETS. In the Windows Sockets implementation, the following processes are processed for blocked operations that cannot be completed immediately: DLL initialization → loop operation.
In the loop, it sends any Windows messages and checks if this Windows sockets call is completed. It is necessary when necessary, it can discard the CPU to make other application execution (of course, there will be this kind of CPU with the ultra-thread, there will be this trouble ^ _ ^) . We can call the wsacancelblockingCall () function to cancel this blocking operation. In Windows Sockets, there is a default blocking process routine BlockingHook () simply acquires and sends a Windows message. If you want to process complex programs, WSASetBlockingHook () is available in Windows Sockets, providing users to install their own blocking process routine; SwaunhookBlockingHook () is SwaunhookBlockingHook (), which is used to delete any of previously installed occlusion processing examples Cheng, and reinstall the default processing routine. Note that when you design your own blocking process, in addition to the function WSAcAncelBlockingHook (), it cannot use other Windows Sockets API functions. Calling the wsacancelblockinghook () function in the process routine will cancel the blocking operation, which will end the blocking loop. 4, error handling Windows Sockets is compatible with later multi-threaded environments (Windows / Unix), which provides two error handages to get the nearest error number of the current thread. (Wsagetlasteror () and WSasetLastError ()) 5, start and terminate use functions WSAStartup () and wsacleanup () boot and terminate the socket. Third, Windows Sockets Network Program Design core We finally start the real Windows Sockets network program. But we still take a look at the content involved in each Windows Sockets network program. Let's walk slowly step by step. 1. Start and terminate in all Windows Sockets functions, only the start function wsaStartup () and termination functions WSACLEANUP () must be used. The startup function must be the first function, and it allows you to specify the version of the Windows Sockets API and get some specific technical details for Sockets. This structure is as follows: int Pascal Far WSAStartup (Word WVersionRequested, LPWSADATA LPWSADATA); where WVersionRequested ensures that Sockets can run the DLL version, if not, return error messages. Let's take a look at the code below, look at how to call WSASTARTUP () call word wvelsisRequested; // Define version information variables WSADATA WSADATA; / / Define data information variables
INT ERR; / / Define Error number variables
WVersionRequested = MakeWord (1, 1); / / assigning version information
Err = WSAStartup (WVersionRequested, & WSADATA); / / Assignment to Error Information
IF (Err! = 0)
{
Return; / / tell the user to find the right version
}
/ / Confirm that Windows Sockets DLL supports 1.1 version
// DLL version can be higher than 1.1
/ / The version number returned by the system is always the minimum requirements 1.1, that is, the minimum version number supported in the application and the DLL.
IF (LobyTe (Wsadata.WVersion)! = 1 || Hibyte (Wsadata.WVersion)! = 1)
{
WSACLEANUP (); // tells the user to find the right version
Return;
}
// Windows Sockets DLL is accepted by the process, you can go to the next step, when you turn off the function, any open and connected Sock_Stream socket is reset, but those that have been closed but still not send data by the closesocket () function The terminals are not affected, and the data that is not transmitted will still be sent. The WSASTARTUO () function may be called multiple times when running, but must ensure that the value of WVersionRequested each time the call is the same. 2, asynchronous request service Windows sockets In addition to supporting Synchronous requests in Berkeley Sockets, a class of asynchronous request service functions WSAAsyncgerXBYY (). This function is an asynchronous version of the blocking request function. When the application calls it, this operation is initialized by the Windows Sockets DLL and returns the caller. This function returns an asynchronous handle to identify this operation. When the result is stored in the buffer provided by the caller, a message is sent to the application corresponding window. The common structure is as follows: Handle Taskhnd; char hostname = "rs6000";
Taskhnd = WSaasyncBethostByname (HWND, WMSG, Hostname, BUF, BUFLEN); It should be noted that since Windows memory objects can be set to removable and discarded, the operation memory object is, must ensure that the Wiindows Sockets DLL object is available of. 3. Asynchronous data transmission uses the send () or sendto () function to send data, use RECV () or Recvfrom () to receive data. Windows Sockets does not encourage users to transfer data using blocked mode, because it may block the entire Windows environment. Let's take a look at an asynchronous data transfer: Assume that the socket s has used the function wsaasyncselect () to register the network event fd_read and fd_write on it, and the WMSG value is UM_SOCK, then we can cycle on the Windows message Add the following branch statement: Case Um_sock:
Switch (lparam)
{
Case FD_READ:
Len = RECV (WPARAM, LPBUFFER, Length, 0);
Break;
Case FD_WRITE:
While (Send (WParam, Lpbuffer, Len, 0)! = Socket_ERROR)
Break;
}
Break;
4. The error handling Windows provides a function to get the most recent error code WsageTlasterror (), the recommended write method is as follows: len = send (s, lpbuffer, len, 0);
OF ((len == Socket_ERROR) && (wsagetlasterror () == wsawouldblock) {...}
