ConnectNamedPipe

The ConnectNamedPipe function enables a named pipe server process to wait for a client process to connect to an instance of a named pipe. A client process connects by calling either the CreateFile or CallNamedPipe function.

BOOL ConnectNamedPipe(

HANDLE hNamedPipe,	// handle to named pipe to connect
LPOVERLAPPED lpOverlapped	// pointer to overlapped structure
);

Parameters

hNamedPipe

Identifies the server end of a named pipe instance. This handle is returned by the CreateNamedPipe function.

lpOverlapped

Points to an OVERLAPPED structure.

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

A named pipe server process can use ConnectNamedPipe with a newly created pipe instance. It can also be used with an instance that was previously connected to another client process; in this case, the server process must first call the DisconnectNamedPipe function to disconnect the handle from the previous client before the handle can be reconnected to a new client. Otherwise, ConnectNamedPipe returns FALSE, and GetLastError returns ERROR_NO_DATA if the previous client has closed its handle or ERROR_PIPE_CONNECTED if it has not closed its handle.

The behavior of ConnectNamedPipe depends on two conditions: whether the pipe handle's wait mode is set to blocking or nonblocking and whether the function is set to execute synchronously or in overlapped mode. A server initially specifies a pipe handle's wait mode in the CreateNamedPipe function, and it can be changed by using the SetNamedPipeHandleState function.

If hNamedPipe was opened with FILE_FLAG_OVERLAPPED, the lpOverlapped parameter must not be NULL. It must point to a valid OVERLAPPED structure. If hNamedPipe was opened with FILE_FLAG_OVERLAPPED and lpOverlapped is NULL, the function can incorrectly report that the connect operation is complete.

If hNamedPipe was created with FILE_FLAG_OVERLAPPED and lpOverlapped is not NULL, the OVERLAPPED structure pointed to by lpOverlapped must contain a handle to a manual-reset event object (which the server can create by using the CreateEvent function).

If hNamedPipe was not opened with FILE_FLAG_OVERLAPPED and lpOverlapped is NULL, the function does not return until a client is connected or an error occurs. Successful synchronous operations result in the function returning TRUE if a client connects after the function is called. If a client connects before the function is called, the function returns FALSE and GetLastError returns ERROR_PIPE_CONNECTED. This can happen if a client connects in the interval between the call to CreateNamedPipe and the call to ConnectNamedPipe. In this situation, there is a good connection between client and server, even though the function returns FALSE.

If hNamedPipe was not opened with FILE_FLAG_OVERLAPPED and lpOverlapped is not NULL, the operation executes asynchronously. The function returns immediately with a return value of FALSE. If a client process connects before the function is called, GetLastError returns ERROR_PIPE_CONNECTED. Otherwise, GetLastError returns ERROR_IO_PENDING, which indicates that the operation is executing in the background. When this happens, the event object in the OVERLAPPED structure is set to the nonsignaled state before ConnectNamedPipe returns, and it is set to the signaled state when a client connects to this instance of the pipe.

The server process can use any of the wait functions or SleepEx to determine when the state of the event object is signaled, and it can then use the GetOverlappedResult function to determine the results of the ConnectNamedPipe operation.

If the specified pipe handle is in nonblocking mode, ConnectNamedPipe always returns immediately. In nonblocking mode, ConnectNamedPipe returns TRUE the first time it is called for a pipe instance that is disconnected from a previous client. This indicates that the pipe is now available to be connected to a new client process. In all other situations when the pipe handle is in nonblocking mode, ConnectNamedPipe returns FALSE. In these situations, GetLastError returns ERROR_PIPE_LISTENING if no client is connected, ERROR_PIPE_CONNECTED if a client is connected, and ERROR_NO_DATA if a previous client has closed its pipe handle but the server has not disconnected. Note that a good connection between client and server exists only after the ERROR_PIPE_CONNECTED error is received.

Note that nonblocking mode is supported for compatibility with Microsoft LAN Manager version 2.0, and it should not be used to achieve asynchronous input and output (I/O) with named pipes.

See Also

CallNamedPipe, CreateEvent, CreateFile, CreateNamedPipe, DisconnectNamedPipe, GetOverlappedResult, SetNamedPipeHandleState, SleepEx, OVERLAPPED

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