Example Code - Named Pipes (Python 2.4 + ctypes on Windows)

Hello,
Here is an example of Multithreaded Pipe Server and Client using the
excellent ctypes library (Windows).

Reference - MSDN:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ipc/base/multithreaded_pipe_server.asp
 and
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ipc/base/named_pipe_client.asp

Best Regards,
Srijit

Named Pipe Server Source Code:

from ctypes import *

PIPE_ACCESS_DUPLEX = 0x3
PIPE_TYPE_MESSAGE = 0x4
PIPE_READMODE_MESSAGE = 0x2
PIPE_WAIT = 0
PIPE_UNLIMITED_INSTANCES = 255
BUFSIZE = 4096
NMPWAIT_USE_DEFAULT_WAIT = 0
INVALID_HANDLE_VALUE = -1
ERROR_PIPE_CONNECTED = 535

MESSAGE = "Default answer from server\0"
szPipename = "\\\\.\\pipe\\mynamedpipe"


def ReadWrite_ClientPipe_Thread(hPipe):
    chBuf = create_string_buffer(BUFSIZE)
    cbRead = c_ulong(0)
    while 1:
        fSuccess = windll.kernel32.ReadFile(hPipe, chBuf, BUFSIZE,
byref(cbRead), None)
        if ((fSuccess ==1) or (cbRead.value != 0)):
            print chBuf.value
            cbWritten = c_ulong(0)
            fSuccess = windll.kernel32.WriteFile(hPipe,
                                                 c_char_p(MESSAGE),
                                                 len(MESSAGE),
                                                 byref(cbWritten),
                                                 None
                                                )
        else:
            break
        if ( (not fSuccess) or (len(MESSAGE) != cbWritten.value)):
            print "Could not reply to the client's request from the
pipe"
            break
        else:
            print "Number of bytes written:", cbWritten.value

    windll.kernel32.FlushFileBuffers(hPipe)
    windll.kernel32.DisconnectNamedPipe(hPipe)
    windll.kernel32.CloseHandle(hPipe)
    return 0

def main():
    THREADFUNC = CFUNCTYPE(c_int, c_int)
    thread_func = THREADFUNC(ReadWrite_ClientPipe_Thread)
    while 1:
        hPipe = windll.kernel32.CreateNamedPipeA(szPipename,
                                                 PIPE_ACCESS_DUPLEX,
                                                 PIPE_TYPE_MESSAGE |
                                                 PIPE_READMODE_MESSAGE
|
                                                 PIPE_WAIT,

PIPE_UNLIMITED_INSTANCES,
                                                 BUFSIZE, BUFSIZE,

NMPWAIT_USE_DEFAULT_WAIT,
                                                 None
                                                )
        if (hPipe == INVALID_HANDLE_VALUE):
            print "Error in creating Named Pipe"
            return 0

        fConnected = windll.kernel32.ConnectNamedPipe(hPipe, None)
        if ((fConnected == 0) and (windll.kernel32.GetLastError() ==
ERROR_PIPE_CONNECTED)):
            fConnected = 1
        if (fConnected == 1):
            dwThreadId = c_ulong(0)
            hThread = windll.kernel32.CreateThread(None, 0,
thread_func, hPipe, 0, byref(dwThreadId))
            if (hThread == -1):
                print "Create Thread failed"
                return 0
            else:
                windll.kernel32.CloseHandle(hThread)
        else:
            print "Could not connect to the Named Pipe"
            windll.kernel32.CloseHandle(hPipe)
    return 0


if __name__ == "__main__":
    main()



Named Pipe Client Source Code:

from ctypes import *

GENERIC_READ = 0x80000000
GENERIC_WRITE = 0x40000000
OPEN_EXISTING = 0x3
INVALID_HANDLE_VALUE = -1
PIPE_READMODE_MESSAGE = 0x2
ERROR_PIPE_BUSY = 231
ERROR_MORE_DATA = 234
BUFSIZE = 512

MESSAGE = "Default message from client\0"
szPipename = "\\\\.\\pipe\\mynamedpipe"

def main():
    while 1:
        hPipe = windll.kernel32.CreateFileA(szPipename, GENERIC_READ |
GENERIC_WRITE, 0, None, OPEN_EXISTING, 0, None)
        if (hPipe != INVALID_HANDLE_VALUE):
             break
        else:
            print "Invalid Handle Value"
        if (windll.kernel32.GetLastError() != ERROR_PIPE_BUSY):
            print "Could not open pipe"
            return
        elif ((windll.kernel32.WaitNamedPipeA(szPipename, 20000)) ==
0):
            print "Could not open pipe\n"
            return


    dwMode = c_ulong(PIPE_READMODE_MESSAGE)
    fSuccess = windll.kernel32.SetNamedPipeHandleState(hPipe,
byref(dwMode), None, None);
    if (not fSuccess):
        print "SetNamedPipeHandleState failed"
    cbWritten = c_ulong(0)
    fSuccess = windll.kernel32.WriteFile(hPipe, c_char_p(MESSAGE),
len(MESSAGE), byref(cbWritten), None)
    if ((not fSuccess) or (len(MESSAGE) != cbWritten.value)):
        print "Write File failed"
        return
    else:
        print "Number of bytes written:", cbWritten.value

    fSuccess = 0
    chBuf = create_string_buffer(BUFSIZE)
    cbRead = c_ulong(0)
    while (not fSuccess): # repeat loop if ERROR_MORE_DATA
        fSuccess = windll.kernel32.ReadFile(hPipe, chBuf, BUFSIZE,
byref(cbRead), None)
        if (fSuccess == 1):
            print "Number of bytes read:", cbRead.value
            print chBuf.value
            break
        elif (windll.kernel32.GetLastError() != ERROR_MORE_DATA):
            break

    windll.kernel32.CloseHandle(hPipe)
    return
    
    
if __name__ == "__main__":
    main()