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

[Srijit Kumar Bhadra]

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

Reference - MSDN:
http://msdn.microsoft.com/library/d.../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()

 

[Paul L. Du Bois]

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

Coincidentally, the other day I just used named pipes in for the first
time. I recommend using the excellent win32api extension; I believe it
is included by deafult in the ActiveState distro.

The API calls look fairly similar, but you pass strings instead of
c_whatever_p(), they return tuples, and they throw exceptions instead
of returning HRESULT h s.t. FAILED(h). The resulting code feels much
more Pythonic. For example, my first test looked like this:

def testread(self):
"""Read all data currently in pipe."""
while True:
try:
(nRead, nAvail, nMessage) =
win32pipe.PeekNamedPipe(self.hFile, 0)
if nAvail:
(hr, data) = win32file.ReadFile(self.hFile, nAvail)
return data
except pywintypes.error, e:
errno = e.args[0]
if errno == 109: # other end disconnected
self.disconnect()
self.connect()
else:
raise

It's kind of cool that you can directly port C code to Python, but the
end result is IMO nigh-unreadable.

p

 

[Srijit Kumar Bhadra]

Hello,
I am quite familiar with Mark Hammond's win32all. It is excellent.
However, I wish that there was more documentation of win32all beyond
existing PyWin32.chm. I am aware of "Python Programming on Win32" but I
do not have access to it at present.

Best Regards,
/Srijit

 

[Harald Massa]

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

Excellent. Maybe you would also like to post it to the

http://starship.python.net/crew/theller/moin.cgi/CtypesModule

Ctypes-Wiki for easier reference?

best regards,

Harald

 

[Thomas Heller]

Hello,
I am quite familiar with Mark Hammond's win32all. It is excellent.
However, I wish that there was more documentation of win32all beyond
existing PyWin32.chm. I am aware of "Python Programming on Win32" but I
do not have access to it at present.

At least one chapter of PPW32 is available as sample chapter somewhere
on an OReilly site - but you should buy the book anyway imo. For the
windows api functions you should refer to Microsoft's docs at MSDN.

Thomas

 

[Thomas Heller]

Excellent. Maybe you would also like to post it to the

http://starship.python.net/crew/theller/moin.cgi/CtypesModule

Ctypes-Wiki for easier reference?

Or the activestate Python cookbook.

Thonas

 

[Paul Du Bois]

However, I wish that there was more documentation of win32all beyond
existing PyWin32.chm.

I suspect you have already used the "more documentation" -- it's the
MSDN docs.

p