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/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_DUP LEX = 0x3
PIPE_TYPE_MESSA GE = 0x4
PIPE_READMODE_M ESSAGE = 0x2
PIPE_WAIT = 0
PIPE_UNLIMITED_ INSTANCES = 255
BUFSIZE = 4096
NMPWAIT_USE_DEF AULT_WAIT = 0
INVALID_HANDLE_ VALUE = -1
ERROR_PIPE_CONN ECTED = 535

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


def ReadWrite_Clien tPipe_Thread(hP ipe):
chBuf = create_string_b uffer(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(hPip e,
c_char_p(MESSAG E),
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 .FlushFileBuffe rs(hPipe)
windll.kernel32 .DisconnectName dPipe(hPipe)
windll.kernel32 .CloseHandle(hP ipe)
return 0

def main():
THREADFUNC = CFUNCTYPE(c_int , c_int)
thread_func = THREADFUNC(Read Write_ClientPip e_Thread)
while 1:
hPipe = windll.kernel32 .CreateNamedPip eA(szPipename,
PIPE_ACCESS_DUP LEX,
PIPE_TYPE_MESSA GE |
PIPE_READMODE_M ESSAGE
|
PIPE_WAIT,

PIPE_UNLIMITED_ INSTANCES,
BUFSIZE, BUFSIZE,

NMPWAIT_USE_DEF AULT_WAIT,
None
)
if (hPipe == INVALID_HANDLE_ VALUE):
print "Error in creating Named Pipe"
return 0

fConnected = windll.kernel32 .ConnectNamedPi pe(hPipe, None)
if ((fConnected == 0) and (windll.kernel3 2.GetLastError( ) ==
ERROR_PIPE_CONN ECTED)):
fConnected = 1
if (fConnected == 1):
dwThreadId = c_ulong(0)
hThread = windll.kernel32 .CreateThread(N one, 0,
thread_func, hPipe, 0, byref(dwThreadI d))
if (hThread == -1):
print "Create Thread failed"
return 0
else:
windll.kernel32 .CloseHandle(hT hread)
else:
print "Could not connect to the Named Pipe"
windll.kernel32 .CloseHandle(hP ipe)
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_M ESSAGE = 0x2
ERROR_PIPE_BUSY = 231
ERROR_MORE_DATA = 234
BUFSIZE = 512

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

def main():
while 1:
hPipe = windll.kernel32 .CreateFileA(sz Pipename, GENERIC_READ |
GENERIC_WRITE, 0, None, OPEN_EXISTING, 0, None)
if (hPipe != INVALID_HANDLE_ VALUE):
break
else:
print "Invalid Handle Value"
if (windll.kernel3 2.GetLastError( ) != ERROR_PIPE_BUSY ):
print "Could not open pipe"
return
elif ((windll.kernel 32.WaitNamedPip eA(szPipename, 20000)) ==
0):
print "Could not open pipe\n"
return


dwMode = c_ulong(PIPE_RE ADMODE_MESSAGE)
fSuccess = windll.kernel32 .SetNamedPipeHa ndleState(hPipe ,
byref(dwMode), None, None);
if (not fSuccess):
print "SetNamedPipeHa ndleState failed"
cbWritten = c_ulong(0)
fSuccess = windll.kernel32 .WriteFile(hPip e, c_char_p(MESSAG E),
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_b uffer(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.kernel3 2.GetLastError( ) != ERROR_MORE_DATA ):
break

windll.kernel32 .CloseHandle(hP ipe)
return


if __name__ == "__main__":
main()

[Paul L. Du Bois]

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


Srijit Kumar Bhadra wrote:[color=blue]
> Hello,
> Here is an example of Multithreaded Pipe Server and Client using the
> excellent ctypes library (Windows).[/color]

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.PeekN amedPipe(self.h File, 0)
if nAvail:
(hr, data) = win32file.ReadF ile(self.hFile, nAvail)
return data
except pywintypes.erro r, 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]

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

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]

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

"Srijit Kumar Bhadra" <srijit@yahoo.c om> wrote in[color=blue]
> Here is an example of Multithreaded Pipe Server and Client using the
> excellent ctypes library (Windows).[/color]

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]

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

"Srijit Kumar Bhadra" <srijit@yahoo.c om> writes:
[color=blue]
> 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.[/color]

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]

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

Harald Massa <cpl.19.ghum@sp amgourmet.com> writes:
[color=blue]
> "Srijit Kumar Bhadra" <srijit@yahoo.c om> wrote in[color=green]
>> Here is an example of Multithreaded Pipe Server and Client using the
>> excellent ctypes library (Windows).[/color]
>
> Excellent. Maybe you would also like to post it to the
>
> http://starship.python.net/crew/thel...i/CtypesModule
>
> Ctypes-Wiki for easier reference?[/color]

Or the activestate Python cookbook.

Thonas

[Paul Du Bois]

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

Srijit Kumar Bhadra wrote:[color=blue]
> However, I wish that there was more documentation of win32all beyond
> existing PyWin32.chm.[/color]

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

p