[python-win32] Duplex pipes issue (was (no subject))

[dan at shragmir.com]

Thank you, Tim,

That fixed it!
(and apologies to the list for initially sending this with no subject).
--Dan


> dan at shragmir.com wrote:
>> This is not the end of the world, because I can write the client
>> application to use win32 API calls instead of the Python calls.  But
>> does
>> anyone have any notion of why this is happening?  I am hoping the answer
>> may help me write clients in other applications (where I don’t have
>> access
>> to the win32 API).
>>
>> This code demonstrates the behavior:
>>
>> import win32file
>> import win32pipe
>> import threading
>> import time
>> class Server( threading.Thread ):
>>     def run( self ):
>>         self.pipeHandle = win32pipe.CreateNamedPipe(
>>             '\\\\.\\pipe\\testpipe',
>>             win32pipe.PIPE_ACCESS_DUPLEX,
>>             win32pipe.PIPE_TYPE_BYTE |
>>             win32pipe.PIPE_READMODE_BYTE |
>>             win32pipe.PIPE_WAIT,
>>             50,
>>             4096,
>>             4096,
>>             10000,
>>             None)
>>
>>         if self.pipeHandle == win32file.INVALID_HANDLE_VALUE:
>>             print 'Failed to create named pipe!'
>>             print 'Exiting...'
>>             sys.exit(1)
>>
>>         win32pipe.ConnectNamedPipe( self.pipeHandle )
>>         while True:
>>             e, v = win32file.ReadFile( self.pipeHandle, 1, None )
>>             if v == 'A':
>>                 print 'SERVER: Received request "%s"--answering' %v
>>                 err, j = win32file.WriteFile( self.pipeHandle, 'B' )
>>                 win32file.FlushFileBuffers( self.pipeHandle )
>>             else:
>>                 print 'SERVER: Received request "%s"--exiting' %v
>>                 break
>>
>>         print "SERVER: Exiting server"
>>
>> SERVER = Server()
>> SERVER.start()
>> time.sleep(0.1)
>> CLIENT_PIPE = open( '\\\\.\\pipe\\testpipe', 'a+b' )
>>
>
> You probably want "r+b", although I don't think it really makes a
> difference here.
>
>> for i in range( 10 ):
>>     CLIENT_PIPE.write( 'A' )
>>     CLIENT_PIPE.flush()
>>     reply = CLIENT_PIPE.read( 1 )
>>     print 'CLIENT: answer %d received: "%s"'%(i, reply)
>>
>
> The issue here is with the Python file wrappers.  You have to take SOME
> kind of action to allow the Python file wrapper to turn around from
> reading back to writing.  If you add
>     CLIENT_PIPE.seek(0,0)
> at the end of the loop, after the read, then it works.  That is...
>
>> CLIENT_PIPE.WRITE( 'C' )
>> CLIENT_PIPE.flush()
>>
>
> ...it works after you fix the spelling of "WRITE" there.  ;)
>
> --
> Tim Roberts, timr at probo.com
> Providenza & Boekelheide, Inc.
>
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