npipes

Python based Named Pipes Wrapper for Windows

Introduction

This module provides an easy wrapper for the windows named pipes using pywin32, which can be integrated with any of your projects dealing with the named pipes. This also includes an optional CRC32 validation for the data sent/received.

Install

Install the module using pip install npipes

Usage

The module exposes 2 important APIs from the class IPC

send_message
receive_message

These 2 APIs provide a high level wrapper around the methods in the Pipes class which are a direct interface to the win32file APIs

win32file.Writefile 
win32file.Readfile

Sample code for sending data

from npipes.ipc import IPC
ipc = IPC()
ipc.send_message('Hello')

The above code, first creates a PIPE using win32pipe.CreateNamedPipe with a win32pipe.PIPE_WAIT and win32pipe.PIPE_ACCESS_DUPLEX flags set to wait for the client to connect and also open the PIPE in a duplex mode. It then waits for the client to connect to the PIPE and then sends the encoded data (encoding will be explained further below) to the client. The send_message API also provides an option to generate and encode the 32-bit CRC code for the data being sent out, which can be used at the other end to validate. To enable CRC validation the call from the above code must be modified to

ipc.send_message('Hello', crc=True)

Sample code for receiving data

from npipes.ipc import IPC
ipc = IPC()
ipc.receive_message()

The above code again creates a PIPE in a Duplex mode with the Wait flag set. Please note that this module (for the purpose of being modular and generic) first tries to connect to the server by opening the connection even on the client end, as the .NET API NamedPipeServerStream (which was one of the framewors I've tested my module with to validate interoperability) doesn't appear to be opening a connection to allow the client to connect and the above was introduced as a workaround for this. In case opening a connection to the PIPE fails with a PIPE Busy error: 231, then the Pipes.open() method automatically tries using the API win32file.CreateFile to connect to the server end of the PIPE. The ReceiveMessage API returns a decoded data string upon receiving a message from the server and the decoded data can also be accessed using the property method message. Similar to the send_message API call, one can also validate the 32-bit CRC code by enabling it from the below call

ipc.receive_message(crc = True)

Message Format and Encoding

Packing and Encoding the data is done in the Message class. The data supplied to the API send_message is first packed into the following fields

Message Length is the size of the whole packet and is 4 bytes long.
Data Length is the size of the data or payload and is also 4 bytes long.
Data/Payload is the data supplied to the send_message API call.
CRC-32 is the 32-bit CRC code for the data, and is 4 bytes long.

The message is sent out encoded in binary and the data field is encoded in ascii by default, but this is configurable, by passing the relevant encoding format to the constructor. The message is forced to be in little endian system by default, but this is configurable by the value set in constructor.