Named Pipes between C# and Python

Posted on Thu 13 December 2012 in blog

There's a lot of over-complicated information on the internet for communicating between a C# process and a Python process using named pipes on Windows. I'll start with the code:

import time
import struct
f = open(r'\\.\pipe\NPtest', 'r+b', 0)
i = 1
while True:
s = 'Message[{0}]'.format(i).encode('ascii')
i += 1
f.write(struct.pack('I', len(s)) + s) # Write str length and str
f.seek(0) # EDIT: This is also necessary
print('Wrote:', s)
n = struct.unpack('I', f.read(4))[0] # Read str length
s = f.read(n).decode('ascii') # Read str
f.seek(0) # Important!!!
print('Read:', s)
time.sleep(2)
view raw pipe_client.py hosted with ❤ by GitHub
void run_server()
{
// Open the named pipe.
var server = new NamedPipeServerStream("NPtest");
Console.WriteLine("Waiting for connection...");
server.WaitForConnection();
Console.WriteLine("Connected.");
var br = new BinaryReader(server);
var bw = new BinaryWriter(server);
while (true) {
try {
var len = (int) br.ReadUInt32(); // Read string length
var str = new string(br.ReadChars(len)); // Read string
Console.WriteLine("Read: \"{0}\"", str);
str = new string(str.Reverse().ToArray()); // Just for fun
var buf = Encoding.ASCII.GetBytes(str); // Get ASCII byte array
bw.Write((uint) buf.Length); // Write string length
bw.Write(buf); // Write string
Console.WriteLine("Wrote: \"{0}\"", str);
}
catch (EndOfStreamException) {
break; // When client disconnects
}
}
Console.WriteLine("Client disconnected.");
server.Close();
server.Dispose();
}
view raw pipe_server.cs hosted with ❤ by GitHub

In this example, I implement a very simple protocol, where every "message" is a 4-byte integer (UInt32 in C#, I (un)pack format in Python), which indicates the length of the string that follows. The string is ASCII. Important things to note here:

  • Python
    • The third parameter to open() means "unbuffered". Otherwise, it will default to line-buffered, which means it will wait for a newline character before actually sending it through the pipe.
    • I'm not sure why, but omitting the seek(0) will cause an IOError #0. I was clued to this by a StackOverflow question.

References

C# Python