How to send messages between c++ .dll and C# app using named pipe?

Question

I\'m making an injected .dll written in C++, and I want to communicate with a C# app using named pipes.

Now, I am using the built in System.IO.Pipe .net classes in the C

Answer 1

A few things.

1- Are you using the same pipe name
C++ : "\\.\pipe\HyperPipe"
C# : "HyperPipe"

2- I think on the C# side it might be better to use ReadToEnd(), I have only used named pipes in C++, but I assume that ReadToEnd() will read a message since you are using message based pipes.

3- On the C++ side, you are trying to use non-blocking pipes and polling the pipe for connection and data etc. I would suggest one of three things.

  a - Use a blocking pipe on a separate thread or
  b - Use non blocking pipes using Overlapped IO
  c - Use non blocking pipes using IOCompletion ports

The first option would be the easiest and for what it sounds like you are doing, it will scale fine. Here is a link to a simple sample to (a) http://msdn.microsoft.com/en-us/library/aa365588(VS.85).aspx

4- Make sure that your encodings match on both sides. For example, if your C++ code is compiled for Unicode, you must read the Pipe stream on the C# side using Unicode encoding. Some thing like the following.

using (StreamReader rdr = new StreamReader(pipe, System.Text.Encoding.Unicode))
{
  System.Console.WriteLine(rdr.ReadToEnd());
}

Update: Since I had not worked with this in C# I thought I would write a small test. Just using blocking pipes no threading or anything, just to confirm the basics work, here is the very rough test code.

C++ Server

#include <tchar.h>
#include <windows.h>

int _tmain(int argc, _TCHAR* argv[])
{
  HANDLE hPipe = ::CreateNamedPipe(_T("\\\\.\\pipe\\HyperPipe"),
    PIPE_ACCESS_DUPLEX,
    PIPE_TYPE_MESSAGE | PIPE_READMODE_MESSAGE,
    PIPE_UNLIMITED_INSTANCES,
    4096,
    4096,
    0,
    NULL);


  ConnectNamedPipe(hPipe, NULL);

  LPTSTR data = _T("Hello");
  DWORD bytesWritten = 0;
  WriteFile(hPipe, data, _tcslen(data) * sizeof(TCHAR), &bytesWritten, NULL);
  CloseHandle(hPipe);
  return 0;
}

C# Client

using System;
using System.Text;
using System.IO;
using System.IO.Pipes;

namespace CSPipe
{
  class Program
  {
    static void Main(string[] args)
    {
      NamedPipeClientStream pipe = new NamedPipeClientStream(".", "HyperPipe", PipeDirection.InOut);
      pipe.Connect();
      using (StreamReader rdr = new StreamReader(pipe, Encoding.Unicode))
      {
        System.Console.WriteLine(rdr.ReadToEnd());
      }

      Console.ReadKey();
    }
  }
}