Named pipes: C# server, C++ client

Crazy Joe Devola

I wrote 2 pairs of named pipe client/server programs: 1st pair in C# (.NET 4) 2nd pair in C++ (un-managed) All 4 test programs use the same pipe name \\\\.\pipe\mypipe The C# pair work fine with each other - I send a message from the client and it is received by the server. The C++ pair work also fine with each other. But... when I try to run the C# client with the C++ server, or the C++ client with the C# server - then it doesn't work. The client is unable to connect to the server. Is there something preventing the C++ client from working with the .NET server? Should it work? Thank you.

Richard Andrew x64

Crazy Joe Devola wrote:

The client is unable to connect to the server.

When running the C++ client and it doesn't connect, check the error code: GetLastError()

The difficult we do right away... ...the impossible takes slightly longer.

Crazy Joe Devola

it returns error code 2 - ERROR_FILE_NOT_FOUND

Richard Andrew x64

You might want to try Sysinternals' Process Explorer. It can enumerate every kernel object (that includes pipes) that exists inside a process. This way you could be sure the pipe name is being created the way you intend.

The difficult we do right away... ...the impossible takes slightly longer.

Crazy Joe Devola

thank you. I have Process Explorer but I don't know how to see list of objects for a process. I used the search option to search for "mypipe". It shows that the server has a handle to \Device\NamedPipe\pipe\mypipe . I tried to check the client to open "\\Device\\NamedPipe\\pipe\\mypipe" but that didn't help (I didn't expect it to work anyway).

Crazy Joe Devola

This is how the client opens the pipe:

hPipe=CreateFile("\\\\.\\pipe\\mypipe",
GENERIC_WRITE,//GENERIC_READ | GENERIC_WRITE,
0,
NULL,
OPEN_EXISTING,
0,
NULL) ;

if ( hPipe!=INVALID_HANDLE_VALUE)
{
return 0; //Success!!!
}

err = GetLastError();
if(err!=ERROR_PIPE_BUSY)
{
printf("Could not open pipe, GetLastError=%u\n", err);
return -1 ;
}

Create file returns an invalid handle. GetLastError() returns 2.

Richard Andrew x64

You do know that backslashes need to be escaped in C++, right? It should be:

hPipe=CreateFile("\\\\.\\pipe\\mypipe",
GENERIC_WRITE,//GENERIC_READ | GENERIC_WRITE,
0,
NULL,
OPEN_EXISTING,
0,
NULL) ;

The difficult we do right away... ...the impossible takes slightly longer.

Crazy Joe Devola

Yes i do :-) for some reason the codeproject shows just 1 backslash. I do have it like this:

"\\\\.\\pipe\\mypipe"

Richard Andrew x64

Let's see the code that creates the pipes in both projects.

The difficult we do right away... ...the impossible takes slightly longer.

Crazy Joe Devola

Server: C# NamedPipeServerStream pipeServer = new NamedPipeServerStream("\\\\.\\pipe\\mypipe", PipeDirection.In, 1, PipeTransmissionMode.Byte, PipeOptions.Asynchronous); // Wait for a connection pipeServer.BeginWaitForConnection(new AsyncCallback(WaitForConnectionCallBack), pipeServer); Client: C++

	hPipe=CreateFile("\\\\\\\\\\\\\\\\.\\\\\\\\pipe\\\\\\\\mypipe", 
	                 GENERIC\_READ | GENERIC\_WRITE,
	                 0,
	                 NULL,
	                 OPEN\_EXISTING,
	                 0,
	                 NULL) ;
	if ( hPipe!=INVALID\_HANDLE\_VALUE) 
	{
		return 0; //Success!!!
	}

	err = GetLastError();
	if(err!=ERROR\_PIPE\_BUSY)
	{
		printf("Could not open pipe, GetLastError=%u\\n", err);
		return -1 ;
	}

	printf("Could not open pipe, GetLastError=%u. WaitNamedPipe.\\n", err);
	if(! WaitNamedPipe(pipe\_name,2000))
	{
		printf("Could not open pipe\\n");
		return -1 ;
	}

again: C++ client with C++ server - works. C# client with C# server - works. C++ client with C# server - does not works. Thank you.

Richard Andrew x64

This is just a guess, but could it be that since you have specified both GENERIC_READ and GENERIC_WRITE for the client, then you need to open the server as "InOut"?

The difficult we do right away... ...the impossible takes slightly longer.

Crazy Joe Devola

I thought of that. I tried changing the server side to InOut - it did not help. i also tried changing the client to GENERIC_WRITE without GENERIC_READ - it didn't work either. Thank you for all the advise, tips and time you spent trying to help - much appreciated.

Crazy Joe Devola

I think the problem was found.... On stackoverflow, someone posted this answer: C#'s NamedPipeClientStream, NamedPipeServerStream automatically append "\.\\pipe\" to the name I changed the C# code to open the pipe just as "mypipe" and now the connection is successful.

Richard Andrew x64

Glad you got it sorted. :)

The difficult we do right away... ...the impossible takes slightly longer.