Using File.Exists to check the pipe created will make the NamedPipeClientStream connect fail

[lindexi]

Description

We can use File.Exists to check whether the pipe exists, just as the code:

File.Exists(@"\\.\pipe\" + PipeName);

But after we use the File.Exists method, the NamedPipeClientStream may connect fail.

Reproduction Steps

Step 1: Using NamedPipeServerStream to create the Pipe

void StartServer()
{
    var server = new NamedPipeServerStream(PipeName,
        PipeDirection.InOut, 1, PipeTransmissionMode.Byte, PipeOptions.Asynchronous, 1024, 1024);

    server.BeginWaitForConnection(OnWaitForConnection, server);
}

Step 2: Using File.Exists to check the pipe exists.

File.Exists(@"\\.\pipe\" + PipeName);

Step 3: Using NamedPipeClientStream to connect the pipe.

void StartClient()
{
    var localServer = ".";
    var pipeDirection = PipeDirection.InOut;
    var client = new NamedPipeClientStream(localServer,
        PipeName, pipeDirection, PipeOptions.Asynchronous);

    var timeout = 1000 * 5;
    client.Connect(timeout);
}

And you can find the client.Connect(timeout); throw the TimeoutException

All the demo code in: https://github.com/lindexi/lindexi_gd/tree/e26bdd0bced93db8edf8be18f1062e571f3d1861/HallwhallkernarbafejaNakeldibi

Expected behavior

The NamedPipeClientStream can connect the pipe.

Actual behavior

The client.Connect will throw timeout exception.

Regression?

No response

Known Workarounds

No response

Configuration

.NET 6 (all version)

Windows 10.

Other information

Is my method of use wrong?

Tagging subscribers to this area: @dotnet/area-system-io
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

We can use File.Exists to check whether the pipe exists, just as the code:

File.Exists(@"\\.\pipe\" + PipeName);

But after we use the File.Exists method and the NamedPipeClientStream may connect fail.

Reproduction Steps

Step 1: Using NamedPipeServerStream to create the Pipe

void StartServer()
{
    var server = new NamedPipeServerStream(PipeName,
        PipeDirection.InOut, 1, PipeTransmissionMode.Byte, PipeOptions.Asynchronous, 1024, 1024);

    server.BeginWaitForConnection(OnWaitForConnection, server);
}

Step 2: Using File.Exists to check the pipe exists.

File.Exists(@"\\.\pipe\" + PipeName);

Step 3: Using NamedPipeClientStream to connect the pipe.

void StartClient()
{
    var localServer = ".";
    var pipeDirection = PipeDirection.InOut;
    var client = new NamedPipeClientStream(localServer,
        PipeName, pipeDirection, PipeOptions.Asynchronous);

    var timeout = 1000 * 5;
    client.Connect(timeout);
}

All the demo code in: https://github.com/lindexi/lindexi_gd/tree/e26bdd0bced93db8edf8be18f1062e571f3d1861/HallwhallkernarbafejaNakeldibi

Expected behavior

The client.Connect will throw timeout exception.

Actual behavior

The NamedPipeClientStream can connect the pipe.

Regression?

No response

Known Workarounds

No response

Configuration

.NET 6 (all version)

Windows 10.

Other information

Is my method of use wrong?

Author:	lindexi
Assignees:	-
Labels:	area-System.IO, untriaged
Milestone:	-

[kkwpsv]

.NET 6 will call GetFileAttributesW first to check if it exists, and this will make the pipe gone.
It says GetFileAttributesW has undefined behavior for non-filesystem objects.

But .NET Framework will call FindFirstFile first.

[iSazonov]

The same for reference microsoft/BuildXL#546

[adamsitnik]

I was able to confirm that this bug applies to .NET Framework as well:

using System;
using System.IO;
using System.IO.Pipes;
using System.Threading.Tasks;

namespace FileExistsPipes
{
    internal class Program
    {
        static void Main(string[] args)
        {
            const string PipeName = "testname123";

            using (NamedPipeServerStream server = new NamedPipeServerStream(PipeName, PipeDirection.InOut, 1, PipeTransmissionMode.Byte, PipeOptions.Asynchronous))
            {
                Task serverTask = server.WaitForConnectionAsync();

                Console.WriteLine($"File.Exists: {File.Exists(@"\\.\pipe\" + PipeName)}");

                using (NamedPipeClientStream client = new NamedPipeClientStream(".", PipeName, PipeDirection.InOut, PipeOptions.Asynchronous))
                {
                    Task clientTask = client.ConnectAsync(/*timeout*/);

                    Task.WaitAll(serverTask, clientTask);
                }
            }

            Console.WriteLine($"both client and server have connected");
        }
    }
}

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFrameworks>net5.0;net48;net6.0;net7.0</TargetFrameworks>
  </PropertyGroup>

</Project>

[adamsitnik]

Fun fact: Python and Java have similar bugs despite using different sys-calls:

https://stackoverflow.com/a/40843237/5852046
https://stackoverflow.com/a/67102903/5852046

[adamsitnik]

I was not able to find any solution that does not come without a perf hit (https://berserkerdotnet.github.io/blog/detecting-namedpipe-exists/), but I have used internal MS mail list to ask Windows experts if there is any API that we could use.

[lindexi]

@adamsitnik Can I ask any update? Thank you