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It looks like there is some difference in how character devices are treated in .NET 5 vs. .NET 6.

e.g. this simple console program:

using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
//using Xunit;

FileTests fileTests = new();
await fileTests.ReadAllBytes_NonSeekableFileStream_InUnix();
Console.WriteLine("Passed!");

public class FileTests
{
        // [Fact]
        public async Task ReadAllBytes_NonSeekableFileStream_InUnix()
        {
            var path = "/dev/tty";
            if (!File.Exists(path))
            {
                throw new Exception(path + " is not available in this environment.");
            }

            var contentBytes = new byte[] { 1, 2, 3 };

            using (var cts = new CancellationTokenSource())
            {
                Task writingTask = File.WriteAllBytesAsync(path, contentBytes, cts.Token);
                cts.CancelAfter(TimeSpan.FromMilliseconds(500));

                await writingTask;
            }
        }
}

prints Passed! in .NET 5 on macOS, but with .NET 6 it throws Unhandled exception. System.IO.IOException: Device not configured : '/dev/tty'.

@tmds, @stephentoub, is this a known breaking change?

is this a known breaking change?

Not to my knowledge.
cc: @jeffhandley, @adamsitnik.

prints Passed! in .NET 5 on macOS, but with .NET 6 it throws Unhandled exception. System.IO.IOException: Device not configured : '/dev/tty'.

On Linux, it prints Passed! with rc1.

From the CI stack trace it looks like the open call fails. Running the macOS equivalent of strace may reveal the difference between .NET 5 and .NET 6.

@am11 can you create an issue for this?

On Linux, it prints Passed! with rc1.

I can confirm that it's macOS-only regression in .NET 6.

@am11 can you create an issue for this?

#59754

/backport to release/6.0

Started backporting to release/6.0: https://github.com/dotnet/runtime/actions/runs/1412920156

@adamsitnik backporting to release/6.0 failed, the patch most likely resulted in conflicts:

$ git am --3way --ignore-whitespace --keep-non-patch changes.patch

Applying: lateapexearlyspeed-issue-58383 Support unseekable filestream when ReadAllBytes[Async].
Applying: issue-58383 Refine code; Add test cases.
Applying: the docs were wrong, offsets are not ignored for non-seekable files
Using index info to reconstruct a base tree...
M	src/libraries/System.Private.CoreLib/src/System/IO/RandomAccess.Windows.cs
Falling back to patching base and 3-way merge...
Auto-merging src/libraries/System.Private.CoreLib/src/System/IO/RandomAccess.Windows.cs
CONFLICT (content): Merge conflict in src/libraries/System.Private.CoreLib/src/System/IO/RandomAccess.Windows.cs
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0003 the docs were wrong, offsets are not ignored for non-seekable files
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!