Fix ESPIPE error when accessing SafeFileHandle on pseudofiles (#120751)

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: Adam Sitnik <[email protected]>

Author: Copilot

src/libraries/System.Private.CoreLib/src/System/IO/Strategies/OSFileStreamStrategy.cs

@@ -93,7 +93,7 @@ public sealed override long Position
         internal sealed override bool IsClosed => _fileHandle.IsClosed;
 
         // Flushing is the responsibility of BufferedFileStreamStrategy
-        internal sealed override SafeFileHandle SafeFileHandle
+        internal override SafeFileHandle SafeFileHandle
         {
             get
             {

src/libraries/System.Private.CoreLib/src/System/IO/Strategies/UnixFileStreamStrategy.cs

@@ -15,5 +15,32 @@ internal UnixFileStreamStrategy(string path, FileMode mode, FileAccess access, F
             base(path, mode, access, share, options, preallocationSize, unixCreateMode)
         {
         }
+
+        internal override SafeFileHandle SafeFileHandle
+        {
+            get
+            {
+                if (CanSeek)
+                {
+                    // The base SafeFileHandle getter synchronizes the file offset before exposing the handle
+                    // since the in-memory position may be out-of-sync with the actual file position.
+                    // However, some files such as certain pseudofiles on AzureLinux may report CanSeek = true
+                    // but still fail with ESPIPE when attempting to seek. We tolerate this specific error
+                    // to match the behavior in RandomAccess where we ignore pwrite and pread failures on certain file types.
+                    long result = Interop.Sys.LSeek(_fileHandle, _filePosition, Interop.Sys.SeekWhence.SEEK_SET);
+                    if (result < 0)
+                    {
+                        Interop.ErrorInfo errorInfo = Interop.Sys.GetLastErrorInfo();
+                        if (errorInfo.Error != Interop.Error.ESPIPE)
+                        {
+                            throw Interop.GetExceptionForIoErrno(errorInfo, _fileHandle.Path);
+                        }
+                        _fileHandle.SupportsRandomAccess = false;
+                    }
+                }
+
+                return _fileHandle;
+            }
+        }
     }
 }

src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/FileStream/SafeFileHandle.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using Microsoft.DotNet.XUnitExtensions;
 using Microsoft.Win32.SafeHandles;
 using System;
 using System.IO;
@@ -64,5 +65,25 @@ public void AccessFlushesFileClosesHandle()
                 Assert.Equal(TestBuffer.Length, fsr.Length);
             }
         }
+
+        [ConditionalFact]
+        [PlatformSpecific(TestPlatforms.Linux)]
+        public void SafeFileHandle_PseudoFile_DoesNotThrow()
+        {
+            // On some Linux distributions (e.g., AzureLinux 3), pseudofiles may report CanSeek = true
+            // but fail when attempting to seek. Accessing SafeFileHandle should not throw in these cases.
+            string path = File.Exists("/proc/net/route")
+                ? "/proc/net/route" 
+                : File.Exists("/proc/version")
+                    ? "/proc/version"
+                    : throw new SkipTestException("Can't find a pseudofile to test.");
+
+            using FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
+            // This should not throw even if the file reports CanSeek = true but doesn't support seeking
+            SafeFileHandle handle = fs.SafeFileHandle;
+            
+            Assert.NotNull(handle);
+            Assert.False(handle.IsClosed);
+        }
     }
 }