[Discussion] Using BufferedStream

src/libraries/System.IO.FileSystem/tests/FileStream/Flush.cs

@@ -105,11 +105,15 @@ public void FlushWriteWithOtherClient(bool? flushToDisk)
             using (FileStream fsr = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
             {
                 fs.Write(TestBuffer, 0, TestBuffer.Length);
-                Assert.Equal(TestBuffer.Length, fs.Length);
 
                 // Make sure that we've actually buffered it, read handle won't see any changes
                 Assert.Equal(0, fsr.Length);
 
+                // previously accessing Length was not causing a Flush of the internal buffer
+                // after using BufferedStream by FileStream iternally, now it does
+                // TODO: verify with the reviewers if such change is OK
+                Assert.Equal(TestBuffer.Length, fs.Length);
+
                 // This should cause a write, after it completes the two handles should be in sync
                 Flush(fs, flushToDisk);
                 Assert.Equal(TestBuffer.Length, fsr.Length);

src/libraries/System.IO.FileSystem/tests/FileStream/FlushAsync.cs

@@ -37,11 +37,15 @@ public async Task FlushAsyncWriteWithOtherClient()
             using (FileStream fsr = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
             {
                 fs.Write(TestBuffer, 0, TestBuffer.Length);
-                Assert.Equal(TestBuffer.Length, fs.Length);
 
                 // Make sure that we've actually buffered it, read handle won't see any changes
                 Assert.Equal(0, fsr.Length);
 
+                // previously accessing Length was not causing a Flush of the internal buffer
+                // after using BufferedStream by FileStream iternally, now it does
+                // TODO: verify with the reviewers if such change is OK
+                Assert.Equal(TestBuffer.Length, fs.Length);
+
                 // This should cause a write, after it completes the two handles should be in sync
                 await fs.FlushAsync();
                 Assert.Equal(TestBuffer.Length, fsr.Length);

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

@@ -37,6 +37,19 @@ public void DisposeClosesHandle()
             }
         }
 
+        [Fact]
+        public void DisposingBufferedStreamThatWrapsAFileStreamWhichHasBennClosedViaSafeFileHandleCloseDoesNotThrow()
+        {
+            using (FileStream fs = new FileStream(GetTestFilePath(), FileMode.Create))
+            {
+                var bufferedStream = new BufferedStream(fs, 100);
+
+                fs.SafeFileHandle.Dispose();
+
+                bufferedStream.Dispose(); // must not throw
+            }
+        }
+
         [Fact]
         public void AccessFlushesFileClosesHandle()
         {
@@ -104,14 +117,7 @@ private async Task ThrowWhenHandlePositionIsChanged(bool useAsync)
 
                     fs.WriteByte(0);
                     fsr.Position++;
-                    if (useAsync && OperatingSystem.IsWindows()) // Async I/O behaviors differ due to kernel-based implementation on Windows
-                    {
-                        Assert.Throws<IOException>(() => FSAssert.CompletesSynchronously(fs.ReadAsync(new byte[1], 0, 1)));
-                    }
-                    else
-                    {
-                        await Assert.ThrowsAsync<IOException>(() => fs.ReadAsync(new byte[1], 0, 1));
-                    }
+                    await Assert.ThrowsAsync<IOException>(() => fs.ReadAsync(new byte[1], 0, 1));
 
                     fs.WriteByte(0);
                     fsr.Position++;

src/libraries/System.IO.FileSystem/tests/FileStream/WriteAsync.cs

@@ -220,7 +220,7 @@ public async Task ManyConcurrentWriteAsyncs_OuterLoop(
                 {
                     writes[i] = WriteAsync(fs, expectedData, i * writeSize, writeSize, cancellationToken);
                     Assert.Null(writes[i].Exception);
-                    if (useAsync)
+                    if (useAsync && writes[i].IsCompletedSuccessfully) // TODO: breaking change, verify with reviewers
                     {
                         Assert.Equal((i + 1) * writeSize, fs.Position);
                     }

src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

@@ -388,6 +388,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\BinaryReader.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\BinaryWriter.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\BufferedStream.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\IO\BufferedFileStreamStrategy.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\DerivedFileStreamStrategy.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\DirectoryNotFoundException.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\EncodingCache.cs" />
@@ -1623,13 +1624,15 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Globalization\GlobalizationMode.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Globalization\HijriCalendar.Win32.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Guid.Windows.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\IO\AsyncWindowsFileStreamStrategy.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\DisableMediaInsertionPrompt.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\DriveInfoInternal.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\FileStreamHelpers.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\FileStreamCompletionSource.Win32.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\Path.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\PathHelper.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\PathInternal.Windows.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\IO\SyncWindowsFileStreamStrategy.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\WindowsFileStreamStrategy.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\PasteArguments.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Loader\LibraryNameVariation.Windows.cs" />