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Fix the buffering bug that blocks SDK #51151

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Merged
carlossanlop merged 2 commits into from
Apr 13, 2021
Merged

Fix the buffering bug that blocks SDK #51151

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7c5ecf2
add a failing test that mimcs the SDK bug
adamsitnik Apr 12, 2021
0b1742b
fix the buffering bug
adamsitnik Apr 12, 2021
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25 changes: 25 additions & 0 deletions src/libraries/System.IO.FileSystem/tests/FileStream/FileStreamConformanceTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -161,6 +161,31 @@ public async Task LengthIsNotCachedAfterHandleHasBeenExposed(FileAccess fileAcce
Assert.Equal(2, stream.Length);
Assert.Equal(2, createdFromHandle.Length);
}

[Fact]
public async Task WriteByteFlushesTheBufferWhenItBecomesFull()
{
string filePath;
List<byte> writtenBytes = new List<byte>();

using (FileStream stream = (FileStream)await CreateWriteOnlyStreamCore(Array.Empty<byte>()))
{
filePath = stream.Name;

stream.WriteByte(0);
writtenBytes.Add(0);

byte[] bytes = new byte[BufferSize - 1];
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@danmoseley danmoseley Apr 12, 2021

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Is it worth putting something other than zeros in here? So it's distinct from the first byte you wrote

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@carlossanlop carlossanlop Apr 12, 2021

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Doesn't really matter. What matters is that we are attempting to write an 11th character on the stream when the buffer can only hold 10 characters.

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@jozkee jozkee Apr 12, 2021 •
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...and the problem was that the internal buffer is not being reset/flushed when WriteByte is called when this buffer is already full.

stream.Write(bytes.AsSpan());
writtenBytes.AddRange(bytes);

stream.WriteByte(1);
writtenBytes.Add(1);
}

byte[] allBytes = File.ReadAllBytes(filePath);
Assert.Equal(writtenBytes.ToArray(), allBytes);
}
}

public class UnbufferedSyncFileStreamStandaloneConformanceTests : FileStreamStandaloneConformanceTests
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2 changes: 1 addition & 1 deletion src/libraries/System.Private.CoreLib/src/System/IO/Strategies/BufferedFileStreamStrategy.cs
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Expand Up @@ -602,7 +602,7 @@ private void WriteByteSlow(byte value)
ClearReadBufferBeforeWrite();
EnsureBufferAllocated();
}
else if (_writePos == _bufferSize - 1)
else
{
FlushWrite();
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@jozkee jozkee Apr 12, 2021

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So this method should only be called when either _writePos == 0 or _writePos == _bufferSize, right?
Consider adding the assertion, but not in this PR since we want to merge it ASAP.

Suggested change
FlushWrite();
Debug.Assert(_writePos == _bufferSize);
FlushWrite();

}
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