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Fix StreamReader EOF handling and improve perf #69888

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merged 3 commits into from
Nov 7, 2022
Merged

Fix StreamReader EOF handling and improve perf #69888

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cd0fa34
Fix StreamReader EOF handling and improve perf
GrabYourPitchforks May 26, 2022
5638093
Address PR feedback
stephentoub Nov 5, 2022
ff4b245
Remove erroneous asserts
stephentoub Nov 5, 2022
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153 changes: 153 additions & 0 deletions src/libraries/System.IO/tests/StreamReader/StreamReaderTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -676,5 +676,158 @@ public void StreamReader_WithOptionalArguments()
Assert.False(tempStream.CanRead);
}
}

[Fact]
public void Read_ShortStream_PerformsFinalFlushCorrectly()
{
MemoryStream memStream = new MemoryStream(new byte[] { 0x61 /* 'a' */, 0xF0 });

// First, use ReadToEnd API.

memStream.Position = 0;
StreamReader reader = new StreamReader(memStream, Encoding.UTF8);
Assert.Equal("a\uFFFD", reader.ReadToEnd());

// Next, use Read() API.

memStream.Position = 0;
reader = new StreamReader(memStream, Encoding.UTF8);
Assert.Equal('a', reader.Read());
Assert.Equal('\uFFFD', reader.Read());
Assert.Equal(-1, reader.Read());

// Next, use Read(Span<char>) API.

StringBuilder builder = new StringBuilder();
Span<char> destBuffer = new char[1024];
memStream.Position = 0;
reader = new StreamReader(memStream, Encoding.UTF8);
int charsRead;
while ((charsRead = reader.Read(destBuffer)) > 0)
{
builder.Append(destBuffer.Slice(0, charsRead));
}
Assert.Equal("a\uFFFD", builder.ToString());

// Finally, use ReadLine API.

memStream.Position = 0;
reader = new StreamReader(memStream, Encoding.UTF8);
Assert.Equal("a\uFFFD", reader.ReadLine());
Assert.Null(reader.ReadLine());
}

[Fact]
public void Read_LongStreamIntoShortBuffer_PerformsFinalFlushCorrectly()
{
MemoryStream memStream = new MemoryStream();
memStream.Write(Enumerable.Repeat((byte)'a', 32 * 1024).ToArray());
memStream.WriteByte(0xF0);
string expected = new string('a', 32 * 1024) + "\uFFFD";

// First, use ReadToEnd API.

memStream.Position = 0;
StreamReader reader = new StreamReader(memStream, encoding: Encoding.UTF8, bufferSize: 32);
Assert.Equal(expected, reader.ReadToEnd());

// Next, use Read() API.

memStream.Position = 0;
reader = new StreamReader(memStream, encoding: Encoding.UTF8, bufferSize: 32);
for (int i = 0; i < 32 * 1024; i++)
{
Assert.Equal('a', reader.Read());
}
Assert.Equal('\uFFFD', reader.Read());
Assert.Equal(-1, reader.Read());

// Next, use Read(Span<char>) API.

StringBuilder builder = new StringBuilder();
Span<char> destBuffer = new char[47]; // prime number, because why not
memStream.Position = 0;
reader = new StreamReader(memStream, encoding: Encoding.UTF8, bufferSize: 32);
int charsRead;
while ((charsRead = reader.Read(destBuffer)) > 0)
{
builder.Append(destBuffer.Slice(0, charsRead));
}
Assert.Equal(expected, builder.ToString());

// Finally, use ReadLine API.

memStream.Position = 0;
reader = new StreamReader(memStream, encoding: Encoding.UTF8, bufferSize: 32);
Assert.Equal(expected, reader.ReadLine());
Assert.Null(reader.ReadLine());
}

[Fact]
public async Task ReadAsync_ShortStream_PerformsFinalFlushCorrectly()
{
MemoryStream memStream = new MemoryStream(new byte[] { 0x61 /* 'a' */, 0xF0 });

// First, use ReadToEndAsync API.

memStream.Position = 0;
StreamReader reader = new StreamReader(memStream, Encoding.UTF8);
Assert.Equal("a\uFFFD", await reader.ReadToEndAsync());

// Next, use ReadAsync(Memory<char>) API.

StringBuilder builder = new StringBuilder();
Memory<char> destBuffer = new char[1024];
memStream.Position = 0;
reader = new StreamReader(memStream, Encoding.UTF8);
int charsRead;
while ((charsRead = await reader.ReadAsync(destBuffer)) > 0)
{
builder.Append(destBuffer.Slice(0, charsRead));
}
Assert.Equal("a\uFFFD", builder.ToString());

// Finally, use ReadLineAsync API.

memStream.Position = 0;
reader = new StreamReader(memStream, Encoding.UTF8);
Assert.Equal("a\uFFFD", await reader.ReadLineAsync());
Assert.Null(await reader.ReadLineAsync());
}

[Fact]
public async Task ReadAsync_LongStreamIntoShortBuffer_PerformsFinalFlushCorrectly()
{
MemoryStream memStream = new MemoryStream();
memStream.Write(Enumerable.Repeat((byte)'a', 32 * 1024).ToArray());
memStream.WriteByte(0xF0);
string expected = new string('a', 32 * 1024) + "\uFFFD";

// First, use ReadToEndAsync API.

memStream.Position = 0;
StreamReader reader = new StreamReader(memStream, encoding: Encoding.UTF8, bufferSize: 32);
Assert.Equal(expected, await reader.ReadToEndAsync());

// Next, use Read(Memory<char>) API.

StringBuilder builder = new StringBuilder();
Memory<char> destBuffer = new char[47]; // prime number, because why not
memStream.Position = 0;
reader = new StreamReader(memStream, encoding: Encoding.UTF8, bufferSize: 32);
int charsRead;
while ((charsRead = await reader.ReadAsync(destBuffer)) > 0)
{
builder.Append(destBuffer.Slice(0, charsRead));
}
Assert.Equal(expected, builder.ToString());

// Finally, use ReadLineAsync API.

memStream.Position = 0;
reader = new StreamReader(memStream, encoding: Encoding.UTF8, bufferSize: 32);
Assert.Equal(expected, await reader.ReadLineAsync());
Assert.Null(await reader.ReadLineAsync());
}
}
}
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