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fix: cap test output at 1M chars to prevent OOM #5561

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Merged
thomhurst merged 3 commits into from
Apr 15, 2026
Merged

fix: cap test output at 1M chars to prevent OOM #5561

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c371396
fix: cap test output at 1M chars to prevent OOM (#5560)
thomhurst Apr 15, 2026
048952d
refactor: use LazyInitializer for writer fields matching Context pattern
thomhurst Apr 15, 2026
a80e6db
fix: avoid splitting surrogate pairs at trim boundary
thomhurst Apr 15, 2026
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117 changes: 71 additions & 46 deletions TUnit.Core/Context.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -45,11 +45,16 @@ private ReaderWriterLockSlim GetOutputLock() =>
private ReaderWriterLockSlim GetErrorOutputLock() =>
LazyInitializer.EnsureInitialized(ref _errorOutputLock, static () => new ReaderWriterLockSlim(LockRecursionPolicy.NoRecursion))!;

[field: AllowNull, MaybeNull]
public TextWriter OutputWriter => field ??= new ConcurrentStringWriter(GetOutputBuilder(), GetOutputLock());
private ConcurrentStringWriter? _outputWriter;
private ConcurrentStringWriter? _errorOutputWriter;
private ConcurrentStringWriter GetOutputWriter() =>
LazyInitializer.EnsureInitialized(ref _outputWriter, () => new ConcurrentStringWriter(GetOutputBuilder(), GetOutputLock()))!;
private ConcurrentStringWriter GetErrorOutputWriter() =>
LazyInitializer.EnsureInitialized(ref _errorOutputWriter, () => new ConcurrentStringWriter(GetErrorOutputBuilder(), GetErrorOutputLock()))!;

[field: AllowNull, MaybeNull]
public TextWriter ErrorOutputWriter => field ??= new ConcurrentStringWriter(GetErrorOutputBuilder(), GetErrorOutputLock());
public TextWriter OutputWriter => GetOutputWriter();

public TextWriter ErrorOutputWriter => GetErrorOutputWriter();

// Internal accessors for console interceptor line buffers
internal ConsoleLineBuffer ConsoleStdOutLineBuffer =>
Expand Down Expand Up @@ -101,49 +106,9 @@ public void AddAsyncLocalValues()
#endif
}

public virtual string GetStandardOutput()
{
if (_outputBuilder == null)
{
return string.Empty;
}

var outputLock = GetOutputLock();
outputLock.EnterReadLock();

try
{
return _outputBuilder.Length == 0
? string.Empty
: _outputBuilder.ToString();
}
finally
{
outputLock.ExitReadLock();
}
}
public virtual string GetStandardOutput() => _outputWriter?.GetContent() ?? string.Empty;

public virtual string GetErrorOutput()
{
if (_errorOutputBuilder == null)
{
return string.Empty;
}

var errorOutputLock = GetErrorOutputLock();
errorOutputLock.EnterReadLock();

try
{
return _errorOutputBuilder.Length == 0
? string.Empty
: _errorOutputBuilder.ToString();
}
finally
{
errorOutputLock.ExitReadLock();
}
}
public virtual string GetErrorOutput() => _errorOutputWriter?.GetContent() ?? string.Empty;

public DefaultLogger GetDefaultLogger()
{
Expand All @@ -167,8 +132,17 @@ public void Dispose()
/// </summary>
internal sealed class ConcurrentStringWriter : TextWriter
{
private const int MaxOutputLength = 1_048_576; // 1M chars (~2MB)

// Trim to 75% of max to avoid re-trimming on every subsequent write
private const int TrimTarget = MaxOutputLength * 3 / 4;

private static readonly string TruncationNotice =
$"[... output truncated — exceeded {MaxOutputLength:N0} character limit, showing most recent output ...]{Environment.NewLine}";

private readonly StringBuilder _builder;
private readonly ReaderWriterLockSlim _lock;
private bool _truncated;

public ConcurrentStringWriter(StringBuilder builder, ReaderWriterLockSlim lockSlim)
{
Expand All @@ -184,6 +158,7 @@ public override void Write(char value)
try
{
_builder.Append(value);
TrimIfNeeded();
}
finally
{
Expand All @@ -199,6 +174,7 @@ public override void Write(string? value)
try
{
_builder.Append(value);
TrimIfNeeded();
}
finally
{
Expand All @@ -215,6 +191,7 @@ public override void Write(char[] buffer, int index, int count)
try
{
_builder.Append(buffer, index, count);
TrimIfNeeded();
}
finally
{
Expand All @@ -229,6 +206,7 @@ public override void WriteLine()
try
{
_builder.AppendLine();
TrimIfNeeded();
}
finally
{
Expand All @@ -242,6 +220,7 @@ public override void WriteLine(string? value)
try
{
_builder.AppendLine(value);
TrimIfNeeded();
}
finally
{
Expand All @@ -257,6 +236,7 @@ public override void Write(char[]? buffer)
try
{
_builder.Append(buffer);
TrimIfNeeded();
}
finally
{
Expand All @@ -271,6 +251,7 @@ public override void Write(bool value)
try
{
_builder.Append(value);
TrimIfNeeded();
}
finally
{
Expand All @@ -284,6 +265,7 @@ public override void Write(int value)
try
{
_builder.Append(value);
TrimIfNeeded();
}
finally
{
Expand All @@ -297,6 +279,7 @@ public override void Write(uint value)
try
{
_builder.Append(value);
TrimIfNeeded();
}
finally
{
Expand All @@ -310,6 +293,7 @@ public override void Write(long value)
try
{
_builder.Append(value);
TrimIfNeeded();
}
finally
{
Expand All @@ -323,6 +307,7 @@ public override void Write(ulong value)
try
{
_builder.Append(value);
TrimIfNeeded();
}
finally
{
Expand All @@ -336,6 +321,7 @@ public override void Write(float value)
try
{
_builder.Append(value);
TrimIfNeeded();
}
finally
{
Expand All @@ -349,6 +335,7 @@ public override void Write(double value)
try
{
_builder.Append(value);
TrimIfNeeded();
}
finally
{
Expand All @@ -362,6 +349,7 @@ public override void Write(decimal value)
try
{
_builder.Append(value);
TrimIfNeeded();
}
finally
{
Expand All @@ -377,6 +365,7 @@ public override void Write(object? value)
try
{
_builder.Append(value);
TrimIfNeeded();
}
finally
{
Expand All @@ -385,6 +374,42 @@ public override void Write(object? value)
}
}

private void TrimIfNeeded()
{
if (_builder.Length > MaxOutputLength)
{
var removeCount = _builder.Length - TrimTarget;

// Avoid splitting a surrogate pair at the trim boundary
if (removeCount > 0 && char.IsHighSurrogate(_builder[removeCount - 1]))
{
removeCount--;
}

_builder.Remove(0, removeCount);
_truncated = true;
}
}

internal string GetContent()
{
_lock.EnterReadLock();
try
{
if (_builder.Length == 0)
{
return string.Empty;
}

var content = _builder.ToString();
return _truncated ? string.Concat(TruncationNotice, content) : content;
}
finally
{
_lock.ExitReadLock();
}
}

public override void Flush()
{
// StringBuilder doesn't need flushing
Expand Down
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