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Fix WriteRecordsAsync writing a delimiter instead of a blank line for null records #2384

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Fix WriteRecordsAsync writing a delimiter instead of a blank line for null records #2384

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835666d
Write a blank line for a null record in WriteRecordsAsync
virzak Jul 27, 2026
9d6b467
Generate the synchronous overloads instead of maintaining them
virzak Jul 27, 2026
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7 changes: 7 additions & 0 deletions src/CsvHelper/CsvHelper.csproj
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,13 @@
<None Include="Icon.png" Pack="true" PackagePath="\" />
</ItemGroup>

<ItemGroup>
<PackageReference Include="Zomp.SyncMethodGenerator" Version="2.0.33">
<PrivateAssets>all</PrivateAssets>
<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
</PackageReference>
</ItemGroup>

<!-- .NET 4.6.2 -->
<ItemGroup Condition="'$(TargetFramework)' == 'net462'">
<PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="8.0.0" />
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37 changes: 2 additions & 35 deletions src/CsvHelper/CsvParser.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@ namespace CsvHelper;
/// <summary>
/// Parses a CSV file.
/// </summary>
public class CsvParser : IParser, IDisposable
public partial class CsvParser : IParser, IDisposable
{
private readonly IParserConfiguration configuration;
private readonly FieldCache fieldCache = new FieldCache();
Expand Down Expand Up @@ -204,42 +204,9 @@ public CsvParser(TextReader reader, IParserConfiguration configuration, bool lea
processedFields = new string[128];
}

/// <inheritdoc/>
public bool Read()
{
isRecordProcessed = false;
rowStartPosition = bufferPosition;
fieldStartPosition = rowStartPosition;
fieldsPosition = 0;
quoteCount = 0;
row++;
rawRow++;
var c = '\0';
var cPrev = c;

while (true)
{
if (bufferPosition >= charsRead)
{
if (!FillBuffer())
{
return ReadEndOfFile();
}

if (row == 1 && detectDelimiter)
{
DetectDelimiter();
}
}

if (ReadLine(ref c, ref cPrev) == ReadLineResult.Complete)
{
return true;
}
}
}

/// <inheritdoc/>
[Zomp.SyncMethodGenerator.CreateSyncVersion]
public async Task<bool> ReadAsync()
{
isRecordProcessed = false;
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36 changes: 2 additions & 34 deletions src/CsvHelper/CsvReader.cs
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Expand Up @@ -14,7 +14,7 @@ namespace CsvHelper;
/// <summary>
/// Reads data that was parsed from <see cref="IParser" />.
/// </summary>
public class CsvReader : IReader
public partial class CsvReader : IReader
{
private readonly Lazy<RecordManager> recordManager;
private readonly bool detectColumnCountChanges;
Expand Down Expand Up @@ -237,41 +237,9 @@ protected virtual void ValidateHeader(ClassMap map, List<InvalidHeader> invalidH
}
}

/// <inheritdoc/>
public virtual bool Read()
{
// Don't forget about the async method below!

bool hasMoreRecords;
do
{
hasMoreRecords = parser.Read();
hasBeenRead = true;
}
while (hasMoreRecords && (shouldSkipRecord?.Invoke(new ShouldSkipRecordArgs(this)) ?? false));

currentIndex = -1;

if (detectColumnCountChanges && hasMoreRecords)
{
if (prevColumnCount > 0 && prevColumnCount != parser.Count)
{
var csvException = new BadDataException(string.Empty, parser.RawRecord, context, "An inconsistent number of columns has been detected.");

var args = new ReadingExceptionOccurredArgs(csvException);
if (readingExceptionOccurred?.Invoke(args) ?? true)
{
throw csvException;
}
}

prevColumnCount = parser.Count;
}

return hasMoreRecords;
}

/// <inheritdoc/>
[Zomp.SyncMethodGenerator.CreateSyncVersion]
public virtual async Task<bool> ReadAsync()
{
bool hasMoreRecords;
Expand Down
145 changes: 15 additions & 130 deletions src/CsvHelper/CsvWriter.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,7 @@ namespace CsvHelper;
/// <summary>
/// Used to write CSV files.
/// </summary>
public class CsvWriter : IWriter
public partial class CsvWriter : IWriter
{
private readonly TextWriter writer;
private readonly CsvContext context;
Expand Down Expand Up @@ -346,119 +346,9 @@ public virtual void WriteRecord<T>(T? record)
}
}

/// <inheritdoc/>
public virtual void WriteRecords(IEnumerable records)
{
// Changes in this method require changes in method WriteRecords<T>(IEnumerable<T> records) also.

var enumerator = records.GetEnumerator();

try
{
if (!enumerator.MoveNext())
{
return;
}

if (WriteHeaderFromRecord(enumerator.Current))
{
NextRecord();
}

Action<object>? write = null;
RecordTypeInfo writeType = default;

do
{
var record = enumerator.Current;

if (record == null)
{
// Since every record could be a different type, just write a blank line.
NextRecord();
continue;
}

if (write == null || writeType.RecordType != record.GetType())
{
writeType = GetTypeInfoForRecord(record);
write = recordManager.Value.GetWriteDelegate<object>(writeType);
}

write(record);
NextRecord();
}
while (enumerator.MoveNext());
}
catch (Exception ex) when (ex is not CsvHelperException)
{
throw new WriterException(context, "An unexpected error occurred. See inner exception for details.", ex);
}
finally
{
if (enumerator is IDisposable en)
{
en.Dispose();
}
}
}

/// <inheritdoc/>
public virtual void WriteRecords<T>(IEnumerable<T> records)
{
// Changes in this method require changes in method WriteRecords(IEnumerable records) also.

var enumerator = records.GetEnumerator() ?? throw new InvalidOperationException("Enumerator is null.");

try
{
if (WriteHeaderFromType<T>())
{
NextRecord();
}

if (!enumerator.MoveNext())
{
return;
}

if (WriteHeaderFromRecord(enumerator.Current))
{
NextRecord();
}

Action<T>? write = null;
RecordTypeInfo writeType = default;

do
{
var record = enumerator.Current;

if (write == null || (record != null && writeType.RecordType != typeof(T)))
{
writeType = GetTypeInfoForRecord(record);
write = recordManager.Value.GetWriteDelegate<T>(writeType);
}

write(record);
NextRecord();
}
while (enumerator.MoveNext());
}
catch (Exception ex) when (ex is not CsvHelperException)
{
throw new WriterException(context, "An unexpected error occurred. See inner exception for details.", ex);
}
finally
{
if (enumerator is IDisposable en)
{
en.Dispose();
}
}
}

/// <inheritdoc/>
[Zomp.SyncMethodGenerator.CreateSyncVersion]
public virtual async Task WriteRecordsAsync(IEnumerable records, CancellationToken cancellationToken = default)
{
// These methods should all be the same;
Expand Down Expand Up @@ -489,7 +379,14 @@ public virtual async Task WriteRecordsAsync(IEnumerable records, CancellationTok

var record = enumerator.Current;

if (write == null || (record != null && writeType.RecordType != record.GetType()))
if (record == null)
{
// Since every record could be a different type, just write a blank line.
await NextRecordAsync().ConfigureAwait(false);
continue;
}

if (write == null || writeType.RecordType != record.GetType())
{
writeType = GetTypeInfoForRecord(record);
write = recordManager.Value.GetWriteDelegate<object?>(writeType);
Expand All @@ -514,6 +411,7 @@ public virtual async Task WriteRecordsAsync(IEnumerable records, CancellationTok
}

/// <inheritdoc/>
[Zomp.SyncMethodGenerator.CreateSyncVersion]
public virtual async Task WriteRecordsAsync<T>(IEnumerable<T> records, CancellationToken cancellationToken = default)
{
// These methods should all be the same;
Expand Down Expand Up @@ -574,6 +472,8 @@ public virtual async Task WriteRecordsAsync<T>(IEnumerable<T> records, Cancellat
}

/// <inheritdoc/>
[Zomp.SyncMethodGenerator.CreateSyncVersion]
[Zomp.SyncMethodGenerator.SkipSyncVersion]
public virtual async Task WriteRecordsAsync<T>(IAsyncEnumerable<T> records, CancellationToken cancellationToken = default)
{
// These methods should all be the same;
Expand Down Expand Up @@ -631,16 +531,7 @@ public virtual async Task WriteRecordsAsync<T>(IAsyncEnumerable<T> records, Canc
}

/// <inheritdoc/>
public virtual void NextRecord()
{
WriteToBuffer(newLine);
FlushBuffer();

index = 0;
row++;
}

/// <inheritdoc/>
[Zomp.SyncMethodGenerator.CreateSyncVersion]
public virtual async Task NextRecordAsync()
{
WriteToBuffer(newLine);
Expand All @@ -651,13 +542,7 @@ public virtual async Task NextRecordAsync()
}

/// <inheritdoc/>
public virtual void Flush()
{
FlushBuffer();
writer.Flush();
}

/// <inheritdoc/>
[Zomp.SyncMethodGenerator.CreateSyncVersion]
public virtual async Task FlushAsync()
{
await FlushBufferAsync().ConfigureAwait(false);
Expand Down
53 changes: 53 additions & 0 deletions tests/CsvHelper.Tests/Writing/WriteNullTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Threading.Tasks;
using Xunit;

namespace CsvHelper.Tests.Writing
Expand Down Expand Up @@ -80,6 +81,58 @@ public void WriteRecord_RecordIsNull_WritesEmptyRecord()
}
}

[Fact]
public async Task WriteRecordsEnumerableGenericAsync_RecordIsNull_WritesEmptyRecord()
{
var records = new List<Foo?>
{
new Foo { Id = 1, Name = "one"},
null,
new Foo { Id = 2, Name = "two" },
};
var config = new CsvConfiguration(CultureInfo.InvariantCulture);
using (var writer = new StringWriter())
using (var csv = new CsvWriter(writer, config))
{
await csv.WriteRecordsAsync(records);
await csv.FlushAsync();

var expected = new TestStringBuilder(config.NewLine);
expected.AppendLine("Id,Name");
expected.AppendLine("1,one");
expected.AppendLine(",");
expected.AppendLine("2,two");

Assert.Equal(expected, writer.ToString());
}
}

[Fact]
public async Task WriteRecordsEnumerableAsync_RecordIsNull_WritesEmptyRecord()
{
IEnumerable records = new List<Foo?>
{
new Foo { Id = 1, Name = "one"},
null,
new Foo { Id = 2, Name = "two" },
};
var config = new CsvConfiguration(CultureInfo.InvariantCulture);
using (var writer = new StringWriter())
using (var csv = new CsvWriter(writer, config))
{
await csv.WriteRecordsAsync(records);
await csv.FlushAsync();

var expected = new TestStringBuilder(config.NewLine);
expected.AppendLine("Id,Name");
expected.AppendLine("1,one");
expected.AppendLine("");
expected.AppendLine("2,two");

Assert.Equal(expected, writer.ToString());
}
}

private class Foo
{
public int Id { get; set; }
Expand Down