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[JSON] Fix source generator serializing null byte[] as empty string #129834

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[JSON] Fix source generator serializing null byte[] as empty string #129834

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99eedd0
[JSON] Fix source generator serializing null byte[] as empty string
lezzi Jun 25, 2026
895c967
Apply suggestions from code review
eiriktsarpalis Jun 25, 2026
be0f0b9
Fix indentation and use 'is not null' instead of pattern variable
eiriktsarpalis Jun 25, 2026
919805c
Add null byte[] assertions and multi-byte[] source-gen roundtrip test
eiriktsarpalis Jun 25, 2026
0ac125c
Emit byte[] null-handling via on-demand context helper
eiriktsarpalis Jun 25, 2026
079d57f
Remove redundant byte[] explanatory comments at call sites
eiriktsarpalis Jun 25, 2026
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45 changes: 41 additions & 4 deletions src/libraries/System.Text.Json/gen/JsonSourceGenerator.Emitter.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@ private sealed partial class Emitter
private const string JsonSerializerOptionsTypeRef = "global::System.Text.Json.JsonSerializerOptions";
private const string JsonSerializerContextTypeRef = "global::System.Text.Json.Serialization.JsonSerializerContext";
private const string Utf8JsonWriterTypeRef = "global::System.Text.Json.Utf8JsonWriter";
private const string ByteArrayValueWriterMethodName = "WriteByteArrayValue";
private const string JsonCommentHandlingTypeRef = "global::System.Text.Json.JsonCommentHandling";
private const string JsonConverterTypeRef = "global::System.Text.Json.Serialization.JsonConverter";
private const string JsonConverterFactoryTypeRef = "global::System.Text.Json.Serialization.JsonConverterFactory";
Expand Down Expand Up @@ -84,6 +85,12 @@ private sealed partial class Emitter
/// </summary>
private bool _emitValueTypeSetterDelegate;

/// <summary>
/// Indicates that the fast-path serializer writes a <see cref="byte"/> array value,
/// requiring the on-demand byte[] writer helper to be emitted on the context.
/// </summary>
private bool _emitByteArrayValueHelper;

/// <summary>
/// The SourceText emit implementation filled by the individual Roslyn versions.
/// </summary>
Expand Down Expand Up @@ -112,7 +119,7 @@ public void Emit(ContextGenerationSpec contextGenerationSpec)
string contextName = contextGenerationSpec.ContextType.Name;

// Add root context implementation.
AddSource($"{contextName}.g.cs", GetRootJsonContextImplementation(contextGenerationSpec, _emitGetConverterForNullablePropertyMethod, _emitValueTypeSetterDelegate));
AddSource($"{contextName}.g.cs", GetRootJsonContextImplementation(contextGenerationSpec, _emitGetConverterForNullablePropertyMethod, _emitValueTypeSetterDelegate, _emitByteArrayValueHelper));

// Add GetJsonTypeInfo override implementation.
AddSource($"{contextName}.GetJsonTypeInfo.g.cs", GetGetTypeInfoImplementation(contextGenerationSpec));
Expand All @@ -122,6 +129,7 @@ public void Emit(ContextGenerationSpec contextGenerationSpec)

_emitGetConverterForNullablePropertyMethod = false;
_emitValueTypeSetterDelegate = false;
_emitByteArrayValueHelper = false;
_propertyNames.Clear();
_typeIndex.Clear();
}
Expand Down Expand Up @@ -1775,14 +1783,19 @@ private static void GenerateFastPathFuncHeader(SourceWriter writer, TypeGenerati
}
}

private static void GenerateSerializeValueStatement(SourceWriter writer, TypeGenerationSpec typeSpec, string valueExpr)
private void GenerateSerializeValueStatement(SourceWriter writer, TypeGenerationSpec typeSpec, string valueExpr)
{
if (GetPrimitiveWriterMethod(typeSpec) is string primitiveWriterMethod)
{
if (typeSpec.PrimitiveTypeKind is JsonPrimitiveTypeKind.Char)
{
writer.WriteLine($"writer.{primitiveWriterMethod}Value({valueExpr}.ToString());");
}
else if (typeSpec.PrimitiveTypeKind is JsonPrimitiveTypeKind.ByteArray)
{
writer.WriteLine($"{ByteArrayValueWriterMethodName}(writer, {valueExpr});");
_emitByteArrayValueHelper = true;
}
else
{
writer.WriteLine($"writer.{primitiveWriterMethod}Value({valueExpr});");
Expand All @@ -1801,14 +1814,20 @@ private static void GenerateSerializeValueStatement(SourceWriter writer, TypeGen
}
}

private static void GenerateSerializePropertyStatement(SourceWriter writer, TypeGenerationSpec typeSpec, string propertyNameExpr, string valueExpr)
private void GenerateSerializePropertyStatement(SourceWriter writer, TypeGenerationSpec typeSpec, string propertyNameExpr, string valueExpr)
{
if (GetPrimitiveWriterMethod(typeSpec) is string primitiveWriterMethod)
{
if (typeSpec.PrimitiveTypeKind is JsonPrimitiveTypeKind.Char)
{
writer.WriteLine($"writer.{primitiveWriterMethod}({propertyNameExpr}, {valueExpr}.ToString());");
}
else if (typeSpec.PrimitiveTypeKind is JsonPrimitiveTypeKind.ByteArray)
{
writer.WriteLine($"writer.WritePropertyName({propertyNameExpr});");
writer.WriteLine($"{ByteArrayValueWriterMethodName}(writer, {valueExpr});");
_emitByteArrayValueHelper = true;
}
else
{
writer.WriteLine($"writer.{primitiveWriterMethod}({propertyNameExpr}, {valueExpr});");
Expand Down Expand Up @@ -1892,7 +1911,7 @@ private static void GenerateTypeInfoFactoryFooter(SourceWriter writer)
""");
}

private static SourceText GetRootJsonContextImplementation(ContextGenerationSpec contextSpec, bool emitGetConverterForNullablePropertyMethod, bool emitValueTypeSetterDelegate)
private static SourceText GetRootJsonContextImplementation(ContextGenerationSpec contextSpec, bool emitGetConverterForNullablePropertyMethod, bool emitValueTypeSetterDelegate, bool emitByteArrayValueHelper)
{
string contextTypeRef = contextSpec.ContextType.FullyQualifiedName;
string contextTypeName = contextSpec.ContextType.Name;
Expand Down Expand Up @@ -1946,6 +1965,24 @@ private static SourceText GetRootJsonContextImplementation(ContextGenerationSpec

writer.WriteLine();

if (emitByteArrayValueHelper)
{
writer.WriteLine($$"""
private static void {{ByteArrayValueWriterMethodName}}({{Utf8JsonWriterTypeRef}} writer, byte[]? value)
{
if (value is null)
{
writer.WriteNullValue();
}
else
{
writer.WriteBase64StringValue(value);
}
}
""");
writer.WriteLine();
}

GenerateConverterHelpers(writer, emitGetConverterForNullablePropertyMethod);

return CompleteSourceFileAndReturnText(writer);
Expand Down
37 changes: 37 additions & 0 deletions ...tem.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/JsonSerializerContextTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1164,5 +1164,42 @@ public static void SupportsAsymmetricNestedConverterWithManyParams()
internal partial class NestedGenericConverterContext : JsonSerializerContext
{
}

public class ClassWithMultipleByteArrayProperties
{
public byte[]? Data1 { get; set; }
public byte[]? Data2 { get; set; }
public byte[]? Data3 { get; set; }
}

[JsonSerializable(typeof(ClassWithMultipleByteArrayProperties))]
internal partial class MultipleByteArrayContext : JsonSerializerContext
{
}

[Theory]
[InlineData(new byte[] { 1, 2, 3 }, new byte[] { 4, 5, 6 }, null)]
[InlineData(null, new byte[] { 4, 5, 6 }, new byte[] { 7, 8, 9 })]
[InlineData(null, null, null)]
public static void ClassWithMultipleByteArrayProperties_Roundtrip(byte[]? data1, byte[]? data2, byte[]? data3)
{
var value = new ClassWithMultipleByteArrayProperties
{
Data1 = data1,
Data2 = data2,
Data3 = data3,
};

string json = JsonSerializer.Serialize(value, MultipleByteArrayContext.Default.ClassWithMultipleByteArrayProperties);

if (data1 is null) Assert.Contains("\"Data1\":null", json);
if (data2 is null) Assert.Contains("\"Data2\":null", json);
if (data3 is null) Assert.Contains("\"Data3\":null", json);

ClassWithMultipleByteArrayProperties deserialized = JsonSerializer.Deserialize(json, MultipleByteArrayContext.Default.ClassWithMultipleByteArrayProperties);
Assert.Equal(value.Data1, deserialized.Data1);
Assert.Equal(value.Data2, deserialized.Data2);
Assert.Equal(value.Data3, deserialized.Data3);
}
}
}
9 changes: 9 additions & 0 deletions ...s/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/RealWorldContextTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -873,6 +873,7 @@ public virtual void ClassWithNullableProperties_Roundtrip()
{
Uri = new Uri("http://contoso.com"),
Array = new int[] { 42 },
ByteArray = new byte[] { 1, 2, 3 },
Poco = new ClassWithNullableProperties.MyPoco(),

NullableUri = new Uri("http://contoso.com"),
Expand All @@ -885,10 +886,17 @@ public virtual void ClassWithNullableProperties_Roundtrip()
void RunTest(ClassWithNullableProperties expected)
{
string json = JsonSerializer.Serialize(expected, DefaultContext.ClassWithNullableProperties);

if (expected.ByteArray is null)
{
Assert.Contains("\"ByteArray\":null", json);
}

ClassWithNullableProperties actual = JsonSerializer.Deserialize(json, DefaultContext.ClassWithNullableProperties);

Assert.Equal(expected.Uri, actual.Uri);
Assert.Equal(expected.Array, actual.Array);
Assert.Equal(expected.ByteArray, actual.ByteArray);
Assert.Equal(expected.Poco, actual.Poco);

Assert.Equal(expected.NullableUri, actual.NullableUri);
Expand Down Expand Up @@ -943,6 +951,7 @@ public class ClassWithNullableProperties
{
public Uri? Uri { get; set; }
public int[]? Array { get; set; }
public byte[]? ByteArray { get; set; }
public MyPoco? Poco { get; set; }

public Uri? NullableUri { get; set; }
Expand Down
8 changes: 8 additions & 0 deletions ...stem.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/SerializationContextTests.cs
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Expand Up @@ -455,6 +455,7 @@ public override void ClassWithNullableProperties_Roundtrip()
{
Uri = new Uri("http://contoso.com"),
Array = new int[] { 42 },
ByteArray = new byte[] { 1, 2, 3 },
Comment thread
eiriktsarpalis marked this conversation as resolved.
Poco = new ClassWithNullableProperties.MyPoco(),

NullableUri = new Uri("http://contoso.com"),
Expand All @@ -467,10 +468,17 @@ public override void ClassWithNullableProperties_Roundtrip()
void RunTest(ClassWithNullableProperties expected)
{
string json = JsonSerializer.Serialize(expected, DefaultContext.ClassWithNullableProperties);

if (expected.ByteArray is null)
{
Assert.Contains("\"ByteArray\":null", json);
}

ClassWithNullableProperties actual = JsonSerializer.Deserialize(json, ((ITestContext)MetadataWithPerTypeAttributeContext.Default).ClassWithNullableProperties);

Assert.Equal(expected.Uri, actual.Uri);
Assert.Equal(expected.Array, actual.Array);
Assert.Equal(expected.ByteArray, actual.ByteArray);
Assert.Equal(expected.Poco, actual.Poco);

Assert.Equal(expected.NullableUri, actual.NullableUri);
Expand Down
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