Custom JsonConverter<string> implementation throws NotSupportedException when serializing a dictionary of strings in .NET 6 preview 4 #53241
Description
Description
In a line-of-business application we have the following custom JsonConverter for strings used to remove "bad" Unicode from strings in serialized JSON.
internal sealed class BadUnicodeRemovingJsonConverter : JsonConverter<string>
{
public override string Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
=> reader.GetString();
public override void Write(Utf8JsonWriter writer, string value, JsonSerializerOptions options)
{
static string RemoveBadUnicode(string input, string pattern)
{
return Regex.Replace(input, pattern, string.Empty, RegexOptions.IgnoreCase);
}
string sanitized = RemoveBadUnicode(value, "[\u0000-\u0009]");
sanitized = RemoveBadUnicode(sanitized, "[\u000b-\u000c]");
sanitized = RemoveBadUnicode(sanitized, "[\u000e-\u001f]");
writer.WriteStringValue(sanitized);
}
}After updating the application to .NET 6 preview 4, a NotSupportedException is thrown with a message similar to:
System.NotSupportedException: The type 'System.String' is not a supported dictionary key using converter of type 'MyApp.BadUnicodeRemovingJsonConverter'. Path: $.Foo.Bar.
For the specific type being serialized, $.Foo.Bar is an IDictionary<string, string> property Bar on a custom type Foo, which is in turn a property of another custom type at the root.
public class RootObject
{
public ChildObject Foo { get; set; }
}
public class ChildObject
{
public IDictionary<string, string> Bar { get; set; }
}The object is serialized with the following settings:
var options = new JsonSerializerOptions
{
WriteIndented = false,
};
options.Converters.Add(new BadUnicodeRemovingJsonConverter());
string json = JsonSerializer.Serialize(rootObject, options);Configuration
.NET 6 preview 4 (SDK version 6.0.100-preview.4.21255.9)
Regression?
Yes, this code works today with .NET 5.0.6. The issue was uncovered by the application's tests when updated to .NET 6.0 preview 4. The issue was also not present in previous previews of .NET 6.
Other information
System.NotSupportedException: The type 'System.String' is not a supported dictionary key using converter of type 'MyApp.BadUnicodeRemovingJsonConverter'. Path: $.Foo.Bar.
---> System.NotSupportedException: The type 'System.String' is not a supported dictionary key using converter of type 'MyApp.BadUnicodeRemovingJsonConverter'.
at System.Text.Json.ThrowHelper.ThrowNotSupportedException_DictionaryKeyTypeNotSupported(Type keyType, JsonConverter converter) in System.Text.Json.dll:token 0x60000f2+0x16
at System.Text.Json.Serialization.JsonConverter`1.WriteWithQuotes(Utf8JsonWriter writer, T value, JsonSerializerOptions options, WriteStack& state) in System.Text.Json.dll:token 0x60006fd+0x0
at System.Text.Json.Serialization.Converters.IDictionaryOfTKeyTValueConverter`3.OnWriteResume(Utf8JsonWriter writer, TCollection value, JsonSerializerOptions options, WriteStack& state) in System.Text.Json.dll:token 0x6000868+0xc3
at System.Text.Json.Serialization.Converters.DictionaryDefaultConverter`3.OnTryWrite(Utf8JsonWriter writer, TCollection dictionary, JsonSerializerOptions options, WriteStack& state) in System.Text.Json.dll:token 0x6000840+0x70
at System.Text.Json.Serialization.JsonConverter`1.TryWrite(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state) in System.Text.Json.dll:token 0x60006f6+0x206
at System.Text.Json.Serialization.Metadata.JsonPropertyInfo`1.GetMemberAndWriteJson(Object obj, WriteStack& state, Utf8JsonWriter writer) in System.Text.Json.dll:token 0x60007b7+0x130
at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryWrite(Utf8JsonWriter writer, T value, JsonSerializerOptions options, WriteStack& state) in System.Text.Json.dll:token 0x60008d8+0xa7
at System.Text.Json.Serialization.JsonConverter`1.TryWrite(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state) in System.Text.Json.dll:token 0x60006f6+0x206
at System.Text.Json.Serialization.Metadata.JsonPropertyInfo`1.GetMemberAndWriteJson(Object obj, WriteStack& state, Utf8JsonWriter writer) in System.Text.Json.dll:token 0x60007b7+0x130
at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryWrite(Utf8JsonWriter writer, T value, JsonSerializerOptions options, WriteStack& state) in System.Text.Json.dll:token 0x60008d8+0xa7
at System.Text.Json.Serialization.JsonConverter`1.TryWrite(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state) in System.Text.Json.dll:token 0x60006f6+0x206
at System.Text.Json.Serialization.JsonConverter`1.WriteCore(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state) in System.Text.Json.dll:token 0x60006e1+0x0
--- End of inner exception stack trace ---