How to serialize byte[] as simple JSON Array and not as base64 in JSON.net?

JSON.NET is selecting the BinaryConverter to read and write an array of bytes. You can see in the source that it uses the WriteValue operation on the JsonWriter class with the array of bytes which causes them to be written to as Base-64.

To modify this, you can write your own converter which reads and writes an array in the format you expect:

public class ByteArrayConverter : JsonConverter{    public override void WriteJson(        JsonWriter writer,        object value,        JsonSerializer serializer)    {        if (value == null)        {            writer.WriteNull();            return;        }        byte[] data = (byte[])value;        // Compose an array.        writer.WriteStartArray();        for (var i = 0; i < data.Length; i++)        {            writer.WriteValue(data[i]);        }        writer.WriteEndArray();    }    public override object ReadJson(        JsonReader reader,        Type objectType,        object existingValue,        JsonSerializer serializer)    {        if (reader.TokenType == JsonToken.StartArray)        {            var byteList = new List<byte>();            while (reader.Read())            {                switch (reader.TokenType)                {                    case JsonToken.Integer:                        byteList.Add(Convert.ToByte(reader.Value));                        break;                    case JsonToken.EndArray:                        return byteList.ToArray();                    case JsonToken.Comment:                        // skip                        break;                    default:                        throw new Exception(                        string.Format(                            "Unexpected token when reading bytes: {0}",                            reader.TokenType));                }            }            throw new Exception("Unexpected end when reading bytes.");        }        else        {            throw new Exception(                string.Format(                    "Unexpected token parsing binary. "                    + "Expected StartArray, got {0}.",                    reader.TokenType));        }    }    public override bool CanConvert(Type objectType)    {        return objectType == typeof(byte[]);    }}

You would use this by applying the JsonConverterAttribute to the member:

[JsonConverter(typeof(ByteArrayConverter))]public byte[] Data { get; set; }

Simplest way I can think of is to convert the byte array into an integer array, like:

var intArray = byteArray.Select(b => (int)b).ToArray();

This wouldn't require any special handling of the JSON library, or any custom serialization or anything like that.

EDIT: This would mean having to customize your data object to handle the different type. Maybe:

public class CustomFoo : Foo{    // SomeBytesHere is a byte[] in the base class    public new int[] SomeBytesHere { get;set; }}

So maybe it's not the simplest - depending on how much stuff you have to serialize

Ref my answer, JSON.net can customze serialization in setting for all instead of attribute in property.

You can easily change it from base64 to number array, just write a square bracketed csv raw value.