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I have a simple class with the following property:

[JsonObject(MemberSerialization.OptIn)]
public class Person
{
    ...
    [JsonProperty(PropertyName = "Photograph"]
    public byte[] Photograph { get; set; }
    ...
}

but this doesn't work when I populate the Photograph property with an image and transfer over http. This may sound like a simple question but I've yet to find a solution after looking online for hours, but, how do I serialise/deserialise a byte array in Json.NET? What attribute tags do I need, or, should I be doing this another way? Many thanks!

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  • 4
    Have you found a way to set the correct object's properties? The information is somewhat fragmented. I'm looking for a clean solution for the exact same problem. the byte[] should be converted to an array, not a string. Commented Feb 26, 2013 at 7:19
  • 1
    I think JSON.NET has issues with fixed-length arrays when you preserve references and type information. When preserving type names in the "$type" member, it throws an error while trying to deserialize a fixed-length or read-only array. You have to use List<T> instead, or use a JsonConverter to serialize the byte[] member. It really needs to be fixed, because it should not have issues with such basic things. Commented Dec 3, 2013 at 20:36
  • 4
    Maybe you can use Base64 : Convert.ToBase64String(File.ReadAllBytes(downloadPth) and Convert.FromBase64String(b64Str) Commented Oct 2, 2018 at 4:31
  • Convert.ToBase64String worked for me! also ascii or utf8 are too small for store images data Commented Oct 10, 2022 at 12:08

4 Answers 4

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40 
public static T Deserialize<T>(byte[] data) where T : class
{
    using (var stream = new MemoryStream(data))
    using (var reader = new StreamReader(stream, Encoding.UTF8))
        return JsonSerializer.Create().Deserialize(reader, typeof(T)) as T;
}
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5 Comments

I like this answer, but you may want to throw an Encoding.UTF8 argument into the second argument of the StreamReader constructor. I am always a bit leery about using the default encoding.
Updated the snippet to have Encoding.UTF8
Notice this answer is >2 years old. I'm not sure when the System.Text.Json namespace was added, but JsonSerializer doesn't have a Create method.
System.Text.Json is a part of .NET Core 3, which was made GA one month ago
Plus, the method mentioned is from Newtonsoft.Json
32

You can convert the byte[] into a string then use the JsonConvert method to get the object:

var bytesAsString = Encoding.UTF8.GetString(bytes);
var person = JsonConvert.DeserializeObject<Person>(bytesAsString);
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4 Comments

Be wary of using this method for large objects as you will get OutOfMemory Exceptions. Methods that use Stream(s) would be better equipped to handle OutOfMemory scenarios.
There are a few standards that use ASCII. JSON is not one of them. It uses UTF-8 (or, older standard, UTF-8, UTF-16, or UTF-32—all easily distinguished, given that the data is JSON syntax).
@TomBlodget I have updated my answer to reflect your suggestions.
If you have "random" byte from photography, I think that you will get exceptions sometime: T:System.ArgumentException: The byte array contains invalid Unicode code points. In the documentation of Json.NET it is declared that a Byte[] will be serialized as a Base64 encoded string.
8

If you are using LINQ to JSON, you can do this:

JObject.Parse(Encoding.UTF8.GetString(data));

The result will be a dynamic JObject.

While this might not be exactly what the OP was looking to do, it might come in handy for others looking to deserialize a byte[] that come across this question.

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1

Based on this answer, you could use the one below in net core:

using System.IO;
using System.Text.Json;
using System.Threading.Tasks;

namespace <MyNameSpace>
{
    public static class ByteArrayExtensions
    {
        public static async Task<T> Deserialize<T>(this byte[] data) where T : class
        {
            using (var stream = new MemoryStream(data))
            {
                return await JsonSerializer.DeserializeAsync(stream, typeof(T)) as T;
            }
        }
    }
}

Which may be considered to have the edge on readability:

var deserialized = await mySerializedByteArray.Deserialize<MyObjectClass>();
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1 Comment

In STJ version 6, this can be collapsed to JsonSerializer.Deseralize<T> (I assume there is an Async variant too) - the byte[] gets implictly converted to fit. static TValue? Deserialize<TValue>(ReadOnlySpan<byte> utf8Json, JsonSerializerOptions? options = null)

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