C#•3w ago

Storing types as strings

I need to store a Type as a string, then convert it back to a type. How do i do this? I've tried Type.Name then doing Type.GetType(typeName) but this returns null

17 Replies

Kouhai•3w ago

You need the full type name Type.FullName

jcotton42•3w ago

@hutonahill what for? Just out of curiosity.

hutonahill•3w ago

I working on a system for saving configruable settings in a json. I need to save the datatype so i can pasre the user input into the right type for the new setting value

public abstract class SettingBase {
    public string Description { get; set; }
    
    public abstract Type getType();
}

public class Setting<T> : SettingBase {
    public T Value { get; set; }

    public override string ToString() {
        return $"\t- {Description}\n" +
               $"\t- Type: '{typeof(T)}' \n" +
               $"\t- Value: '{Value}'";
    }

    public override Type getType() {
        return typeof(T);
    }
    
    public Setting(string description, T value) {
        Description = description;
        Value = value;
    }
}

public abstract class SettingBase {
    public string Description { get; set; }
    
    public abstract Type getType();
}

public class Setting<T> : SettingBase {
    public T Value { get; set; }

    public override string ToString() {
        return $"\t- {Description}\n" +
               $"\t- Type: '{typeof(T)}' \n" +
               $"\t- Value: '{Value}'";
    }

    public override Type getType() {
        return typeof(T);
    }
    
    public Setting(string description, T value) {
        Description = description;
        Value = value;
    }
}

So parsing that to and from JSON

Kouhai•3w ago

This might lead to some security risks 😅

hutonahill•3w ago

very likely not doing anything super secure with it though this is the settings for a personal discord bot. what risks do you see though?

Kouhai•3w ago

Well it depends on how you're loading the data back, because if you're creating an instance of any type you read then it's probably not secure

hutonahill•3w ago

not sure what you mean... an instance of SettingBase?

Kouhai•3w ago

No the actual type you're reading from the JSON file How are you loading the data from the JSON file?

jcotton42•3w ago

https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/polymorphism?pivots=dotnet-8-0

How to serialize properties of derived classes with System.Text.Jso...

Learn how to serialize polymorphic objects while serializing to and deserializing from JSON in .NET.

hutonahill•3w ago

i made an implimentation of JsonConverter

public class SettingBaseConverter : JsonConverter {
   
    public override bool CanConvert(Type objectType) {
        return typeof(SettingBase).IsAssignableFrom(objectType);
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) {
        var settingBase = value as SettingBase;
        
        Debug.Assert(settingBase != null, nameof(settingBase) + " != null");

        writer.WriteStartObject();
        writer.WritePropertyName("Description");
        writer.WriteValue(settingBase.Description);
        writer.WritePropertyName("Type");
        writer.WriteValue(settingBase.getType().FullName);
        writer.WritePropertyName("Value");
        serializer.Serialize(writer, ((dynamic)settingBase).Value);
        writer.WriteEndObject();
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) {
        JObject obj = JObject.Load(reader);

        string description = obj["Description"].ToString();
        string typeName = obj["Type"].ToString();
        JToken valueToken = obj["Value"];

        Type? type = Type.GetType(typeName);
        if (type == null) {
            throw new JsonException($"Unable to find the type: {typeName}");
        }

        Type settingType = typeof(Setting<>).MakeGenericType(type);
        object value = valueToken.ToObject(type, serializer);

        return Activator.CreateInstance(settingType, description, value);
    }
}

public class SettingBaseConverter : JsonConverter {
   
    public override bool CanConvert(Type objectType) {
        return typeof(SettingBase).IsAssignableFrom(objectType);
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) {
        var settingBase = value as SettingBase;
        
        Debug.Assert(settingBase != null, nameof(settingBase) + " != null");

        writer.WriteStartObject();
        writer.WritePropertyName("Description");
        writer.WriteValue(settingBase.Description);
        writer.WritePropertyName("Type");
        writer.WriteValue(settingBase.getType().FullName);
        writer.WritePropertyName("Value");
        serializer.Serialize(writer, ((dynamic)settingBase).Value);
        writer.WriteEndObject();
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) {
        JObject obj = JObject.Load(reader);

        string description = obj["Description"].ToString();
        string typeName = obj["Type"].ToString();
        JToken valueToken = obj["Value"];

        Type? type = Type.GetType(typeName);
        if (type == null) {
            throw new JsonException($"Unable to find the type: {typeName}");
        }

        Type settingType = typeof(Setting<>).MakeGenericType(type);
        object value = valueToken.ToObject(type, serializer);

        return Activator.CreateInstance(settingType, description, value);
    }
}

Kouhai•3w ago

I don't personally see any security problems here, but I'm no security expert But you're probably better off following what jcotton linked, although it's for STJ not Newtonsoft

Angius•3w ago

Which is additional reason to go with it All that said, by the by, I find it interesting that configuration/settings would have no enforced shape Kinda hard to reason about it in the code, if the config file can be "whatever lmao"

hutonahill•3w ago

no that's the great part. i can store values in any shape, i do have a data type that stores all these values, my config file has a List<SettingBase> and my bot allows you to manage all the values in that list. That's the whole point of this data structure: a settings file you can easily add and configure in the command line.

jcotton42•3w ago

But what consumes those settings?

hutonahill•3w ago

on start up i load them into an object and methods read the object then ive got a method to update the object and save its current state when i run the methods that let me modify the settings is taht what you mean?

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Storing types as strings