Issue with inheritance and SDK decoding

[AymanDev]

Not sure where to ask or create issue on this one.

I have problem with some schemas using inheritance. I debugged this for awhile and found out that on C# SDK i receive this fields

As you can see there are few repeating ones as i assume from inheritance. By field names I found what scheme it was.

@entity
export class Enemy extends EntityLiving {
  @type('string')
  targetPlayer: string = undefined;

  agroDistnace: number;

  lastDistanceToTarget: number = 0;

  constructor(type: EntityType, agroDistance: number, attributes: Attributes) {
    super(attributes);

    this.type = type;

    this.agroDistnace = agroDistance;
  }

... other functions
}

@entity
export abstract class EntityLiving extends UpdatebleEntity implements ILiving {
  @type(Attributes)
  attributes: Attributes;

  constructor(attributes: Attributes) {
    super();

    this.attributes = attributes;
  }
}

@entity
export abstract class UpdatebleEntity extends Entity implements IUpdate {
  shouldBeRemoved = false;

  abstract shouldUpdate(world: GameWorldState): boolean;

  onUpdate(_world: GameWorldState) {}
}

@entity
export abstract class Entity extends Schema {
  @type(Vector2D)
  position: Vector2D;

  @type('string')
  uuid: UUID;

  @type('string')
  type: EntityType = EntityType.GENERIC;

  constructor() {
    super();

    this.uuid = randomUUID();

    this.position = Vector2D.ZERO.clone();
  }

  abstract onSpawn(world: GameWorld): void;
  abstract onDespawn(world: GameWorld): void;
}

So for some reason receiving fields does not represent any type and it result in null in C# sdk and will print out schema mismatch https://github.com/colyseus/colyseus-unity-sdk/blob/master/Assets/Colyseus/Runtime/Colyseus/Serializer/SchemaSerializer.cs#L80

All this happening at handshake moment and no state is updated, it only initialized as room been created

I tried checking generated classes from schema-codegen and they are matching in inherited types, name and order of fields
I tried adding @entity decorator as this entities a stored in state in MapSchema which resolved nothing.

I'm kinda out of ideas what is i'm doing wrong here...

[endel]

Hi @AymanDev 👋 I hope you are well!

The @entity tag is only a requirement if your Schema does not have any additional @type()'d fields. (The @type() is going to perform the same static call @entity does - that is registering the class into the internal TypeContext)

The Unity SDK needs to assign the types to their respective class definitions before decoding, and I'm afraid the @entity types (without additional fields) may cause the comparator function to fail: https://github.com/colyseus/colyseus-unity-sdk/blob/master/Assets/Colyseus/Runtime/Colyseus/Serializer/SchemaSerializer.cs#L86-L133 - The "handshake" contains all the "reflected" types from the state, and during this step, the SDK maps all the type ids registered on the server's TypeContext to their respective types defined in the client-side.

We don't have tests for this specific scenario... Could you please share a minimal way to reproduce this issue so I can investigate?

Thank you!

[endel]

Thank you so much for providing the minimal reproduction @AymanDev. I'm going to investigate and get back to you asap.

[endel]

Quick update @AymanDev: I had some progress investigating the cause of this issue today and I hope to push a fix tomorrow 🙏 Thanks for your patience

[AymanDev]

Thank you! I'll be waiting for the fix.

[endel]

Hi @AymanDev, let me try to explain what happened. Hopefully these changes fix the issue for you.

The following changes were made:

• Your project: changed how to attach the nested callback. It is currently not possible to use nesting (e.g. state.property1.property2), so it's required to .Listen() for .property1 to be available first - Please check this PR at fix nested OnAdd callback AymanDev/colyseus-inheritance-issue#1
• @colyseus/schema fixed the Reflection encode order - some types were exposed before their Parent/base type was available, causing issue at decoding time on C# (colyseus/schema@273baf9)
• Colyseus Unity SDK: prevent assigning the same Type for more than one typeid during handshake colyseus/colyseus-unity-sdk@8e2c5c8

I'm afraid that during handshake in C#, it is still not possible to determine which structure is which between these:

• StaticEntitiesMap extends EntitiesMap
• DynamicEntitiesMap extends EntitiesMap
• PlayerMap extends DynamicEntitiesMap

Because all these structures have the same number and name of fields, their type reference may get mixed up, causing the staticEntities to be instantiated as DynamicEntitiesMap on the client-side, dynamicEntities as PlayerMap, and so on. This limitation could be fixed if we also send the name of the structure at the encoded reflection, so they could be mapped directly. This would increase the amount of bytes for the handshake, though. I'm not sure if a different solution is viable here.

Please let me know if you can get your project to work with these changes. If you have any suggestions on how to improve the state of things, they're very welcome, too!

Cheers!

[AymanDev]

Hi @endel! I tested out your fixes and it seems to be working except few issues with my implementation.

About structures with same number of fields. Could some optional decorator for specifying custom name for this type of structures work?

I also have question about map schemas. I merged your PR, but how we can listen to update of inner properties of entity in MapSchema?

Would it be needed something like this?

NetworkManager.Instance.Callbacks.Listen(state => state.dynamicEntities, (dynamicEntities, _) =>
{
    NetworkManager.Instance.Callbacks.OnAdd(dynamicEntities, state => state.entities, (key, entity) =>
    {
        NetworkManager.Instance.Callbacks.Listen(entity, e => e.position, (pos, _) =>
        {
            // do something with it...
        });
    });
});

Of course instead just making this pretty ladder named callbacks would be used, but as idea is this how it supposed to used or is there something else?

Because I'm kinda confused as in 0.14 versions I was able to store pointer to Schema in MonoBehaviour and listen to changes for field via OnChanged

[AymanDev]

Oh, I found out about BindTo, so I was able to do something more simple like this:

NetworkManager.Instance.Callbacks.OnAdd(dynamicEntities, state => state.entities, (key, entity) =>
  {
      someVariable = entity;
      NetworkManager.Instance.Callbacks.BindTo(key, someVariable);
  });

And we can do everything needed with values from schema via someVariable in OnUpdate for example if it is something that needs to be accessed frequently like position.