Sequential use of smallCaps.ref for the same object omits its boardID in capData Slots

[Jorge-Lopes]

Context

I’d like to bring up an issue I encountered while working on test cases running in the z:acceptance test phase, specifically when using the smallCapsContext method, provided by @agoric/synthetic-chain, to handle brands object to construct the body of required offers.

Although this might not be relevant for everyone, it could be useful for anyone facing a similar issue in the future. Here's a summary of the situation.

The smallCapsContext implementation is as follows:

export const smallCapsContext = () => {
  const slots = [] as string[]; // XXX global mutable state
  const smallCaps = {
    Nat: (n: number | bigint) => `+${n}`,
    // XXX mutates obj
    ref: (obj: any) => {
      if (obj.ix) return obj.ix;
      const ix = slots.length;
      slots.push(obj.boardID);
      obj.ix = `$${ix}.Alleged: ${obj.iface}`;
      return obj.ix;
    },
  };

  const toCapData = (body: unknown) => {
    const capData = { body: `#${JSON.stringify(body)}`, slots };
    return JSON.stringify(capData);
  };

  return { smallCaps, toCapData };
};

The Problem

When making multiple sequential offers using the same brand object, I encountered an error where the boardID was not being included in the capData slots array.

The issue arises because the ix property is added to the brand object after the first call to ref. As a result, subsequent calls skip the logic that pushes the boardID into the slots array, since the condition if (obj.ix) is satisfied.

It is important to highlight that I have failed to noticed the comment present on the smallCapsContext function that clearly specified that smallCaps.ref mutates the object.

Solution

This occurs because the same reference to the brand object is used across multiple offers, and the ix attribute remains in the object. To resolve this, you can either:

• Clone the brand object before passing it to smallCaps.ref, ensuring the ix attribute does not persist across calls.
• Delete the ix attribute from the brand object before each reference to smallCaps.ref.

To illustrate this behavior more clearly, I’ve created a simple test that demonstrates the issue in detail:
smallCapsContext.test.js

[dckc]

smallCapsContext is a kludge - it's a partial implementation of @agoric/marshal. If you run into limitations, I suggest using the real toCapData function.

I'm a little surprised that smallCapsContext is exported from any package. It was originally written to be used in a constrained context where such limitations aren't relevant. If you're working on acceptance testing, I suggest adding @deprecated to smallCapsContext.

[Jorge-Lopes]

Thank you very much for the feedback.

I have followed your advice and removed the use of smallCapsContext from the the acceptance test.
I was using that method to build offers to interact with the KREAd contract, the current implementation is the following:
kread.js