Resolve stellar ClaimPredicates

On the stellar network ClaimableBalances can used to send funds to another wallet that does not have a trust-line established to a given asset, yet. In addition to just sending funds, the validity can be limited using predicates.

These predicates are described by a time-constraint and can be nested using boolean operators (see https://stellar.github.io/js-stellar-base/Claimant.html for details).

The js-stellar-sdk lacks methods to resolve any given predicate to a specific timestamp.

This module aims at resolving claimable balance predicates to a specific timestamp so that stellar-clients can check if a ClaimableBalance can be claimed at a given time (i.e. when displaying). This can be used to filter out ClaimableBalances that are currently not claimable (e.g. expired or not yet claimable).

Usage

Installation

npm install -S stellar-resolve-claimant-predicates

---

Convert horizon response to xdr.ClaimPredicate

When querying horizon for claimable balances, the response is less easy to parse and process than the xdr.ClaimPredicate objects. For further processing just convert the response back to xdr.ClaimPredicate objects:

const { predicateFromHorizonResponse } = require('stellar-resolve-claimant-predicates');
server.claimableBalances
  .claimant('GB7U....NMRQ')
  .call()
  .then(({records}) => records.map(r => ({
    ...r,
    claimants: r.claimants
      // here the predicate is mapped from horizon-response format to xdr.ClaimPredicate
      .map(c => ({...c, predicate: predicateFromHorizonResponse(c.predicate)})
  })))
  .then(records => {
      // have the xdr.ClaimPredicates available inside the response here 
  });

The code above will replace the Horizon.Predicate data with xdr.ClaimPredicate data inside the response.

Getting information on a certain predicate

The PredicateInformation holds the information necessary to determine if a predicate can be claimed. The status field makes determination easy. validFrom & validTo only hold values if the original predicate defined 'before' (i.e. predicateBeforeAbsoluteTime(...)) or 'after' (i.e. predicateNot(predicateBeforeAbsoluteTime(...))) times.

{
    status: 'claimable' | 'expired' | 'upcoming';
    predicate: xdr.ClaimPredicate,
    validFrom?: number,
    validTo?: number,
}

To retrieve the information object simply call getPredicateInformation() with the predicate and optionally a Date object as of when the claimable balance is supposed to be claimed:

const info = getPredicateInformation(xdrClaimPredicate, new Date());

Resolve a predicate to a timestamp

Predicates can potentially cover different time-slots when a claimable balance is claimable. flattenPredicate() resolves the nested structure of predicates to a given timestamp (e.g. now) for easy inspection by leaving out irrelevant predicates. For example a predicate defining a claimable window of one hour can be resolved to three different predicates:

const beginOfClaimWindowPredicate = Claimant.predicateNot(Claimant.predicateBeforeAbsoluteTime("1637017200"));
const endOfClaimWindowPredicate = Claimant.predicateBeforeAbsoluteTime("1637020800");

// this defines a claimable time window of one hour
const claimPredicate = Claimant.predicateAnd(beginOfClaimWindowPredicate, endOfClaimWindowPredicate);

// a second before the claimable time window the predicate will be resolved only to the starting time 
flattenPredicate(claimPredicate, new Date(1637017199)) === beginOfClaimWindowPredicate;

// within the claimable time window the predicate will be resoved as is
flattenPredicate(claimPredicate, new Date(1637019000)) === claimPredicate;

// a second after the claimable time window the predicate will be resolved to the predicate describing the end
// of the claimable window only, as the start-time is irrelevant for an expired predicate
flattenPredicate(claimPredicate, new Date(1637020801)) === endOfClaimWindowPredicate;

Tests

To run the tests, simply execute them via npm:

npm test