chore: add makeFeePurse method

packages/zoe/src/zoeService/feePurse.js

@@ -0,0 +1,41 @@
+// @ts-check
+
+import { Far } from '@agoric/marshal';
+
+/**
+ *
+ * @param {Issuer} feeIssuer
+ * @returns {{
+ *   makeFeePurse: MakeFeePurse
+ *   isFeePurse: (feePurse: Purse) => boolean
+ * }}
+ */
+const setupMakeFeePurse = feeIssuer => {
+  const feePurses = new WeakSet();
+
+  /** @type {MakeFeePurse} */
+  const makeFeePurse = () => {
+    const purse = feeIssuer.makeEmptyPurse();
+    /** @type {FeePurse} */
+    const feePurse = Far('feePurse', {
+      ...purse,
+    });
+    feePurses.add(feePurse);
+
+    // After keeping the purse methods, we throw away the purse
+    return feePurse;
+  };
+
+  /**
+   * @param {Purse} feePurse
+   */
+  const isFeePurse = feePurse => feePurses.has(feePurse);
+
+  return {
+    makeFeePurse,
+    isFeePurse,
+  };
+};
+
+harden(setupMakeFeePurse);
+export { setupMakeFeePurse };

packages/zoe/src/zoeService/types.js

@@ -39,13 +39,23 @@
  * object with the instance, installation, description, invitation
  * handle, and any custom properties specific to the contract.
  * @property {GetFeeIssuer} getFeeIssuer
+ * @property {MakeFeePurse} makeFeePurse
  */
 
 /**
  * @callback GetFeeIssuer
  * @returns {Issuer}
  */
 
+/**
+ * @typedef {Purse} FeePurse
+ */
+
+/**
+ * @callback MakeFeePurse
+ * @returns {FeePurse}
+ */
+
 /**
  * @callback GetPublicFacet
  * @param {Instance} instance

packages/zoe/src/zoeService/zoe.js

@@ -25,6 +25,7 @@ import { makeOffer } from './offer/offer.js';
 import { makeInvitationQueryFns } from './invitationQueries.js';
 import { setupCreateZCFVat } from './createZCFVat.js';
 import { createFeeMint } from './feeMint.js';
+import { setupMakeFeePurse } from './feePurse.js';
 
 /**
  * Create an instance of Zoe.
@@ -53,6 +54,8 @@ const makeZoe = (
     feeIssuerConfig,
   );
 
+  const { makeFeePurse } = setupMakeFeePurse(feeIssuer);
+
   // This method contains the power to create a new ZCF Vat, and must
   // be closely held. vatAdminSvc is even more powerful - any vat can
   // be created. We severely restrict access to vatAdminSvc for this reason.
@@ -103,6 +106,7 @@ const makeZoe = (
     install,
     startInstance,
     offer,
+    makeFeePurse,
 
     // The functions below are getters only and have no impact on
     // state within Zoe

packages/zoe/test/unitTests/test-zoe.js

@@ -4,6 +4,7 @@ import { test } from '@agoric/zoe/tools/prepare-test-env-ava.js';
 
 import path from 'path';
 
+import { AmountMath } from '@agoric/ertp';
 import { E } from '@agoric/eventual-send';
 import { makePromiseKit } from '@agoric/promise-kit';
 import { passStyleOf } from '@agoric/marshal';
@@ -371,3 +372,27 @@ test(`zoe.getInvitationDetails - no invitation`, async t => {
     message: /A Zoe invitation is required, not "\[undefined\]"/,
   });
 });
+
+test(`zoe.makeFeePurse`, async t => {
+  const { zoe, zcf, feeMintAccess } = await setupZCFTest();
+
+  const feePurse = E(zoe).makeFeePurse();
+  const feeIssuer = E(zoe).getFeeIssuer();
+  const feeBrand = await E(feeIssuer).getBrand();
+
+  const zcfMint = await zcf.registerFeeMint('RUN', feeMintAccess);
+  const { zcfSeat, userSeat } = zcf.makeEmptySeatKit();
+
+  const fee1000 = AmountMath.make(feeBrand, 1000n);
+  zcfMint.mintGains({ Fee: fee1000 }, zcfSeat);
+
+  zcfSeat.exit();
+  const payment = await E(userSeat).getPayout('Fee');
+  await E(feePurse).deposit(payment);
+
+  t.true(AmountMath.isEqual(await E(feePurse).getCurrentAmount(), fee1000));
+
+  await E(feePurse).withdraw(fee1000);
+
+  t.true(AmountMath.isEmpty(await E(feePurse).getCurrentAmount()));
+});

packages/zoe/test/unitTests/zcf/setupZcfTest.js

@@ -23,7 +23,7 @@ export const setupZCFTest = async (issuerKeywordRecord, terms) => {
   };
   // The contract provides the `zcf` via `setTestJig` upon `start`.
   const fakeVatAdmin = makeFakeVatAdmin(setZCF);
-  const { zoeService: zoe } = makeZoe(fakeVatAdmin.admin);
+  const { zoeService: zoe, feeMintAccess } = makeZoe(fakeVatAdmin.admin);
   const bundle = await bundleSource(contractRoot);
   const installation = await E(zoe).install(bundle);
   const { creatorFacet, instance } = await E(zoe).startInstance(
@@ -34,5 +34,13 @@ export const setupZCFTest = async (issuerKeywordRecord, terms) => {
   const { vatAdminState } = fakeVatAdmin;
   // @ts-ignore fix types to understand that zcf is always defined
   assert(zcf !== undefined);
-  return { zoe, zcf, instance, installation, creatorFacet, vatAdminState };
+  return {
+    zoe,
+    zcf,
+    instance,
+    installation,
+    creatorFacet,
+    vatAdminState,
+    feeMintAccess,
+  };
 };

packages/zoe/test/unitTests/zoe/test-feePurse.js

@@ -0,0 +1,45 @@
+// @ts-check
+
+// eslint-disable-next-line import/no-extraneous-dependencies
+import { test } from '@agoric/zoe/tools/prepare-test-env-ava.js';
+
+import { makeIssuerKit, AssetKind, AmountMath } from '@agoric/ertp';
+
+import { setupMakeFeePurse } from '../../../src/zoeService/feePurse.js';
+
+const setup = () => {
+  const runIssuerKit = makeIssuerKit('RUN', AssetKind.NAT, {
+    decimalPlaces: 6,
+  });
+  const { makeFeePurse, isFeePurse } = setupMakeFeePurse(runIssuerKit.issuer);
+  return { makeFeePurse, isFeePurse, runIssuerKit };
+};
+
+test('feePurse starts empty', async t => {
+  const { makeFeePurse } = setup();
+  const feePurse = makeFeePurse();
+
+  t.true(AmountMath.isEmpty(feePurse.getCurrentAmount()));
+});
+
+test('depositing into and withdrawing from feePurse', async t => {
+  const { makeFeePurse, runIssuerKit } = setup();
+  const feePurse = makeFeePurse();
+
+  const run1000 = AmountMath.make(runIssuerKit.brand, 1000n);
+  const payment = runIssuerKit.mint.mintPayment(run1000);
+  feePurse.deposit(payment);
+
+  t.true(AmountMath.isEqual(feePurse.getCurrentAmount(), run1000));
+
+  feePurse.withdraw(run1000);
+
+  t.true(AmountMath.isEmpty(feePurse.getCurrentAmount()));
+});
+
+test('isFeePurse', async t => {
+  const { makeFeePurse, isFeePurse } = setup();
+  const feePurse = makeFeePurse();
+
+  t.true(isFeePurse(feePurse));
+});