feat: implement and test makeNameHubKit as specified

packages/cosmic-swingset/lib/ag-solo/vats/nameHub.js

@@ -0,0 +1,82 @@
+// @ts-check
+
+import { E } from '@agoric/eventual-send';
+import { Far } from '@agoric/marshal';
+import { makePromiseKit } from '@agoric/promise-kit';
+import { makeStore } from '@agoric/store';
+
+import './types.js';
+
+/**
+ * @returns {NameHubKit}
+ */
+export const makeNameHubKit = () => {
+  /** @typedef {Partial<PromiseRecord<unknown> & { value: unknown }>} NameRecord */
+  /** @type {Store<unknown, NameRecord>} */
+  const keyToRecord = makeStore('nameKey');
+
+  /** @type {NameHub} */
+  const nameHub = {
+    async lookup(...path) {
+      if (path.length === 0) {
+        return nameHub;
+      }
+      const [first, ...remaining] = path;
+      const record = keyToRecord.get(first);
+      /** @type {any} */
+      const firstValue = record.promise || record.value;
+      if (remaining.length === 0) {
+        return firstValue;
+      }
+      return E(firstValue).lookup(...remaining);
+    },
+  };
+
+  /** @type {NameAdmin} */
+  const nameAdmin = {
+    reserve(key) {
+      if (keyToRecord.has(key)) {
+        // If we already have a promise, don't use a new one.
+        if (keyToRecord.get(key).promise) {
+          return;
+        }
+        keyToRecord.set(key, makePromiseKit());
+      } else {
+        keyToRecord.init(key, makePromiseKit());
+      }
+    },
+    update(key, newValue) {
+      const record = harden({ value: newValue });
+      if (keyToRecord.has(key)) {
+        const old = keyToRecord.get(key);
+        if (old.resolve) {
+          old.resolve(newValue);
+        }
+        keyToRecord.set(key, record);
+      } else {
+        keyToRecord.init(key, record);
+      }
+    },
+    delete(key) {
+      if (keyToRecord.has(key)) {
+        // Reject only if already exists.
+        const old = keyToRecord.get(key);
+        if (old.reject) {
+          old.reject(Error(`Value has been deleted`));
+          // Silence unhandled rejections.
+          old.promise && old.promise.catch(_ => {});
+        }
+      }
+      // This delete may throw.  Reflect it to callers.
+      keyToRecord.delete(key);
+    },
+  };
+
+  const nameHubKit = {
+    nameHub: Far('nameHub', nameHub),
+    nameAdmin: Far('nameAdmin', nameAdmin),
+  };
+
+  harden(nameHubKit);
+  return nameHubKit;
+};

packages/cosmic-swingset/lib/ag-solo/vats/types.js

@@ -1,7 +1,34 @@
+// @ts-check
+
 /**
  * @typedef {Object} Board
  * @property {(id: string) => any} getValue
  * @property {(value: any) => string} getId
  * @property {(value: any) => boolean} has
  * @property {() => string[]} ids
  */
+
+/**
+ * @typedef {Object} NameHub
+ * @property {(...path: Array<unknown>) => Promise<unknown>} lookup Look up a
+ * path of keys starting from the current NameHub.
+ */
+
+/**
+ * @typedef {Object} NameAdmin
+ * @property {(key: unknown) => void} reserve Mark a key as reserved; will
+ * return a promise that is fulfilled when the key is updated (or rejected when
+ * deleted).
+ * @property {(key: unknown, newValue: unknown) => void} update Fulfill an
+ * outstanding reserved promise (if any) to the newValue and set the key to the
+ * newValue.
+ * @property {(key: unknown) => void} delete Delete a value and reject an
+ * outstanding reserved promise (if any).
+ */
+
+/**
+ * @typedef {Object} NameHubKit A kit of a NameHub and its corresponding
+ * NameAdmin.
+ * @property {NameHub} nameHub
+ * @property {NameAdmin} nameAdmin
+ */

packages/cosmic-swingset/test/unitTests/test-name-hub.js

@@ -0,0 +1,53 @@
+import '@agoric/install-ses';
+import test from 'ava';
+
+import { makeNameHubKit } from '../../lib/ag-solo/vats/nameHub';
+
+test('makeNameHubKit - reserve and update', async t => {
+  const { nameAdmin, nameHub } = makeNameHubKit();
+
+  await t.throwsAsync(() => nameHub.lookup('hello'), {
+    message: '"nameKey" not found: (a string)',
+  });
+
+  // Try reserving and looking up.
+  nameAdmin.reserve('hello');
+
+  let lookedUpHello = false;
+  const lookupHelloP = nameHub
+    .lookup('hello')
+    .finally(() => (lookedUpHello = true));
+
+  t.falsy(lookedUpHello);
+  nameAdmin.update('hello', 'foo');
+  t.is(await lookupHelloP, 'foo');
+  t.truthy(lookedUpHello);
+
+  nameAdmin.update('hello', 'foo2');
+  t.is(await nameHub.lookup('hello'), 'foo2');
+});
+
+test('makeNameHubKit - reserve and delete', async t => {
+  const { nameAdmin, nameHub } = makeNameHubKit();
+
+  await t.throwsAsync(() => nameHub.lookup('goodbye'), {
+    message: '"nameKey" not found: (a string)',
+  });
+
+  nameAdmin.reserve('goodbye');
+  let lookedUpGoodbye = false;
+  const lookupGoodbyeP = nameHub
+    .lookup('bar')
+    .finally(() => (lookedUpGoodbye = true));
+
+  t.falsy(lookedUpGoodbye);
+  nameAdmin.delete('goodbye');
+  await t.throwsAsync(lookupGoodbyeP, {
+    message: '"nameKey" not found: (a string)',
+  });
+  t.truthy(lookedUpGoodbye);
+
+  await t.throwsAsync(() => nameHub.lookup('goodbye'), {
+    message: '"nameKey" not found: (a string)',
+  });
+});