feat: introduces ExpirableMap (#794)

* feat: introduces ExpirableMap

* prunes on every get

* supports source iterator in constructor

Author: krpeacock

docs/generated/changelog.html

@@ -33,6 +33,10 @@ <h2>Version x.x.x</h2>
           <li>new Verify export on ed25519 because why not</li>
         </ul>
         <li>Adds support for Uint8Arrays in Principal.from()</li>
+        <li>
+          feat: introduces ExpirableMap, a utility class that will return values up until a
+          configured expiry
+        </li>
         <li>
           chore: increases size limit for agent-js to allow for Ed25519 support for node key
           signature verification

packages/agent/src/utils/expirableMap.test.ts

@@ -0,0 +1,37 @@
+import { ExpirableMap } from './expirableMap';
+
+jest.useFakeTimers();
+describe('ExpirableMap', () => {
+  it('should return undefined if the key is not present', () => {
+    const map = new ExpirableMap();
+    expect(map.get('key')).toBeUndefined();
+  });
+  it('should return a key if one has been recently set', () => {
+    const map = new ExpirableMap();
+    map.set('key', 'value');
+    expect(map.get('key')).toBe('value');
+  });
+  it('should return undefined if the key has expired', () => {
+    const map = new ExpirableMap({ expirationTime: 10 });
+    map.set('key', 'value');
+    jest.advanceTimersByTime(11);
+    expect(map.get('key')).toBeUndefined();
+  });
+  it('should support iterable operations', () => {
+    const map = new ExpirableMap({
+      source: [
+        ['key1', 8],
+        ['key2', 1234],
+      ],
+    });
+
+    expect(Array.from(map)).toStrictEqual([
+      ['key1', 8],
+      ['key2', 1234],
+    ]);
+
+    for (const [key, value] of map) {
+      expect(map.get(key)).toBe(value);
+    }
+  });
+});

packages/agent/src/utils/expirableMap.ts

@@ -0,0 +1,161 @@
+export type ExpirableMapOptions<K, V> = {
+  source?: Iterable<[K, V]>;
+  expirationTime?: number;
+};
+
+/**
+ * A map that expires entries after a given time.
+ * Defaults to 10 minutes.
+ */
+export class ExpirableMap<K, V> implements Map<K, V> {
+  // Internals
+  #inner: Map<K, { value: V; timestamp: number }>;
+  #expirationTime: number;
+
+  [Symbol.iterator]: () => IterableIterator<[K, V]> = this.entries.bind(this);
+  [Symbol.toStringTag] = 'ExpirableMap';
+
+  /**
+   * Create a new ExpirableMap.
+   * @param {ExpirableMapOptions<any, any>} options - options for the map.
+   * @param {Iterable<[any, any]>} options.source - an optional source of entries to initialize the map with.
+   * @param {number} options.expirationTime - the time in milliseconds after which entries will expire.
+   */
+  constructor(options: ExpirableMapOptions<K, V> = {}) {
+    const { source = [], expirationTime = 10 * 60 * 1000 } = options;
+    const currentTime = Date.now();
+    this.#inner = new Map(
+      [...source].map(([key, value]) => [key, { value, timestamp: currentTime }]),
+    );
+    this.#expirationTime = expirationTime;
+  }
+
+  /**
+   * Prune removes all expired entries.
+   */
+  prune() {
+    const currentTime = Date.now();
+    for (const [key, entry] of this.#inner.entries()) {
+      if (currentTime - entry.timestamp > this.#expirationTime) {
+        this.#inner.delete(key);
+      }
+    }
+    return this;
+  }
+
+  // Implementing the Map interface
+
+  /**
+   * Set the value for the given key. Prunes expired entries.
+   * @param key for the entry
+   * @param value of the entry
+   * @returns this
+   */
+  set(key: K, value: V) {
+    this.prune();
+    const entry = {
+      value,
+      timestamp: Date.now(),
+    };
+    this.#inner.set(key, entry);
+
+    return this;
+  }
+
+  /**
+   * Get the value associated with the key, if it exists and has not expired.
+   * @param key K
+   * @returns the value associated with the key, or undefined if the key is not present or has expired.
+   */
+  get(key: K) {
+    const entry = this.#inner.get(key);
+    if (entry === undefined) {
+      return undefined;
+    }
+    if (Date.now() - entry.timestamp > this.#expirationTime) {
+      this.#inner.delete(key);
+      return undefined;
+    }
+    return entry.value;
+  }
+
+  /**
+   * Clear all entries.
+   */
+  clear() {
+    this.#inner.clear();
+  }
+
+  /**
+   * Entries returns the entries of the map, without the expiration time.
+   * @returns an iterator over the entries of the map.
+   */
+  entries(): IterableIterator<[K, V]> {
+    const iterator = this.#inner.entries();
+    const generator = function* () {
+      for (const [key, value] of iterator) {
+        yield [key, value.value] as [K, V];
+      }
+    };
+    return generator();
+  }
+
+  /**
+   * Values returns the values of the map, without the expiration time.
+   * @returns an iterator over the values of the map.
+   */
+  values(): IterableIterator<V> {
+    const iterator = this.#inner.values();
+    const generator = function* () {
+      for (const value of iterator) {
+        yield value.value;
+      }
+    };
+    return generator();
+  }
+
+  /**
+   * Keys returns the keys of the map
+   * @returns an iterator over the keys of the map.
+   */
+  keys(): IterableIterator<K> {
+    return this.#inner.keys();
+  }
+
+  /**
+   * forEach calls the callbackfn on each entry of the map.
+   * @param callbackfn to call on each entry
+   * @param thisArg to use as this when calling the callbackfn
+   */
+  forEach(callbackfn: (value: V, key: K, map: Map<K, V>) => void, thisArg?: ExpirableMap<K, V>) {
+    for (const [key, value] of this.#inner.entries()) {
+      callbackfn.call(thisArg, value.value, key, this);
+    }
+  }
+
+  /**
+   * has returns true if the key exists and has not expired.
+   * @param key K
+   * @returns true if the key exists and has not expired.
+   */
+  has(key: K): boolean {
+    return this.#inner.has(key);
+  }
+
+  /**
+   * delete the entry for the given key.
+   * @param key K
+   * @returns true if the key existed and has been deleted.
+   */
+  delete(key: K) {
+    return this.#inner.delete(key);
+  }
+
+  /**
+   * get size of the map.
+   * @returns the size of the map.
+   */
+  get size() {
+    return this.#inner.size;
+  }
+}