feat: Add ParallelHandler.

src/index.ts

@@ -189,6 +189,7 @@ export * from './util/errors/UnsupportedMediaTypeHttpError';
 
 // Util/Handlers
 export * from './util/handlers/AsyncHandler';
+export * from './util/handlers/ParallelHandler';
 export * from './util/handlers/SequenceHandler';
 export * from './util/handlers/UnsupportedAsyncHandler';
 export * from './util/handlers/WaterfallHandler';

src/util/handlers/ParallelHandler.ts

@@ -0,0 +1,23 @@
+import { AsyncHandler } from './AsyncHandler';
+
+/**
+ * A composite handler that executes handlers in parallel.
+ */
+export class ParallelHandler<TIn = void, TOut = void> extends AsyncHandler<TIn, TOut[]> {
+  private readonly handlers: AsyncHandler<TIn, TOut>[];
+
+  public constructor(handlers: AsyncHandler<TIn, TOut>[]) {
+    super();
+    this.handlers = [ ...handlers ];
+  }
+
+  public async canHandle(input: TIn): Promise<void> {
+    // eslint-disable-next-line @typescript-eslint/promise-function-async
+    await Promise.all(this.handlers.map((handler): Promise<void> => handler.canHandle(input)));
+  }
+
+  public async handle(input: TIn): Promise<TOut[]> {
+    // eslint-disable-next-line @typescript-eslint/promise-function-async
+    return Promise.all(this.handlers.map((handler): Promise<TOut> => handler.handle(input)));
+  }
+}

test/unit/util/handlers/ParallelHandler.test.ts

@@ -0,0 +1,100 @@
+import type { AsyncHandler } from '../../../../src/util/handlers/AsyncHandler';
+import { ParallelHandler } from '../../../../src/util/handlers/ParallelHandler';
+
+describe('A ParallelHandler', (): void => {
+  const handlers: jest.Mocked<AsyncHandler<string, string>>[] = [
+    {
+      canHandle: jest.fn(),
+      handle: jest.fn().mockResolvedValue('0'),
+    },
+    {
+      canHandle: jest.fn(),
+      handle: jest.fn().mockResolvedValue('1'),
+    },
+    {
+      canHandle: jest.fn(),
+      handle: jest.fn().mockResolvedValue('2'),
+    },
+  ] as any;
+  const composite: ParallelHandler<string, string> = new ParallelHandler<string, string>(handlers);
+
+  afterEach(jest.clearAllMocks);
+
+  describe('canHandle', (): void => {
+    it('succeeds if all handlers succeed.', async(): Promise<void> => {
+      await expect(composite.canHandle('abc')).resolves.toBeUndefined();
+
+      expect(handlers[0].canHandle).toHaveBeenCalledTimes(1);
+      expect(handlers[1].canHandle).toHaveBeenCalledTimes(1);
+      expect(handlers[2].canHandle).toHaveBeenCalledTimes(1);
+
+      expect(handlers[0].canHandle).toHaveBeenCalledWith('abc');
+      expect(handlers[1].canHandle).toHaveBeenCalledWith('abc');
+      expect(handlers[2].canHandle).toHaveBeenCalledWith('abc');
+    });
+
+    it('fails if one handler fails.', async(): Promise<void> => {
+      const error = new Error('failure');
+      handlers[1].canHandle.mockRejectedValueOnce(error);
+      await expect(composite.canHandle('abc')).rejects.toThrow(error);
+    });
+  });
+
+  describe('handle', (): void => {
+    it('succeeds if all handlers succeed.', async(): Promise<void> => {
+      await expect(composite.handle('abc')).resolves.toEqual([ '0', '1', '2' ]);
+
+      expect(handlers[0].handle).toHaveBeenCalledTimes(1);
+      expect(handlers[1].handle).toHaveBeenCalledTimes(1);
+      expect(handlers[2].handle).toHaveBeenCalledTimes(1);
+
+      expect(handlers[0].handle).toHaveBeenCalledWith('abc');
+      expect(handlers[1].handle).toHaveBeenCalledWith('abc');
+      expect(handlers[2].handle).toHaveBeenCalledWith('abc');
+    });
+
+    it('fails if one handler fails.', async(): Promise<void> => {
+      const error = new Error('failure');
+      handlers[1].handle.mockRejectedValueOnce(error);
+      await expect(composite.handle('abc')).rejects.toThrow(error);
+    });
+  });
+
+  describe('handleSafe', (): void => {
+    it('succeeds if all handlers succeed.', async(): Promise<void> => {
+      await expect(composite.handleSafe('abc')).resolves.toEqual([ '0', '1', '2' ]);
+
+      expect(handlers[0].canHandle).toHaveBeenCalledTimes(1);
+      expect(handlers[1].canHandle).toHaveBeenCalledTimes(1);
+      expect(handlers[2].canHandle).toHaveBeenCalledTimes(1);
+
+      expect(handlers[0].canHandle).toHaveBeenCalledWith('abc');
+      expect(handlers[1].canHandle).toHaveBeenCalledWith('abc');
+      expect(handlers[2].canHandle).toHaveBeenCalledWith('abc');
+
+      expect(handlers[0].handle).toHaveBeenCalledTimes(1);
+      expect(handlers[1].handle).toHaveBeenCalledTimes(1);
+      expect(handlers[2].handle).toHaveBeenCalledTimes(1);
+
+      expect(handlers[0].handle).toHaveBeenCalledWith('abc');
+      expect(handlers[1].handle).toHaveBeenCalledWith('abc');
+      expect(handlers[2].handle).toHaveBeenCalledWith('abc');
+    });
+
+    it('fails if one canHandle fails.', async(): Promise<void> => {
+      const error = new Error('failure');
+      handlers[1].canHandle.mockRejectedValueOnce(error);
+      await expect(composite.handleSafe('abc')).rejects.toThrow(error);
+
+      expect(handlers[0].handle).toHaveBeenCalledTimes(0);
+      expect(handlers[1].handle).toHaveBeenCalledTimes(0);
+      expect(handlers[2].handle).toHaveBeenCalledTimes(0);
+    });
+
+    it('fails if one handle fails.', async(): Promise<void> => {
+      const error = new Error('failure');
+      handlers[1].handle.mockRejectedValueOnce(error);
+      await expect(composite.handleSafe('abc')).rejects.toThrow(error);
+    });
+  });
+});