change: Refactor AllVoidCompositeHandler into SequenceHandler.

config/presets/http.json

@@ -20,8 +20,8 @@
     },
     {
       "@id": "urn:solid-server:default:HttpHandler",
-      "@type": "AllVoidCompositeHandler",
-      "AllVoidCompositeHandler:_handlers": [
+      "@type": "SequenceHandler",
+      "SequenceHandler:_handlers": [
         {
           "@id": "urn:solid-server:default:Middleware"
         },

config/presets/init.json

@@ -3,8 +3,8 @@
   "@graph": [
     {
       "@id": "urn:solid-server:default:Initializer",
-      "@type": "AllVoidCompositeHandler",
-      "AllVoidCompositeHandler:_handlers": [
+      "@type": "SequenceHandler",
+      "SequenceHandler:_handlers": [
         {
           "@type": "LoggerInitializer",
           "LoggerInitializer:_loggerFactory": {

config/presets/ldp/response-writer.json

@@ -3,8 +3,8 @@
   "@graph": [
     {
       "@id": "urn:solid-server:default:MetadataSerializer",
-      "@type": "AllVoidCompositeHandler",
-      "AllVoidCompositeHandler:_handlers": [
+      "@type": "SequenceHandler",
+      "SequenceHandler:_handlers": [
         {
           "@type": "MappedMetadataWriter",
           "MappedMetadataWriter:_headerMap": [

config/presets/middleware.json

@@ -3,8 +3,8 @@
   "@graph": [
     {
       "@id": "urn:solid-server:default:Middleware",
-      "@type": "AllVoidCompositeHandler",
-      "AllVoidCompositeHandler:_handlers": [
+      "@type": "SequenceHandler",
+      "SequenceHandler:_handlers": [
         {
           "@type": "CorsHandler",
           "CorsHandler:_options_methods": [

src/index.ts

@@ -181,10 +181,10 @@ export * from './util/locking/SingleThreadedResourceLocker';
 export * from './util/locking/WrappedExpiringResourceLocker';
 
 // Util
-export * from './util/AllVoidCompositeHandler';
 export * from './util/AsyncHandler';
 export * from './util/FirstCompositeHandler';
 export * from './util/HeaderUtil';
 export * from './util/PathUtil';
 export * from './util/QuadUtil';
+export * from './util/SequenceHandler';
 export * from './util/StreamUtil';

src/util/AsyncHandler.ts

@@ -1,7 +1,7 @@
 /**
  * Simple interface for classes that can potentially handle a specific kind of data asynchronously.
  */
-export abstract class AsyncHandler<TInput = void, TOutput = void> {
+export abstract class AsyncHandler<TIn = void, TOut = void> {
   /**
    * Checks if the input data can be handled by this class.
    * Throws an error if it can't handle the data.
@@ -10,7 +10,7 @@ export abstract class AsyncHandler<TInput = void, TOutput = void> {
    * @returns A promise resolving if this input can be handled, rejecting with an Error if not.
    */
   // eslint-disable-next-line @typescript-eslint/no-unused-vars
-  public async canHandle(input: TInput): Promise<void> {
+  public async canHandle(input: TIn): Promise<void> {
     // Support any input by default
   }
 
@@ -20,7 +20,7 @@ export abstract class AsyncHandler<TInput = void, TOutput = void> {
    *
    * @returns A promise resolving when the handling is finished. Return value depends on the given type.
    */
-  public abstract handle(input: TInput): Promise<TOutput>;
+  public abstract handle(input: TIn): Promise<TOut>;
 
   /**
    * Helper function that first runs the canHandle function followed by the handle function.
@@ -30,7 +30,7 @@ export abstract class AsyncHandler<TInput = void, TOutput = void> {
    *
    * @returns The result of the handle function of the handler.
    */
-  public async handleSafe(data: TInput): Promise<TOutput> {
+  public async handleSafe(data: TIn): Promise<TOut> {
     await this.canHandle(data);
 
     return this.handle(data);

src/util/SequenceHandler.ts

@@ -0,0 +1,32 @@
+import { AsyncHandler } from './AsyncHandler';
+
+/**
+ * A composite handler that will try to run all supporting handlers sequentially
+ * and return the value of the last supported handler.
+ * The `canHandle` check of this handler will always succeed.
+ */
+export class SequenceHandler<TIn = void, TOut = void> extends AsyncHandler<TIn, TOut | undefined> {
+  private readonly handlers: AsyncHandler<TIn, TOut>[];
+
+  public constructor(handlers: AsyncHandler<TIn, TOut>[]) {
+    super();
+    this.handlers = [ ...handlers ];
+  }
+
+  public async handle(input: TIn): Promise<TOut | undefined> {
+    let result: TOut | undefined;
+    for (const handler of this.handlers) {
+      let supported: boolean;
+      try {
+        await handler.canHandle(input);
+        supported = true;
+      } catch {
+        supported = false;
+      }
+      if (supported) {
+        result = await handler.handle(input);
+      }
+    }
+    return result;
+  }
+}

test/configs/Util.ts

@@ -13,7 +13,7 @@ import type {
   OperationHandler,
 } from '../../src/index';
 import {
-  AcceptPreferenceParser, AllVoidCompositeHandler,
+  AcceptPreferenceParser,
   BasicMetadataExtractor,
   BasicRequestParser,
   BasicResponseWriter,
@@ -35,6 +35,7 @@ import {
   PutOperationHandler,
   RawBodyParser,
   RepresentationConvertingStore,
+  SequenceHandler,
   SingleThreadedResourceLocker,
   SlugParser,
   SparqlUpdatePatchHandler,
@@ -117,7 +118,7 @@ export const getOperationHandler = (store: ResourceStore): OperationHandler => {
 };
 
 export const getResponseWriter = (): ResponseWriter => {
-  const serializer = new AllVoidCompositeHandler([
+  const serializer = new SequenceHandler([
     new MappedMetadataWriter({
       [CONTENT_TYPE]: 'content-type',
       [HTTP.location]: 'location',

test/unit/util/SequenceHandler.test.ts

@@ -0,0 +1,64 @@
+import type { AsyncHandler } from '../../../src/util/AsyncHandler';
+import { SequenceHandler } from '../../../src/util/SequenceHandler';
+
+describe('A SequenceHandler', (): void => {
+  const handlers: jest.Mocked<AsyncHandler<string, string>>[] = [
+    {
+      canHandle: jest.fn(),
+      handle: jest.fn().mockResolvedValue('0'),
+    } as any,
+    {
+      canHandle: jest.fn().mockRejectedValue(new Error('not supported')),
+      handle: jest.fn().mockRejectedValue(new Error('should not be called')),
+    } as any,
+    {
+      canHandle: jest.fn(),
+      handle: jest.fn().mockResolvedValue('2'),
+    } as any,
+  ];
+  let composite: SequenceHandler<string, string>;
+
+  beforeEach(async(): Promise<void> => {
+    composite = new SequenceHandler<string, string>(handlers);
+  });
+
+  it('can handle all input.', async(): Promise<void> => {
+    await expect(composite.canHandle('test')).resolves.toBeUndefined();
+  });
+
+  it('runs all supported handlers.', async(): Promise<void> => {
+    await composite.handleSafe('test');
+
+    expect(handlers[0].canHandle).toHaveBeenCalledTimes(1);
+    expect(handlers[0].canHandle).toHaveBeenLastCalledWith('test');
+    expect(handlers[0].handle).toHaveBeenCalledTimes(1);
+    expect(handlers[0].handle).toHaveBeenLastCalledWith('test');
+
+    expect(handlers[1].canHandle).toHaveBeenCalledTimes(1);
+    expect(handlers[1].canHandle).toHaveBeenLastCalledWith('test');
+    expect(handlers[1].handle).toHaveBeenCalledTimes(0);
+
+    expect(handlers[2].canHandle).toHaveBeenCalledTimes(1);
+    expect(handlers[2].canHandle).toHaveBeenLastCalledWith('test');
+    expect(handlers[2].handle).toHaveBeenCalledTimes(1);
+    expect(handlers[2].handle).toHaveBeenLastCalledWith('test');
+  });
+
+  it('returns the result of the last supported handler.', async(): Promise<void> => {
+    await expect(composite.handleSafe('test')).resolves.toBe('2');
+
+    handlers[2].canHandle.mockRejectedValueOnce(new Error('not supported'));
+    await expect(composite.handleSafe('test')).resolves.toBe('0');
+  });
+
+  it('returns undefined if no handler is supported.', async(): Promise<void> => {
+    handlers[0].canHandle.mockRejectedValueOnce(new Error('not supported'));
+    handlers[2].canHandle.mockRejectedValueOnce(new Error('not supported'));
+    await expect(composite.handleSafe('test')).resolves.toBeUndefined();
+  });
+
+  it('errors if a handler errors.', async(): Promise<void> => {
+    handlers[2].handle.mockRejectedValueOnce(new Error('failure'));
+    await expect(composite.handleSafe('test')).rejects.toThrow('failure');
+  });
+});