feat: Implement HEAD request support

* feat: Implement HEAD request support

* feat: Integrate HEAD handler with other code

* fix: Improve test by using arrayifyStream

* fix: Use Promise chaining

* refactor: Unwrap destroy stream promise

config/presets/ldp/operation-handler.json

@@ -17,6 +17,12 @@
             "@id": "urn:solid-server:default:ResourceStore_Patching"
           }
         },
+        {
+          "@type": "HeadOperationHandler",
+          "HeadOperationHandler:_store": {
+            "@id": "urn:solid-server:default:ResourceStore_Patching"
+          }
+        },
         {
           "@type": "PatchOperationHandler",
           "PatchOperationHandler:_store": {

index.ts

@@ -42,6 +42,7 @@ export * from './src/logging/WinstonLoggerFactory';
 // LDP/Operations
 export * from './src/ldp/operations/DeleteOperationHandler';
 export * from './src/ldp/operations/GetOperationHandler';
+export * from './src/ldp/operations/HeadOperationHandler';
 export * from './src/ldp/operations/Operation';
 export * from './src/ldp/operations/OperationHandler';
 export * from './src/ldp/operations/PatchOperationHandler';

src/ldp/operations/HeadOperationHandler.ts

@@ -0,0 +1,37 @@
+import { Readable } from 'stream';
+import type { ResourceStore } from '../../storage/ResourceStore';
+import { UnsupportedHttpError } from '../../util/errors/UnsupportedHttpError';
+import type { Operation } from './Operation';
+import { OperationHandler } from './OperationHandler';
+import type { ResponseDescription } from './ResponseDescription';
+
+/**
+ * Handles HEAD {@link Operation}s.
+ * Calls the getRepresentation function from a {@link ResourceStore}.
+ */
+export class HeadOperationHandler extends OperationHandler {
+  private readonly store: ResourceStore;
+
+  public constructor(store: ResourceStore) {
+    super();
+    this.store = store;
+  }
+
+  public async canHandle(input: Operation): Promise<void> {
+    if (input.method !== 'HEAD') {
+      throw new UnsupportedHttpError('This handler only supports HEAD operations.');
+    }
+  }
+
+  public async handle(input: Operation): Promise<ResponseDescription> {
+    const body = await this.store.getRepresentation(input.target, input.preferences);
+
+    // Close the Readable as we will not return it.
+    body.data.destroy();
+    body.data = new Readable();
+    body.data._read = function(): void {
+      body.data.push(null);
+    };
+    return { identifier: input.target, body };
+  }
+}

test/configs/Util.ts

@@ -14,6 +14,7 @@ import {
   DeleteOperationHandler,
   FileResourceStore,
   GetOperationHandler,
+  HeadOperationHandler,
   InMemoryResourceStore,
   InteractionController,
   MetadataController,
@@ -94,6 +95,7 @@ export const getPatchingStore = (store: ResourceStore): PatchingStore => {
 export const getOperationHandler = (store: ResourceStore): CompositeAsyncHandler<Operation, ResponseDescription> => {
   const handlers = [
     new GetOperationHandler(store),
+    new HeadOperationHandler(store),
     new PostOperationHandler(store),
     new PutOperationHandler(store),
     new PatchOperationHandler(store),

test/unit/ldp/operations/HeadOperationHandler.test.ts

@@ -0,0 +1,28 @@
+import arrayifyStream from 'arrayify-stream';
+import streamifyArray from 'streamify-array';
+import { HeadOperationHandler } from '../../../../src/ldp/operations/HeadOperationHandler';
+import type { Operation } from '../../../../src/ldp/operations/Operation';
+import type { Representation } from '../../../../src/ldp/representation/Representation';
+import type { ResourceStore } from '../../../../src/storage/ResourceStore';
+import { UnsupportedHttpError } from '../../../../src/util/errors/UnsupportedHttpError';
+
+describe('A HeadOperationHandler', (): void => {
+  const store = {
+    getRepresentation: async(): Promise<Representation> => ({ binary: false, data: streamifyArray([ 1, 2, 3 ]) } as
+      Representation),
+  } as unknown as ResourceStore;
+  const handler = new HeadOperationHandler(store);
+
+  it('only supports HEAD operations.', async(): Promise<void> => {
+    await expect(handler.canHandle({ method: 'HEAD' } as Operation)).resolves.toBeUndefined();
+    await expect(handler.canHandle({ method: 'GET' } as Operation)).rejects.toThrow(UnsupportedHttpError);
+    await expect(handler.canHandle({ method: 'POST' } as Operation)).rejects.toThrow(UnsupportedHttpError);
+  });
+
+  it('returns the representation from the store with the input identifier and empty data.', async(): Promise<void> => {
+    const result = await handler.handle({ target: { path: 'url' }} as Operation);
+    expect(result.identifier.path).toBe('url');
+    expect(result.body?.binary).toBe(false);
+    await expect(arrayifyStream(result.body!.data)).resolves.toEqual([]);
+  });
+});