feat: 🎸 implement read() method

src/fsa-to-node/FsaNodeFs.ts

@@ -195,7 +195,22 @@ export class FsaNodeFs implements FsCallbackApi, FsCommonObjects {
     position: number,
     callback: (err?: Error | null, bytesRead?: number, buffer?: Buffer | ArrayBufferView | DataView) => void,
   ): void => {
-    throw new Error('Not implemented');
+    validateCallback(callback);
+    // This `if` branch is from Node.js
+    if (length === 0) {
+      return process.nextTick(() => {
+        if (callback) callback(null, 0, buffer);
+      });
+    }
+    (async () => {
+      const openFile = await this.getFileByFd(fd, 'read');
+      const file = await openFile.file.getFile();
+      const src = await file.arrayBuffer();
+      const slice = new Uint8Array(src, Number(position), Number(length));
+      const dest = new Uint8Array(buffer.buffer, buffer.byteOffset + offset, slice.length);
+      dest.set(slice, 0);
+      return slice.length;
+    })().then((bytesWritten) => callback(null, bytesWritten, buffer), error => callback(error));
   };
 
   public readonly readFile: FsCallbackApi['readFile'] = (

src/fsa-to-node/__tests__/FsaNodeFs.test.ts

@@ -579,3 +579,34 @@ describe('.writeFile()', () => {
     });
   });
 });
+
+describe('.read()', () => {
+  test('can read from a file at offset into Buffer', async () => {
+    const { fs } = setup({ folder: { file: 'test' }, 'empty-folder': null, 'f.html': 'test' });
+    const handle = await fs.promises.open('/folder/file', 'r');
+    const [buffer, length] = await new Promise<[Buffer, number]>((resolve, reject) => {
+      const buffer = Buffer.alloc(4);
+      fs.read(handle.fd, buffer, 0, 2, 1, (error, bytesRead, buffer) => {
+        if (error) reject(error);
+        else resolve([buffer as Buffer, bytesRead!]);
+      });
+    });
+    expect(length).toBe(2);
+    expect(buffer.slice(0, 2).toString()).toBe('es');
+  });
+
+  test('can read from a file at offset into Uint8Array', async () => {
+    const { fs } = setup({ folder: { file: 'test' }, 'empty-folder': null, 'f.html': 'test' });
+    const handle = await fs.promises.open('/folder/file', 'r');
+    const [buffer, length] = await new Promise<[Buffer, number]>((resolve, reject) => {
+      const buffer = new Uint8Array(4);
+      fs.read(handle.fd, buffer, 0, 2, 1, (error, bytesRead, buffer) => {
+        if (error) reject(error);
+        else resolve([buffer as Buffer, bytesRead!]);
+      });
+    });
+    expect(length).toBe(2);
+    expect(buffer[0]).toBe(101);
+    expect(buffer[1]).toBe(115);
+  });
+});