Fix fs stream read buffer size check

src/crud/__tests__/matryoshka.test.ts

@@ -1,3 +1,5 @@
+import { fromStream } from '@jsonjoy.com/util/lib/streams/fromStream';
+import { bufferToUint8Array } from '@jsonjoy.com/util/lib/buffers/bufferToUint8Array';
 import { memfs } from '../..';
 import { onlyOnNode20 } from '../../__tests__/util';
 import { NodeFileSystemDirectoryHandle } from '../../node-to-fsa';
@@ -6,6 +8,11 @@ import { NodeCrud } from '../../node-to-crud';
 import { testCrudfs } from '../../crud/__tests__/testCrudfs';
 import { FsaCrud } from '../../fsa-to-crud';
 
+const b = (str: string) => {
+  const buf = Buffer.from(str);
+  return new Uint8Array(buf.buffer, buf.byteOffset, buf.byteLength);
+};
+
 onlyOnNode20('CRUD matryoshka', () => {
   describe('crud(memfs)', () => {
     testCrudfs(() => {
@@ -54,6 +61,17 @@ onlyOnNode20('CRUD matryoshka', () => {
       expect(await fs2.promises.readFile('/file3.txt', 'utf8')).toBe('a.c');
     });
 
+    test('can read as stream', async () => {
+      const { fs } = memfs();
+      const fsa = new NodeFileSystemDirectoryHandle(fs, '/', { mode: 'readwrite' });
+      const fs2 = new FsaNodeFs(fsa);
+      await fs2.promises.writeFile('/foo', 'bar');
+      const handle = await fs2.promises.open('/foo', 'r+');
+      const stream = handle.readableWebStream();
+      const blob = bufferToUint8Array((await fromStream(stream)) as any);
+      expect(blob).toStrictEqual(b('bar'));
+    });
+
     testCrudfs(() => {
       const { fs } = memfs();
       const fsa = new NodeFileSystemDirectoryHandle(fs, '/', { mode: 'readwrite' });

src/crud/__tests__/testCrudfs.ts

@@ -52,6 +52,33 @@ export const testCrudfs = (setup: Setup) => {
       });
     });
 
+    test('truncates overwritten resource', async () => {
+      const { crud, snapshot } = setup();
+      await crud.put(['a', 'b'], 'bar', b('abc'));
+      await crud.put(['a', 'b'], 'bar', b('.'));
+      expect(snapshot()).toStrictEqual({
+        '/a/b/bar': '.',
+      });
+    });
+
+    test('can overwrite with empty file', async () => {
+      const { crud, snapshot } = setup();
+      await crud.put(['a', 'b'], 'bar', b('abc'));
+      await crud.put(['a', 'b'], 'bar', b(''));
+      expect(snapshot()).toStrictEqual({
+        '/a/b/bar': '',
+      });
+    });
+
+    test('overwrites existing data', async () => {
+      const { crud, snapshot } = setup();
+      await crud.put(['a', 'b'], 'bar', b('abc'));
+      await crud.put(['a', 'b'], 'bar', b('.'));
+      expect(snapshot()).toStrictEqual({
+        '/a/b/bar': '.',
+      });
+    });
+
     test('can choose to throw if item already exists', async () => {
       const { crud } = setup();
       await crud.put(['a', 'b'], 'bar', b('abc'), { throwIf: 'exists' });

src/fsa-to-node/FsaNodeFs.ts

@@ -94,7 +94,12 @@ export class FsaNodeFs extends FsaNodeCore implements FsCallbackApi, FsSynchrono
       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));
+      position = Number(position);
+      length = Number(length);
+      const slice =
+        position > src.byteLength
+          ? new Uint8Array(0)
+          : new Uint8Array(src, position, Math.min(length, src.byteLength - position));
       const dest = new Uint8Array(buffer.buffer, buffer.byteOffset + offset, slice.length);
       dest.set(slice, 0);
       return slice.length;