fix: extend with null bytes when calling truncate with a len grea…

…ter than the current file size (#875)

* fix: truncate to larger size

* chore: add missing semicolon

src/__tests__/promises.test.ts

@@ -193,6 +193,8 @@ describe('Promises API', () => {
         const fileHandle = await promises.open('/foo', 'r+');
         await fileHandle.truncate(5);
         expect(vol.readFileSync('/foo').toString()).toEqual('01234');
+        await fileHandle.truncate(7);
+        expect(vol.readFileSync('/foo').toString()).toEqual('01234\0\0');
         await fileHandle.close();
       });
       it('Reject when the file handle was closed', async () => {
@@ -592,6 +594,8 @@ describe('Promises API', () => {
     it('Truncate an existing file', async () => {
       await promises.truncate('/foo', 5);
       expect(vol.readFileSync('/foo').toString()).toEqual('01234');
+      await promises.truncate('/foo', 7);
+      expect(vol.readFileSync('/foo').toString()).toEqual('01234\0\0');
     });
     it('Reject when file does not exist', () => {
       return expect(promises.truncate('/bar')).rejects.toBeInstanceOf(Error);

src/__tests__/volume.test.ts

@@ -955,6 +955,13 @@ describe('volume', () => {
         vol.truncateSync('/1', 2);
         expect(vol.readFileSync('/1', 'utf8')).toBe('12');
       });
+      it('Larger truncate', () => {
+        const fd = vol.openSync('/2', 'w');
+        vol.writeFileSync(fd, '12345');
+        expect(vol.readFileSync('/2', 'utf8')).toBe('12345');
+        vol.truncateSync('/2', 10);
+        expect(vol.readFileSync('/2', 'utf8')).toBe('12345\0\0\0\0\0');
+      });
     });
     describe('.truncate(path[, len], callback)', () => {
       xit('...', () => {});

src/node.ts

@@ -143,9 +143,10 @@ export class Node extends EventEmitter {
       if (len <= this.buf.length) {
         this.buf = this.buf.slice(0, len);
       } else {
-        const buf = bufferAllocUnsafe(0);
+        const buf = bufferAllocUnsafe(len);
         this.buf.copy(buf);
-        buf.fill(0, len);
+        buf.fill(0, this.buf.length);
+        this.buf = buf;
       }
     }