fs: fix fs.promises.writeFile with typed arrays

Before this change, only the first part of typed arrays which have more
than 1 byte per element (e.g. Uint16Array) would be written.
This also removes the use of the `slice` method to avoid unnecessary
copying the data.

Fixes: #35343

PR-URL: #35376
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Zeyu Yang <himself65@outlook.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/internal/fs/promises.js

@@ -10,12 +10,13 @@ const kReadFileMaxChunkSize = 2 ** 14;
 const kWriteFileMaxChunkSize = 2 ** 14;
 
 const {
+  Error,
   MathMax,
   MathMin,
   NumberIsSafeInteger,
-  Symbol,
-  Error,
   Promise,
+  Symbol,
+  Uint8Array,
 } = primordials;
 
 const {
@@ -237,14 +238,20 @@ async function fsCall(fn, handle, ...args) {
 }
 
 async function writeFileHandle(filehandle, data) {
+  // `data` could be any kind of typed array.
+  data = new Uint8Array(data.buffer, data.byteOffset, data.byteLength);
   let remaining = data.length;
   if (remaining === 0) return;
   do {
     const { bytesWritten } =
       await write(filehandle, data, 0,
                   MathMin(kWriteFileMaxChunkSize, data.length));
     remaining -= bytesWritten;
-    data = data.slice(bytesWritten);
+    data = new Uint8Array(
+      data.buffer,
+      data.byteOffset + bytesWritten,
+      data.byteLength - bytesWritten
+    );
   } while (remaining > 0);
 }
 

test/parallel/test-fs-promises-writefile-typedarray.js

@@ -0,0 +1,24 @@
+'use strict';
+
+const common = require('../common');
+const fs = require('fs');
+const fsPromises = fs.promises;
+const path = require('path');
+const tmpdir = require('../common/tmpdir');
+const assert = require('assert');
+const tmpDir = tmpdir.path;
+
+tmpdir.refresh();
+
+const dest = path.resolve(tmpDir, 'tmp.txt');
+// Use a file size larger than `kReadFileMaxChunkSize`.
+const buffer = Buffer.from('012'.repeat(2 ** 14));
+
+(async () => {
+  for (const Constructor of [Uint8Array, Uint16Array, Uint32Array]) {
+    const array = new Constructor(buffer.buffer);
+    await fsPromises.writeFile(dest, array);
+    const data = await fsPromises.readFile(dest);
+    assert.deepStrictEqual(data, buffer);
+  }
+})().then(common.mustCall());