From 99a79e32a6a8dfcad5c03430fb3ad863f7303201 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C3=ABl=20Zasso?= <targos@protonmail.com>
Date: Sun, 27 Sep 2020 14:34:05 +0200
Subject: [PATCH] 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: https://github.com/nodejs/node/issues/35343

PR-URL: https://github.com/nodejs/node/pull/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                   | 13 +++++++---
 .../test-fs-promises-writefile-typedarray.js  | 24 +++++++++++++++++++
 2 files changed, 34 insertions(+), 3 deletions(-)
 create mode 100644 test/parallel/test-fs-promises-writefile-typedarray.js

diff --git a/lib/internal/fs/promises.js b/lib/internal/fs/promises.js
index a938b382eb1268..60a28735a982ec 100644
--- a/lib/internal/fs/promises.js
+++ b/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 {
@@ -237,6 +238,8 @@ 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 {
@@ -244,7 +247,11 @@ async function writeFileHandle(filehandle, data) {
       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);
 }
 
diff --git a/test/parallel/test-fs-promises-writefile-typedarray.js b/test/parallel/test-fs-promises-writefile-typedarray.js
new file mode 100644
index 00000000000000..32d9cffa236e57
--- /dev/null
+++ b/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());