fs: use byteLength to handle ArrayBuffer views

lib/fs.js

@@ -531,7 +531,7 @@ function read(fd, buffer, offset, length, position, callback) {
     ({
       buffer = Buffer.alloc(16384),
       offset = 0,
-      length = buffer.length,
+      length = buffer.byteLength,
       position
     } = options);
   }
@@ -586,15 +586,15 @@ ObjectDefineProperty(read, internalUtil.customPromisifyArgs,
 function readSync(fd, buffer, offset, length, position) {
   fd = getValidatedFd(fd);
 
+  validateBuffer(buffer);
+
   if (arguments.length <= 3) {
     // Assume fs.read(fd, buffer, options)
     const options = offset || {};
 
-    ({ offset = 0, length = buffer.length, position } = options);
+    ({ offset = 0, length = buffer.byteLength, position } = options);
   }
 
-  validateBuffer(buffer);
-
   if (offset == null) {
     offset = 0;
   } else {
@@ -681,7 +681,7 @@ function write(fd, buffer, offset, length, position, callback) {
       validateInteger(offset, 'offset');
     }
     if (typeof length !== 'number')
-      length = buffer.length - offset;
+      length = buffer.byteLength - offset;
     if (typeof position !== 'number')
       position = null;
     validateOffsetLengthWrite(offset, length, buffer.byteLength);

test/parallel/test-fs-write-buffer.js

@@ -146,3 +146,20 @@ tmpdir.refresh();
     fs.closeSync(fd);
   }));
 }
+
+// fs.write with a DataView, without the offset and length parameters:
+{
+  const filename = path.join(tmpdir.path, 'write8.txt');
+  fs.open(filename, 'w', 0o644, common.mustSucceed((fd) => {
+    const cb = common.mustSucceed((written) => {
+      assert.strictEqual(written, expected.length);
+      fs.closeSync(fd);
+
+      const found = fs.readFileSync(filename, 'utf8');
+      assert.strictEqual(found, expected.toString());
+    });
+
+    const uint8 = Uint8Array.from(expected);
+    fs.write(fd, new DataView(uint8.buffer), cb);
+  }));
+}