fs: support util.promisify for fs.readv

PR-URL: #33590
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: Zeyu Yang <himself65@outlook.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

Author: lholmquist

doc/api/fs.md

@@ -3191,6 +3191,9 @@ from the current position.
 The callback will be given three arguments: `err`, `bytesRead`, and
 `buffers`. `bytesRead` is how many bytes were read from the file.
 
+If this method is invoked as its [`util.promisify()`][]ed version, it returns
+a `Promise` for an `Object` with `bytesRead` and `buffers` properties.
+
 ## `fs.readvSync(fd, buffers[, position])`
 <!-- YAML
 added: v14.0.0

lib/fs.js

@@ -597,6 +597,9 @@ function readv(fd, buffers, position, callback) {
 returnbinding.readBuffers(fd,buffers,position,req);
 }
 
+ObjectDefineProperty(readv,internalUtil.customPromisifyArgs,
+{value: ['bytesRead','buffers'],enumerable: false});
+
 functionreadvSync(fd,buffers,position){
 validateInt32(fd,'fd',0);
 validateBufferArray(buffers);

test/parallel/test-fs-readv-promisify.js

@@ -0,0 +1,18 @@
+'use strict';
+
+constcommon=require('../common');
+constfixtures=require('../common/fixtures');
+constfs=require('fs');
+constreadv=require('util').promisify(fs.readv);
+constassert=require('assert');
+constfilepath=fixtures.path('x.txt');
+constfd=fs.openSync(filepath,'r');
+
+constexpected=[Buffer.from('xyz\n')];
+
+readv(fd,expected)
+.then(function({ bytesRead, buffers }){
+assert.deepStrictEqual(bytesRead,expected[0].length);
+assert.deepStrictEqual(buffers,expected);
+})
+.then(common.mustCall());