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fs: support util.promisify for fs.read/fs.write

PR-URL: #12442
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: William Kapke <william.kapke@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Teddy Katz <teddy.katz@gmail.com>
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addaleax committed Apr 16, 2017
1 parent e7c5145 commit fbcb4f50b81cc57774998b2c3172626b6e4288be
Showing with 46 additions and 2 deletions.
  1. +9 −2 doc/api/fs.md
  2. +6 −0 lib/fs.js
  3. +31 −0 test/parallel/test-fs-promisified.js
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@@ -1612,6 +1612,9 @@ If `position` is `null`, data will be read from the current file position.
The callback is given the three arguments, `(err, bytesRead, buffer)`.
If this method is invoked as its [`util.promisify()`][]ed version, it returns
a Promise for an object with `bytesRead` and `buffer` properties.
## fs.readdir(path[, options], callback)
<!-- YAML
added: v0.1.8
@@ -2393,8 +2396,11 @@ an integer specifying the number of bytes to write.
should be written. If `typeof position !== 'number'`, the data will be written
at the current position. See pwrite(2).
The callback will be given three arguments `(err, written, buffer)` where
`written` specifies how many _bytes_ were written from `buffer`.
The callback will be given three arguments `(err, bytesWritten, buffer)` where
`bytesWritten` specifies how many _bytes_ were written from `buffer`.
If this method is invoked as its [`util.promisify()`][]ed version, it returns
a Promise for an object with `bytesWritten` and `buffer` properties.
Note that it is unsafe to use `fs.write` multiple times on the same file
without waiting for the callback. For this scenario,
@@ -2810,6 +2816,7 @@ The following constants are meant for use with the [`fs.Stats`][] object's
[`net.Socket`]: net.html#net_class_net_socket
[`stat()`]: fs.html#fs_fs_stat_path_callback
[`util.inspect(stats)`]: util.html#util_util_inspect_object_options
[`util.promisify()`]: util.html#util_util_promisify_original
[Caveats]: #fs_caveats
[Common System Errors]: errors.html#errors_common_system_errors
[FS Constants]: #fs_fs_constants_1
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@@ -656,6 +656,9 @@ fs.read = function(fd, buffer, offset, length, position, callback) {
binding.read(fd, buffer, offset, length, position, req);
};
Object.defineProperty(fs.read, internalUtil.customPromisifyArgs,
{ value: ['bytesRead', 'buffer'], enumerable: false });
fs.readSync = function(fd, buffer, offset, length, position) {
if (length === 0) {
return 0;
@@ -706,6 +709,9 @@ fs.write = function(fd, buffer, offset, length, position, callback) {
return binding.writeString(fd, buffer, offset, length, req);
};
Object.defineProperty(fs.write, internalUtil.customPromisifyArgs,
{ value: ['bytesWritten', 'buffer'], enumerable: false });
// usage:
// fs.writeSync(fd, buffer[, offset[, length[, position]]]);
// OR
@@ -0,0 +1,31 @@
'use strict';
const common = require('../common');
const assert = require('assert');
const fs = require('fs');
const path = require('path');
const { promisify } = require('util');
common.crashOnUnhandledRejection();
const read = promisify(fs.read);
const write = promisify(fs.write);
{
const fd = fs.openSync(__filename, 'r');
read(fd, Buffer.alloc(1024), 0, 1024, null).then(common.mustCall((obj) => {
assert.strictEqual(typeof obj.bytesRead, 'number');
assert(obj.buffer instanceof Buffer);
fs.closeSync(fd);
}));
}
common.refreshTmpDir();
{
const filename = path.join(common.tmpDir, 'write-promise.txt');
const fd = fs.openSync(filename, 'w');
write(fd, Buffer.from('foobar')).then(common.mustCall((obj) => {
assert.strictEqual(typeof obj.bytesWritten, 'number');
assert.strictEqual(obj.buffer.toString(), 'foobar');
fs.closeSync(fd);
}));
}

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