Javascript 如何使用 Bluebird 保证 Node 的 child_process.exec 和 child_process.execFile 函数？
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How to promisify Node's child_process.exec and child_process.execFile functions with Bluebird?
提问by Zoltan
I'm using the Bluebird promise library under Node.js, it's great! But I have a question:
我在 Node.js 下使用 Bluebird promise 库，很棒！但我有一个问题：
If you take a look at the documentation of Node's child_process.execand child_process.execFileyou can see that both of these functions are returning a ChildProcess object.
如果您查看 Node 的child_process.exec和child_process.execFile的文档，您会发现这两个函数都返回一个 ChildProcess 对象。
So what's the recommended way to promisify such functions?
那么承诺这些功能的推荐方法是什么？
Note that the following works (I get a Promise object):
请注意，以下工作（我得到一个 Promise 对象）：
var Promise = require('bluebird');
var execAsync = Promise.promisify(require('child_process').exec);
var execFileAsync = Promise.promisify(require('child_process').execFile);
But how can one get access to the original return value of the original Node.js functions? (In these cases I would need to be able to access the originally returned ChildProcess objects.)
但是如何才能访问原始 Node.js 函数的原始返回值呢？（在这些情况下，我需要能够访问最初返回的 ChildProcess 对象。）
Any suggestion would be appreciated!
任何建议将不胜感激！
EDIT:
编辑：
Here is an example code which is using the return value of the child_process.exec function:
这是使用 child_process.exec 函数的返回值的示例代码：
var exec = require('child_process').exec;
var child = exec('node ./commands/server.js');
child.stdout.on('data', function(data) {
console.log('stdout: ' + data);
});
child.stderr.on('data', function(data) {
console.log('stderr: ' + data);
});
child.on('close', function(code) {
console.log('closing code: ' + code);
});
But if I would use the promisified version of the exec function ( execAsync from above ) then the return value will be a promise, not a ChildProcess object. This is the real problem I am talking about.
但是如果我使用 exec 函数的 promisified 版本（上面的 execAsync ），那么返回值将是一个承诺，而不是一个 ChildProcess 对象。这是我正在谈论的真正问题。
回答by Ivan Hamilton
It sounds like you'd like to return two things from the call:
听起来您想从通话中返回两件事：
- the ChildProcess
- a promise that resolves when the ChildProcess completes
- 子进程
- 在 ChildProcess 完成时解决的承诺
So "the recommended way to promisify such functions"? Don't.
那么“承诺此类功能的推荐方法”？不要。
You're outside the convention. Promise returning functions are expected to return a promise, and that's it. You could return an object with two members (the ChildProcess & the promise), but that'll just confuse people.
你在公约之外。Promise 返回函数应该返回一个 Promise，仅此而已。您可以返回具有两个成员（ChildProcess 和承诺）的对象，但这只会使人们感到困惑。
I'd suggest calling the unpromisified function, and creating a promise based off the returned childProcess. (Maybe wrap that into a helper function)
我建议调用 unpromisified 函数，并根据返回的 childProcess 创建一个承诺。（也许把它包装成一个辅助函数）
This way, it's quite explicit for the next person who reads the code.
这样，对于下一个阅读代码的人来说，这是非常明确的。
Something like:
就像是：
var Promise = require('bluebird');
var exec = require('child_process').execFile;
function promiseFromChildProcess(child) {
return new Promise(function (resolve, reject) {
child.addListener("error", reject);
child.addListener("exit", resolve);
});
}
var child = exec('ls');
promiseFromChildProcess(child).then(function (result) {
console.log('promise complete: ' + result);
}, function (err) {
console.log('promise rejected: ' + err);
});
child.stdout.on('data', function (data) {
console.log('stdout: ' + data);
});
child.stderr.on('data', function (data) {
console.log('stderr: ' + data);
});
child.on('close', function (code) {
console.log('closing code: ' + code);
});
回答by shmck
I would recommend using standard JS promises built into the language over an additional library dependency like Bluebird.
我建议使用语言中内置的标准 JS 承诺，而不是像 Bluebird 这样的附加库依赖项。
If you're using Node 10+, the Node.js docsrecommend using util.promisifywhich returns a Promise<{ stdout, stderr }>object. See an example below:
如果您使用的是 Node 10+，Node.js 文档建议使用util.promisifywhich 返回一个Promise<{ stdout, stderr }>对象。请参阅下面的示例：
const util = require('util');
const exec = util.promisify(require('child_process').exec);
async function lsExample() {
try {
const { stdout, stderr } = await exec('ls');
console.log('stdout:', stdout);
console.log('stderr:', stderr);
} catch (e) {
console.error(e); // should contain code (exit code) and signal (that caused the termination).
}
}
lsExample()
Handle errors first from stderr.
首先从stderr.
回答by Lacho Tomov
Here's another way:
这是另一种方式：
function execPromise(command) {
return new Promise(function(resolve, reject) {
exec(command, (error, stdout, stderr) => {
if (error) {
reject(error);
return;
}
resolve(stdout.trim());
});
});
}
Use the function:
使用函数：
execPromise(command).then(function(result) {
console.log(result);
}).catch(function(e) {
console.error(e.message);
});
Or with async/await:
或者使用异步/等待：
try {
var result = await execPromise(command);
} catch (e) {
console.error(e.message);
}
回答by edan
There's probably not a way to do nicely that covers all use cases. But for limited cases, you can do something like this:
可能没有一种方法可以很好地涵盖所有用例。但是对于有限的情况，您可以执行以下操作：
/**
* Promisified child_process.exec
*
* @param cmd
* @param opts See child_process.exec node docs
* @param {stream.Writable} opts.stdout If defined, child process stdout will be piped to it.
* @param {stream.Writable} opts.stderr If defined, child process stderr will be piped to it.
*
* @returns {Promise<{ stdout: string, stderr: stderr }>}
*/
function execp(cmd, opts) {
opts || (opts = {});
return new Promise((resolve, reject) => {
const child = exec(cmd, opts,
(err, stdout, stderr) => err ? reject(err) : resolve({
stdout: stdout,
stderr: stderr
}));
if (opts.stdout) {
child.stdout.pipe(opts.stdout);
}
if (opts.stderr) {
child.stderr.pipe(opts.stderr);
}
});
}
This accepts opts.stdoutand opts.stderrarguments, so that stdio can be captured from the child process.
这接受opts.stdout和opts.stderr参数，以便可以从子进程中捕获 stdio。
For example:
例如：
execp('ls ./', {
stdout: new stream.Writable({
write: (chunk, enc, next) => {
console.log(chunk.toString(enc));
next();
}
}),
stderr: new stream.Writable({
write: (chunk, enc, next) => {
console.error(chunk.toString(enc));
next();
}
})
}).then(() => console.log('done!'));
Or simply:
或者干脆：
execp('ls ./', {
stdout: process.stdout,
stderr: process.stderr
}).then(() => console.log('done!'));
回答by Tobias
Just want to mention that there's a nice tool that will solve your problem completely:
只想提一下，有一个很好的工具可以完全解决您的问题：
https://www.npmjs.com/package/core-worker
https://www.npmjs.com/package/core-worker
This package makes it a lot easier to handle processes.
这个包使得处理过程变得更加容易。
import { process } from "CoreWorker";
import fs from "fs";
const result = await process("node Server.js", "Server is ready.").ready(1000);
const result = await process("cp path/to/file /newLocation/newFile").death();
or combine these functions:
或结合这些功能：
import { process } from "core-worker";
const simpleChat = process("node chat.js", "Chat ready");
setTimeout(() => simpleChat.kill(), 360000); // wait an hour and close the chat
simpleChat.ready(500)
.then(console.log.bind(console, "You are now able to send messages."))
.then(::simpleChat.death)
.then(console.log.bind(console, "Chat closed"))
.catch(() => /* handle err */);
回答by Jay
Here's mine. It doesn't deal with stdin or stdout, so if you need those then use one of the other answers on this page. :)
这是我的。它不处理标准输入或标准输出，因此如果您需要这些，请使用此页面上的其他答案之一。:)
// promisify `child_process`
// This is a very nice trick :-)
this.promiseFromChildProcess = function (child) {
return new Promise((resolve, reject) => {
child.addListener('error', (code, signal) => {
console.log('ChildProcess error', code, signal);
reject(code);
});
child.addListener('exit', (code, signal) => {
if (code === 0) {
resolve(code);
} else {
console.log('ChildProcess error', code, signal);
reject(code);
}
});
});
};
