有什么方法可以确定 nodejs 子进程是需要输入还是只是发送反馈？

Question

I had a little freetime so I decided to rewrite all my bash scripts in JavaScript (NodeJS - ES6) with child processes. Everything went smoothly until I wanted to automate user input.

Yes, you can do automate the user input. But there is one Problem - you can't determine if the given data event is a feedback or a request for input. At least I can't find a way to do it.

So basically you can do this:

// new Spawn.
let spawn = require('child_process');
// new ufw process.
let ufw = spawn('ufw', ['enable']);

// Use defined input.
ufw.stdin.setEncoding('utf-8');
ufw.stdout.pipe(process.stdout);
ufw.stdin.write('y\n');

// Event Standard Out.
ufw.stdout.on('data', (data) => {
  console.log(data.toString('utf8'));
});

// Event Standard Error.
ufw.stderr.on('data', (err) => {
  // Logerror.
  console.log(err);
});

// When job is finished (with or without error) it ends up here.
ufw.on('close', (code) => {
  // Check if there were errors.
  if (code !== 0) console.log('Exited with code: ' + code.toString());
  // End input stream.
  ufw.stdin.end();
});

The above example works totally fine. But there are 2 things giving me an headache:

1. Will ufw.stdin.write('y\\n'); wait until it is needed and what happens if I have multiple inputs? For example 'yes', 'yes', 'no'. Do I have to write 3 lines of stdin.write() ?

2. Isn't the position where I use ufw.stdin.write('y\\n'); a little confusing? I thought I need the input after my prompt made a request for input so I decided to change my code that my stdin.write() could run at the right time, makes sense right? However the only way to check when the 'right' time is on the stdout.on('data', callback) event. That makes thinks a little difficult, since I need to know if the prompt is aksing for user input or not...

Here is my code which I think is totally wrong:

// new Spawn.
let spawn = require('child_process');
// new ufw process.
let ufw = spawn('ufw', ['enable']);

// Event Standard Out.
ufw.stdout.on('data', (data) => {
  console.log(data.toString('utf8'));

  // Use defined input.
  ufw.stdin.setEncoding('utf-8');
  ufw.stdout.pipe(process.stdout);
  ufw.stdin.write('y\n');
});

// Event Standard Error.
ufw.stderr.on('data', (err) => {
  // Logerror.
  console.log(err);
});

// When job is finished (with or without error) it ends up here.
ufw.on('close', (code) => {
  // Check if there were errors.
  if (code !== 0) console.log('Exited with code: ' + code.toString());
  // End input stream.
  ufw.stdin.end();
});

My major misunderstanding is when to use stdin for user input (automated) and where to place it in my code so it will be used at the right time, for example if I have multiple inputs for something like mysql_secure_installation .

Answer 1

So I was wondering if it is possible and it seems not. I posted an issue for node which ended up beeing closed: https://github.com/nodejs/node/issues/16214

 I am asking for a way to determine if the current process is waiting for an input.

There isn't one. I think you have wrong expectations about pipe I/O because that's simply not how it works.

Talking about expectations, check out expect. There is probably a node.js port if you look around.

I'll close this out because it's not implementable as a feature, and as a question nodejs/help is the more appropriate place.

So if anyone has the same problem as I had you can simply write multiple lines into stdin and use that as predefined values. Keep in mind that will eventually break the stream if any input is broken or wrong in feature updates:

// new Spawn.
let spawn = require('child_process');
// new msqlsec process.
let msqlsec = spawn('mysql_secure_installation', ['']);
// Arguments as Array.
let inputArgs = ['password', 'n', 'y', 'y', 'y', 'y'];

// Set correct encodings for logging.
msqlsec.stdin.setEncoding('utf-8');
msqlsec.stdout.setEncoding('utf-8');
msqlsec.stderr.setEncoding('utf-8');

// Use defined input and write line for each of them.
for (let a = 0; a < inputArgs.length; a++) {
  msqlsec.stdin.write(inputArgs[a] + '\n');
}

// Event Standard Out.
msqlsec.stdout.on('data', (data) => {
  console.log(data.toString('utf8'));
});

// Event Standard Error.
msqlsec.stderr.on('data', (err) => {
  // Logerror.
  console.log(err);
});

// When job is finished (with or without error) it ends up here.
msqlsec.on('close', (code) => {
  // Check if there were errors.
  if (code !== 0) console.log('Exited with code: ' + code.toString());
  // close input to writeable stream.
  msqlsec.stdin.end();
});

---

For the sake of completeness if someone wants to fill the user input manually you can simply start the given process like this:

// new msqlsec process.
let msqlsec = spawn('mysql_secure_installation', [''], { stdio: 'inherit', shell: true });