node.js child_process#spawn bypass stdin/stdout inner buffers - node.js

Question

I'm using child_process#spawn to use external binaries through node.js. Each binary search for precise words in a string, depending on a language, and produce an output depending on an input text. They don't have inner buffers. usage examples :
echo "I'm a random input" | ./my-english-binary
produces text like The word X is in the sentence
cat /dev/urandom | ./my-english-binary produces infinite ouptut
I want to use each of these binaries as "server". I want to launch a new binary instance after a language never found before is met, send data to it with stdin.write() when necessary, and get its output directly with stdout.on('data') event. The problem is that stdout.on('data') isn't called before a huge amount of data is sent to stdin.write(). stdout or stdin (or both) might have inner blocking buffers... But I want the output as soon as possible because otherwise, the program might wait hours before new input showed up and unlock stdin.write() or stdout.on('data'). How can I change their inner buffer size ? Or maybe can I use another non-blocking system ?
My code is:
const spawn = require('child_process').spawn;
const path = require('path');
class Driver {
constructor() {
// I have one binary per language
this.instances = {
frFR: {
instance: null,
path: path.join(__dirname, './my-french-binary')
},
enGB: {
instance: null,
path: path.join(__dirname, './my-english-binary')
}
}
};
// this function just check if an instance is running for a language
isRunning(lang) {
if (this.instances[lang] === undefined)
throw new Error("Language not supported by TreeTagger: " + lang);
return this.instances[lang].instance !== null;
}
// launch a binary according to a language and attach the function 'onData' to the stdout.on('data') event
run(lang, onData) {
const instance = spawn(this.instances[lang].path,{cwd:__dirname});
instance.stdout.on('data', buf => onData(buf.toString()));
// if a binary instance is killed, it will be relaunched later
instance.on('close', () => this.instances[lang].instance = null );
this.instances[lang].instance = instance;
}
/**
* indefinitely write to instance.stdin()
* I want to avoid this behavior by just writing one time to stdin
* But if I write only one time, stdout.on('data') is never called
* Everything works if I use stdin.end() but I don't want to use it
*/
write(lang, text) {
const id = setInterval(() => {
console.log('setInterval');
this.instances[lang].instance.stdin.write(text + '\n');
}, 1000);
}
};
// simple usage example
const driver = new Driver;
const txt = "This is a random input.";
if (driver.isRunning('enGB') === true)
driver.write('enGB', txt);
else {
/**
* the arrow function is called once every N stdin.write()
* While I want it to be called after each write
*/
driver.run('enGB', data => console.log('Data received!', data));
driver.write('enGB', txt);
}
I tried to:
use cork() and uncork() around stdin.write().
pipe child_process.stdout() to a custom Readable and a Socket.
Override the highWaterMark value to 1 and 0 in stdin, stdout and the aforementioned Readable
Lots of other things I forgot...
Moreover, I can't use stdin.end() because I don't want to kill my binaries instances each time a new text arrives. Does anyone have an idea ?