How to call C function from nodeJS

Question

I have some C functions that I need to call frequently from nodeJS (less than 1 second time intervals). The C function takes in an argument and returns a value, which might be an int or an array.

It can be as simple as below:

int main() {
    int x = 2;
    return x;
}

And I need to get the value x in nodeJS and be able to do console.log(x)

I tried using node-ffi, but I read from the internet that it has a large overhead and is thus inefficient for frequent function calls.

I also considered writing addons but it seems very troublesome (with unfamiliar V8, C++ code and all that...)

And there is not much resources regarding integration between nodeJS and C (they are mostly nodeJS with C++)

Could somebody help shed some light on this? Thanks.

Answer 1

change your c code to

// myProgram.c
#include <stdio.h>
int main(void){
    puts("4");
    return 0;
}

compile it with gcc, in the same directory as your node file

$ gcc -o myProgram myProgram.c

in your node file, require exec()

const { exec } = require("child_process");

and use it like so:

exec("./myProgram", (error, stdout, stderr) => console.log(stdout));

This works well, it spins up a new process every time.

If, on the other hand, you want to keep the child process running, and call a function in that code from node, you can do that like this:

// multiplyBy2.c

#include <stdio.h>
#include <stdlib.h>

int timesTwo(int x){
    return x*2;
}

int main(void){
  char buff[100];
  int input,output;
  while(1){
    gets(buff);
    input = atoi(buff);
    output = timesTwo(input);
    printf("%d", output);
    // you must flush stdout or else node will hang!
    fflush(stdout);
  }
  return 0;
}

compile multiplyBy2.c and then:

// myNodeApp.js

const {spawn} = require('child_process');
const __delay__ = t => new Promise(resolve=>setTimeout(()=>resolve(), t))
const ch = spawn('./multiplyBy2')

var result=undefined;

ch.stdout.on("data",(data)=>{
    result = parseInt(data.toString())
})

async function multiplyBy2InC(num){
    ch.stdin.write(`${num}\n`)
    while(result==undefined)
      await __delay__(1)
    const output = result
    result = undefined
    return output
}

// now you could call it like this, it will print 20 to the console
multiplyBy2InC(10).then(r=>console.log(r))