IPC : Node JS server communication with simple C code - c

Question

I have a C code, that within a infinite loop waits for an input and produces an output.
#include<stdio.h>
void flush() {
int c;
while ((c = getchar()) != '\n' && c != EOF);
}
int main() {
/*
* Load many files here
*/
double d = 0;
char input[1024];
while (1) {
d = d + 0.1;
scanf("%[^\n]", input);
printf("%lf\n",d);
fflush(stdout);
flush();
}
}
I need another Node JS service that will listen to on some port and send the output as response.
I have this code written
var http = require('http');
var spawn = require('child_process').spawn;
var child = spawn('./dummyNLU.out');
child.stdin.setEncoding('utf-8');
child.stdin.cork();
var buffer = new Buffer(100);
var app = http.createServer(function(req,res){
var string = buffer.write("HelloWorld!"); //this is for testing purpose
child.stdin.write(buffer);
child.stdin.end();
child.stdout.on('data', function(data) {
res.setHeader('Content-Type', 'text/plain');
res.end(data);
});
});
app.listen(3001);
This code I have doesn't seem seem working at all.
Node JS server terminates with an error and the web response consist of 283 lines of response instead of 1.
Can anyone please help me?? Some other approaches to solve the problem (reply to web request from a C executable code output) are also welcome.
Thank you in advance.

Answer 1

child_process.spawn
Spawn your C code binary as a child from Node (bidirectional communication)
var spawn = require('child_process').spawn
var child = spawn('main.exe')
child.stdin.end('7')
child.stdout.on('data', (data) => { console.log(data); })
child.on('close', (code) => console.log('Exit code: ' + code))
This can be tricky if its receiving multiple simultaneos requests, You will need to track the client (origin request) to do the correct response (answer to the correct requesting client)
Or make a queu and spawn a children for each request (having a maximum of X simultaneos children working at a time) so they are spawned as requested and killed once not needed (having the queu is to throttle the total number of active C process)
PoC node spawning a child command (ls) and printing the result (stdout of the spawned process)
const spawn = require('child_process').spawn
const C = spawn('ls');let r=''
C.stdout.on('data',d=>r+=d)
C.on('close', () => console.log(r));
streaming-worker
designed to give you a simple interface for sending and receiving
events/messages from a long running asynchronous C++ Node.js Addon.
Streaming data from C to Node.js