Node.js: devided stdout using SPAWN with exe program - c++

Question

I wrote some C++ program which is waiting for 103 data strings and response on the output with 9 strings. I would like to send data from the node app and receive the data from the output. Unfortunately I found that the output data, that I display in the console, it is not from the same reading cycle.
So the question is: Does stdin and stdout in node app has any buffer which I can flush or something?
Here is my c++ program:
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
cout << "Program is running";
vector <string> tab(103);
string nazwa;
int index = 0;
do {
for (int i = 0; i < 103; i++) {
getline(cin, nazwa);
if (!nazwa.empty() && nazwa[nazwa.size() - 1] == '\n')
nazwa.erase(nazwa.size() - 1);
if (!nazwa.empty() && nazwa[nazwa.size() - 1] == '\r')
nazwa.erase(nazwa.size() - 1);
tab[i] = nazwa;
}
for (int i = 0; i < 9; i++) {
cout << index << ": " << i+1 << endl;
}
index++;
} while (true);
return 0;
}
It simply wait for 103 strings with data from node and give back 9 stings.
Here is my node program:
var prg = null;
var str = "";
var counter = 0;
var spawn = require('child_process').spawn;
var fun = function(){
console.log("fun() start");
prg = spawn('test.exe');
};
fun();
setInterval(function() {
//console.log(".");
prg.stdin.write('0.5\n');
}, 10);
prg.stdout.on('data', function(data) {
str = data.toString(), lines = str.split(/(\r&\n)/g);
for (var i=0;i<lines.length; i++) {
console.log('node counter: '+counter+", passed data: "+lines[i]);
}
counter++;
});
The output in the node console proving that the output is divided:
fun() start
node counter: 0, passed data: Program is running
node counter: 1, passed data: 0: 1
0: 2
0: 3
0: 4
0: 5
0: 6
0: 7
node counter: 2, passed data: 0: 8
0: 9
node counter: 3, passed data: 1: 1
1: 2
1: 3
1: 4
1: 5
1: 6
1: 7
1: 8
1: 9
UPDATE:
I found 3 solutions. I had to pass data via IPC (Inter Process Communication) to avoid these standard in/out buffers.
Possible ways:
Nodejs Addons
Named pipe
Sockets communication
I used great git project JSON for Modern C++ to pass easy in use data container.
I created JSON structure and put it into the file. Now I can read this file and send it to the pipe. The main problem with pipes is that its hard to control databytes from the pipe. But if you use JSON for Modern C++ addon, you will know when you have all data.
Because in every pipe reading I wont know how many bytes I will send this time, so I created bigger buffer and after reading all data from pipe I just cut them and use JSON parser again.
After reading data (c++ side) Im preparing this data to send it back to node.
Node code:
var prg = null;
var fs = require('fs');
//parse JSON from file
var obj = JSON.parse(fs.readFileSync('data.json', 'utf8'));
var net = require('net');
var path = require('path');
var counter = 0;
//create pipe
var server = net.createServer(function(req) {
setInterval(function() {
var strobj = JSON.stringify(obj);
req.write(strobj); // send data to pipe every second
}, 1000);
rehttps://stackoverflow.com/questionsq.on('data', function(c) {
var size = c.length;
console.log(counter+': bytesize of JSON: ' + size);
var reciv = JSON.parse(c);
counter++;
console.log("Display JSON:\n %j ",reciv);
});
});
server.listen('\\\\.\\pipe\\JointsPipe');
// Spawning EXE program
var spawn = require('child_process').spawn;
var prg = spawn('test.exe');
prg.on('close', function(){
console.log("Pipe Closed");
});
C++ Program
I hope it will help someone.

Answer 1

I assume that node.js child_process.spawn creates a child process, which is sharing it's parents stdin, stdout and stderr streams. Since both the parent and the child are writing to those streams you'll get an 'intermixed' output. You can try to redirect each of those to different files and get not divided output. Or you could try to use some shared resource to communicate between the parent and the child process (eg. some socket or named pipe)