C++ non-blocking proxy check/open

Question

I have an issue with a program written in C++. I want to open a SOCKS5 proxy on a free port then check if is ok (check with curl), then release the I/O blocking. This is the code :

C++

main()
{
    char* s_sockshost = "127.0.0.1";
    socks_port = find_empty_port();

    if(fork())
    {
        // child process continues and opens a socks
        open_proxy();
    }
    else
    {
        // parrent process just checks something then dies      
        for(int i = 0; i < 20; i++)
        {
            proxytest = curlsockstest(s_sockshost,socks_port);

            if(proxytest)
            {
                break;
            }

            sleep(1);
        }

        if(proxytest)
        {
            if(hitdebug >= 3) printf("check_result : is opened on %s",socks_port);

            exit(0); // kill just this process
        }
        else
        {
            if(hitdebug >= 3) printf("check_result : is bad\n");

            kill(getppid(), SIGKILL); // kill both processes
        }
    }
}

If i do this from cmd like

./proxy; ls -al;

then it is executing and executes the command after it, but if i do it from PHP or NODEJS it is hanging, like expecting to finish.

NODEJS:

var exec = require('child_process').exec;
var cmd = './proxy; ls -al;';


setTimeout(function(){

    console.log("Timer");

    exec(cmd, function(error, stdout, stderr) {
        console.log("error: ");
        console.log(error);
        console.log();

        console.log("stdout: ");
        console.log(stdout);
        console.log();

        console.log("stderr: ");
        console.log(stderr);
        console.log();
    });

    console.log("Timer end");

},2000);

PHP:

<?php

echo "Run start\n";
$array_exec = array();
// exec("./proxy",$array_exec);
system("./proxy");

var_dump($array_exec);
echo "Run end\n";

?>

What is the explination and how can i solve this?

I am thinking to make PHP and NODEJS comunicating with this C++ app with sqlite or something like that...

Answer 1

The system() function would wait until the process is finished and collect the entire output.

You should either use daemon for your C++ or you can simply change it to: ./proxy & and if you don't need output, ./proxy & > /dev/null

<?php
echo "Run start\n";
$array_exec = array();

shell_exec("./proxy &",$array_exec);
var_dump($array_exec);
echo "Run end\n";
?>

Answer 2

Node.js

const { spawn } = require('child_process');
const ls = spawn('proxy');//@see https://nodejs.org/api/child_process.html#child_process_class_childprocess

ls.stdout.on('data', (data) => {
  console.log(`stdout: ${data}`);
});

ls.stderr.on('data', (data) => {
  console.log(`stderr: ${data}. We should stop the child_process`);
  ls.kill('SIGTSTP');
});

ls.on('close', (code) => {
  console.log(`child process exited with code ${code}`);
});

Update

instead of kill can it be something as deatach() instead of ls.kill('SIGTERM'); ? like send it in background? i will try also your variant, it will help me also

This is not part of Node.js staff. There is a part of the Unix signals list:

• SIGINT means interrupt. By default, this signal causes the process to terminate. In terminal you can press Ctrl-C (in older Unixes, DEL) for sending SIGINT;
• SIGTSTP means terminal stop. By default, this signal causes the process to suspend execution. In terminal you can press Ctrl-Z for sending SIGTSTP;
• SIGQUIT means quit. This signal causes the process to terminate and dump core. In terminal you can press Ctrl-| for sending SIGTSTP.