Q:

Difficulties in building socket communication between c++ and node.js (server)

I try to build a socket communication between c++ and a node.js server.
This is my index.js code:
'use strict';

const express     = require('express');
const app         = express();
const serverHttp  = require('http').Server(app); 
const io = require('socket.io')(serverHttp);

const port = 8081;

io.on('connection', function (socket) {   
    socket.on('message', function (data) {
        console.log("key received!!!" + data);
    socket.emit('server', 'hello socket io');
        console.log("sent server msg");
    });
});

serverHttp.listen(port, function() {  
    console.log("init!!!");    
});

and this is my c++ code which compiles successfully:
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

#ifdef _WIN32
#include <winsock2.h>
#include <ws2tcpip.h>
#else
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#endif

#ifdef _WIN32
#define close(sockdep) closesocket(sockdep)
#define perror(errmsg) { fprintf(stderr, "%s: %d\n", (errmsg), WSAGetLastError()); }
#endif

#define net_assert(err, errmsg) { if ((err)) { perror(errmsg); assert(!(err)); } }

#define SERVER "localhost"
#define PORT 8081
#define BLEN 128

int
main(int argc, char *argv[])
{
  struct sockaddr_in server;
  struct hostent *sp;
  int sd;
  int n;
  char buf[BLEN];
#ifdef _WIN32
  int err;
  WSADATA wsa;
  extern int write();
  
  err = WSAStartup(MAKEWORD(2,2), &wsa);  // winsock 2.2
  net_assert(err, "sample client: WSAStartup");
#endif

  sd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);

  memset((char *) &server, 0, sizeof(struct sockaddr_in));
  server.sin_family = AF_INET;
  server.sin_port = htons((u_short) PORT);
  sp = gethostbyname(SERVER);
  memcpy(&server.sin_addr, sp->h_addr, sp->h_length);

  connect(sd, (struct sockaddr *) &server, sizeof(struct sockaddr_in));
    
  n = recv(sd, buf, sizeof(buf), 0);
  while (n > 0) {
    write(1, buf, n);
    n = recv(sd, buf, sizeof(buf), 0);
  } 

  close(sd);

#ifdef _WIN32
  WSACleanup();
#endif
  exit(0);
}

My environment is Mac, and I am using Xcode to compile the c++. I connect the node with node index.js to the localhost and also compiled and run the c++ program. However, when I open localhost:8081, I receive this error in the console:
GET http://localhost:8081/ 404 (Not Found)        localhost/:1 

Refused to load the image 'http://localhost:8081/favicon.ico' because it violates the following Content Security Policy directive: "default-src 'none'". Note that 'img-src' was not explicitly set, so 'default-src' is used as a fallback.            localhost/:1

I am very new to programming, and I would appreciate it if you clarify what is wrong. I cannot recognize where is the send and receive codes in the c++, as it is very different from JavaScript. So, how can I just build a simple communication where I only want to send an array from the c++ to the index.js?

A:

Your approach can not work because of the confusion made between socket.io, which is a protocol defined to work with other socket.io clients or servers, and the raw TCP socket created in C++, which will work with other TCP sockets.
What you are creating in the C++ code is a TCP socket, which sadly has nothing to do with what socket.io uses. Socket.io enables communication using HTTP streaming or WebSocket (another protocol) wherever available.
Here is an example of a C++ library that seems to implement the socket.io protocol. I have never used it myself, but it seems to be what you are searching for. Try using this on the C++ side, or implementing a raw tcp socket on the node.js side. This library might be well-suited for that.
I recommend this tutorial to get you started on the basics of implementing a client-server communication in straight C++, then you can go from there to figure how to create the client in nodejs.

