How to write a JSON File over TCP Socket in express to C++ program

Question

This is in connection with the question About server-client architecture in express.js

I am currently writing the client part of the program which is supposed to be in express.jsvar

var request = require('request'),
    express = require('express'),
    path    = require('path');

const net = require('net');

var app = express();

// for Express 4.16 above use this instead of
// using body-Parser: app.use(bodyParser.json())
app.use(express.json());


// configuration setting
const PORT1 = 5000;
const port2 = 5001;
const PORT3 = 1337;
const HOST = '127.0.0.1';

app.set('port', (process.env.PORT || PORT1));

var client = new net.Socket();
var id = 0;

// start a tcp connection to connect to server
client.connect(PORT3, HOST, function() {
    console.log('SEND PORT CONNECTED TO: ' + HOST + ':' + PORT3);
});

// using Github for testing web hook
app.post('/getGithub', function(req, res) 
{
    // tester code
    //var data = "20a980dc00b413dc3d0000a3";
    //var data = "e36ace0044ed3d0cc3810000";
    var data = req.body;
    console.log(data);
        
    client.write('Hello, server! Love, Client.' + id + " ");
    client.write(data);
    res.json(data);

});

// http server location
var server = app.listen(app.get('port'), function() {
    var host   = server.address().address
    var portid = server.address().port

    console.log('App listening at http://%s:%s', host, portid)
    console.log("App listening on port " + app.get('port'));
});

// error handler
app.use(function (err, req, res, next) {
    res.status(400).send(err.message)
});

I have some questions here

How do I write a JSON object over to my server application (C++). I know of JSON.stringify(obj) will return string and could be written over?
How do I write my C++ program over the other end? I have written some C++ program but it seem there is some problem while using another express program it seem ok. when I run the C++ program, the client program in express keeps on giving me ECONNECT refused

My C++ program

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <jsoncpp/json/json.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>

int main()
{
    /* all previous code until
    printf("Reading from client\n"); */

   int listenfd = 0, connfd = 0;    //related with the server
   int MAX_SIZE = 158;
   struct sockaddr_in serv_addr;

   //json_object * jobj;
   char buf[MAX_SIZE], i;

   memset(&buf, '0', sizeof(buf));
   listenfd = socket(AF_INET, SOCK_STREAM, 0);

   serv_addr.sin_family = AF_INET;
   serv_addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
   serv_addr.sin_port = htons(1337); 

   bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr));
   printf("binding\n");

   listen(listenfd, 5);
   printf("listening\n");
   connfd = accept(listenfd, (struct sockaddr*)NULL, NULL);

   printf("Reading from client\n");
    ssize_t r;

    for (;;)
    {
        r = read(connfd, buf, MAX_SIZE);

        if (r == -1)
        {
            perror("read");
            return EXIT_FAILURE;
        }
        if (r == 0)
            break;

        printf("READ: %s\n", buf);
    }

    return EXIT_SUCCESS;
}

The error is:

Error: connect ECONNREFUSED 127.0.0.1:1337
    at Object._errnoException (util.js:1022:11)
    at _exceptionWithHostPort (util.js:1044:20)
    at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1198:14)

You need to send it as text. And the server should receive it as any other data it receives. But note that the data it receives will not be a null-terminated string. If you want to print the data using the printf format %s you need to add the null-terminator. — Some programmer dude
– Some programmer dude, Commented Dec 16, 2020 at 7:15
@Someprogrammerdude : so I should just call it client.write(JSON.stringify(data)); while on the server end(C++ code) i should just read incoming messages as text? — user1538798
– user1538798, Commented Dec 16, 2020 at 7:19
Yes that's about it. But remember that null-terminator part in the C++ program. — Some programmer dude
– Some programmer dude, Commented Dec 16, 2020 at 7:20
@Someprogrammerdude : Then could I trouble with you why my C++ server program could not work... everytime I start it up and then using the client(express) it will have the error message ECONNECT refused. — user1538798
– user1538798, Commented Dec 16, 2020 at 7:23
Now is the time to do something you should have done immediately: Add error checking in your server program. All the socket functions you call can fail, but you only check read. — Some programmer dude
– Some programmer dude, Commented Dec 16, 2020 at 7:31

Hiperion · Accepted Answer · 2020-12-16 07:21:25Z

2

It doesn't matter wich languaje is the server: once you send a Json string, is server independent: You can have a java program, a C++ program, or even, a Apache/PHP program (in this last case, with a HTTP call, using a library, or adding the headers).

First you need your json data

var obj = { name: "John", age: 30, city: "New York" };
var myJSONData = JSON.stringify(obj);

And then, you shoud do a raw socket connection:

var net = require('net');
var HOST = '127.0.0.1';
var PORT = 1337;

// (a) =========
var client = new net.Socket();
client.connect(PORT, HOST, function() {

    console.log('CONNECTED TO: ' + HOST + ':' + PORT);
    // Write a message to the socket as soon as the client is connected, the server will receive it as message from the client
    client.write(myJSONData );

});
client.destroy();

answered Dec 16, 2020 at 7:21

Hiperion

4516 silver badges12 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How to write a JSON File over TCP Socket in express to C++ program

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related