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How to use sockets to send information from javascript to python

I want to send information from my Node.js code to Python using sockets. How can I achieve that?
In pseudo-code, what I want is this:
js:
sendInformation(information)
python:
recieveInformation()
sendNewInformation()
js:
recievNewInformation()

You should determine which code is the server and which one is the client. I assume your Python code is your server.
You can run a server in python using:
import socket
HOST = '0.0.0.0'
PORT = 9999
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
s.bind((HOST, PORT))
s.listen()
conn, addr = s.accept()
with conn:
print('Connected by', addr)
while True:
data = conn.recv(1024)
if not data:
break
conn.sendall(data)
And then you can connect your Nodejs client code to the server:
var net = require('net');
var HOST = '127.0.0.1';
var PORT = 9999;
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('Message from client');
});
// Add a 'data' event handler for the client socket
// data is what the server sent to this socket
client.on('data', function(data) {
console.log('DATA: ' + data);
// Close the client socket completely
client.destroy();
});
// Add a 'close' event handler for the client socket
client.on('close', function() {
console.log('Connection closed');
});

Socket.io client disconnects due to ping timeout / transport closed

Here's my setup:
Raspberry Pi 2 (192.168.1.101):
Sensor recording temperature, pressure and humidity.
Python3 script connected to a Raspberry Pi 3, reading sensor data and sending to Pi 3, in JSON format, every 5 seconds.
Raspberry Pi 3 (192.168.1.100):
Node.js server listening for python client on port 8888.
Socket.io listening for web clients on port 3000 (port 3000 and 80 have been opened on my router).
Web server (on port 80) with a website displaying sensor data.
JavaScript connecting to node server, using socket.io, via foobar.ddns.net:3000.
Misc:
I'm using noip.com to have a domain serving my dynamic IP address, my router lets noip know when my public IP changes. I have a URL that looks like foobar.ddns.net.
This setup seems to be working. The Python script is sending data to the node server, which is forwarding it on to any web client connected, which is displayed correctly on the website.
My issue is that the web client disconnects after 1 round of ping/pong between the client and node server.
Here's the chrome console log when connected to the server and receiving data:
The web client connects, receives some data, does a ping/pong with the server, receives some more data, then when it's supposed to ping/pong again it disconnects, then after a while it tries reconnecting and the cycle continues.
And here's the node.js log:
The first New Connection is the Python client (I'm not sure why the IP is the Pi3 address), the rest are the same web client connecting, being disconnected for ping time out, then reconnecting. The client appears to be disconnecting based on on the servers pingInterval + pingTimeout values.
Changing the pingTimeout and pingInterval values just delays the disconnect.
Here's my code:
Python Client:
import json
import socket
import bme280_sensor
import time
import os
class Connection():
def __init__(self, host, port):
self.host = host
self.port = port
def connect(self):
print('Creating socket')
try:
self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
except socket.error as msg:
print('Failed to create socket: %s' % msg)
raise
print('Socket created')
server_address = (self.host, self.port)
print('Connecting to %s:%s' % server_address)
try:
self.sock.connect(server_address)
except socket.error as msg:
print('Failed to connect: %s' % msg)
raise
print('Connected')
def shutdown(self):
print('Shutting down')
self.sock.shutdown(socket.SHUT_RDWR)
self.sock.close()
def measure_temp():
bme_data = bme280_sensor.read_all()
obj = {}
obj['temp'] = round(bme_data[2], 2)
obj['humidity'] = round(bme_data[0], 2)
obj['pressure'] = round(bme_data[1], 2)
return json.dumps(obj)
def sendData(sock):
print('Sending data')
while True:
try:
data = 'data,' + measure_temp()
sock.sendall(data.encode())
except socket.error as msg:
print("Cannot send to server: %s" % msg)
break
time.sleep(5)
connection = Connection('192.168.1.100', 8888)
while True:
try:
connection.connect()
sendData(connection.sock)
connection.shutdown()
break
except socket.error as msg:
print('Connection failed, retrying in 3 seconds.')
time.sleep(3)
print('Done')
Node.js Server:
var net = require('net');
var port = 8888;
var server = net.createServer();
// socket io listens for clients on port 3000
var io = require('socket.io')(3000,{
pingInterval: 10000,
pingTimeout: 5000,
});
// server listens for python client on port 8888
server.listen(port);
console.log('Server started');
// store the last data recorded, so when a socket.io client connects, they can get the last reading instead of waiting for the next one
global.last;
server.on('connection', function(socket){
console.log('New server connection ' + socket.address().address);
// when the server recieves data, send it to the connected socket clients
socket.on('data', function(data){
// strip the first 5 characters from the input string, parse json from the result
var actual = generateJSON(data.toString().substring(5));
// store the dta
global.last = actual;
//send the data
io.sockets.emit('data', actual);
});
});
io.on('connection', function(socket){
console.log('New io connection ' + socket.id);
// if the server has data previously recorded, send it to the new client
if(global.last){
io.emit('data', global.last);
}
socket.on('disconnect', function(reason){
console.log('io disconnect: ' + reason);
});
});
function generateJSON(data){
var dataJSON = JSON.parse(data);
var obj = new Object();
obj.temperature = dataJSON.temp;
obj.humidity = dataJSON.humidity;
obj.pressure = dataJSON.pressure;
obj.datetime = new Date().toString();
return JSON.stringify(obj);
}
Website Javascript:
var socket;
var connected = false;
function connect(){
console.log('connecting...')
if(socket){
socket.destroy()
delete socket;
socket = null;
}
socket = io.connect("http://foobar.ddns.net:3000", {
forceNew: true,
reconnection: true,
reconnectionDelay: 3000,
reconnectionDelayMax: 5000,
reconnectionAttempts: Infinity
});
console.log(socket);
socket.on("data", function(data){
var obj = JSON.parse(data);
console.log(data);
$('#temperature-value').text(obj.temperature);
$('#humidity-value').text(obj.humidity);
$('#pressure-value').text(obj.pressure);
lastUpdate = new Date();
});
socket.on('connect_error', function(error){
console.log('connection error: ' + error);
});
socket.on('connect_timeout', function(){
console.log('connection timeout');
});
socket.on('reconnect', function(){
console.log('reconnect');
});
socket.on('reconnect_attempt', function(){
console.log('reconnect attempt');
});
socket.on('reconnect_failed', function(){
console.log('reconnect_failed');
});
socket.on('reconnect_error', function(){
console.log('reconnect_error');
});
socket.on('reconnecting', function(){
console.log('reconnecting');
});
socket.on('ping', function(){
console.log('ping');
});
socket.on('pong', function(ms){
console.log('pong ' + ms + "ms");
});
socket.on('connect', function(){
console.log('connected to server');
connected = true;
});
socket.on('disconnect', function(reason){
console.log('disconnected from server: ' + reason);
connected = false;
});
}
$(document).ready(function(){
connect();
});
I'm accessing the socket.io.js script with this in my index.html:
<script src="http://foobar.ddns.net:3000/socket.io/socket.io.js"></script>
This is functional but the disconnects are rather annoying, I'd rather the client stays connected. I have a feeling that my node.js server is not setup correctly, but I can't figure out what the issue is. If there's a better way to feed data from the python script > node.js server > web clients then please let me know.
Thanks

I've solved the issue! It had nothing to do with node.js or socket.io.
The issue was on the web page I have displaying the data, I had this method to update a span showing the seconds since the last update:
function updateLastUpdateTimer(){
var seconds = (new Date() - lastUpdate) / 1000;
$('#time-since-last-update').text(formatTime(seconds) + " ago");
$('#last-updated-time').text(lastUpdate);
setInterval(updateLastUpdateTimer, 1000);
}
The issue was setInterval when it should have been setTimeout. I realised that my web page was eating up RAM, which was causing the client socket to hang and not send any data to the server, which was causing the time out!
The setInterval method runs a function every x milliseconds. DO NOT put it in the method you want to call! Call it once instead.
To anyone reading this who has the same issue with ping timeout and transport closed disconnects, check your client!

When can be socket client disconnected

please look at the code below. It's a simple program in nodeJS.
Question is why disconnect is not printed? (If you uncomment setTimeout, problem is gone)
What is the real question?: Why can't I start socketIO client and server together and close a socket immediately after connection? What is the know-how regarding connections with socketIO?
"use strict";
var Promise = require("bluebird");
var socketio = require("socket.io");
var socketio_client = require("socket.io-client");
var http = require("http");
var port = 7457;
var hostandport = "http://localhost:" + port.toString();
var server = socketio.listen(port);
var client = socketio_client(hostandport);
server.sockets.on("connect", function (socket) {
console.log("connect");
socket.on("disconnect", function () {
console.log("disconnect");
});
//setTimeout(function() {
client.disconnect();
//}, 1000);
});

You have set up your server incorrectly, do this instead:
var server = require('http').createServer(handler);
var io = require('socket.io')(server);
io.on("connect", function (socket) {
console.log("connect");
socket.on("disconnect", function () {
console.log("disconnect");
});
//More importantly, you have done this part wrong,
//the rest of your code may be functional,
//but it does not adhere to what socket.io sets out in its own API
//(http://socket.io/docs/)
socket.disconnect();
});

In Socket.io there is no such thing as connection on server side and/or browser side. There is only one connection. If one of the sides closes it, then it is closed. So you can close it from Server using socket.disconnect()
var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);
io.on('connection', function(socket){
console.log('a user connected');
socket.on('disconnect', function(){
console.log('user disconnected');
});
setTimeout(function() {
socket.disconnect();
}, 1000);
});
Goto http://socket.io/get-started/chat/ for more clarifications.

Cannot connect to secure socket.io server : ERR_SSL_PROTOCOL_ERROR

I'm trying to use socket.io with existing application. My application runs on https://somedomain.com. Its using this code to connect to socket io server:
var socket = io('https://localhost:3456/');
socket.on('connect', function () {
socket.send('hi');
socket.on('message', function (msg) {
// my msg
});
});
My socket.io server has this code to listen to incoming connections:
var io = require('socket.io').listen(3456);
io.sockets.on('connection', function(socket) {
console.log("dupa");
socket.on('message', function() {});
socket.on('disconnect', function() {});
});
dupa is never displayed on server side and in Chrome browser console I receive:
GET https://localhost:3456/socket.io/?EIO=3&transport=polling&t=1412901063154-0 net::ERR_SSL_PROTOCOL_ERROR
How can I get this possibly working?

Change https to http
var socket = io.connect("http://localhost:4000");

Your socket server is not using SSL.
First, add the secure parameter to your client (maybe redundant with the https but SSL+socket.io does weird stuff sometimes):
var socket = io.connect('https://localhost', {secure: true});
Then, you need your socket to be secure too :
var privateKey = fs.readFileSync('YOUR SSL KEY').toString();
var certificate = fs.readFileSync('YOUR SSL CRT').toString();
var ca = fs.readFileSync('YOUR SSL CA').toString();
var io = require('socket.io').listen(3456,{key:privateKey,cert:certificate,ca:ca});

User receive more than 1 notification from nodejs

This is my first time with nodejs and I have some issues with it. The main problem is that the user receive more than 1 signal from the server. The count is based on the refresh of the page.
Below is my code:
var http = require('http');
var server = http.createServer().listen(1332);
var io = require('socket.io').listen(server);
var redis = require('redis');
var sub = redis.createClient();
//Subscribe to the Redis chat channel
sub.subscribe('notification_count');
console.log("Server is running...\nClick on Ctrl+C to exit");
io.sockets.on('connection', function (socket) {
var user_id = socket["handshake"]["query"]["user_id"];
console.log("user_id", user_id);
socket.room = user_id;
socket.join(user_id);
socket.on('disconnect', function(){
socket.leave(socket.room);
});
//Grab message from Redis and send to client
sub.on('message', function(channel, message){
io.sockets.in(message).emit('message', message );
});
});
And here is the client side js code:
var socket = io.connect('localhost:1332', { query: "user_id={{ request.user.id }}" });
socket.on('connect', function(){
console.log("connected");
});
socket.on('message', function(message) {
//something
});
Basically on connection from the server I send to the server the user_id. After that I create a new room which name is the same as the user_id. Of course on disconnect the room should be delete. I have noticed that sub.on() is fired more than once, but I cannot figure out why. I will appreciate any help. Thank you in advance !

The problem is that you are using a handler inside the connection event, everytime a client connects it will execute everything inside the connection event including your sub.on
Place sub.on out of the connection event and it should stop the double messages