Socket.io - Preventing multiple connections from a client - javascript

I just got started in node.js and created a server where browser clients can connect to it.
Problem: When there is an error in the nodejs server and it crashes and restarts, the connected clients will usually reconnect automatically, but I notice that many clients usually make multiple reconnections back to the server!
How can I prevent that from happening, either serverside or clientside?

I suggest implementing it server-side. Apperantly, there is no implementation of it in socket.io (Source Code), so you can use key-value caches like Redis and map every connection in the Redis and check if user is already connected.

Related

Where does all data send with nodejs method socket.write?

Good day! Where does all data send when nodejs method socket.write is called? I understand that socket runs of the server side for each client. But where exactly does data go? to client? On official nodejs documentanion there is no info about destination. Thank you for response.
You cannot successfully write to a socket unless you (or some part of your nodejs software) first connects it to some other socket somewhere.
A socket server listens for connection requests, and then accepts them as they arrive. (When you use node express to make a web server, express handles this for you.) A client connects to a socket server. Once the pair of sockets are connected, data you write into one of the sockets causes a data event on the other one.
The two sockets may be on different machines in different locations. That's the miracle of global networking.
So where does data you write go? To the other socket in the pair.
If you are using datagrams (not connections) it's slightly different. The data you write contains the destination address. But you probably are not using databgrams. If you are, you are probably using a protocol stack like RTSP or UDP instead of TCP.

Alternate of server polling?

As we know, if running application also manage sessions in main memory then is there any way for server to send responses to all web clients/browsers for new recorded data in a database.
Remember: I have not made any request to server or polling to server for new records update..
Let server make responses without web request..
Objective :
No all web browsers making request or polling to server for every certain interval therefore reducing the performance issue with the application memory..
Am just against of making so many ajax calls from every web client..
Need your ideas from your past, if experienced similar..
read about websockets and socket.io.
basically with socket.io you have a connection open between browser (client) and server and server can send data which the client than receives as an event.
the client doesn't need to send a request to get that data, only open the web socket connection.
you can look at socket.io chat example: http://socket.io/get-started/chat/
WebSocket is the best and easy solution if you don't want to go through the hassle to learn Angular or others.
Both server-side and client-side can build WebSocket, and it acts as a bridge to transmit data back and forth.
I just created an easy solution for this.
Please check my new library wsm - WebSocket Manager, it works for both server-side and client-side.
Websocket Server can be built easily; this library includes several useful features.

Connect two socket.io clients together (Establish a socket to socket, cross browser connection)

I'd like to know if there's any way to establish a P2P connection between two browsers using socket.io-client (but I'm willing to use anything else that may do the trick).
Both browsers are currently connected to a node.js app serving HTTP requests with Express, which stores both clients's IP addresses (and ports when running locally). What I'd like to do is add a third connection that links both clients (let's call them A and B) directly, so that messages/data will go straight from one client to another, without transiting through the node.js server.
Is that feasible? If so, how?
So far, I've tried connecting the two clients (let's call them A and B) with the following code:
Client A:
A_to_server_socket = io();
A_to_server_socket.on('p2p', function(address_B){
A_to_B_socket = io(address_B); // Instantiates a new socket
A_to_B_socket.on('connect', function() {
console.log('Connected!');
});
});
I'm not sure about the code for client B. However I've tried:
repeat the above code for B, using B's own address (to override the default of connecting to the server)
repeat the above code for B, this time using A's address
having B_to_server_socket listen for a new connect event
However regardless of B's code, when running A's code I'm confronted with a "Cross-Origin Request blocked" error on Firefox, or "Failed to load resource: net::ERR_CONNECTION_REFUSED" followed by "net::ERR_CONNECTION_REFUSED" on Chrome.
Any hints towards a solution, or insights for better understanding the problem and how sockets work would be most welcome.
I'll try to summarize my comments into an answer.
In TCP, a connection is made when one endpoint A connects to another endpoint B. To connect to endpoint B, that host must be "listening" for incoming connections originating from other hosts. In a typical web request, the browser establishes a TCP connection to the web server and this works because the web server is listening for incoming requests on a specific port and when one of those requests comes in, it accepts the incoming request to establish an active TCP connection. So, you must have one side initiating the request and another side listening for the request.
For various security reasons, browsers themselves don't "listen" for incoming connections so you can't connect directly to them. They only allow you to connect outbound to some other listening agent on the internet. So, if a browser never listens for an incoming webSocket connection, then you can't establish a true peer-to-peer (e.g. browser-to-browser) webSocket connection.
Furthermore, TCP is designed so that you can't have two browsers both connect to a common server and then somehow have that server connect up their pipelines such that the two browser are now just wired directly to each other. TCP just doesn't work that way. It is possible to have an agent in the middle forwarding packets from one client to another via a separate connection to each (that's how Chat applications generally work), but the agent in the middle can't simply plug the two TCP connections together such that the packets go directly from one client to the other (and no longer go through the server) as a fireman would connect two firehoses. TCP just doens't work that way. It might be possible to have some complicated scheme that involved rewriting packet headers to a packet sent from endPoint A was forwarded to endPoint B and looked like it came from the server instead, but that still involves the server as the middleman or proxy.
The usual way to solve this problem is to just let each browser connect to a common server and have the server act as the middleman or traffic cop, forwarding packets from one browser to another.
Existing P2P applications (outside of browsers) work by having each client actually listen for incoming connections (act like a server) so that another client can connect directly to them. P2P itself is more complicated than this because one needs to have a means of discovering an IP address to connect to (since clients typically aren't in DNS) and often there are firewalls in the way that need some cooperation between the two ends in order to make the firewall allow the incoming connection. But, alas, this capability of listening for an incoming connection is not something a browser from plain javascript will allow you to do.
There is no something like "connection between two browsers using socket.io-client."
But there is "Both browsers are connected to a node.js app serving HTTP requests with Express, which keeps track of both clients's IP addresses (and ports when running locally)."
If you want to have P2P connection between two browser, following may be a way to do so.
when you get client A connection, join to a room "P2P"
when you get client B connection, join to a room "P2P"
to exchange between client A and client B, use
socket.broadcast.to('P2P').emit("message", "Good Morning");
Hope this may help.

Express web sockets and a central server

I'm creating an app where the server and the clients will run on the same local network. Is it possible to use web sockets, or rather more specifically, socket.io to have one central server and many clients that are running native apps
? The way I understand socket.io to work is that the clients read the web-pages that are served from the server but what happens when your clients become tablet devices running native apps instead of web pages in a browser?
The scenario I'm working with at the minute will have one central server containing a MEAN app and the clients (iPads) will make GET requests to the data available on the server. However, I'd also like there to be real-time functionality so if someone triggers a POST request on their iPad, the server acknowledges it and displays it in the server's client-side. The iPad apps will (ideally) be running native phonegap applications rather than accessing 192.168.1.1:9000 from their browser.
Is this technically possible to connect to the socket server from the native apps or would the devices have to send POST requests to a central server that's constantly listening for new 'messages'? I'm totally new to the whole real-time stuff so I'm just trying to wrap my head around it all.
Apologies if this isn't totally clear, it's a bit hard to describe with just text but I think you get the idea?
Correct me if I am wrong.
You have multiple iPads running native app. They send a POST request to your node JS server which is running in a computer in the same local network. Whenever the server receives a request from app, you want to display that a request has been received in your computer screen.
If my assumptions about the scenario is correct, then it is fairly easy to do. Here are the steps to do it.
Create a small webpage (front end). Load socket IO in the front end page like this -
<script type="text/javascript" src="YOUR_SERVER_IP/socket.io/socket.io.js"></script>
Then connect to server using var socket = io(). This should trigger connection event in your backend.
Handle all POST request from apps normally. Nothing special. Just add a small snippet in between. socket.emit('new_request', request_data). This sends new_request event to front end.
Handle the new_request in your front end using socket.on('new_request', function(request_data) { ... });. That's it. No need to add anything to your native app for realtime update.
The second step would be a little complicated as it is necessary to make socket variable available inside all POST requests. Since you chose node.js, I don't think you need any help with that.
Not totally clear on your project, but I'll try to give you some pointers.
An effective way to send data between native apps and a server is using a REST server. REST is based on HTTP requests and allows you to modify data on the server, which can connect to your database. The data returned is typically either JSON or XML formatted. See here for a brief intro: http://www.infoq.com/articles/rest-introduction
Android/iOS/etc have built in APIs for making HTTP requests. Your native app would send a request to the server, parse the response, and update your native UI accordingly. The same server can be used from a website using jQuery ajax HTTP requests.
Express.js is more suited to serving web pages and includes things like templating. Look into "restify" (see here: mcavage.me/node-restify/) if you just want to have a REST server that handles requests. Both run on top of node.js (nodejs.org).
As far as real-time communication, if you're developing for iOS look into APNS (Apple Push Notification Service). Apple maintains a persistent connection, and by going through their servers you can easily send messages to your app. The equivalent of this on Android is GCM (Google Cloud Messaging).
You can also do sockets directly if that's easier for you. Be careful with maintaining an open socket on a mobile device though, it can be a huge battery drain. Here's a library for connecting ObjC to Socket.IO using websockets, it may be useful for you: https://github.com/pkyeck/socket.IO-objc
Hope that helps!
To answer your question, it is definitely possible. Socket.io would serve as the central server that can essentially emit messages to all of the client. You can also make Socket.io listen for the messages from any of the clients and serve the emitted message to the rest of the clients.
Here's an example of how socket.io can be used. Simply clone, npm install, and run using 'node app.js'
All you have to do is to provide a valid server address when you connect your socket from the iPad clients:
var socket = io.connect( 'http://my.external.nodejs.server' );
Let us know if you need help with actual sending/receiving of socket events.
It is possible to connect to Websockets from your apps.
If you are using PhoneGap then you need a pluging that gives support to websockets in your app (the client) and then use websocket like normal way using Javascript see this.
If your app is native iOS look into this it could help you.
The primary use of the Sockets in your case is to be a bidirectional "pipe" between an app and server. There is no need of server sending the whole web-page to the native app. All what you need is to send some data from server to the client(app) in response to POST (or GET) request and then using this data on client side to update client's UI in real-time. If you are going to use moderate amount of devices (say tens of them), you may have connected all of them to the server permanently keeping individual socket connection open for every individual link server-to-app. Thus you may deliver data and update client's state in real time.
In fact web browsers also employ sockets to communicate to web servers. However as in general case there is no control on amount of concurrent clients in Internet, for the sake of limited networking resources conservation, servers do not keep sockets open for a long time, closing it just after the web-page was sent to client (or timeout has expired). That's how HTTP protocol works on the low level. The server waiting for the HTTP clients (browsers) by listening the 80 port, responding them by sending the whole web page content, then closing the connection and keep waiting for another requests on the same port.
In your case it's basically a good idea to use socket.io as it's a uniform implementation of sockets (ok WebSockets) on both client and server side. The good starting point is here

Can you connect client to client via web sockets without touching the server?

I don't quite know how to search this in google:
"client to client websocket connections"
"browser to browser websockets"
"websockets without a server"
Haha, is there a way for someone on a webpage in the browser to communicate directly to another person on a web page in the browser, without touching the server?
I am very familiar with socket.io, but that requires all clients emit messages to the server, which can broadcast them to the other connected clients. I am not familiar with the details of web sockets though, so maybe there's a way to communicate without sending messages through the server.
Is this possible? I just want to know the scope of web socket functionality, the limits you can take them too, etc.
Not Web Sockets, but four years later and now we've got browser-to-browser communication!
http://www.webrtc.org/
There are JS libraries built around it to make it easier (e.g. https://simplewebrtc.com/). However, it does still require a server to orchestrate connections.
I know this question is ancient, but it showed up in Google when I searched so it likely will for others!
This is not possible, you have to have the server in the middle.
For an application to accept connections, it has to have a server port open and listening for incoming requests. You cannot have a server socket exposed from a browser. I dont know if you can expose a server socket from within an applet. But even if you could, you would need to know the IP address of the other client for establishing a peer to peer connection.
Well, technically when you broadcast, the client emits to the server, the server broadcasts to everyone. I don't think with the current architecture of the web peer to peer connections like this is possible.
But it is possible that a client send a message to server specifying another client ID, and the server sending it to the other clients using sessions.
The moment you have a client listening for websockets (which you have to do in other to communicate), it becomes a server.

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