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

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.

Related

Sending JSON to all online clients without them making a request. [NodeJS]

I'm building a website, and one of the features is a public chat that anyone online can use. When a message is entered it is sent to the server and then saved to a SQL database. How could I relay this information to all the online clients without them making a request to the server? I've thought about having all clients make a request to the server every 500ms or so but I feel that would be incredibly inefficient. Any suggestions?
What you're looking for is typically called "server push" where the server can unilaterally send data to the client without the client having to "poll" or repeatedly ask for new info.
The two general technologies for server push these days are webSockets and server-sent events (SSE). In both cases, the client initiates a connection to the server and that connection is held open so that the server can send data to the client whenever it wants to without the client having to specifically poll for that data.
A webSocket is a full, two-way data channel. Either client or server can send data in either direction.
SSE is a one-way channel, the server can send data to a listening client.
You can see these articles on comparing the pros/cons of each.
WebSockets vs Server-Sent Events - ably.com
Server-sent events vs. WebSockets - logrocket.com
Difference between server sent events and Websockets in HTML5 - geeksforgeeks.org
And, there are dozens of other articles here.
You may also want to be aware of socket.io which is a widely used layer built on top of webSockets that adds more features than either of these have (a named message layer, auto-reconnect, message acknowledgement, direct message response, built-in JSON support, etc...).
Any of these can do what you're asking for. Which of these to choose really depends upon the details of your requirements.
Try making a WebSocket server. There is ws package for Node.js, and alternatively socket.io. However if your client is a web client, you can use socket.io for easy-use and setup.

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

Maintain a backend connection on NodeJS across page requests?

I'm making connections via thrift (node-thrift) to a backend server to make api calls, but the communication is bidirectional (push/pull) to NodeJS.
While a user is browsing around different URLs, and Node is churning out jade templates and javascript files via Connect/Express routes, how do I maintain the connection to the backend server, and output (as an example) the connection status as part of the rendered jade output?
I have the connection object, but what do I do with it?
Sockets and port communication is generally a new area for me, so any help would be appreciated.
Keep in mind that backend server is not communicating to the web browser as the client, but rather the NodeJS server as the client.
(updated after discussion in comments)
So it looks like thrift is TCP-based which means the node client is going to keep the connection to your thrift API server open. This is entirely independent of what your node/express app server is doing with the browser clients. So if you keep a reference to your thrift client available to all requests, by attaching it to the app object for example, you should be able to determine it's current status and include that information in HTTP responses to the browser. There's not going to be any automatic coordination or association of any kind between your express app server handling browser HTTP requests and your thrift client making RPC calls to the API server. If you want coordination, you need to code that explicitly, but sending an HTTP response to a browser isn't going to automatically close your thrift TCP connection to the thrift RPC server (and same story vice versa).

Server WebSockets and server http with node.js

All
I am developing an application which needs to communicate with WebSockets with customers online in the browser. For this I started with Node.js to create the server, so far so good, my problem is that there is another application that must communicate via http POST to my server then passes this information to my server my server passes to clients web.
I am new to the use of this technology so I apologize if I say nonsense.
1 - I can send a POST request to my server WebSocket, the application that connects customers via WebSocket, Server, may also receive the POST request and send this information to each client by ws?
2 - There is a way to open a client socket with a tag that allows me, server, send information to that client only and not at all, depending on a parameter. I want to know that each socket belongs to a specific customer and only send information to that client.
1.) If I understand you correctly then you want to broadcast information through websockets to other clients. Just take a look at the node.js modules socket.io or ws.
2.) You want to open different sockets for different urls? Like a separate websocket connection for /foo/a/bar and /foo/b/bar? Have a look at my answer here

Socket.io - Preventing multiple connections from a client

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.

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