I am working on a home automation hub -- a Raspberry Pi running locally that displays weather info, controls my lights, etc. It is "networked" (and I use that term loosely) to a website via a shared MongoDB. Both the site and the hub are running Node.js/Express servers.
Essentially, I am looking to be able to enter text into a field on my website and then display it on my hub.
I'm struggling to figure out how to pass data between them. I can think of a couple ways that might get it done, but the only way I know I could get working is to implement some sort of Mongo watcher/listener to watch for changes on a specific collection. Essentially, you enter the text into the site, that updates the document in Mongo, the watcher informs the locally-running hub, which then fetches and displays the new content.
This seems hacky. Is there a better way? Is this something socket.io could manage? Maybe I'm overthinking it? Help!
You can use Socket.io, WebSocket or TCP socket to connect the two servers together and communicate that way. Or you can use a queue system like ZeroMQ or RabbitMQ and communicate that way. Or you can even make an HTTP request from one server to the other one every time you want it to grab new data - or you could even sent that data right in the request.
It would be much easier if you used Redis that supports pub/sub, see:
https://redis.io/topics/pubsub
or CouchDB that supports the changes feed:
http://docs.couchdb.org/en/2.0.0/api/database/changes.html
or RethinkDB that supports changefeeds:
https://rethinkdb.com/docs/changefeeds/javascript/
I don't think Mongo supports anything like that.
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I need my website to get real time data from the server (it is for a project in html5, css3, javascript, php, mysql).
Initially I thought about websockets but maybe it is something "beast", since I don't need two-way communication, I just need to capture on the web (in real time without the user doing anything) the values of a mysql field and depending on the themselves do one thing or another in javascript.
My system could have about 1,000 users at a time.
What system do you recommend me? Would you know of any example?
So you basically have a website and you plan on receiving notifications from the server.That to me seems like a continous flow of data from the server to you the client at irregular intervals , and the reasonable way to do it (unless you plan on saving in an IP table your clients) is via websockets.This would be the push based approach.
Once you have established connection it remains open and you can get your data continously.
Another option like mentioned above would be to continously pull data from the server (query server for changes) and this could be done with HTTP.
So if you choose push based option you could you Websockets or you could look at Server Sent Events.
For pulling (request-response) you could use HTTP or something lighter like gRPC.
For more information check the options here
The question is not if the communication is one- or two-way but which communication partner initiates a speech act. If the real-time data of your application changes asynchronously and not in a certain rhythm then the server should send updates asynchronously to the webclient. And this is actually one of the standard usages of websockets which cannot be well implemented with HTTP request/response pairs (client would have to poll).
Currently I have a Flask server that runs a small web frontend as well as a command line interface to that same server. The basic idea looks like this:
<Top section: allows file upload>
* list of files from database
<Second section: allows file manipulation/ upload>
* list of files from database
<Third section: Not files, but still allows for database changes>
* list of things made from database
Now this works well from the front end, but currently if the CLI or another client makes a change to the database, it doesn't update other clients. I have it somewhat working with JS polling and rewriting the list of files every 10s, but that seems both inefficient and also would look very messy if I had to do it for every section. I saw websockets mentioned in various forums, but I've never used them and am unsure if it would be a pain to add. I'm not trying to rewrite the whole thing for a single feature.
Final takeaway: How to update all clients better than polling/ how to do polling efficiently?
Yes you are correct. You need sockets. There are bunch of articles over the internet but I would like to give a summary and try to explain why sockets will be the best fit to your requirements.
Sockets are way of achieving two way communication between client and server without the need of polling.
There is a package called Flask-SocketIO
Flask-SocketIO gives Flask applications access to low latency
bi-directional communications between the clients and the server.
Then for the scenario where you would like to send changes to all the connected client when one client does some work to your database or something similar, you will need to use broadcasting. When a message is sent with the broadcast option enabled, all clients connected to the namespace receive it, including the sender. Here you can find details of the broadcasting using Flask-SocketIO.
Is there any simple way to make a real-time private messaging website without having to use node.js & socket.io?
I'm not asking for the code, I just want to get some sort of starting point since I really have no idea how to do it.
You can use Ajax Jquery & HTML to make a chat.
Here is one I found on Github, this might help you to learn how to make one using these coding langugaes.
Github link: https://github.com/Frug/AJAX-Chat
Why do not you want to use sockets? You will be obliged to make requests every second(you say real-time chat) and it will be hard for the sever. How about if more than 100, 1000 or 5000 users are chating ?
You better use socket.io because it avoids this kind of overloading
Writing a chat application with popular web applications stacks like LAMP (PHP) has traditionally been very hard. It involves polling the server for changes, keeping track of timestamps, and it’s a lot slower than it should be.
Sockets have traditionally been the solution around which most realtime chat systems are architected, providing a bi-directional communication channel between a client and a server.
This means that the server can push messages to clients. Whenever you write a chat message, the idea is that the server will get it and push it to all other connected clients.
I'm creating a personal project, an Android application, where user sign ins via a server are essentially. Also users will be able to share important "updates" in both a data stream that all users can have access to, and potentially down the line a data stream that will be specific to local users.
Unfortunately I have basically no idea of how to implement the server for this application. I'm confident that I'll be able to create a solution though, I just need to be pointed in the right direction. Are there any existing servers/api's that I could access that will allow me to handle my "connected" tasks? If I were to make a server myself for this application where should I start?
If you have absolutely no experience with server side coding, you should start with PHP and MySQL to create a simple API for your app.
For getting started download the XAMPP bundle that has everything you need.
SQL and PHP are fairly easy for beginners. On the client(Android) side use Volley as it is simple to understand.
However if you want to get started with Node.js, your server can be up in a few minutes with express.js
I write a browser game (php, javascript) and I do not know how to make a callback. necessary that the server itself
found a client and call the function (only had one)
Don't write a browsergame if you don't know the basics! Browsergames are way too complex to learn programming.
If you want to make the server notify a client about something you will need to keep a connection open (search keywords: COMET, long polling) as you cannot initiate connections from the server to clients.
For this I can suggest you using Firebase. It is a API that let you to add cloud Data management that your user clients do. You can use that communication to search for client.
If I understand your question, what you need is a socket. Since you're using PHP and Javascript, a WebSocket might be just what you're looking for. With WebSockets, the connection between the client and the server is persisted, so the server can just push data/messages to any or all of the clients connected to it at any point in time. Likewise, the any client connected to the server can push messages/data up to the server.
Here's a video that describes how it works a bit https://www.youtube.com/watch?v=oJxWhmt5m-o