This question isn't a code-level issue but merely a functionality question / brainstorm.
Within my PHP script I want to send a notification to another user in real time, there's 1 way I've thought of to do this, if you know any better ones be sure to leave them in the comments!
My idea for this functionality is to insert into a databse table with the user's id and the message, then on the user's end constantly loop a select request looking for notifications corresponding to their id within $_SESSION, if it's found a message then delete it from the table and display it to the user.
This seems like it could "strain" my database and I'm wondering if there's a cleaner way to do this, it would also be much appreciated if somebody could post a javascript loop with a 3 second delay and an ajax post to a php file within it,
Thanks all,
James
The cleaner way to do this would be with websockets. Polling, long polling, and streaming are going to have exactly the problem you thought you were going to have.
The message recipient needs to be listening via broadcast also through websockets. The server will notify all websockets listening for that particular event.
You don't want to block with database read and writes. Just take the action from one user and send it to all the other websockets listening for that event (the other user's client side instances)
For event history you would consider persisting to a database with a message queue.
With a properly indexed, well-structured table, it won't be a strain to the db at all. Of course, this assumes your interval is reasonable (3 seconds you mentioned is great). That's how all real-time session-checking websites work. Those that need more than that, such as chat systems, basically anything that passes data more frequently and/or in larger packets, they use websockets.
Use Websockets or Server-Sent-Events
just an idea:
User-1 send message to the Server {"message" : "hello", "target" : "User-2"}
Server checks the message and redirect it to the target User
User-2 listening for events from Websocket or Server-Sent-Events
Related
Hi so first I apologize if my query may seem unclear, it’s first trying to do what I’m doing and I haven’t full idea around the intricacies and lingo lol.
So basically I’m running a NodeJs web server with React handling my front end. I’ve got Express to help manipulate user sessions and I just came by Server-Sent-Events as a way to send one-way messages(which is what I need to do). So far I’m able to send updates and messages via cURL on the terminal and running JS scripts, however these updates/messages go to every active client session but I want/need to be able to send these messages to specific active client sessions/connections.
Example: 5 client connections are established (session IDs A,B,C,D,E), now I want to send an alert message to session E only and manually.
I’m still green with NodeJs/Express and the concept of SSEs however I’m learning as I go for this pet project.
Send help
What you want is how SSE works. It is a dedicated connection between a client and a server process.
however these updates/messages go to every active client session
If that is what you see then your node script is running the exact same code for each client.
I think your question might be higher up - how to organize the data messaging? That is too big a topic for a single StackOverflow question, because it will depend on so many factors specific to your use case.
But one way would be to have an SQL database, with one record for each user. The node script polls that database table and if the record for the current user changes, it sends the new data to them. Then to send data to user E, you just edit the database record for user E.
I have built a web application using AngularJS (front-end) and PHP/MySQL (back-end).
I was wondering if there is a way to "watch" the MySQL database (without Node.js), so if one user adds some data to it, the changes are synced to other users too.
E.g. I know Firebase does that, but it's object oriented database and I am unable to do the advanced queries there like I do with SQL.
I was thinking to use $interval and $http and do ajax requests, so that way I could detect changes in the database. Well, that's possible, but it'll then do thousands of http requests to the server everyday and plus interpret php on each request.
I believe nothing is impossible, I just need an idea to do this, which I don't have, so that's why I am asking for a help here.
If you want a form of "real-time communication" you'll likely have to incorporate some form of long-polling from the client. Unless you use web sockets, but that's a big post about a bunch of different things. You're right to be concerned about bandwidth and demand on the DB though. So here's my suggestion:
If you don't have experience with web sockets then log your events in a separate table/view and use the pub/sub method to subscribe entities to an event, and broadcast that event to the table. Then long-poll against the watcher view to see when changes may have occurred. If one did occur then you query for the exact value.
Another option would be to use some query system with "deciders" that hold messages. Take a look at Amazon's SQS platform for a better explanation of how this could work. Basically you have a queue that holds messages and a decider chooses where to store the message using some hash or sorting method (to reduce run time). When the client requests an update, the decider finds any messages that would apply based on the hash/sort and returns them. Then you just have to decide how and when to destruct the messages.
The second option would require a lot more tinkering though, so it's really about your preference. I think what you'll find the difficulty to be is that most solutions have to deal with the fact that the message has to be delivered 1 or More times and you'll need to track when someone received the message and if it can now be deleted from the queue/event table or if you still need to wait. Otherwise you'll consume a lot of memory.
Server: NGINX/PHP running Laravel 5
Let's assume I have two users on different computers with sessions to the application.
User 1: makes an ajax call that is handled by one of the server controllers.
User 2: needs to get notified of this as soon as user 1 made this call to the controller.
Now, user 2 can have a javascript polling mechanism which asks the question "has this happened?" repeatedly, but ideally I'd like to avoid the constant calling and have him/her notified upon occurance instead.
Is there any way to have like an "open socket" for user 2 to be notified when certain events occur in the controller?
Ideally I'd like to avoid installing a third party messaging system, XMPP Etc on my server. Is there any best practice where this functionality can be achieved?
Sockets.io is indeed a good solution for this. I'll be using it on both the server side (Separate NodeJS server for this), and the client javascript side.
I wrote a web page where there is a zone for user's comments.
Any authenticated users could post a comment.
As many users could post comments almost simultaneously, I want the comments list to be auto-refreshed.
Thus, I think about using WebSockets.
My thought are about a good/best practice for this use case:
Once a comment is posted, should WebSockets process read the current comments list on database and send a Json response containing all the new comments? This would allow the client to directly append the new comments on the DOM (JS).
Or should WebSocket just check the database (or queue if using a message queue (Redis, RabbitMQ etc..) for instance) and act just like: "Hey, I have new comments, click here if you want to see them !". This solution would only signal the presence of new comments, without bringing all those comments to the client. The workflow of retrieving the events would then involve by the client (by clicking on this sentence for instance) e.g using the traditional Ajax direction: client => server.
It is highly possible that a user posts a comment, then navigates to another page of the website. Therefore, a websocket response containing the whole new comments would be useless. A simple notification would then be possible, as most of known websites do for instance with the "+1" counter or more relevant to the "comments" scenario: "1 new comment available".
Which way should I choose?
I think to decide which data to push is mostly a matter of UI usability / user experience, as opposed to which technology is being used to interact with the server. We should avoid changing the UI with server pushed data in a way that would surprise the user in a negative way, for example having the comment feed constantly growing without any intervention from him.
But in the case of a realtime chart, it's probably better to push the data directly into the chart, that would be what the user expects.
In the case of the comment feed the reason why most sites go with the 'click to load' approach is because of user experience, so I think that is probably the best approach.
I use a combination of both....
In some pages the websocket communication contains the actual data--sort of like a stock ticker update.
And in other cases, the websocket communication just says -- all users viewing xyz data--refresh it. And then the browsers performs an ajax to obtain the new data and the grid is smartly refreshed in such a way that only the changed cells are modified on screen using innerHTML and the new rows are added and deleted rows are removed.
In cases like stackoverflow, it makes sense to show a message, "Got new stuff to show--want to see it?"
When I establish the websocket in the browser, I pass a page Id in the url and the cookies are passed too. So websocket server knows--the user cookie and the page which is being viewed.
Then in the database (or middle tier logic) communicates to the websocket server with messages such as: This message is for users viewing 'xyz' page: smartly refresh grid 'abc'. And the websocket server broadcasts the message.
Because the protocol allows you to pass anything you like, you have the ability to make it anyway you like.
My advise it to do what's best in each particular situation.
I'm not really sure where to begin.
I'd like to be able to update a users current page when another user either updates my database or sends a specific GET/POST request (I could write it either way).
I was thinking server sent events but I made a quick test using my php server and realized a couple things. First I would need an event loop based server because using php I'd have to create a loop to keep checking my database for a specific change. Second I realized this would be very server intensive so I should look into another method.
So to explicitly ask my questions...
Is it possible to update a users current page when someone else sends a GET request to a php file on my server? How?
If I need an event loop based server what is my best option? node.js?
Is this possible with sockets if not with SSE? SSE makes more sense because I'm not looking for any user feedback.
Thanks
Websockets and something like SignalR for ASP.Net could help you. Check out the options here
You can use Ajax too.
Like this : Here