I am completely new to Rust and Actix so apologies if this is a stupid question but i cant seem to find any information or examples on how this would be done.
I am trying to build a server with Actix in rust that is able to sent SSEs to connected clients. Ive followed the code in this example and it seems to work fine but what i want to do is for my server to decide to suddenly send SSEs and not when its driven through client interactions. Right now the only way to send an SSE is if a client sends it through a URL call which actix has a handler for. What if i have some other part of my server, perhaps another worker thread that reads data from a disk or another dll and then based on that decides to suddenly send SSEs to all clients?
I find it hard to see how thats supposed to work because if you want access to your mutable data that holds the registered SSE clients, it needs a copy/clone of the mutable data wrapped in an arc. Could someone give some guidelines on how i should proceed in getting actix to send SSE data thats not client driven from the web?
Related
I wonder how do I use socket.io properly with my express app.
I have a REST API written in express/node.js and I want to use socket.io to add real-time feature for my app. Consider that I want to do something I can do just by sending a request to my REST API. What should I do with socket.io? Should I send request to the REST API and send socket.io client the result of the process or handle the whole process within socket.io emitter and then send the result to socket.io client?
Thanks in advance.
Question is not that clear but from what I'm getting from it, is that you want to know what you would use it for that you cant already do with your current API?
The short answer is, well nothing really.. Websockets are just the natural progression of API's and the need for a more 'real-time' interface between systems.
Old methods (and still used and relevant for the right use case) is long polling where you keep checking back to the server for updated items and if so grab them.. This works but it can be expensive in terms of establishing a connection, performing a lookup, then closing a connection.
websockets keep that connection open, allowing both the client and server to communicate real time. So for example, lets say you make an update to your backend data and want users to get that update, using long polling you would rely on each client to ping back to the server, check if there is an update and if so grab it. This can cause lags between updates, some users have updated data while other do not etc.
Now, take the same scenario with websockets, you make an update to the backend data, hit submit, this then emits to your socket server. Socket server takes the call, performs the task ( grabs updated data ) and emits it to the users, each connected user instantly gets that update.
Socket servers are typically used for things like real time chats or polling where packets are smaller but they are also used for web games etc. Depending on the size of your payloads will determine how best to send data back and forth because the larger the payload the more resources / bandwidth it will take on the socket server so its something to consider.
I'm currently working with node.js, using the socket.io library, to implement a simple chat application. In this applicatio, for irrelevant reasons, I want to setup a system in which a client can ask for a piece of information to the server. The server then broadcasts this request to all other online sockets which will respond with the the answer if they have it. The server then finally returns (the first) response it receives to this original client socket that made the request.
Naturally, the client might receive multiple responses, while only one is needed. Therefor, as soon as one has been received, the others should be discarded. However, it feels like I should use some kind of synchronized datastructure/code to make sure this check for "If an answer has already been received" works as intended.
I've done some searching on this subject but I've seen several mentions of node.js using an event-driven model and not requiring any synchronized code/datastructures, as there are no multiple threads. Is this true? Would my scenario not require any kind of special attention to synchronization and would it just work? Or would I need to use some synchronization methods and if so, which ones?
Code example:
socket.on('new_response', async data => {
await processResponse(data)
});
Due to the fact I am working with encryption I have to make use of async/await, which further complicates things. The processResponse function does a check whether a response has been received already, if not, it processes it, else, it ignores it.
I would suggest something as simple as including a uniqueID in each broadcast to the clients asking if they have a piece of information. The clients then include that same uniqueID in any response they send.
With that, your server can receive answers from the clients and just keep track of which uniqueID values it has already received an answer for and then, if an answer has already been received for that uniqueID, then it would just ignore the later clients that respond.
The uniqueID is server-side generated so it can literally just be an increasing number. You can store the numbers used so far in a server-side Set object so you can quickly look up if you've already received a response for that uniqueID.
Then, the only thing left to do is to age these uniqueIDs away in the Set at some point so they don't accumulate forever. A simple way to do that would be just replace the Set object with a second one every 15 minutes or so, keeping one older generation around so you can check both of them.
I'm working on a chat application and using socket.io / node for that. Basically I came up with the following strategies:
Send message from the client which is received by the socket server which then sends it to the receiving client. On the background I store that to the message on the DB to be retrieved later if the user wishes to seee his old conversations.
The pros of this approach is that the user gets the message almost instantly since we don't wait for the DB operation to complete, but the con is that if the DB operation failed and exactly that time the client refreshed its page to fetch the message, it won't get that.
Send message form the client to the server, the server then stores it on the DB first and then only sends it to the receiving client.
The pros is that we make sure that the message will be received to the client only if its stored in the DB. The con is that it will be no way close to real time since we'll be doing a DB operation in between slowing down the message passing.
Send message to the client which then is stored on a cache layer(redis for example) and then instantly broadcast it to the receiving client. On background keep fetching records from redis and updating DB. If the client refreshes the page, we first look into the DB and then the redis layer.
The pros is that we make the communication faster and also make sure messages are presented correctly on demand. The con is that this is quite complex as compared to above implementations, and I'm wondering if there's any easier way to achieve this?
My question is whats the way to go if you're building a serious chat application that ensures both - faster communication and data persistence. What are some strategies that app like facebook, whatsapp etc. use for the same? I'm not looking for exact example, but a few pointers will help.
Thanks.
I would go for the option number 2. I've been doing myself Chat apps in node and I found out that this is the best option. Saving in a database takes few milliseconds, which includes the 0.x milliseconds to write in the databse and the few milliseconds of latency in communication ( https://blog.serverdensity.com/mongodb-benchmarks/ ).
SO I would consider this approach realtime. The good thing with this is that if it fails, you can display a message to the sender that it failed, for whatever reason.
Facebook, whatsapp and many other big messaging apps are based on XMPP (jabber) which is a very, very big protocol for instant messaging and everything is very well documented on how to do things but it is based in XML, so you still have to parse everything etc but luckily there are very good libraries to handle with xmpp. So if you want to go the common way, using XMPP you can, but most of the big players in this area are not following anymore all the standards, since does not have all the features we are used to use today.
I would go with doing my own version, actually, I already something made (similar to slack), if you want I could give you access to it in private.
So to end this, number 2 is the way to go (for me). XMPP is cool but brings also a lot of complexity.
Is it possible to detect new data from the server as it is sent? For example, with express.js:
res.write('Processing 14% or something');
and then display that on the page with a progress bar.
Edit:
My original question was a bit confusing so let me explain the situation. I have created a page where users can upload song files. These files are then converted (using ffmpeg) to .ogg and .mp3 files for the web. The conversion takes a long time. Is it possible to send real time data about the conversion back to the client using the same XMLHttpRequest that sent the files?
If i understand correctly you are trying to implement event based actions. Yes node.js has got some excellent web socket libraries such as socket.io and sack.js
You need to understand nodejs event driven pattern.
Websocket protocol helps maintain full duplex connection between server and client. You can notify clients when any action happens in server and similar you can notify server when any action happens in client. Libraries provide flexibility to broadcast event to all connected client or selected ones.
So it is basically emit and on that you will be using often.
Go through the documentation, it will not take much time to learn. Let me know if you need any help.
Brief Description:
Well, since many days I've been looking for an answer to this question but there seems to be answers for 'How to create a Push Notification Server' and like questions. I am using node.js and it's quite easy to 'create' a push notification server using sock.js (I've heard socket.io isn't good as compared to sock.js). No problem till here. But what I want is how to model such a server.
Details:
OK, so, let's say I've an application where there's a chat service (just an example this is, actual thing is big as you might have guessed). A person sends a message in a room and all the people in the room get notified. But what I want is a 'stateful' chat - that is, I want to store the messages in a data store. Here's where the trouble comes. Storing the message in the database and later telling everyone that "Hey, there's a message for you". This seems easy when we need the real-time activity for just one part of the app. What to do when the whole app is based on real-time communication? Besides this, I also want to have a RESTful api.
My solution (with which I am not really happy)
What I thought of doing was this: (on the server side of course)
Data Store
||
Data Layer (which talks to data store)
||
------------------
| |
Real-Time Server Restful server
And here, the Real-time server listens to interesting events that the data-layer publishes. Whenever something interesting happens, the server notifies the client. But which client? - This is the problem with my method
Hope you can be of help. :)
UPDATE:
I think I forgot to emphasize an important part of my question. How to implement a pub-sub system? (NOTE: I don't want the actual code, I'll manage that myself; just how to go about doing it is where I need some help). The problem is that I get quite boggled when writing the code - what to do how (my confusion is quite apparent from this question itself). Could please provide some references to read or some advice as to how to begin with this thing?
I am not sure if I understood you correctly; but I will summarize how I read it:
We have a real-time chat server that uses socket connections to publish new messages to all connected clients.
We have a database where we want to keep chat logs.
We have also a restful interface to access the realtime server to get current chats in a lazier manner.
And you want to architect your system this way:
In the above diagram, the components I circled with purple curve wants to be updated like all other clients. Am I right? I don't know what you meant with "Data Layer" but I thought it is a daemon that will be writing to database and also interfacing database for other components.
In this architecture, everything is okay in the direction you meant. I mean DataStore is connected by servers to access data, maybe to query client credentials for authentication, maybe to read user preferences etc.
For your other expectation from these components, I mean to allow these components to be updated like connected clients, why don't you allow them to be clients, too?
Your realtime server is a server for clients; but it is also a client for data layer, or database server, if we prefer a more common naming. So we already know that there is nothing that stops a server from being a client. Then, why can't our database system and restful system also be clients? Connect them to realtime server the same way you connect browsers and other clients. Let them enjoy being one of the people. :)
I hope I did not understand everything completely wrong and this makes sense for the question.