I am new to Websockets. While reading about websockets, I am not been able to find answers to some of my doubts. I would like if someone clarifies it.
Does websocket only broadcasts the data to all clients connected instead of sending to a particular client? Whatever example (mainly chat apps) I tried they sends data to all the clients. Is it possible to alter this?
How it works on clients located on NAT (behind router).
Since client server connection will always remain open, how will it affect server performance for large number of connections?
Since I want all my clients to get real time updates, it is required to connect all my clients to server, so how should I handele the client connection limit?
NOTE:- My client is not a Web browser but a desktop application.
No, websocket is not only for broadcasting. You send messages to specific clients, when you broadcast you just send the same message to all connected clients, but you can send different messages to different clients, for example a game session.
The clients connect to the server and initialise the connections, so NAT is not a problem.
It's good to use a scalable server, e.g. an event driven server (e.g. Node.js) that doesn't use a seperate thread for each connection, or an erlang server with lightweight processes (a good choice for a game server).
This should not be a problem if you use a good server OS (e.g. Linux), but may be a limitation if your server uses a desktop version of Windows (e.g. may be limited to 200 connections).
Related
I'm a beginner to TCP client-server architecture. I am making a client-server application in C++ I need the server to be able to accept messages from multiple clients at once. I used this IBM example as my starter for the server
server.
The client side is irrelevant but this is my source client.
The problem is with the server side it allows multiple clients to connect but not asynchronously, so the server will connect with the second client after the first one finishes. I want the server to watch for messages from both clients.
I tried to read about select() on the Internet but I couldn't find anything to make the IBM code async. How can I edit the server code to allow the clients to connect and interact at the same time?
When taking a look at the Pusher Servcer and their Client / Server API I am having some problems trying to figure out how Pusher will help me allow bi-directional communication between devices / apps.
I am having multiple smaller devices / apps in the field that should return their status to a server or another client, which acts as a dashboard to browse all those devices and monitor status, etc.
In my understanding this can be done using traditional WebSockets and a cloud-server in between which manages all connections between those clients - something I though Pusher would be.
But after reading through the docs I can't really see a concept of bi-directional data communication. Here's why:
To push data to the clients I have to use one of Pushers Server Libraries
To receive that Data I have to use one of Pusher Client Libraries
This concept however does not fit into what I need. I want to:
Broadcast to Clients.
Clients can send Data directly to Clients (Server acting as Gateway / Routing).
Clients can send Data to Server.
Server can send / response to unique Client.
When reading about Pusher, they state: "Bi-Directional Communication" which I currently cannot see. So how to implement that advertised Bi-Directional Communication?
Pusher does PubSub only. Using this, you can simulate bi-directional communication: Both sides of the conversation each need to have a topic dedicated to the conversation, and you then publish to this.
This is not ideal. For something which is probably closer to what you seem to want, take a look at WAMP (Web Application Messaging Protocol), which has more than just PubSub. There is a list of implementations at http://wamp-proto.org/implementations. For a router I would recommend Crossbar.io (http://crossbar.io), which has the most documentation to help you get started. Full disclosure: I am involved both with WAMP and Crossbar.io - but it's all open source and may just be what you need.
Right now I'm using socket.io with mandatory websockets as the transport. I'm thinking about moving to raw websockets but I'm not clear on what functionality I will lose moving off of socket.io. Thanks for any guidance.
The socket.io library adds the following features beyond standard webSockets:
Automatic selection of long polling vs. webSocket if the browser does not support webSockets or if the network path has a proxy/firewall that blocks webSockets.
Automatic client reconnection if the connection goes down (even if the server restarts).
Automatic detection of a dead connection (by using regular pings to detect a non-functioning connection)
Message passing scheme with automatic conversion to/from JSON.
The server-side concept of rooms where it's easy to communicate with a group of connected users.
The notion of connecting to a namespace on the server rather than just connecting to the server. This can be used for a variety of different capabilities, but I use it to tell the server what types of information I want to subscribe to. It's like connection to a particular channel.
Server-side data structures that automatically keep track of all connected clients so you can enumerate them at any time.
Middleware architecture built-in to the socket.io library that can be used to implement things like authentication with access to cookies from the original connection.
Automatic storage of the cookies and other headers present on the connection when it was first connected (very useful for identifying what user is connected).
Server-side broadcast capabilities to send a common message to either to all connected clients, all clients in a room or all clients in a namespace.
Tagging of every message with a message name and routing of message names into an eventEmitter so you listen for incoming messages by listening on an eventEmitter for the desired message name.
The ability for either client or server to send a message and then wait for a response to that specific message (a reply feature or request/response model).
I have an API running on a server, which handle users connection and a messaging system.
Beside that, I launched a websocket on that same server, waiting for connections and stuff.
And let's say we can get access to this by an Android app.
I'm having troubles to figure out what I should do now, here are my thoughts:
1 - When a user connect to the app, the API connect to the websocket. We allow the Android app only to listen on this socket to get new messages. When the user want to answer, the Android app send a message to the API. The API writes itself the received message to the socket, which will be read back by the Android app used by another user.
This way, the API can store the message in database before writing it in the socket.
2- The API does not connect to the websocket in any way. The Android app listen and write to the websocket when needed, and should, when writing to the websocket, also send a request to the API so it can store the message in DB.
May be none of the above is correct, please let me know
EDIT
I already understood why I should use a websocket, seems like it's the best way to have this "real time" system (when getting a new message for example) instead of forcing the client to make an HTTP request every x seconds to check if there are new messages.
What I still don't understand, is how it is suppose to communicate with my database. Sorry if my example is not clear, but I'll try to keep going with it :
My messaging system need to store all messages in my API database, to have some kind of historic of the conversation.
But it seems like a websocket must be running separately from the API, I mean it's another program right? Because it's not for HTTP requests
So should the API also listen to this websocket to catch new messages and store them?
You really have not described what the requirements are for your application so it's hard for us to directly advise what your app should do. You really shouldn't start out your analysis by saying that you have a webSocket and you're trying to figure out what to do with it. Instead, lay out the requirements of your app and figure out what technology will best meet those requirements.
Since your requirements are not clear, I'll talk about what a webSocket is best used for and what more traditional http requests are best used for.
Here are some characteristics of a webSocket:
It's designed to be continuously connected over some longer duration of time (much longer than the duration of one exchange between client and server).
The connection is typically made from a client to a server.
Once the connection is established, then data can be sent in either direction from client to server or from server to client at any time. This is a huge difference from a typical http request where data can only be requested by the client - with an http request the server can not initiate the sending of data to the client.
A webSocket is not a request/response architecture by default. In fact to make it work like request/response requires building a layer on top of the webSocket protocol so you can tell which response goes with which request. http is natively request/response.
Because a webSocket is designed to be continuously connected (or at least connected for some duration of time), it works very well (and with lower overhead) for situations where there is frequent communication between the two endpoints. The connection is already established and data can just be sent without any connection establishment overhead. In addition, the overhead per message is typically smaller with a webSocket than with http.
So, here are a couple typical reasons why you might choose one over the other.
If you need to be able to send data from server to client without having the client regular poll for new data, then a webSocket is very well designed for that and http cannot do that.
If you are frequently sending lots of small bits of data (for example, a temperature probe sending the current temperature every 10 seconds), then a webSocket will incur less network and server overhead than initiating a new http request for every new piece of data.
If you don't have either of the above situations, then you may not have any real need for a webSocket and an http request/response model may just be simpler.
If you really need request/response where a specific response is tied to a specific request, then that is built into http and is not a built-in feature of webSockets.
You may also find these other posts useful:
What are the pitfalls of using Websockets in place of RESTful HTTP?
What's the difference between WebSocket and plain socket communication?
Push notification | is websocket mandatory?
How does WebSockets server architecture work?
Response to Your Edit
But it seems like a websocket must be running separately from the API,
I mean it's another program right? Because it's not for HTTP requests
The same process that supports your API can also be serving the webSocket connections. Thus, when you get incoming data on the webSocket, you can just write it directly to the database the same way the API would access the database. So, NO the webSocket server does not have to be a separate program or process.
So should the API also listen to this websocket to catch new messages
and store them?
No, I don't think so. Only one process can be listening to a set of incoming webSocket connections.
I'm evaluating some messaging libraries and protocols (e.g. ZeroMQ, WAMP). One of my main requirements is that sending messages from client to server and vice verse (two way communication) must be absolute safe with respect to client/server crashes. This means to me that e.g. the client must continue sending all not delivered messages after a spontaneous reboot. So the library should implement some kind of file based buffering. Is there anything there I can use out of the box?
[EDIT]
Some note on my use case:
In my scenario there are around 1000 clients communicating with one server. There is no direct client to client communication required. But I need a two-way communication, so both, the clients can push some data to the server and vice versa. The clients are connected via 3G mobile network. Both, client and server are written in C#. I focused on using ZeroMQ, Apache Thrift or WAMP. But one of the main requirements is to ensure asynchronous but safe messaging with respect to system crashes. So when the client starts an asynchronous data push to the server, and it will crash before the message can be delivered to the server, it is required that the client will continue sending the message after a reboot.
You might look into the Apache.org's Kafka project.
The problem is harder than it looks, and most people don't want to pay the price to make it happen.
Also, there is a UX issue with old queued up messages replaying without the user's understanding.