We are using tomcat websocket implementation in our web application. Messages are pushed from server to client through websockets. Web socket messages are not pushed when intermittant connection drop or network is switch over but still web application is connected.
Let say for example i am connected to LAN and logged in app, now i connecting through wifi after wifi successfully connected i am disconnecting LAN with in fraction of second network is switched from LAN to wifi But after this messages are not pushed from server to client through websockets.
After network switch if i check the state of the websocket(readyState) which says 1 which means websocket connection is open but actually its not.
Can anyone faced this issue earlier and provide your suggestions.
Thanks
You must create a connection drop detection mechanism. The WebSocket protocol has ping/pong frames, but I don't know if Tomcat has that functionality. In some Webscoket frameworks you can define a timeout interval, and the server will ping the client regularly, if the client miss some pongs is disconnected.
If that functionality is not provided by Tomcat, you can still create your own. Just define a special type of message and repeat it to the server from the client. If you do not get any of those messages for a while, disconnect.
Related
I am setting up an MQTT/Websockets server, my client is an flutter app, which connects to the broker on main screen, and in other screens it sends and receive messages from the broker. My understanding of keepAlive is how often the client and server should share ping/pong, so they make sure the connection is still alive. being said, if my flutter app, connects to the broker in main screen, of 3600/1 hour keepAlive, and suppose to share and receive messages on other screens, if i disconnect the client from the internet for 2 minutes, and reconnect after that, it will not send/receive messages, maybe my understanding of keepAlive is not correct. Well, How would i structure my app/server to reconnect automatically to the internet as soon as internet connection is back and up again.
I have also tried On.Disconnect method, which i noticed it will never get called, and the app even though still thinks its connected to the broker.
I mentioned websockets, on the tags as i could do mqtt over websockets.
I see that no-one else has responded, so I'll try (however I'm new to this also).
Also, have you looked at the Flutter connectivity package?
From my reading of the Mqtt specification, it seems the Mqtt client ** should** disconnect the TCP/IP connection if it doesn't receive a PINGRESP to its PINGREQ in the keep alive period (ie it's not required to disconnect).
My Flutter + Mqtt app checks the connection state, and reconnects if needed, every time it sends a message. I haven't needed to check for internet dropouts, but I have noticed the connection is lost on some application state changes. The main app widget. is notified of these using didChangeAppLifecycleState() and sends a dummy message if needed.
So this doesn't answer exactly what you asked, but I hope it's useful anyway.
In short we have two separate servers for our web app. The first one is the main server that uses Websockets for handling "chat rooms", and the second server only handles WebRTC audio chat rooms via Websocket. Both servers use Express to create a HTTPS server, use secure Websocket and the port 443.
I recently encountered a problem where a corporate client's firewall blocked the wss-connection to only the WebRTC server. The error logged in the user's browser was "ERR_CONNECTION_TIMED_OUT", which means the user never connects via Websocket. This has not happened with any other clients.
The Websocket connection works normally between the user and the main server, and no rules have been added to their firewall to use our app.
Has anyone encountered something similar? What kind of a firewall setting might cause this? Could this be a cors problem, since the servers are on their own sub-domains?
The main server could be restricting the type of data sent on port 443, which will use SSL to secure that transmitted data.
Refer to this page for information on the "Well-know port numbers".
The WebRTC audio data may need to be transmitted on its own dedicated port number that has been configured on the main server for this.
The problem was that the main server WebSocket used TCP and the WebRTC server used UDP, and UDP was blocked by corporate firewall on default.
WebRTC should use TCP as a backup, but I'm assuming UDP is still needed for the handshake.
my question is simple
When you send data through TCP/IP protocol with EX:firefox you can receive reply on some random port that the browser listen on, while when i try to use a port for another task like CS Gaming or anything else it don't work unless i use kind of VPN ?
PS: there r no firewall blocking connection and port forwarding from my router didn't work as well.
Browsers are client apps that make outbound connections to web servers. When connecting to a server through a router’s NAT, the NAT takes note of the source and destination IP/port pairs so messages sent back from the server on the same connection are automatically routed to the correct client IP/port.
Browsers also support the websocket protocol. This feature makes it seem like the browser is listening on a specific port. However, in reality, it is initiated on a new connection to the server, a connection which remains open all throughout the websocket communication.
What matters is which peer is behind the NAT — the server or the client. For an outbound connection from a client, it can usually use any random port that is available at the time. For an inbound connection to a server, the server's IP/port must be known ahead of time and be routable. If the server is behind a NAT, the router(s) must be configured to make the server reachable from the other side of the NAT.
The server software can make a UPnP request to ask a router to forward inbound packets to the correct IP/Port. The router, depending on its configuration, may or may not honor such a request. If not, the router has to be configured manually by a network administrator.
Case:
A WebSocket connection have been established between the client and server endpoint.
Now I have the network connection go down (for example the ADSL dies), after 10 min I recover the network, I find that the client and server are still able to communicate with each
other. Why?
Note:
The client was developed with Java-WebSocket framework, and the client did with ws4py.
1 - If they did not try to exchange any data and only the connection (not the endpoints) between them is down, this is normal behaviour.
2 - If the websocket connection ended, Browser may have re-established it without you knowing about it. I just checked that this is not normal behaviour. But maybe there is some parameter somewhere :-)
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).