I use soŃket.io (transport flashsockets), the client flash application with websockets library (binary sockets). How can I detect client disconnection immediately, such as if the Internet connection is broken? Currently, the disconnect event is triggered after a delay that is set to heartbeattimeout. What happens if you turn off heartbeats? If the connection is closed from flash, then all is well.
The frontend is nginx with tcp-proxy-module. Does this require specific settings timeouts?
io.set("close timeout", 1);
Refer to:https://github.com/LearnBoost/Socket.IO/wiki/Configuring-Socket.IO
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I'm using uwsgi's websockets support and so far it's looking great, the server detects when the client disconnects and the client as well when the server goes down. But i'm concerned this will not work in every case/browser.
In other frameworks, namely sockjs, the connection is monitored by sending regular messages that work as heartbeats/pings. But uwsgi sends PING/PONG frames (ie. not regular messages/control frames) according to the websockets spec and so from the client side i have no way to know when the last ping was received from the server. So my question is this:
If the connection is dropped or blocked by some proxy will browsers reliably (ie. Chrome, IE, Firefox, Opera) detect no PING was received from the server and signal the connection as down or should i implement some additional ping/pong system so that the connection is detected as closed from the client side?
Thanks
You are totally right. There is no way from client side to track or send ping/pongs. So if the connection drops, the server is able of detecting this condition through the ping/pong, but the client is let hung... until it tries to send something and the underlying TCP mechanism detect that the other side is not ACKnowledging its packets.
Therefore, if the client application expects to be "listening" most of the time, it may be convenient to implement a keep alive system that works "both ways" as Stephen Clearly explains in the link you posted. But, this keep alive system would be part of your application layer, rather than part of the transport layer as ping/pongs.
For example you can have a message "{token:'whatever'}" that the server and client just echoes with a 5 seconds delay. The client should have a timer with a 10 seconds timeout that stops every time that messages is received and starts every time the message is echoed, if the timer triggers, the connection can be consider dropped.
Although browsers that implement the same RFC as uWSGI should detect reliably when the server closes the connection cleanly they won't detect when the connection is interrupted midway (half open connections)t. So from what i understand we should employ an extra mechanism like application level pings.
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.
If I use my app(ios with c++ websocket code) with websocket connect nitrous.io, it will close connection if there is no signal.
Somebody has answered that this is nitrous.io feature,
but if I use web browser/html websocket connect to nitrous.io, it never closes the connection.
Confused by the different behavior.
(***web browser/html websocket connect to nitrous.io also closes after no signal for few hours)
Your comment welcome
I have a webapp, which is running in a browser. That webapp is connected to a server, which uses websockets. So the communication between the server and my client/browser is based on websockets. If some magic event occurs on the server, some webservice sends a new XML / JSON to my webapp and the new data gets displayed.
But how do i, as the client / browser, know if the connection is stil alive? Lets say i do not get any new XML for about 30 seconds. How would i know if the connection is closed/broken/server offline or everything is fine, but on the server himself no new magic event occured.
A websocket connection object has a readyState field which will tell you if the connection is still active (from the dart documentation). The readyState can be either
0 - connection not yet established
1 - conncetion established
2 - in closing handshake
3 - connection closed or could not open
You can also define an event handler for the websocket close event if this is something you'd like to handle (try to reconnect, etc).
3 ways:
rely on TCP to detect loss of connectivity, which will ultimately pop up in JS onclose event
send WebSocket pings from server .. browsers will reply with WS pongs, loss of connectivity is probably more robustly detected also on client side
send app level heartbeats from browser to server, server need to have logic to reply. you can't trigger WS pings from browsers (in JS)
I have observed the following behavior in Firefox 4 and Chrome 7:
If the server running the websocket daemon crashes, reboots, loses network connectivity, etc then the 'onclose' or 'onerror' events are not fired on the client-side. I would expect one of those events to be fired when the connection is broken for any reason.
If however the daemon is shutdown cleanly first, then the 'onclose' event is fired (as expected).
Why do the clients perceive the websocket connection as open when the daemon is not shutdown properly?
I want to rely on the expected behavior to inform the user that the server has become unavailable or that the client's internet connection has suffered a disruption.
TCP is like that. The most recent WebSockets standard draft (v76) has a clean shutdown message mechanism. But without that (or if it doesn't have a chance to be sent) you are relying on normal TCP socket cleanup which make take several minutes (or hours).
I would suggest adding some sort of signal handler/exit trap to the server so that when the server is killed/shutdown, a clean shutdown message is sent to all connected clients.
You could also add a heartbeat mechanism (ala TCP keep alive) to your application to detect when the other side goes away.