How decrease disconnect detection time in SignalR?

Question

Hello, i am working on .net framework and in our web app we are using SignalR connection for transmitting data and etc. We want to catch client disconnection as soon as possible using signalr hub methods (OnDisconnected or if there is any other).I read the this documentation about connection lifetimes Understanding and Handling Connection Lifetime Events in SignalR | Microsoft Learn and i decreased time at minimum for this parameters in global.asax file as it was mentioned in docs.

Parameters - GlobalHost.Configuration.KeepAlive = TimeSpan.FromSeconds(2);   (2 is minimum)
                     GlobalHost.Configuration.DisconnectTimeout = TimeSpan.FromSeconds(6); (6 is minimum)
But this does not work properly for us. Disconnect detection in real life needs way more time(25-30 secs) than it is configured by parameters. Please help me to find problem, are we doing something wrong or just this is how it works. If there is alternatives please advice us.

Answer 1

Hi @Zuka Esakia,

There is no reliable method of detecting that the cable has been unplugged and pending HTTP requests might not be terminated if this happens.

Related Links

https://github.com/SignalR/SignalR/issues/3919#issuecomment-297896803

SignalR bare WebSocket. How to detect that client lost internet connection

But we can change the retry Count inside the withAutomaticReconnect to decrease disconnect detection time.

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Jason Pan

Answer 2

first the keep-alive is only used for http not web sockets. so it only affects signal/r when ajax polling is used instead of web sockets. when polling you want the keep-alive greater than the poll interval.

there is no reliable way to detect a lost tcp connection except by sending a message that fails.

If you need fast detection of lost connection then the client and server need to ping each other. this of course increases traffic. so, for a 6 second server detection, your server needs to ping the client at least every 6 seconds to verify the connection is valid.