SignalR long polling reconnection behavior

Question

Using a SignalR persistent connection with a JS long polling client we see inconsistent reconnection behavior in different scenarios. When the client machine's network cable is unplugged the JS connection does not enter the reconnecting state and it never (at least not after 5 minutes) reaches the disconnected state. For other scenarios such as a restart of the IIS web application a long polling JS connection does enter the reconnecting state and successfully reconnects. I understand that the reasoning behind this is that keep-alive is not supported for the long polling transport.

I can see that a suggestion has been made on github to better support reconnections for the long polling transport (https://github.com/SignalR/SignalR/issues/1781), but it seems that there is no commitment to change it.

First, is there a proper workaround for detecting disconnections on the client in the case of long polling. Second, does anyone know if there are plans to support reconnection in the case described?

Cheers

Answer 1

We've debated different alternatives to support a keep alive "like" feature for long polling; however, due to how long polling works under the covers it's not easy to implement without affecting the vast majority of users. As we continue to debate the "correct" solution I'll leave you with one work around for detecting network failure in the long polling client (if it's absolutely needed).

Create a server method, lets call it ping:

public class MyHub : Hub
{
    public void Ping()
    {
    }
}

Now on the client create an interval in which you will "ping" the server:

var proxy = $.connection.myHub,
    intervalHandle;  
...
$.connection.hub.disconnected(function() {
    clearInterval(intervalHandle);
});  
...  
$.connection.hub.start().done(function() {
    // Only when long polling
    if($.connection.hub.transport.name === "longPolling") {
        // Ping every 10s
        intervalHandle = setInterval(function() {
            // Ensure we're connected (don't want to be pinging in any other state).
            if($.connection.hub.state === $.signalR.connectionState.connected) {
                proxy.server.ping().fail(function() {
                    // Failed to ping the server, we could either try one more time to ensure we can't reach the server
                    // or we could fail right here.
                    TryAndRestartConnection(); // Your method
                });
            }
        }, 10000); 
    }
});

Hope this helps!