Link failure detection [question] about pushy HOT 6 CLOSED

We are, indeed, aware of the issue (I think it first came up in #14). I regret that I don't have a great solution to offer right now, but now that I'm thinking about it more, I'm surprised that SO_KEEPALIVE doesn't solve this problem for us. Let me investigate that a little more thoroughly.

Cheers!

from pushy.

Thanks for quick response. Actually, I think this is not a Pushy issue but a defect in design of APNS protocol. The lack of successful response makes it almost impossible to detect connection state.

To minimize the risk of writing to a dead connection, I'm going to recreate the connection every, for example, 5 minutes.

Edit: sorry I didn't notice this is already listed in the known issue. But I hope you can keep this open for users to track.

from pushy.

Actually, I think this is not a Pushy issue but a defect in design of APNS protocol.

Agreed, but I'd still like to work around it if we can ;)

Regarding SO_KEEPALIVE specifically, the problem seems to be that connections have to sit for a really long time (hours by default) before keepalive packets will start flowing. This is configurable at the OS level, but not really on a per-process basis. Lower-level networking stuff can configure the keepalive interval for individual sockets, but that's not really something we can do here (or anywhere in Java, really).

Will keep thinking about it.

from pushy.

With all of the attention SSL heartbeats have been getting lately, it occurs to me that they may also be a viable way to detect link failure, though I am (again) surprised that it's not just happening automatically. I'll admit I know very little about SSL heartbeats, but it seems like an avenue worth exploring.

from pushy.

I am (again) surprised that it's not just happening automatically

Given how APNs is designed to avoid any sort of acknowledgement, I imagine they have SSL heartbeats disabled on their side.

from pushy.

Though we still have no way to detect link failure, #116, #117, and #118 should jointly cover this issue. I regret that we can't do something that offers stronger guarantees.

from pushy.