XEP-0215: management of the field expires

[mid1221213]

Add a field in Xmpp.Xep.ExternalServiceDiscovery to keep track of the expires TURN service value and use it (divided by 2) to restart periodically the external services discovery.

Without this patch, calls (actually ICE) fail to initiate after 24h of Dino uptime because of the expiry of the TURN credentials.

This happened on my setup using prosody (using the default credentials' TTL of 86400) and coturn.

[fiaxh]

Thanks for looking into this.

There are some issues:

• A new Timeout is added whenever a stream is negotiated and they are not cancelled when the stream is broken. That means, there can exist a number of superflurous Timeouts. This is also problematic because the closure captures the stream, preventing it from getting freed.
• Within the closure, you check whether the account has is connected, but it could be connected via another stream. If the account is connected with a different stream, you would still call the on_stream_negotiated function, but with a broken stream.
• Please use a DateTime for storing the expired value instead of an int64? - we try to avoid using question-primitives, as accessing them wrongly leads to crashes.
• Also with those changes, we should rename on_stream_negotiated, since it's not only called on stream negotiation anymore 🙂

[mid1221213]

Thanks @fiaxh for your comments. Here is a new version, hopefully better 😉