nuntium exits when call to ofono DBus method fails

[Alfonso Sanchez-Beato]

nuntium exits when call to ofono DBus method "org.ofono.PushNotification.RegisterAgent" fails. Log is:

2015/05/14 02:13:50 Received GetServices()
2015/05/14 02:13:51 Initializing modem /ril_0
2015/05/14 02:13:53 Modem online: true
2015/05/14 02:13:55 Identity added 460012721610698
2015/05/14 02:13:55 Service added /org/ofono/mms/460012721610698
2015/05/14 02:13:55 Push interface state: true
2015/05/14 02:13:55 Registering agent for /ril_0 on path /nuntium and name :1.92
2015/05/14 02:13:55 Modem online: false
2015/05/14 02:13:55 Cannot register agent for /ril_0: org.freedesktop.DBus.Error.UnknownMethod: Method "RegisterAgent" with signature "o" on interface "org.ofono.PushNotification" doesn't exist

This happens when the modem changes from online to offline in a quick sequence: when we receive the signal that tells us that the modem is online we start the call, but meanwhile the modem has been powered off (we have still not processed the online=false signal, which is received by another thread) and org.ofono.PushNotification does not exist anymore.

We cannot avoid this kind of sequences so we should be able to handle this ground-moves-under-your-feet problems: we must assume that DBus calls can fail and handle that gracefully.

This concrete problem was triggered in arale when switching China Mobile and China Unicom SIMs and then rebooting: this forces a modem FW re-load that makes the modem go online, then offline, then online again in quick sequence.