More correctly manage VPN service lifetime

Previously we never explicitly stopped, we just moved to
the background. Later we got killed (very reasonably), and
then afterwards we got restarted (because we're sticky) but
with a null intent, which makes Kotlin unhappy.

Now we either stop properly, or ask for the intent to be
redelivered correctly.

Author: pimterry

app/src/main/java/tech/httptoolkit/android/ProxyVpnService.kt

@@ -50,6 +50,16 @@ class ProxyVpnService : VpnService(), IProtectSocket {
     private var vpnInterface: ParcelFileDescriptor? = null
     private var vpnRunnable: ProxyVpnRunnable? = null
 
+    override fun onCreate() {
+        super.onCreate()
+        currentService = this
+    }
+
+    override fun onDestroy() {
+        super.onDestroy()
+        currentService = null
+    }
+
     override fun onStartCommand(intent: Intent, flags: Int, startId: Int): Int {
         currentService = this
         Log.i(TAG, "onStartCommand called")
@@ -63,11 +73,17 @@ class ProxyVpnService : VpnService(), IProtectSocket {
         if (intent.action == START_VPN_ACTION) {
             val proxyConfig = intent.getParcelableExtra<ProxyConfig>(PROXY_CONFIG_EXTRA)
             startVpn(proxyConfig)
+
+            // If the system briefly kills us for some reason (memory, the user, whatever) whilst
+            // running the VPN, it should redeliver the VPN setup intent ASAP.
+            return Service.START_REDELIVER_INTENT
         } else if (intent.action == STOP_VPN_ACTION) {
             stopVpn()
         }
 
-        return Service.START_STICKY
+        // Shouldn't matter (we should've stopped already), but in general: if we're not running a
+        // VPN, then the service doesn't need to be sticky.
+        return Service.START_NOT_STICKY
     }
 
     override fun onRevoke() {
@@ -160,6 +176,8 @@ class ProxyVpnService : VpnService(), IProtectSocket {
 
         stopForeground(true)
         localBroadcastManager!!.sendBroadcast(Intent(VPN_STOPPED_BROADCAST))
+        stopSelf()
+        currentService = null
     }
 
     fun isActive(): Boolean {