Fix: Don't update quota in an endless loop (#2726)

The problem was:
When opening the connectivity view while there is no network,
get_connectivity_html() calls schedule_quota_update(), which schedules a
UpdateRecentQuota job. But in update_recent_quota(), connecting fails
and a ConnectivityChanged event is emitted (connectivity changes from
Error to Connecting and back). Therefore the UI calls
get_connectivity_html() again, and the loop is complete.

This made the UI completely unresponsible. To reproduce, just turn wi-fi
off and open the connectivity view.

The fix is:
schedule_quota_update() now only schedules a new job if there is no old
job. To prevent the possible (though probably unlikely) problem that an
old quota update job has a backoff of, like, a day and therefore quota
is not updated, I reduced the backoff time for quota jobs to 10s.

Fixes possibly https://github.com/deltachat/deltachat-android/issues/2043, but we should "re-try" this

src/job.rs

@@ -1084,7 +1084,7 @@ pub(crate) async fn perform_job(context: &Context, mut connection: Connection<'_
                     "{} thread increases job {} tries to {}", &connection, job, tries
                 );
                 job.tries = tries;
-                let time_offset = get_backoff_time_offset(tries);
+                let time_offset = get_backoff_time_offset(tries, job.action);
                 job.desired_timestamp = time() + time_offset;
                 info!(
                     context,
@@ -1170,15 +1170,24 @@ async fn perform_job_action(
     try_res
 }
 
-fn get_backoff_time_offset(tries: u32) -> i64 {
-    let n = 2_i32.pow(tries - 1) * 60;
-    let mut rng = thread_rng();
-    let r: i32 = rng.gen();
-    let mut seconds = r % (n + 1);
-    if seconds < 1 {
-        seconds = 1;
+fn get_backoff_time_offset(tries: u32, action: Action) -> i64 {
+    match action {
+        // Just try every 10s to update the quota
+        // If all retries are exhausted, a new job will be created when the quota information is needed
+        Action::UpdateRecentQuota => 10,
+
+        _ => {
+            // Exponential backoff
+            let n = 2_i32.pow(tries - 1) * 60;
+            let mut rng = thread_rng();
+            let r: i32 = rng.gen();
+            let mut seconds = r % (n + 1);
+            if seconds < 1 {
+                seconds = 1;
+            }
+            seconds as i64
+        }
     }
-    seconds as i64
 }
 
 async fn send_mdn(context: &Context, msg: &Message) -> Result<()> {

src/quota.rs

@@ -110,12 +110,13 @@ pub fn needs_quota_warning(curr_percentage: u64, warned_at_percentage: u64) -> b
 impl Context {
     // Adds a job to update `quota.recent`
     pub(crate) async fn schedule_quota_update(&self) -> Result<()> {
-        job::kill_action(self, Action::UpdateRecentQuota).await?;
-        job::add(
-            self,
-            job::Job::new(Action::UpdateRecentQuota, 0, Params::new(), 0),
-        )
-        .await?;
+        if !job::action_exists(self, Action::UpdateRecentQuota).await? {
+            job::add(
+                self,
+                job::Job::new(Action::UpdateRecentQuota, 0, Params::new(), 0),
+            )
+            .await?;
+        }
         Ok(())
     }