fix: do not fake idle after trigger_reconnect()

In this case connection failure
may be a connection timeout (currently 1 minute),
so it does not make sense to fake idle for another minute immediately after.

However, failure may be immediate if the port is closed
and the server refuses connection every time.
To prevent busy loop in this case
we apply ratelimit to connection attempts rather than login attempts.
This partially reverts ccec26ffa7

src/imap.rs

@@ -94,16 +94,11 @@ pub struct Imap {
 
     pub(crate) connectivity: ConnectivityStore,
 
-    /// Rate limit for IMAP connection usage attempts.
+    /// Rate limit for IMAP connection attempts.
     ///
-    /// Rate limit is checked before connecting
-    /// and updated right before login attempt.
-    /// It does not limit the number of connection attempts
-    /// if the network is bad as only successful connections are counted.
-    ///
-    /// Main purpose of this rate limit is
-    /// to prevent busy loop in case
-    /// connection gets dropped over and over due to IMAP bug,
+    /// This rate limit prevents busy loop
+    /// in case the server refuses connections
+    /// or in case connection gets dropped over and over due to IMAP bug,
     /// e.g. the server returning invalid response to SELECT command
     /// immediately after logging in or returning an error in response to LOGIN command
     /// due to internal server error.
@@ -280,7 +275,7 @@ impl Imap {
             session: None,
             login_failed_once: false,
             connectivity: Default::default(),
-            // 1 login per minute + a burst of 2.
+            // 1 connection per minute + a burst of 2.
             ratelimit: RwLock::new(Ratelimit::new(Duration::new(120, 0), 2.0)),
         };
 
@@ -331,11 +326,6 @@ impl Imap {
 
         self.connectivity.set_connecting(context).await;
 
-        // Check rate limit before trying to connect
-        // to avoid connecting and not using the connection
-        // in case we are currently ratelimited.
-        // Otherwise connection may become unusable due to NAT forgetting about it
-        // before we attempt to actually login.
         let ratelimit_duration = self.ratelimit.read().await.until_can_send();
         if !ratelimit_duration.is_zero() {
             warn!(
@@ -347,6 +337,7 @@ impl Imap {
         }
 
         info!(context, "Connecting to IMAP server");
+        self.ratelimit.write().await.send();
         let connection_res: Result<Client> = if self.config.lp.security == Socket::Starttls
             || self.config.lp.security == Socket::Plain
         {
@@ -397,7 +388,6 @@ impl Imap {
             }
         };
         let client = connection_res?;
-        self.ratelimit.write().await.send();
 
         let config = &self.config;
         let imap_user: &str = config.lp.user.as_ref();

src/scheduler.rs

@@ -559,9 +559,6 @@ async fn fetch_idle(ctx: &Context, connection: &mut Imap, folder_meaning: Folder
     {
         warn!(ctx, "{:#}", err);
         connection.trigger_reconnect(ctx);
-        connection
-            .fake_idle(ctx, Some(watch_folder), folder_meaning)
-            .await;
         return;
     }