refactor(imap): remove Session from Imap structure

Connection establishment now happens only in one place in each IMAP loop.
Now all connection establishment happens in one place
and is limited by the ratelimit.

Backoff was removed from fake_idle
as it does not establish connections anymore.
If connection fails, fake_idle will return an error.
We then drop the connection and get back to the beginning of IMAP
loop.

Backoff may be still nice to have to delay retries
in case of constant connection failures
so we don't immediately hit ratelimit if the network is unusable
and returns immediate error on each connection attempt
(e.g. ICMP network unreachable error),
but adding backoff for connection failures is out of scope for this change.

src/imap/idle.rs

@@ -4,13 +4,12 @@ use anyhow::{bail, Context as _, Result};
 use async_channel::Receiver;
 use async_imap::extensions::idle::IdleResponse;
 use futures_lite::FutureExt;
+use tokio::time::timeout;
 
 use super::session::Session;
 use super::Imap;
-use crate::config::Config;
 use crate::context::Context;
 use crate::imap::{client::IMAP_TIMEOUT, FolderMeaning};
-use crate::log::LogExt;
 use crate::tools::{self, time_elapsed};
 
 /// Timeout after which IDLE is finished
@@ -98,90 +97,38 @@ impl Session {
 }
 
 impl Imap {
+    /// Idle using polling.
     pub(crate) async fn fake_idle(
         &mut self,
         context: &Context,
+        session: &mut Session,
         watch_folder: String,
         folder_meaning: FolderMeaning,
-    ) {
-        // Idle using polling. This is also needed if we're not yet configured -
-        // in this case, we're waiting for a configure job (and an interrupt).
-
+    ) -> Result<()> {
         let fake_idle_start_time = tools::Time::now();
 
-        // Do not poll, just wait for an interrupt when no folder is passed in.
         info!(context, "IMAP-fake-IDLEing folder={:?}", watch_folder);
 
-        const TIMEOUT_INIT_MS: u64 = 60_000;
-        let mut timeout_ms: u64 = TIMEOUT_INIT_MS;
-        enum Event {
-            Tick,
-            Interrupt,
-        }
-        // loop until we are interrupted or if we fetched something
+        // Loop until we are interrupted or until we fetch something.
         loop {
-            use futures::future::FutureExt;
-            use rand::Rng;
-
-            let mut interval = tokio::time::interval(Duration::from_millis(timeout_ms));
-            timeout_ms = timeout_ms
-                .saturating_add(rand::thread_rng().gen_range((timeout_ms / 2)..=timeout_ms));
-            interval.tick().await; // The first tick completes immediately.
-            match interval
-                .tick()
-                .map(|_| Event::Tick)
-                .race(
-                    self.idle_interrupt_receiver
-                        .recv()
-                        .map(|_| Event::Interrupt),
-                )
-                .await
-            {
-                Event::Tick => {
-                    // try to connect with proper login params
-                    // (setup_handle_if_needed might not know about them if we
-                    // never successfully connected)
-                    if let Err(err) = self.prepare(context).await {
-                        warn!(context, "fake_idle: could not connect: {}", err);
-                        continue;
-                    }
-                    if let Some(session) = &self.session {
-                        if session.can_idle()
-                            && !context
-                                .get_config_bool(Config::DisableIdle)
-                                .await
-                                .context("Failed to get disable_idle config")
-                                .log_err(context)
-                                .unwrap_or_default()
-                        {
-                            // we only fake-idled because network was gone during IDLE, probably
-                            break;
-                        }
-                    }
-                    info!(context, "fake_idle is connected");
-                    // we are connected, let's see if fetching messages results
+            match timeout(Duration::from_secs(60), self.idle_interrupt_receiver.recv()).await {
+                Err(_) => {
+                    // Let's see if fetching messages results
                     // in anything.  If so, we behave as if IDLE had data but
                     // will have already fetched the messages so perform_*_fetch
                     // will not find any new.
-                    match self
-                        .fetch_new_messages(context, &watch_folder, folder_meaning, false)
-                        .await
-                    {
-                        Ok(res) => {
-                            info!(context, "fetch_new_messages returned {:?}", res);
-                            timeout_ms = TIMEOUT_INIT_MS;
-                            if res {
-                                break;
-                            }
-                        }
-                        Err(err) => {
-                            error!(context, "could not fetch from folder: {:#}", err);
-                            self.trigger_reconnect(context);
-                        }
+                    let res = self
+                        .fetch_new_messages(context, session, &watch_folder, folder_meaning, false)
+                        .await?;
+
+                    info!(context, "fetch_new_messages returned {:?}", res);
+
+                    if res {
+                        break;
                     }
                 }
-                Event::Interrupt => {
-                    info!(context, "Fake IDLE interrupted");
+                Ok(_) => {
+                    info!(context, "Fake IDLE interrupted.");
                     break;
                 }
             }
@@ -192,5 +139,6 @@ impl Imap {
             "IMAP-fake-IDLE done after {:.4}s",
             time_elapsed(&fake_idle_start_time).as_millis() as f64 / 1000.,
         );
+        Ok(())
     }
 }