fix(imap): allow maybe_network to interrupt connection ratelimit

ratelimit can be exhausted quickly if the network is not available,
i.e. if every connection attempt returns "network unreachable" error.
When the network becomes available, we want to retry connecting
as soon as maybe_network is called without waiting for ratelimiter.

src/imap.rs

@@ -15,7 +15,8 @@ use std::{
 use anyhow::{bail, format_err, Context as _, Result};
 use async_channel::Receiver;
 use async_imap::types::{Fetch, Flag, Name, NameAttribute, UnsolicitedResponse};
-use futures::{StreamExt, TryStreamExt};
+use futures::{FutureExt as _, StreamExt, TryStreamExt};
+use futures_lite::FutureExt;
 use num_traits::FromPrimitive;
 use ratelimit::Ratelimit;
 use tokio::sync::RwLock;
@@ -331,7 +332,18 @@ impl Imap {
                 "IMAP got rate limited, waiting for {} until can connect",
                 duration_to_str(ratelimit_duration),
             );
-            tokio::time::sleep(ratelimit_duration).await;
+            let interrupted = async {
+                tokio::time::sleep(ratelimit_duration).await;
+                false
+            }
+            .race(self.idle_interrupt_receiver.recv().map(|_| true))
+            .await;
+            if interrupted {
+                info!(
+                    context,
+                    "Connecting to IMAP without waiting for ratelimit due to interrupt."
+                );
+            }
         }
 
         info!(context, "Connecting to IMAP server");