Put connection delays into constant

src/imap/client.rs

@@ -1,6 +1,5 @@
 use std::net::SocketAddr;
 use std::ops::{Deref, DerefMut};
-use std::time::Duration;
 
 use anyhow::{format_err, Context as _, Result};
 use async_imap::Client as ImapClient;
@@ -16,7 +15,9 @@ use crate::login_param::{ConnectionCandidate, ConnectionSecurity};
 use crate::net::dns::{lookup_host_with_cache, update_connect_timestamp};
 use crate::net::session::SessionStream;
 use crate::net::tls::wrap_tls;
-use crate::net::{connect_tcp_inner, connect_tls_inner, update_connection_history};
+use crate::net::{
+    connect_tcp_inner, connect_tls_inner, update_connection_history, CONNECTION_DELAYS,
+};
 use crate::socks::Socks5Config;
 use crate::tools::time;
 
@@ -206,12 +207,7 @@ impl Client {
                 connection_attempt_set.spawn(fut);
             }
 
-            // Start second, third and fourth connection attempt 300 ms, 10 s and 15 s after the first.
-            for delay in [
-                Duration::from_millis(300),
-                Duration::from_secs(10),
-                Duration::from_secs(15),
-            ] {
+            for delay in CONNECTION_DELAYS {
                 delay_set.spawn(tokio::time::sleep(delay));
             }
 

src/net.rs

@@ -37,6 +37,15 @@ pub(crate) const TRANSACTION_TIMEOUT: Duration = Duration::from_secs(300);
 /// TTL for caches in seconds.
 pub(crate) const CACHE_TTL: u64 = 30 * 24 * 60 * 60;
 
+/// Start additional connection attempts after 300 ms, 5 s, 10 s and 15 s.
+/// This way we can have up to 5 parallel connection attempts at the same time.
+pub(crate) const CONNECTION_DELAYS: [Duration; 4] = [
+    Duration::from_millis(300),
+    Duration::from_secs(5),
+    Duration::from_secs(10),
+    Duration::from_secs(15),
+];
+
 /// Removes connection history entries after `CACHE_TTL`.
 pub(crate) async fn prune_connection_history(context: &Context) -> Result<()> {
     let now = time();

src/smtp/connect.rs

@@ -1,7 +1,6 @@
 //! SMTP connection establishment.
 
 use std::net::SocketAddr;
-use std::time::Duration;
 
 use anyhow::{bail, format_err, Context as _, Result};
 use async_smtp::{SmtpClient, SmtpTransport};
@@ -13,7 +12,9 @@ use crate::login_param::{ConnectionCandidate, ConnectionSecurity};
 use crate::net::dns::{lookup_host_with_cache, update_connect_timestamp};
 use crate::net::session::SessionBufStream;
 use crate::net::tls::wrap_tls;
-use crate::net::{connect_tcp_inner, connect_tls_inner, update_connection_history};
+use crate::net::{
+    connect_tcp_inner, connect_tls_inner, update_connection_history, CONNECTION_DELAYS,
+};
 use crate::oauth2::get_oauth2_access_token;
 use crate::socks::Socks5Config;
 use crate::tools::time;
@@ -177,12 +178,7 @@ async fn connect_stream(
             connection_attempt_set.spawn(fut);
         }
 
-        // Start second, third and fourth connection attempt 300 ms, 10 s and 15 s after the first.
-        for delay in [
-            Duration::from_millis(300),
-            Duration::from_secs(10),
-            Duration::from_secs(15),
-        ] {
+        for delay in CONNECTION_DELAYS {
             delay_set.spawn(tokio::time::sleep(delay));
         }