feat: sort DNS results by successful connection timestamp (#5818)

src/imap/client.rs

@@ -4,6 +4,7 @@ use std::ops::{Deref, DerefMut};
 use anyhow::{bail, format_err, Context as _, Result};
 use async_imap::Client as ImapClient;
 use async_imap::Session as ImapSession;
+use fast_socks5::client::Socks5Stream;
 use tokio::io::BufWriter;
 
 use super::capabilities::Capabilities;
@@ -12,10 +13,11 @@ use crate::context::Context;
 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::update_connection_history;
 use crate::net::{connect_tcp_inner, connect_tls_inner};
 use crate::provider::Socket;
 use crate::socks::Socks5Config;
-use fast_socks5::client::Socks5Stream;
+use crate::tools::time;
 
 #[derive(Debug)]
 pub(crate) struct Client {
@@ -123,7 +125,9 @@ impl Client {
             let mut first_error = None;
             let load_cache =
                 strict_tls && (security == Socket::Ssl || security == Socket::Starttls);
-            for resolved_addr in lookup_host_with_cache(context, host, port, load_cache).await? {
+            for resolved_addr in
+                lookup_host_with_cache(context, host, port, "imap", load_cache).await?
+            {
                 let res = match security {
                     Socket::Automatic => bail!("IMAP port security is not configured"),
                     Socket::Ssl => Client::connect_secure(resolved_addr, host, strict_tls).await,
@@ -138,6 +142,8 @@ impl Client {
                         if load_cache {
                             update_connect_timestamp(context, host, &ip_addr).await?;
                         }
+                        update_connection_history(context, "imap", host, port, &ip_addr, time())
+                            .await?;
                         return Ok(client);
                     }
                     Err(err) => {

src/net.rs

@@ -10,6 +10,7 @@ use tokio::time::timeout;
 use tokio_io_timeout::TimeoutStream;
 
 use crate::context::Context;
+use crate::tools::time;
 
 pub(crate) mod dns;
 pub(crate) mod http;
@@ -25,6 +26,65 @@ use tls::wrap_tls;
 /// This constant should be more than the largest expected RTT.
 pub(crate) const TIMEOUT: Duration = Duration::from_secs(60);
 
+/// TTL for caches in seconds.
+pub(crate) const CACHE_TTL: u64 = 30 * 24 * 60 * 60;
+
+/// Removes connection history entries after `CACHE_TTL`.
+pub(crate) async fn prune_connection_history(context: &Context) -> Result<()> {
+    let now = time();
+    context
+        .sql
+        .execute(
+            "DELETE FROM connection_history
+             WHERE ? > timestamp + ?",
+            (now, CACHE_TTL),
+        )
+        .await?;
+    Ok(())
+}
+
+pub(crate) async fn update_connection_history(
+    context: &Context,
+    alpn: &str,
+    host: &str,
+    port: u16,
+    addr: &str,
+    now: i64,
+) -> Result<()> {
+    context
+        .sql
+        .execute(
+            "INSERT INTO connection_history (host, port, alpn, addr, timestamp)
+             VALUES (?, ?, ?, ?, ?)
+             ON CONFLICT (host, port, alpn, addr)
+             DO UPDATE SET timestamp=excluded.timestamp",
+            (host, port, alpn, addr, now),
+        )
+        .await?;
+    Ok(())
+}
+
+pub(crate) async fn load_connection_timestamp(
+    context: &Context,
+    alpn: &str,
+    host: &str,
+    port: u16,
+    addr: &str,
+) -> Result<Option<i64>> {
+    let timestamp = context
+        .sql
+        .query_get_value(
+            "SELECT timestamp FROM connection_history
+             WHERE host = ?
+               AND port = ?
+               AND alpn = ?
+               AND addr = ?",
+            (host, port, alpn, addr),
+        )
+        .await?;
+    Ok(timestamp)
+}
+
 /// Returns a TCP connection stream with read/write timeouts set
 /// and Nagle's algorithm disabled with `TCP_NODELAY`.
 ///
@@ -75,7 +135,7 @@ pub(crate) async fn connect_tcp(
 ) -> Result<Pin<Box<TimeoutStream<TcpStream>>>> {
     let mut first_error = None;
 
-    for resolved_addr in lookup_host_with_cache(context, host, port, load_cache).await? {
+    for resolved_addr in lookup_host_with_cache(context, host, port, "", load_cache).await? {
         match connect_tcp_inner(resolved_addr).await {
             Ok(stream) => {
                 return Ok(stream);

src/net/dns.rs

@@ -6,15 +6,68 @@ use std::str::FromStr;
 use tokio::net::lookup_host;
 use tokio::time::timeout;
 
+use super::load_connection_timestamp;
 use crate::context::Context;
 use crate::tools::time;
 
-async fn lookup_host_with_timeout(hostname: &str, port: u16) -> Result<Vec<SocketAddr>> {
+/// Inserts entry into DNS cache
-    let res = timeout(super::TIMEOUT, lookup_host((hostname, port)))
+/// or updates existing one with a new timestamp.
+async fn update_cache(context: &Context, host: &str, addr: &str, now: i64) -> Result<()> {
+    context
+        .sql
+        .execute(
+            "INSERT INTO dns_cache
+             (hostname, address, timestamp)
+             VALUES (?, ?, ?)
+             ON CONFLICT (hostname, address)
+             DO UPDATE SET timestamp=excluded.timestamp",
+            (host, addr, now),
+        )
+        .await?;
+    Ok(())
+}
+
+pub(crate) async fn prune_dns_cache(context: &Context) -> Result<()> {
+    let now = time();
+    context
+        .sql
+        .execute(
+            "DELETE FROM dns_cache
+             WHERE ? > timestamp + ?",
+            (now, super::CACHE_TTL),
+        )
+        .await?;
+    Ok(())
+}
+
+/// Looks up the hostname and updates DNS cache
+/// on success.
+async fn lookup_host_and_update_cache(
+    context: &Context,
+    hostname: &str,
+    port: u16,
+    now: i64,
+) -> Result<Vec<SocketAddr>> {
+    let res: Vec<SocketAddr> = timeout(super::TIMEOUT, lookup_host((hostname, port)))
         .await
         .context("DNS lookup timeout")?
-        .context("DNS lookup failure")?;
+        .context("DNS lookup failure")?
-    Ok(res.collect())
+        .collect();
+
+    for addr in &res {
+        let ip_string = addr.ip().to_string();
+        if ip_string == hostname {
+            // IP address resolved into itself, not interesting to cache.
+            continue;
+        }
+
+        info!(context, "Resolved {hostname}:{port} into {addr}.");
+
+        // Update the cache.
+        update_cache(context, hostname, &ip_string, now).await?;
+    }
+
+    Ok(res)
 }
 
 // Updates timestamp of the cached entry
@@ -53,18 +106,161 @@ pub(crate) async fn update_connect_timestamp(
     Ok(())
 }
 
+/// Load hardcoded cache if everything else fails.
+///
+/// See <https://support.delta.chat/t/no-dns-resolution-result/2778> and
+/// <https://github.com/deltachat/deltachat-core-rust/issues/4920> for reasons.
+///
+/// In the future we may pre-resolve all provider database addresses
+/// and build them in.
+fn load_hardcoded_cache(hostname: &str, port: u16) -> Vec<SocketAddr> {
+    match hostname {
+        "mail.sangham.net" => {
+            vec![
+                SocketAddr::new(
+                    IpAddr::V6(Ipv6Addr::new(0x2a01, 0x4f8, 0xc17, 0x798c, 0, 0, 0, 1)),
+                    port,
+                ),
+                SocketAddr::new(IpAddr::V4(Ipv4Addr::new(159, 69, 186, 85)), port),
+            ]
+        }
+        "nine.testrun.org" => {
+            vec![
+                SocketAddr::new(
+                    IpAddr::V6(Ipv6Addr::new(0x2a01, 0x4f8, 0x241, 0x4ce8, 0, 0, 0, 2)),
+                    port,
+                ),
+                SocketAddr::new(IpAddr::V4(Ipv4Addr::new(116, 202, 233, 236)), port),
+            ]
+        }
+        "disroot.org" => {
+            vec![SocketAddr::new(
+                IpAddr::V4(Ipv4Addr::new(178, 21, 23, 139)),
+                port,
+            )]
+        }
+        "mail.riseup.net" => {
+            vec![
+                SocketAddr::new(IpAddr::V4(Ipv4Addr::new(198, 252, 153, 70)), port),
+                SocketAddr::new(IpAddr::V4(Ipv4Addr::new(198, 252, 153, 71)), port),
+            ]
+        }
+        "imap.gmail.com" => {
+            vec![
+                SocketAddr::new(
+                    IpAddr::V6(Ipv6Addr::new(0x2a00, 0x1450, 0x400c, 0xc1f, 0, 0, 0, 0x6c)),
+                    port,
+                ),
+                SocketAddr::new(
+                    IpAddr::V6(Ipv6Addr::new(0x2a00, 0x1450, 0x400c, 0xc1f, 0, 0, 0, 0x6d)),
+                    port,
+                ),
+                SocketAddr::new(IpAddr::V4(Ipv4Addr::new(142, 250, 110, 109)), port),
+                SocketAddr::new(IpAddr::V4(Ipv4Addr::new(142, 250, 110, 108)), port),
+            ]
+        }
+        "smtp.gmail.com" => {
+            vec![
+                SocketAddr::new(
+                    IpAddr::V6(Ipv6Addr::new(0x2a00, 0x1450, 0x4013, 0xc04, 0, 0, 0, 0x6c)),
+                    port,
+                ),
+                SocketAddr::new(IpAddr::V4(Ipv4Addr::new(142, 250, 110, 109)), port),
+            ]
+        }
+        _ => Vec::new(),
+    }
+}
+
+async fn lookup_cache(
+    context: &Context,
+    host: &str,
+    port: u16,
+    alpn: &str,
+    now: i64,
+) -> Result<Vec<SocketAddr>> {
+    let mut res = Vec::new();
+    for cached_address in context
+        .sql
+        .query_map(
+            "SELECT dns_cache.address
+             FROM dns_cache
+             LEFT JOIN connection_history
+               ON dns_cache.hostname = connection_history.host
+               AND dns_cache.address = connection_history.addr
+               AND connection_history.port = ?
+               AND connection_history.alpn = ?
+             WHERE dns_cache.hostname = ?
+             AND ? < dns_cache.timestamp + ?
+             ORDER BY IFNULL(connection_history.timestamp, dns_cache.timestamp) DESC
+             LIMIT 50",
+            (port, alpn, host, now, super::CACHE_TTL),
+            |row| {
+                let address: String = row.get(0)?;
+                Ok(address)
+            },
+            |rows| {
+                rows.collect::<std::result::Result<Vec<String>, _>>()
+                    .map_err(Into::into)
+            },
+        )
+        .await?
+    {
+        match IpAddr::from_str(&cached_address) {
+            Ok(ip_addr) => {
+                let addr = SocketAddr::new(ip_addr, port);
+                res.push(addr);
+            }
+            Err(err) => {
+                warn!(
+                    context,
+                    "Failed to parse cached address {:?}: {:#}.", cached_address, err
+                );
+            }
+        }
+    }
+    Ok(res)
+}
+
+/// Sorts DNS resolution results by connection timestamp in descending order
+/// so IP addresses that we recently connected to successfully are tried first.
+async fn sort_by_connection_timestamp(
+    context: &Context,
+    input: Vec<SocketAddr>,
+    alpn: &str,
+    host: &str,
+) -> Result<Vec<SocketAddr>> {
+    let mut res: Vec<(Option<i64>, SocketAddr)> = Vec::new();
+    for addr in input {
+        let timestamp =
+            load_connection_timestamp(context, alpn, host, addr.port(), &addr.ip().to_string())
+                .await?;
+        res.push((timestamp, addr));
+    }
+    res.sort_by_key(|(ts, _addr)| std::cmp::Reverse(*ts));
+    Ok(res.into_iter().map(|(_ts, addr)| addr).collect())
+}
+
 /// Looks up hostname and port using DNS and updates the address resolution cache.
 ///
+/// `alpn` is used to sort DNS results by the time we have successfully
+/// connected to the IP address using given `alpn`.
+/// If result sorting is not needed or `alpn` is unknown,
+/// pass empty string here, e.g. for HTTP requests
+/// or when resolving the IP address of SOCKS proxy.
+///
 /// If `load_cache` is true, appends cached results not older than 30 days to the end
 /// or entries from fallback cache if there are no cached addresses.
 pub(crate) async fn lookup_host_with_cache(
     context: &Context,
     hostname: &str,
     port: u16,
+    alpn: &str,
     load_cache: bool,
 ) -> Result<Vec<SocketAddr>> {
     let now = time();
-    let mut resolved_addrs = match lookup_host_with_timeout(hostname, port).await {
+    let mut resolved_addrs = match lookup_host_and_update_cache(context, hostname, port, now).await
+    {
         Ok(res) => res,
         Err(err) => {
             warn!(
@@ -74,144 +270,257 @@ pub(crate) async fn lookup_host_with_cache(
             Vec::new()
         }
     };
-
+    if !alpn.is_empty() {
-    for addr in &resolved_addrs {
+        resolved_addrs =
-        let ip_string = addr.ip().to_string();
+            sort_by_connection_timestamp(context, resolved_addrs, alpn, hostname).await?;
-        if ip_string == hostname {
-            // IP address resolved into itself, not interesting to cache.
-            continue;
-        }
-
-        info!(context, "Resolved {}:{} into {}.", hostname, port, &addr);
-
-        // Update the cache.
-        context
-            .sql
-            .execute(
-                "INSERT INTO dns_cache
-                 (hostname, address, timestamp)
-                 VALUES (?, ?, ?)
-                 ON CONFLICT (hostname, address)
-                 DO UPDATE SET timestamp=excluded.timestamp",
-                (hostname, ip_string, now),
-            )
-            .await?;
     }
 
     if load_cache {
-        for cached_address in context
+        for addr in lookup_cache(context, hostname, port, alpn, now).await? {
-            .sql
+            if !resolved_addrs.contains(&addr) {
-            .query_map(
+                resolved_addrs.push(addr);
-                "SELECT address
-                 FROM dns_cache
-                 WHERE hostname = ?
-                 AND ? < timestamp + 30 * 24 * 3600
-                 ORDER BY timestamp DESC",
-                (hostname, now),
-                |row| {
-                    let address: String = row.get(0)?;
-                    Ok(address)
-                },
-                |rows| {
-                    rows.collect::<std::result::Result<Vec<_>, _>>()
-                        .map_err(Into::into)
-                },
-            )
-            .await?
-        {
-            match IpAddr::from_str(&cached_address) {
-                Ok(ip_addr) => {
-                    let addr = SocketAddr::new(ip_addr, port);
-                    if !resolved_addrs.contains(&addr) {
-                        resolved_addrs.push(addr);
-                    }
-                }
-                Err(err) => {
-                    warn!(
-                        context,
-                        "Failed to parse cached address {:?}: {:#}.", cached_address, err
-                    );
-                }
             }
         }
 
         if resolved_addrs.is_empty() {
-            // Load hardcoded cache if everything else fails.
+            return Ok(load_hardcoded_cache(hostname, port));
-            //
-            // See <https://support.delta.chat/t/no-dns-resolution-result/2778> and
-            // <https://github.com/deltachat/deltachat-core-rust/issues/4920> for reasons.
-            //
-            // In the future we may pre-resolve all provider database addresses
-            // and build them in.
-            match hostname {
-                "mail.sangham.net" => {
-                    resolved_addrs.push(SocketAddr::new(
-                        IpAddr::V6(Ipv6Addr::new(0x2a01, 0x4f8, 0xc17, 0x798c, 0, 0, 0, 1)),
-                        port,
-                    ));
-                    resolved_addrs.push(SocketAddr::new(
-                        IpAddr::V4(Ipv4Addr::new(159, 69, 186, 85)),
-                        port,
-                    ));
-                }
-                "nine.testrun.org" => {
-                    resolved_addrs.push(SocketAddr::new(
-                        IpAddr::V6(Ipv6Addr::new(0x2a01, 0x4f8, 0x241, 0x4ce8, 0, 0, 0, 2)),
-                        port,
-                    ));
-                    resolved_addrs.push(SocketAddr::new(
-                        IpAddr::V4(Ipv4Addr::new(116, 202, 233, 236)),
-                        port,
-                    ));
-                }
-                "disroot.org" => {
-                    resolved_addrs.push(SocketAddr::new(
-                        IpAddr::V4(Ipv4Addr::new(178, 21, 23, 139)),
-                        port,
-                    ));
-                }
-                "mail.riseup.net" => {
-                    resolved_addrs.push(SocketAddr::new(
-                        IpAddr::V4(Ipv4Addr::new(198, 252, 153, 70)),
-                        port,
-                    ));
-                    resolved_addrs.push(SocketAddr::new(
-                        IpAddr::V4(Ipv4Addr::new(198, 252, 153, 71)),
-                        port,
-                    ));
-                }
-                "imap.gmail.com" => {
-                    resolved_addrs.push(SocketAddr::new(
-                        IpAddr::V6(Ipv6Addr::new(0x2a00, 0x1450, 0x400c, 0xc1f, 0, 0, 0, 0x6c)),
-                        port,
-                    ));
-                    resolved_addrs.push(SocketAddr::new(
-                        IpAddr::V6(Ipv6Addr::new(0x2a00, 0x1450, 0x400c, 0xc1f, 0, 0, 0, 0x6d)),
-                        port,
-                    ));
-                    resolved_addrs.push(SocketAddr::new(
-                        IpAddr::V4(Ipv4Addr::new(142, 250, 110, 109)),
-                        port,
-                    ));
-                    resolved_addrs.push(SocketAddr::new(
-                        IpAddr::V4(Ipv4Addr::new(142, 250, 110, 108)),
-                        port,
-                    ));
-                }
-                "smtp.gmail.com" => {
-                    resolved_addrs.push(SocketAddr::new(
-                        IpAddr::V6(Ipv6Addr::new(0x2a00, 0x1450, 0x4013, 0xc04, 0, 0, 0, 0x6c)),
-                        port,
-                    ));
-                    resolved_addrs.push(SocketAddr::new(
-                        IpAddr::V4(Ipv4Addr::new(142, 250, 110, 109)),
-                        port,
-                    ));
-                }
-                _ => {}
-            }
         }
     }
 
     Ok(resolved_addrs)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::net::update_connection_history;
+    use crate::test_utils::TestContext;
+
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_sort_by_connection_timestamp() {
+        let alice = &TestContext::new_alice().await;
+        let now = time();
+
+        let ipv6_addr = IpAddr::V6(Ipv6Addr::new(0x2a01, 0x4f8, 0x241, 0x4ce8, 0, 0, 0, 2));
+        let ipv4_addr = IpAddr::V4(Ipv4Addr::new(116, 202, 233, 236));
+
+        assert_eq!(
+            sort_by_connection_timestamp(
+                alice,
+                vec![
+                    SocketAddr::new(ipv6_addr, 993),
+                    SocketAddr::new(ipv4_addr, 993)
+                ],
+                "imap",
+                "nine.testrun.org"
+            )
+            .await
+            .unwrap(),
+            vec![
+                SocketAddr::new(ipv6_addr, 993),
+                SocketAddr::new(ipv4_addr, 993)
+            ]
+        );
+        update_connection_history(
+            alice,
+            "imap",
+            "nine.testrun.org",
+            993,
+            "116.202.233.236",
+            now,
+        )
+        .await
+        .unwrap();
+        assert_eq!(
+            sort_by_connection_timestamp(
+                alice,
+                vec![
+                    SocketAddr::new(ipv6_addr, 993),
+                    SocketAddr::new(ipv4_addr, 993)
+                ],
+                "imap",
+                "nine.testrun.org"
+            )
+            .await
+            .unwrap(),
+            vec![
+                SocketAddr::new(ipv4_addr, 993),
+                SocketAddr::new(ipv6_addr, 993),
+            ]
+        );
+
+        assert_eq!(
+            sort_by_connection_timestamp(
+                alice,
+                vec![
+                    SocketAddr::new(ipv6_addr, 465),
+                    SocketAddr::new(ipv4_addr, 465)
+                ],
+                "smtp",
+                "nine.testrun.org"
+            )
+            .await
+            .unwrap(),
+            vec![
+                SocketAddr::new(ipv6_addr, 465),
+                SocketAddr::new(ipv4_addr, 465),
+            ]
+        );
+        update_connection_history(
+            alice,
+            "smtp",
+            "nine.testrun.org",
+            465,
+            "116.202.233.236",
+            now,
+        )
+        .await
+        .unwrap();
+        assert_eq!(
+            sort_by_connection_timestamp(
+                alice,
+                vec![
+                    SocketAddr::new(ipv6_addr, 465),
+                    SocketAddr::new(ipv4_addr, 465)
+                ],
+                "smtp",
+                "nine.testrun.org"
+            )
+            .await
+            .unwrap(),
+            vec![
+                SocketAddr::new(ipv4_addr, 465),
+                SocketAddr::new(ipv6_addr, 465),
+            ]
+        );
+
+        update_connection_history(
+            alice,
+            "imap",
+            "nine.testrun.org",
+            993,
+            "2a01:4f8:241:4ce8::2",
+            now,
+        )
+        .await
+        .unwrap();
+        assert_eq!(
+            sort_by_connection_timestamp(
+                alice,
+                vec![
+                    SocketAddr::new(ipv6_addr, 993),
+                    SocketAddr::new(ipv4_addr, 993)
+                ],
+                "imap",
+                "nine.testrun.org"
+            )
+            .await
+            .unwrap(),
+            vec![
+                SocketAddr::new(ipv6_addr, 993),
+                SocketAddr::new(ipv4_addr, 993)
+            ]
+        );
+    }
+
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_lookup_cache() {
+        let alice = &TestContext::new_alice().await;
+
+        let ipv4_addr = IpAddr::V4(Ipv4Addr::new(116, 202, 233, 236));
+        let ipv6_addr = IpAddr::V6(Ipv6Addr::new(0x2a01, 0x4f8, 0x241, 0x4ce8, 0, 0, 0, 2));
+
+        let now = time();
+        assert!(lookup_cache(alice, "nine.testrun.org", 587, "smtp", now)
+            .await
+            .unwrap()
+            .is_empty());
+
+        update_cache(alice, "nine.testrun.org", "116.202.233.236", now)
+            .await
+            .unwrap();
+
+        assert_eq!(
+            lookup_cache(alice, "nine.testrun.org", 587, "smtp", now)
+                .await
+                .unwrap(),
+            vec![SocketAddr::new(ipv4_addr, 587)]
+        );
+
+        // Cache should be returned for other ports and no ALPN as well,
+        // port and ALPN should only affect the order
+        assert_eq!(
+            lookup_cache(alice, "nine.testrun.org", 443, "", now)
+                .await
+                .unwrap(),
+            vec![SocketAddr::new(ipv4_addr, 443)]
+        );
+
+        update_cache(alice, "nine.testrun.org", "2a01:4f8:241:4ce8::2", now + 30)
+            .await
+            .unwrap();
+
+        // New DNS cache entry should go first.
+        assert_eq!(
+            lookup_cache(alice, "nine.testrun.org", 443, "", now + 60)
+                .await
+                .unwrap(),
+            vec![
+                SocketAddr::new(ipv6_addr, 443),
+                SocketAddr::new(ipv4_addr, 443)
+            ],
+        );
+
+        // After successful connection to SMTP over port 465 using IPv4 address,
+        // IPv4 address has higher priority.
+        update_connection_history(
+            alice,
+            "smtp",
+            "nine.testrun.org",
+            465,
+            "116.202.233.236",
+            now + 100,
+        )
+        .await
+        .unwrap();
+        assert_eq!(
+            lookup_cache(alice, "nine.testrun.org", 465, "smtp", now + 120)
+                .await
+                .unwrap(),
+            vec![
+                SocketAddr::new(ipv4_addr, 465),
+                SocketAddr::new(ipv6_addr, 465)
+            ]
+        );
+
+        // For other ports and ALPNs order remains the same.
+        assert_eq!(
+            lookup_cache(alice, "nine.testrun.org", 993, "imap", now + 120)
+                .await
+                .unwrap(),
+            vec![
+                SocketAddr::new(ipv6_addr, 993),
+                SocketAddr::new(ipv4_addr, 993)
+            ],
+        );
+        assert_eq!(
+            lookup_cache(alice, "nine.testrun.org", 465, "imap", now + 120)
+                .await
+                .unwrap(),
+            vec![
+                SocketAddr::new(ipv6_addr, 465),
+                SocketAddr::new(ipv4_addr, 465)
+            ],
+        );
+        assert_eq!(
+            lookup_cache(alice, "nine.testrun.org", 993, "smtp", now + 120)
+                .await
+                .unwrap(),
+            vec![
+                SocketAddr::new(ipv6_addr, 993),
+                SocketAddr::new(ipv4_addr, 993)
+            ],
+        );
+    }
+}

src/net/http.rs

@@ -119,7 +119,7 @@ impl reqwest::dns::Resolve for CustomResolver {
             let port = 443; // Actual port does not matter.
 
             let socket_addrs =
-                lookup_host_with_cache(&context, hostname.as_str(), port, load_cache).await;
+                lookup_host_with_cache(&context, hostname.as_str(), port, "", load_cache).await;
             match socket_addrs {
                 Ok(socket_addrs) => {
                     let addrs: reqwest::dns::Addrs = Box::new(socket_addrs.into_iter());

src/smtp/connect.rs

@@ -10,9 +10,11 @@ use crate::context::Context;
 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::update_connection_history;
 use crate::net::{connect_tcp_inner, connect_tls_inner};
 use crate::provider::Socket;
 use crate::socks::Socks5Config;
+use crate::tools::time;
 
 /// Returns TLS, STARTTLS or plaintext connection
 /// using SOCKS5 or direct connection depending on the given configuration.
@@ -50,7 +52,8 @@ pub(crate) async fn connect_stream(
         let mut first_error = None;
         let load_cache = strict_tls && (security == Socket::Ssl || security == Socket::Starttls);
 
-        for resolved_addr in lookup_host_with_cache(context, host, port, load_cache).await? {
+        for resolved_addr in lookup_host_with_cache(context, host, port, "smtp", load_cache).await?
+        {
             let res = match security {
                 Socket::Automatic => bail!("SMTP port security is not configured"),
                 Socket::Ssl => connect_secure(resolved_addr, host, strict_tls).await,
@@ -63,6 +66,8 @@ pub(crate) async fn connect_stream(
                     if load_cache {
                         update_connect_timestamp(context, host, &ip_addr).await?;
                     }
+                    update_connection_history(context, "smtp", host, port, &ip_addr, time())
+                        .await?;
                     return Ok(stream);
                 }
                 Err(err) => {

src/sql.rs

@@ -18,6 +18,8 @@ use crate::imex::BLOBS_BACKUP_NAME;
 use crate::location::delete_orphaned_poi_locations;
 use crate::log::LogExt;
 use crate::message::{Message, MsgId, Viewtype};
+use crate::net::dns::prune_dns_cache;
+use crate::net::prune_connection_history;
 use crate::param::{Param, Params};
 use crate::peerstate::Peerstate;
 use crate::stock_str;
@@ -787,6 +789,17 @@ pub async fn housekeeping(context: &Context) -> Result<()> {
         .log_err(context)
         .ok();
 
+    prune_connection_history(context)
+        .await
+        .context("Failed to prune connection history")
+        .log_err(context)
+        .ok();
+    prune_dns_cache(context)
+        .await
+        .context("Failed to prune DNS cache")
+        .log_err(context)
+        .ok();
+
     // Delete POI locations
     // which don't have corresponding message.
     delete_orphaned_poi_locations(context)

src/sql/migrations.rs

@@ -955,6 +955,22 @@ CREATE INDEX msgs_status_updates_index2 ON msgs_status_updates (uid);
         .await?;
     }
 
+    inc_and_check(&mut migration_version, 117)?;
+    if dbversion < migration_version {
+        sql.execute_migration(
+            "CREATE TABLE connection_history (
+                host TEXT NOT NULL, -- server hostname
+                port INTEGER NOT NULL, -- server port
+                alpn TEXT NOT NULL, -- ALPN such as smtp or imap
+                addr TEXT NOT NULL, -- IP address
+                timestamp INTEGER NOT NULL, -- timestamp of the most recent successful connection
+                UNIQUE (host, port, alpn, addr)
+            ) STRICT",
+            migration_version,
+        )
+        .await?;
+    }
+
     let new_version = sql
         .get_raw_config_int(VERSION_CFG)
         .await?