fix(cli): back off while waiting for a stored session

The daemon's wait-for-login loop slept a flat 3 seconds between checks and
never gave up, so an enabled service with no saved session polled the keyring
28,800 times a day. Each check is more than a sleep: auth::load() builds a
fresh keyring::Entry, so every iteration opens a new D-Bus connection to the
Secret Service and negotiates a session on it.

Back off from 3s to a 60s ceiling and say "not logged in" once at INFO rather
than on every iteration, which also stops the journal filling with tens of
thousands of identical lines.

The wait is extracted into wait_for_session() taking the load and sleep calls
as parameters, so the schedule is testable without a keyring and without real
time passing.

Refs #21

crates/pdfs-cli/src/main.rs

@@ -1448,6 +1448,54 @@ fn cmd_mount(mountpoint: Option<PathBuf>) -> Result<()> {
     Ok(())
 }
 
+/// How long to wait before the next login check, after `attempts` checks have
+/// already come back [`pdfs_core::Error::NotLoggedIn`].
+///
+/// Doubles from 3s to a 60s ceiling. The interval is not just a sleep:
+/// [`auth::load`] builds a fresh `keyring::Entry` on every call, so each check
+/// opens a new D-Bus connection to the Secret Service and negotiates an
+/// encrypted session over it. A flat 3s poll meant roughly 48,000 of those a
+/// day from a daemon that had nothing to do.
+fn login_poll_delay(attempts: u32) -> std::time::Duration {
+    const BASE_SECS: u64 = 3;
+    const MAX_SECS: u64 = 60;
+
+    // `checked_shl` rather than `<<`: the daemon can sit unauthenticated for
+    // weeks, and a shift past the width of the type is a panic, not a big number.
+    let factor = 1u64.checked_shl(attempts).unwrap_or(u64::MAX);
+    std::time::Duration::from_secs(BASE_SECS.saturating_mul(factor).min(MAX_SECS))
+}
+
+/// Block until a session is stored, backing off between checks.
+///
+/// `load` and `sleep` are parameters rather than direct calls so the backoff
+/// schedule can be tested without a keyring and without real time passing.
+fn wait_for_session<L, S>(mut load: L, mut sleep: S) -> Result<()>
+where
+    L: FnMut() -> std::result::Result<(), pdfs_core::Error>,
+    S: FnMut(std::time::Duration),
+{
+    let mut attempts: u32 = 0;
+    loop {
+        match load() {
+            Ok(()) => return Ok(()),
+            Err(pdfs_core::Error::NotLoggedIn) => {
+                let delay = login_poll_delay(attempts);
+                // Say it once at INFO. Repeating it every interval buried the
+                // journal in tens of thousands of identical lines a day.
+                if attempts == 0 {
+                    tracing::info!("not logged in; waiting for a session…");
+                } else {
+                    tracing::debug!(delay_secs = delay.as_secs(), "still not logged in");
+                }
+                sleep(delay);
+                attempts = attempts.saturating_add(1);
+            }
+            Err(e) => return Err(e.into()),
+        }
+    }
+}
+
 /// Run the auto-mount daemon loop. Waits for a stored login, mounts, and keeps
 /// the mount alive: a clean stop (SIGTERM via `systemctl --user stop`) exits 0;
 /// an external unmount triggers a remount; errors back off and retry. This is
@@ -1456,16 +1504,7 @@ fn cmd_daemon(mountpoint: Option<PathBuf>) -> Result<()> {
     loop {
         // Wait until a session is stored. The GUI enables this service on login,
         // but the service may also start at boot before the user has logged in.
-        loop {
-            match auth::load() {
-                Ok(_) => break,
-                Err(pdfs_core::Error::NotLoggedIn) => {
-                    tracing::info!("not logged in; waiting…");
-                    std::thread::sleep(std::time::Duration::from_secs(3));
-                }
-                Err(e) => return Err(e.into()),
-            }
-        }
+        wait_for_session(|| auth::load().map(|_| ()), std::thread::sleep)?;
 
         match mount_once(mountpoint.clone()) {
             Ok(pdfs_fuse::MountOutcome::Shutdown) => {
@@ -2537,3 +2576,64 @@ mod diagnose_tests {
         std::fs::remove_dir(dir).unwrap();
     }
 }
+
+#[cfg(test)]
+mod login_wait_tests {
+    use super::*;
+    use std::time::Duration;
+
+    #[test]
+    fn poll_delay_doubles_then_holds_at_the_ceiling() {
+        assert_eq!(login_poll_delay(0), Duration::from_secs(3));
+        assert_eq!(login_poll_delay(1), Duration::from_secs(6));
+        assert_eq!(login_poll_delay(2), Duration::from_secs(12));
+        assert_eq!(login_poll_delay(3), Duration::from_secs(24));
+        assert_eq!(login_poll_delay(4), Duration::from_secs(48));
+        assert_eq!(login_poll_delay(5), Duration::from_secs(60));
+        // A daemon left unauthenticated for weeks reaches attempt counts well
+        // past the width of the shift; that must cap, not panic.
+        assert_eq!(login_poll_delay(64), Duration::from_secs(60));
+        assert_eq!(login_poll_delay(u32::MAX), Duration::from_secs(60));
+    }
+
+    #[test]
+    fn waiting_for_a_session_stops_hammering_the_keyring() {
+        let mut checks_left = 20;
+        let mut slept: Vec<Duration> = Vec::new();
+
+        wait_for_session(
+            || {
+                if checks_left == 0 {
+                    Ok(())
+                } else {
+                    checks_left -= 1;
+                    Err(pdfs_core::Error::NotLoggedIn)
+                }
+            },
+            |delay| slept.push(delay),
+        )
+        .unwrap();
+
+        assert_eq!(slept.len(), 20, "one wait per failed check");
+        assert!(
+            slept.windows(2).all(|w| w[1] >= w[0]),
+            "the interval must never shrink: {slept:?}"
+        );
+
+        // The point of the change. Every check is a fresh D-Bus session against
+        // the Secret Service, so 20 of them must not fit inside a single minute
+        // the way a flat 3s poll did.
+        let total: Duration = slept.iter().sum();
+        assert!(
+            total >= Duration::from_secs(15 * 60),
+            "20 checks should span at least 15 minutes, spanned {total:?}"
+        );
+    }
+
+    #[test]
+    fn a_stored_session_is_not_waited_for_at_all() {
+        let mut slept = 0;
+        wait_for_session(|| Ok(()), |_| slept += 1).unwrap();
+        assert_eq!(slept, 0);
+    }
+}