keep silent strangers for a day

2 files changed, 40 insertions, 3 deletions

diff --git a/src/swarm/peer/forget.rs b/src/swarm/peer/forget.rs
index 624ca97..df09c3c 100644
--- a/src/swarm/peer/forget.rs
+++ b/src/swarm/peer/forget.rs
@@ -1,5 +1,8 @@
 //! Swarm-wide forget records (`_continuum/forgotten/<pk>`): a peer forgotten on one
-//! node is forgotten by all; a forgotten node that is alive cancels its record.
+//! node is forgotten by all; a forgotten node that is alive cancels its record. And
+//! locally, strangers that went silent.
+
+use std::time::Duration;
 
 use automerge::AutoCommit;
 use tokio::time::Instant;
@@ -7,7 +10,7 @@ use tracing::{info, warn};
 
 use crate::document::meta;
 use crate::document::store::{self, StoreError};
-use crate::state::AppState;
+use crate::state::{AppState, Standing};
 
 fn forgotten_dir() -> Vec<String> {
     meta::path(&[meta::FORGOTTEN])
@@ -77,3 +80,36 @@ pub(super) async fn apply_forget_records(state: &AppState) {
         })
         .await;
 }
+
+/// How long a peer that never became a member is kept once nothing more is heard from
+/// it: one listed to us that never answered, or one that keeps failing the handshake
+/// (another swarm, a wrong key). Anyone can name peers to a node, so without a limit
+/// the map of peers would only grow.
+const STRANGER_KEPT: Duration = Duration::from_secs(24 * 3600);
+
+/// Forgets peers that never became members and were silent for `STRANGER_KEPT`. Only
+/// here, not swarm-wide; one that comes back is a stranger again.
+pub(super) async fn forget_strangers(state: &AppState) {
+    let now = Instant::now();
+    let mut strangers = Vec::new();
+    for (peer, peer_state) in state.peers_snapshot().await {
+        let peer_state = peer_state.lock().await;
+        let quiet_since = peer_state.last_seen.unwrap_or(peer_state.added_at);
+        if !matches!(peer_state.standing, Standing::Member { .. })
+            && now.saturating_duration_since(quiet_since) >= STRANGER_KEPT
+        {
+            strangers.push(peer);
+        }
+    }
+    if strangers.is_empty() {
+        return;
+    }
+    let mut peer_states = state.peer_states.write().await;
+    for peer in &strangers {
+        peer_states.remove(peer);
+    }
+    info!(
+        forgotten = strangers.len(),
+        "Forgot peers that never became members and were silent for a day"
+    );
+}
diff --git a/src/swarm/peer/worker.rs b/src/swarm/peer/worker.rs
index a27f144..5161ae6 100644
--- a/src/swarm/peer/worker.rs
+++ b/src/swarm/peer/worker.rs
@@ -8,7 +8,7 @@ use std::time::Duration;
 use tokio::time::{Instant, MissedTickBehavior};
 use tracing::{debug, info, warn};
 
-use super::forget::apply_forget_records;
+use super::forget::{apply_forget_records, forget_strangers};
 use super::handshake::retry_hello_if_due;
 use super::keepalive::send_ping;
 use crate::locks::MutexExt;
@@ -94,6 +94,7 @@ pub(crate) async fn run_peer_worker(state: AppState) {
 
         if last_forget_check.is_none_or(|t| t.elapsed() >= FORGET_CHECK_INTERVAL) {
             apply_forget_records(&state).await;
+            forget_strangers(&state).await;
             crate::swarm::members::ensure_registered(&state).await;
             crate::swarm::stability::tick(&state).await;
             crate::swarm::stats::measure_saved_size(&state);