keep silent strangers for a day

1 files changed, 38 insertions, 2 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"
+    );
+}