swarm: changes taken unjudged, dropped (REFUSALS)

A node refusing changes a peer brought tells it which broke a rule; the
peer judges them itself, and if its rules refuse them too, drops them
with all built on them (its document forked without them, a fresh
actor), quarantining its own writes among them. Wire version 42.

Auth plan M6 (rejoin on taint).

1 files changed, 16 insertions, 0 deletions

diff --git a/src/document/sync.rs b/src/document/sync.rs
index 823d4a3..b172dd1 100644
--- a/src/document/sync.rs
+++ b/src/document/sync.rs
@@ -212,6 +212,9 @@ pub(crate) struct SyncSession {
     /// The wait before answering a peer that offers again only changes we refused
     /// (`refused_again`).
     refused_backoff: Backoff,
+    /// When we last told the peer which of the changes it brought we refused
+    /// (`refusals_due`).
+    refusals_told: Option<Instant>,
 
     /// The answer we expect to our last sync message(s), if any.
     pub(crate) reply: Option<SyncReplyWait>,
@@ -264,6 +267,7 @@ impl SyncSession {
             assumed_lately: std::collections::VecDeque::new(),
             said_heads: None,
             refused_backoff: Backoff::new(REFUSED_WAIT, REFUSED_WAIT_MAX),
+            refusals_told: None,
             reply: None,
             reply_backoff,
         }
@@ -993,6 +997,18 @@ impl SyncSession {
         delay
     }
 
+    /// Whether to tell the peer which of the changes it brought we refused, now
+    /// (`swarm::refusals`): at most every `refusals::TELL_EVERY`.
+    pub(crate) fn refusals_due(&mut self, now: Instant) -> bool {
+        let due = self.refusals_told.is_none_or(|told| {
+            now.saturating_duration_since(told) >= crate::swarm::refusals::TELL_EVERY
+        });
+        if due {
+            self.refusals_told = Some(now);
+        }
+        due
+    }
+
     /// The peer brought changes we took (or none refused before): answered at once again.
     pub(crate) fn refusals_settled(&mut self) {
         self.refused_backoff.reset();