Merge remote-tracking branch 'origin/main-iroh' into chore-merge-upstream

quinn-proto/src/connection/mod.rs

@@ -2259,6 +2259,12 @@ impl Connection {
         path: PathId,
         ack: frame::Ack,
     ) -> Result<(), TransportError> {
+        if self.abandoned_paths.contains(&path) {
+            // See also https://www.ietf.org/archive/id/draft-ietf-quic-multipath-17.html#section-3.4.3-3
+            // > PATH_ACK frames received with an abandoned path ID are silently ignored, as specified in Section 4.
+            trace!("silently ignoring PATH_ACK on abandoned path");
+            return Ok(());
+        }
         if ack.largest >= self.spaces[space].for_path(path).next_packet_number {
             return Err(TransportError::PROTOCOL_VIOLATION("unsent packet acked"));
         }