Add a note that `peer_disconnected` impls must be idempotent

It appears our code is already correct here, but its also nice to
add a quick safety check in `channel.rs` which ensures we will
remain idempotent.

diff --git a/lightning/src/ln/channel.rs b/lightning/src/ln/channel.rs
index b37550b0d2a91eb909bb997dc3dda39a91de887b..c8209a9eac6f984f76514987729d9ca04dde192f 100644 (file)
--- a/lightning/src/ln/channel.rs
+++ b/lightning/src/ln/channel.rs
@@ -3550,6 +3550,12 @@ impl<Signer: Sign> Channel<Signer> {
                        return;
                }
 
+               if self.channel_state & (ChannelState::PeerDisconnected as u32) == (ChannelState::PeerDisconnected as u32) {
+                       // While the below code should be idempotent, it's simpler to just return early, as
+                       // redundant disconnect events can fire, though they should be rare.
+                       return;
+               }
+
                if self.announcement_sigs_state == AnnouncementSigsState::MessageSent || self.announcement_sigs_state == AnnouncementSigsState::Committed {
                        self.announcement_sigs_state = AnnouncementSigsState::NotSent;
                }

diff --git a/lightning/src/ln/msgs.rs b/lightning/src/ln/msgs.rs
index 747107c08221c41b04a5283a91804031d981325f..98831137b303b6a9edaae8e393bd32fae2ec48ec 100644 (file)
--- a/lightning/src/ln/msgs.rs
+++ b/lightning/src/ln/msgs.rs
@@ -883,6 +883,9 @@ pub trait ChannelMessageHandler : MessageSendEventsProvider {
        /// is believed to be possible in the future (eg they're sending us messages we don't
        /// understand or indicate they require unknown feature bits), no_connection_possible is set
        /// and any outstanding channels should be failed.
+       ///
+       /// Note that in some rare cases this may be called without a corresponding
+       /// [`Self::peer_connected`].
        fn peer_disconnected(&self, their_node_id: &PublicKey, no_connection_possible: bool);
 
        /// Handle a peer reconnecting, possibly generating channel_reestablish message(s).
@@ -979,6 +982,9 @@ pub trait OnionMessageHandler : OnionMessageProvider {
        fn peer_connected(&self, their_node_id: &PublicKey, init: &Init);
        /// Indicates a connection to the peer failed/an existing connection was lost. Allows handlers to
        /// drop and refuse to forward onion messages to this peer.
+       ///
+       /// Note that in some rare cases this may be called without a corresponding
+       /// [`Self::peer_connected`].
        fn peer_disconnected(&self, their_node_id: &PublicKey, no_connection_possible: bool);
 
        // Handler information: