Document exactly our CLTV sanitization policy for incoming HTLCs

diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs
index f9ccc18a0c707b66773a7421e9115a3b329f57b9..4f71f406bd7872c01aed72d45b28f16105d06a1d 100644 (file)
--- a/lightning/src/ln/channelmanager.rs
+++ b/lightning/src/ln/channelmanager.rs
@@ -1160,7 +1160,8 @@ impl<ChanSigner: ChannelKeys, M: Deref, T: Deref, K: Deref, F: Deref> ChannelMan
                                                break Some(("Forwarding node has tampered with the intended HTLC values or origin node has an obsolete cltv_expiry_delta", 0x1000 | 13, Some(self.get_channel_update(chan).unwrap())));
                                        }
                                        let cur_height = self.latest_block_height.load(Ordering::Acquire) as u32 + 1;
-                                       // We want to have at least LATENCY_GRACE_PERIOD_BLOCKS to fail prior to going on chain CLAIM_BUFFER blocks before expiration
+                                       // Theoritically, channel counterparty shouldn't send us a HLC expiring now, but we want to be robust wrt to counterparty
+                                       // packet sanitization.
                                        if msg.cltv_expiry <= cur_height + CLTV_CLAIM_BUFFER + LATENCY_GRACE_PERIOD_BLOCKS as u32 { // expiry_too_soon
                                                break Some(("CLTV expiry is too close", 0x1000 | 14, Some(self.get_channel_update(chan).unwrap())));
                                        }