+ // For inbound HTLCs which we know the preimage for, we have to ensure we hit the
+ // chain with enough room to claim the HTLC without our counterparty being able to
+ // time out the HTLC first.
+ // For outbound HTLCs which our counterparty hasn't failed/claimed, our primary
+ // concern is being able to claim the corresponding inbound HTLC (on another
+ // channel) before it expires. In fact, we don't even really care if our
+ // counterparty here claims such an outbound HTLC after it expired as long as we
+ // can still claim the corresponding HTLC. Thus, to avoid needlessly hitting the
+ // chain when our counterparty is waiting for expiration to off-chain fail an HTLC
+ // we give ourselves a few blocks of headroom after expiration before going
+ // on-chain for an expired HTLC.
+ // Note that, to avoid a potential attack whereby a node delays claiming an HTLC
+ // from us until we've reached the point where we go on-chain with the
+ // corresponding inbound HTLC, we must ensure that outbound HTLCs go on chain at
+ // least CLTV_CLAIM_BUFFER blocks prior to the inbound HTLC.
+ // aka outbound_cltv + HTLC_FAIL_TIMEOUT_BLOCKS == height - CLTV_CLAIM_BUFFER
+ // inbound_cltv == height + CLTV_CLAIM_BUFFER
+ // outbound_cltv + HTLC_FAIL_TIMEOUT_BLOCKS + CLTV_CLAIM_BUFER <= inbound_cltv - CLTV_CLAIM_BUFFER
+ // HTLC_FAIL_TIMEOUT_BLOCKS + 2*CLTV_CLAIM_BUFER <= inbound_cltv - outbound_cltv
+ // HTLC_FAIL_TIMEOUT_BLOCKS + 2*CLTV_CLAIM_BUFER <= CLTV_EXPIRY_DELTA
+ if ( htlc.offered && htlc.cltv_expiry + HTLC_FAIL_TIMEOUT_BLOCKS <= height) ||
+ (!htlc.offered && htlc.cltv_expiry <= height + CLTV_CLAIM_BUFFER && self.payment_preimages.contains_key(&htlc.payment_hash)) {
+ return true;