Merge pull request #1527 from wpaulino/update-htlc-relay-policy

[rust-lightning] / lightning / src / ln / channelmanager.rs

diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs
index ef37dabc8ade68150602216d2ae42ad29fc67d4d..9f18671064b66cc2da4478fbe9fc977c4b8f230e 100644 (file)
--- a/lightning/src/ln/channelmanager.rs
+++ b/lightning/src/ln/channelmanager.rs
@@ -870,7 +870,13 @@ pub(crate) const MAX_LOCAL_BREAKDOWN_TIMEOUT: u16 = 2 * 6 * 24 * 7;
 // the HTLC via a full update_fail_htlc/commitment_signed dance before we hit the
 // CLTV_CLAIM_BUFFER point (we static assert that it's at least 3 blocks more).
 pub const MIN_CLTV_EXPIRY_DELTA: u16 = 6*7;
-pub(super) const CLTV_FAR_FAR_AWAY: u32 = 6 * 24 * 7; //TODO?
+// This should be long enough to allow a payment path drawn across multiple routing hops with substantial
+// `cltv_expiry_delta`. Indeed, the length of those values is the reaction delay offered to a routing node
+// in case of HTLC on-chain settlement. While appearing less competitive, a node operator could decide to
+// scale them up to suit its security policy. At the network-level, we shouldn't constrain them too much,
+// while avoiding to introduce a DoS vector. Further, a low CTLV_FAR_FAR_AWAY could be a source of
+// routing failure for any HTLC sender picking up an LDK node among the first hops.
+pub(super) const CLTV_FAR_FAR_AWAY: u32 = 14 * 24 * 6;
 
 /// Minimum CLTV difference between the current block height and received inbound payments.
 /// Invoices generated for payment to us must set their `min_final_cltv_expiry` field to at least
@@ -2784,6 +2790,9 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
        /// Returns an [`APIError::APIMisuseError`] if the funding_transaction spent non-SegWit outputs
        /// or if no output was found which matches the parameters in [`Event::FundingGenerationReady`].
        ///
+       /// Returns [`APIError::APIMisuseError`] if the funding transaction is not final for propagation
+       /// across the p2p network.
+       ///
        /// Returns [`APIError::ChannelUnavailable`] if a funding transaction has already been provided
        /// for the channel or if the channel has been closed as indicated by [`Event::ChannelClosed`].
        ///
@@ -2799,6 +2808,11 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
        /// not currently support replacing a funding transaction on an existing channel. Instead,
        /// create a new channel with a conflicting funding transaction.
        ///
+       /// Note to keep the miner incentives aligned in moving the blockchain forward, we recommend
+       /// the wallet software generating the funding transaction to apply anti-fee sniping as
+       /// implemented by Bitcoin Core wallet. See <https://bitcoinops.org/en/topics/fee-sniping/>
+       /// for more details.
+       ///
        /// [`Event::FundingGenerationReady`]: crate::util::events::Event::FundingGenerationReady
        /// [`Event::ChannelClosed`]: crate::util::events::Event::ChannelClosed
        pub fn funding_transaction_generated(&self, temporary_channel_id: &[u8; 32], counterparty_node_id: &PublicKey, funding_transaction: Transaction) -> Result<(), APIError> {
@@ -2811,6 +2825,18 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
                                });
                        }
                }
+               {
+                       let height = self.best_block.read().unwrap().height();
+                       // Transactions are evaluated as final by network mempools at the next block. However, the modules
+                       // constituting our Lightning node might not have perfect sync about their blockchain views. Thus, if
+                       // the wallet module is in advance on the LDK view, allow one more block of headroom.
+                       // TODO: updated if/when https://github.com/rust-bitcoin/rust-bitcoin/pull/994 landed and rust-bitcoin bumped.
+                       if !funding_transaction.input.iter().all(|input| input.sequence == 0xffffffff) && funding_transaction.lock_time < 500_000_000 && funding_transaction.lock_time > height + 2 {
+                               return Err(APIError::APIMisuseError {
+                                       err: "Funding transaction absolute timelock is non-final".to_owned()
+                               });
+                       }
+               }
                self.funding_transaction_generated_intern(temporary_channel_id, counterparty_node_id, funding_transaction, |chan, tx| {
                        let mut output_index = None;
                        let expected_spk = chan.get_funding_redeemscript().to_v0_p2wsh();