Use bitcoin core's logic for anti-fee-sniping

diff --git a/src/sweep.rs b/src/sweep.rs
index ad1e9ef4d8698993c2615fd7e0fccfd46114a6bb..94120f9088ba377a659faf867ac394d1981ee80a 100644 (file)
--- a/src/sweep.rs
+++ b/src/sweep.rs
@@ -12,6 +12,7 @@ use lightning::util::ser::{Readable, WithoutLength};
 
 use bitcoin::secp256k1::Secp256k1;
 use bitcoin::{LockTime, PackedLockTime};
+use rand::{thread_rng, Rng};
 
 use crate::hex_utils;
 use crate::BitcoindClient;
@@ -111,7 +112,19 @@ pub(crate) async fn periodic_sweep(
                                        bitcoind_client.get_est_sat_per_1000_weight(ConfirmationTarget::Background);
 
                                // We set nLockTime to the current height to discourage fee sniping.
-                               let cur_height = channel_manager.current_best_block().height();
+                               // Occasionally randomly pick a nLockTime even further back, so
+                               // that transactions that are delayed after signing for whatever reason,
+                               // e.g. high-latency mix networks and some CoinJoin implementations, have
+                               // better privacy.
+                               // Logic copied from core: https://github.com/bitcoin/bitcoin/blob/1d4846a8443be901b8a5deb0e357481af22838d0/src/wallet/spend.cpp#L936
+                               let mut cur_height = channel_manager.current_best_block().height();
+
+                               // 10% of the time
+                               if thread_rng().gen_range(0, 10) == 0 {
+                                       // subtract random number between 0 and 100
+                                       cur_height = cur_height.saturating_sub(thread_rng().gen_range(0, 100));
+                               }
+
                                let locktime: PackedLockTime =
                                        LockTime::from_height(cur_height).map_or(PackedLockTime::ZERO, |l| l.into());