Check that reserves are met or progress is made on commitment tx gen

diff --git a/src/ln/channel.rs b/src/ln/channel.rs
index 001137cb304ec656cb96b82263fc2d20c03d302b..f5dc76d4511702988deaea3f9ffb4f2b61e650af 100644 (file)
--- a/src/ln/channel.rs
+++ b/src/ln/channel.rs
@@ -319,6 +319,13 @@ pub(super) struct Channel {
        channel_update_count: u32,
        feerate_per_kw: u64,
 
+       #[cfg(debug_assertions)]
+       /// Max to_local and to_remote outputs in a locally-generated commitment transaction
+       max_commitment_tx_output_local: ::std::sync::Mutex<(u64, u64)>,
+       #[cfg(debug_assertions)]
+       /// Max to_local and to_remote outputs in a remote-generated commitment transaction
+       max_commitment_tx_output_remote: ::std::sync::Mutex<(u64, u64)>,
+
        #[cfg(test)]
        // Used in ChannelManager's tests to send a revoked transaction
        pub last_local_commitment_txn: Vec<Transaction>,
@@ -491,6 +498,11 @@ impl Channel {
                        next_remote_htlc_id: 0,
                        channel_update_count: 1,
 
+                       #[cfg(debug_assertions)]
+                       max_commitment_tx_output_local: ::std::sync::Mutex::new((channel_value_satoshis * 1000 - push_msat, push_msat)),
+                       #[cfg(debug_assertions)]
+                       max_commitment_tx_output_remote: ::std::sync::Mutex::new((channel_value_satoshis * 1000 - push_msat, push_msat)),
+
                        last_local_commitment_txn: Vec::new(),
 
                        last_sent_closing_fee: None,
@@ -641,6 +653,11 @@ impl Channel {
                        next_remote_htlc_id: 0,
                        channel_update_count: 1,
 
+                       #[cfg(debug_assertions)]
+                       max_commitment_tx_output_local: ::std::sync::Mutex::new((msg.push_msat, msg.funding_satoshis * 1000 - msg.push_msat)),
+                       #[cfg(debug_assertions)]
+                       max_commitment_tx_output_remote: ::std::sync::Mutex::new((msg.push_msat, msg.funding_satoshis * 1000 - msg.push_msat)),
+
                        last_local_commitment_txn: Vec::new(),
 
                        last_sent_closing_fee: None,
@@ -826,9 +843,32 @@ impl Channel {
                }
 
 
+               let value_to_self_msat: i64 = (self.value_to_self_msat - local_htlc_total_msat) as i64 + value_to_self_msat_offset;
+               let value_to_remote_msat: i64 = (self.channel_value_satoshis * 1000 - self.value_to_self_msat - remote_htlc_total_msat) as i64 - value_to_self_msat_offset;
+
+               #[cfg(debug_assertions)]
+               {
+                       // Make sure that the to_self/to_remote is always either past the appropriate
+                       // channel_reserve *or* it is making progress towards it.
+                       // TODO: This should happen after fee calculation, but we don't handle that correctly
+                       // yet!
+                       let mut max_commitment_tx_output = if generated_by_local {
+                               self.max_commitment_tx_output_local.lock().unwrap()
+                       } else {
+                               self.max_commitment_tx_output_remote.lock().unwrap()
+                       };
+                       debug_assert!(max_commitment_tx_output.0 <= value_to_self_msat as u64 || value_to_self_msat / 1000 >= self.their_channel_reserve_satoshis as i64);
+                       max_commitment_tx_output.0 = cmp::max(max_commitment_tx_output.0, value_to_self_msat as u64);
+                       debug_assert!(max_commitment_tx_output.1 <= value_to_remote_msat as u64 || value_to_remote_msat / 1000 >= Channel::get_our_channel_reserve_satoshis(self.channel_value_satoshis) as i64);
+                       max_commitment_tx_output.1 = cmp::max(max_commitment_tx_output.1, value_to_remote_msat as u64);
+               }
+
                let total_fee: u64 = feerate_per_kw * (COMMITMENT_TX_BASE_WEIGHT + (txouts.len() as u64) * COMMITMENT_TX_WEIGHT_PER_HTLC) / 1000;
-               let value_to_self: i64 = ((self.value_to_self_msat - local_htlc_total_msat) as i64 + value_to_self_msat_offset) / 1000 - if self.channel_outbound { total_fee as i64 } else { 0 };
-               let value_to_remote: i64 = (((self.channel_value_satoshis * 1000 - self.value_to_self_msat - remote_htlc_total_msat) as i64 - value_to_self_msat_offset) / 1000) - if self.channel_outbound { 0 } else { total_fee as i64 };
+               let (value_to_self, value_to_remote) = if self.channel_outbound {
+                       (value_to_self_msat / 1000 - total_fee as i64, value_to_remote_msat / 1000)
+               } else {
+                       (value_to_self_msat / 1000, value_to_remote_msat / 1000 - total_fee as i64)
+               };
 
                let value_to_a = if local { value_to_self } else { value_to_remote };
                let value_to_b = if local { value_to_remote } else { value_to_self };