@@ -48,21 +48,103 @@ pub trait BroadcasterInterface {
4848/// estimation.
4949#[ derive( Clone , Copy , Debug , Hash , PartialEq , Eq ) ]
5050pub enum ConfirmationTarget {
51- /// We'd like a transaction to confirm in the future, but don't want to commit most of the fees
52- /// required to do so yet. The remaining fees will come via a Child-Pays-For-Parent (CPFP) fee
53- /// bump of the transaction.
54- ///
55- /// The feerate returned should be the absolute minimum feerate required to enter most node
56- /// mempools across the network. Note that if you are not able to obtain this feerate estimate,
57- /// you should likely use the furthest-out estimate allowed by your fee estimator.
58- MempoolMinimum ,
59- /// We are happy with a transaction confirming slowly, at least within a day or so worth of
60- /// blocks.
61- Background ,
62- /// We'd like a transaction to confirm without major delayed, i.e., within the next 12-24 blocks.
63- Normal ,
64- /// We'd like a transaction to confirm in the next few blocks.
65- HighPriority ,
51+ /// We have some funds available on chain which we need to spend prior to some expiry time at
52+ /// which point our counterparty may be able to steal them. Generally we have in the high tens
53+ /// to low hundreds of blocks to get our transaction on-chain, but we shouldn't risk too low a
54+ /// fee - this should be a relatively high priority feerate.
55+ OnChainSweep ,
56+ /// The highest feerate we will allow our channel counterparty to have in a non-anchor channel.
57+ ///
58+ /// This is the feerate on the transaction which we (or our counterparty) will broadcast in
59+ /// order to close the channel unilaterally. Because our counterparty must ensure they can
60+ /// always broadcast the latest state, this value being too low will cause immediate
61+ /// force-closures.
62+ ///
63+ /// Allowing this value to be too high can allow our counterparty to burn our HTLC outputs to
64+ /// dust, which can result in HTLCs failing or force-closures (when the dust HTLCs exceed
65+ /// [`ChannelConfig::max_dust_htlc_exposure`]).
66+ ///
67+ /// Because most nodes use a feerate estimate which is based on a relatively high priority
68+ /// transaction entering the current mempool, setting this to a small multiple of your current
69+ /// high priority feerate estimate should suffice.
70+ ///
71+ /// [`ChannelConfig::max_dust_htlc_exposure`]: crate::util::config::ChannelConfig::max_dust_htlc_exposure
72+ MaxAllowedNonAnchorChannelRemoteFee ,
73+ /// This is the lowest feerate we will allow our channel counterparty to have in an anchor
74+ /// channel in order to close the channel if a channel party goes away. Because our counterparty
75+ /// must ensure they can always broadcast the latest state, this value being too high will cause
76+ /// immediate force-closures.
77+ ///
78+ /// This needs to be sufficient to get into the mempool when the channel needs to
79+ /// be force-closed. Setting too low may result in force-closures. Because this is for anchor
80+ /// channels, we can always bump the feerate later, the feerate here only needs to suffice to
81+ /// enter the mempool.
82+ ///
83+ /// A good estimate is the expected mempool minimum at the time of force-closure. Obviously this
84+ /// is not an estimate which is very easy to calculate because we do not know the future. Using
85+ /// a simple long-term fee estimate or tracking of the mempool minimum is a good approach to
86+ /// ensure you can always close the channel. A future change to Bitcoin's P2P network
87+ /// (package relay) may obviate the need for this entirely.
88+ MinAllowedAnchorChannelRemoteFee ,
89+ /// The lowest feerate we will allow our channel counterparty to have in a non-anchor channel.
90+ /// This needs to be sufficient to get confirmed when the channel needs to be force-closed.
91+ /// Setting too low may result in force-closures.
92+ ///
93+ /// This is the feerate on the transaction which we (or our counterparty) will broadcast in
94+ /// order to close the channel if a channel party goes away. Because our counterparty must
95+ /// ensure they can always broadcast the latest state, this value being too high will cause
96+ /// immediate force-closures.
97+ ///
98+ /// This feerate represents the fee we pick now, which must be sufficient to enter a block at an
99+ /// arbitrary time in the future. Obviously this is not an estimate which is very easy to
100+ /// calculate. This can leave channels subject to being unable to close if feerates rise, and in
101+ /// general you should prefer anchor channels to ensure you can increase the feerate when the
102+ /// transactions need broadcasting.
103+ ///
104+ /// Do note some fee estimators round up to the next full sat/vbyte (ie 250 sats per kw),
105+ /// causing occasional issues with feerate disagreements between an initiator that wants a
106+ /// feerate of 1.1 sat/vbyte and a receiver that wants 1.1 rounded up to 2. If your fee
107+ /// estimator rounds subtracting 250 to your desired feerate here can help avoid this issue.
108+ ///
109+ /// [`ChannelConfig::max_dust_htlc_exposure`]: crate::util::config::ChannelConfig::max_dust_htlc_exposure
110+ MinAllowedNonAnchorChannelRemoteFee ,
111+ /// This is the feerate on the transaction which we (or our counterparty) will broadcast in
112+ /// order to close the channel if a channel party goes away.
113+ ///
114+ /// This needs to be sufficient to get into the mempool when the channel needs to
115+ /// be force-closed. Setting too low may result in force-closures. Because this is for anchor
116+ /// channels, it can be a low value as we can always bump the feerate later.
117+ ///
118+ /// A good estimate is the expected mempool minimum at the time of force-closure. Obviously this
119+ /// is not an estimate which is very easy to calculate because we do not know the future. Using
120+ /// a simple long-term fee estimate or tracking of the mempool minimum is a good approach to
121+ /// ensure you can always close the channel. A future change to Bitcoin's P2P network
122+ /// (package relay) may obviate the need for this entirely.
123+ AnchorChannelFee ,
124+ /// Lightning is built around the ability to broadcast a transaction in the future to close our
125+ /// channel and claim all pending funds. In order to do so, non-anchor channels are built with
126+ /// transactions which we need to be able to broadcast at some point in the future.
127+ ///
128+ /// This feerate represents the fee we pick now, which must be sufficient to enter a block at an
129+ /// arbitrary time in the future. Obviously this is not an estimate which is very easy to
130+ /// calculate, so most lightning nodes use some relatively high-priority feerate using the
131+ /// current mempool. This leaves channels subject to being unable to close if feerates rise, and
132+ /// in general you should prefer anchor channels to ensure you can increase the feerate when the
133+ /// transactions need broadcasting.
134+ ///
135+ /// Since this should represent the feerate of a channel close that does not need fee
136+ /// bumping, this is also used as an upper bound for our attempted feerate when doing cooperative
137+ /// closure of any channel.
138+ NonAnchorChannelFee ,
139+ /// When cooperatively closing a channel, this is the minimum feerate we will accept.
140+ /// Recommended at least within a day or so worth of blocks.
141+ ///
142+ /// This will also be used when initiating a cooperative close of a channel. When closing a
143+ /// channel you can override this fee by using
144+ /// [`ChannelManager::close_channel_with_feerate_and_script`].
145+ ///
146+ /// [`ChannelManager::close_channel_with_feerate_and_script`]: crate::ln::channelmanager::ChannelManager::close_channel_with_feerate_and_script
147+ ChannelCloseMinimum ,
66148}
67149
68150/// A trait which should be implemented to provide feerate information on a number of time
@@ -135,7 +217,7 @@ mod tests {
135217 let test_fee_estimator = & TestFeeEstimator { sat_per_kw } ;
136218 let fee_estimator = LowerBoundedFeeEstimator :: new ( test_fee_estimator) ;
137219
138- assert_eq ! ( fee_estimator. bounded_sat_per_1000_weight( ConfirmationTarget :: Background ) , FEERATE_FLOOR_SATS_PER_KW ) ;
220+ assert_eq ! ( fee_estimator. bounded_sat_per_1000_weight( ConfirmationTarget :: AnchorChannelFee ) , FEERATE_FLOOR_SATS_PER_KW ) ;
139221 }
140222
141223 #[ test]
@@ -144,6 +226,6 @@ mod tests {
144226 let test_fee_estimator = & TestFeeEstimator { sat_per_kw } ;
145227 let fee_estimator = LowerBoundedFeeEstimator :: new ( test_fee_estimator) ;
146228
147- assert_eq ! ( fee_estimator. bounded_sat_per_1000_weight( ConfirmationTarget :: Background ) , sat_per_kw) ;
229+ assert_eq ! ( fee_estimator. bounded_sat_per_1000_weight( ConfirmationTarget :: AnchorChannelFee ) , sat_per_kw) ;
148230 }
149231}
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