[rust-lightning] / lightning / src / util / config.rs

// This file is Copyright its original authors, visible in version control
// history.
//
// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
// You may not use this file except in accordance with one or both of these
// licenses.

//! Various user-configurable channel limits and settings which ChannelManager
//! applies for you.

use ln::channelmanager::{BREAKDOWN_TIMEOUT, MAX_LOCAL_BREAKDOWN_TIMEOUT};

/// Configuration we set when applicable.
///
/// Default::default() provides sane defaults.
#[derive(Copy, Clone, Debug)]
pub struct ChannelHandshakeConfig {
        /// Confirmations we will wait for before considering the channel locked in.
        /// Applied only for inbound channels (see ChannelHandshakeLimits::max_minimum_depth for the
        /// equivalent limit applied to outbound channels).
        ///
        /// Default value: 6.
        pub minimum_depth: u32,
        /// Set to the number of blocks we require our counterparty to wait to claim their money (ie
        /// the number of blocks we have to punish our counterparty if they broadcast a revoked
        /// transaction).
        ///
        /// This is one of the main parameters of our security model. We (or one of our watchtowers) MUST
        /// be online to check for revoked transactions on-chain at least once every our_to_self_delay
        /// blocks (minus some margin to allow us enough time to broadcast and confirm a transaction,
        /// possibly with time in between to RBF the spending transaction).
        ///
        /// Meanwhile, asking for a too high delay, we bother peer to freeze funds for nothing in
        /// case of an honest unilateral channel close, which implicitly decrease the economic value of
        /// our channel.
        ///
        /// Default value: [`BREAKDOWN_TIMEOUT`], we enforce it as a minimum at channel opening so you
        /// can tweak config to ask for more security, not less.
        pub our_to_self_delay: u16,
        /// Set to the smallest value HTLC we will accept to process.
        ///
        /// This value is sent to our counterparty on channel-open and we close the channel any time
        /// our counterparty misbehaves by sending us an HTLC with a value smaller than this.
        ///
        /// Default value: 1. If the value is less than 1, it is ignored and set to 1, as is required
        /// by the protocol.
        pub our_htlc_minimum_msat: u64,
        /// If set, we attempt to negotiate the `scid_privacy` (referred to as `scid_alias` in the
        /// BOLTs) option for outbound private channels. This provides better privacy by not including
        /// our real on-chain channel UTXO in each invoice and requiring that our counterparty only
        /// relay HTLCs to us using the channel's SCID alias.
        ///
        /// If this option is set, channels may be created that will not be readable by LDK versions
        /// prior to 0.0.106, causing [`ChannelManager`]'s read method to return a
        /// [`DecodeError:InvalidValue`].
        ///
        /// Note that setting this to true does *not* prevent us from opening channels with
        /// counterparties that do not support the `scid_alias` option; we will simply fall back to a
        /// private channel without that option.
        ///
        /// Ignored if the channel is negotiated to be announced, see
        /// [`ChannelConfig::announced_channel`] and
        /// [`ChannelHandshakeLimits::force_announced_channel_preference`] for more.
        ///
        /// Default value: false. This value is likely to change to true in the future.
        ///
        /// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
        /// [`DecodeError:InvalidValue`]: crate::ln::msgs::DecodeError::InvalidValue
        pub negotiate_scid_privacy: bool,
}

impl Default for ChannelHandshakeConfig {
        fn default() -> ChannelHandshakeConfig {
                ChannelHandshakeConfig {
                        minimum_depth: 6,
                        our_to_self_delay: BREAKDOWN_TIMEOUT,
                        our_htlc_minimum_msat: 1,
                        negotiate_scid_privacy: false,
                }
        }
}

/// Optional channel limits which are applied during channel creation.
///
/// These limits are only applied to our counterparty's limits, not our own.
///
/// Use 0/<type>::max_value() as appropriate to skip checking.
///
/// Provides sane defaults for most configurations.
///
/// Most additional limits are disabled except those with which specify a default in individual
/// field documentation. Note that this may result in barely-usable channels, but since they
/// are applied mostly only to incoming channels that's not much of a problem.
#[derive(Copy, Clone, Debug)]
pub struct ChannelHandshakeLimits {
        /// Minimum allowed satoshis when a channel is funded, this is supplied by the sender and so
        /// only applies to inbound channels.
        ///
        /// Default value: 0.
        pub min_funding_satoshis: u64,
        /// The remote node sets a limit on the minimum size of HTLCs we can send to them. This allows
        /// you to limit the maximum minimum-size they can require.
        ///
        /// Default value: u64::max_value.
        pub max_htlc_minimum_msat: u64,
        /// The remote node sets a limit on the maximum value of pending HTLCs to them at any given
        /// time to limit their funds exposure to HTLCs. This allows you to set a minimum such value.
        ///
        /// Default value: 0.
        pub min_max_htlc_value_in_flight_msat: u64,
        /// The remote node will require we keep a certain amount in direct payment to ourselves at all
        /// time, ensuring that we are able to be punished if we broadcast an old state. This allows to
        /// you limit the amount which we will have to keep to ourselves (and cannot use for HTLCs).
        ///
        /// Default value: u64::max_value.
        pub max_channel_reserve_satoshis: u64,
        /// The remote node sets a limit on the maximum number of pending HTLCs to them at any given
        /// time. This allows you to set a minimum such value.
        ///
        /// Default value: 0.
        pub min_max_accepted_htlcs: u16,
        /// Before a channel is usable the funding transaction will need to be confirmed by at least a
        /// certain number of blocks, specified by the node which is not the funder (as the funder can
        /// assume they aren't going to double-spend themselves).
        /// This config allows you to set a limit on the maximum amount of time to wait.
        ///
        /// Default value: 144, or roughly one day and only applies to outbound channels.
        pub max_minimum_depth: u32,
        /// Set to force an incoming channel to match our announced channel preference in
        /// [`ChannelConfig::announced_channel`].
        ///
        /// For a node which is not online reliably, this should be set to true and
        /// [`ChannelConfig::announced_channel`] set to false, ensuring that no announced (aka public)
        /// channels will ever be opened.
        ///
        /// Default value: true.
        pub force_announced_channel_preference: bool,
        /// Set to the amount of time we're willing to wait to claim money back to us.
        ///
        /// Not checking this value would be a security issue, as our peer would be able to set it to
        /// max relative lock-time (a year) and we would "lose" money as it would be locked for a long time.
        ///
        /// Default value: 2016, which we also enforce as a maximum value so you can tweak config to
        /// reduce the loss of having useless locked funds (if your peer accepts)
        pub their_to_self_delay: u16
}

impl Default for ChannelHandshakeLimits {
        fn default() -> Self {
                ChannelHandshakeLimits {
                        min_funding_satoshis: 0,
                        max_htlc_minimum_msat: <u64>::max_value(),
                        min_max_htlc_value_in_flight_msat: 0,
                        max_channel_reserve_satoshis: <u64>::max_value(),
                        min_max_accepted_htlcs: 0,
                        max_minimum_depth: 144,
                        force_announced_channel_preference: true,
                        their_to_self_delay: MAX_LOCAL_BREAKDOWN_TIMEOUT,
                }
        }
}

/// Options which apply on a per-channel basis and may change at runtime or based on negotiation
/// with our counterparty.
#[derive(Copy, Clone, Debug)]
pub struct ChannelConfig {
        /// Amount (in millionths of a satoshi) charged per satoshi for payments forwarded outbound
        /// over the channel.
        /// This may be allowed to change at runtime in a later update, however doing so must result in
        /// update messages sent to notify all nodes of our updated relay fee.
        ///
        /// Default value: 0.
        pub forwarding_fee_proportional_millionths: u32,
        /// Amount (in milli-satoshi) charged for payments forwarded outbound over the channel, in
        /// excess of [`forwarding_fee_proportional_millionths`].
        /// This may be allowed to change at runtime in a later update, however doing so must result in
        /// update messages sent to notify all nodes of our updated relay fee.
        ///
        /// The default value of a single satoshi roughly matches the market rate on many routing nodes
        /// as of July 2021. Adjusting it upwards or downwards may change whether nodes route through
        /// this node.
        ///
        /// Default value: 1000.
        ///
        /// [`forwarding_fee_proportional_millionths`]: ChannelConfig::forwarding_fee_proportional_millionths
        pub forwarding_fee_base_msat: u32,
        /// The difference in the CLTV value between incoming HTLCs and an outbound HTLC forwarded over
        /// the channel this config applies to.
        ///
        /// This is analogous to [`ChannelHandshakeConfig::our_to_self_delay`] but applies to in-flight
        /// HTLC balance when a channel appears on-chain whereas
        /// [`ChannelHandshakeConfig::our_to_self_delay`] applies to the remaining
        /// (non-HTLC-encumbered) balance.
        ///
        /// Thus, for HTLC-encumbered balances to be enforced on-chain when a channel is force-closed,
        /// we (or one of our watchtowers) MUST be online to check for broadcast of the current
        /// commitment transaction at least once per this many blocks (minus some margin to allow us
        /// enough time to broadcast and confirm a transaction, possibly with time in between to RBF
        /// the spending transaction).
        ///
        /// Default value: 72 (12 hours at an average of 6 blocks/hour).
        /// Minimum value: [`MIN_CLTV_EXPIRY_DELTA`], any values less than this will be treated as
        ///                [`MIN_CLTV_EXPIRY_DELTA`] instead.
        ///
        /// [`MIN_CLTV_EXPIRY_DELTA`]: crate::ln::channelmanager::MIN_CLTV_EXPIRY_DELTA
        pub cltv_expiry_delta: u16,
        /// Set to announce the channel publicly and notify all nodes that they can route via this
        /// channel.
        ///
        /// This should only be set to true for nodes which expect to be online reliably.
        ///
        /// As the node which funds a channel picks this value this will only apply for new outbound
        /// channels unless [`ChannelHandshakeLimits::force_announced_channel_preference`] is set.
        ///
        /// This cannot be changed after the initial channel handshake.
        ///
        /// Default value: false.
        pub announced_channel: bool,
        /// When set, we commit to an upfront shutdown_pubkey at channel open. If our counterparty
        /// supports it, they will then enforce the mutual-close output to us matches what we provided
        /// at intialization, preventing us from closing to an alternate pubkey.
        ///
        /// This is set to true by default to provide a slight increase in security, though ultimately
        /// any attacker who is able to take control of a channel can just as easily send the funds via
        /// lightning payments, so we never require that our counterparties support this option.
        ///
        /// This cannot be changed after a channel has been initialized.
        ///
        /// Default value: true.
        pub commit_upfront_shutdown_pubkey: bool,
        /// Limit our total exposure to in-flight HTLCs which are burned to fees as they are too
        /// small to claim on-chain.
        ///
        /// When an HTLC present in one of our channels is below a "dust" threshold, the HTLC will
        /// not be claimable on-chain, instead being turned into additional miner fees if either
        /// party force-closes the channel. Because the threshold is per-HTLC, our total exposure
        /// to such payments may be sustantial if there are many dust HTLCs present when the
        /// channel is force-closed.
        ///
        /// This limit is applied for sent, forwarded, and received HTLCs and limits the total
        /// exposure across all three types per-channel. Setting this too low may prevent the
        /// sending or receipt of low-value HTLCs on high-traffic nodes, and this limit is very
        /// important to prevent stealing of dust HTLCs by miners.
        ///
        /// Default value: 5_000_000 msat.
        pub max_dust_htlc_exposure_msat: u64,
        /// The additional fee we're willing to pay to avoid waiting for the counterparty's
        /// `to_self_delay` to reclaim funds.
        ///
        /// When we close a channel cooperatively with our counterparty, we negotiate a fee for the
        /// closing transaction which both sides find acceptable, ultimately paid by the channel
        /// funder/initiator.
        ///
        /// When we are the funder, because we have to pay the channel closing fee, we bound the
        /// acceptable fee by our [`Background`] and [`Normal`] fees, with the upper bound increased by
        /// this value. Because the on-chain fee we'd pay to force-close the channel is kept near our
        /// [`Normal`] feerate during normal operation, this value represents the additional fee we're
        /// willing to pay in order to avoid waiting for our counterparty's to_self_delay to reclaim our
        /// funds.
        ///
        /// When we are not the funder, we require the closing transaction fee pay at least our
        /// [`Background`] fee estimate, but allow our counterparty to pay as much fee as they like.
        /// Thus, this value is ignored when we are not the funder.
        ///
        /// Default value: 1000 satoshis.
        ///
        /// [`Normal`]: crate::chain::chaininterface::ConfirmationTarget::Normal
        /// [`Background`]: crate::chain::chaininterface::ConfirmationTarget::Background
        pub force_close_avoidance_max_fee_satoshis: u64,
}

impl Default for ChannelConfig {
        /// Provides sane defaults for most configurations (but with zero relay fees!).
        fn default() -> Self {
                ChannelConfig {
                        forwarding_fee_proportional_millionths: 0,
                        forwarding_fee_base_msat: 1000,
                        cltv_expiry_delta: 6 * 12, // 6 blocks/hour * 12 hours
                        announced_channel: false,
                        commit_upfront_shutdown_pubkey: true,
                        max_dust_htlc_exposure_msat: 5_000_000,
                        force_close_avoidance_max_fee_satoshis: 1000,
                }
        }
}

impl_writeable_tlv_based!(ChannelConfig, {
        (0, forwarding_fee_proportional_millionths, required),
        (1, max_dust_htlc_exposure_msat, (default_value, 5_000_000)),
        (2, cltv_expiry_delta, required),
        (3, force_close_avoidance_max_fee_satoshis, (default_value, 1000)),
        (4, announced_channel, required),
        (6, commit_upfront_shutdown_pubkey, required),
        (8, forwarding_fee_base_msat, required),
});

/// Top-level config which holds ChannelHandshakeLimits and ChannelConfig.
///
/// Default::default() provides sane defaults for most configurations
/// (but currently with 0 relay fees!)
#[derive(Copy, Clone, Debug)]
pub struct UserConfig {
        /// Channel config that we propose to our counterparty.
        pub own_channel_config: ChannelHandshakeConfig,
        /// Limits applied to our counterparty's proposed channel config settings.
        pub peer_channel_config_limits: ChannelHandshakeLimits,
        /// Channel config which affects behavior during channel lifetime.
        pub channel_options: ChannelConfig,
        /// If this is set to false, we will reject any HTLCs which were to be forwarded over private
        /// channels. This prevents us from taking on HTLC-forwarding risk when we intend to run as a
        /// node which is not online reliably.
        ///
        /// For nodes which are not online reliably, you should set all channels to *not* be announced
        /// (using [`ChannelConfig::announced_channel`] and
        /// [`ChannelHandshakeLimits::force_announced_channel_preference`]) and set this to false to
        /// ensure you are not exposed to any forwarding risk.
        ///
        /// Note that because you cannot change a channel's announced state after creation, there is no
        /// way to disable forwarding on public channels retroactively. Thus, in order to change a node
        /// from a publicly-announced forwarding node to a private non-forwarding node you must close
        /// all your channels and open new ones. For privacy, you should also change your node_id
        /// (swapping all private and public key material for new ones) at that time.
        ///
        /// Default value: false.
        pub accept_forwards_to_priv_channels: bool,
        /// If this is set to false, we do not accept inbound requests to open a new channel.
        /// Default value: true.
        pub accept_inbound_channels: bool,
        /// If this is set to true, the user needs to manually accept inbound requests to open a new
        /// channel.
        ///
        /// When set to true, [`Event::OpenChannelRequest`] will be triggered once a request to open a
        /// new inbound channel is received through a [`msgs::OpenChannel`] message. In that case, a
        /// [`msgs::AcceptChannel`] message will not be sent back to the counterparty node unless the
        /// user explicitly chooses to accept the request.
        ///
        /// Default value: false.
        ///
        /// [`Event::OpenChannelRequest`]: crate::util::events::Event::OpenChannelRequest
        /// [`msgs::OpenChannel`]: crate::ln::msgs::OpenChannel
        /// [`msgs::AcceptChannel`]: crate::ln::msgs::AcceptChannel
        pub manually_accept_inbound_channels: bool,
}

impl Default for UserConfig {
        fn default() -> Self {
                UserConfig {
                        own_channel_config: ChannelHandshakeConfig::default(),
                        peer_channel_config_limits: ChannelHandshakeLimits::default(),
                        channel_options: ChannelConfig::default(),
                        accept_forwards_to_priv_channels: false,
                        accept_inbound_channels: true,
                        manually_accept_inbound_channels: false,
                }
        }
}