Skip to content

Channel Establishment for V3 Channels #3792

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 8 commits into from
Jun 6, 2025
Merged

Channel Establishment for V3 Channels #3792

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
8 commits
Select commit Hold shift + click to select a range
588f490
ln/refactor: add helper test function for channel type downgrade
carlaKC Jun 4, 2025
3b1e691
ln/refactor: use get_initial_channel_type for channel downgrade
carlaKC Jun 4, 2025
ffddb20
ln+util: add test option to enable negotiation of zero fee channels
carlaKC Jun 4, 2025
e4465c4
ln/refactor: add helper function for channel type tests
carlaKC May 19, 2025
aab2d29
ln: do not set or accept non-zero feerates in open_channel for v3
carlaKC May 19, 2025
67e394d
ln/refactor: add helper function for manual acceptance tests
carlaKC Jun 4, 2025
41d8529
ln: do not automatically accept zero fee commitment channels
carlaKC Jun 4, 2025
23de01c
ln: set `max_htlcs` based on the channel type
TheBlueMatt Mar 9, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
9 changes: 9 additions & 0 deletions lightning-types/src/features.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1024,6 +1024,15 @@ impl ChannelTypeFeatures {
<sealed::ChannelTypeContext as sealed::AnchorsZeroFeeHtlcTx>::set_required_bit(&mut ret);
ret
}

/// Constructs a ChannelTypeFeatures with zero fee commitment anchors support.
pub fn anchors_zero_fee_commitments() -> Self {
let mut ret = Self::empty();
<sealed::ChannelTypeContext as sealed::AnchorZeroFeeCommitments>::set_required_bit(
&mut ret,
);
ret
}
}

impl<T: sealed::Context> Features<T> {
Expand Down
9 changes: 7 additions & 2 deletions lightning/src/ln/chan_utils.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -58,8 +58,13 @@ use crate::prelude::*;
/// 483 for non-zero-fee-commitment channels and 114 for zero-fee-commitment channels.
///
/// Actual maximums can be set equal to or below this value by each channel participant.
pub fn max_htlcs(_channel_type: &ChannelTypeFeatures) -> u16 {
483
pub fn max_htlcs(channel_type: &ChannelTypeFeatures) -> u16 {
if channel_type.supports_anchor_zero_fee_commitments() {
// TRUC restricts the size of our commitment transactions to 10K vB rather than 100K vB
114
} else {
483
}
}
/// The weight of a BIP141 witnessScript for a BOLT3's "offered HTLC output" on a commitment transaction, non-anchor variant.
pub const OFFERED_HTLC_SCRIPT_WEIGHT: usize = 133;
Expand Down
188 changes: 144 additions & 44 deletions lightning/src/ln/channel.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1557,6 +1557,7 @@ impl<SP: Deref> Channel<SP> where

pub fn maybe_handle_error_without_close<F: Deref, L: Deref>(
&mut self, chain_hash: ChainHash, fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L,
user_config: &UserConfig, their_features: &InitFeatures,
) -> Result<Option<OpenChannelMessage>, ()>
where
F::Target: FeeEstimator,
Expand All @@ -1567,13 +1568,17 @@ impl<SP: Deref> Channel<SP> where
ChannelPhase::Funded(_) => Ok(None),
ChannelPhase::UnfundedOutboundV1(chan) => {
let logger = WithChannelContext::from(logger, &chan.context, None);
chan.maybe_handle_error_without_close(chain_hash, fee_estimator, &&logger)
chan.maybe_handle_error_without_close(
chain_hash, fee_estimator, &&logger, user_config, their_features,
)
.map(|msg| Some(OpenChannelMessage::V1(msg)))
},
ChannelPhase::UnfundedInboundV1(_) => Ok(None),
ChannelPhase::UnfundedV2(chan) => {
if chan.funding.is_outbound() {
chan.maybe_handle_error_without_close(chain_hash, fee_estimator)
chan.maybe_handle_error_without_close(
chain_hash, fee_estimator, user_config, their_features,
)
.map(|msg| Some(OpenChannelMessage::V2(msg)))
} else {
Ok(None)
Expand Down Expand Up @@ -3072,12 +3077,18 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
debug_assert!(!channel_type.supports_any_optional_bits());
debug_assert!(!channel_type.requires_unknown_bits_from(&channelmanager::provided_channel_type_features(&config)));

let (commitment_conf_target, anchor_outputs_value_msat) = if channel_type.supports_anchors_zero_fee_htlc_tx() {
(ConfirmationTarget::AnchorChannelFee, ANCHOR_OUTPUT_VALUE_SATOSHI * 2 * 1000)
} else {
(ConfirmationTarget::NonAnchorChannelFee, 0)
};
let commitment_feerate = fee_estimator.bounded_sat_per_1000_weight(commitment_conf_target);
let (commitment_feerate, anchor_outputs_value_msat) =
if channel_type.supports_anchor_zero_fee_commitments() {
(0, 0)
} else if channel_type.supports_anchors_zero_fee_htlc_tx() {
let feerate = fee_estimator
.bounded_sat_per_1000_weight(ConfirmationTarget::AnchorChannelFee);
(feerate, ANCHOR_OUTPUT_VALUE_SATOSHI * 2 * 1000)
} else {
let feerate = fee_estimator
.bounded_sat_per_1000_weight(ConfirmationTarget::NonAnchorChannelFee);
(feerate, 0)
};

let value_to_self_msat = channel_value_satoshis * 1000 - push_msat;
let commitment_tx_fee = commit_tx_fee_sat(commitment_feerate, MIN_AFFORDABLE_HTLC_COUNT, &channel_type) * 1000;
Expand Down Expand Up @@ -4868,7 +4879,8 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
/// of the channel type we tried, not of our ability to open any channel at all. We can see if a
/// downgrade of channel features would be possible so that we can still open the channel.
pub(crate) fn maybe_downgrade_channel_features<F: Deref>(
&mut self, funding: &mut FundingScope, fee_estimator: &LowerBoundedFeeEstimator<F>
&mut self, funding: &mut FundingScope, fee_estimator: &LowerBoundedFeeEstimator<F>,
user_config: &UserConfig, their_features: &InitFeatures,
) -> Result<(), ()>
where
F::Target: FeeEstimator
Expand All @@ -4885,25 +4897,47 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
// We've exhausted our options
return Err(());
}

// We should never have negotiated `anchors_nonzero_fee_htlc_tx` because it can result in a
// loss of funds.
let channel_type = &funding.channel_transaction_parameters.channel_type_features;
assert!(!channel_type.supports_anchors_nonzero_fee_htlc_tx());
Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Moved this assert up because we should never negotiate a non-zero-htlc-anchor channel, and it's a risk of lost funds if we do.

Couldn't see a historical reason why we only checked it if the channel type was supports_anchors_zero_fee_htlc_tx - went back a few commits and couldn't find reasoning. cc @TheBlueMatt


// We support opening a few different types of channels. Try removing our additional
// features one by one until we've either arrived at our default or the counterparty has
// accepted one.
//
// Due to the order below, we may not negotiate `option_anchors_zero_fee_htlc_tx` if the
// counterparty doesn't support `option_scid_privacy`. Since `get_initial_channel_type`
// checks whether the counterparty supports every feature, this would only happen if the
// counterparty is advertising the feature, but rejecting channels proposing the feature for
// whatever reason.
let channel_type = &mut funding.channel_transaction_parameters.channel_type_features;
if channel_type.supports_anchors_zero_fee_htlc_tx() {
channel_type.clear_anchors_zero_fee_htlc_tx();
self.feerate_per_kw = fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::NonAnchorChannelFee);
assert!(!channel_type.supports_anchors_nonzero_fee_htlc_tx());
// accepted one. Features are un-set for the current channel type or any that come before
// it in our order of preference, allowing us to negotiate the "next best" based on the
// counterparty's remaining features per our ranking in `get_initial_channel_type`.
let mut eligible_features = their_features.clone();
if channel_type.supports_anchor_zero_fee_commitments() {
eligible_features.clear_anchor_zero_fee_commitments();
} else if channel_type.supports_anchors_zero_fee_htlc_tx() {
eligible_features.clear_anchor_zero_fee_commitments();
eligible_features.clear_anchors_zero_fee_htlc_tx();
} else if channel_type.supports_scid_privacy() {
channel_type.clear_scid_privacy();
eligible_features.clear_scid_privacy();
eligible_features.clear_anchors_zero_fee_htlc_tx();
eligible_features.clear_anchor_zero_fee_commitments();
}

let next_channel_type = get_initial_channel_type(user_config, &eligible_features);

// Note that we can't get `anchor_zero_fee_commitments` type here, which requires zero
// fees, because we downgrade from this channel type first. If there were a superior
// channel type that downgrades to `anchor_zero_fee_commitments`, we'd need to handle
// fee setting differently here. If we proceeded to open a `anchor_zero_fee_commitments`
// channel with non-zero fees, we could produce a non-standard commitment transaction that
// puts us at risk of losing funds. We would expect our peer to reject such a channel
// open, but we don't want to rely on their validation.
assert!(!next_channel_type.supports_anchor_zero_fee_commitments());
let conf_target = if next_channel_type.supports_anchors_zero_fee_htlc_tx() {
ConfirmationTarget::AnchorChannelFee
} else {
*channel_type = ChannelTypeFeatures::only_static_remote_key();
}
ConfirmationTarget::NonAnchorChannelFee
};
self.feerate_per_kw = fee_estimator.bounded_sat_per_1000_weight(conf_target);
funding.channel_transaction_parameters.channel_type_features = next_channel_type;

Ok(())
}

Expand Down Expand Up @@ -5262,6 +5296,15 @@ impl<SP: Deref> FundedChannel<SP> where
feerate_per_kw: u32, cur_feerate_per_kw: Option<u32>, logger: &L
) -> Result<(), ChannelError> where F::Target: FeeEstimator, L::Target: Logger,
{
if channel_type.supports_anchor_zero_fee_commitments() {
if feerate_per_kw != 0 {
let err = "Zero Fee Channels must never attempt to use a fee".to_owned();
return Err(ChannelError::close(err));
} else {
return Ok(());
}
}

let lower_limit_conf_target = if channel_type.supports_anchors_zero_fee_htlc_tx() {
ConfirmationTarget::MinAllowedAnchorChannelRemoteFee
} else {
Expand Down Expand Up @@ -9893,13 +9936,16 @@ impl<SP: Deref> OutboundV1Channel<SP> where SP::Target: SignerProvider {
/// not of our ability to open any channel at all. Thus, on error, we should first call this
/// and see if we get a new `OpenChannel` message, otherwise the channel is failed.
pub(crate) fn maybe_handle_error_without_close<F: Deref, L: Deref>(
&mut self, chain_hash: ChainHash, fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L
&mut self, chain_hash: ChainHash, fee_estimator: &LowerBoundedFeeEstimator<F>, logger: &L,
user_config: &UserConfig, their_features: &InitFeatures,
) -> Result<msgs::OpenChannel, ()>
where
F::Target: FeeEstimator,
L::Target: Logger,
{
self.context.maybe_downgrade_channel_features(&mut self.funding, fee_estimator)?;
self.context.maybe_downgrade_channel_features(
&mut self.funding, fee_estimator, user_config, their_features,
)?;
self.get_open_channel(chain_hash, logger).ok_or(())
}

Expand Down Expand Up @@ -10078,8 +10124,9 @@ pub(super) fn channel_type_from_open_channel(

// We only support the channel types defined by the `ChannelManager` in
// `provided_channel_type_features`. The channel type must always support
// `static_remote_key`.
if !channel_type.requires_static_remote_key() {
// `static_remote_key`, either implicitly with `option_zero_fee_commitments`
// or explicitly.
if !channel_type.requires_static_remote_key() && !channel_type.requires_anchor_zero_fee_commitments() {
return Err(ChannelError::close("Channel Type was not understood - we require static remote key".to_owned()));
}
// Make sure we support all of the features behind the channel type.
Expand Down Expand Up @@ -10405,12 +10452,15 @@ impl<SP: Deref> PendingV2Channel<SP> where SP::Target: SignerProvider {
/// not of our ability to open any channel at all. Thus, on error, we should first call this
/// and see if we get a new `OpenChannelV2` message, otherwise the channel is failed.
pub(crate) fn maybe_handle_error_without_close<F: Deref>(
&mut self, chain_hash: ChainHash, fee_estimator: &LowerBoundedFeeEstimator<F>
&mut self, chain_hash: ChainHash, fee_estimator: &LowerBoundedFeeEstimator<F>,
user_config: &UserConfig, their_features: &InitFeatures,
) -> Result<msgs::OpenChannelV2, ()>
where
F::Target: FeeEstimator
{
self.context.maybe_downgrade_channel_features(&mut self.funding, fee_estimator)?;
self.context.maybe_downgrade_channel_features(
&mut self.funding, fee_estimator, user_config, their_features,
)?;
Ok(self.get_open_channel_v2(chain_hash))
}

Expand Down Expand Up @@ -10663,10 +10713,21 @@ fn get_initial_channel_type(config: &UserConfig, their_features: &InitFeatures)
ret.set_scid_privacy_required();
}

// Optionally, if the user would like to negotiate the `anchors_zero_fee_htlc_tx` option, we
// set it now. If they don't understand it, we'll fall back to our default of
// `only_static_remotekey`.
if config.channel_handshake_config.negotiate_anchors_zero_fee_htlc_tx &&
// Optionally, if the user would like to negotiate `option_zero_fee_commitments` we set it now.
// If they don't understand it (or we don't want it), we check the same conditions for
// `option_anchors_zero_fee_htlc_tx`. The counterparty can still refuse the channel and we'll
// try to fall back (all the way to `only_static_remotekey`).
#[cfg(not(test))]
let negotiate_zero_fee_commitments = false;

#[cfg(test)]
let negotiate_zero_fee_commitments = config.channel_handshake_config.negotiate_anchor_zero_fee_commitments;

if negotiate_zero_fee_commitments && their_features.supports_anchor_zero_fee_commitments() {
ret.set_anchor_zero_fee_commitments_required();
// `option_static_remote_key` is assumed by `option_zero_fee_commitments`.
ret.clear_static_remote_key();
} else if config.channel_handshake_config.negotiate_anchors_zero_fee_htlc_tx &&
their_features.supports_anchors_zero_fee_htlc_tx() {
ret.set_anchors_zero_fee_htlc_tx_required();
}
Expand Down Expand Up @@ -13267,6 +13328,45 @@ mod tests {
fn test_supports_anchors_zero_htlc_tx_fee() {
// Tests that if both sides support and negotiate `anchors_zero_fee_htlc_tx`, it is the
// resulting `channel_type`.
let mut config = UserConfig::default();
config.channel_handshake_config.negotiate_anchors_zero_fee_htlc_tx = true;

let mut expected_channel_type = ChannelTypeFeatures::empty();
expected_channel_type.set_static_remote_key_required();
expected_channel_type.set_anchors_zero_fee_htlc_tx_required();

do_test_supports_channel_type(config, expected_channel_type)
}

#[test]
fn test_supports_zero_fee_commitments() {
// Tests that if both sides support and negotiate `anchors_zero_fee_commitments`, it is
// the resulting `channel_type`.
let mut config = UserConfig::default();
config.channel_handshake_config.negotiate_anchor_zero_fee_commitments = true;

let mut expected_channel_type = ChannelTypeFeatures::empty();
expected_channel_type.set_anchor_zero_fee_commitments_required();

do_test_supports_channel_type(config, expected_channel_type)
}

#[test]
fn test_supports_zero_fee_commitments_and_htlc_tx_fee() {
// Tests that if both sides support and negotiate `anchors_zero_fee_commitments` and
// `anchors_zero_fee_htlc_tx`, the resulting `channel_type` is
// `anchors_zero_fee_commitments`.
let mut config = UserConfig::default();
config.channel_handshake_config.negotiate_anchors_zero_fee_htlc_tx = true;
config.channel_handshake_config.negotiate_anchor_zero_fee_commitments = true;

let mut expected_channel_type = ChannelTypeFeatures::empty();
expected_channel_type.set_anchor_zero_fee_commitments_required();

do_test_supports_channel_type(config, expected_channel_type)
}

fn do_test_supports_channel_type(config: UserConfig, expected_channel_type: ChannelTypeFeatures) {
let secp_ctx = Secp256k1::new();
let fee_estimator = LowerBoundedFeeEstimator::new(&TestFeeEstimator{fee_est: 15000});
let network = Network::Testnet;
Expand All @@ -13276,21 +13376,13 @@ mod tests {
let node_id_a = PublicKey::from_secret_key(&secp_ctx, &SecretKey::from_slice(&[1; 32]).unwrap());
let node_id_b = PublicKey::from_secret_key(&secp_ctx, &SecretKey::from_slice(&[2; 32]).unwrap());

let mut config = UserConfig::default();
config.channel_handshake_config.negotiate_anchors_zero_fee_htlc_tx = true;

// It is not enough for just the initiator to signal `option_anchors_zero_fee_htlc_tx`, both
// need to signal it.
// Assert that we get `static_remotekey` when no custom config is negotiated.
let channel_a = OutboundV1Channel::<&TestKeysInterface>::new(
&fee_estimator, &&keys_provider, &&keys_provider, node_id_b,
&channelmanager::provided_init_features(&UserConfig::default()), 10000000, 100000, 42,
&config, 0, 42, None, &logger
).unwrap();
assert!(!channel_a.funding.get_channel_type().supports_anchors_zero_fee_htlc_tx());

let mut expected_channel_type = ChannelTypeFeatures::empty();
expected_channel_type.set_static_remote_key_required();
expected_channel_type.set_anchors_zero_fee_htlc_tx_required();
assert_eq!(channel_a.funding.get_channel_type(), &ChannelTypeFeatures::only_static_remote_key());

let mut channel_a = OutboundV1Channel::<&TestKeysInterface>::new(
&fee_estimator, &&keys_provider, &&keys_provider, node_id_b,
Expand All @@ -13307,6 +13399,14 @@ mod tests {

assert_eq!(channel_a.funding.get_channel_type(), &expected_channel_type);
assert_eq!(channel_b.funding.get_channel_type(), &expected_channel_type);

if expected_channel_type.supports_anchor_zero_fee_commitments() {
assert_eq!(channel_a.context.feerate_per_kw, 0);
assert_eq!(channel_b.context.feerate_per_kw, 0);
} else {
assert_ne!(channel_a.context.feerate_per_kw, 0);
assert_ne!(channel_b.context.feerate_per_kw, 0);
}
}

#[test]
Expand Down
Loading
Loading