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Merge pull request #2319 from valentinewallace/2023-05-forward-less-t…
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…han-onion

Allow forwarding less than the amount in the onion
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@tnull
tnull authored Jun 21, 2023
2 parents ba342de + 2127eb8 commit 15b1c9b
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33 changes: 29 additions & 4 deletions lightning/src/events/mod.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -385,8 +385,25 @@ pub enum Event {
///
/// Payments received on LDK versions prior to 0.0.115 will have this field unset.
onion_fields: Option<RecipientOnionFields>,
/// The value, in thousandths of a satoshi, that this payment is for.
/// The value, in thousandths of a satoshi, that this payment is claimable for. May be greater
/// than the invoice amount.
///
/// May be less than the invoice amount if [`ChannelConfig::accept_underpaying_htlcs`] is set
/// and the previous hop took an extra fee.
///
/// # Note
/// If [`ChannelConfig::accept_underpaying_htlcs`] is set and you claim without verifying this
/// field, you may lose money!
///
/// [`ChannelConfig::accept_underpaying_htlcs`]: crate::util::config::ChannelConfig::accept_underpaying_htlcs
amount_msat: u64,
/// The value, in thousands of a satoshi, that was skimmed off of this payment as an extra fee
/// taken by our channel counterparty.
///
/// Will always be 0 unless [`ChannelConfig::accept_underpaying_htlcs`] is set.
///
/// [`ChannelConfig::accept_underpaying_htlcs`]: crate::util::config::ChannelConfig::accept_underpaying_htlcs
counterparty_skimmed_fee_msat: u64,
/// Information for claiming this received payment, based on whether the purpose of the
/// payment is to pay an invoice or to send a spontaneous payment.
purpose: PaymentPurpose,
Expand Down Expand Up @@ -428,7 +445,8 @@ pub enum Event {
/// The payment hash of the claimed payment. Note that LDK will not stop you from
/// registering duplicate payment hashes for inbound payments.
payment_hash: PaymentHash,
/// The value, in thousandths of a satoshi, that this payment is for.
/// The value, in thousandths of a satoshi, that this payment is for. May be greater than the
/// invoice amount.
amount_msat: u64,
/// The purpose of the claimed payment, i.e. whether the payment was for an invoice or a
/// spontaneous payment.
Expand Down Expand Up @@ -621,6 +639,7 @@ pub enum Event {
inbound_amount_msat: u64,
/// How many msats the payer intended to route to the next node. Depending on the reason you are
/// intercepting this payment, you might take a fee by forwarding less than this amount.
/// Forwarding less than this amount may break compatibility with LDK versions prior to 0.0.116.
///
/// Note that LDK will NOT check that expected fees were factored into this value. You MUST
/// check that whatever fee you want has been included here or subtract it as required. Further,
Expand Down Expand Up @@ -830,8 +849,8 @@ impl Writeable for Event {
// We never write out FundingGenerationReady events as, upon disconnection, peers
// drop any channels which have not yet exchanged funding_signed.
},
&Event::PaymentClaimable { ref payment_hash, ref amount_msat, ref purpose,
ref receiver_node_id, ref via_channel_id, ref via_user_channel_id,
&Event::PaymentClaimable { ref payment_hash, ref amount_msat, counterparty_skimmed_fee_msat,
ref purpose, ref receiver_node_id, ref via_channel_id, ref via_user_channel_id,
ref claim_deadline, ref onion_fields
} => {
1u8.write(writer)?;
Expand All @@ -846,6 +865,8 @@ impl Writeable for Event {
payment_preimage = Some(*preimage);
}
}
let skimmed_fee_opt = if counterparty_skimmed_fee_msat == 0 { None }
else { Some(counterparty_skimmed_fee_msat) };
write_tlv_fields!(writer, {
(0, payment_hash, required),
(1, receiver_node_id, option),
Expand All @@ -857,6 +878,7 @@ impl Writeable for Event {
(7, claim_deadline, option),
(8, payment_preimage, option),
(9, onion_fields, option),
(10, skimmed_fee_opt, option),
});
},
&Event::PaymentSent { ref payment_id, ref payment_preimage, ref payment_hash, ref fee_paid_msat } => {
Expand Down Expand Up @@ -1056,6 +1078,7 @@ impl MaybeReadable for Event {
let mut payment_preimage = None;
let mut payment_secret = None;
let mut amount_msat = 0;
let mut counterparty_skimmed_fee_msat_opt = None;
let mut receiver_node_id = None;
let mut _user_payment_id = None::<u64>; // Used in 0.0.103 and earlier, no longer written in 0.0.116+.
let mut via_channel_id = None;
Expand All @@ -1073,6 +1096,7 @@ impl MaybeReadable for Event {
(7, claim_deadline, option),
(8, payment_preimage, option),
(9, onion_fields, option),
(10, counterparty_skimmed_fee_msat_opt, option),
});
let purpose = match payment_secret {
Some(secret) => PaymentPurpose::InvoicePayment {
Expand All @@ -1086,6 +1110,7 @@ impl MaybeReadable for Event {
receiver_node_id,
payment_hash,
amount_msat,
counterparty_skimmed_fee_msat: counterparty_skimmed_fee_msat_opt.unwrap_or(0),
purpose,
via_channel_id,
via_user_channel_id,
Expand Down
103 changes: 88 additions & 15 deletions lightning/src/ln/channel.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -224,6 +224,7 @@ struct OutboundHTLCOutput {
payment_hash: PaymentHash,
state: OutboundHTLCState,
source: HTLCSource,
skimmed_fee_msat: Option<u64>,
}

/// See AwaitingRemoteRevoke ChannelState for more info
Expand All @@ -235,6 +236,8 @@ enum HTLCUpdateAwaitingACK {
payment_hash: PaymentHash,
source: HTLCSource,
onion_routing_packet: msgs::OnionPacket,
// The extra fee we're skimming off the top of this HTLC.
skimmed_fee_msat: Option<u64>,
},
ClaimHTLC {
payment_preimage: PaymentPreimage,
Expand Down Expand Up @@ -3052,8 +3055,13 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
// handling this case better and maybe fulfilling some of the HTLCs while attempting
// to rebalance channels.
match &htlc_update {
&HTLCUpdateAwaitingACK::AddHTLC {amount_msat, cltv_expiry, ref payment_hash, ref source, ref onion_routing_packet, ..} => {
match self.send_htlc(amount_msat, *payment_hash, cltv_expiry, source.clone(), onion_routing_packet.clone(), false, logger) {
&HTLCUpdateAwaitingACK::AddHTLC {
amount_msat, cltv_expiry, ref payment_hash, ref source, ref onion_routing_packet,
skimmed_fee_msat, ..
} => {
match self.send_htlc(amount_msat, *payment_hash, cltv_expiry, source.clone(),
onion_routing_packet.clone(), false, skimmed_fee_msat, logger)
{
Ok(update_add_msg_option) => update_add_htlcs.push(update_add_msg_option.unwrap()),
Err(e) => {
match e {
Expand Down Expand Up @@ -3695,6 +3703,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
payment_hash: htlc.payment_hash,
cltv_expiry: htlc.cltv_expiry,
onion_routing_packet: (**onion_packet).clone(),
skimmed_fee_msat: htlc.skimmed_fee_msat,
});
}
}
Expand Down Expand Up @@ -5042,11 +5051,13 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
/// commitment update.
///
/// `Err`s will only be [`ChannelError::Ignore`].
pub fn queue_add_htlc<L: Deref>(&mut self, amount_msat: u64, payment_hash: PaymentHash, cltv_expiry: u32, source: HTLCSource,
onion_routing_packet: msgs::OnionPacket, logger: &L)
-> Result<(), ChannelError> where L::Target: Logger {
pub fn queue_add_htlc<L: Deref>(
&mut self, amount_msat: u64, payment_hash: PaymentHash, cltv_expiry: u32, source: HTLCSource,
onion_routing_packet: msgs::OnionPacket, skimmed_fee_msat: Option<u64>, logger: &L
) -> Result<(), ChannelError> where L::Target: Logger {
self
.send_htlc(amount_msat, payment_hash, cltv_expiry, source, onion_routing_packet, true, logger)
.send_htlc(amount_msat, payment_hash, cltv_expiry, source, onion_routing_packet, true,
skimmed_fee_msat, logger)
.map(|msg_opt| assert!(msg_opt.is_none(), "We forced holding cell?"))
.map_err(|err| {
if let ChannelError::Ignore(_) = err { /* fine */ }
Expand All @@ -5071,9 +5082,11 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
/// on this [`Channel`] if `force_holding_cell` is false.
///
/// `Err`s will only be [`ChannelError::Ignore`].
fn send_htlc<L: Deref>(&mut self, amount_msat: u64, payment_hash: PaymentHash, cltv_expiry: u32, source: HTLCSource,
onion_routing_packet: msgs::OnionPacket, mut force_holding_cell: bool, logger: &L)
-> Result<Option<msgs::UpdateAddHTLC>, ChannelError> where L::Target: Logger {
fn send_htlc<L: Deref>(
&mut self, amount_msat: u64, payment_hash: PaymentHash, cltv_expiry: u32, source: HTLCSource,
onion_routing_packet: msgs::OnionPacket, mut force_holding_cell: bool,
skimmed_fee_msat: Option<u64>, logger: &L
) -> Result<Option<msgs::UpdateAddHTLC>, ChannelError> where L::Target: Logger {
if (self.context.channel_state & (ChannelState::ChannelReady as u32 | BOTH_SIDES_SHUTDOWN_MASK)) != (ChannelState::ChannelReady as u32) {
return Err(ChannelError::Ignore("Cannot send HTLC until channel is fully established and we haven't started shutting down".to_owned()));
}
Expand Down Expand Up @@ -5125,6 +5138,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
cltv_expiry,
source,
onion_routing_packet,
skimmed_fee_msat,
});
return Ok(None);
}
Expand All @@ -5136,6 +5150,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
cltv_expiry,
state: OutboundHTLCState::LocalAnnounced(Box::new(onion_routing_packet.clone())),
source,
skimmed_fee_msat,
});

let res = msgs::UpdateAddHTLC {
Expand All @@ -5145,6 +5160,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
payment_hash,
cltv_expiry,
onion_routing_packet,
skimmed_fee_msat,
};
self.context.next_holder_htlc_id += 1;

Expand Down Expand Up @@ -5283,8 +5299,12 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
///
/// Shorthand for calling [`Self::send_htlc`] followed by a commitment update, see docs on
/// [`Self::send_htlc`] and [`Self::build_commitment_no_state_update`] for more info.
pub fn send_htlc_and_commit<L: Deref>(&mut self, amount_msat: u64, payment_hash: PaymentHash, cltv_expiry: u32, source: HTLCSource, onion_routing_packet: msgs::OnionPacket, logger: &L) -> Result<Option<&ChannelMonitorUpdate>, ChannelError> where L::Target: Logger {
let send_res = self.send_htlc(amount_msat, payment_hash, cltv_expiry, source, onion_routing_packet, false, logger);
pub fn send_htlc_and_commit<L: Deref>(
&mut self, amount_msat: u64, payment_hash: PaymentHash, cltv_expiry: u32, source: HTLCSource,
onion_routing_packet: msgs::OnionPacket, skimmed_fee_msat: Option<u64>, logger: &L
) -> Result<Option<&ChannelMonitorUpdate>, ChannelError> where L::Target: Logger {
let send_res = self.send_htlc(amount_msat, payment_hash, cltv_expiry, source,
onion_routing_packet, false, skimmed_fee_msat, logger);
if let Err(e) = &send_res { if let ChannelError::Ignore(_) = e {} else { debug_assert!(false, "Sending cannot trigger channel failure"); } }
match send_res? {
Some(_) => {
Expand Down Expand Up @@ -6609,9 +6629,10 @@ impl<Signer: WriteableEcdsaChannelSigner> Writeable for Channel<Signer> {
}

let mut preimages: Vec<&Option<PaymentPreimage>> = vec![];
let mut pending_outbound_skimmed_fees: Vec<Option<u64>> = Vec::new();

(self.context.pending_outbound_htlcs.len() as u64).write(writer)?;
for htlc in self.context.pending_outbound_htlcs.iter() {
for (idx, htlc) in self.context.pending_outbound_htlcs.iter().enumerate() {
htlc.htlc_id.write(writer)?;
htlc.amount_msat.write(writer)?;
htlc.cltv_expiry.write(writer)?;
Expand Down Expand Up @@ -6647,18 +6668,37 @@ impl<Signer: WriteableEcdsaChannelSigner> Writeable for Channel<Signer> {
reason.write(writer)?;
}
}
if let Some(skimmed_fee) = htlc.skimmed_fee_msat {
if pending_outbound_skimmed_fees.is_empty() {
for _ in 0..idx { pending_outbound_skimmed_fees.push(None); }
}
pending_outbound_skimmed_fees.push(Some(skimmed_fee));
} else if !pending_outbound_skimmed_fees.is_empty() {
pending_outbound_skimmed_fees.push(None);
}
}

let mut holding_cell_skimmed_fees: Vec<Option<u64>> = Vec::new();
(self.context.holding_cell_htlc_updates.len() as u64).write(writer)?;
for update in self.context.holding_cell_htlc_updates.iter() {
for (idx, update) in self.context.holding_cell_htlc_updates.iter().enumerate() {
match update {
&HTLCUpdateAwaitingACK::AddHTLC { ref amount_msat, ref cltv_expiry, ref payment_hash, ref source, ref onion_routing_packet } => {
&HTLCUpdateAwaitingACK::AddHTLC {
ref amount_msat, ref cltv_expiry, ref payment_hash, ref source, ref onion_routing_packet,
skimmed_fee_msat,
} => {
0u8.write(writer)?;
amount_msat.write(writer)?;
cltv_expiry.write(writer)?;
payment_hash.write(writer)?;
source.write(writer)?;
onion_routing_packet.write(writer)?;

if let Some(skimmed_fee) = skimmed_fee_msat {
if holding_cell_skimmed_fees.is_empty() {
for _ in 0..idx { holding_cell_skimmed_fees.push(None); }
}
holding_cell_skimmed_fees.push(Some(skimmed_fee));
} else if !holding_cell_skimmed_fees.is_empty() { holding_cell_skimmed_fees.push(None); }
},
&HTLCUpdateAwaitingACK::ClaimHTLC { ref payment_preimage, ref htlc_id } => {
1u8.write(writer)?;
Expand Down Expand Up @@ -6825,6 +6865,8 @@ impl<Signer: WriteableEcdsaChannelSigner> Writeable for Channel<Signer> {
(29, self.context.temporary_channel_id, option),
(31, channel_pending_event_emitted, option),
(33, self.context.pending_monitor_updates, vec_type),
(35, pending_outbound_skimmed_fees, optional_vec),
(37, holding_cell_skimmed_fees, optional_vec),
});

Ok(())
Expand Down Expand Up @@ -6935,6 +6977,7 @@ impl<'a, 'b, 'c, ES: Deref, SP: Deref> ReadableArgs<(&'a ES, &'b SP, u32, &'c Ch
},
_ => return Err(DecodeError::InvalidValue),
},
skimmed_fee_msat: None,
});
}

Expand All @@ -6948,6 +6991,7 @@ impl<'a, 'b, 'c, ES: Deref, SP: Deref> ReadableArgs<(&'a ES, &'b SP, u32, &'c Ch
payment_hash: Readable::read(reader)?,
source: Readable::read(reader)?,
onion_routing_packet: Readable::read(reader)?,
skimmed_fee_msat: None,
},
1 => HTLCUpdateAwaitingACK::ClaimHTLC {
payment_preimage: Readable::read(reader)?,
Expand Down Expand Up @@ -7103,6 +7147,9 @@ impl<'a, 'b, 'c, ES: Deref, SP: Deref> ReadableArgs<(&'a ES, &'b SP, u32, &'c Ch

let mut pending_monitor_updates = Some(Vec::new());

let mut pending_outbound_skimmed_fees_opt: Option<Vec<Option<u64>>> = None;
let mut holding_cell_skimmed_fees_opt: Option<Vec<Option<u64>>> = None;

read_tlv_fields!(reader, {
(0, announcement_sigs, option),
(1, minimum_depth, option),
Expand All @@ -7126,6 +7173,8 @@ impl<'a, 'b, 'c, ES: Deref, SP: Deref> ReadableArgs<(&'a ES, &'b SP, u32, &'c Ch
(29, temporary_channel_id, option),
(31, channel_pending_event_emitted, option),
(33, pending_monitor_updates, vec_type),
(35, pending_outbound_skimmed_fees_opt, optional_vec),
(37, holding_cell_skimmed_fees_opt, optional_vec),
});

let (channel_keys_id, holder_signer) = if let Some(channel_keys_id) = channel_keys_id {
Expand Down Expand Up @@ -7180,6 +7229,25 @@ impl<'a, 'b, 'c, ES: Deref, SP: Deref> ReadableArgs<(&'a ES, &'b SP, u32, &'c Ch

let holder_max_accepted_htlcs = holder_max_accepted_htlcs.unwrap_or(DEFAULT_MAX_HTLCS);

if let Some(skimmed_fees) = pending_outbound_skimmed_fees_opt {
let mut iter = skimmed_fees.into_iter();
for htlc in pending_outbound_htlcs.iter_mut() {
htlc.skimmed_fee_msat = iter.next().ok_or(DecodeError::InvalidValue)?;
}
// We expect all skimmed fees to be consumed above
if iter.next().is_some() { return Err(DecodeError::InvalidValue) }
}
if let Some(skimmed_fees) = holding_cell_skimmed_fees_opt {
let mut iter = skimmed_fees.into_iter();
for htlc in holding_cell_htlc_updates.iter_mut() {
if let HTLCUpdateAwaitingACK::AddHTLC { ref mut skimmed_fee_msat, .. } = htlc {
*skimmed_fee_msat = iter.next().ok_or(DecodeError::InvalidValue)?;
}
}
// We expect all skimmed fees to be consumed above
if iter.next().is_some() { return Err(DecodeError::InvalidValue) }
}

Ok(Channel {
context: ChannelContext {
user_id,
Expand Down Expand Up @@ -7522,7 +7590,8 @@ mod tests {
session_priv: SecretKey::from_slice(&hex::decode("0fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff").unwrap()[..]).unwrap(),
first_hop_htlc_msat: 548,
payment_id: PaymentId([42; 32]),
}
},
skimmed_fee_msat: None,
});

// Make sure when Node A calculates their local commitment transaction, none of the HTLCs pass
Expand Down Expand Up @@ -8079,6 +8148,7 @@ mod tests {
payment_hash: PaymentHash([0; 32]),
state: OutboundHTLCState::Committed,
source: HTLCSource::dummy(),
skimmed_fee_msat: None,
};
out.payment_hash.0 = Sha256::hash(&hex::decode("0202020202020202020202020202020202020202020202020202020202020202").unwrap()).into_inner();
out
Expand All @@ -8091,6 +8161,7 @@ mod tests {
payment_hash: PaymentHash([0; 32]),
state: OutboundHTLCState::Committed,
source: HTLCSource::dummy(),
skimmed_fee_msat: None,
};
out.payment_hash.0 = Sha256::hash(&hex::decode("0303030303030303030303030303030303030303030303030303030303030303").unwrap()).into_inner();
out
Expand Down Expand Up @@ -8492,6 +8563,7 @@ mod tests {
payment_hash: PaymentHash([0; 32]),
state: OutboundHTLCState::Committed,
source: HTLCSource::dummy(),
skimmed_fee_msat: None,
};
out.payment_hash.0 = Sha256::hash(&hex::decode("0505050505050505050505050505050505050505050505050505050505050505").unwrap()).into_inner();
out
Expand All @@ -8504,6 +8576,7 @@ mod tests {
payment_hash: PaymentHash([0; 32]),
state: OutboundHTLCState::Committed,
source: HTLCSource::dummy(),
skimmed_fee_msat: None,
};
out.payment_hash.0 = Sha256::hash(&hex::decode("0505050505050505050505050505050505050505050505050505050505050505").unwrap()).into_inner();
out
Expand Down
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