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Consider anchor outputs value on channel open
We should make sure the funding amount of a channel can cover all its associated costs, including the value of anchor outputs, to make sure that it is actually usable once "opened".
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+11
-6
lines changed

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+11
-6
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lightning/src/ln/channel.rs

Lines changed: 11 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -5740,16 +5740,16 @@ impl<SP: Deref> OutboundV1Channel<SP> where SP::Target: SignerProvider {
57405740
let channel_type = Self::get_initial_channel_type(&config, their_features);
57415741
debug_assert!(channel_type.is_subset(&channelmanager::provided_channel_type_features(&config)));
57425742

5743-
let commitment_conf_target = if channel_type.supports_anchors_zero_fee_htlc_tx() {
5744-
ConfirmationTarget::MempoolMinimum
5743+
let (commitment_conf_target, anchor_outputs_value_msat) = if channel_type.supports_anchors_zero_fee_htlc_tx() {
5744+
(ConfirmationTarget::MempoolMinimum, ANCHOR_OUTPUT_VALUE_SATOSHI * 2 * 1000)
57455745
} else {
5746-
ConfirmationTarget::Normal
5746+
(ConfirmationTarget::Normal, 0)
57475747
};
57485748
let commitment_feerate = fee_estimator.bounded_sat_per_1000_weight(commitment_conf_target);
57495749

57505750
let value_to_self_msat = channel_value_satoshis * 1000 - push_msat;
57515751
let commitment_tx_fee = commit_tx_fee_msat(commitment_feerate, MIN_AFFORDABLE_HTLC_COUNT, &channel_type);
5752-
if value_to_self_msat < commitment_tx_fee {
5752+
if value_to_self_msat - anchor_outputs_value_msat < commitment_tx_fee {
57535753
return Err(APIError::APIMisuseError{ err: format!("Funding amount ({}) can't even pay fee for initial commitment transaction fee of {}.", value_to_self_msat / 1000, commitment_tx_fee / 1000) });
57545754
}
57555755

@@ -6366,13 +6366,18 @@ impl<SP: Deref> InboundV1Channel<SP> where SP::Target: SignerProvider {
63666366

63676367
// check if the funder's amount for the initial commitment tx is sufficient
63686368
// for full fee payment plus a few HTLCs to ensure the channel will be useful.
6369+
let anchor_outputs_value = if channel_type.supports_anchors_zero_fee_htlc_tx() {
6370+
ANCHOR_OUTPUT_VALUE_SATOSHI * 2
6371+
} else {
6372+
0
6373+
};
63696374
let funders_amount_msat = msg.funding_satoshis * 1000 - msg.push_msat;
63706375
let commitment_tx_fee = commit_tx_fee_msat(msg.feerate_per_kw, MIN_AFFORDABLE_HTLC_COUNT, &channel_type) / 1000;
6371-
if funders_amount_msat / 1000 < commitment_tx_fee {
6376+
if funders_amount_msat / 1000 - anchor_outputs_value < commitment_tx_fee {
63726377
return Err(ChannelError::Close(format!("Funding amount ({} sats) can't even pay fee for initial commitment transaction fee of {} sats.", funders_amount_msat / 1000, commitment_tx_fee)));
63736378
}
63746379

6375-
let to_remote_satoshis = funders_amount_msat / 1000 - commitment_tx_fee;
6380+
let to_remote_satoshis = funders_amount_msat / 1000 - commitment_tx_fee - anchor_outputs_value;
63766381
// While it's reasonable for us to not meet the channel reserve initially (if they don't
63776382
// want to push much to us), our counterparty should always have more than our reserve.
63786383
if to_remote_satoshis < holder_selected_channel_reserve_satoshis {

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