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funding: require explicit channel type in all negotiations #11064

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68 changes: 18 additions & 50 deletions funding/commitment_type_negotiation.go
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -18,61 +18,30 @@ var (
// negotiateCommitmentType negotiates the commitment type of a newly opened
// channel. If a desiredChanType is provided, explicit negotiation for said type
// will be attempted if the set of both local and remote features support it.
// Otherwise, implicit negotiation will be attempted.
// Otherwise, a default type is selected based on feature compatibility,
// particularly when the RPC caller does not request a specific channel type.
//
// The returned ChannelType is nil when implicit negotiation is used. An error
// is only returned if desiredChanType is not supported.
// The returned ChannelType is always non-nil. An error is only returned if
// desiredChanType is not supported.
func negotiateCommitmentType(desiredChanType *lnwire.ChannelType, local,
remote *lnwire.FeatureVector) (*lnwire.ChannelType,
lnwallet.CommitmentType, error) {

// BOLT#2 specifies we MUST use explicit negotiation if both peers
// signal for it.
explicitNegotiation := hasFeatures(
local, remote, lnwire.ExplicitChannelTypeOptional,
)

chanTypeRequested := desiredChanType != nil

switch {
case explicitNegotiation && chanTypeRequested:
// If a specific channel type was provided, verify it's supported.
if desiredChanType != nil {
commitType, err := explicitNegotiateCommitmentType(
*desiredChanType, local, remote,
)

return desiredChanType, commitType, err
}

// We don't have a specific channel type requested, so we select a
// default type as if implicit negotiation were used, and then we
// explicitly signal that default type.
case explicitNegotiation && !chanTypeRequested:
defaultChanType, commitType := implicitNegotiateCommitmentType(
local, remote,
)

return defaultChanType, commitType, nil

// A specific channel type was requested, but we can't explicitly signal
// it. So if implicit negotiation wouldn't select the desired channel
// type, we must return an error.
case !explicitNegotiation && chanTypeRequested:
implicitChanType, commitType := implicitNegotiateCommitmentType(
local, remote,
)

expected := lnwire.RawFeatureVector(*desiredChanType)
actual := lnwire.RawFeatureVector(*implicitChanType)
if !expected.Equals(&actual) {
return nil, 0, errUnsupportedChannelType
}

return nil, commitType, nil

default: // !explicitNegotiation && !chanTypeRequested
_, commitType := implicitNegotiateCommitmentType(local, remote)
// No specific channel type was requested. Select a default type based
// on locally-known feature compatibility. This default is then sent
// explicitly over the wire.
defaultChanType, commitType := selectDefaultChannelType(local, remote)

return nil, commitType, nil
}
return defaultChanType, commitType, nil
}

// explicitNegotiateCommitmentType attempts to explicitly negotiate for a
Expand Down Expand Up @@ -454,15 +423,14 @@ func explicitNegotiateCommitmentType(channelType lnwire.ChannelType, local,
}
}

// implicitNegotiateCommitmentType negotiates the commitment type of a channel
// implicitly by choosing the latest non-taproot type supported by the local and
// remote features. Taproot channels must be requested explicitly, keeping
// implicit opens on channel types that can be used for both public and private
// channels.
// selectDefaultChannelType selects a default channel type by choosing the
// latest non-taproot type supported by the local and remote features.
// Taproot channels must be requested explicitly, keeping default selections
// on channel types that can be used for both public and private channels.
//
// TODO(yy): Revisit implicit taproot negotiation once public taproot channel
// TODO(yy): Revisit taproot channel selection once public taproot channel
// announcements are supported.
func implicitNegotiateCommitmentType(local,
func selectDefaultChannelType(local,
remote *lnwire.FeatureVector) (*lnwire.ChannelType,
lnwallet.CommitmentType) {

Expand Down
36 changes: 23 additions & 13 deletions funding/commitment_type_negotiation_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -39,10 +39,14 @@ func TestCommitmentTypeNegotiation(t *testing.T) {
lnwire.StaticRemoteKeyOptional,
lnwire.AnchorsZeroFeeHtlcTxOptional,
),
//nolint:ll
expectsCommitType: lnwallet.CommitmentTypeAnchorsZeroFeeHtlcTx,
expectsChanType: nil,
expectsErr: nil,
expectsChanType: (*lnwire.ChannelType)(
lnwire.NewRawFeatureVector(
lnwire.StaticRemoteKeyRequired,
lnwire.AnchorsZeroFeeHtlcTxRequired,
),
),
expectsErr: nil,
},
{
name: "explicit missing remote commitment feature",
Expand Down Expand Up @@ -282,7 +286,7 @@ func TestCommitmentTypeNegotiation(t *testing.T) {
expectsErr: nil,
},
{
name: "implicit tweakless",
name: "default tweakless",
channelFeatures: nil,
localFeatures: lnwire.NewRawFeatureVector(
lnwire.StaticRemoteKeyRequired,
Expand All @@ -292,20 +296,26 @@ func TestCommitmentTypeNegotiation(t *testing.T) {
lnwire.StaticRemoteKeyOptional,
),
expectsCommitType: lnwallet.CommitmentTypeTweakless,
expectsChanType: nil,
expectsErr: nil,
expectsChanType: (*lnwire.ChannelType)(
lnwire.NewRawFeatureVector(
lnwire.StaticRemoteKeyRequired,
),
),
expectsErr: nil,
},
{
name: "implicit legacy",
name: "default legacy",
channelFeatures: nil,
localFeatures: lnwire.NewRawFeatureVector(),
remoteFeatures: lnwire.NewRawFeatureVector(
lnwire.StaticRemoteKeyOptional,
lnwire.AnchorsZeroFeeHtlcTxOptional,
),
expectsCommitType: lnwallet.CommitmentTypeLegacy,
expectsChanType: nil,
expectsErr: nil,
expectsChanType: (*lnwire.ChannelType)(
lnwire.NewRawFeatureVector(),
),
expectsErr: nil,
},

// Test cases for final taproot channels with explicit
Expand Down Expand Up @@ -432,11 +442,11 @@ func TestCommitmentTypeNegotiation(t *testing.T) {
expectsErr: errUnsupportedChannelType,
},

// Test cases for implicit negotiation ignoring taproot feature
// Test cases for default negotiation ignoring taproot feature
// bits. Taproot channels require an explicit channel type.
{
//nolint:ll
name: "implicit anchors preferred over taproot",
name: "default anchors preferred over taproot",
channelFeatures: nil,
localFeatures: lnwire.NewRawFeatureVector(
lnwire.AnchorsZeroFeeHtlcTxOptional,
Expand All @@ -461,7 +471,7 @@ func TestCommitmentTypeNegotiation(t *testing.T) {
},
{
//nolint:ll
name: "implicit ignores staging taproot without anchors",
name: "default ignores staging taproot without anchors",
channelFeatures: nil,
localFeatures: lnwire.NewRawFeatureVector(
lnwire.SimpleTaprootChannelsOptionalFinal,
Expand All @@ -480,7 +490,7 @@ func TestCommitmentTypeNegotiation(t *testing.T) {
},
{
//nolint:ll
name: "implicit ignores final taproot without anchors",
name: "default ignores final taproot without anchors",
channelFeatures: nil,
localFeatures: lnwire.NewRawFeatureVector(
lnwire.SimpleTaprootChannelsOptionalFinal,
Expand Down
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