multi: move routing.TlvTrafficShaper => htlcswitch.AuxTrafficShaper

With this commit we move the traffic shaper definition from the routing
package to the HTLC switch package as a preparation for being able to
use it there as well.
At the same time we rename it to AuxTrafficShaper to be more in line
with the other auxiliary components.

htlcswitch/interfaces.go

@@ -206,6 +206,11 @@ const (
 	Outgoing LinkDirection = true
 )
 
+// OptionalBandwidth is a type alias for the result of a bandwidth query that
+// may return a bandwidth value or fn.None if the bandwidth is not available or
+// not applicable.
+type OptionalBandwidth = fn.Option[lnwire.MilliSatoshi]
+
 // ChannelLink is an interface which represents the subsystem for managing the
 // incoming htlc requests, applying the changes to the channel, and also
 // propagating/forwarding it to htlc switch.
@@ -284,8 +289,8 @@ type ChannelLink interface {
 	// total sent/received milli-satoshis.
 	Stats() (uint64, lnwire.MilliSatoshi, lnwire.MilliSatoshi)
 
-	// Peer returns the serialized public key of remote peer with which we
-	// have the channel link opened.
+	// PeerPubKey returns the serialized public key of remote peer with
+	// which we have the channel link opened.
 	PeerPubKey() [33]byte
 
 	// AttachMailBox delivers an active MailBox to the link. The MailBox may
@@ -302,9 +307,18 @@ type ChannelLink interface {
 	// commitment of the channel that this link is associated with.
 	CommitmentCustomBlob() fn.Option[tlv.Blob]
 
-	// Start/Stop are used to initiate the start/stop of the channel link
-	// functioning.
+	// AuxBandwidth returns the bandwidth that can be used for a channel,
+	// expressed in milli-satoshi. This might be different from the regular
+	// BTC bandwidth for custom channels. This will always return fn.None()
+	// for a regular (non-custom) channel.
+	AuxBandwidth(amount lnwire.MilliSatoshi, cid lnwire.ShortChannelID,
+		htlcBlob fn.Option[tlv.Blob],
+		ts AuxTrafficShaper) fn.Result[OptionalBandwidth]
+
+	// Start starts the channel link.
 	Start() error
+
+	// Stop requests the channel link to be shut down.
 	Stop()
 }
 
@@ -440,7 +454,7 @@ type htlcNotifier interface {
 	NotifyForwardingEvent(key HtlcKey, info HtlcInfo,
 		eventType HtlcEventType)
 
-	// NotifyIncomingLinkFailEvent notifies that a htlc has failed on our
+	// NotifyLinkFailEvent notifies that a htlc has failed on our
 	// incoming link. It takes an isReceive bool to differentiate between
 	// our node's receives and forwards.
 	NotifyLinkFailEvent(key HtlcKey, info HtlcInfo,
@@ -461,3 +475,36 @@ type htlcNotifier interface {
 	NotifyFinalHtlcEvent(key models.CircuitKey,
 		info channeldb.FinalHtlcInfo)
 }
+
+// AuxHtlcModifier is an interface that allows the sender to modify the outgoing
+// HTLC of a payment by changing the amount or the wire message tlv records.
+type AuxHtlcModifier interface {
+	// ProduceHtlcExtraData is a function that, based on the previous extra
+	// data blob of an HTLC, may produce a different blob or modify the
+	// amount of bitcoin this htlc should carry.
+	ProduceHtlcExtraData(totalAmount lnwire.MilliSatoshi,
+		htlcCustomRecords lnwire.CustomRecords) (lnwire.MilliSatoshi,
+		lnwire.CustomRecords, error)
+}
+
+// AuxTrafficShaper is an interface that allows the sender to determine if a
+// payment should be carried by a channel based on the TLV records that may be
+// present in the `update_add_htlc` message or the channel commitment itself.
+type AuxTrafficShaper interface {
+	AuxHtlcModifier
+
+	// ShouldHandleTraffic is called in order to check if the channel
+	// identified by the provided channel ID may have external mechanisms
+	// that would allow it to carry out the payment.
+	ShouldHandleTraffic(cid lnwire.ShortChannelID,
+		fundingBlob fn.Option[tlv.Blob]) (bool, error)
+
+	// PaymentBandwidth returns the available bandwidth for a custom channel
+	// decided by the given channel aux blob and HTLC blob. A return value
+	// of 0 means there is no bandwidth available. To find out if a channel
+	// is a custom channel that should be handled by the traffic shaper, the
+	// ShouldHandleTraffic method should be called first.
+	PaymentBandwidth(htlcBlob, commitmentBlob fn.Option[tlv.Blob],
+		linkBandwidth,
+		htlcAmt lnwire.MilliSatoshi) (lnwire.MilliSatoshi, error)
+}