chainntnfs: extend SpendEvent with reorg channel

In this commit, we add a new channel within the SpendEvent struct that
will be sent upon whenever the spending transaction of the registered
outpoint gets reorged out of the chain. This will pave the road for
successfully handling a funding transaction getting reorged out of the
chain among other things.

chainntnfs/interface.go

@@ -159,19 +159,39 @@ type ConfirmationEvent struct {
 	// Confirmed is a channel that will be sent upon once the transaction
 	// has been fully confirmed. The struct sent will contain all the
 	// details of the channel's confirmation.
-	Confirmed chan *TxConfirmation // MUST be buffered.
+	//
+	// NOTE: This channel must be buffered.
+	Confirmed chan *TxConfirmation
 
 	// Updates is a channel that will sent upon, at every incremental
 	// confirmation, how many confirmations are left to declare the
 	// transaction as fully confirmed.
-	Updates chan uint32 // MUST be buffered.
+	//
+	// NOTE: This channel must be buffered with the number of required
+	// confirmations.
+	Updates chan uint32
 
 	// TODO(roasbeef): all goroutines on ln channel updates should also
 	// have a struct chan that's closed if funding gets re-org out. Need
 	// to sync, to request another confirmation event ntfn, then re-open
 	// channel after confs.
 
-	NegativeConf chan int32 // MUST be buffered.
+	// NegativeConf is a channel that will be sent upon if the transaction
+	// confirms, but is later reorged out of the chain. The integer sent
+	// through the channel represents the reorg depth.
+	//
+	// NOTE: This channel must be buffered.
+	NegativeConf chan int32
+}
+
+// NewConfirmationEvent constructs a new ConfirmationEvent with newly opened
+// channels.
+func NewConfirmationEvent(numConfs uint32) *ConfirmationEvent {
+	return &ConfirmationEvent{
+		Confirmed:    make(chan *TxConfirmation, 1),
+		Updates:      make(chan uint32, numConfs),
+		NegativeConf: make(chan int32, 1),
+	}
 }
 
 // SpendDetail contains details pertaining to a spent output. This struct itself
@@ -196,7 +216,16 @@ type SpendDetail struct {
 type SpendEvent struct {
 	// Spend is a receive only channel which will be sent upon once the
 	// target outpoint has been spent.
-	Spend <-chan *SpendDetail // MUST be buffered.
+	//
+	// NOTE: This channel must be buffered.
+	Spend chan *SpendDetail
+
+	// Reorg is a channel that will be sent upon once we detect the spending
+	// transaction of the outpoint in question has been reorged out of the
+	// chain.
+	//
+	// NOTE: This channel must be buffered.
+	Reorg chan struct{}
 
 	// Cancel is a closure that should be executed by the caller in the
 	// case that they wish to prematurely abandon their registered spend
@@ -204,6 +233,15 @@ type SpendEvent struct {
 	Cancel func()
 }
 
+// NewSpendEvent constructs a new SpendEvent with newly opened channels.
+func NewSpendEvent(cancel func()) *SpendEvent {
+	return &SpendEvent{
+		Spend:  make(chan *SpendDetail, 1),
+		Reorg:  make(chan struct{}, 1),
+		Cancel: cancel,
+	}
+}
+
 // BlockEpoch represents metadata concerning each new block connected to the
 // main chain.
 type BlockEpoch struct {
@@ -225,7 +263,9 @@ type BlockEpoch struct {
 type BlockEpochEvent struct {
 	// Epochs is a receive only channel that will be sent upon each time a
 	// new block is connected to the end of the main chain.
-	Epochs <-chan *BlockEpoch // MUST be buffered.
+	//
+	// NOTE: This channel must be buffered.
+	Epochs <-chan *BlockEpoch
 
 	// Cancel is a closure that should be executed by the caller in the
 	// case that they wish to abandon their registered spend notification.

chainntnfs/txnotifier.go

@@ -126,14 +126,6 @@ type HistoricalConfDispatch struct {
 	EndHeight uint32
 }
 
-// NewConfirmationEvent constructs a new ConfirmationEvent with newly opened
-// channels.
-func NewConfirmationEvent(numConfs uint32) *ConfirmationEvent {
-	return &ConfirmationEvent{
-		Confirmed:    make(chan *TxConfirmation, 1),
-		Updates:      make(chan uint32, numConfs),
-		NegativeConf: make(chan int32, 1),
-	}
 }
 
 // TxNotifier is used to register transaction confirmation notifications and