lnwallet: remove the closeObserver from the channel state machine

In this PR, we entirely remove the closeObserver from the channel state
machine. It was added very early on before most of the other aspects of
the daemon were built out. This goroutine was responsible for
dispatching notifications to outside parties if the commitment
transaction was spent at all. This had several issues, since it was
linked to the *lifetime* of the channel state machine itself. As a
result of this linkage, we had to do weird stuff like hand off in
memory pointers to the state machine in order to ensure notifications
were properly dispatched.

lnwallet/wallet.go

@@ -534,6 +534,8 @@ func (l *LightningWallet) handleFundingReserveRequest(req *initFundingReserveMsg
 	// for the duration of the channel. The keys include: our multi-sig
 	// key, the base revocation key, the base htlc key,the base payment
 	// key, and the delayed payment key.
+	//
+	// TODO(roasbeef): special derivaiton?
 	reservation.ourContribution.MultiSigKey, err = l.NewRawKey()
 	if err != nil {
 		req.err <- err
@@ -845,7 +847,7 @@ func (l *LightningWallet) handleContributionMsg(req *addContributionMsg) {
 	// both commitment transactions.
 	var stateObfuscator [StateHintSize]byte
 	if chanState.ChanType == channeldb.SingleFunder {
-		stateObfuscator = deriveStateHintObfuscator(
+		stateObfuscator = DeriveStateHintObfuscator(
 			ourContribution.PaymentBasePoint,
 			theirContribution.PaymentBasePoint,
 		)
@@ -854,12 +856,12 @@ func (l *LightningWallet) handleContributionMsg(req *addContributionMsg) {
 		theirSer := theirContribution.PaymentBasePoint.SerializeCompressed()
 		switch bytes.Compare(ourSer, theirSer) {
 		case -1:
-			stateObfuscator = deriveStateHintObfuscator(
+			stateObfuscator = DeriveStateHintObfuscator(
 				ourContribution.PaymentBasePoint,
 				theirContribution.PaymentBasePoint,
 			)
 		default:
-			stateObfuscator = deriveStateHintObfuscator(
+			stateObfuscator = DeriveStateHintObfuscator(
 				theirContribution.PaymentBasePoint,
 				ourContribution.PaymentBasePoint,
 			)
@@ -1161,7 +1163,7 @@ func (l *LightningWallet) handleSingleFunderSigs(req *addSingleFunderSigsMsg) {
 	// With both commitment transactions constructed, we can now use the
 	// generator state obfuscator to encode the current state number within
 	// both commitment transactions.
-	stateObfuscator := deriveStateHintObfuscator(
+	stateObfuscator := DeriveStateHintObfuscator(
 		pendingReservation.theirContribution.PaymentBasePoint,
 		pendingReservation.ourContribution.PaymentBasePoint)
 	err = initStateHints(ourCommitTx, theirCommitTx, stateObfuscator)
@@ -1349,7 +1351,7 @@ func (l *LightningWallet) deriveMasterRevocationRoot() (*btcec.PrivateKey, error
 	return masterElkremRoot.ECPrivKey()
 }
 
-// deriveStateHintObfuscator derives the bytes to be used for obfuscating the
+// DeriveStateHintObfuscator derives the bytes to be used for obfuscating the
 // state hints from the root to be used for a new channel. The obsfucsator is
 // generated via the following computation:
 //
@@ -1357,7 +1359,7 @@ func (l *LightningWallet) deriveMasterRevocationRoot() (*btcec.PrivateKey, error
 //     * where both keys are the multi-sig keys of the respective parties
 //
 // The first 6 bytes of the resulting hash are used as the state hint.
-func deriveStateHintObfuscator(key1, key2 *btcec.PublicKey) [StateHintSize]byte {
+func DeriveStateHintObfuscator(key1, key2 *btcec.PublicKey) [StateHintSize]byte {
 	h := sha256.New()
 	h.Write(key1.SerializeCompressed())
 	h.Write(key2.SerializeCompressed())