contractcourt: abstract call to GetStateNumHint within the closeObserver

In this commit, we abstract the call to `GetStateNumHint` within the
`closeObserver` method to a function closure in the primary config. This
allows us to feed in an arbitrary broadcast state number within unit
tests.

contractcourt/chain_arbitrator.go

@@ -375,6 +375,7 @@ func (c *ChainArbitrator) Start() error {
 				contractBreach: func(retInfo *lnwallet.BreachRetribution) error {
 					return c.cfg.ContractBreach(chanPoint, retInfo)
 				},
+				extractStateNumHint: lnwallet.GetStateNumHint,
 			},
 		)
 		if err != nil {
@@ -710,6 +711,7 @@ func (c *ChainArbitrator) WatchNewChannel(newChan *channeldb.OpenChannel) error
 			contractBreach: func(retInfo *lnwallet.BreachRetribution) error {
 				return c.cfg.ContractBreach(chanPoint, retInfo)
 			},
+			extractStateNumHint: lnwallet.GetStateNumHint,
 		},
 	)
 	if err != nil {

contractcourt/chain_watcher.go

@@ -105,6 +105,11 @@ type chainWatcherConfig struct {
 	// isOurAddr is a function that returns true if the passed address is
 	// known to us.
 	isOurAddr func(btcutil.Address) bool
+
+	// extractStateNumHint extracts the encoded state hint using the passed
+	// obfuscater. This is used by the chain watcher to identify which
+	// state was broadcast and confirmed on-chain.
+	extractStateNumHint func(*wire.MsgTx, [lnwallet.StateHintSize]byte) uint64
 }
 
 // chainWatcher is a system that's assigned to every active channel. The duty
@@ -350,10 +355,9 @@ func (c *chainWatcher) closeObserver(spendNtfn *chainntnfs.SpendEvent) {
 			"ChannelPoint(%v) ", c.cfg.chanState.FundingOutpoint)
 
 		// Decode the state hint encoded within the commitment
-		// transaction to determine if this is a revoked state
+		// transaction to determine if this is a revoked state or not.
-		// or not.
 		obfuscator := c.stateHintObfuscator
-		broadcastStateNum := lnwallet.GetStateNumHint(
+		broadcastStateNum := c.cfg.extractStateNumHint(
 			commitTxBroadcast, obfuscator,
 		)
 		remoteStateNum := remoteCommit.CommitHeight
@@ -418,6 +422,7 @@ func (c *chainWatcher) closeObserver(spendNtfn *chainntnfs.SpendEvent) {
 			// point, there's not much we can do other than wait
 			// for us to retrieve it. We will attempt to retrieve
 			// it from the peer each time we connect to it.
+			//
 			// TODO(halseth): actively initiate re-connection to
 			// the peer?
 			var commitPoint *btcec.PublicKey
@@ -458,6 +463,7 @@ func (c *chainWatcher) closeObserver(spendNtfn *chainntnfs.SpendEvent) {
 			// state, we'll just pass an empty commitment. Note
 			// that this means we won't be able to recover any HTLC
 			// funds.
+			//
 			// TODO(halseth): can we try to recover some HTLCs?
 			err = c.dispatchRemoteForceClose(
 				commitSpend, channeldb.ChannelCommitment{},