deposit: guard unconfirmed deposits against expiry

Unconfirmed deposits (ConfirmationHeight <= 0) cannot have started their
CSV timer, so IsExpired now returns false for them. Update the Deposited
state and OnStart event documentation to reflect that deposits are
detected from the mempool rather than after reaching a confirmation
threshold.

Author: hieblmi

staticaddr/deposit/deposit.go

@@ -82,6 +82,10 @@ func (d *Deposit) IsExpired(currentHeight, expiry uint32) bool {
 	d.Lock()
 	defer d.Unlock()
 
+	if d.ConfirmationHeight <= 0 {
+		return false
+	}
+
 	return currentHeight >= uint32(d.ConfirmationHeight)+expiry
 }
 

staticaddr/deposit/deposit_test.go

@@ -0,0 +1,15 @@
+package deposit
+
+import "testing"
+
+// TestIsExpiredUnconfirmed checks that unconfirmed deposits don't start their
+// expiry timer.
+func TestIsExpiredUnconfirmed(t *testing.T) {
+	deposit := &Deposit{
+		ConfirmationHeight: 0,
+	}
+
+	if deposit.IsExpired(500, 100) {
+		t.Fatal("unconfirmed deposit should not be expired")
+	}
+}

staticaddr/deposit/fsm.go

@@ -42,8 +42,8 @@ var (
 
 // States.
 var (
-	// Deposited signals that funds at a static address have reached the
-	// confirmation height.
+	// Deposited signals that funds at a static address have been detected
+	// and are available to the client.
 	Deposited = fsm.StateType("Deposited")
 
 	// Replaced signals that an unconfirmed deposit disappeared from the
@@ -105,8 +105,8 @@ var (
 // Events.
 var (
 	// OnStart is sent to the fsm once the deposit outpoint has been
-	// sufficiently confirmed. It transitions the fsm into the Deposited
-	// state from where we can trigger a withdrawal, a loopin or an expiry.
+	// detected. It transitions the fsm into the Deposited state from where
+	// we can trigger a withdrawal, a loopin or an expiry.
 	OnStart = fsm.EventType("OnStart")
 
 	// OnWithdrawInitiated is sent to the fsm when a withdrawal has been