trie: change the Value.Hash() to return pointer.

When nil is returned by Hash(), the merkle generation will treat it as a
nil node, and ignore the hash along the way.

claim/hash.go

@@ -9,7 +9,7 @@ import (
 	"github.com/btcsuite/btcd/wire"
 )
 
-func calNodeHash(op wire.OutPoint, tookover Height) chainhash.Hash {
+func calNodeHash(op wire.OutPoint, tookover Height) *chainhash.Hash {
 	txHash := chainhash.DoubleHashH(op.Hash[:])
 
 	nOut := []byte(strconv.Itoa(int(op.Index)))
@@ -24,5 +24,6 @@ func calNodeHash(op wire.OutPoint, tookover Height) chainhash.Hash {
 	h = append(h, nOutHash[:]...)
 	h = append(h, heightHash[:]...)
 
-	return chainhash.DoubleHashH(h)
+	hh := chainhash.DoubleHashH(h)
+	return &hh
 }

claim/node.go

@@ -165,9 +165,9 @@ func (n *Node) FindNextUpdateHeight() Height {
 }
 
 // Hash calculates the Hash value based on the OutPoint and at which height it tookover.
-func (n *Node) Hash() chainhash.Hash {
+func (n *Node) Hash() *chainhash.Hash {
 	if n.BestClaim() == nil {
-		return chainhash.Hash{}
+		return nil
 	}
 	return calNodeHash(n.BestClaim().OutPoint, n.Tookover())
 }

cmd/claimtrie/main.go

@@ -223,7 +223,7 @@ func (a *args) all() bool {
 
 var showNode = func(showJSON bool) trie.Visit {
 	return func(prefix trie.Key, val trie.Value) error {
-		if val == nil {
+		if val == nil || val.Hash() == nil {
 			fmt.Printf("%-8s:\n", prefix)
 			return nil
 		}

trie/cmd/triesh/main.go

@@ -103,8 +103,9 @@ func main() {
 
 type strValue string
 
-func (s strValue) Hash() chainhash.Hash {
-	return chainhash.DoubleHashH([]byte(s))
+func (s strValue) Hash() *chainhash.Hash {
+	h := chainhash.DoubleHashH([]byte(s))
+	return &h
 }
 
 var (

trie/node.go

@@ -84,8 +84,9 @@ func merkle(n *node) *chainhash.Hash {
 		}
 	}
 	if n.value != nil {
-		h := n.value.Hash()
-		buf = append(buf, h[:]...)
+		if h := n.value.Hash(); h != nil {
+			buf = append(buf, h[:]...)
+		}
 	}
 
 	if len(buf) != 0 {

trie/test.go

@@ -10,8 +10,9 @@ import (
 
 type strValue string
 
-func (s strValue) Hash() chainhash.Hash {
-	return chainhash.DoubleHashH([]byte(s))
+func (s strValue) Hash() *chainhash.Hash {
+	h := chainhash.DoubleHashH([]byte(s))
+	return &h
 }
 
 func dump(prefix Key, value Value) error {

trie/trie.go

@@ -16,7 +16,7 @@ type Key []byte
 
 // Value implements value for the MerkleTrie.
 type Value interface {
-	Hash() chainhash.Hash
+	Hash() *chainhash.Hash
 }
 
 // MerkleTrie implements a 256-way prefix tree, which takes Key as key and any value that implements the Value interface.