trie: support proof generation from the iterator

trie/iterator.go

@@ -22,6 +22,7 @@ import (
 	"errors"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/rlp"
 )
 
 // Iterator is a key-value trie iterator that traverses a Trie.
@@ -55,31 +56,50 @@ func (it *Iterator) Next() bool {
 	return false
 }
 
+// Prove generates the Merkle proof for the leaf node the iterator is currently
+// positioned on.
+func (it *Iterator) Prove() [][]byte {
+	return it.nodeIt.LeafProof()
+}
+
 // NodeIterator is an iterator to traverse the trie pre-order.
 type NodeIterator interface {
 	// Next moves the iterator to the next node. If the parameter is false, any child
 	// nodes will be skipped.
 	Next(bool) bool
+
 	// Error returns the error status of the iterator.
 	Error() error
 
 	// Hash returns the hash of the current node.
 	Hash() common.Hash
+
 	// Parent returns the hash of the parent of the current node. The hash may be the one
 	// grandparent if the immediate parent is an internal node with no hash.
 	Parent() common.Hash
+
 	// Path returns the hex-encoded path to the current node.
 	// Callers must not retain references to the return value after calling Next.
 	// For leaf nodes, the last element of the path is the 'terminator symbol' 0x10.
 	Path() []byte
 
 	// Leaf returns true iff the current node is a leaf node.
-	// LeafBlob, LeafKey return the contents and key of the leaf node. These
-	// method panic if the iterator is not positioned at a leaf.
-	// Callers must not retain references to their return value after calling Next
 	Leaf() bool
-	LeafBlob() []byte
+
+	// LeafKey returns the key of the leaf. The method panics if the iterator is not
+	// positioned at a leaf. Callers must not retain references to the value after
+	// calling Next.
 	LeafKey() []byte
+
+	// LeafBlob returns the content of the leaf. The method panics if the iterator
+	// is not positioned at a leaf. Callers must not retain references to the value
+	// after calling Next.
+	LeafBlob() []byte
+
+	// LeafProof returns the Merkle proof of the leaf. The method panics if the
+	// iterator is not positioned at a leaf. Callers must not retain references
+	// to the value after calling Next.
+	LeafProof() [][]byte
 }
 
 // nodeIteratorState represents the iteration state at one particular node of the
@@ -139,6 +159,15 @@ func (it *nodeIterator) Leaf() bool {
 	return hasTerm(it.path)
 }
 
+func (it *nodeIterator) LeafKey() []byte {
+	if len(it.stack) > 0 {
+		if _, ok := it.stack[len(it.stack)-1].node.(valueNode); ok {
+			return hexToKeybytes(it.path)
+		}
+	}
+	panic("not at leaf")
+}
+
 func (it *nodeIterator) LeafBlob() []byte {
 	if len(it.stack) > 0 {
 		if node, ok := it.stack[len(it.stack)-1].node.(valueNode); ok {
@@ -148,10 +177,22 @@ func (it *nodeIterator) LeafBlob() []byte {
 	panic("not at leaf")
 }
 
-func (it *nodeIterator) LeafKey() []byte {
+func (it *nodeIterator) LeafProof() [][]byte {
 	if len(it.stack) > 0 {
 		if _, ok := it.stack[len(it.stack)-1].node.(valueNode); ok {
-			return hexToKeybytes(it.path)
+			hasher := newHasher(0, 0, nil)
+			proofs := make([][]byte, 0, len(it.stack))
+
+			for i, item := range it.stack[:len(it.stack)-1] {
+				// Gather nodes that end up as hash nodes (or the root)
+				node, _, _ := hasher.hashChildren(item.node, nil)
+				hashed, _ := hasher.store(node, nil, false)
+				if _, ok := hashed.(hashNode); ok || i == 0 {
+					enc, _ := rlp.EncodeToBytes(node)
+					proofs = append(proofs, enc)
+				}
+			}
+			return proofs
 		}
 	}
 	panic("not at leaf")
@@ -361,12 +402,16 @@ func (it *differenceIterator) Leaf() bool {
 	return it.b.Leaf()
 }
 
+func (it *differenceIterator) LeafKey() []byte {
+	return it.b.LeafKey()
+}
+
 func (it *differenceIterator) LeafBlob() []byte {
 	return it.b.LeafBlob()
 }
 
-func (it *differenceIterator) LeafKey() []byte {
-	return it.b.LeafKey()
+func (it *differenceIterator) LeafProof() [][]byte {
+	return it.b.LeafProof()
 }
 
 func (it *differenceIterator) Path() []byte {
@@ -464,12 +509,16 @@ func (it *unionIterator) Leaf() bool {
 	return (*it.items)[0].Leaf()
 }
 
+func (it *unionIterator) LeafKey() []byte {
+	return (*it.items)[0].LeafKey()
+}
+
 func (it *unionIterator) LeafBlob() []byte {
 	return (*it.items)[0].LeafBlob()
 }
 
-func (it *unionIterator) LeafKey() []byte {
-	return (*it.items)[0].LeafKey()
+func (it *unionIterator) LeafProof() [][]byte {
+	return (*it.items)[0].LeafProof()
 }
 
 func (it *unionIterator) Path() []byte {
@@ -509,12 +558,10 @@ func (it *unionIterator) Next(descend bool) bool {
 			heap.Push(it.items, skipped)
 		}
 	}
-
 	if least.Next(descend) {
 		it.count++
 		heap.Push(it.items, least)
 	}
-
 	return len(*it.items) > 0
 }