Merge pull request #782 from rsksmart/unitrie_nodereference

Create a NodeReference abstraction for the trie

rskj-core/src/main/java/co/rsk/trie/NodeReference.java

@@ -0,0 +1,96 @@
+/*
+ * This file is part of RskJ
+ * Copyright (C) 2019 RSK Labs Ltd.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+package co.rsk.trie;
+
+import co.rsk.crypto.Keccak256;
+
+import javax.annotation.Nullable;
+import java.util.Objects;
+import java.util.Optional;
+
+public class NodeReference {
+    private final TrieStore store;
+
+    private TrieImpl lazyNode;
+    private Keccak256 lazyHash;
+
+    public NodeReference(TrieStore store, @Nullable TrieImpl node, @Nullable Keccak256 hash) {
+        this.store = store;
+        if (node != null && node.isEmptyTrie()) {
+            this.lazyNode = null;
+            this.lazyHash = null;
+        } else {
+            this.lazyNode = node;
+            this.lazyHash = hash;
+        }
+    }
+
+    public boolean isEmpty() {
+        return lazyHash == null && lazyNode == null;
+    }
+
+    /**
+     * If the node is not present, this is either an empty reference, or the hash points to a node already in storage.
+     */
+    public void save() {
+        if (lazyNode != null) {
+            lazyNode.save();
+        }
+    }
+
+    /**
+     * The node or empty if this is an empty reference.
+     * If the node is not present but its hash is known, it will be retrieved from the store.
+     */
+    public Optional<TrieImpl> getNode() {
+        if (lazyNode != null) {
+            return Optional.of(lazyNode);
+        }
+
+        if (lazyHash == null) {
+            return Optional.empty();
+        }
+
+        lazyNode = Objects.requireNonNull(
+                (TrieImpl) store.retrieve(lazyHash.getBytes()),
+                "The node with this hash is not present in the trie store"
+        );
+        return Optional.of(lazyNode);
+    }
+
+    /**
+     * The hash or empty if this is an empty reference.
+     * If the hash is not present but its node is known, it will be calculated.
+     */
+    public Optional<Keccak256> getHash() {
+        if (lazyHash != null) {
+            return Optional.of(lazyHash);
+        }
+
+        if (lazyNode == null) {
+            return Optional.empty();
+        }
+
+        lazyHash = lazyNode.getHash();
+        return Optional.of(lazyHash);
+    }
+
+    public static NodeReference empty() {
+        return new NodeReference(null, null, null);
+    }
+}