chain: fix tree interval reorg bug. see #248.

lib/blockchain/chain.js

@@ -147,7 +147,7 @@ class Chain extends AsyncEmitter {
 
       assert((height % this.network.names.treeInterval) !== 0);
 
-      await this.db.saveNames(view, height);
+      await this.db.saveNames(view, entry, false);
     }
 
     this.logger.info('Synchronized Tree Root: %x.', this.db.txn.rootHash());

lib/blockchain/chaindb.js

@@ -1824,10 +1824,11 @@ class ChainDB {
    * Commit names to tree.
    * @private
    * @param {CoinView} view
-   * @param {Number} height
+   * @param {ChainEntry} entry
+   * @param {Boolean} revert
    */
 
-  async saveNames(view, height) {
+  async saveNames(view, entry, revert) {
     for (const ns of view.names.values()) {
       const {nameHash} = ns;
 
@@ -1839,37 +1840,57 @@ class ChainDB {
       await this.txn.insert(nameHash, ns.encode());
     }
 
-    if ((height % this.network.names.treeInterval) === 0)
-      this.put(layout.s.encode(), await this.txn.commit());
+    if ((entry.height % this.network.names.treeInterval) === 0) {
+      // Explanation:
+      //
+      // During a reorg, we must revert the snapshot
+      // back to the beginning of the interval. We
+      // can still incrementally revert the database
+      // transaction with state deltas, but unless
+      // we get the tree hash back to what it was
+      // at the start, we will end up rejecting blocks
+      // during reconnection.
+      //
+      // This is an invalid state that cannot be
+      // recovered from. Luckily, the block we're
+      // disconnecting commits to the _previous_ tree
+      // root, not the current one.
+      if (revert)
+        await this.tree.inject(entry.treeRoot);
+      else
+        await this.txn.commit();
+
+      this.put(layout.s.encode(), this.tree.rootHash());
+    }
   }
 
   /**
    * Connect names to tree.
    * @private
    * @param {CoinView} view
-   * @param {Number} height
+   * @param {ChainEntry} entry
    */
 
-  async connectNames(view, height) {
+  async connectNames(view, entry) {
     const undo = view.toNameUndo();
 
     if (undo.names.length === 0)
-      this.del(layout.w.encode(height));
+      this.del(layout.w.encode(entry.height));
     else
-      this.put(layout.w.encode(height), undo.encode());
+      this.put(layout.w.encode(entry.height), undo.encode());
 
-    return this.saveNames(view, height);
+    return this.saveNames(view, entry, false);
   }
 
   /**
    * Disconnect names from tree.
    * @private
    * @param {CoinView} view
-   * @param {Number} height
+   * @param {ChainEntry} entry
    */
 
-  async disconnectNames(view, height) {
-    const raw = await this.db.get(layout.w.encode(height));
+  async disconnectNames(view, entry) {
+    const raw = await this.db.get(layout.w.encode(entry.height));
 
     if (raw) {
       const undo = NameUndo.decode(raw);
@@ -1880,10 +1901,10 @@ class ChainDB {
         ns.applyState(delta);
       }
 
-      this.del(layout.w.encode(height));
+      this.del(layout.w.encode(entry.height));
     }
 
-    return this.saveNames(view, height - 1);
+    return this.saveNames(view, entry, true);
   }
 
   /**
@@ -1946,7 +1967,7 @@ class ChainDB {
     await this.pruneBlock(entry);
 
     // Connect name state.
-    return this.connectNames(view, entry.height);
+    return this.connectNames(view, entry);
   }
 
   /**
@@ -2018,7 +2039,7 @@ class ChainDB {
     this.del(layout.u.encode(hash));
 
     // Connect name state.
-    await this.disconnectNames(view, entry.height);
+    await this.disconnectNames(view, entry);
 
     return view;
   }