trie: added error handling

Created alternate versions of Trie and SecureTrie functions that can return a MissingNodeError (used by ODR services)

trie/errors.go

@@ -0,0 +1,41 @@
+// Copyright 2014 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library 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.
+//
+// The go-ethereum library 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 the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package trie
+
+import (
+	"fmt"
+
+	"github.com/ethereum/go-ethereum/common"
+)
+
+// MissingNodeError is returned by the trie functions (TryGet, TryUpdate, TryDelete)
+// in the case where a trie node is not present in the local database. Contains
+// information necessary for retrieving the missing node through an ODR service.
+//
+// NodeHash is the hash of the missing node
+// RootHash is the original root of the trie that contains the node
+// KeyPrefix is the prefix that leads from the root to the missing node (hex encoded)
+// KeySuffix (optional) contains the rest of the key we were looking for, gives a
+//  hint on which further nodes should also be retrieved (hex encoded)
+type MissingNodeError struct {
+	RootHash, NodeHash   common.Hash
+	KeyPrefix, KeySuffix []byte
+}
+
+func (err *MissingNodeError) Error() string {
+	return fmt.Sprintf("Missing trie node %064x", err.NodeHash)
+}