From 8572c36ee7fc2e53f8d1b40344298d9ac89bb5e8 Mon Sep 17 00:00:00 2001
From: Roy Crihfield <roy@manteia.ltd>
Date: Mon, 6 Jun 2022 20:08:38 +0800
Subject: [PATCH] decrement path from restored iterator

to cover node gaps
---
 pkg/snapshot/tracker.go |  1 +
 pkg/snapshot/util.go    | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/pkg/snapshot/tracker.go b/pkg/snapshot/tracker.go
index 8ca9b34..3bbdec6 100644
--- a/pkg/snapshot/tracker.go
+++ b/pkg/snapshot/tracker.go
@@ -139,6 +139,7 @@ func (tr *iteratorTracker) restore(tree state.Trie) ([]trie.NodeIterator, error)
 
 		// Force the lower bound path to an even length
 		if len(paths[0])&0b1 == 1 {
+			decrementPath(paths[0]) // decrement first to avoid skipped nodes
 			paths[0] = append(paths[0], 0)
 		}
 		it := iter.NewPrefixBoundIterator(tree.NodeIterator(iter.HexToKeyBytes(paths[0])), paths[1])
diff --git a/pkg/snapshot/util.go b/pkg/snapshot/util.go
index a2ca7ee..e9db47d 100644
--- a/pkg/snapshot/util.go
+++ b/pkg/snapshot/util.go
@@ -28,3 +28,26 @@ func NewPublisher(mode SnapshotMode, config *Config) (snapt.Publisher, error) {
 	}
 	return nil, fmt.Errorf("invalid snapshot mode: %s", mode)
 }
+
+// Subtracts 1 from the last byte in a path slice, carrying if needed.
+// Does nothing, returning false, for all-zero inputs.
+func decrementPath(path []byte) bool {
+	// check for all zeros
+	allzero := true
+	for i := 0; i < len(path); i++ {
+		allzero = allzero && path[i] == 0
+	}
+	if allzero {
+		return false
+	}
+	for i := len(path) - 1; i >= 0; i-- {
+		val := path[i]
+		path[i]--
+		if val == 0 {
+			path[i] = 0xf
+		} else {
+			return true
+		}
+	}
+	return true
+}