From d5df4d593f1cbaab82880981ce7605a428439748 Mon Sep 17 00:00:00 2001
From: Max Wash <mbswash@gmail.com>
Date: Sat, 26 Apr 2025 21:23:50 +0100
Subject: [PATCH] b-tree: fix corruption bug when inserting an entry in the
 middle of a node

---
 src/b-tree.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/src/b-tree.c b/src/b-tree.c
index 304632b..3179962 100644
--- a/src/b-tree.c
+++ b/src/b-tree.c
@@ -180,8 +180,10 @@ static void node_shift_entries(
 	unsigned long count = nr_entries - shift_from;
 
 	for (unsigned long i = 0; i < count; i++) {
-		b_tree_node_entry *entry = node_get_entry(tree, node, src + i);
-		node_set_entry(tree, node, dest + i, entry);
+		unsigned long from = (src + count - 1) - i;
+		unsigned long to = (dest + count - 1) - i;
+		b_tree_node_entry *entry = node_get_entry(tree, node, from);
+		node_set_entry(tree, node, to, entry);
 	}
 
 	if (shift_by < 0) {
@@ -323,15 +325,28 @@ static int node_put(
 	}
 
 	int insert_at = -1;
+	bool exact_match = false;
+
 	for (unsigned long i = 0; i < nr_entries; i++) {
 		const b_tree_node_entry *cur = node_get_entry(tree, n, i);
 		int cmp = entry_compare(tree, cur, e);
+		if (cmp == 0) {
+			insert_at = i;
+			exact_match = true;
+			break;
+		}
+
 		if (cmp == 1) {
 			insert_at = i;
 			break;
 		}
 	}
 
+	if (exact_match) {
+		node_set_entry(tree, n, insert_at, e);
+		return insert_at;
+	}
+
 	if (insert_at != -1) {
 		node_shift_entries(tree, n, insert_at, 1);
 	} else {
@@ -443,9 +458,9 @@ int b_tree_put(struct b_tree *tree, const b_tree_node_entry *to_put)
 
 		/* this node is full, split it. */
 
-		/* half the nodes from `next` will be moved into `n3`. the other
-		   half will stay put. the median entry will be moved to
-		   `current`.
+		/* half the nodes from `next` will be moved into `n3`.
+		   the other half will stay put. the median entry will
+		   be moved to `current`.
 
 		   `n3` will become the right sibling of `next` */
 		b_tree_node *n3 = cache_alloc_node(tree);