From 4132080333b1cb0e96b7b8732e763f96d69074ee Mon Sep 17 00:00:00 2001
From: Ben Johnson <benbjohnson@yahoo.com>
Date: Thu, 13 Mar 2014 14:39:28 -0600
Subject: [PATCH] Fix Cursor.Last() on empty buckets.

@tv42 reported that creating a cursor on an empty bucket and then calling
Cursor.Last() causes an index out of range error and panics. This commit
adds a check for the page's item count being greater than zero.

Fixes #63.
---
 cursor.go  |  2 +-
 tx_test.go | 27 +++++++++++++++++++++------
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/cursor.go b/cursor.go
index 244c915..d66f1c1 100644
--- a/cursor.go
+++ b/cursor.go
@@ -235,7 +235,7 @@ func (c *Cursor) nsearch(key []byte) {
 // keyValue returns the key and value of the current leaf element.
 func (c *Cursor) keyValue() ([]byte, []byte) {
 	ref := &c.stack[len(c.stack)-1]
-	if ref.index >= ref.count() {
+	if ref.count() == 0 || ref.index >= ref.count() {
 		return nil, nil
 	}
 
diff --git a/tx_test.go b/tx_test.go
index 1274476..abdd6d4 100644
--- a/tx_test.go
+++ b/tx_test.go
@@ -190,12 +190,27 @@ func TestTxDeleteBucketNotFound(t *testing.T) {
 func TestTxCursorEmptyBucket(t *testing.T) {
 	withOpenDB(func(db *DB, path string) {
 		db.CreateBucket("widgets")
-		tx, _ := db.Tx()
-		c := tx.Bucket("widgets").Cursor()
-		k, v := c.First()
-		assert.Nil(t, k)
-		assert.Nil(t, v)
-		tx.Commit()
+		db.With(func(tx *Tx) error {
+			c := tx.Bucket("widgets").Cursor()
+			k, v := c.First()
+			assert.Nil(t, k)
+			assert.Nil(t, v)
+			return nil
+		})
+	})
+}
+
+// Ensure that a Tx cursor can reverse iterate over an empty bucket without error.
+func TestCursorEmptyBucketReverse(t *testing.T) {
+	withOpenDB(func(db *DB, path string) {
+		db.CreateBucket("widgets")
+		db.With(func(tx *Tx) error {
+			c := tx.Bucket("widgets").Cursor()
+			k, v := c.Last()
+			assert.Nil(t, k)
+			assert.Nil(t, v)
+			return nil
+		})
 	})
 }