From d343b0db5744d5516fe6ffa368dda792c47e9ee3 Mon Sep 17 00:00:00 2001
From: Chris Lu <chris.lu@gmail.com>
Date: Sun, 3 Oct 2021 01:15:14 -0700
Subject: [PATCH] update value

---
 weed/util/skiplist/skiplist.go      | 13 +++++++++++++
 weed/util/skiplist/skiplist_test.go | 29 ++++++++++++++++++++++++++++-
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/weed/util/skiplist/skiplist.go b/weed/util/skiplist/skiplist.go
index 19fa556ae..50ce53525 100644
--- a/weed/util/skiplist/skiplist.go
+++ b/weed/util/skiplist/skiplist.go
@@ -1,5 +1,7 @@
 package skiplist
 
+// adapted from https://github.com/MauriceGit/skiplist/blob/master/skiplist.go
+
 import (
 	"bytes"
 	"fmt"
@@ -402,6 +404,17 @@ func (t *SkipList) Prev(e *SkipListElement) *SkipListElement {
 	return e.Prev.Load()
 }
 
+// ChangeValue can be used to change the actual value of a node in the skiplist
+// without the need of Deleting and reinserting the node again.
+// Be advised, that ChangeValue only works, if the actual key from ExtractKey() will stay the same!
+// ok is an indicator, wether the value is actually changed.
+func (t *SkipList) ChangeValue(e *SkipListElement, newValue []byte) (ok bool) {
+	// The key needs to stay correct, so this is very important!
+	e.Value = newValue
+	e.Save()
+	return true
+}
+
 // String returns a string format of the skiplist. Useful to get a graphical overview and/or debugging.
 func (t *SkipList) println() {
 
diff --git a/weed/util/skiplist/skiplist_test.go b/weed/util/skiplist/skiplist_test.go
index 811fd5be9..b414c267b 100644
--- a/weed/util/skiplist/skiplist_test.go
+++ b/weed/util/skiplist/skiplist_test.go
@@ -242,4 +242,31 @@ func TestFindGreaterOrEqual(t *testing.T) {
 		}
 	}
 
-}
\ No newline at end of file
+}
+
+func TestChangeValue(t *testing.T) {
+	list := New()
+
+	for i := 0; i < maxN; i++ {
+		list.Insert(Element(i), []byte("value"))
+	}
+
+	for i := 0; i < maxN; i++ {
+		// The key only looks at the int so the string doesn't matter here!
+		f1, ok := list.Find(Element(i))
+		if !ok {
+			t.Fail()
+		}
+		ok = list.ChangeValue(f1, []byte("different value"))
+		if !ok {
+			t.Fail()
+		}
+		f2, ok := list.Find(Element(i))
+		if !ok {
+			t.Fail()
+		}
+		if bytes.Compare(f2.GetValue(), []byte("different value")) != 0 {
+			t.Fail()
+		}
+	}
+}