fix: Fixes memiterator (#21775)

Co-authored-by: marbar3778 <marbar3778@yahoo.com>

server/v2/stf/branch/changeset.go

@@ -99,7 +99,7 @@ type memIterator struct {
 }
 
 // newMemIterator creates a new memory iterator for a given range of keys in a B-tree.
-// The iterator starts at the specified start key and ends at the specified end key.
+// The iterator creates a copy then starts at the specified start key and ends at the specified end key.
 // The `tree` parameter is the B-tree to iterate over.
 // The `ascending` parameter determines the direction of iteration.
 // If `ascending` is true, the iterator will iterate in ascending order.
@@ -111,7 +111,7 @@ type memIterator struct {
 // The `valid` field of the iterator indicates whether the iterator is positioned at a valid key.
 // The `start` and `end` fields of the iterator store the start and end keys respectively.
 func newMemIterator(start, end []byte, tree *btree.BTreeG[item], ascending bool) *memIterator {
-	iter := tree.Iter()
+	iter := tree.Copy().Iter()
 	var valid bool
 	if ascending {
 		if start != nil {
@@ -207,6 +207,9 @@ func (mi *memIterator) keyInRange(key []byte) bool {
 	if !mi.ascending && mi.start != nil && bytes.Compare(key, mi.start) < 0 {
 		return false
 	}
+	if !mi.ascending && mi.end != nil && bytes.Compare(key, mi.end) >= 0 {
+		return false
+	}
 	return true
 }
 

server/v2/stf/branch/changeset_test.go

@@ -4,7 +4,7 @@ import (
 	"testing"
 )
 
-func Test_memIterator(t *testing.T) {
+func TestMemIteratorWithWriteToRebalance(t *testing.T) {
 	t.Run("iter is invalid after close", func(t *testing.T) {
 		cs := newChangeSet()
 		for i := byte(0); i < 32; i++ {
@@ -26,3 +26,62 @@ func Test_memIterator(t *testing.T) {
 		}
 	})
 }
+
+func TestKeyInRange(t *testing.T) {
+	specs := map[string]struct {
+		mi  *memIterator
+		src []byte
+		exp bool
+	}{
+		"equal start": {
+			mi:  &memIterator{ascending: true, start: []byte{0}, end: []byte{2}},
+			src: []byte{0},
+			exp: true,
+		},
+		"equal end": {
+			mi:  &memIterator{ascending: true, start: []byte{0}, end: []byte{2}},
+			src: []byte{2},
+			exp: false,
+		},
+		"between": {
+			mi:  &memIterator{ascending: true, start: []byte{0}, end: []byte{2}},
+			src: []byte{1},
+			exp: true,
+		},
+		"equal start - open end": {
+			mi:  &memIterator{ascending: true, start: []byte{0}},
+			src: []byte{0},
+			exp: true,
+		},
+		"greater start - open end": {
+			mi:  &memIterator{ascending: true, start: []byte{0}},
+			src: []byte{2},
+			exp: true,
+		},
+		"equal end - open start": {
+			mi:  &memIterator{ascending: true, end: []byte{2}},
+			src: []byte{2},
+			exp: false,
+		},
+		"smaller end - open start": {
+			mi:  &memIterator{ascending: true, end: []byte{2}},
+			src: []byte{1},
+			exp: true,
+		},
+	}
+	for name, spec := range specs {
+		for _, asc := range []bool{true, false} {
+			order := "asc_"
+			if !asc {
+				order = "desc_"
+			}
+			t.Run(order+name, func(t *testing.T) {
+				spec.mi.ascending = asc
+				got := spec.mi.keyInRange(spec.src)
+				if spec.exp != got {
+					t.Errorf("expected %v, got %v", spec.exp, got)
+				}
+			})
+		}
+	}
+}