packing: Bug fix: Extend could create a too big page

Closes #1454

internal/packing/packing.go

@@ -217,24 +217,33 @@ func (p *Page) Extend(count int) bool {
 	if p.size >= p.maxSize {
 		return false
 	}
+
 	newSize := p.size
 	for i := 0; i < count; i++ {
 		newSize *= 2
 	}
+
+	if newSize > p.maxSize {
+		return false
+	}
+
 	edgeNodes := []*Node{}
 	abort := errors.New("abort")
 	aborted := false
-	_ = walk(p.root, func(n *Node) error {
-		if n.x+n.width < p.size && n.y+n.height < p.size {
+	if p.root != nil {
+		_ = walk(p.root, func(n *Node) error {
+			if n.x+n.width < p.size && n.y+n.height < p.size {
+				return nil
+			}
+			if n.used {
+				aborted = true
+				return abort
+			}
+			edgeNodes = append(edgeNodes, n)
 			return nil
-		}
-		if n.used {
-			aborted = true
-			return abort
-		}
-		edgeNodes = append(edgeNodes, n)
-		return nil
-	})
+		})
+	}
+
 	if aborted {
 		origRoot := *p.root
 
@@ -306,6 +315,7 @@ func (p *Page) Extend(count int) bool {
 	}
 
 	p.size = newSize
+
 	return true
 }
 

internal/packing/packing_test.go

@@ -328,3 +328,34 @@ func TestExtend2(t *testing.T) {
 		t.Errorf("p.Alloc(%d, %d) must fail but not", s, s)
 	}
 }
+
+// Issue #1454
+func TestExtendTooMuch(t *testing.T) {
+	p := NewPage(1024, 4096)
+	p.Alloc(1, 1)
+	if got, want := p.Extend(3), false; got != want {
+		t.Errorf("got: %t, want: %t", got, want)
+	}
+}
+
+func TestExtendWithoutAllocation(t *testing.T) {
+	p := NewPage(1024, 4096)
+
+	if got, want := p.Extend(2), true; got != want {
+		t.Errorf("got: %t, want: %t", got, want)
+	}
+
+	p.RollbackExtension()
+	if got, want := p.Size(), 1024; got != want {
+		t.Errorf("p.Size(): got: %d, want: %d", got, want)
+	}
+
+	if got, want := p.Extend(2), true; got != want {
+		t.Errorf("got: %t, want: %t", got, want)
+	}
+
+	p.CommitExtension()
+	if got, want := p.Size(), 4096; got != want {
+		t.Errorf("p.Size(): got: %d, want: %d", got, want)
+	}
+}