util/buffer: add DelayedBuffer

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

util/buffer/buffer_test.go

@@ -0,0 +1,22 @@
+package buffer
+
+import (
+	"bytes"
+	"testing"
+	"time"
+)
+
+func TestTimedBuffer(t *testing.T) {
+	buf := bytes.NewBuffer(nil)
+	b := NewDelayedBuffer(100, 300*time.Millisecond, buf)
+	for i := 0; i < 100; i++ {
+		_, _ = b.Write([]byte(`test`))
+	}
+	if buf.Len() != 0 {
+		t.Fatal("delayed write not worked")
+	}
+	time.Sleep(400 * time.Millisecond)
+	if buf.Len() == 0 {
+		t.Fatal("delayed write not worked")
+	}
+}