storage/mem: implement size enforcer for #88

pkg/storage/mem/maxsize.go

@@ -0,0 +1,73 @@
+package mem
+
+import "container/list"
+
+type msgDone struct {
+	msg  *Message
+	done chan struct{}
+}
+
+// enforceMaxSize will delete the oldest message until the entire mail store is equal to or less
+// than Store.maxSize bytes.
+func (s *Store) maxSizeEnforcer(maxSize int64) {
+	all := &list.List{}
+	curSize := int64(0)
+	for {
+		select {
+		case md, ok := <-s.incoming:
+			if !ok {
+				return
+			}
+			// Add message to all.
+			m := md.msg
+			el := all.PushBack(m)
+			m.el = el
+			curSize += int64(m.Size())
+			for curSize > maxSize {
+				// Remove oldest message.
+				el := all.Front()
+				all.Remove(el)
+				m := el.Value.(*Message)
+				if s.removeMessage(m.mailbox, m.id) != nil {
+					curSize -= int64(m.Size())
+				}
+			}
+			close(md.done)
+		case md, ok := <-s.remove:
+			if !ok {
+				return
+			}
+			// Remove message from all.
+			m := md.msg
+			el := all.Remove(m.el)
+			if el != nil {
+				curSize -= int64(m.Size())
+			}
+			close(md.done)
+		}
+	}
+}
+
+// enforcerDeliver sends delivery to enforcer if configured, and waits for completion.
+func (s *Store) enforcerDeliver(m *Message) {
+	if s.incoming != nil {
+		md := &msgDone{
+			msg:  m,
+			done: make(chan struct{}),
+		}
+		s.incoming <- md
+		<-md.done
+	}
+}
+
+// enforcerRemove sends removal to enforcer if configured, and waits for completion.
+func (s *Store) enforcerRemove(m *Message) {
+	if s.remove != nil {
+		md := &msgDone{
+			msg:  m,
+			done: make(chan struct{}),
+		}
+		s.remove <- md
+		<-md.done
+	}
+}