beam.Tree: plumbing for an in-memory object tree

Signed-off-by: Solomon Hykes <solomon@docker.com>

beam/tree.go

@@ -0,0 +1,44 @@
+package beam
+
+import (
+	"sort"
+)
+
+type Tree struct {
+	*Server
+	children map[string]Sender
+}
+
+func NewTree() *Tree {
+	t := &Tree{
+		Server:   NewServer(),
+		children: make(map[string]Sender),
+	}
+	t.OnAttach(Handler(func(msg *Message) error {
+		if len(msg.Args) == 0 || msg.Args[0] == "" {
+			msg.Ret.Send(&Message{Name: "ack", Ret: t})
+			return nil
+		}
+		if child, exists := t.children[msg.Args[0]]; exists {
+			msg.Ret.Send(&Message{Name: "ack", Ret: child})
+			return nil
+		}
+		Obj(msg.Ret).Error("not found")
+		return nil
+	}))
+	t.OnLs(Handler(func(msg *Message) error {
+		names := make([]string, 0, len(t.children))
+		for name := range t.children {
+			names = append(names, name)
+		}
+		sort.Strings(names)
+		Obj(msg.Ret).Set(names...)
+		return nil
+	}))
+	return t
+}
+
+func (t *Tree) Bind(name string, dst Sender) *Tree {
+	t.children[name] = dst
+	return t
+}