beam/data: convenience Message type for chained manipulation

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)

beam/data/message.go

@@ -0,0 +1,47 @@
+package data
+
+import (
+)
+
+type Message string
+
+func Empty() Message {
+	return Message(Encode(nil))
+}
+
+func (m Message) Add(k, v string) Message {
+	data, err := Decode(string(m))
+	if err != nil {
+		return m
+	}
+	if values, exists := data[k]; exists {
+		data[k] = append(values, v)
+	} else {
+		data[k] = []string{v}
+	}
+	return Message(Encode(data))
+}
+
+func (m Message) Set(k string, v ...string) Message {
+	data, err := Decode(string(m))
+	if err != nil {
+		panic(err)
+		return m
+	}
+	data[k] = v
+	return Message(Encode(data))
+}
+
+func (m Message) Del(k string) Message {
+	data, err := Decode(string(m))
+	if err != nil {
+		panic(err)
+		return m
+	}
+	delete(data, k)
+	return Message(Encode(data))
+}
+
+func (m Message) String() string {
+	return string(m)
+}