GODT-35: New pmapi client and manager using resty

pkg/pmapi/observer.go

@@ -0,0 +1,23 @@
+package pmapi
+
+type ConnectionObserver interface {
+	OnDown()
+	OnUp()
+}
+
+type observer struct {
+	onDown, onUp func()
+}
+
+// NewConnectionObserver is a helper function to create a new connection observer from two callbacks.
+// It doesn't need to be used; anything which implements the ConnectionObserver interface can be an observer.
+func NewConnectionObserver(onDown, onUp func()) ConnectionObserver {
+	return &observer{
+		onDown: onDown,
+		onUp:   onUp,
+	}
+}
+
+func (o observer) OnDown() { o.onDown() }
+
+func (o observer) OnUp() { o.onUp() }