channel/channel.go
func SendJSON(c context.Context, clientID string, value interface{}) error {
	m, err := json.Marshal(value)
	if err != nil {
		return err
	}
	return Send(c, clientID, string(m))
}
func SendJSON(c context.Context, clientID string, value interface{}) error {
	m, err := json.Marshal(value)
	if err != nil {
		return err
	}
	return Send(c, clientID, string(m))
}
// SendJSON is a helper function that sends a JSON-encoded value
// on the channel associated with clientID.