Channel with an unrestricted buffer in the middle

elastic.go

type Message struct {
	Value string
}

func MakeElastic() (<-chan Message, chan<- Message) {
	input := make(chan Message, 64)
	output := make(chan Message, 64)
	middle := make(chan []Message, 1)
	go func(middle chan []Message, input <-chan Message) {
		defer close(middle)
		for message := range(input) {
			var buffer []Message
			select {
			case buffer = <-middle:
				buffer = append(buffer, message)
			default:
				buffer = []Message{message}
			}
			middle <- buffer
		}
	}(middle, input)
	go func(output chan<- Message, middle <-chan []Message) {
		defer close(output)
		for messages := range(middle) {
			for _, message := range(messages) {
				output <- message
			}
		}
	}(output, middle)
	return output, input
}