or-done & tee

gistfile1.txt

func orDone(done, c <-chan interface{}) <-chan interface{} {
	valStream := make(chan interface{})
	go func() {
		defer close(valStream)
		for {
			select {
			case <-done:
				return
			case v, ok := <-c:
				if ok == false {
					return
				}
				select {
				case valStream <- v:
				case <-done:
				}
			}
		}
	}()
	return valStream
}

func tee(done <-chan interface{}, in <-chan interface{}) (<-chan interface{}, <-chan interface{}) {
	out1 := make(chan interface{})
	out2 := make(chan interface{})
	go func() {
		defer close(out1)
		defer close(out2)
		for val := range orDone(done, in) {
			var out1, out2 = out1, out2 // Shadow variables for closure
			// Two iterations of select statement for each outbound channel
			for i := 0; i < 2; i++ {
				// Select so that out1 and out2 don't block each other
				select {
				case <-done:
				case out1 <- val:
					// Set shadowed variable to nil so that further writes will block
					// and other channel can continue
					out1 = nil
				case out2 <- val:
					out2 = nil
				}
			}
		}
	}()
	return out1, out2
}