Duplicate a stream n times, and have a notifier to tell you when it is done.

mcopy.go

package mcopy

import (
	"io"
)

func DuplicateToManyStreams(r io.Reader, n uint) ([]io.Reader, chan bool) {
	var readers []io.Reader
	var writers []io.Writer

	for i := uint(0); i < n; i++ {
		prc, pwc := io.Pipe()
		readers = append(readers, prc)
		writers = append(writers, pwc)
	}

	doneChan := make(chan bool, 1)
	go func() {
		defer func() { doneChan <- true; close(doneChan) }()
		mw := io.MultiWriter(writers...)
		_, _ = io.Copy(mw, r)
		for _, w := range writers {
			if c, ok := w.(io.Closer); ok {
				_ = c.Close()
			}
		}

	}()

	return readers, doneChan
}