Bidirectional stream copy

readme.md

This implementation of bidirectional stream copy has the right behavior for closing streams. The first stream to return io.EOF as a reader triggers a close on the second stream, and then the bidirectional copy may be considered done. The close on the second stream should trigger an error (e.g. io.EOF) on the read of the first stream, closing that stream too.

streamcopy.go

package main

func CopyBidirectional(a, b io.ReadWriteCloser) {
	select {
	case <-copyStream(a, b):
	case <-copyStream(b, a):
	}
}

func copyStream(dst io.WriteCloser, src io.Reader) <-chan struct{} {
	done := make(chan struct{})
	go func() {
		defer close(done)
		defer dst.Close()
		io.Copy(dst, src)
	}()
	return done
}