Tee Copy in Go

tee_copy.go

package debug

import (
	"fmt"
	"io"
)

func teeCopy(w1 io.Writer, w2 io.Writer, r io.Reader) (totalN int, err error) {
	buf := make([]byte, 1024)
	for {
		var n int
		n, err = r.Read(buf)
		totalN += n
		if err != nil {
			return
		}

		var writeN int
		writeN, err = w1.Write(buf[:n])
		if err != nil {
			return
		}
		if n != writeN {
			return totalN, fmt.Errorf("incomplete data written. expected to write %d bytes, but wrote %d bytes", n, writeN)
		}
		writeN, err = w2.Write(buf[:n])
		if err != nil {
			return
		}
		if n != writeN {
			return totalN, fmt.Errorf("incomplete data written. expected to write %d bytes, but wrote %d bytes", n, writeN)
		}
	}
}