You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: copy.go
    path of file: ./repos/podman/vendor/github.com/containers/common/pkg/detach
    
    the code of the file until where you have to start completion: package detach

import (
	"errors"
	"io"
)

// ErrDetach indicates that an attach session was manually detached by
// the user.
var ErrDetach = errors.New("detached from container")

//
    
func Copy(dst io.Writer, src io.Reader, keys []byte) (written int64, err error) {
	buf := make([]byte, 32*1024)
	for {
		nr, er := src.Read(buf)
		if nr > 0 {
			preservBuf := []byte{}
			for i, key := range keys {
				preservBuf = append(preservBuf, buf[0:nr]...)
				if nr != 1 || buf[0] != key {
					break
				}
				if i == len(keys)-1 {
					return 0, ErrDetach
				}
				nr, er = src.Read(buf)
			}
			var nw int
			var ew error
			if len(preservBuf) > 0 {
				nw, ew = dst.Write(preservBuf)
				nr = len(preservBuf)
			} else {
				nw, ew = dst.Write(buf[0:nr])
			}
			if nw > 0 {
				written += int64(nw)
			}
			if ew != nil {
				err = ew
				break
			}
			if nr != nw {
				err = io.ErrShortWrite
				break
			}
		}
		if er != nil {
			if er != io.EOF {
				err = er
			}
			break
		}
	}
	return written, err
}