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/moby/vendor/github.com/moby/buildkit/session/sshforward
    
    the code of the file until where you have to start completion: package sshforward

import (
	"context"
	"io"

	"github.com/pkg/errors"
	"golang.org/x/sync/errgroup"
)

type Stream interface {
	SendMsg(m interface{}) error
	RecvMsg(m interface{}) error
}

func Copy(ctx context.Context, conn io.ReadWriteCloser, stream Stream, closeStream func() error) error {
	defer conn.Close()
	g, ctx := errgroup.WithContext(ctx)

	g.Go(func() (retErr error) {
		p := &BytesMessage{}
		for {
			if err := stream.RecvMsg(p); err != nil {
				if err == io.EOF {
					// indicates client performed CloseSend, but they may still be
					// reading data
					if closeWriter, ok := conn.(interface {
						CloseWrite() error
					}); ok {
						closeWriter.CloseWrite()
					} else {
						conn.Close()
					}
					return nil
				}
				conn.Close()
				return errors.WithStack(err)
			}
			select {
			case <-ctx.Done():
    
func Copy(ctx context.Context, conn io.ReadWriteCloser, stream Stream, closeStream func() error) error {
	defer conn.Close()
	g, ctx := errgroup.WithContext(ctx)

	g.Go(func() (retErr error) {
		p := &BytesMessage{}
		for {
			if err := stream.RecvMsg(p); err != nil {
				if err == io.EOF {
					// indicates client performed CloseSend, but they may still be
					// reading data
					if closeWriter, ok := conn.(interface {
						CloseWrite() error
					}); ok {
						closeWriter.CloseWrite()
					} else {
						conn.Close()
					}
					return nil
				}
				conn.Close()
				return errors.WithStack(err)
			}
			select {
			case <-ctx.Done():
				conn.Close()
				return context.Cause(ctx)
			default:
			}
			if _, err := conn.Write(p.Data); err != nil {
				conn.Close()
				return errors.WithStack(err)
			}
			p.Data = p.Data[:0]
		}
	})

	g.Go(func() (retErr error) {
		for {
			buf := make([]byte, 32*1024)
			n, err := conn.Read(buf)
			switch {
			case err == io.EOF:
				if closeStream != nil {
					closeStream()
				}
				return nil
			case err != nil:
				return errors.WithStack(err)
			}
			select {
			case <-ctx.Done():
				return context.Cause(ctx)
			default:
			}
			p := &BytesMessage{Data: buf[:n]}
			if err := stream.SendMsg(p); err != nil {
				return errors.WithStack(err)
			}
		}
	})

	return g.Wait()
}