//go:build e2e

package e2e

import (
	"archive/tar"
	"errors"
	"io"
	"strings"
)

// firstFileInTar returns the contents of the first regular file in an archive
// produced by the Docker archive API.
func firstFileInTar(r io.Reader) (string, error) {
	tr := tar.NewReader(r)
	for {
		hdr, err := tr.Next()
		if errors.Is(err, io.EOF) {
			return "", errors.New("archive contains no regular file")
		}
		if err != nil {
			return "", err
		}
		if hdr.Typeflag != tar.TypeReg {
			continue
		}
		var b strings.Builder
		if _, err := io.Copy(&b, tr); err != nil {
			return "", err
		}
		return b.String(), nil
	}
}