moby/pkg/fileutils/fileutils.go

package fileutils // import "github.com/docker/docker/pkg/fileutils"

import (
	"fmt"
	"io"
	"os"
	"path/filepath"
)

// CopyFile copies from src to dst until either EOF is reached
// on src or an error occurs. It verifies src exists and removes
// the dst if it exists.
func CopyFile(src, dst string) (int64, error) {
	cleanSrc := filepath.Clean(src)
	cleanDst := filepath.Clean(dst)
	if cleanSrc == cleanDst {
		return 0, nil
	}
	sf, err := os.Open(cleanSrc)
	if err != nil {
		return 0, err
	}
	defer sf.Close()
	if err := os.Remove(cleanDst); err != nil && !os.IsNotExist(err) {
		return 0, err
	}
	df, err := os.Create(cleanDst)
	if err != nil {
		return 0, err
	}
	defer df.Close()
	return io.Copy(df, sf)
}

// ReadSymlinkedDirectory returns the target directory of a symlink.
// The target of the symbolic link may not be a file.
func ReadSymlinkedDirectory(path string) (realPath string, err error) {
	if realPath, err = filepath.Abs(path); err != nil {
		return "", fmt.Errorf("unable to get absolute path for %s: %w", path, err)
	}
	if realPath, err = filepath.EvalSymlinks(realPath); err != nil {
		return "", fmt.Errorf("failed to canonicalise path for %s: %w", path, err)
	}
	realPathInfo, err := os.Stat(realPath)
	if err != nil {
		return "", fmt.Errorf("failed to stat target '%s' of '%s': %w", realPath, path, err)
	}
	if !realPathInfo.Mode().IsDir() {
		return "", fmt.Errorf("canonical path points to a file '%s'", realPath)
	}
	return realPath, nil
}

// CreateIfNotExists creates a file or a directory only if it does not already exist.
func CreateIfNotExists(path string, isDir bool) error {
	if _, err := os.Stat(path); err != nil {
		if os.IsNotExist(err) {
			if isDir {
				return os.MkdirAll(path, 0o755)
			}
			if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
				return err
			}
			f, err := os.OpenFile(path, os.O_CREATE, 0o755)
			if err != nil {
				return err
			}
			f.Close()
		}
	}
	return nil
}