osutil.go

package osutil

import (
	"fmt"
	"os"
	"runtime"
	"syscall"
)

// Exists returns whether the given file or directory exists or not.
func Exists(path string) (bool, error) {
	_, err := os.Stat(path)
	if err == nil {
		return true, nil
	}
	if os.IsNotExist(err) {
		return false, nil
	}
	return true, err
}

// SymlinkWithFallback attempts to symlink a file or directory, but falls back to a move operation
// in the event of the user not having the required privileges to create the symlink.
func SymlinkWithFallback(oldname, newname string) (err error) {
	err = os.Symlink(oldname, newname)
	if runtime.GOOS == "windows" {
		// If creating the symlink fails on Windows because the user
		// does not have the required privileges, ignore the error and
		// fall back to renaming the file.
		//
		// ERROR_PRIVILEGE_NOT_HELD is 0x522:
		// https://msdn.microsoft.com/en-us/library/windows/desktop/ms681385(v=vs.85).aspx
		if lerr, ok := err.(*os.LinkError); ok && lerr.Err == syscall.Errno(0x522) {
			err = os.Rename(oldname, newname)
		}
	}
	return
}

// EnsureDirectory checks if a directory exists and creates it if it doesn't
func EnsureDirectory(dir string) error {
	if fi, err := os.Stat(dir); err != nil {
		if err := os.MkdirAll(dir, 0755); err != nil {
			return fmt.Errorf("Could not create %s: %s", dir, err)
		}
	} else if !fi.IsDir() {
		return fmt.Errorf("%s must be a directory", dir)
	}

	return nil
}

// EnsureFile checks if a file exists and creates it if it doesn't
func EnsureFile(file string) error {
	fi, err := os.Stat(file)
	if err != nil {
		f, err := os.Create(file)
		if err != nil {
			return fmt.Errorf("Could not create %s: %s", file, err)
		}
		defer f.Close()
	} else if fi.IsDir() {
		return fmt.Errorf("%s must not be a directory", file)
	}

	return nil
}