Copy a folder in go

Question

Is there an easy way to copy a directory in go? I have the following function:

err = CopyDir("sourceFolder","destinationFolder")

Nothing so far has worked, including libraries such as github.com/cf-guardian/guardian/kernel/fileutils

One important thing to note is that I need to preserve directory structure, including the sourceFolder itself, not simply copy all contents of the folder.

Answer 1

I believe that docker implementation can be considered as complete solution for handling edge cases: https://github.com/moby/moby/blob/master/daemon/graphdriver/copy/copy.go

There are following good things:

• unsupported file type rise error
• preserving permissions and ownership
• preserving extended attributes
• preserving timestamp

but because of a lot of imports your tiny application becomes huge.

I've tried to combine several solutions but use stdlib and for Linux only:

func CopyDirectory(scrDir, dest string) error {
    entries, err := os.ReadDir(scrDir)
    if err != nil {
        return err
    }
    for _, entry := range entries {
        sourcePath := filepath.Join(scrDir, entry.Name())
        destPath := filepath.Join(dest, entry.Name())

        fileInfo, err := os.Stat(sourcePath)
        if err != nil {
            return err
        }

        stat, ok := fileInfo.Sys().(*syscall.Stat_t)
        if !ok {
            return fmt.Errorf("failed to get raw syscall.Stat_t data for '%s'", sourcePath)
        }

        switch fileInfo.Mode() & os.ModeType{
        case os.ModeDir:
            if err := CreateIfNotExists(destPath, 0755); err != nil {
                return err
            }
            if err := CopyDirectory(sourcePath, destPath); err != nil {
                return err
            }
        case os.ModeSymlink:
            if err := CopySymLink(sourcePath, destPath); err != nil {
                return err
            }
        default:
            if err := Copy(sourcePath, destPath); err != nil {
                return err
            }
        }

        if err := os.Lchown(destPath, int(stat.Uid), int(stat.Gid)); err != nil {
            return err
        }

        fInfo, err := entry.Info()
        if err != nil {
            return err
        }

        isSymlink := fInfo.Mode()&os.ModeSymlink != 0
        if !isSymlink {
            if err := os.Chmod(destPath, fInfo.Mode()); err != nil {
                return err
            }
        }
    }
    return nil
}

func Copy(srcFile, dstFile string) error {
    out, err := os.Create(dstFile)
    if err != nil {
        return err
    }

    defer out.Close()

    in, err := os.Open(srcFile)
    if err != nil {
        return err
    }

    defer in.Close()

    _, err = io.Copy(out, in)
    if err != nil {
        return err
    }

    return nil
}

func Exists(filePath string) bool {
    if _, err := os.Stat(filePath); os.IsNotExist(err) {
        return false
    }

    return true
}

func CreateIfNotExists(dir string, perm os.FileMode) error {
    if Exists(dir) {
        return nil
    }

    if err := os.MkdirAll(dir, perm); err != nil {
        return fmt.Errorf("failed to create directory: '%s', error: '%s'", dir, err.Error())
    }

    return nil
}

func CopySymLink(source, dest string) error {
    link, err := os.Readlink(source)
    if err != nil {
        return err
    }
    return os.Symlink(link, dest)
}