feat: unified osutil.Mkdir API with options

Implement a unified osutil.Mkdir API, refactor existing osutil.MkdirChown and osutil.MkdirAllChown.

Closes #372.

Background

There is an issue (372) where umask settings would affect the permissions of the newly created directories.

There was originally a PR to implement the feature (see here), but the code became even more complicated. As per our discussion (see here), we decide to refactor Mkdir and implement the required feature.

The original PR was closed, using this one instead. This PR only refactors the existing code, the support for chmod will come in a separate PR.

Spec

See here.

API

func Mkdir(path string, perm os.FileMode, options *MkdirOptions) error { ... }

Options

type MkdirOptions struct {
    // If false (default), a missing parent raises an error.
    // If true, any missing parents of this path are created as needed.
    MakeParents bool

    // If false (default), an error is raised if the target directory already exists. In case MakeParents is true but ExistOK is false, an error won't be raised if the parent directory already exists but the target directory doesn't.
    // If true, an error won't be raised unless the given path already exists in the file system and isn't a directory (same behaviour as the POSIX mkdir -p command).
    ExistOK bool

    // If false (default), no explicit chmod is performed. In this case, the permission of the created directories will be affected by umask settings.
    // If true, perform an explicit chmod on any directories created.
    Chmod bool

    // If false (default), no explicit chmod is performed. In this case, the permission of the created directories will be affected by umask settings.
    // If true, perform an explicit chmod on any directories created.
    Chown bool // NOTE: additional bool is needed because 0 is a valid value for UserID and GroupID (root)

    UserID sys.UserID

    GroupID sys.GroupID
}

Manual Tests

Tests	Before	After
mkdir ~/normal	755, same user/group as pebble, exist not ok	same behaviour
mkdir -p ~/nested/folder; mkdir -p ~/nested1	755, parent/child both the same user/group as pebble, exist ok	same behaviour
mkdir ~/normal-chown --user test --group test	755, user/group changed exist not ok, error: rename /root/normal-chown.mkdir-new /root/normal-chown: file exists	same behaviour, better error msg: error: mkdir /root/normal-chown: file exists
mkdir -p ~/nested1/folder-chown --user test --group test	755, parent/child user/group both changed, exist OK	same behaviour

canonical / pebble