Start api directory, which will become a module.

api/filesys/confirmeddir.go

@@ -0,0 +1,79 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package filesys
+
+import (
+	"io/ioutil"
+	"path/filepath"
+	"strings"
+)
+
+// ConfirmedDir is a clean, absolute, delinkified path
+// that was confirmed to point to an existing directory.
+type ConfirmedDir string
+
+// NewTmpConfirmedDir returns a temporary dir, else error.
+// The directory is cleaned, no symlinks, etc. so it's
+// returned as a ConfirmedDir.
+func NewTmpConfirmedDir() (ConfirmedDir, error) {
+	n, err := ioutil.TempDir("", "kustomize-")
+	if err != nil {
+		return "", err
+	}
+
+	// In MacOs `ioutil.TempDir` creates a directory
+	// with root in the `/var` folder, which is in turn
+	// a symlinked path to `/private/var`.
+	// Function `filepath.EvalSymlinks`is used to
+	// resolve the real absolute path.
+	deLinked, err := filepath.EvalSymlinks(n)
+	return ConfirmedDir(deLinked), err
+}
+
+// HasPrefix returns true if the directory argument
+// is a prefix of self (d) from the point of view of
+// a file system.
+//
+// I.e., it's true if the argument equals or contains
+// self (d) in a file path sense.
+//
+// HasPrefix emulates the semantics of strings.HasPrefix
+// such that the following are true:
+//
+//   strings.HasPrefix("foobar", "foobar")
+//   strings.HasPrefix("foobar", "foo")
+//   strings.HasPrefix("foobar", "")
+//
+//   d := fSys.ConfirmDir("/foo/bar")
+//   d.HasPrefix("/foo/bar")
+//   d.HasPrefix("/foo")
+//   d.HasPrefix("/")
+//
+// Not contacting a file system here to check for
+// actual path existence.
+//
+// This is tested on linux, but will have trouble
+// on other operating systems.
+// TODO(monopole) Refactor when #golang/go/18358 closes.
+// See also:
+//   https://github.com/golang/go/issues/18358
+//   https://github.com/golang/dep/issues/296
+//   https://github.com/golang/dep/blob/master/internal/fs/fs.go#L33
+//   https://codereview.appspot.com/5712045
+func (d ConfirmedDir) HasPrefix(path ConfirmedDir) bool {
+	if path.String() == string(filepath.Separator) || path == d {
+		return true
+	}
+	return strings.HasPrefix(
+		string(d),
+		string(path)+string(filepath.Separator))
+}
+
+func (d ConfirmedDir) Join(path string) string {
+	return filepath.Join(string(d), path)
+}
+
+func (d ConfirmedDir) String() string {
+	return string(d)
+}

api/filesys/confirmeddir_test.go

@@ -0,0 +1,109 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package filesys_test
+
+import (
+	"path/filepath"
+	"testing"
+
+	. "sigs.k8s.io/kustomize/v3/api/filesys"
+)
+
+func TestJoin(t *testing.T) {
+	fSys := MakeFsInMemory()
+	err := fSys.Mkdir("/foo")
+	if err != nil {
+		t.Fatalf("unexpected err: %v", err)
+	}
+	d, f, err := fSys.CleanedAbs("/foo")
+	if err != nil {
+		t.Fatalf("unexpected err: %v", err)
+	}
+	if f != "" {
+		t.Fatalf("unexpected file: %v", f)
+	}
+	if d.Join("bar") != "/foo/bar" {
+		t.Fatalf("expected join %s", d.Join("bar"))
+	}
+}
+
+func TestHasPrefix_Slash(t *testing.T) {
+	fSys := MakeFsInMemory()
+	d, f, err := fSys.CleanedAbs("/")
+	if err != nil {
+		t.Fatalf("unexpected err: %v", err)
+	}
+	if f != "" {
+		t.Fatalf("unexpected file: %v", f)
+	}
+	if d.HasPrefix("/hey") {
+		t.Fatalf("should be false")
+	}
+	if !d.HasPrefix("/") {
+		t.Fatalf("/ should have the prefix /")
+	}
+}
+
+func TestHasPrefix_SlashFoo(t *testing.T) {
+	fSys := MakeFsInMemory()
+	err := fSys.Mkdir("/foo")
+	if err != nil {
+		t.Fatalf("unexpected err: %v", err)
+	}
+	d, _, err := fSys.CleanedAbs("/foo")
+	if err != nil {
+		t.Fatalf("unexpected err: %v", err)
+	}
+	if d.HasPrefix("/fo") {
+		t.Fatalf("/foo does not have path prefix /fo")
+	}
+	if d.HasPrefix("/fod") {
+		t.Fatalf("/foo does not have path prefix /fod")
+	}
+	if !d.HasPrefix("/foo") {
+		t.Fatalf("/foo should have prefix /foo")
+	}
+}
+
+func TestHasPrefix_SlashFooBar(t *testing.T) {
+	fSys := MakeFsInMemory()
+	err := fSys.MkdirAll("/foo/bar")
+	if err != nil {
+		t.Fatalf("unexpected err: %v", err)
+	}
+	d, _, err := fSys.CleanedAbs("/foo/bar")
+	if err != nil {
+		t.Fatalf("unexpected err: %v", err)
+	}
+	if d.HasPrefix("/fo") {
+		t.Fatalf("/foo/bar does not have path prefix /fo")
+	}
+	if d.HasPrefix("/foobar") {
+		t.Fatalf("/foo/bar does not have path prefix /foobar")
+	}
+	if !d.HasPrefix("/foo/bar") {
+		t.Fatalf("/foo/bar should have prefix /foo/bar")
+	}
+	if !d.HasPrefix("/foo") {
+		t.Fatalf("/foo/bar should have prefix /foo")
+	}
+	if !d.HasPrefix("/") {
+		t.Fatalf("/foo/bar should have prefix /")
+	}
+}
+
+func TestNewTempConfirmDir(t *testing.T) {
+	tmp, err := NewTmpConfirmedDir()
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	delinked, err := filepath.EvalSymlinks(string(tmp))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if string(tmp) != delinked {
+		t.Fatalf("unexpected path containing symlinks")
+	}
+}

api/filesys/file.go

@@ -0,0 +1,41 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package filesys
+
+import (
+	"io"
+	"os"
+	"time"
+)
+
+var _ os.FileInfo = &fileInfo{}
+
+// fileInfo implements os.FileInfo for a fileInMemory instance.
+type fileInfo struct {
+	*fileInMemory
+}
+
+// Name returns the name of the file
+func (fi *fileInfo) Name() string { return fi.name }
+
+// Size returns the size of the file
+func (fi *fileInfo) Size() int64 { return int64(len(fi.content)) }
+
+// Mode returns the file mode
+func (fi *fileInfo) Mode() os.FileMode { return 0777 }
+
+// ModTime returns the modification time
+func (fi *fileInfo) ModTime() time.Time { return time.Time{} }
+
+// IsDir returns if it is a directory
+func (fi *fileInfo) IsDir() bool { return fi.dir }
+
+// Sys should return underlying data source, but it now returns nil
+func (fi *fileInfo) Sys() interface{} { return nil }
+
+// File groups the basic os.File methods.
+type File interface {
+	io.ReadWriteCloser
+	Stat() (os.FileInfo, error)
+}

api/filesys/fileinmemory.go

@@ -0,0 +1,56 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package filesys
+
+import (
+	"bytes"
+	"os"
+)
+
+var _ File = &fileInMemory{}
+
+// fileInMemory implements File in-memory for tests.
+type fileInMemory struct {
+	name    string
+	content []byte
+	dir     bool
+	open    bool
+}
+
+// makeDir makes a fake directory.
+func makeDir(name string) *fileInMemory {
+	return &fileInMemory{name: name, dir: true}
+}
+
+// Close marks the fake file closed.
+func (f *fileInMemory) Close() error {
+	f.open = false
+	return nil
+}
+
+// Read never fails, and doesn't mutate p.
+func (f *fileInMemory) Read(p []byte) (n int, err error) {
+	return len(p), nil
+}
+
+// Write saves the contents of the argument to memory.
+func (f *fileInMemory) Write(p []byte) (n int, err error) {
+	f.content = p
+	return len(p), nil
+}
+
+// ContentMatches returns true if v matches fake file's content.
+func (f *fileInMemory) ContentMatches(v []byte) bool {
+	return bytes.Equal(v, f.content)
+}
+
+// GetContent the content of a fake file.
+func (f *fileInMemory) GetContent() []byte {
+	return f.content
+}
+
+// Stat returns nil.
+func (f *fileInMemory) Stat() (os.FileInfo, error) {
+	return nil, nil
+}

api/filesys/fileondisk.go

@@ -0,0 +1,27 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package filesys
+
+import (
+	"os"
+)
+
+var _ File = &fileOnDisk{}
+
+// fileOnDisk implements File using the local filesystem.
+type fileOnDisk struct {
+	file *os.File
+}
+
+// Close closes a file.
+func (f *fileOnDisk) Close() error { return f.file.Close() }
+
+// Read reads a file's content.
+func (f *fileOnDisk) Read(p []byte) (n int, err error) { return f.file.Read(p) }
+
+// Write writes bytes to a file
+func (f *fileOnDisk) Write(p []byte) (n int, err error) { return f.file.Write(p) }
+
+// Stat returns an interface which has all the information regarding the file.
+func (f *fileOnDisk) Stat() (os.FileInfo, error) { return f.file.Stat() }

api/filesys/filesystem.go

@@ -0,0 +1,41 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+// Package filesys provides a file system abstraction layer.
+package filesys
+
+import (
+	"path/filepath"
+)
+
+// FileSystem groups basic os filesystem methods.
+type FileSystem interface {
+	// Create a file.
+	Create(name string) (File, error)
+	// MkDir makes a directory.
+	Mkdir(path string) error
+	// MkDir makes a directory path, creating intervening directories.
+	MkdirAll(path string) error
+	// RemoveAll removes path and any children it contains.
+	RemoveAll(path string) error
+	// Open opens the named file for reading.
+	Open(path string) (File, error)
+	// IsDir returns true if the path is a directory.
+	IsDir(path string) bool
+	// CleanedAbs converts the given path into a
+	// directory and a file name, where the directory
+	// is represented as a ConfirmedDir and all that implies.
+	// If the entire path is a directory, the file component
+	// is an empty string.
+	CleanedAbs(path string) (ConfirmedDir, string, error)
+	// Exists is true if the path exists in the file system.
+	Exists(path string) bool
+	// Glob returns the list of matching files
+	Glob(pattern string) ([]string, error)
+	// ReadFile returns the contents of the file at the given path.
+	ReadFile(path string) ([]byte, error)
+	// WriteFile writes the data to a file at the given path.
+	WriteFile(path string, data []byte) error
+	// Walk walks the file system with the given WalkFunc.
+	Walk(path string, walkFn filepath.WalkFunc) error
+}

api/filesys/fsinmemory.go

@@ -0,0 +1,223 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package filesys
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+)
+
+var _ FileSystem = &fsInMemory{}
+
+// fsInMemory implements FileSystem using a in-memory filesystem
+// primarily for use in tests.
+type fsInMemory struct {
+	m map[string]*fileInMemory
+}
+
+// MakeFsInMemory returns an instance of fsInMemory with no files in it.
+func MakeFsInMemory() FileSystem {
+	result := &fsInMemory{m: map[string]*fileInMemory{}}
+	result.Mkdir(separator)
+	return result
+}
+
+const (
+	separator = string(filepath.Separator)
+	doubleSep = separator + separator
+)
+
+// Create assures a fake file appears in the in-memory file system.
+func (fs *fsInMemory) Create(name string) (File, error) {
+	f := &fileInMemory{}
+	f.open = true
+	fs.m[name] = f
+	return fs.m[name], nil
+}
+
+// Mkdir assures a fake directory appears in the in-memory file system.
+func (fs *fsInMemory) Mkdir(name string) error {
+	fs.m[name] = makeDir(name)
+	return nil
+}
+
+// MkdirAll delegates to Mkdir
+func (fs *fsInMemory) MkdirAll(name string) error {
+	return fs.Mkdir(name)
+}
+
+// RemoveAll presumably does rm -r on a path.
+// There's no error.
+func (fs *fsInMemory) RemoveAll(name string) error {
+	var toRemove []string
+	for k := range fs.m {
+		if strings.HasPrefix(k, name) {
+			toRemove = append(toRemove, k)
+		}
+	}
+	for _, k := range toRemove {
+		delete(fs.m, k)
+	}
+	return nil
+}
+
+// Open returns a fake file in the open state.
+func (fs *fsInMemory) Open(name string) (File, error) {
+	if _, found := fs.m[name]; !found {
+		return nil, fmt.Errorf("file %q cannot be opened", name)
+	}
+	return fs.m[name], nil
+}
+
+// CleanedAbs cannot fail.
+func (fs *fsInMemory) CleanedAbs(path string) (ConfirmedDir, string, error) {
+	if fs.IsDir(path) {
+		return ConfirmedDir(path), "", nil
+	}
+	d := filepath.Dir(path)
+	if d == path {
+		return ConfirmedDir(d), "", nil
+	}
+	return ConfirmedDir(d), filepath.Base(path), nil
+}
+
+// Exists returns true if file is known.
+func (fs *fsInMemory) Exists(name string) bool {
+	_, found := fs.m[name]
+	return found
+}
+
+// Glob returns the list of matching files
+func (fs *fsInMemory) Glob(pattern string) ([]string, error) {
+	var result []string
+	for p := range fs.m {
+		if fs.pathMatch(p, pattern) {
+			result = append(result, p)
+		}
+	}
+	sort.Strings(result)
+	return result, nil
+}
+
+// IsDir returns true if the file exists and is a directory.
+func (fs *fsInMemory) IsDir(name string) bool {
+	f, found := fs.m[name]
+	if found && f.dir {
+		return true
+	}
+	if !strings.HasSuffix(name, separator) {
+		name = name + separator
+	}
+	for k := range fs.m {
+		if strings.HasPrefix(k, name) {
+			return true
+		}
+	}
+	return false
+}
+
+// ReadFile always returns an empty bytes and error depending on content of m.
+func (fs *fsInMemory) ReadFile(name string) ([]byte, error) {
+	if ff, found := fs.m[name]; found {
+		return ff.content, nil
+	}
+	return nil, fmt.Errorf("cannot read file %q", name)
+}
+
+// WriteFile always succeeds and does nothing.
+func (fs *fsInMemory) WriteFile(name string, c []byte) error {
+	ff := &fileInMemory{}
+	ff.Write(c)
+	fs.m[name] = ff
+	return nil
+}
+
+// Walk implements filepath.Walk using the fake filesystem.
+func (fs *fsInMemory) Walk(path string, walkFn filepath.WalkFunc) error {
+	info, err := fs.lstat(path)
+	if err != nil {
+		err = walkFn(path, info, err)
+	} else {
+		err = fs.walk(path, info, walkFn)
+	}
+	if err == filepath.SkipDir {
+		return nil
+	}
+	return err
+}
+
+func (fs *fsInMemory) pathMatch(path, pattern string) bool {
+	match, _ := filepath.Match(pattern, path)
+	return match
+}
+
+func (fs *fsInMemory) lstat(path string) (*fileInfo, error) {
+	f, found := fs.m[path]
+	if !found {
+		return nil, os.ErrNotExist
+	}
+	return &fileInfo{f}, nil
+}
+
+func (fs *fsInMemory) join(elem ...string) string {
+	for i, e := range elem {
+		if e != "" {
+			return strings.Replace(
+				strings.Join(elem[i:], separator), doubleSep, separator, -1)
+		}
+	}
+	return ""
+}
+
+func (fs *fsInMemory) readDirNames(path string) []string {
+	var names []string
+	if !strings.HasSuffix(path, separator) {
+		path += separator
+	}
+	pathSegments := strings.Count(path, separator)
+	for name := range fs.m {
+		if name == path {
+			continue
+		}
+		if strings.Count(name, separator) > pathSegments {
+			continue
+		}
+		if strings.HasPrefix(name, path) {
+			names = append(names, filepath.Base(name))
+		}
+	}
+	sort.Strings(names)
+	return names
+}
+
+func (fs *fsInMemory) walk(path string, info os.FileInfo, walkFn filepath.WalkFunc) error {
+	if !info.IsDir() {
+		return walkFn(path, info, nil)
+	}
+
+	names := fs.readDirNames(path)
+	if err := walkFn(path, info, nil); err != nil {
+		return err
+	}
+	for _, name := range names {
+		filename := fs.join(path, name)
+		fileInfo, err := fs.lstat(filename)
+		if err != nil {
+			if err := walkFn(filename, fileInfo, os.ErrNotExist); err != nil && err != filepath.SkipDir {
+				return err
+			}
+		} else {
+			err = fs.walk(filename, fileInfo, walkFn)
+			if err != nil {
+				if !fileInfo.IsDir() || err != filepath.SkipDir {
+					return err
+				}
+			}
+		}
+	}
+	return nil
+}

api/filesys/fsinmemory_test.go

@@ -0,0 +1,149 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package filesys_test
+
+import (
+	"bytes"
+	"reflect"
+	"testing"
+
+	. "sigs.k8s.io/kustomize/v3/api/filesys"
+)
+
+func TestExists(t *testing.T) {
+	fSys := MakeFsInMemory()
+	if fSys.Exists("foo") {
+		t.Fatalf("expected no foo")
+	}
+	fSys.Mkdir("/")
+	if !fSys.IsDir("/") {
+		t.Fatalf("expected dir at /")
+	}
+}
+
+func TestIsDir(t *testing.T) {
+	fSys := MakeFsInMemory()
+	expectedName := "my-dir"
+	err := fSys.Mkdir(expectedName)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	shouldExist(t, fSys, expectedName)
+	if !fSys.IsDir(expectedName) {
+		t.Fatalf(expectedName + " should be a dir")
+	}
+}
+
+func shouldExist(t *testing.T, fSys FileSystem, name string) {
+	if !fSys.Exists(name) {
+		t.Fatalf(name + " should exist")
+	}
+}
+
+func shouldNotExist(t *testing.T, fSys FileSystem, name string) {
+	if fSys.Exists(name) {
+		t.Fatalf(name + " should not exist")
+	}
+}
+
+func TestRemoveAll(t *testing.T) {
+	fSys := MakeFsInMemory()
+	fSys.WriteFile("/foo/project/file.yaml", []byte("Unused"))
+	fSys.WriteFile("/foo/project/subdir/file.yaml", []byte("Unused"))
+	fSys.WriteFile("/foo/apple/subdir/file.yaml", []byte("Unused"))
+	shouldExist(t, fSys, "/foo/project/file.yaml")
+	shouldExist(t, fSys, "/foo/project/subdir/file.yaml")
+	shouldExist(t, fSys, "/foo/apple/subdir/file.yaml")
+	err := fSys.RemoveAll("/foo/project")
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	shouldNotExist(t, fSys, "/foo/project/file.yaml")
+	shouldNotExist(t, fSys, "/foo/project/subdir/file.yaml")
+	shouldExist(t, fSys, "/foo/apple/subdir/file.yaml")
+}
+
+func TestIsDirDeeper(t *testing.T) {
+	fSys := MakeFsInMemory()
+	fSys.WriteFile("/foo/project/file.yaml", []byte("Unused"))
+	fSys.WriteFile("/foo/project/subdir/file.yaml", []byte("Unused"))
+	if !fSys.IsDir("/") {
+		t.Fatalf("/ should be a dir")
+	}
+	if !fSys.IsDir("/foo") {
+		t.Fatalf("/foo should be a dir")
+	}
+	if !fSys.IsDir("/foo/project") {
+		t.Fatalf("/foo/project should be a dir")
+	}
+	if fSys.IsDir("/fo") {
+		t.Fatalf("/fo should not be a dir")
+	}
+	if fSys.IsDir("/x") {
+		t.Fatalf("/x should not be a dir")
+	}
+}
+
+func TestCreate(t *testing.T) {
+	fSys := MakeFsInMemory()
+	f, err := fSys.Create("foo")
+	if f == nil {
+		t.Fatalf("expected file")
+	}
+	if err != nil {
+		t.Fatalf("unexpected error")
+	}
+	shouldExist(t, fSys, "foo")
+}
+
+func TestReadFile(t *testing.T) {
+	fSys := MakeFsInMemory()
+	f, err := fSys.Create("foo")
+	if f == nil {
+		t.Fatalf("expected file")
+	}
+	if err != nil {
+		t.Fatalf("unexpected error")
+	}
+	content, err := fSys.ReadFile("foo")
+	if len(content) != 0 {
+		t.Fatalf("expected no content")
+	}
+	if err != nil {
+		t.Fatalf("expected no error")
+	}
+}
+
+func TestWriteFile(t *testing.T) {
+	fSys := MakeFsInMemory()
+	c := []byte("heybuddy")
+	err := fSys.WriteFile("foo", c)
+	if err != nil {
+		t.Fatalf("expected no error")
+	}
+	content, err := fSys.ReadFile("foo")
+	if err != nil {
+		t.Fatalf("expected read to work: %v", err)
+	}
+	if bytes.Compare(c, content) != 0 {
+		t.Fatalf("incorrect content: %v", content)
+	}
+}
+
+func TestGlob(t *testing.T) {
+	fSys := MakeFsInMemory()
+	fSys.Create("dir/foo")
+	fSys.Create("dir/bar")
+	files, err := fSys.Glob("dir/*")
+	if err != nil {
+		t.Fatalf("expected no error")
+	}
+	expected := []string{
+		"dir/bar",
+		"dir/foo",
+	}
+	if !reflect.DeepEqual(files, expected) {
+		t.Fatalf("incorrect files found by glob: %v", files)
+	}
+}

api/filesys/fsondisk.go

@@ -0,0 +1,114 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package filesys
+
+import (
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+	"path/filepath"
+)
+
+var _ FileSystem = fsOnDisk{}
+
+// fsOnDisk implements FileSystem using the local filesystem.
+type fsOnDisk struct{}
+
+// MakeFsOnDisk makes an instance of fsOnDisk.
+func MakeFsOnDisk() FileSystem {
+	return fsOnDisk{}
+}
+
+// Create delegates to os.Create.
+func (fsOnDisk) Create(name string) (File, error) { return os.Create(name) }
+
+// Mkdir delegates to os.Mkdir.
+func (fsOnDisk) Mkdir(name string) error {
+	return os.Mkdir(name, 0777|os.ModeDir)
+}
+
+// MkdirAll delegates to os.MkdirAll.
+func (fsOnDisk) MkdirAll(name string) error {
+	return os.MkdirAll(name, 0777|os.ModeDir)
+}
+
+// RemoveAll delegates to os.RemoveAll.
+func (fsOnDisk) RemoveAll(name string) error {
+	return os.RemoveAll(name)
+}
+
+// Open delegates to os.Open.
+func (fsOnDisk) Open(name string) (File, error) { return os.Open(name) }
+
+// CleanedAbs converts the given path into a
+// directory and a file name, where the directory
+// is represented as a ConfirmedDir and all that implies.
+// If the entire path is a directory, the file component
+// is an empty string.
+func (x fsOnDisk) CleanedAbs(
+	path string) (ConfirmedDir, string, error) {
+	absRoot, err := filepath.Abs(path)
+	if err != nil {
+		return "", "", fmt.Errorf(
+			"abs path error on '%s' : %v", path, err)
+	}
+	deLinked, err := filepath.EvalSymlinks(absRoot)
+	if err != nil {
+		return "", "", fmt.Errorf(
+			"evalsymlink failure on '%s' : %v", path, err)
+	}
+	if x.IsDir(deLinked) {
+		return ConfirmedDir(deLinked), "", nil
+	}
+	d := filepath.Dir(deLinked)
+	if !x.IsDir(d) {
+		// Programmer/assumption error.
+		log.Fatalf("first part of '%s' not a directory", deLinked)
+	}
+	if d == deLinked {
+		// Programmer/assumption error.
+		log.Fatalf("d '%s' should be a subset of deLinked", d)
+	}
+	f := filepath.Base(deLinked)
+	if filepath.Join(d, f) != deLinked {
+		// Programmer/assumption error.
+		log.Fatalf("these should be equal: '%s', '%s'",
+			filepath.Join(d, f), deLinked)
+	}
+	return ConfirmedDir(d), f, nil
+}
+
+// Exists returns true if os.Stat succeeds.
+func (fsOnDisk) Exists(name string) bool {
+	_, err := os.Stat(name)
+	return err == nil
+}
+
+// Glob returns the list of matching files
+func (fsOnDisk) Glob(pattern string) ([]string, error) {
+	return filepath.Glob(pattern)
+}
+
+// IsDir delegates to os.Stat and FileInfo.IsDir
+func (fsOnDisk) IsDir(name string) bool {
+	info, err := os.Stat(name)
+	if err != nil {
+		return false
+	}
+	return info.IsDir()
+}
+
+// ReadFile delegates to ioutil.ReadFile.
+func (fsOnDisk) ReadFile(name string) ([]byte, error) { return ioutil.ReadFile(name) }
+
+// WriteFile delegates to ioutil.WriteFile with read/write permissions.
+func (fsOnDisk) WriteFile(name string, c []byte) error {
+	return ioutil.WriteFile(name, c, 0666)
+}
+
+// Walk delegates to filepath.Walk.
+func (fsOnDisk) Walk(path string, walkFn filepath.WalkFunc) error {
+	return filepath.Walk(path, walkFn)
+}

api/filesys/fsondisk_test.go

@@ -0,0 +1,165 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package filesys_test
+
+import (
+	"io/ioutil"
+	"os"
+	"path"
+	"path/filepath"
+	"reflect"
+	"testing"
+
+	. "sigs.k8s.io/kustomize/v3/api/filesys"
+)
+
+func makeTestDir(t *testing.T) (FileSystem, string) {
+	fSys := MakeFsOnDisk()
+	td, err := ioutil.TempDir("", "kustomize_testing_dir")
+	if err != nil {
+		t.Fatalf("unexpected error %s", err)
+	}
+	testDir, err := filepath.EvalSymlinks(td)
+	if err != nil {
+		t.Fatalf("unexpected error %s", err)
+	}
+	if !fSys.Exists(testDir) {
+		t.Fatalf("expected existence")
+	}
+	if !fSys.IsDir(testDir) {
+		t.Fatalf("expected directory")
+	}
+	return fSys, testDir
+}
+
+func TestCleanedAbs_1(t *testing.T) {
+	fSys, testDir := makeTestDir(t)
+	defer os.RemoveAll(testDir)
+
+	d, f, err := fSys.CleanedAbs("")
+	if err != nil {
+		t.Fatalf("unexpected err=%v", err)
+	}
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("unexpected err=%v", err)
+	}
+	if d.String() != wd {
+		t.Fatalf("unexpected d=%s", d)
+	}
+	if f != "" {
+		t.Fatalf("unexpected f=%s", f)
+	}
+}
+
+func TestCleanedAbs_2(t *testing.T) {
+	fSys, testDir := makeTestDir(t)
+	defer os.RemoveAll(testDir)
+
+	d, f, err := fSys.CleanedAbs("/")
+	if err != nil {
+		t.Fatalf("unexpected err=%v", err)
+	}
+	if d != "/" {
+		t.Fatalf("unexpected d=%s", d)
+	}
+	if f != "" {
+		t.Fatalf("unexpected f=%s", f)
+	}
+}
+
+func TestCleanedAbs_3(t *testing.T) {
+	fSys, testDir := makeTestDir(t)
+	defer os.RemoveAll(testDir)
+
+	err := fSys.WriteFile(
+		filepath.Join(testDir, "foo"), []byte(`foo`))
+	if err != nil {
+		t.Fatalf("unexpected err=%v", err)
+	}
+
+	d, f, err := fSys.CleanedAbs(filepath.Join(testDir, "foo"))
+	if err != nil {
+		t.Fatalf("unexpected err=%v", err)
+	}
+	if d.String() != testDir {
+		t.Fatalf("unexpected d=%s", d)
+	}
+	if f != "foo" {
+		t.Fatalf("unexpected f=%s", f)
+	}
+}
+
+func TestCleanedAbs_4(t *testing.T) {
+	fSys, testDir := makeTestDir(t)
+	defer os.RemoveAll(testDir)
+
+	err := fSys.MkdirAll(filepath.Join(testDir, "d1", "d2"))
+	if err != nil {
+		t.Fatalf("unexpected err=%v", err)
+	}
+	err = fSys.WriteFile(
+		filepath.Join(testDir, "d1", "d2", "bar"),
+		[]byte(`bar`))
+	if err != nil {
+		t.Fatalf("unexpected err=%v", err)
+	}
+
+	d, f, err := fSys.CleanedAbs(
+		filepath.Join(testDir, "d1", "d2"))
+	if err != nil {
+		t.Fatalf("unexpected err=%v", err)
+	}
+	if d.String() != filepath.Join(testDir, "d1", "d2") {
+		t.Fatalf("unexpected d=%s", d)
+	}
+	if f != "" {
+		t.Fatalf("unexpected f=%s", f)
+	}
+
+	d, f, err = fSys.CleanedAbs(
+		filepath.Join(testDir, "d1", "d2", "bar"))
+	if err != nil {
+		t.Fatalf("unexpected err=%v", err)
+	}
+	if d.String() != filepath.Join(testDir, "d1", "d2") {
+		t.Fatalf("unexpected d=%s", d)
+	}
+	if f != "bar" {
+		t.Fatalf("unexpected f=%s", f)
+	}
+}
+
+func TestReadFilesRealFS(t *testing.T) {
+	fSys, testDir := makeTestDir(t)
+	defer os.RemoveAll(testDir)
+
+	err := fSys.WriteFile(path.Join(testDir, "foo"), []byte(`foo`))
+	if err != nil {
+		t.Fatalf("unexpected error %s", err)
+	}
+	if !fSys.Exists(path.Join(testDir, "foo")) {
+		t.Fatalf("expected foo")
+	}
+	if fSys.IsDir(path.Join(testDir, "foo")) {
+		t.Fatalf("expected foo not to be a directory")
+	}
+
+	err = fSys.WriteFile(path.Join(testDir, "bar"), []byte(`bar`))
+	if err != nil {
+		t.Fatalf("unexpected error %s", err)
+	}
+
+	files, err := fSys.Glob(path.Join("testDir", "*"))
+	expected := []string{
+		path.Join(testDir, "bar"),
+		path.Join(testDir, "foo"),
+	}
+	if err != nil {
+		t.Fatalf("expected no error")
+	}
+	if reflect.DeepEqual(files, expected) {
+		t.Fatalf("incorrect files found by glob: %v", files)
+	}
+}

api/filesys/rpath.go

@@ -0,0 +1,12 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package filesys
+
+import "path/filepath"
+
+// RootedPath returns a rooted path, e.g. "/foo/bar" as
+// opposed to "foo/bar".
+func RootedPath(elem ...string) string {
+	return separator + filepath.Join(elem...)
+}