mgmt/engine/resources/file.go

// Mgmt
// Copyright (C) 2013-2019+ James Shubin and the project contributors
// Written by James Shubin <james@shubin.ca> and the project contributors
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package resources

import (
	"bytes"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path"
	"path/filepath"
	"strconv"
	"strings"
	"syscall"

	"github.com/purpleidea/mgmt/engine"
	"github.com/purpleidea/mgmt/engine/traits"
	engineUtil "github.com/purpleidea/mgmt/engine/util"
	"github.com/purpleidea/mgmt/recwatch"
	"github.com/purpleidea/mgmt/util"
	"github.com/purpleidea/mgmt/util/errwrap"
)

func init() {
	engine.RegisterResource("file", func() engine.Res { return &FileRes{} })
}

const (
	// FileStateExists is the string that represents that the file should be
	// present.
	FileStateExists = "exists"
	// FileStateAbsent is the string that represents that the file should
	// not exist.
	FileStateAbsent = "absent"
	// FileStateUndefined means the file state has not been specified.
	// TODO: consider moving to *string and express this state as a nil.
	FileStateUndefined = ""
)

// FileRes is a file and directory resource. Dirs are defined by names ending
// in a slash.
type FileRes struct {
	traits.Base // add the base methods without re-implementation
	traits.Edgeable
	//traits.Groupable // TODO: implement this
	traits.Recvable

	init *engine.Init

	// Path, which defaults to the name if not specified, represents the
	// destination path for the file or directory being managed. It must be
	// an absolute path, and as a result must start with a slash.
	Path     string `lang:"path" yaml:"path"`
	Dirname  string `lang:"dirname" yaml:"dirname"`   // override the path dirname
	Basename string `lang:"basename" yaml:"basename"` // override the path basename

	// Content specifies the file contents to use. If this is nil, they are
	// left undefined. It cannot be combined with Source.
	Content *string `lang:"content" yaml:"content"`
	// Source specifies the source contents for the file resource. It cannot
	// be combined with the Content parameter.
	Source string `lang:"source" yaml:"source"`
	// State specifies the desired state of the file. It can be either
	// `exists` or `absent`. If you do not specify this, it will be
	// undefined, and determined based on the other parameters.
	State string `lang:"state" yaml:"state"`

	Owner   string `lang:"owner" yaml:"owner"`
	Group   string `lang:"group" yaml:"group"`
	Mode    string `lang:"mode" yaml:"mode"`
	Recurse bool   `lang:"recurse" yaml:"recurse"`
	Force   bool   `lang:"force" yaml:"force"`

	sha256sum  string
	recWatcher *recwatch.RecWatcher
}

// Default returns some sensible defaults for this resource.
func (obj *FileRes) Default() engine.Res {
	return &FileRes{
		//State: FileStateUndefined, // the default must be undefined!
	}
}

// Validate reports any problems with the struct definition.
func (obj *FileRes) Validate() error {
	if obj.getPath() == "" {
		return fmt.Errorf("path is empty")
	}

	if obj.Dirname != "" && !strings.HasSuffix(obj.Dirname, "/") {
		return fmt.Errorf("dirname must end with a slash")
	}

	if strings.HasPrefix(obj.Basename, "/") {
		return fmt.Errorf("basename must not start with a slash")
	}

	if !strings.HasPrefix(obj.getPath(), "/") {
		return fmt.Errorf("resultant path must be absolute")
	}

	if obj.Content != nil && obj.Source != "" {
		return fmt.Errorf("can't specify both Content and Source")
	}

	if obj.isDir() && obj.Content != nil { // makes no sense
		return fmt.Errorf("can't specify Content when creating a Dir")
	}

	if obj.State != FileStateExists && obj.State != FileStateAbsent && obj.State != FileStateUndefined {
		return fmt.Errorf("the State is invalid")
	}

	if obj.State == FileStateAbsent && obj.Content != nil {
		return fmt.Errorf("can't specify content for an absent file")
	}

	if obj.Mode != "" {
		if _, err := obj.mode(); err != nil {
			return err
		}
	}

	if obj.Owner != "" || obj.Group != "" {
		fileInfo, err := os.Stat("/") // pick root just to do this test
		if err != nil {
			return fmt.Errorf("can't stat root to get system information")
		}
		_, ok := fileInfo.Sys().(*syscall.Stat_t)
		if !ok {
			return fmt.Errorf("can't set Owner or Group on this platform")
		}
	}
	if _, err := engineUtil.GetUID(obj.Owner); obj.Owner != "" && err != nil {
		return err
	}

	if _, err := engineUtil.GetGID(obj.Group); obj.Group != "" && err != nil {
		return err
	}

	// XXX: should this specify that we create an empty directory instead?
	//if obj.Source == "" && obj.isDir() {
	//	return fmt.Errorf("can't specify an empty source when creating a Dir.")
	//}

	return nil
}

// mode returns the file permission specified on the graph. It doesn't handle
// the case where the mode is not specified. The caller should check obj.Mode is
// not empty.
func (obj *FileRes) mode() (os.FileMode, error) {
	m, err := strconv.ParseInt(obj.Mode, 8, 32)
	if err != nil {
		return os.FileMode(0), errwrap.Wrapf(err, "mode should be an octal number (%s)", obj.Mode)
	}
	return os.FileMode(m), nil
}

// Init runs some startup code for this resource.
func (obj *FileRes) Init(init *engine.Init) error {
	obj.init = init // save for later

	obj.sha256sum = ""

	return nil
}

// Close is run by the engine to clean up after the resource is done.
func (obj *FileRes) Close() error {
	return nil
}

// getPath returns the actual path to use for this resource. It computes this
// after analysis of the Path, Dirname and Basename values. Dirs end with slash.
// TODO: memoize the result if this seems important.
func (obj *FileRes) getPath() string {
	p := obj.Path
	if obj.Path == "" { // use the name as the path default if missing
		p = obj.Name()
	}

	d := util.Dirname(p)
	b := util.Basename(p)
	if obj.Dirname == "" && obj.Basename == "" {
		return p
	}
	if obj.Dirname == "" {
		return d + obj.Basename
	}
	if obj.Basename == "" {
		return obj.Dirname + b
	}
	// if obj.dirname != "" && obj.basename != ""
	return obj.Dirname + obj.Basename
}

// isDir is a helper function to specify whether the path should be a dir.
func (obj *FileRes) isDir() bool {
	return strings.HasSuffix(obj.getPath(), "/") // dirs have trailing slashes
}

// Watch is the primary listener for this resource and it outputs events.
// This one is a file watcher for files and directories.
// Modify with caution, it is probably important to write some test cases first!
// If the Watch returns an error, it means that something has gone wrong, and it
// must be restarted. On a clean exit it returns nil.
// FIXME: Also watch the source directory when using obj.Source !!!
func (obj *FileRes) Watch() error {
	var err error
	obj.recWatcher, err = recwatch.NewRecWatcher(obj.getPath(), obj.Recurse)
	if err != nil {
		return err
	}
	defer obj.recWatcher.Close()

	obj.init.Running() // when started, notify engine that we're running

	var send = false // send event?
	for {
		if obj.init.Debug {
			obj.init.Logf("watching: %s", obj.getPath()) // attempting to watch...
		}

		select {
		case event, ok := <-obj.recWatcher.Events():
			if !ok { // channel shutdown
				return nil
			}
			if err := event.Error; err != nil {
				return errwrap.Wrapf(err, "unknown %s watcher error", obj)
			}
			if obj.init.Debug { // don't access event.Body if event.Error isn't nil
				obj.init.Logf("event(%s): %v", event.Body.Name, event.Body.Op)
			}
			send = true

		case <-obj.init.Done: // closed by the engine to signal shutdown
			return nil
		}

		// do all our event sending all together to avoid duplicate msgs
		if send {
			send = false
			obj.init.Event() // notify engine of an event (this can block)
		}
	}
}

// fileCheckApply is the CheckApply operation for a source and destination file.
// It can accept an io.Reader as the source, which can be a regular file, or it
// can be a bytes Buffer struct. It can take an input sha256 hash to use instead
// of computing the source data hash, and it returns the computed value if this
// function reaches that stage. As usual, it respects the apply action variable,
// and it symmetry with the main CheckApply function returns checkOK and error.
func (obj *FileRes) fileCheckApply(apply bool, src io.ReadSeeker, dst string, sha256sum string) (string, bool, error) {
	// TODO: does it make sense to switch dst to an io.Writer ?
	// TODO: use obj.Force when dealing with symlinks and other file types!
	if obj.init.Debug {
		obj.init.Logf("fileCheckApply: %v -> %s", src, dst)
	}

	srcFile, isFile := src.(*os.File)
	_, isBytes := src.(*bytes.Reader) // supports seeking!
	if !isFile && !isBytes {
		return "", false, fmt.Errorf("can't open src as either file or buffer")
	}

	var srcStat os.FileInfo
	if isFile {
		var err error
		srcStat, err = srcFile.Stat()
		if err != nil {
			return "", false, err
		}
		// TODO: deal with symlinks
		if !srcStat.Mode().IsRegular() { // can't copy non-regular files or dirs
			return "", false, fmt.Errorf("non-regular src file: %s (%q)", srcStat.Name(), srcStat.Mode())
		}
	}

	dstFile, err := os.Open(dst)
	if err != nil && !os.IsNotExist(err) { // ignore ErrNotExist errors
		return "", false, err
	}
	dstClose := func() error {
		return dstFile.Close() // calling this twice is safe :)
	}
	defer dstClose()
	dstExists := !os.IsNotExist(err)

	dstStat, err := dstFile.Stat()
	if err != nil && dstExists {
		return "", false, err
	}

	if dstExists && dstStat.IsDir() { // oops, dst is a dir, and we want a file...
		if !apply {
			return "", false, nil
		}
		if !obj.Force {
			return "", false, fmt.Errorf("can't force dir into file: %s", dst)
		}

		cleanDst := path.Clean(dst)
		if cleanDst == "" || cleanDst == "/" {
			return "", false, fmt.Errorf("don't want to remove root") // safety
		}
		// FIXME: respect obj.Recurse here...
		// there is a dir here, where we want a file...
		obj.init.Logf("fileCheckApply: removing (force): %s", cleanDst)
		if err := os.RemoveAll(cleanDst); err != nil { // dangerous ;)
			return "", false, err
		}
		dstExists = false // now it's gone!

	} else if err == nil {
		if !dstStat.Mode().IsRegular() {
			return "", false, fmt.Errorf("non-regular dst file: %s (%q)", dstStat.Name(), dstStat.Mode())
		}
		if isFile && os.SameFile(srcStat, dstStat) { // same inode, we're done!
			return "", true, nil
		}
	}

	if dstExists { // if dst doesn't exist, no need to compare hashes
		// hash comparison (efficient because we can cache hash of content str)
		if sha256sum == "" { // cache is invalid
			hash := sha256.New()
			// TODO: file existence test?
			if _, err := io.Copy(hash, src); err != nil {
				return "", false, err
			}
			sha256sum = hex.EncodeToString(hash.Sum(nil))
			// since we re-use this src handler below, it is
			// *critical* to seek to 0, or we'll copy nothing!
			if n, err := src.Seek(0, 0); err != nil || n != 0 {
				return sha256sum, false, err
			}
		}

		// dst hash
		hash := sha256.New()
		if _, err := io.Copy(hash, dstFile); err != nil {
			return "", false, err
		}
		if h := hex.EncodeToString(hash.Sum(nil)); h == sha256sum {
			return sha256sum, true, nil // same!
		}
	}

	// state is not okay, no work done, exit, but without error
	if !apply {
		return sha256sum, false, nil
	}
	if obj.init.Debug {
		obj.init.Logf("fileCheckApply: apply: %v -> %s", src, dst)
	}

	dstClose() // unlock file usage so we can write to it
	dstFile, err = os.Create(dst)
	if err != nil {
		return sha256sum, false, err
	}
	defer dstFile.Close() // TODO: is this redundant because of the earlier defered Close() ?

	if isFile { // set mode because it's a new file
		if err := dstFile.Chmod(srcStat.Mode()); err != nil {
			return sha256sum, false, err
		}
	}

	// TODO: attempt to reflink with Splice() and int(file.Fd()) as input...
	// syscall.Splice(rfd int, roff *int64, wfd int, woff *int64, len int, flags int) (n int64, err error)

	// TODO: should we offer a way to cancel the copy on ^C ?
	if obj.init.Debug {
		obj.init.Logf("fileCheckApply: copy: %v -> %s", src, dst)
	}
	if n, err := io.Copy(dstFile, src); err != nil {
		return sha256sum, false, err
	} else if obj.init.Debug {
		obj.init.Logf("fileCheckApply: copied: %v", n)
	}
	return sha256sum, false, dstFile.Sync()
}

// dirCheckApply is the CheckApply operation for an empty directory.
func (obj *FileRes) dirCheckApply(apply bool) (bool, error) {
	// check if the path exists and is a directory
	fileInfo, err := os.Stat(obj.getPath())
	if err != nil && !os.IsNotExist(err) {
		return false, errwrap.Wrapf(err, "error checking file resource existence")
	}

	if err == nil && fileInfo.IsDir() {
		return true, nil // already a directory, nothing to do
	}
	if err == nil && !fileInfo.IsDir() && !obj.Force {
		return false, fmt.Errorf("can't force file into dir: %s", obj.getPath())
	}

	if !apply {
		return false, nil
	}

	// the path exists and is not a directory
	// delete the file if force is given
	if err == nil && !fileInfo.IsDir() {
		obj.init.Logf("dirCheckApply: removing (force): %s", obj.getPath())
		if err := os.Remove(obj.getPath()); err != nil {
			return false, err
		}
	}

	// create the empty directory
	var mode os.FileMode
	if obj.Mode != "" {
		mode, err = obj.mode()
		if err != nil {
			return false, err
		}
	} else {
		mode = os.ModePerm
	}

	if obj.Force {
		// FIXME: respect obj.Recurse here...
		// TODO: add recurse limit here
		return false, os.MkdirAll(obj.getPath(), mode)
	}

	return false, os.Mkdir(obj.getPath(), mode)
}

// syncCheckApply is the CheckApply operation for a source and destination dir.
// It is recursive and can create directories directly, and files via the usual
// fileCheckApply method. It returns checkOK and error as is normally expected.
func (obj *FileRes) syncCheckApply(apply bool, src, dst string) (bool, error) {
	if obj.init.Debug {
		obj.init.Logf("syncCheckApply: %s -> %s", src, dst)
	}
	if src == "" || dst == "" {
		return false, fmt.Errorf("the src and dst must not be empty")
	}

	checkOK := true
	// TODO: handle ./ cases or ../ cases that need cleaning ?

	srcIsDir := strings.HasSuffix(src, "/")
	dstIsDir := strings.HasSuffix(dst, "/")

	if srcIsDir != dstIsDir {
		return false, fmt.Errorf("the src and dst must be both either files or directories")
	}

	if !srcIsDir && !dstIsDir {
		if obj.init.Debug {
			obj.init.Logf("syncCheckApply: %s -> %s", src, dst)
		}
		fin, err := os.Open(src)
		if err != nil {
			if obj.init.Debug && os.IsNotExist(err) { // if we get passed an empty src
				obj.init.Logf("syncCheckApply: missing src: %s", src)
			}
			return false, err
		}

		_, checkOK, err := obj.fileCheckApply(apply, fin, dst, "")
		if err != nil {
			fin.Close()
			return false, err
		}
		return checkOK, fin.Close()
	}

	// else: if srcIsDir && dstIsDir
	srcFiles, err := ReadDir(src)          // if src does not exist...
	if err != nil && !os.IsNotExist(err) { // an empty map comes out below!
		return false, err
	}
	dstFiles, err := ReadDir(dst)
	if err != nil && !os.IsNotExist(err) {
		return false, err
	}
	//obj.init.Logf("syncCheckApply: srcFiles: %v", srcFiles)
	//obj.init.Logf("syncCheckApply: dstFiles: %v", dstFiles)
	smartSrc := mapPaths(srcFiles)
	smartDst := mapPaths(dstFiles)

	for relPath, fileInfo := range smartSrc {
		absSrc := fileInfo.AbsPath // absolute path
		absDst := dst + relPath    // absolute dest

		if _, exists := smartDst[relPath]; !exists {
			if fileInfo.IsDir() {
				if !apply { // only checking and not identical!
					return false, nil
				}

				// file exists, but we want a dir: we need force
				// we check for the file w/o the smart dir slash
				relPathFile := strings.TrimSuffix(relPath, "/")
				if _, ok := smartDst[relPathFile]; ok {
					absCleanDst := path.Clean(absDst)
					if !obj.Force {
						return false, fmt.Errorf("can't force file into dir: %s", absCleanDst)
					}
					if absCleanDst == "" || absCleanDst == "/" {
						return false, fmt.Errorf("don't want to remove root") // safety
					}
					obj.init.Logf("syncCheckApply: removing (force): %s", absCleanDst)
					if err := os.Remove(absCleanDst); err != nil {
						return false, err
					}
					delete(smartDst, relPathFile) // rm from purge list
				}

				if obj.init.Debug {
					obj.init.Logf("syncCheckApply: mkdir -m %s '%s'", fileInfo.Mode(), absDst)
				}
				if err := os.Mkdir(absDst, fileInfo.Mode()); err != nil {
					return false, err
				}
				checkOK = false // we did some work
			}
			// if we're a regular file, the recurse will create it
		}

		if obj.init.Debug {
			obj.init.Logf("syncCheckApply: recurse: %s -> %s", absSrc, absDst)
		}
		if obj.Recurse {
			if c, err := obj.syncCheckApply(apply, absSrc, absDst); err != nil { // recurse
				return false, errwrap.Wrapf(err, "syncCheckApply: recurse failed")
			} else if !c { // don't let subsequent passes make this true
				checkOK = false
			}
		}
		if !apply && !checkOK { // check failed, and no apply to do, so exit!
			return false, nil
		}
		delete(smartDst, relPath) // rm from purge list
	}

	if !apply && len(smartDst) > 0 { // we know there are files to remove!
		return false, nil // so just exit now
	}
	// any files that now remain in smartDst need to be removed...
	for relPath, fileInfo := range smartDst {
		absSrc := src + relPath    // absolute dest (should not exist!)
		absDst := fileInfo.AbsPath // absolute path (should get removed)
		absCleanDst := path.Clean(absDst)
		if absCleanDst == "" || absCleanDst == "/" {
			return false, fmt.Errorf("don't want to remove root") // safety
		}

		// FIXME: respect obj.Recurse here...

		// NOTE: we could use os.RemoveAll instead of recursing, but I
		// think the symmetry is more elegant and correct here for now
		// Avoiding this is also useful if we had a recurse limit arg!
		if true { // switch
			obj.init.Logf("syncCheckApply: removing: %s", absCleanDst)
			if apply {
				if err := os.RemoveAll(absCleanDst); err != nil { // dangerous ;)
					return false, err
				}
				checkOK = false
			}
			continue
		}
		_ = absSrc
		//obj.init.Logf("syncCheckApply: Recurse rm: %s -> %s", absSrc, absDst)
		//if c, err := obj.syncCheckApply(apply, absSrc, absDst); err != nil {
		//	return false, errwrap.Wrapf(err, "syncCheckApply: Recurse rm failed")
		//} else if !c { // don't let subsequent passes make this true
		//	checkOK = false
		//}
		//obj.init.Logf("syncCheckApply: Removing: %s", absCleanDst)
		//if apply { // safety
		//	if err := os.Remove(absCleanDst); err != nil {
		//		return false, err
		//	}
		//	checkOK = false
		//}
	}

	return checkOK, nil
}

// state performs a CheckApply of the file state to create an empty file.
func (obj *FileRes) stateCheckApply(apply bool) (bool, error) {
	if obj.State == FileStateUndefined { // state is not specified
		return true, nil
	}

	_, err := os.Stat(obj.getPath())

	if err != nil && !os.IsNotExist(err) {
		return false, errwrap.Wrapf(err, "could not stat file")
	}

	if obj.State == FileStateAbsent && os.IsNotExist(err) {
		return true, nil
	}

	if obj.State == FileStateExists && err == nil {
		return true, nil
	}

	// state is not okay, no work done, exit, but without error
	if !apply {
		return false, nil
	}

	if obj.State == FileStateAbsent {
		return false, nil // defer the work to contentCheckApply
	}

	if obj.Content == nil && !obj.isDir() {
		// Create an empty file to ensure one exists. Don't O_TRUNC it,
		// in case one is magically created right after our exists test.
		// The chmod used is what is used by the os.Create function.
		// TODO: is using O_EXCL okay?
		f, err := os.OpenFile(obj.getPath(), os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0666)
		if err != nil {
			return false, errwrap.Wrapf(err, "problem creating empty file")
		}
		if err := f.Close(); err != nil {
			return false, errwrap.Wrapf(err, "problem closing empty file")
		}
	}

	return false, nil // defer the Content != nil and isDir work to later...
}

// contentCheckApply performs a CheckApply for the file existence and content.
func (obj *FileRes) contentCheckApply(apply bool) (bool, error) {
	obj.init.Logf("contentCheckApply(%t)", apply)

	if obj.State == FileStateAbsent {
		if _, err := os.Stat(obj.getPath()); os.IsNotExist(err) {
			// no such file or directory, but
			// file should be missing, phew :)
			return true, nil

		} else if err != nil { // what could this error be?
			return false, err
		}

		// state is not okay, no work done, exit, but without error
		if !apply {
			return false, nil
		}

		// apply portion
		if obj.getPath() == "" || obj.getPath() == "/" {
			return false, fmt.Errorf("don't want to remove root") // safety
		}
		obj.init.Logf("contentCheckApply: removing: %s", obj.getPath())
		// FIXME: respect obj.Recurse here...
		// TODO: add recurse limit here
		err := os.RemoveAll(obj.getPath()) // dangerous ;)
		return false, err                  // either nil or not
	}

	if obj.isDir() && obj.Source == "" {
		return obj.dirCheckApply(apply)
	}

	// content is not defined, leave it alone...
	if obj.Content == nil && obj.Source == "" {
		return true, nil
	}

	if obj.Source == "" { // do the obj.Content checks first...
		bufferSrc := bytes.NewReader([]byte(*obj.Content))
		sha256sum, checkOK, err := obj.fileCheckApply(apply, bufferSrc, obj.getPath(), obj.sha256sum)
		if sha256sum != "" { // empty values mean errored or didn't hash
			// this can be valid even when the whole function errors
			obj.sha256sum = sha256sum // cache value
		}
		if err != nil {
			return false, err
		}
		// if no err, but !ok, then...
		return checkOK, nil // success
	}

	checkOK, err := obj.syncCheckApply(apply, obj.Source, obj.getPath())
	if err != nil {
		obj.init.Logf("syncCheckApply: Error: %v", err)
		return false, err
	}

	return checkOK, nil
}

// chmodCheckApply performs a CheckApply for the file permissions.
func (obj *FileRes) chmodCheckApply(apply bool) (bool, error) {
	obj.init.Logf("chmodCheckApply(%t)", apply)

	if obj.State == FileStateAbsent {
		// file is absent
		return true, nil
	}

	if obj.Mode == "" {
		// no mode specified, everything is ok
		return true, nil
	}

	mode, err := obj.mode()

	// If the file does not exist and we are in
	// noop mode, do not throw an error.
	if os.IsNotExist(err) && !apply {
		return false, nil
	}

	if err != nil {
		return false, err
	}

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

	// nothing to do
	if fileInfo.Mode() == mode {
		return true, nil
	}

	// not clean but don't apply
	if !apply {
		return false, nil
	}

	err = os.Chmod(obj.getPath(), mode)
	return false, err
}

// chownCheckApply performs a CheckApply for the file ownership.
func (obj *FileRes) chownCheckApply(apply bool) (bool, error) {
	var expectedUID, expectedGID int
	obj.init.Logf("chownCheckApply(%t)", apply)

	if obj.State == FileStateAbsent {
		// file is absent or no owner specified
		return true, nil
	}

	fileInfo, err := os.Stat(obj.getPath())

	// If the file does not exist and we are in
	// noop mode, do not throw an error.
	if os.IsNotExist(err) && !apply {
		return false, nil
	}

	if err != nil {
		return false, err
	}

	stUnix, ok := fileInfo.Sys().(*syscall.Stat_t)
	if !ok { // this check is done in Validate, but it's done here again...
		// not unix
		return false, fmt.Errorf("can't set Owner or Group on this platform")
	}

	if obj.Owner != "" {
		expectedUID, err = engineUtil.GetUID(obj.Owner)
		if err != nil {
			return false, err
		}
	} else {
		// nothing specified, no changes to be made, expect same as actual
		expectedUID = int(stUnix.Uid)
	}

	if obj.Group != "" {
		expectedGID, err = engineUtil.GetGID(obj.Group)
		if err != nil {
			return false, err
		}
	} else {
		// nothing specified, no changes to be made, expect same as actual
		expectedGID = int(stUnix.Gid)
	}

	// nothing to do
	if int(stUnix.Uid) == expectedUID && int(stUnix.Gid) == expectedGID {
		return true, nil
	}

	// not clean, but don't apply
	if !apply {
		return false, nil
	}

	return false, os.Chown(obj.getPath(), expectedUID, expectedGID)
}

// CheckApply checks the resource state and applies the resource if the bool
// input is true. It returns error info and if the state check passed or not.
func (obj *FileRes) CheckApply(apply bool) (bool, error) {
	// NOTE: all send/recv change notifications *must* be processed before
	// there is a possibility of failure in CheckApply. This is because if
	// we fail (and possibly run again) the subsequent send->recv transfer
	// might not have a new value to copy, and therefore we won't see this
	// notification of change. Therefore, it is important to process these
	// promptly, if they must not be lost, such as for cache invalidation.
	if val, exists := obj.init.Recv()["Content"]; exists && val.Changed {
		// if we received on Content, and it changed, invalidate the cache!
		obj.init.Logf("contentCheckApply: invalidating sha256sum of `Content`")
		obj.sha256sum = "" // invalidate!!
	}

	checkOK := true

	// always run stateCheckApply before contentCheckApply, they go together
	if c, err := obj.stateCheckApply(apply); err != nil {
		return false, err
	} else if !c {
		checkOK = false
	}
	if c, err := obj.contentCheckApply(apply); err != nil {
		return false, err
	} else if !c {
		checkOK = false
	}

	if c, err := obj.chmodCheckApply(apply); err != nil {
		return false, err
	} else if !c {
		checkOK = false
	}

	if c, err := obj.chownCheckApply(apply); err != nil {
		return false, err
	} else if !c {
		checkOK = false
	}

	return checkOK, nil // w00t
}

// Cmp compares two resources and returns an error if they are not equivalent.
func (obj *FileRes) Cmp(r engine.Res) error {
	// we can only compare FileRes to others of the same resource kind
	res, ok := r.(*FileRes)
	if !ok {
		return fmt.Errorf("not a %s", obj.Kind())
	}

	// We don't need to compare Path, Dirname or Basename-- we only care if
	// the resultant path is different or not.
	if obj.getPath() != res.getPath() {
		return fmt.Errorf("the Path differs")
	}
	if (obj.Content == nil) != (res.Content == nil) { // xor
		return fmt.Errorf("the Content differs")
	}
	if obj.Content != nil && res.Content != nil {
		if *obj.Content != *res.Content { // compare the strings
			return fmt.Errorf("the contents of Content differ")
		}
	}
	if obj.Source != res.Source {
		return fmt.Errorf("the Source differs")
	}
	if obj.State != res.State {
		return fmt.Errorf("the State differs")
	}

	if obj.Owner != res.Owner {
		return fmt.Errorf("the Owner differs")
	}
	if obj.Group != res.Group {
		return fmt.Errorf("the Group differs")
	}
	// TODO: when we start to allow alternate representations for the mode,
	// ensure that we compare in the same format. Eg: `ug=rw` == `0660`.
	if obj.Mode != res.Mode {
		return fmt.Errorf("the Mode differs")
	}

	if obj.Recurse != res.Recurse {
		return fmt.Errorf("the Recurse option differs")
	}
	if obj.Force != res.Force {
		return fmt.Errorf("the Force option differs")
	}

	return nil
}

// FileUID is the UID struct for FileRes.
type FileUID struct {
	engine.BaseUID
	path string
}

// IFF aka if and only if they are equivalent, return true. If not, false.
func (obj *FileUID) IFF(uid engine.ResUID) bool {
	res, ok := uid.(*FileUID)
	if !ok {
		return false
	}
	return obj.path == res.path
}

// FileResAutoEdges holds the state of the auto edge generator.
type FileResAutoEdges struct {
	data    []engine.ResUID
	pointer int
	found   bool
}

// Next returns the next automatic edge.
func (obj *FileResAutoEdges) Next() []engine.ResUID {
	if obj.found {
		panic("Shouldn't be called anymore!")
	}
	if len(obj.data) == 0 { // check length for rare scenarios
		return nil
	}
	value := obj.data[obj.pointer]
	obj.pointer++
	return []engine.ResUID{value} // we return one, even though api supports N
}

// Test gets results of the earlier Next() call, & returns if we should continue!
func (obj *FileResAutoEdges) Test(input []bool) bool {
	// if there aren't any more remaining
	if len(obj.data) <= obj.pointer {
		return false
	}
	if obj.found { // already found, done!
		return false
	}
	if len(input) != 1 { // in case we get given bad data
		panic("Expecting a single value!")
	}
	if input[0] { // if a match is found, we're done!
		obj.found = true // no more to find!
		return false
	}
	return true // keep going
}

// AutoEdges generates a simple linear sequence of each parent directory from
// the bottom up!
func (obj *FileRes) AutoEdges() (engine.AutoEdge, error) {
	var data []engine.ResUID // store linear result chain here...
	// don't use any memoization run in Init (this gets called before Init)
	values := util.PathSplitFullReversed(obj.getPath())
	_, values = values[0], values[1:] // get rid of first value which is me!
	for _, x := range values {
		var reversed = true // cheat by passing a pointer
		data = append(data, &FileUID{
			BaseUID: engine.BaseUID{
				Name:     obj.Name(),
				Kind:     obj.Kind(),
				Reversed: &reversed,
			},
			path: x, // what matters
		}) // build list
	}
	return &FileResAutoEdges{
		data:    data,
		pointer: 0,
		found:   false,
	}, nil
}

// UIDs includes all params to make a unique identification of this object.
// Most resources only return one, although some resources can return multiple.
func (obj *FileRes) UIDs() []engine.ResUID {
	x := &FileUID{
		BaseUID: engine.BaseUID{Name: obj.Name(), Kind: obj.Kind()},
		path:    obj.getPath(),
	}
	return []engine.ResUID{x}
}

// GroupCmp returns whether two resources can be grouped together or not.
//func (obj *FileRes) GroupCmp(r engine.GroupableRes) error {
//	_, ok := r.(*FileRes)
//	if !ok {
//		return fmt.Errorf("resource is not the same kind")
//	}
//	// TODO: we might be able to group directory children into a single
//	// recursive watcher in the future, thus saving fanotify watches
//	return fmt.Errorf("not possible at the moment")
//}

// CollectPattern applies the pattern for collection resources.
func (obj *FileRes) CollectPattern(pattern string) {
	// XXX: currently the pattern for files can only override the Dirname variable :P
	obj.Dirname = pattern // XXX: simplistic for now
}

// UnmarshalYAML is the custom unmarshal handler for this struct.
// It is primarily useful for setting the defaults.
func (obj *FileRes) UnmarshalYAML(unmarshal func(interface{}) error) error {
	type rawRes FileRes // indirection to avoid infinite recursion

	def := obj.Default()      // get the default
	res, ok := def.(*FileRes) // put in the right format
	if !ok {
		return fmt.Errorf("could not convert to FileRes")
	}
	raw := rawRes(*res) // convert; the defaults go here

	if err := unmarshal(&raw); err != nil {
		return err
	}

	*obj = FileRes(raw) // restore from indirection with type conversion!
	return nil
}

// Copy copies the resource. Don't call it directly, use engine.ResCopy instead.
// TODO: should this copy internal state?
func (obj *FileRes) Copy() engine.CopyableRes {
	var content *string
	if obj.Content != nil { // copy the string contents, not the pointer...
		s := *obj.Content
		content = &s
	}
	return &FileRes{
		Path:     obj.Path,
		Dirname:  obj.Dirname,
		Basename: obj.Basename,
		Content:  content,
		Source:   obj.Source,
		State:    obj.State, // TODO: if this becomes a pointer, copy the string!
		Owner:    obj.Owner,
		Group:    obj.Group,
		Mode:     obj.Mode,
		Recurse:  obj.Recurse,
		Force:    obj.Force,
	}
}

// smartPath adds a trailing slash to the path if it is a directory.
func smartPath(fileInfo os.FileInfo) string {
	smartPath := fileInfo.Name() // absolute path
	if fileInfo.IsDir() {
		smartPath += "/" // add a trailing slash for dirs
	}
	return smartPath
}

// FileInfo is an enhanced variant of the traditional os.FileInfo struct. It can
// store both the absolute and the relative paths (when built from our ReadDir),
// and those two paths contain a trailing slash when they refer to a directory.
type FileInfo struct {
	os.FileInfo        // embed
	AbsPath     string // smart variant
	RelPath     string // smart variant
}

// ReadDir reads a directory path, and returns a list of enhanced FileInfo's.
func ReadDir(path string) ([]FileInfo, error) {
	if !strings.HasSuffix(path, "/") { // dirs have trailing slashes
		return nil, fmt.Errorf("path must be a directory")
	}
	output := []FileInfo{} // my file info
	fileInfos, err := ioutil.ReadDir(path)
	if os.IsNotExist(err) {
		return output, err // return empty list
	}
	if err != nil {
		return nil, err
	}
	for _, fi := range fileInfos {
		abs := path + smartPath(fi)
		rel, err := filepath.Rel(path, abs) // NOTE: calls Clean()
		if err != nil {                     // shouldn't happen
			return nil, errwrap.Wrapf(err, "unhandled error in ReadDir")
		}
		if fi.IsDir() {
			rel += "/" // add a trailing slash for dirs
		}
		x := FileInfo{
			FileInfo: fi,
			AbsPath:  abs,
			RelPath:  rel,
		}
		output = append(output, x)
	}
	return output, nil
}

// smartMapPaths adds a trailing slash to every path that is a directory. It
// returns the data as a map where the keys are the smart paths and where the
// values are the original os.FileInfo entries.
func mapPaths(fileInfos []FileInfo) map[string]FileInfo {
	paths := make(map[string]FileInfo)
	for _, fileInfo := range fileInfos {
		paths[fileInfo.RelPath] = fileInfo
	}
	return paths
}