syncthing/lib/model/rwfolder.go

// Copyright (C) 2014 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at http://mozilla.org/MPL/2.0/.

package model

import (
	"errors"
	"fmt"
	"io/ioutil"
	"math/rand"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"time"

	"github.com/syncthing/syncthing/lib/config"
	"github.com/syncthing/syncthing/lib/db"
	"github.com/syncthing/syncthing/lib/events"
	"github.com/syncthing/syncthing/lib/ignore"
	"github.com/syncthing/syncthing/lib/osutil"
	"github.com/syncthing/syncthing/lib/protocol"
	"github.com/syncthing/syncthing/lib/scanner"
	"github.com/syncthing/syncthing/lib/symlinks"
	"github.com/syncthing/syncthing/lib/sync"
	"github.com/syncthing/syncthing/lib/versioner"
)

// TODO: Stop on errors

// A pullBlockState is passed to the puller routine for each block that needs
// to be fetched.
type pullBlockState struct {
	*sharedPullerState
	block protocol.BlockInfo
}

// A copyBlocksState is passed to copy routine if the file has blocks to be
// copied.
type copyBlocksState struct {
	*sharedPullerState
	blocks []protocol.BlockInfo
}

// Which filemode bits to preserve
const retainBits = os.ModeSetgid | os.ModeSetuid | os.ModeSticky

var (
	activity    = newDeviceActivity()
	errNoDevice = errors.New("peers who had this file went away, or the file has changed while syncing. will retry later")
)

const (
	dbUpdateHandleDir = iota
	dbUpdateDeleteDir
	dbUpdateHandleFile
	dbUpdateDeleteFile
	dbUpdateShortcutFile
)

const (
	defaultCopiers     = 1
	defaultPullers     = 16
	defaultPullerSleep = 10 * time.Second
	defaultPullerPause = 60 * time.Second
)

type dbUpdateJob struct {
	file    protocol.FileInfo
	jobType int
}

type rwFolder struct {
	stateTracker

	model            *Model
	progressEmitter  *ProgressEmitter
	virtualMtimeRepo *db.VirtualMtimeRepo

	folder         string
	dir            string
	scanIntv       time.Duration
	versioner      versioner.Versioner
	ignorePerms    bool
	copiers        int
	pullers        int
	shortID        uint64
	order          config.PullOrder
	maxConflicts   int
	sleep          time.Duration
	pause          time.Duration
	allowSparse    bool
	checkFreeSpace bool

	stop        chan struct{}
	queue       *jobQueue
	dbUpdates   chan dbUpdateJob
	scanTimer   *time.Timer
	pullTimer   *time.Timer
	delayScan   chan time.Duration
	scanNow     chan rescanRequest
	remoteIndex chan struct{} // An index update was received, we should re-evaluate needs

	errors    map[string]string // path -> error string
	errorsMut sync.Mutex
}

func newRWFolder(m *Model, shortID uint64, cfg config.FolderConfiguration) *rwFolder {
	p := &rwFolder{
		stateTracker: stateTracker{
			folder: cfg.ID,
			mut:    sync.NewMutex(),
		},

		model:            m,
		progressEmitter:  m.progressEmitter,
		virtualMtimeRepo: db.NewVirtualMtimeRepo(m.db, cfg.ID),

		folder:         cfg.ID,
		dir:            cfg.Path(),
		scanIntv:       time.Duration(cfg.RescanIntervalS) * time.Second,
		ignorePerms:    cfg.IgnorePerms,
		copiers:        cfg.Copiers,
		pullers:        cfg.Pullers,
		shortID:        shortID,
		order:          cfg.Order,
		maxConflicts:   cfg.MaxConflicts,
		allowSparse:    !cfg.DisableSparseFiles,
		checkFreeSpace: cfg.MinDiskFreePct != 0,

		stop:        make(chan struct{}),
		queue:       newJobQueue(),
		pullTimer:   time.NewTimer(time.Second),
		scanTimer:   time.NewTimer(time.Millisecond), // The first scan should be done immediately.
		delayScan:   make(chan time.Duration),
		scanNow:     make(chan rescanRequest),
		remoteIndex: make(chan struct{}, 1), // This needs to be 1-buffered so that we queue a notification if we're busy doing a pull when it comes.

		errorsMut: sync.NewMutex(),
	}

	if p.copiers == 0 {
		p.copiers = defaultCopiers
	}
	if p.pullers == 0 {
		p.pullers = defaultPullers
	}

	if cfg.PullerPauseS == 0 {
		p.pause = defaultPullerPause
	} else {
		p.pause = time.Duration(cfg.PullerPauseS) * time.Second
	}

	if cfg.PullerSleepS == 0 {
		p.sleep = defaultPullerSleep
	} else {
		p.sleep = time.Duration(cfg.PullerSleepS) * time.Second
	}

	return p
}

// Helper function to check whether either the ignorePerm flag has been
// set on the local host or the FlagNoPermBits has been set on the file/dir
// which is being pulled.
func (p *rwFolder) ignorePermissions(file protocol.FileInfo) bool {
	return p.ignorePerms || file.Flags&protocol.FlagNoPermBits != 0
}

// Serve will run scans and pulls. It will return when Stop()ed or on a
// critical error.
func (p *rwFolder) Serve() {
	l.Debugln(p, "starting")
	defer l.Debugln(p, "exiting")

	defer func() {
		p.pullTimer.Stop()
		p.scanTimer.Stop()
		// TODO: Should there be an actual FolderStopped state?
		p.setState(FolderIdle)
	}()

	var prevVer int64
	var prevIgnoreHash string

	rescheduleScan := func() {
		if p.scanIntv == 0 {
			// We should not run scans, so it should not be rescheduled.
			return
		}

		// Sleep a random time between 3/4 and 5/4 of the configured interval.
		sleepNanos := (p.scanIntv.Nanoseconds()*3 + rand.Int63n(2*p.scanIntv.Nanoseconds())) / 4
		intv := time.Duration(sleepNanos) * time.Nanosecond

		l.Debugln(p, "next rescan in", intv)
		p.scanTimer.Reset(intv)
	}

	// We don't start pulling files until a scan has been completed.
	initialScanCompleted := false

	for {
		select {
		case <-p.stop:
			return

		case <-p.remoteIndex:
			prevVer = 0
			p.pullTimer.Reset(0)
			l.Debugln(p, "remote index updated, rescheduling pull")

		case <-p.pullTimer.C:
			if !initialScanCompleted {
				l.Debugln(p, "skip (initial)")
				p.pullTimer.Reset(p.sleep)
				continue
			}

			p.model.fmut.RLock()
			curIgnores := p.model.folderIgnores[p.folder]
			p.model.fmut.RUnlock()

			if newHash := curIgnores.Hash(); newHash != prevIgnoreHash {
				// The ignore patterns have changed. We need to re-evaluate if
				// there are files we need now that were ignored before.
				l.Debugln(p, "ignore patterns have changed, resetting prevVer")
				prevVer = 0
				prevIgnoreHash = newHash
			}

			// RemoteLocalVersion() is a fast call, doesn't touch the database.
			curVer, ok := p.model.RemoteLocalVersion(p.folder)
			if !ok || curVer == prevVer {
				l.Debugln(p, "skip (curVer == prevVer)", prevVer, ok)
				p.pullTimer.Reset(p.sleep)
				continue
			}

			if err := p.model.CheckFolderHealth(p.folder); err != nil {
				l.Infoln("Skipping folder", p.folder, "pull due to folder error:", err)
				p.pullTimer.Reset(p.sleep)
				continue
			}

			l.Debugln(p, "pulling", prevVer, curVer)

			p.setState(FolderSyncing)
			p.clearErrors()
			tries := 0

			for {
				tries++

				changed := p.pullerIteration(curIgnores)
				l.Debugln(p, "changed", changed)

				if changed == 0 {
					// No files were changed by the puller, so we are in
					// sync. Remember the local version number and
					// schedule a resync a little bit into the future.

					if lv, ok := p.model.RemoteLocalVersion(p.folder); ok && lv < curVer {
						// There's a corner case where the device we needed
						// files from disconnected during the puller
						// iteration. The files will have been removed from
						// the index, so we've concluded that we don't need
						// them, but at the same time we have the local
						// version that includes those files in curVer. So we
						// catch the case that localVersion might have
						// decreased here.
						l.Debugln(p, "adjusting curVer", lv)
						curVer = lv
					}
					prevVer = curVer
					l.Debugln(p, "next pull in", p.sleep)
					p.pullTimer.Reset(p.sleep)
					break
				}

				if tries > 10 {
					// We've tried a bunch of times to get in sync, but
					// we're not making it. Probably there are write
					// errors preventing us. Flag this with a warning and
					// wait a bit longer before retrying.
					l.Infof("Folder %q isn't making progress. Pausing puller for %v.", p.folder, p.pause)
					l.Debugln(p, "next pull in", p.pause)

					if folderErrors := p.currentErrors(); len(folderErrors) > 0 {
						events.Default.Log(events.FolderErrors, map[string]interface{}{
							"folder": p.folder,
							"errors": folderErrors,
						})
					}

					p.pullTimer.Reset(p.pause)
					break
				}
			}
			p.setState(FolderIdle)

		// The reason for running the scanner from within the puller is that
		// this is the easiest way to make sure we are not doing both at the
		// same time.
		case <-p.scanTimer.C:
			if err := p.model.CheckFolderHealth(p.folder); err != nil {
				l.Infoln("Skipping folder", p.folder, "scan due to folder error:", err)
				rescheduleScan()
				continue
			}

			l.Debugln(p, "rescan")

			if err := p.model.internalScanFolderSubs(p.folder, nil); err != nil {
				// Potentially sets the error twice, once in the scanner just
				// by doing a check, and once here, if the error returned is
				// the same one as returned by CheckFolderHealth, though
				// duplicate set is handled by setError.
				p.setError(err)
				rescheduleScan()
				continue
			}

			if p.scanIntv > 0 {
				rescheduleScan()
			}
			if !initialScanCompleted {
				l.Infoln("Completed initial scan (rw) of folder", p.folder)
				initialScanCompleted = true
			}

		case req := <-p.scanNow:
			if err := p.model.CheckFolderHealth(p.folder); err != nil {
				l.Infoln("Skipping folder", p.folder, "scan due to folder error:", err)
				req.err <- err
				continue
			}

			l.Debugln(p, "forced rescan")

			if err := p.model.internalScanFolderSubs(p.folder, req.subs); err != nil {
				// Potentially sets the error twice, once in the scanner just
				// by doing a check, and once here, if the error returned is
				// the same one as returned by CheckFolderHealth, though
				// duplicate set is handled by setError.
				p.setError(err)
				req.err <- err
				continue
			}

			req.err <- nil

		case next := <-p.delayScan:
			p.scanTimer.Reset(next)
		}
	}
}

func (p *rwFolder) Stop() {
	close(p.stop)
}

func (p *rwFolder) IndexUpdated() {
	select {
	case p.remoteIndex <- struct{}{}:
	default:
		// We might be busy doing a pull and thus not reading from this
		// channel. The channel is 1-buffered, so one notification will be
		// queued to ensure we recheck after the pull, but beyond that we must
		// make sure to not block index receiving.
	}
}

func (p *rwFolder) Scan(subs []string) error {
	req := rescanRequest{
		subs: subs,
		err:  make(chan error),
	}
	p.scanNow <- req
	return <-req.err
}

func (p *rwFolder) String() string {
	return fmt.Sprintf("rwFolder/%s@%p", p.folder, p)
}

// pullerIteration runs a single puller iteration for the given folder and
// returns the number items that should have been synced (even those that
// might have failed). One puller iteration handles all files currently
// flagged as needed in the folder.
func (p *rwFolder) pullerIteration(ignores *ignore.Matcher) int {
	pullChan := make(chan pullBlockState)
	copyChan := make(chan copyBlocksState)
	finisherChan := make(chan *sharedPullerState)

	updateWg := sync.NewWaitGroup()
	copyWg := sync.NewWaitGroup()
	pullWg := sync.NewWaitGroup()
	doneWg := sync.NewWaitGroup()

	l.Debugln(p, "c", p.copiers, "p", p.pullers)

	p.dbUpdates = make(chan dbUpdateJob)
	updateWg.Add(1)
	go func() {
		// dbUpdaterRoutine finishes when p.dbUpdates is closed
		p.dbUpdaterRoutine()
		updateWg.Done()
	}()

	for i := 0; i < p.copiers; i++ {
		copyWg.Add(1)
		go func() {
			// copierRoutine finishes when copyChan is closed
			p.copierRoutine(copyChan, pullChan, finisherChan)
			copyWg.Done()
		}()
	}

	for i := 0; i < p.pullers; i++ {
		pullWg.Add(1)
		go func() {
			// pullerRoutine finishes when pullChan is closed
			p.pullerRoutine(pullChan, finisherChan)
			pullWg.Done()
		}()
	}

	doneWg.Add(1)
	// finisherRoutine finishes when finisherChan is closed
	go func() {
		p.finisherRoutine(finisherChan)
		doneWg.Done()
	}()

	p.model.fmut.RLock()
	folderFiles := p.model.folderFiles[p.folder]
	p.model.fmut.RUnlock()

	// !!!
	// WithNeed takes a database snapshot (by necessity). By the time we've
	// handled a bunch of files it might have become out of date and we might
	// be attempting to sync with an old version of a file...
	// !!!

	changed := 0

	fileDeletions := map[string]protocol.FileInfo{}
	dirDeletions := []protocol.FileInfo{}
	buckets := map[string][]protocol.FileInfo{}

	folderFiles.WithNeed(protocol.LocalDeviceID, func(intf db.FileIntf) bool {
		// Needed items are delivered sorted lexicographically. We'll handle
		// directories as they come along, so parents before children. Files
		// are queued and the order may be changed later.

		file := intf.(protocol.FileInfo)

		if ignores.Match(file.Name) {
			// This is an ignored file. Skip it, continue iteration.
			return true
		}

		l.Debugln(p, "handling", file.Name)

		switch {
		case file.IsDeleted():
			// A deleted file, directory or symlink
			if file.IsDirectory() {
				dirDeletions = append(dirDeletions, file)
			} else {
				fileDeletions[file.Name] = file
				df, ok := p.model.CurrentFolderFile(p.folder, file.Name)
				// Local file can be already deleted, but with a lower version
				// number, hence the deletion coming in again as part of
				// WithNeed, furthermore, the file can simply be of the wrong
				// type if we haven't yet managed to pull it.
				if ok && !df.IsDeleted() && !df.IsSymlink() && !df.IsDirectory() {
					// Put files into buckets per first hash
					key := string(df.Blocks[0].Hash)
					buckets[key] = append(buckets[key], df)
				}
			}
		case file.IsDirectory() && !file.IsSymlink():
			// A new or changed directory
			l.Debugln("Creating directory", file.Name)
			p.handleDir(file)
		default:
			// A new or changed file or symlink. This is the only case where we
			// do stuff concurrently in the background
			p.queue.Push(file.Name, file.Size(), file.Modified)
		}

		changed++
		return true
	})

	// Reorder the file queue according to configuration

	switch p.order {
	case config.OrderRandom:
		p.queue.Shuffle()
	case config.OrderAlphabetic:
		// The queue is already in alphabetic order.
	case config.OrderSmallestFirst:
		p.queue.SortSmallestFirst()
	case config.OrderLargestFirst:
		p.queue.SortLargestFirst()
	case config.OrderOldestFirst:
		p.queue.SortOldestFirst()
	case config.OrderNewestFirst:
		p.queue.SortNewestFirst()
	}

	// Process the file queue

nextFile:
	for {
		fileName, ok := p.queue.Pop()
		if !ok {
			break
		}

		f, ok := p.model.CurrentGlobalFile(p.folder, fileName)
		if !ok {
			// File is no longer in the index. Mark it as done and drop it.
			p.queue.Done(fileName)
			continue
		}

		// Local file can be already deleted, but with a lower version
		// number, hence the deletion coming in again as part of
		// WithNeed, furthermore, the file can simply be of the wrong type if
		// the global index changed while we were processing this iteration.
		if !f.IsDeleted() && !f.IsSymlink() && !f.IsDirectory() {
			key := string(f.Blocks[0].Hash)
			for i, candidate := range buckets[key] {
				if scanner.BlocksEqual(candidate.Blocks, f.Blocks) {
					// Remove the candidate from the bucket
					lidx := len(buckets[key]) - 1
					buckets[key][i] = buckets[key][lidx]
					buckets[key] = buckets[key][:lidx]

					// candidate is our current state of the file, where as the
					// desired state with the delete bit set is in the deletion
					// map.
					desired := fileDeletions[candidate.Name]
					// Remove the pending deletion (as we perform it by renaming)
					delete(fileDeletions, candidate.Name)

					p.renameFile(desired, f)

					p.queue.Done(fileName)
					continue nextFile
				}
			}
		}

		// Not a rename or a symlink, deal with it.
		p.handleFile(f, copyChan, finisherChan)
	}

	// Signal copy and puller routines that we are done with the in data for
	// this iteration. Wait for them to finish.
	close(copyChan)
	copyWg.Wait()
	close(pullChan)
	pullWg.Wait()

	// Signal the finisher chan that there will be no more input.
	close(finisherChan)

	// Wait for the finisherChan to finish.
	doneWg.Wait()

	for _, file := range fileDeletions {
		l.Debugln("Deleting file", file.Name)
		p.deleteFile(file)
	}

	for i := range dirDeletions {
		dir := dirDeletions[len(dirDeletions)-i-1]
		l.Debugln("Deleting dir", dir.Name)
		p.deleteDir(dir)
	}

	// Wait for db updates to complete
	close(p.dbUpdates)
	updateWg.Wait()

	return changed
}

// handleDir creates or updates the given directory
func (p *rwFolder) handleDir(file protocol.FileInfo) {
	var err error
	events.Default.Log(events.ItemStarted, map[string]string{
		"folder": p.folder,
		"item":   file.Name,
		"type":   "dir",
		"action": "update",
	})

	defer func() {
		events.Default.Log(events.ItemFinished, map[string]interface{}{
			"folder": p.folder,
			"item":   file.Name,
			"error":  events.Error(err),
			"type":   "dir",
			"action": "update",
		})
	}()

	realName := filepath.Join(p.dir, file.Name)
	mode := os.FileMode(file.Flags & 0777)
	if p.ignorePermissions(file) {
		mode = 0777
	}

	if shouldDebug() {
		curFile, _ := p.model.CurrentFolderFile(p.folder, file.Name)
		l.Debugf("need dir\n\t%v\n\t%v", file, curFile)
	}

	info, err := osutil.Lstat(realName)
	switch {
	// There is already something under that name, but it's a file/link.
	// Most likely a file/link is getting replaced with a directory.
	// Remove the file/link and fall through to directory creation.
	case err == nil && (!info.IsDir() || info.Mode()&os.ModeSymlink != 0):
		err = osutil.InWritableDir(osutil.Remove, realName)
		if err != nil {
			l.Infof("Puller (folder %q, dir %q): %v", p.folder, file.Name, err)
			p.newError(file.Name, err)
			return
		}
		fallthrough
	// The directory doesn't exist, so we create it with the right
	// mode bits from the start.
	case err != nil && os.IsNotExist(err):
		// We declare a function that acts on only the path name, so
		// we can pass it to InWritableDir. We use a regular Mkdir and
		// not MkdirAll because the parent should already exist.
		mkdir := func(path string) error {
			err = os.Mkdir(path, mode)
			if err != nil || p.ignorePermissions(file) {
				return err
			}

			// Stat the directory so we can check its permissions.
			info, err := osutil.Lstat(path)
			if err != nil {
				return err
			}

			// Mask for the bits we want to preserve and add them in to the
			// directories permissions.
			return os.Chmod(path, mode|(info.Mode()&retainBits))
		}

		if err = osutil.InWritableDir(mkdir, realName); err == nil {
			p.dbUpdates <- dbUpdateJob{file, dbUpdateHandleDir}
		} else {
			l.Infof("Puller (folder %q, dir %q): %v", p.folder, file.Name, err)
			p.newError(file.Name, err)
		}
		return
	// Weird error when stat()'ing the dir. Probably won't work to do
	// anything else with it if we can't even stat() it.
	case err != nil:
		l.Infof("Puller (folder %q, dir %q): %v", p.folder, file.Name, err)
		p.newError(file.Name, err)
		return
	}

	// The directory already exists, so we just correct the mode bits. (We
	// don't handle modification times on directories, because that sucks...)
	// It's OK to change mode bits on stuff within non-writable directories.
	if p.ignorePermissions(file) {
		p.dbUpdates <- dbUpdateJob{file, dbUpdateHandleDir}
	} else if err := os.Chmod(realName, mode|(info.Mode()&retainBits)); err == nil {
		p.dbUpdates <- dbUpdateJob{file, dbUpdateHandleDir}
	} else {
		l.Infof("Puller (folder %q, dir %q): %v", p.folder, file.Name, err)
		p.newError(file.Name, err)
	}
}

// deleteDir attempts to delete the given directory
func (p *rwFolder) deleteDir(file protocol.FileInfo) {
	var err error
	events.Default.Log(events.ItemStarted, map[string]string{
		"folder": p.folder,
		"item":   file.Name,
		"type":   "dir",
		"action": "delete",
	})
	defer func() {
		events.Default.Log(events.ItemFinished, map[string]interface{}{
			"folder": p.folder,
			"item":   file.Name,
			"error":  events.Error(err),
			"type":   "dir",
			"action": "delete",
		})
	}()

	realName := filepath.Join(p.dir, file.Name)
	// Delete any temporary files lying around in the directory
	dir, _ := os.Open(realName)
	if dir != nil {
		files, _ := dir.Readdirnames(-1)
		for _, file := range files {
			if defTempNamer.IsTemporary(file) {
				osutil.InWritableDir(osutil.Remove, filepath.Join(realName, file))
			}
		}
		dir.Close()
	}

	err = osutil.InWritableDir(osutil.Remove, realName)
	if err == nil || os.IsNotExist(err) {
		// It was removed or it doesn't exist to start with
		p.dbUpdates <- dbUpdateJob{file, dbUpdateDeleteDir}
	} else if _, serr := os.Lstat(realName); serr != nil && !os.IsPermission(serr) {
		// We get an error just looking at the directory, and it's not a
		// permission problem. Lets assume the error is in fact some variant
		// of "file does not exist" (possibly expressed as some parent being a
		// file and not a directory etc) and that the delete is handled.
		p.dbUpdates <- dbUpdateJob{file, dbUpdateDeleteDir}
	} else {
		l.Infof("Puller (folder %q, dir %q): delete: %v", p.folder, file.Name, err)
		p.newError(file.Name, err)
	}
}

// deleteFile attempts to delete the given file
func (p *rwFolder) deleteFile(file protocol.FileInfo) {
	var err error
	events.Default.Log(events.ItemStarted, map[string]string{
		"folder": p.folder,
		"item":   file.Name,
		"type":   "file",
		"action": "delete",
	})
	defer func() {
		events.Default.Log(events.ItemFinished, map[string]interface{}{
			"folder": p.folder,
			"item":   file.Name,
			"error":  events.Error(err),
			"type":   "file",
			"action": "delete",
		})
	}()

	realName := filepath.Join(p.dir, file.Name)

	cur, ok := p.model.CurrentFolderFile(p.folder, file.Name)
	if ok && p.inConflict(cur.Version, file.Version) {
		// There is a conflict here. Move the file to a conflict copy instead
		// of deleting. Also merge with the version vector we had, to indicate
		// we have resolved the conflict.
		file.Version = file.Version.Merge(cur.Version)
		err = osutil.InWritableDir(p.moveForConflict, realName)
	} else if p.versioner != nil {
		err = osutil.InWritableDir(p.versioner.Archive, realName)
	} else {
		err = osutil.InWritableDir(osutil.Remove, realName)
	}

	if err == nil || os.IsNotExist(err) {
		// It was removed or it doesn't exist to start with
		p.dbUpdates <- dbUpdateJob{file, dbUpdateDeleteFile}
	} else if _, serr := os.Lstat(realName); serr != nil && !os.IsPermission(serr) {
		// We get an error just looking at the file, and it's not a permission
		// problem. Lets assume the error is in fact some variant of "file
		// does not exist" (possibly expressed as some parent being a file and
		// not a directory etc) and that the delete is handled.
		p.dbUpdates <- dbUpdateJob{file, dbUpdateDeleteFile}
	} else {
		l.Infof("Puller (folder %q, file %q): delete: %v", p.folder, file.Name, err)
		p.newError(file.Name, err)
	}
}

// renameFile attempts to rename an existing file to a destination
// and set the right attributes on it.
func (p *rwFolder) renameFile(source, target protocol.FileInfo) {
	var err error
	events.Default.Log(events.ItemStarted, map[string]string{
		"folder": p.folder,
		"item":   source.Name,
		"type":   "file",
		"action": "delete",
	})
	events.Default.Log(events.ItemStarted, map[string]string{
		"folder": p.folder,
		"item":   target.Name,
		"type":   "file",
		"action": "update",
	})
	defer func() {
		events.Default.Log(events.ItemFinished, map[string]interface{}{
			"folder": p.folder,
			"item":   source.Name,
			"error":  events.Error(err),
			"type":   "file",
			"action": "delete",
		})
		events.Default.Log(events.ItemFinished, map[string]interface{}{
			"folder": p.folder,
			"item":   target.Name,
			"error":  events.Error(err),
			"type":   "file",
			"action": "update",
		})
	}()

	l.Debugln(p, "taking rename shortcut", source.Name, "->", target.Name)

	from := filepath.Join(p.dir, source.Name)
	to := filepath.Join(p.dir, target.Name)

	if p.versioner != nil {
		err = osutil.Copy(from, to)
		if err == nil {
			err = osutil.InWritableDir(p.versioner.Archive, from)
		}
	} else {
		err = osutil.TryRename(from, to)
	}

	if err == nil {
		// The file was renamed, so we have handled both the necessary delete
		// of the source and the creation of the target. Fix-up the metadata,
		// and update the local index of the target file.

		p.dbUpdates <- dbUpdateJob{source, dbUpdateDeleteFile}

		err = p.shortcutFile(target)
		if err != nil {
			l.Infof("Puller (folder %q, file %q): rename from %q metadata: %v", p.folder, target.Name, source.Name, err)
			p.newError(target.Name, err)
			return
		}

		p.dbUpdates <- dbUpdateJob{target, dbUpdateHandleFile}
	} else {
		// We failed the rename so we have a source file that we still need to
		// get rid of. Attempt to delete it instead so that we make *some*
		// progress. The target is unhandled.

		err = osutil.InWritableDir(osutil.Remove, from)
		if err != nil {
			l.Infof("Puller (folder %q, file %q): delete %q after failed rename: %v", p.folder, target.Name, source.Name, err)
			p.newError(target.Name, err)
			return
		}

		p.dbUpdates <- dbUpdateJob{source, dbUpdateDeleteFile}
	}
}

// This is the flow of data and events here, I think...
//
// +-----------------------+
// |                       | - - - - > ItemStarted
// |      handleFile       | - - - - > ItemFinished (on shortcuts)
// |                       |
// +-----------------------+
//             |
//             | copyChan (copyBlocksState; unless shortcut taken)
//             |
//             |    +-----------------------+
//             |    | +-----------------------+
//             +--->| |                       |
//                  | |     copierRoutine     |
//                  +-|                       |
//                    +-----------------------+
//                                |
//                                | pullChan (sharedPullerState)
//                                |
//                                |   +-----------------------+
//                                |   | +-----------------------+
//                                +-->| |                       |
//                                    | |     pullerRoutine     |
//                                    +-|                       |
//                                      +-----------------------+
//                                                  |
//                                                  | finisherChan (sharedPullerState)
//                                                  |
//                                                  |   +-----------------------+
//                                                  |   |                       |
//                                                  +-->|    finisherRoutine    | - - - - > ItemFinished
//                                                      |                       |
//                                                      +-----------------------+

// handleFile queues the copies and pulls as necessary for a single new or
// changed file.
func (p *rwFolder) handleFile(file protocol.FileInfo, copyChan chan<- copyBlocksState, finisherChan chan<- *sharedPullerState) {
	curFile, hasCurFile := p.model.CurrentFolderFile(p.folder, file.Name)

	if hasCurFile && len(curFile.Blocks) == len(file.Blocks) && scanner.BlocksEqual(curFile.Blocks, file.Blocks) {
		// We are supposed to copy the entire file, and then fetch nothing. We
		// are only updating metadata, so we don't actually *need* to make the
		// copy.
		l.Debugln(p, "taking shortcut on", file.Name)

		events.Default.Log(events.ItemStarted, map[string]string{
			"folder": p.folder,
			"item":   file.Name,
			"type":   "file",
			"action": "metadata",
		})

		p.queue.Done(file.Name)

		var err error
		if file.IsSymlink() {
			err = p.shortcutSymlink(file)
		} else {
			err = p.shortcutFile(file)
		}

		events.Default.Log(events.ItemFinished, map[string]interface{}{
			"folder": p.folder,
			"item":   file.Name,
			"error":  events.Error(err),
			"type":   "file",
			"action": "metadata",
		})

		if err != nil {
			l.Infoln("Puller: shortcut:", err)
			p.newError(file.Name, err)
		} else {
			p.dbUpdates <- dbUpdateJob{file, dbUpdateShortcutFile}
		}

		return
	}

	// Figure out the absolute filenames we need once and for all
	tempName := filepath.Join(p.dir, defTempNamer.TempName(file.Name))
	realName := filepath.Join(p.dir, file.Name)

	if hasCurFile && !curFile.IsDirectory() && !curFile.IsSymlink() {
		// Check that the file on disk is what we expect it to be according to
		// the database. If there's a mismatch here, there might be local
		// changes that we don't know about yet and we should scan before
		// touching the file. If we can't stat the file we'll just pull it.
		if info, err := osutil.Lstat(realName); err == nil {
			mtime := p.virtualMtimeRepo.GetMtime(file.Name, info.ModTime())
			if mtime.Unix() != curFile.Modified || info.Size() != curFile.Size() {
				l.Debugln("file modified but not rescanned; not pulling:", realName)
				// Scan() is synchronous (i.e. blocks until the scan is
				// completed and returns an error), but a scan can't happen
				// while we're in the puller routine. Request the scan in the
				// background and it'll be handled when the current pulling
				// sweep is complete. As we do retries, we'll queue the scan
				// for this file up to ten times, but the last nine of those
				// scans will be cheap...
				go p.Scan([]string{file.Name})
				return
			}
		}
	}

	scanner.PopulateOffsets(file.Blocks)

	reused := 0
	var blocks []protocol.BlockInfo
	var blocksSize int64

	// Check for an old temporary file which might have some blocks we could
	// reuse.
	tempBlocks, err := scanner.HashFile(tempName, protocol.BlockSize, 0, nil)
	if err == nil {
		// Check for any reusable blocks in the temp file
		tempCopyBlocks, _ := scanner.BlockDiff(tempBlocks, file.Blocks)

		// block.String() returns a string unique to the block
		existingBlocks := make(map[string]struct{}, len(tempCopyBlocks))
		for _, block := range tempCopyBlocks {
			existingBlocks[block.String()] = struct{}{}
		}

		// Since the blocks are already there, we don't need to get them.
		for _, block := range file.Blocks {
			_, ok := existingBlocks[block.String()]
			if !ok {
				blocks = append(blocks, block)
				blocksSize += int64(block.Size)
			}
		}

		// The sharedpullerstate will know which flags to use when opening the
		// temp file depending if we are reusing any blocks or not.
		reused = len(file.Blocks) - len(blocks)
		if reused == 0 {
			// Otherwise, discard the file ourselves in order for the
			// sharedpuller not to panic when it fails to exclusively create a
			// file which already exists
			osutil.InWritableDir(osutil.Remove, tempName)
		}
	} else {
		blocks = file.Blocks
		blocksSize = file.Size()
	}

	if p.checkFreeSpace {
		if free, err := osutil.DiskFreeBytes(p.dir); err == nil && free < blocksSize {
			l.Warnf(`Folder "%s": insufficient disk space in %s for %s: have %.2f MiB, need %.2f MiB`, p.folder, p.dir, file.Name, float64(free)/1024/1024, float64(blocksSize)/1024/1024)
			p.newError(file.Name, errors.New("insufficient space"))
			return
		}
	}

	events.Default.Log(events.ItemStarted, map[string]string{
		"folder": p.folder,
		"item":   file.Name,
		"type":   "file",
		"action": "update",
	})

	s := sharedPullerState{
		file:        file,
		folder:      p.folder,
		tempName:    tempName,
		realName:    realName,
		copyTotal:   len(blocks),
		copyNeeded:  len(blocks),
		reused:      reused,
		ignorePerms: p.ignorePermissions(file),
		version:     curFile.Version,
		mut:         sync.NewMutex(),
		sparse:      p.allowSparse,
	}

	l.Debugf("%v need file %s; copy %d, reused %v", p, file.Name, len(blocks), reused)

	cs := copyBlocksState{
		sharedPullerState: &s,
		blocks:            blocks,
	}
	copyChan <- cs
}

// shortcutFile sets file mode and modification time, when that's the only
// thing that has changed.
func (p *rwFolder) shortcutFile(file protocol.FileInfo) error {
	realName := filepath.Join(p.dir, file.Name)
	if !p.ignorePermissions(file) {
		if err := os.Chmod(realName, os.FileMode(file.Flags&0777)); err != nil {
			l.Infof("Puller (folder %q, file %q): shortcut: chmod: %v", p.folder, file.Name, err)
			p.newError(file.Name, err)
			return err
		}
	}

	t := time.Unix(file.Modified, 0)
	if err := os.Chtimes(realName, t, t); err != nil {
		// Try using virtual mtimes
		info, err := os.Stat(realName)
		if err != nil {
			l.Infof("Puller (folder %q, file %q): shortcut: unable to stat file: %v", p.folder, file.Name, err)
			p.newError(file.Name, err)
			return err
		}

		p.virtualMtimeRepo.UpdateMtime(file.Name, info.ModTime(), t)
	}

	// This may have been a conflict. We should merge the version vectors so
	// that our clock doesn't move backwards.
	if cur, ok := p.model.CurrentFolderFile(p.folder, file.Name); ok {
		file.Version = file.Version.Merge(cur.Version)
	}

	return nil
}

// shortcutSymlink changes the symlinks type if necessary.
func (p *rwFolder) shortcutSymlink(file protocol.FileInfo) (err error) {
	tt := symlinks.TargetFile
	if file.IsDirectory() {
		tt = symlinks.TargetDirectory
	}
	err = symlinks.ChangeType(filepath.Join(p.dir, file.Name), tt)
	if err != nil {
		l.Infof("Puller (folder %q, file %q): symlink shortcut: %v", p.folder, file.Name, err)
		p.newError(file.Name, err)
	}
	return
}

// copierRoutine reads copierStates until the in channel closes and performs
// the relevant copies when possible, or passes it to the puller routine.
func (p *rwFolder) copierRoutine(in <-chan copyBlocksState, pullChan chan<- pullBlockState, out chan<- *sharedPullerState) {
	buf := make([]byte, protocol.BlockSize)

	for state := range in {
		dstFd, err := state.tempFile()
		if err != nil {
			// Nothing more to do for this failed file, since we couldn't create a temporary for it.
			out <- state.sharedPullerState
			continue
		}

		if p.progressEmitter != nil {
			p.progressEmitter.Register(state.sharedPullerState)
		}

		folderRoots := make(map[string]string)
		var folders []string
		p.model.fmut.RLock()
		for folder, cfg := range p.model.folderCfgs {
			folderRoots[folder] = cfg.Path()
			folders = append(folders, folder)
		}
		p.model.fmut.RUnlock()

		for _, block := range state.blocks {
			if p.allowSparse && state.reused == 0 && block.IsEmpty() {
				// The block is a block of all zeroes, and we are not reusing
				// a temp file, so there is no need to do anything with it.
				// If we were reusing a temp file and had this block to copy,
				// it would be because the block in the temp file was *not* a
				// block of all zeroes, so then we should not skip it.

				// Pretend we copied it.
				state.copiedFromOrigin()
				continue
			}

			buf = buf[:int(block.Size)]
			found := p.model.finder.Iterate(folders, block.Hash, func(folder, file string, index int32) bool {
				fd, err := os.Open(filepath.Join(folderRoots[folder], file))
				if err != nil {
					return false
				}

				_, err = fd.ReadAt(buf, protocol.BlockSize*int64(index))
				fd.Close()
				if err != nil {
					return false
				}

				hash, err := scanner.VerifyBuffer(buf, block)
				if err != nil {
					if hash != nil {
						l.Debugf("Finder block mismatch in %s:%s:%d expected %q got %q", folder, file, index, block.Hash, hash)
						err = p.model.finder.Fix(folder, file, index, block.Hash, hash)
						if err != nil {
							l.Warnln("finder fix:", err)
						}
					} else {
						l.Debugln("Finder failed to verify buffer", err)
					}
					return false
				}

				_, err = dstFd.WriteAt(buf, block.Offset)
				if err != nil {
					state.fail("dst write", err)
				}
				if file == state.file.Name {
					state.copiedFromOrigin()
				}
				return true
			})

			if state.failed() != nil {
				break
			}

			if !found {
				state.pullStarted()
				ps := pullBlockState{
					sharedPullerState: state.sharedPullerState,
					block:             block,
				}
				pullChan <- ps
			} else {
				state.copyDone()
			}
		}
		out <- state.sharedPullerState
	}
}

func (p *rwFolder) pullerRoutine(in <-chan pullBlockState, out chan<- *sharedPullerState) {
	for state := range in {
		if state.failed() != nil {
			out <- state.sharedPullerState
			continue
		}

		// Get an fd to the temporary file. Technically we don't need it until
		// after fetching the block, but if we run into an error here there is
		// no point in issuing the request to the network.
		fd, err := state.tempFile()
		if err != nil {
			out <- state.sharedPullerState
			continue
		}

		if p.allowSparse && state.reused == 0 && state.block.IsEmpty() {
			// There is no need to request a block of all zeroes. Pretend we
			// requested it and handled it correctly.
			state.pullDone()
			out <- state.sharedPullerState
			continue
		}

		var lastError error
		potentialDevices := p.model.Availability(p.folder, state.file.Name)
		for {
			// Select the least busy device to pull the block from. If we found no
			// feasible device at all, fail the block (and in the long run, the
			// file).
			selected := activity.leastBusy(potentialDevices)
			if selected == (protocol.DeviceID{}) {
				if lastError != nil {
					state.fail("pull", lastError)
				} else {
					state.fail("pull", errNoDevice)
				}
				break
			}

			potentialDevices = removeDevice(potentialDevices, selected)

			// Fetch the block, while marking the selected device as in use so that
			// leastBusy can select another device when someone else asks.
			activity.using(selected)
			buf, lastError := p.model.requestGlobal(selected, p.folder, state.file.Name, state.block.Offset, int(state.block.Size), state.block.Hash, 0, nil)
			activity.done(selected)
			if lastError != nil {
				l.Debugln("request:", p.folder, state.file.Name, state.block.Offset, state.block.Size, "returned error:", lastError)
				continue
			}

			// Verify that the received block matches the desired hash, if not
			// try pulling it from another device.
			_, lastError = scanner.VerifyBuffer(buf, state.block)
			if lastError != nil {
				l.Debugln("request:", p.folder, state.file.Name, state.block.Offset, state.block.Size, "hash mismatch")
				continue
			}

			// Save the block data we got from the cluster
			_, err = fd.WriteAt(buf, state.block.Offset)
			if err != nil {
				state.fail("save", err)
			} else {
				state.pullDone()
			}
			break
		}
		out <- state.sharedPullerState
	}
}

func (p *rwFolder) performFinish(state *sharedPullerState) error {
	// Set the correct permission bits on the new file
	if !p.ignorePermissions(state.file) {
		if err := os.Chmod(state.tempName, os.FileMode(state.file.Flags&0777)); err != nil {
			return err
		}
	}

	// Set the correct timestamp on the new file
	t := time.Unix(state.file.Modified, 0)
	if err := os.Chtimes(state.tempName, t, t); err != nil {
		// Try using virtual mtimes instead
		info, err := os.Stat(state.tempName)
		if err != nil {
			return err
		}
		p.virtualMtimeRepo.UpdateMtime(state.file.Name, info.ModTime(), t)
	}

	if stat, err := osutil.Lstat(state.realName); err == nil {
		// There is an old file or directory already in place. We need to
		// handle that.

		switch {
		case stat.IsDir() || stat.Mode()&os.ModeSymlink != 0:
			// It's a directory or a symlink. These are not versioned or
			// archived for conflicts, only removed (which of course fails for
			// non-empty directories).

			// TODO: This is the place where we want to remove temporary files
			// and future hard ignores before attempting a directory delete.
			// Should share code with p.deletDir().

			if err = osutil.InWritableDir(osutil.Remove, state.realName); err != nil {
				return err
			}

		case p.inConflict(state.version, state.file.Version):
			// The new file has been changed in conflict with the existing one. We
			// should file it away as a conflict instead of just removing or
			// archiving. Also merge with the version vector we had, to indicate
			// we have resolved the conflict.

			state.file.Version = state.file.Version.Merge(state.version)
			if err = osutil.InWritableDir(p.moveForConflict, state.realName); err != nil {
				return err
			}

		case p.versioner != nil:
			// If we should use versioning, let the versioner archive the old
			// file before we replace it. Archiving a non-existent file is not
			// an error.

			if err = p.versioner.Archive(state.realName); err != nil {
				return err
			}
		}
	}

	// Replace the original content with the new one
	if err := osutil.Rename(state.tempName, state.realName); err != nil {
		return err
	}

	// If it's a symlink, the target of the symlink is inside the file.
	if state.file.IsSymlink() {
		content, err := ioutil.ReadFile(state.realName)
		if err != nil {
			return err
		}

		// Remove the file, and replace it with a symlink.
		err = osutil.InWritableDir(func(path string) error {
			os.Remove(path)
			tt := symlinks.TargetFile
			if state.file.IsDirectory() {
				tt = symlinks.TargetDirectory
			}
			return symlinks.Create(path, string(content), tt)
		}, state.realName)
		if err != nil {
			return err
		}
	}

	// Record the updated file in the index
	p.dbUpdates <- dbUpdateJob{state.file, dbUpdateHandleFile}
	return nil
}

func (p *rwFolder) finisherRoutine(in <-chan *sharedPullerState) {
	for state := range in {
		if closed, err := state.finalClose(); closed {
			l.Debugln(p, "closing", state.file.Name)

			p.queue.Done(state.file.Name)

			if err == nil {
				err = p.performFinish(state)
			}

			if err != nil {
				l.Infoln("Puller: final:", err)
				p.newError(state.file.Name, err)
			}
			events.Default.Log(events.ItemFinished, map[string]interface{}{
				"folder": p.folder,
				"item":   state.file.Name,
				"error":  events.Error(err),
				"type":   "file",
				"action": "update",
			})

			if p.progressEmitter != nil {
				p.progressEmitter.Deregister(state)
			}
		}
	}
}

// Moves the given filename to the front of the job queue
func (p *rwFolder) BringToFront(filename string) {
	p.queue.BringToFront(filename)
}

func (p *rwFolder) Jobs() ([]string, []string) {
	return p.queue.Jobs()
}

func (p *rwFolder) DelayScan(next time.Duration) {
	p.delayScan <- next
}

// dbUpdaterRoutine aggregates db updates and commits them in batches no
// larger than 1000 items, and no more delayed than 2 seconds.
func (p *rwFolder) dbUpdaterRoutine() {
	const (
		maxBatchSize = 1000
		maxBatchTime = 2 * time.Second
	)

	batch := make([]dbUpdateJob, 0, maxBatchSize)
	files := make([]protocol.FileInfo, 0, maxBatchSize)
	tick := time.NewTicker(maxBatchTime)
	defer tick.Stop()

	handleBatch := func() {
		found := false
		var lastFile protocol.FileInfo

		for _, job := range batch {
			files = append(files, job.file)
			if job.file.IsInvalid() || (job.file.IsDirectory() && !job.file.IsSymlink()) {
				continue
			}

			if job.jobType&(dbUpdateHandleFile|dbUpdateDeleteFile) == 0 {
				continue
			}

			found = true
			lastFile = job.file
		}

		p.model.updateLocals(p.folder, files)

		if found {
			p.model.receivedFile(p.folder, lastFile)
		}

		batch = batch[:0]
		files = files[:0]
	}

loop:
	for {
		select {
		case job, ok := <-p.dbUpdates:
			if !ok {
				break loop
			}

			job.file.LocalVersion = 0
			batch = append(batch, job)

			if len(batch) == maxBatchSize {
				handleBatch()
			}

		case <-tick.C:
			if len(batch) > 0 {
				handleBatch()
			}
		}
	}

	if len(batch) > 0 {
		handleBatch()
	}
}

func (p *rwFolder) inConflict(current, replacement protocol.Vector) bool {
	if current.Concurrent(replacement) {
		// Obvious case
		return true
	}
	if replacement.Counter(p.shortID) > current.Counter(p.shortID) {
		// The replacement file contains a higher version for ourselves than
		// what we have. This isn't supposed to be possible, since it's only
		// we who can increment that counter. We take it as a sign that
		// something is wrong (our index may have been corrupted or removed)
		// and flag it as a conflict.
		return true
	}
	return false
}

func removeDevice(devices []protocol.DeviceID, device protocol.DeviceID) []protocol.DeviceID {
	for i := range devices {
		if devices[i] == device {
			devices[i] = devices[len(devices)-1]
			return devices[:len(devices)-1]
		}
	}
	return devices
}

func (p *rwFolder) moveForConflict(name string) error {
	if strings.Contains(filepath.Base(name), ".sync-conflict-") {
		l.Infoln("Conflict for", name, "which is already a conflict copy; not copying again.")
		if err := osutil.Remove(name); err != nil && !os.IsNotExist(err) {
			return err
		}
		return nil
	}

	if p.maxConflicts == 0 {
		if err := osutil.Remove(name); err != nil && !os.IsNotExist(err) {
			return err
		}
		return nil
	}

	ext := filepath.Ext(name)
	withoutExt := name[:len(name)-len(ext)]
	newName := withoutExt + time.Now().Format(".sync-conflict-20060102-150405") + ext
	err := os.Rename(name, newName)
	if os.IsNotExist(err) {
		// We were supposed to move a file away but it does not exist. Either
		// the user has already moved it away, or the conflict was between a
		// remote modification and a local delete. In either way it does not
		// matter, go ahead as if the move succeeded.
		err = nil
	}
	if p.maxConflicts > -1 {
		matches, gerr := osutil.Glob(withoutExt + ".sync-conflict-????????-??????" + ext)
		if gerr == nil && len(matches) > p.maxConflicts {
			sort.Sort(sort.Reverse(sort.StringSlice(matches)))
			for _, match := range matches[p.maxConflicts:] {
				gerr = osutil.Remove(match)
				if gerr != nil {
					l.Debugln(p, "removing extra conflict", gerr)
				}
			}
		} else if gerr != nil {
			l.Debugln(p, "globbing for conflicts", gerr)
		}
	}
	return err
}

func (p *rwFolder) newError(path string, err error) {
	p.errorsMut.Lock()
	defer p.errorsMut.Unlock()

	// We might get more than one error report for a file (i.e. error on
	// Write() followed by Close()); we keep the first error as that is
	// probably closer to the root cause.
	if _, ok := p.errors[path]; ok {
		return
	}

	p.errors[path] = err.Error()
}

func (p *rwFolder) clearErrors() {
	p.errorsMut.Lock()
	p.errors = make(map[string]string)
	p.errorsMut.Unlock()
}

func (p *rwFolder) currentErrors() []fileError {
	p.errorsMut.Lock()
	errors := make([]fileError, 0, len(p.errors))
	for path, err := range p.errors {
		errors = append(errors, fileError{path, err})
	}
	sort.Sort(fileErrorList(errors))
	p.errorsMut.Unlock()
	return errors
}

// A []fileError is sent as part of an event and will be JSON serialized.
type fileError struct {
	Path string `json:"path"`
	Err  string `json:"error"`
}

type fileErrorList []fileError

func (l fileErrorList) Len() int {
	return len(l)
}

func (l fileErrorList) Less(a, b int) bool {
	return l[a].Path < l[b].Path
}

func (l fileErrorList) Swap(a, b int) {
	l[a], l[b] = l[b], l[a]
}