// receives and prints discovery announcements
func recv(bc beacon.Interface) {
	seen := make(map[string]bool)
	for {
		data, src := bc.Recv()
		var ann discover.Announce
		ann.UnmarshalXDR(data)

		if bytes.Equal(ann.This.ID, myID) {
			// This is one of our own fake packets, don't print it.
			continue
		}

		// Print announcement details for the first packet from a given
		// device ID and source address, or if -all was given.
		key := string(ann.This.ID) + src.String()
		if all || !seen[key] {
			log.Printf("Announcement from %v\n", src)
			log.Printf(" %v at %s\n", protocol.DeviceIDFromBytes(ann.This.ID), strings.Join(addrStrs(ann.This), ", "))

			for _, dev := range ann.Extra {
				log.Printf(" %v at %s\n", protocol.DeviceIDFromBytes(dev.ID), strings.Join(addrStrs(dev), ", "))
			}
			seen[key] = true
		}
	}
}

// ldbRemoveFromGlobal removes the device from the global version list for the
// given file. If the version list is empty after this, the file entry is
// removed entirely.
func ldbRemoveFromGlobal(db dbReader, batch dbWriter, folder, device, file []byte) {
	l.Debugf("remove from global; folder=%q device=%v file=%q", folder, protocol.DeviceIDFromBytes(device), file)

	gk := globalKey(folder, file)
	svl, err := db.Get(gk, nil)
	if err != nil {
		// We might be called to "remove" a global version that doesn't exist
		// if the first update for the file is already marked invalid.
		return
	}

	var fl versionList
	err = fl.UnmarshalXDR(svl)
	if err != nil {
		panic(err)
	}

	for i := range fl.versions {
		if bytes.Compare(fl.versions[i].device, device) == 0 {
			fl.versions = append(fl.versions[:i], fl.versions[i+1:]...)
			break
		}
	}

	if len(fl.versions) == 0 {
		l.Debugf("batch.Delete %p %x", batch, gk)
		batch.Delete(gk)
	} else {
		l.Debugf("batch.Put %p %x", batch, gk)
		l.Debugf("new global after remove: %v", fl)
		batch.Put(gk, fl.MustMarshalXDR())
	}
}

func (c *localClient) recvAnnouncements(b beacon.Interface) {
	for {
		buf, addr := b.Recv()

		var pkt Announce
		err := pkt.UnmarshalXDR(buf)
		if err != nil && err != io.EOF {
			l.Debugf("discover: Failed to unmarshal local announcement from %s:\n%s", addr, hex.Dump(buf))
			continue
		}

		if pkt.Magic != AnnouncementMagic {
			l.Debugf("discover: Incorrect magic from %s: %s != %s", addr, pkt.Magic, AnnouncementMagic)
			continue
		}

		l.Debugf("discover: Received local announcement from %s for %s", addr, protocol.DeviceIDFromBytes(pkt.This.ID))

		var newDevice bool
		if !bytes.Equal(pkt.This.ID, c.myID[:]) {
			newDevice = c.registerDevice(addr, pkt.This)
		}

		if newDevice {
			// Force a transmit to announce ourselves, if we are ready to do
			// so right away.
			select {
			case c.forcedBcastTick <- time.Now():
			default:
			}
		}
	}
}

func (t readWriteTransaction) insertFile(folder, device []byte, file protocol.FileInfo) {
	l.Debugf("insert; folder=%q device=%v %v", folder, protocol.DeviceIDFromBytes(device), file)

	name := []byte(file.Name)
	nk := t.db.deviceKey(folder, device, name)
	t.Put(nk, mustMarshal(&file))
}

func ldbAvailability(db *leveldb.DB, folder, file []byte) []protocol.DeviceID {
	k := globalKey(folder, file)
	bs, err := db.Get(k, nil)
	if err == leveldb.ErrNotFound {
		return nil
	}
	if err != nil {
		panic(err)
	}

	var vl versionList
	err = vl.UnmarshalXDR(bs)
	if err != nil {
		panic(err)
	}

	var devices []protocol.DeviceID
	for _, v := range vl.versions {
		if !v.version.Equal(vl.versions[0].version) {
			break
		}
		n := protocol.DeviceIDFromBytes(v.device)
		devices = append(devices, n)
	}

	return devices
}

func (c *localClient) recvAnnouncements(b beacon.Interface) {
	for {
		buf, addr := b.Recv()

		var pkt Announce
		err := pkt.UnmarshalXDR(buf)
		if err != nil && err != io.EOF {
			l.Debugf("discover: Failed to unmarshal local announcement from %s:\n%s", addr, hex.Dump(buf))
			continue
		}

		l.Debugf("discover: Received local announcement from %s for %s", addr, protocol.DeviceIDFromBytes(pkt.This.ID))

		var newDevice bool
		if bytes.Compare(pkt.This.ID, c.myID[:]) != 0 {
			newDevice = c.registerDevice(addr, pkt.This)
		}

		if newDevice {
			select {
			case c.forcedBcastTick <- time.Now():
			}
		}
	}
}

func dump(ldb *db.Instance) {
	it := ldb.NewIterator(nil, nil)
	for it.Next() {
		key := it.Key()
		switch key[0] {
		case db.KeyTypeDevice:
			folder := binary.BigEndian.Uint32(key[1:])
			device := binary.BigEndian.Uint32(key[1+4:])
			name := nulString(key[1+4+4:])
			fmt.Printf("[device] F:%d D:%d N:%q", folder, device, name)

			var f protocol.FileInfo
			err := f.Unmarshal(it.Value())
			if err != nil {
				log.Fatal(err)
			}
			fmt.Printf(" V:%v\n", f)

		case db.KeyTypeGlobal:
			folder := binary.BigEndian.Uint32(key[1:])
			name := nulString(key[1+4:])
			var flv db.VersionList
			flv.Unmarshal(it.Value())
			fmt.Printf("[global] F:%d N:%q V:%s\n", folder, name, flv)

		case db.KeyTypeBlock:
			folder := binary.BigEndian.Uint32(key[1:])
			hash := key[1+4 : 1+4+32]
			name := nulString(key[1+4+32:])
			fmt.Printf("[block] F:%d H:%x N:%q I:%d\n", folder, hash, name, binary.BigEndian.Uint32(it.Value()))

		case db.KeyTypeDeviceStatistic:
			fmt.Printf("[dstat] K:%x V:%x\n", it.Key(), it.Value())

		case db.KeyTypeFolderStatistic:
			fmt.Printf("[fstat] K:%x V:%x\n", it.Key(), it.Value())

		case db.KeyTypeVirtualMtime:
			fmt.Printf("[mtime] K:%x V:%x\n", it.Key(), it.Value())

		case db.KeyTypeFolderIdx:
			key := binary.BigEndian.Uint32(it.Key()[1:])
			fmt.Printf("[folderidx] K:%d V:%q\n", key, it.Value())

		case db.KeyTypeDeviceIdx:
			key := binary.BigEndian.Uint32(it.Key()[1:])
			val := it.Value()
			if len(val) == 0 {
				fmt.Printf("[deviceidx] K:%d V:<nil>\n", key)
			} else {
				dev := protocol.DeviceIDFromBytes(val)
				fmt.Printf("[deviceidx] K:%d V:%s\n", key, dev)
			}

		default:
			fmt.Printf("[???]\n  %x\n  %x\n", it.Key(), it.Value())
		}
	}
}

func (db *Instance) replace(folder, device []byte, fs []protocol.FileInfo, localSize, globalSize *sizeTracker) {
	db.genericReplace(folder, device, fs, localSize, globalSize, func(t readWriteTransaction, folder, device, name []byte, dbi iterator.Iterator) {
		// Database has a file that we are missing. Remove it.
		l.Debugf("delete; folder=%q device=%v name=%q", folder, protocol.DeviceIDFromBytes(device), name)
		t.removeFromGlobal(folder, device, name, globalSize)
		t.Delete(dbi.Key())
	})
}

func ldbReplace(db *leveldb.DB, folder, device []byte, fs []protocol.FileInfo) int64 {
	// TODO: Return the remaining maxLocalVer?
	return ldbGenericReplace(db, folder, device, fs, func(db dbReader, batch dbWriter, folder, device, name []byte, dbi iterator.Iterator) int64 {
		// Database has a file that we are missing. Remove it.
		l.Debugf("delete; folder=%q device=%v name=%q", folder, protocol.DeviceIDFromBytes(device), name)
		ldbRemoveFromGlobal(db, batch, folder, device, name)
		l.Debugf("batch.Delete %p %x", batch, dbi.Key())
		batch.Delete(dbi.Key())
		return 0
	})
}

func (t readWriteTransaction) insertFile(folder, device []byte, file protocol.FileInfo) int64 {
	l.Debugf("insert; folder=%q device=%v %v", folder, protocol.DeviceIDFromBytes(device), file)

	if file.LocalVersion == 0 {
		file.LocalVersion = clock(0)
	}

	name := []byte(file.Name)
	nk := deviceKey(folder, device, name)
	t.Put(nk, file.MustMarshalXDR())

	return file.LocalVersion
}

func (c *localClient) recvAnnouncements(b beacon.Interface) {
	warnedAbout := make(map[string]bool)
	for {
		buf, addr := b.Recv()
		if len(buf) < 4 {
			l.Debugf("discover: short packet from %s")
			continue
		}

		magic := binary.BigEndian.Uint32(buf)
		switch magic {
		case Magic:
			// All good

		case v13Magic:
			// Old version
			if !warnedAbout[addr.String()] {
				l.Warnf("Incompatible (v0.13) local discovery packet from %v - upgrade that device to connect", addr)
				warnedAbout[addr.String()] = true
			}
			continue

		default:
			l.Debugf("discover: Incorrect magic %x from %s", magic, addr)
			continue
		}

		var pkt Announce
		err := pkt.Unmarshal(buf[4:])
		if err != nil && err != io.EOF {
			l.Debugf("discover: Failed to unmarshal local announcement from %s:\n%s", addr, hex.Dump(buf))
			continue
		}

		l.Debugf("discover: Received local announcement from %s for %s", addr, protocol.DeviceIDFromBytes(pkt.ID))

		var newDevice bool
		if !bytes.Equal(pkt.ID, c.myID[:]) {
			newDevice = c.registerDevice(addr, pkt)
		}

		if newDevice {
			// Force a transmit to announce ourselves, if we are ready to do
			// so right away.
			select {
			case c.forcedBcastTick <- time.Now():
			default:
			}
		}
	}
}

func ldbInsert(batch dbWriter, folder, device []byte, file protocol.FileInfo) int64 {
	l.Debugf("insert; folder=%q device=%v %v", folder, protocol.DeviceIDFromBytes(device), file)

	if file.LocalVersion == 0 {
		file.LocalVersion = clock(0)
	}

	name := []byte(file.Name)
	nk := deviceKey(folder, device, name)
	l.Debugf("batch.Put %p %x", batch, nk)
	batch.Put(nk, file.MustMarshalXDR())

	return file.LocalVersion
}

// ldbRemoveFromGlobal removes the device from the global version list for the
// given file. If the version list is empty after this, the file entry is
// removed entirely.
func ldbRemoveFromGlobal(db dbReader, batch dbWriter, folder, device, file []byte, globalSize *sizeTracker) {
	l.Debugf("remove from global; folder=%q device=%v file=%q", folder, protocol.DeviceIDFromBytes(device), file)

	gk := globalKey(folder, file)
	svl, err := db.Get(gk, nil)
	if err != nil {
		// We might be called to "remove" a global version that doesn't exist
		// if the first update for the file is already marked invalid.
		return
	}

	var fl versionList
	err = fl.UnmarshalXDR(svl)
	if err != nil {
		panic(err)
	}

	removed := false
	for i := range fl.versions {
		if bytes.Compare(fl.versions[i].device, device) == 0 {
			if i == 0 && globalSize != nil {
				f, ok := ldbGet(db, folder, device, file)
				if !ok {
					panic("removing nonexistent file")
				}
				globalSize.removeFile(f)
				removed = true
			}
			fl.versions = append(fl.versions[:i], fl.versions[i+1:]...)
			break
		}
	}

	if len(fl.versions) == 0 {
		l.Debugf("batch.Delete %p %x", batch, gk)
		batch.Delete(gk)
	} else {
		l.Debugf("batch.Put %p %x", batch, gk)
		l.Debugf("new global after remove: %v", fl)
		batch.Put(gk, fl.MustMarshalXDR())
		if removed {
			f, ok := ldbGet(db, folder, fl.versions[0].device, file)
			if !ok {
				panic("new global is nonexistent file")
			}
			globalSize.addFile(f)
		}
	}
}

func main() {
	flag.BoolVar(&all, "all", all, "Print all received announcements (not only first)")
	flag.BoolVar(&fake, "fake", fake, "Send fake announcements")
	flag.StringVar(&mc, "mc", mc, "IPv6 multicast address")
	flag.IntVar(&bc, "bc", bc, "IPv4 broadcast port number")
	flag.Parse()

	if fake {
		log.Println("My ID:", protocol.DeviceIDFromBytes(myID))
	}

	runbeacon(beacon.NewMulticast(mc), fake)
	runbeacon(beacon.NewBroadcast(bc), fake)

	select {}
}

// removeFromGlobal removes the device from the global version list for the
// given file. If the version list is empty after this, the file entry is
// removed entirely.
func (t readWriteTransaction) removeFromGlobal(folder, device, file []byte, globalSize *sizeTracker) {
	l.Debugf("remove from global; folder=%q device=%v file=%q", folder, protocol.DeviceIDFromBytes(device), file)

	gk := t.db.globalKey(folder, file)
	svl, err := t.Get(gk, nil)
	if err != nil {
		// We might be called to "remove" a global version that doesn't exist
		// if the first update for the file is already marked invalid.
		return
	}

	var fl VersionList
	err = fl.Unmarshal(svl)
	if err != nil {
		panic(err)
	}

	removed := false
	for i := range fl.Versions {
		if bytes.Equal(fl.Versions[i].Device, device) {
			if i == 0 && globalSize != nil {
				f, ok := t.getFile(folder, device, file)
				if !ok {
					panic("removing nonexistent file")
				}
				globalSize.removeFile(f)
				removed = true
			}
			fl.Versions = append(fl.Versions[:i], fl.Versions[i+1:]...)
			break
		}
	}

	if len(fl.Versions) == 0 {
		t.Delete(gk)
	} else {
		l.Debugf("new global after remove: %v", fl)
		t.Put(gk, mustMarshal(&fl))
		if removed {
			f, ok := t.getFile(folder, fl.Versions[0].Device, file)
			if !ok {
				panic("new global is nonexistent file")
			}
			globalSize.addFile(f)
		}
	}
}

func ldbWithNeed(db *leveldb.DB, folder, device []byte, truncate bool, fn Iterator) {
	runtime.GC()

	start := globalKey(folder, nil)
	limit := globalKey(folder, []byte{0xff, 0xff, 0xff, 0xff})
	snap, err := db.GetSnapshot()
	if err != nil {
		panic(err)
	}
	if debugDB {
		l.Debugf("created snapshot %p", snap)
	}
	defer func() {
		if debugDB {
			l.Debugf("close snapshot %p", snap)
		}
		snap.Release()
	}()

	dbi := snap.NewIterator(&util.Range{Start: start, Limit: limit}, nil)
	defer dbi.Release()

	var fk []byte
nextFile:
	for dbi.Next() {
		var vl versionList
		err := vl.UnmarshalXDR(dbi.Value())
		if err != nil {
			panic(err)
		}
		if len(vl.versions) == 0 {
			l.Debugln(dbi.Key())
			panic("no versions?")
		}

		have := false // If we have the file, any version
		need := false // If we have a lower version of the file
		var haveVersion protocol.Vector
		for _, v := range vl.versions {
			if bytes.Compare(v.device, device) == 0 {
				have = true
				haveVersion = v.version
				// XXX: This marks Concurrent (i.e. conflicting) changes as
				// needs. Maybe we should do that, but it needs special
				// handling in the puller.
				need = !v.version.GreaterEqual(vl.versions[0].version)
				break
			}
		}

		if need || !have {
			name := globalKeyName(dbi.Key())
			needVersion := vl.versions[0].version

		nextVersion:
			for i := range vl.versions {
				if !vl.versions[i].version.Equal(needVersion) {
					// We haven't found a valid copy of the file with the needed version.
					continue nextFile
				}
				fk = deviceKeyInto(fk[:cap(fk)], folder, vl.versions[i].device, name)
				if debugDB {
					l.Debugf("snap.Get %p %x", snap, fk)
				}
				bs, err := snap.Get(fk, nil)
				if err != nil {
					var id protocol.DeviceID
					copy(id[:], device)
					l.Debugf("device: %v", id)
					l.Debugf("need: %v, have: %v", need, have)
					l.Debugf("key: %q (%x)", dbi.Key(), dbi.Key())
					l.Debugf("vl: %v", vl)
					l.Debugf("i: %v", i)
					l.Debugf("fk: %q (%x)", fk, fk)
					l.Debugf("name: %q (%x)", name, name)
					panic(err)
				}

				gf, err := unmarshalTrunc(bs, truncate)
				if err != nil {
					panic(err)
				}

				if gf.IsInvalid() {
					// The file is marked invalid for whatever reason, don't use it.
					continue nextVersion
				}

				if gf.IsDeleted() && !have {
					// We don't need deleted files that we don't have
					continue nextFile
				}

				if debugDB {
					l.Debugf("need folder=%q device=%v name=%q need=%v have=%v haveV=%d globalV=%d", folder, protocol.DeviceIDFromBytes(device), name, need, have, haveVersion, vl.versions[0].version)
				}

				if cont := fn(gf); !cont {
					return
				}
//.........这里部分代码省略.........

// ldbUpdateGlobal adds this device+version to the version list for the given
// file. If the device is already present in the list, the version is updated.
// If the file does not have an entry in the global list, it is created.
func ldbUpdateGlobal(db dbReader, batch dbWriter, folder, device []byte, file protocol.FileInfo) bool {
	if debugDB {
		l.Debugf("update global; folder=%q device=%v file=%q version=%d", folder, protocol.DeviceIDFromBytes(device), file.Name, file.Version)
	}
	name := []byte(file.Name)
	gk := globalKey(folder, name)
	svl, err := db.Get(gk, nil)
	if err != nil && err != leveldb.ErrNotFound {
		panic(err)
	}

	var fl versionList

	// Remove the device from the current version list
	if svl != nil {
		err = fl.UnmarshalXDR(svl)
		if err != nil {
			panic(err)
		}

		for i := range fl.versions {
			if bytes.Compare(fl.versions[i].device, device) == 0 {
				if fl.versions[i].version.Equal(file.Version) {
					// No need to do anything
					return false
				}
				fl.versions = append(fl.versions[:i], fl.versions[i+1:]...)
				break
			}
		}
	}

	nv := fileVersion{
		device:  device,
		version: file.Version,
	}

	// Find a position in the list to insert this file. The file at the front
	// of the list is the newer, the "global".
	for i := range fl.versions {
		switch fl.versions[i].version.Compare(file.Version) {
		case protocol.Equal, protocol.Lesser:
			// The version at this point in the list is equal to or lesser
			// ("older") than us. We insert ourselves in front of it.
			fl.versions = insertVersion(fl.versions, i, nv)
			goto done

		case protocol.ConcurrentLesser, protocol.ConcurrentGreater:
			// The version at this point is in conflict with us. We must pull
			// the actual file metadata to determine who wins. If we win, we
			// insert ourselves in front of the loser here. (The "Lesser" and
			// "Greater" in the condition above is just based on the device
			// IDs in the version vector, which is not the only thing we use
			// to determine the winner.)
			of, ok := ldbGet(db, folder, fl.versions[i].device, name)
			if !ok {
				panic("file referenced in version list does not exist")
			}
			if file.WinsConflict(of) {
				fl.versions = insertVersion(fl.versions, i, nv)
				goto done
			}
		}
	}

	// We didn't find a position for an insert above, so append to the end.
	fl.versions = append(fl.versions, nv)

done:
	if debugDB {
		l.Debugf("batch.Put %p %x", batch, gk)
		l.Debugf("new global after update: %v", fl)
	}
	batch.Put(gk, fl.MustMarshalXDR())

	return true
}

func ldbGenericReplace(db *leveldb.DB, folder, device []byte, fs []protocol.FileInfo, deleteFn deletionHandler) int64 {
	runtime.GC()

	sort.Sort(fileList(fs)) // sort list on name, same as in the database

	start := deviceKey(folder, device, nil)                            // before all folder/device files
	limit := deviceKey(folder, device, []byte{0xff, 0xff, 0xff, 0xff}) // after all folder/device files

	batch := new(leveldb.Batch)
	if debugDB {
		l.Debugf("new batch %p", batch)
	}
	snap, err := db.GetSnapshot()
	if err != nil {
		panic(err)
	}
	if debugDB {
		l.Debugf("created snapshot %p", snap)
	}
	defer func() {
		if debugDB {
			l.Debugf("close snapshot %p", snap)
		}
		snap.Release()
	}()

	dbi := snap.NewIterator(&util.Range{Start: start, Limit: limit}, nil)
	defer dbi.Release()

	moreDb := dbi.Next()
	fsi := 0
	var maxLocalVer int64

	for {
		var newName, oldName []byte
		moreFs := fsi < len(fs)

		if !moreDb && !moreFs {
			break
		}

		if moreFs {
			newName = []byte(fs[fsi].Name)
		}

		if moreDb {
			oldName = deviceKeyName(dbi.Key())
		}

		cmp := bytes.Compare(newName, oldName)

		if debugDB {
			l.Debugf("generic replace; folder=%q device=%v moreFs=%v moreDb=%v cmp=%d newName=%q oldName=%q", folder, protocol.DeviceIDFromBytes(device), moreFs, moreDb, cmp, newName, oldName)
		}

		switch {
		case moreFs && (!moreDb || cmp == -1):
			if debugDB {
				l.Debugln("generic replace; missing - insert")
			}
			// Database is missing this file. Insert it.
			if lv := ldbInsert(batch, folder, device, fs[fsi]); lv > maxLocalVer {
				maxLocalVer = lv
			}
			if fs[fsi].IsInvalid() {
				ldbRemoveFromGlobal(snap, batch, folder, device, newName)
			} else {
				ldbUpdateGlobal(snap, batch, folder, device, fs[fsi])
			}
			fsi++

		case moreFs && moreDb && cmp == 0:
			// File exists on both sides - compare versions. We might get an
			// update with the same version and different flags if a device has
			// marked a file as invalid, so handle that too.
			if debugDB {
				l.Debugln("generic replace; exists - compare")
			}
			var ef FileInfoTruncated
			ef.UnmarshalXDR(dbi.Value())
			if !fs[fsi].Version.Equal(ef.Version) || fs[fsi].Flags != ef.Flags {
				if debugDB {
					l.Debugln("generic replace; differs - insert")
				}
				if lv := ldbInsert(batch, folder, device, fs[fsi]); lv > maxLocalVer {
					maxLocalVer = lv
				}
				if fs[fsi].IsInvalid() {
					ldbRemoveFromGlobal(snap, batch, folder, device, newName)
				} else {
					ldbUpdateGlobal(snap, batch, folder, device, fs[fsi])
				}
			} else if debugDB {
				l.Debugln("generic replace; equal - ignore")
			}

			fsi++
			moreDb = dbi.Next()

		case moreDb && (!moreFs || cmp == 1):
//.........这里部分代码省略.........

func (db *Instance) withNeed(folder, device []byte, truncate bool, fn Iterator) {
	t := db.newReadOnlyTransaction()
	defer t.close()

	dbi := t.NewIterator(util.BytesPrefix(db.globalKey(folder, nil)[:keyPrefixLen+keyFolderLen]), nil)
	defer dbi.Release()

	var fk []byte
nextFile:
	for dbi.Next() {
		var vl VersionList
		err := vl.UnmarshalXDR(dbi.Value())
		if err != nil {
			panic(err)
		}
		if len(vl.versions) == 0 {
			l.Debugln(dbi.Key())
			panic("no versions?")
		}

		have := false // If we have the file, any version
		need := false // If we have a lower version of the file
		var haveVersion protocol.Vector
		for _, v := range vl.versions {
			if bytes.Equal(v.device, device) {
				have = true
				haveVersion = v.version
				// XXX: This marks Concurrent (i.e. conflicting) changes as
				// needs. Maybe we should do that, but it needs special
				// handling in the puller.
				need = !v.version.GreaterEqual(vl.versions[0].version)
				break
			}
		}

		if need || !have {
			name := db.globalKeyName(dbi.Key())
			needVersion := vl.versions[0].version

		nextVersion:
			for i := range vl.versions {
				if !vl.versions[i].version.Equal(needVersion) {
					// We haven't found a valid copy of the file with the needed version.
					continue nextFile
				}
				fk = db.deviceKeyInto(fk[:cap(fk)], folder, vl.versions[i].device, name)
				bs, err := t.Get(fk, nil)
				if err != nil {
					var id protocol.DeviceID
					copy(id[:], device)
					l.Debugf("device: %v", id)
					l.Debugf("need: %v, have: %v", need, have)
					l.Debugf("key: %q (%x)", dbi.Key(), dbi.Key())
					l.Debugf("vl: %v", vl)
					l.Debugf("i: %v", i)
					l.Debugf("fk: %q (%x)", fk, fk)
					l.Debugf("name: %q (%x)", name, name)
					panic(err)
				}

				gf, err := unmarshalTrunc(bs, truncate)
				if err != nil {
					panic(err)
				}

				if gf.IsInvalid() {
					// The file is marked invalid for whatever reason, don't use it.
					continue nextVersion
				}

				if gf.IsDeleted() && !have {
					// We don't need deleted files that we don't have
					continue nextFile
				}

				l.Debugf("need folder=%q device=%v name=%q need=%v have=%v haveV=%d globalV=%d", folder, protocol.DeviceIDFromBytes(device), name, need, have, haveVersion, vl.versions[0].version)

				if cont := fn(gf); !cont {
					return
				}

				// This file is handled, no need to look further in the version list
				continue nextFile
			}
		}
	}
}

func (db *Instance) genericReplace(folder, device []byte, fs []protocol.FileInfo, localSize, globalSize *sizeTracker, deleteFn deletionHandler) int64 {
	sort.Sort(fileList(fs)) // sort list on name, same as in the database

	t := db.newReadWriteTransaction()
	defer t.close()

	dbi := t.NewIterator(util.BytesPrefix(db.deviceKey(folder, device, nil)[:keyPrefixLen+keyFolderLen+keyDeviceLen]), nil)
	defer dbi.Release()

	moreDb := dbi.Next()
	fsi := 0
	var maxLocalVer int64

	isLocalDevice := bytes.Equal(device, protocol.LocalDeviceID[:])
	for {
		var newName, oldName []byte
		moreFs := fsi < len(fs)

		if !moreDb && !moreFs {
			break
		}

		if moreFs {
			newName = []byte(fs[fsi].Name)
		}

		if moreDb {
			oldName = db.deviceKeyName(dbi.Key())
		}

		cmp := bytes.Compare(newName, oldName)

		l.Debugf("generic replace; folder=%q device=%v moreFs=%v moreDb=%v cmp=%d newName=%q oldName=%q", folder, protocol.DeviceIDFromBytes(device), moreFs, moreDb, cmp, newName, oldName)

		switch {
		case moreFs && (!moreDb || cmp == -1):
			l.Debugln("generic replace; missing - insert")
			// Database is missing this file. Insert it.
			if lv := t.insertFile(folder, device, fs[fsi]); lv > maxLocalVer {
				maxLocalVer = lv
			}
			if isLocalDevice {
				localSize.addFile(fs[fsi])
			}
			if fs[fsi].IsInvalid() {
				t.removeFromGlobal(folder, device, newName, globalSize)
			} else {
				t.updateGlobal(folder, device, fs[fsi], globalSize)
			}
			fsi++

		case moreFs && moreDb && cmp == 0:
			// File exists on both sides - compare versions. We might get an
			// update with the same version and different flags if a device has
			// marked a file as invalid, so handle that too.
			l.Debugln("generic replace; exists - compare")
			var ef FileInfoTruncated
			ef.UnmarshalXDR(dbi.Value())
			if !fs[fsi].Version.Equal(ef.Version) || fs[fsi].Flags != ef.Flags {
				l.Debugln("generic replace; differs - insert")
				if lv := t.insertFile(folder, device, fs[fsi]); lv > maxLocalVer {
					maxLocalVer = lv
				}
				if isLocalDevice {
					localSize.removeFile(ef)
					localSize.addFile(fs[fsi])
				}
				if fs[fsi].IsInvalid() {
					t.removeFromGlobal(folder, device, newName, globalSize)
				} else {
					t.updateGlobal(folder, device, fs[fsi], globalSize)
				}
			} else {
				l.Debugln("generic replace; equal - ignore")
			}

			fsi++
			moreDb = dbi.Next()

		case moreDb && (!moreFs || cmp == 1):
			l.Debugln("generic replace; exists - remove")
			if lv := deleteFn(t, folder, device, oldName, dbi); lv > maxLocalVer {
				maxLocalVer = lv
			}
			moreDb = dbi.Next()
		}

		// Write out and reuse the batch every few records, to avoid the batch
		// growing too large and thus allocating unnecessarily much memory.
		t.checkFlush()
	}

	return maxLocalVer
}