lib/model, lib/protocol: Implement temporary indexes (fixes #950)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/2252

cmd/syncthing/gui.go

@@ -32,6 +32,7 @@ import (
 	"github.com/syncthing/syncthing/lib/discover"
 	"github.com/syncthing/syncthing/lib/events"
 	"github.com/syncthing/syncthing/lib/logger"
+	"github.com/syncthing/syncthing/lib/model"
 	"github.com/syncthing/syncthing/lib/osutil"
 	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syncthing/syncthing/lib/relay"
@@ -85,7 +86,7 @@ type modelIntf interface {
 	CurrentFolderFile(folder string, file string) (protocol.FileInfo, bool)
 	CurrentGlobalFile(folder string, file string) (protocol.FileInfo, bool)
 	ResetFolder(folder string)
-	Availability(folder, file string) []protocol.DeviceID
+	Availability(folder, file string, version protocol.Vector, block protocol.BlockInfo) []model.Availability
 	GetIgnores(folder string) ([]string, []string, error)
 	SetIgnores(folder string, content []string) error
 	PauseDevice(device protocol.DeviceID)
@@ -696,7 +697,7 @@ func (s *apiService) getDBFile(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	av := s.model.Availability(folder, file)
+	av := s.model.Availability(folder, file, protocol.Vector{}, protocol.BlockInfo{})
 	sendJSON(w, map[string]interface{}{
 		"global":       jsonFileInfo(gf),
 		"local":        jsonFileInfo(lf),

cmd/syncthing/mocked_model_test.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/syncthing/syncthing/lib/db"
+	"github.com/syncthing/syncthing/lib/model"
 	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syncthing/syncthing/lib/stats"
 )
@@ -57,7 +58,7 @@ func (m *mockedModel) CurrentGlobalFile(folder string, file string) (protocol.Fi
 func (m *mockedModel) ResetFolder(folder string) {
 }
 
-func (m *mockedModel) Availability(folder, file string) []protocol.DeviceID {
+func (m *mockedModel) Availability(folder, file string, version protocol.Vector, block protocol.BlockInfo) []model.Availability {
 	return nil
 }
 

lib/config/config_test.go

@@ -62,6 +62,7 @@ func TestDefaultValues(t *testing.T) {
 		ReleasesURL:             "https://api.github.com/repos/syncthing/syncthing/releases?per_page=30",
 		AlwaysLocalNets:         []string{},
 		OverwriteNames:          false,
+		TempIndexMinBlocks:      10,
 	}
 
 	cfg := New(device1)
@@ -192,6 +193,7 @@ func TestOverriddenValues(t *testing.T) {
 		ReleasesURL:             "https://localhost/releases",
 		AlwaysLocalNets:         []string{},
 		OverwriteNames:          true,
+		TempIndexMinBlocks:      100,
 	}
 
 	cfg, err := Load("testdata/overridenvalues.xml", device1)

lib/config/folderconfiguration.go

@@ -37,6 +37,7 @@ type FolderConfiguration struct {
 	PullerPauseS          int                         `xml:"pullerPauseS" json:"pullerPauseS"`
 	MaxConflicts          int                         `xml:"maxConflicts" json:"maxConflicts"`
 	DisableSparseFiles    bool                        `xml:"disableSparseFiles" json:"disableSparseFiles"`
+	DisableTempIndexes    bool                        `xml:"disableTempIndexes" json:"disableTempIndexes"`
 
 	Invalid    string `xml:"-" json:"invalid"` // Set at runtime when there is an error, not saved
 	cachedPath string

lib/config/optionsconfiguration.go

@@ -40,6 +40,7 @@ type OptionsConfiguration struct {
 	ReleasesURL             string   `xml:"releasesURL" json:"releasesURL" default:"https://api.github.com/repos/syncthing/syncthing/releases?per_page=30"`
 	AlwaysLocalNets         []string `xml:"alwaysLocalNet" json:"alwaysLocalNets"`
 	OverwriteNames          bool     `xml:"overwriteNames" json:"overwriteNames" default:"false"`
+	TempIndexMinBlocks      int      `xml:"tempIndexMinBlocks" json:"tempIndexMinBlocks" default:"10"`
 
 	DeprecatedUPnPEnabled  bool `xml:"upnpEnabled"`
 	DeprecatedUPnPLeaseM   int  `xml:"upnpLeaseMinutes"`

lib/config/testdata/overridenvalues.xml

@@ -35,5 +35,6 @@
         <urPostInsecurely>true</urPostInsecurely>
         <releasesURL>https://localhost/releases</releasesURL>
         <overwriteNames>true</overwriteNames>
+        <tempIndexMinBlocks>100</tempIndexMinBlocks>
     </options>
 </configuration>

lib/model/deviceactivity.go

@@ -26,28 +26,30 @@ func newDeviceActivity() *deviceActivity {
 	}
 }
 
-func (m *deviceActivity) leastBusy(availability []protocol.DeviceID) protocol.DeviceID {
+func (m *deviceActivity) leastBusy(availability []Availability) (Availability, bool) {
 	m.mut.Lock()
 	low := 2<<30 - 1
-	var selected protocol.DeviceID
-	for _, device := range availability {
-		if usage := m.act[device]; usage < low {
+	found := false
+	var selected Availability
+	for _, info := range availability {
+		if usage := m.act[info.ID]; usage < low {
 			low = usage
-			selected = device
+			selected = info
+			found = true
 		}
 	}
 	m.mut.Unlock()
-	return selected
+	return selected, found
 }
 
-func (m *deviceActivity) using(device protocol.DeviceID) {
+func (m *deviceActivity) using(availability Availability) {
 	m.mut.Lock()
-	m.act[device]++
+	m.act[availability.ID]++
 	m.mut.Unlock()
 }
 
-func (m *deviceActivity) done(device protocol.DeviceID) {
+func (m *deviceActivity) done(availability Availability) {
 	m.mut.Lock()
-	m.act[device]--
+	m.act[availability.ID]--
 	m.mut.Unlock()
 }

lib/model/deviceactivity_test.go

@@ -13,46 +13,48 @@ import (
 )
 
 func TestDeviceActivity(t *testing.T) {
-	n0 := protocol.DeviceID([32]byte{1, 2, 3, 4})
-	n1 := protocol.DeviceID([32]byte{5, 6, 7, 8})
-	n2 := protocol.DeviceID([32]byte{9, 10, 11, 12})
-	devices := []protocol.DeviceID{n0, n1, n2}
+	n0 := Availability{protocol.DeviceID([32]byte{1, 2, 3, 4}), false}
+	n1 := Availability{protocol.DeviceID([32]byte{5, 6, 7, 8}), true}
+	n2 := Availability{protocol.DeviceID([32]byte{9, 10, 11, 12}), false}
+	devices := []Availability{n0, n1, n2}
 	na := newDeviceActivity()
 
-	if lb := na.leastBusy(devices); lb != n0 {
+	if lb, ok := na.leastBusy(devices); !ok || lb != n0 {
 		t.Errorf("Least busy device should be n0 (%v) not %v", n0, lb)
 	}
-	if lb := na.leastBusy(devices); lb != n0 {
+	if lb, ok := na.leastBusy(devices); !ok || lb != n0 {
 		t.Errorf("Least busy device should still be n0 (%v) not %v", n0, lb)
 	}
 
-	na.using(na.leastBusy(devices))
-	if lb := na.leastBusy(devices); lb != n1 {
+	lb, _ := na.leastBusy(devices)
+	na.using(lb)
+	if lb, ok := na.leastBusy(devices); !ok || lb != n1 {
 		t.Errorf("Least busy device should be n1 (%v) not %v", n1, lb)
 	}
-
-	na.using(na.leastBusy(devices))
-	if lb := na.leastBusy(devices); lb != n2 {
+	lb, _ = na.leastBusy(devices)
+	na.using(lb)
+	if lb, ok := na.leastBusy(devices); !ok || lb != n2 {
 		t.Errorf("Least busy device should be n2 (%v) not %v", n2, lb)
 	}
 
-	na.using(na.leastBusy(devices))
-	if lb := na.leastBusy(devices); lb != n0 {
+	lb, _ = na.leastBusy(devices)
+	na.using(lb)
+	if lb, ok := na.leastBusy(devices); !ok || lb != n0 {
 		t.Errorf("Least busy device should be n0 (%v) not %v", n0, lb)
 	}
 
 	na.done(n1)
-	if lb := na.leastBusy(devices); lb != n1 {
+	if lb, ok := na.leastBusy(devices); !ok || lb != n1 {
 		t.Errorf("Least busy device should be n1 (%v) not %v", n1, lb)
 	}
 
 	na.done(n2)
-	if lb := na.leastBusy(devices); lb != n1 {
+	if lb, ok := na.leastBusy(devices); !ok || lb != n1 {
 		t.Errorf("Least busy device should still be n1 (%v) not %v", n1, lb)
 	}
 
 	na.done(n0)
-	if lb := na.leastBusy(devices); lb != n0 {
+	if lb, ok := na.leastBusy(devices); !ok || lb != n0 {
 		t.Errorf("Least busy device should be n0 (%v) not %v", n0, lb)
 	}
 }

lib/model/devicedownloadstate.go

@@ -0,0 +1,156 @@
+// Copyright (C) 2015 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 (
+	"github.com/syncthing/syncthing/lib/protocol"
+	"github.com/syncthing/syncthing/lib/sync"
+)
+
+// deviceFolderFileDownloadState holds current download state of a file that
+// a remote device has advertised. blockIndexes represends indexes within
+// FileInfo.Blocks that the remote device already has, and version represents
+// the version of the file that the remote device is downloading.
+type deviceFolderFileDownloadState struct {
+	blockIndexes []int32
+	version      protocol.Vector
+}
+
+// deviceFolderDownloadState holds current download state of all files that
+// a remote device is currently downloading in a specific folder.
+type deviceFolderDownloadState struct {
+	mut                      sync.RWMutex
+	files                    map[string]deviceFolderFileDownloadState
+	numberOfBlocksInProgress int
+}
+
+// Has returns wether a block at that specific index, and that specific version of the file
+// is currently available on the remote device for pulling from a temporary file.
+func (p *deviceFolderDownloadState) Has(file string, version protocol.Vector, index int32) bool {
+	p.mut.RLock()
+	defer p.mut.RUnlock()
+
+	local, ok := p.files[file]
+
+	if !ok || !local.version.Equal(version) {
+		return false
+	}
+
+	for _, existingIndex := range local.blockIndexes {
+		if existingIndex == index {
+			return true
+		}
+	}
+	return false
+}
+
+// Update updates internal state of what has been downloaded into the temporary
+// files by the remote device for this specific folder.
+func (p *deviceFolderDownloadState) Update(updates []protocol.FileDownloadProgressUpdate) {
+	p.mut.Lock()
+	defer p.mut.Unlock()
+
+	for _, update := range updates {
+		local, ok := p.files[update.Name]
+		if update.UpdateType == protocol.UpdateTypeForget && ok && local.version.Equal(update.Version) {
+			p.numberOfBlocksInProgress -= len(local.blockIndexes)
+			delete(p.files, update.Name)
+		} else if update.UpdateType == protocol.UpdateTypeAppend {
+			if !ok {
+				local = deviceFolderFileDownloadState{
+					blockIndexes: update.BlockIndexes,
+					version:      update.Version,
+				}
+			} else if !local.version.Equal(update.Version) {
+				p.numberOfBlocksInProgress -= len(local.blockIndexes)
+				local.blockIndexes = append(local.blockIndexes[:0], update.BlockIndexes...)
+				local.version = update.Version
+			} else {
+				local.blockIndexes = append(local.blockIndexes, update.BlockIndexes...)
+			}
+			p.files[update.Name] = local
+			p.numberOfBlocksInProgress += len(update.BlockIndexes)
+		}
+	}
+}
+
+// NumberOfBlocksInProgress returns the number of blocks the device has downloaded
+// for a specific folder.
+func (p *deviceFolderDownloadState) NumberOfBlocksInProgress() int {
+	p.mut.RLock()
+	n := p.numberOfBlocksInProgress
+	p.mut.RUnlock()
+	return n
+}
+
+// deviceDownloadState represents the state of all in progress downloads
+// for all folders of a specific device.
+type deviceDownloadState struct {
+	mut                      sync.RWMutex
+	folders                  map[string]*deviceFolderDownloadState
+	numberOfBlocksInProgress int
+}
+
+// Update updates internal state of what has been downloaded into the temporary
+// files by the remote device for this specific folder.
+func (t *deviceDownloadState) Update(folder string, updates []protocol.FileDownloadProgressUpdate) {
+	t.mut.RLock()
+	f, ok := t.folders[folder]
+	t.mut.RUnlock()
+
+	if !ok {
+		f = &deviceFolderDownloadState{
+			mut:   sync.NewRWMutex(),
+			files: make(map[string]deviceFolderFileDownloadState),
+		}
+		t.mut.Lock()
+		t.folders[folder] = f
+		t.mut.Unlock()
+	}
+
+	f.Update(updates)
+}
+
+// Has returns wether block at that specific index, and that specific version of the file
+// is currently available on the remote device for pulling from a temporary file.
+func (t *deviceDownloadState) Has(folder, file string, version protocol.Vector, index int32) bool {
+	if t == nil {
+		return false
+	}
+	t.mut.RLock()
+	f, ok := t.folders[folder]
+	t.mut.RUnlock()
+
+	if !ok {
+		return false
+	}
+
+	return f.Has(file, version, index)
+}
+
+// NumberOfBlocksInProgress returns the number of blocks the device has downloaded
+// for all folders.
+func (t *deviceDownloadState) NumberOfBlocksInProgress() int {
+	if t == nil {
+		return 0
+	}
+
+	n := 0
+	t.mut.RLock()
+	for _, folder := range t.folders {
+		n += folder.NumberOfBlocksInProgress()
+	}
+	t.mut.RUnlock()
+	return n
+}
+
+func newDeviceDownloadState() *deviceDownloadState {
+	return &deviceDownloadState{
+		mut:     sync.NewRWMutex(),
+		folders: make(map[string]*deviceFolderDownloadState),
+	}
+}

lib/model/devicedownloadstate_test.go

@@ -0,0 +1,111 @@
+// Copyright (C) 2016 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 (
+	"testing"
+
+	"github.com/syncthing/syncthing/lib/protocol"
+)
+
+func TestDeviceDownloadState(t *testing.T) {
+	v1 := (protocol.Vector{}).Update(0)
+	v2 := (protocol.Vector{}).Update(1)
+
+	// file 1 version 1 part 1
+	f1v1p1 := protocol.FileDownloadProgressUpdate{protocol.UpdateTypeAppend, "f1", v1, []int32{0, 1, 2}}
+	f1v1p2 := protocol.FileDownloadProgressUpdate{protocol.UpdateTypeAppend, "f1", v1, []int32{3, 4, 5}}
+	f1v1del := protocol.FileDownloadProgressUpdate{protocol.UpdateTypeForget, "f1", v1, nil}
+	f1v2p1 := protocol.FileDownloadProgressUpdate{protocol.UpdateTypeAppend, "f1", v2, []int32{10, 11, 12}}
+	f1v2p2 := protocol.FileDownloadProgressUpdate{protocol.UpdateTypeAppend, "f1", v2, []int32{13, 14, 15}}
+	f1v2del := protocol.FileDownloadProgressUpdate{protocol.UpdateTypeForget, "f1", v2, nil}
+
+	f2v1p1 := protocol.FileDownloadProgressUpdate{protocol.UpdateTypeAppend, "f2", v1, []int32{20, 21, 22}}
+	f2v1p2 := protocol.FileDownloadProgressUpdate{protocol.UpdateTypeAppend, "f2", v1, []int32{23, 24, 25}}
+	f2v1del := protocol.FileDownloadProgressUpdate{protocol.UpdateTypeForget, "f2", v1, nil}
+
+	tests := []struct {
+		updates                  []protocol.FileDownloadProgressUpdate
+		shouldHaveIndexesFrom    []protocol.FileDownloadProgressUpdate
+		shouldNotHaveIndexesFrom []protocol.FileDownloadProgressUpdate
+	}{
+		{ //1
+			[]protocol.FileDownloadProgressUpdate{f1v1p1},
+			[]protocol.FileDownloadProgressUpdate{f1v1p1},
+			[]protocol.FileDownloadProgressUpdate{f1v1p2, f1v2p1, f1v2p2},
+		},
+		{ //2
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f1v1p2},
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f1v1p2},
+			[]protocol.FileDownloadProgressUpdate{f1v2p1, f1v2p2},
+		},
+		{ //3
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f1v1p2, f1v1del},
+			nil,
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f1v1p2, f1v2p1, f1v2p2}},
+		{ //4
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f1v1p2, f1v2del},
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f1v1p2},
+			[]protocol.FileDownloadProgressUpdate{f1v2p1, f1v2p2},
+		},
+		{ //5
+			// v2 replaces old v1 data
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f1v1p2, f1v2p1},
+			[]protocol.FileDownloadProgressUpdate{f1v2p1},
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f1v1p2, f1v2p2},
+		},
+		{ //6
+			// v1 delete on v2 data does nothing
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f1v1p2, f1v2p1, f1v1del},
+			[]protocol.FileDownloadProgressUpdate{f1v2p1},
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f1v1p2, f1v2p2},
+		},
+		{ //7
+			// v2 replacees v1, v2 gets deleted, and v2 part 2 gets added.
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f1v1p2, f1v2p1, f1v2del, f1v2p2},
+			[]protocol.FileDownloadProgressUpdate{f1v2p2},
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f1v1p2, f1v2p1},
+		},
+		// Multiple files in one go
+		{ //8
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f2v1p1},
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f2v1p1},
+			[]protocol.FileDownloadProgressUpdate{f1v1p2, f2v1p2},
+		},
+		{ //9
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f2v1p1, f2v1del},
+			[]protocol.FileDownloadProgressUpdate{f1v1p1},
+			[]protocol.FileDownloadProgressUpdate{f2v1p1, f2v1p1},
+		},
+		{ //10
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f2v1del, f2v1p1},
+			[]protocol.FileDownloadProgressUpdate{f1v1p1, f2v1p1},
+			[]protocol.FileDownloadProgressUpdate{f1v1p2, f2v1p2},
+		},
+	}
+
+	for i, test := range tests {
+		s := newDeviceDownloadState()
+		s.Update("folder", test.updates)
+
+		for _, expected := range test.shouldHaveIndexesFrom {
+			for _, n := range expected.BlockIndexes {
+				if !s.Has("folder", expected.Name, expected.Version, n) {
+					t.Error("Test", i+1, "error:", expected.Name, expected.Version, "missing", n)
+				}
+			}
+		}
+
+		for _, unexpected := range test.shouldNotHaveIndexesFrom {
+			for _, n := range unexpected.BlockIndexes {
+				if s.Has("folder", unexpected.Name, unexpected.Version, n) {
+					t.Error("Test", i+1, "error:", unexpected.Name, unexpected.Version, "has extra", n)
+				}
+			}
+		}
+	}
+}

lib/model/model.go

@@ -60,6 +60,11 @@ type service interface {
 	getState() (folderState, time.Time, error)
 }
 
+type Availability struct {
+	ID            protocol.DeviceID `json:"id"`
+	FromTemporary bool              `json:"fromTemporary"`
+}
+
 type Model struct {
 	*suture.Supervisor
 
@@ -87,10 +92,12 @@ type Model struct {
 	folderStatRefs     map[string]*stats.FolderStatisticsReference            // folder -> statsRef
 	fmut               sync.RWMutex                                           // protects the above
 
-	conn          map[protocol.DeviceID]Connection
-	helloMessages map[protocol.DeviceID]protocol.HelloMessage
-	devicePaused  map[protocol.DeviceID]bool
-	pmut          sync.RWMutex // protects the above
+	conn              map[protocol.DeviceID]Connection
+	helloMessages     map[protocol.DeviceID]protocol.HelloMessage
+	deviceClusterConf map[protocol.DeviceID]protocol.ClusterConfigMessage
+	devicePaused      map[protocol.DeviceID]bool
+	deviceDownloads   map[protocol.DeviceID]*deviceDownloadState
+	pmut              sync.RWMutex // protects the above
 }
 
 var (
@@ -129,10 +136,11 @@ func NewModel(cfg *config.Wrapper, id protocol.DeviceID, deviceName, clientName,
 		folderStatRefs:     make(map[string]*stats.FolderStatisticsReference),
 		conn:               make(map[protocol.DeviceID]Connection),
 		helloMessages:      make(map[protocol.DeviceID]protocol.HelloMessage),
+		deviceClusterConf:  make(map[protocol.DeviceID]protocol.ClusterConfigMessage),
 		devicePaused:       make(map[protocol.DeviceID]bool),
-
-		fmut: sync.NewRWMutex(),
-		pmut: sync.NewRWMutex(),
+		deviceDownloads:    make(map[protocol.DeviceID]*deviceDownloadState),
+		fmut:               sync.NewRWMutex(),
+		pmut:               sync.NewRWMutex(),
 	}
 	if cfg.Options().ProgressUpdateIntervalS > -1 {
 		go m.progressEmitter.Serve()
@@ -388,6 +396,11 @@ func (m *Model) Completion(device protocol.DeviceID, folder string) float64 {
 		return true
 	})
 
+	// This might might be more than it really is, because some blocks can be of a smaller size.
+	m.pmut.RLock()
+	need -= int64(m.deviceDownloads[device].NumberOfBlocksInProgress() * protocol.BlockSize)
+	m.pmut.RUnlock()
+
 	needRatio := float64(need) / float64(tot)
 	completionPct := 100 * (1 - needRatio)
 	l.Debugf("%v Completion(%s, %q): %f (%d / %d = %f)", m, device, folder, completionPct, need, tot, needRatio)
@@ -609,6 +622,10 @@ func (m *Model) folderSharedWithUnlocked(folder string, deviceID protocol.Device
 func (m *Model) ClusterConfig(deviceID protocol.DeviceID, cm protocol.ClusterConfigMessage) {
 	// Check the peer device's announced folders against our own. Emits events
 	// for folders that we don't expect (unknown or not shared).
+	// Also, collect a list of folders we do share, and if he's interested in
+	// temporary indexes, subscribe the connection.
+
+	tempIndexFolders := make([]string, 0, len(cm.Folders))
 
 	m.fmut.Lock()
 nextFolder:
@@ -635,9 +652,24 @@ nextFolder:
 			l.Infof("Unexpected folder ID %q sent from device %q; ensure that the folder exists and that this device is selected under \"Share With\" in the folder configuration.", folder.ID, deviceID)
 			continue
 		}
+		if folder.Flags&protocol.FlagFolderDisabledTempIndexes == 0 {
+			tempIndexFolders = append(tempIndexFolders, folder.ID)
+		}
 	}
 	m.fmut.Unlock()
 
+	// This breaks if we send multiple CM messages during the same connection.
+	if len(tempIndexFolders) > 0 {
+		m.pmut.RLock()
+		conn, ok := m.conn[deviceID]
+		m.pmut.RUnlock()
+		// In case we've got ClusterConfig, and the connection disappeared
+		// from infront of our nose.
+		if ok {
+			m.progressEmitter.temporaryIndexSubscribe(conn, tempIndexFolders)
+		}
+	}
+
 	var changed bool
 
 	if m.cfg.Devices()[deviceID].Introducer {
@@ -645,9 +677,6 @@ nextFolder:
 		// and devices and add what we are missing.
 
 		for _, folder := range cm.Folders {
-			// If we don't have this folder yet, skip it. Ideally, we'd
-			// offer up something in the GUI to create the folder, but for the
-			// moment we only handle folders that we already have.
 			if _, ok := m.folderDevices[folder.ID]; !ok {
 				continue
 			}
@@ -736,10 +765,13 @@ func (m *Model) Close(device protocol.DeviceID, err error) {
 
 	conn, ok := m.conn[device]
 	if ok {
+		m.progressEmitter.temporaryIndexUnsubscribe(conn)
 		closeRawConn(conn)
 	}
 	delete(m.conn, device)
 	delete(m.helloMessages, device)
+	delete(m.deviceClusterConf, device)
+	delete(m.deviceDownloads, device)
 	m.pmut.Unlock()
 }
 
@@ -752,19 +784,20 @@ func (m *Model) Request(deviceID protocol.DeviceID, folder, name string, offset
 
 	if !m.folderSharedWith(folder, deviceID) {
 		l.Warnf("Request from %s for file %s in unshared folder %q", deviceID, name, folder)
-		return protocol.ErrInvalid
+		return protocol.ErrNoSuchFile
 	}
 
-	if flags != 0 {
-		// We don't currently support or expect any flags.
-		return protocol.ErrInvalid
+	if flags != 0 && flags != protocol.FlagFromTemporary {
+		// We currently support only no flags, or FromTemporary flag.
+		return fmt.Errorf("protocol error: unknown flags 0x%x in Request message", flags)
 	}
 
 	if deviceID != protocol.LocalDeviceID {
-		l.Debugf("%v REQ(in): %s: %q / %q o=%d s=%d", m, deviceID, folder, name, offset, len(buf))
+		l.Debugf("%v REQ(in): %s: %q / %q o=%d s=%d f=%d", m, deviceID, folder, name, offset, len(buf), flags)
 	}
 	m.fmut.RLock()
-	folderPath := m.folderCfgs[folder].Path()
+	folderCfg := m.folderCfgs[folder]
+	folderPath := folderCfg.Path()
 	folderIgnores := m.folderIgnores[folder]
 	m.fmut.RUnlock()
 
@@ -802,8 +835,6 @@ func (m *Model) Request(deviceID protocol.DeviceID, folder, name string, offset
 		}
 	}
 
-	var reader io.ReaderAt
-	var err error
 	if info, err := os.Lstat(fn); err == nil && info.Mode()&os.ModeSymlink != 0 {
 		target, _, err := symlinks.Read(fn)
 		if err != nil {
@@ -813,28 +844,30 @@ func (m *Model) Request(deviceID protocol.DeviceID, folder, name string, offset
 			}
 			return protocol.ErrGeneric
 		}
-		reader = strings.NewReader(target)
-	} else {
-		// Cannot easily cache fd's because we might need to delete the file
-		// at any moment.
-		reader, err = os.Open(fn)
-		if err != nil {
-			l.Debugln("os.Open:", err)
-			if os.IsNotExist(err) {
-				return protocol.ErrNoSuchFile
-			}
+		if _, err := strings.NewReader(target).ReadAt(buf, offset); err != nil {
+			l.Debugln("symlink.Reader.ReadAt", err)
 			return protocol.ErrGeneric
 		}
+		return nil
+	}
 
-		defer reader.(*os.File).Close()
+	// Only check temp files if the flag is set, and if we are set to advertise
+	// the temp indexes.
+	if flags&protocol.FlagFromTemporary != 0 && !folderCfg.DisableTempIndexes {
+		tempFn := filepath.Join(folderPath, defTempNamer.TempName(name))
+		if err := readOffsetIntoBuf(tempFn, offset, buf); err == nil {
+			return nil
+		}
+		// Fall through to reading from a non-temp file, just incase the temp
+		// file has finished downloading.
 	}
 
-	_, err = reader.ReadAt(buf, offset)
-	if err != nil {
-		l.Debugln("reader.ReadAt:", err)
+	err := readOffsetIntoBuf(fn, offset, buf)
+	if os.IsNotExist(err) {
+		return protocol.ErrNoSuchFile
+	} else if err != nil {
 		return protocol.ErrGeneric
 	}
-
 	return nil
 }
 
@@ -986,6 +1019,7 @@ func (m *Model) AddConnection(conn Connection, hello protocol.HelloMessage) {
 		panic("add existing device")
 	}
 	m.conn[deviceID] = conn
+	m.deviceDownloads[deviceID] = newDeviceDownloadState()
 
 	m.helloMessages[deviceID] = hello
 
@@ -1040,6 +1074,24 @@ func (m *Model) PauseDevice(device protocol.DeviceID) {
 	events.Default.Log(events.DevicePaused, map[string]string{"device": device.String()})
 }
 
+func (m *Model) DownloadProgress(device protocol.DeviceID, folder string, updates []protocol.FileDownloadProgressUpdate, flags uint32, options []protocol.Option) {
+	if !m.folderSharedWith(folder, device) {
+		return
+	}
+
+	m.fmut.RLock()
+	cfg, ok := m.folderCfgs[folder]
+	m.fmut.RUnlock()
+
+	if !ok || cfg.ReadOnly || cfg.DisableTempIndexes {
+		return
+	}
+
+	m.pmut.RLock()
+	m.deviceDownloads[device].Update(folder, updates)
+	m.pmut.RUnlock()
+}
+
 func (m *Model) ResumeDevice(device protocol.DeviceID) {
 	m.pmut.Lock()
 	m.devicePaused[device] = false
@@ -1211,7 +1263,7 @@ func (m *Model) updateLocals(folder string, fs []protocol.FileInfo) {
 	})
 }
 
-func (m *Model) requestGlobal(deviceID protocol.DeviceID, folder, name string, offset int64, size int, hash []byte, flags uint32, options []protocol.Option) ([]byte, error) {
+func (m *Model) requestGlobal(deviceID protocol.DeviceID, folder, name string, offset int64, size int, hash []byte, fromTemporary bool) ([]byte, error) {
 	m.pmut.RLock()
 	nc, ok := m.conn[deviceID]
 	m.pmut.RUnlock()
@@ -1220,9 +1272,9 @@ func (m *Model) requestGlobal(deviceID protocol.DeviceID, folder, name string, o
 		return nil, fmt.Errorf("requestGlobal: no such device: %s", deviceID)
 	}
 
-	l.Debugf("%v REQ(out): %s: %q / %q o=%d s=%d h=%x f=%x op=%s", m, deviceID, folder, name, offset, size, hash, flags, options)
+	l.Debugf("%v REQ(out): %s: %q / %q o=%d s=%d h=%x ft=%t op=%s", m, deviceID, folder, name, offset, size, hash, fromTemporary)
 
-	return nc.Request(folder, name, offset, size, hash, flags, options)
+	return nc.Request(folder, name, offset, size, hash, fromTemporary)
 }
 
 func (m *Model) AddFolder(cfg config.FolderConfiguration) {
@@ -1553,6 +1605,9 @@ func (m *Model) generateClusterConfig(device protocol.DeviceID) protocol.Cluster
 		if folderCfg.IgnoreDelete {
 			flags |= protocol.FlagFolderIgnoreDelete
 		}
+		if folderCfg.DisableTempIndexes {
+			flags |= protocol.FlagFolderDisabledTempIndexes
+		}
 		protocolFolder.Flags = flags
 		for _, device := range m.folderDevices[folder] {
 			// DeviceID is a value type, but with an underlying array. Copy it
@@ -1736,7 +1791,7 @@ func (m *Model) GlobalDirectoryTree(folder, prefix string, levels int, dirsonly
 	return output
 }
 
-func (m *Model) Availability(folder, file string) []protocol.DeviceID {
+func (m *Model) Availability(folder, file string, version protocol.Vector, block protocol.BlockInfo) []Availability {
 	// Acquire this lock first, as the value returned from foldersFiles can
 	// get heavily modified on Close()
 	m.pmut.RLock()
@@ -1744,19 +1799,27 @@ func (m *Model) Availability(folder, file string) []protocol.DeviceID {
 
 	m.fmut.RLock()
 	fs, ok := m.folderFiles[folder]
+	devices := m.folderDevices[folder]
 	m.fmut.RUnlock()
 	if !ok {
 		return nil
 	}
 
-	availableDevices := []protocol.DeviceID{}
+	var availabilities []Availability
 	for _, device := range fs.Availability(file) {
 		_, ok := m.conn[device]
 		if ok {
-			availableDevices = append(availableDevices, device)
+			availabilities = append(availabilities, Availability{ID: device, FromTemporary: false})
 		}
 	}
-	return availableDevices
+
+	for _, device := range devices {
+		if m.deviceDownloads[device].Has(folder, file, version, int32(block.Offset/protocol.BlockSize)) {
+			availabilities = append(availabilities, Availability{ID: device, FromTemporary: true})
+		}
+	}
+
+	return availabilities
 }
 
 // BringToFront bumps the given files priority in the job queue.
@@ -2086,6 +2149,21 @@ func stringSliceWithout(ss []string, s string) []string {
 	return ss
 }
 
+func readOffsetIntoBuf(file string, offset int64, buf []byte) error {
+	fd, err := os.Open(file)
+	if err != nil {
+		l.Debugln("readOffsetIntoBuf.Open", file, err)
+		return err
+	}
+
+	defer fd.Close()
+	_, err = fd.ReadAt(buf, offset)
+	if err != nil {
+		l.Debugln("readOffsetIntoBuf.ReadAt", file, err)
+	}
+	return err
+}
+
 // The exists function is expected to return true for all known paths
 // (excluding "" and ".")
 func unifySubs(dirs []string, exists func(dir string) bool) []string {

lib/model/model_test.go

@@ -203,9 +203,17 @@ func benchmarkIndexUpdate(b *testing.B, nfiles, nufiles int) {
 	b.ReportAllocs()
 }
 
+type downloadProgressMessage struct {
+	folder  string
+	updates []protocol.FileDownloadProgressUpdate
+	flags   uint32
+	options []protocol.Option
+}
+
 type FakeConnection struct {
-	id          protocol.DeviceID
-	requestData []byte
+	id                       protocol.DeviceID
+	requestData              []byte
+	downloadProgressMessages []downloadProgressMessage
 }
 
 func (FakeConnection) Close() error {
@@ -235,7 +243,7 @@ func (FakeConnection) IndexUpdate(string, []protocol.FileInfo, uint32, []protoco
 	return nil
 }
 
-func (f FakeConnection) Request(folder, name string, offset int64, size int, hash []byte, flags uint32, options []protocol.Option) ([]byte, error) {
+func (f FakeConnection) Request(folder, name string, offset int64, size int, hash []byte, fromTemporary bool) ([]byte, error) {
 	return f.requestData, nil
 }
 
@@ -253,6 +261,15 @@ func (FakeConnection) Statistics() protocol.Statistics {
 	return protocol.Statistics{}
 }
 
+func (f *FakeConnection) DownloadProgress(folder string, updates []protocol.FileDownloadProgressUpdate, flags uint32, options []protocol.Option) {
+	f.downloadProgressMessages = append(f.downloadProgressMessages, downloadProgressMessage{
+		folder:  folder,
+		updates: updates,
+		flags:   flags,
+		options: options,
+	})
+}
+
 func BenchmarkRequest(b *testing.B) {
 	db := db.OpenMemory()
 	m := NewModel(defaultConfig, protocol.LocalDeviceID, "device", "syncthing", "dev", db, nil)
@@ -271,7 +288,7 @@ func BenchmarkRequest(b *testing.B) {
 		}
 	}
 
-	fc := FakeConnection{
+	fc := &FakeConnection{
 		id:          device1,
 		requestData: []byte("some data to return"),
 	}
@@ -284,7 +301,7 @@ func BenchmarkRequest(b *testing.B) {
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		data, err := m.requestGlobal(device1, "default", files[i%n].Name, 0, 32, nil, 0, nil)
+		data, err := m.requestGlobal(device1, "default", files[i%n].Name, 0, 32, nil, false)
 		if err != nil {
 			b.Error(err)
 		}
@@ -318,7 +335,7 @@ func TestDeviceRename(t *testing.T) {
 
 	conn := Connection{
 		&net.TCPConn{},
-		FakeConnection{
+		&FakeConnection{
 			id:          device1,
 			requestData: []byte("some data to return"),
 		},

lib/model/progressemitter.go

@@ -9,19 +9,22 @@ package model
 import (
 	"fmt"
 	"path/filepath"
-	"reflect"
 	"time"
 
 	"github.com/syncthing/syncthing/lib/config"
 	"github.com/syncthing/syncthing/lib/events"
+	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syncthing/syncthing/lib/sync"
 )
 
 type ProgressEmitter struct {
-	registry map[string]*sharedPullerState
-	interval time.Duration
-	last     map[string]map[string]*pullerProgress
-	mut      sync.Mutex
+	registry           map[string]*sharedPullerState
+	interval           time.Duration
+	minBlocks          int
+	lastUpdate         time.Time
+	sentDownloadStates map[protocol.DeviceID]*sentDownloadState // States representing what we've sent to the other peer via DownloadProgress messages.
+	connections        map[string][]protocol.Connection
+	mut                sync.Mutex
 
 	timer *time.Timer
 
@@ -32,11 +35,12 @@ type ProgressEmitter struct {
 // DownloadProgress events every interval.
 func NewProgressEmitter(cfg *config.Wrapper) *ProgressEmitter {
 	t := &ProgressEmitter{
-		stop:     make(chan struct{}),
-		registry: make(map[string]*sharedPullerState),
-		last:     make(map[string]map[string]*pullerProgress),
-		timer:    time.NewTimer(time.Millisecond),
-		mut:      sync.NewMutex(),
+		stop:               make(chan struct{}),
+		registry:           make(map[string]*sharedPullerState),
+		timer:              time.NewTimer(time.Millisecond),
+		sentDownloadStates: make(map[protocol.DeviceID]*sentDownloadState),
+		connections:        make(map[string][]protocol.Connection),
+		mut:                sync.NewMutex(),
 	}
 
 	t.CommitConfiguration(config.Configuration{}, cfg.Raw())
@@ -48,6 +52,8 @@ func NewProgressEmitter(cfg *config.Wrapper) *ProgressEmitter {
 // Serve starts the progress emitter which starts emitting DownloadProgress
 // events as the progress happens.
 func (t *ProgressEmitter) Serve() {
+	var lastUpdate time.Time
+	var lastCount, newCount int
 	for {
 		select {
 		case <-t.stop:
@@ -56,21 +62,28 @@ func (t *ProgressEmitter) Serve() {
 		case <-t.timer.C:
 			t.mut.Lock()
 			l.Debugln("progress emitter: timer - looking after", len(t.registry))
-			output := make(map[string]map[string]*pullerProgress)
+
+			newLastUpdated := lastUpdate
+			newCount = len(t.registry)
 			for _, puller := range t.registry {
-				if output[puller.folder] == nil {
-					output[puller.folder] = make(map[string]*pullerProgress)
+				updated := puller.Updated()
+				if updated.After(newLastUpdated) {
+					newLastUpdated = updated
 				}
-				output[puller.folder][puller.file.Name] = puller.Progress()
 			}
-			if !reflect.DeepEqual(t.last, output) {
-				events.Default.Log(events.DownloadProgress, output)
-				t.last = output
-				l.Debugf("progress emitter: emitting %#v", output)
+
+			if !newLastUpdated.Equal(lastUpdate) || newCount != lastCount {
+				lastUpdate = newLastUpdated
+				lastCount = newCount
+				t.sendDownloadProgressEvent()
+				if len(t.connections) > 0 {
+					t.sendDownloadProgressMessages()
+				}
 			} else {
 				l.Debugln("progress emitter: nothing new")
 			}
-			if len(t.registry) != 0 {
+
+			if newCount != 0 {
 				t.timer.Reset(t.interval)
 			}
 			t.mut.Unlock()
@@ -78,6 +91,95 @@ func (t *ProgressEmitter) Serve() {
 	}
 }
 
+func (t *ProgressEmitter) sendDownloadProgressEvent() {
+	// registry lock already held
+	output := make(map[string]map[string]*pullerProgress)
+	for _, puller := range t.registry {
+		if output[puller.folder] == nil {
+			output[puller.folder] = make(map[string]*pullerProgress)
+		}
+		output[puller.folder][puller.file.Name] = puller.Progress()
+	}
+	events.Default.Log(events.DownloadProgress, output)
+	l.Debugf("progress emitter: emitting %#v", output)
+}
+
+func (t *ProgressEmitter) sendDownloadProgressMessages() {
+	// registry lock already held
+	sharedFolders := make(map[protocol.DeviceID][]string)
+	deviceConns := make(map[protocol.DeviceID]protocol.Connection)
+	subscribers := t.connections
+	for folder, conns := range subscribers {
+		for _, conn := range conns {
+			id := conn.ID()
+
+			deviceConns[id] = conn
+			sharedFolders[id] = append(sharedFolders[id], folder)
+
+			state, ok := t.sentDownloadStates[id]
+			if !ok {
+				state = &sentDownloadState{
+					folderStates: make(map[string]*sentFolderDownloadState),
+				}
+				t.sentDownloadStates[id] = state
+			}
+
+			var activePullers []*sharedPullerState
+			for _, puller := range t.registry {
+				if puller.folder != folder || puller.file.IsSymlink() || puller.file.IsDirectory() || len(puller.file.Blocks) <= t.minBlocks {
+					continue
+				}
+				activePullers = append(activePullers, puller)
+			}
+
+			// For every new puller that hasn't yet been seen, it will send all the blocks the puller has available
+			// For every existing puller, it will check for new blocks, and send update for the new blocks only
+			// For every puller that we've seen before but is no longer there, we will send a forget message
+			updates := state.update(folder, activePullers)
+
+			if len(updates) > 0 {
+				conn.DownloadProgress(folder, updates, 0, nil)
+			}
+		}
+	}
+
+	// Clean up sentDownloadStates for devices which we are no longer connected to.
+	for id := range t.sentDownloadStates {
+		_, ok := deviceConns[id]
+		if !ok {
+			// Null out outstanding entries for device
+			delete(t.sentDownloadStates, id)
+		}
+	}
+
+	// If a folder was unshared from some device, tell it that all temp files
+	// are now gone.
+	for id, sharedDeviceFolders := range sharedFolders {
+		state := t.sentDownloadStates[id]
+	nextFolder:
+		// For each of the folders that the state is aware of,
+		// try to match it with a shared folder we've discovered above,
+		for _, folder := range state.folders() {
+			for _, existingFolder := range sharedDeviceFolders {
+				if existingFolder == folder {
+					continue nextFolder
+				}
+			}
+
+			// If we fail to find that folder, we tell the state to forget about it
+			// and return us a list of updates which would clean up the state
+			// on the remote end.
+			updates := state.cleanup(folder)
+			if len(updates) > 0 {
+				// XXX: Don't send this now, as the only way we've unshared a folder
+				// is by breaking the connection and reconnecting, hence sending
+				// forget messages for some random folder currently makes no sense.
+				// deviceConns[id].DownloadProgress(folder, updates, 0, nil)
+			}
+		}
+	}
+}
+
 // VerifyConfiguration implements the config.Committer interface
 func (t *ProgressEmitter) VerifyConfiguration(from, to config.Configuration) error {
 	return nil
@@ -89,6 +191,7 @@ func (t *ProgressEmitter) CommitConfiguration(from, to config.Configuration) boo
 	defer t.mut.Unlock()
 
 	t.interval = time.Duration(to.Options.ProgressUpdateIntervalS) * time.Second
+	t.minBlocks = to.Options.TempIndexMinBlocks
 	l.Debugln("progress emitter: updated interval", t.interval)
 
 	return true
@@ -115,7 +218,9 @@ func (t *ProgressEmitter) Register(s *sharedPullerState) {
 func (t *ProgressEmitter) Deregister(s *sharedPullerState) {
 	t.mut.Lock()
 	defer t.mut.Unlock()
+
 	l.Debugln("progress emitter: deregistering", s.folder, s.file.Name)
+
 	delete(t.registry, filepath.Join(s.folder, s.file.Name))
 }
 
@@ -142,3 +247,38 @@ func (t *ProgressEmitter) lenRegistry() int {
 	defer t.mut.Unlock()
 	return len(t.registry)
 }
+
+func (t *ProgressEmitter) temporaryIndexSubscribe(conn protocol.Connection, folders []string) {
+	t.mut.Lock()
+	for _, folder := range folders {
+		t.connections[folder] = append(t.connections[folder], conn)
+	}
+	t.mut.Unlock()
+}
+
+func (t *ProgressEmitter) temporaryIndexUnsubscribe(conn protocol.Connection) {
+	t.mut.Lock()
+	left := make(map[string][]protocol.Connection, len(t.connections))
+	for folder, conns := range t.connections {
+		connsLeft := connsWithout(conns, conn)
+		if len(connsLeft) > 0 {
+			left[folder] = connsLeft
+		}
+	}
+	t.connections = left
+	t.mut.Unlock()
+}
+
+func connsWithout(conns []protocol.Connection, conn protocol.Connection) []protocol.Connection {
+	if len(conns) == 0 {
+		return nil
+	}
+
+	newConns := make([]protocol.Connection, 0, len(conns)-1)
+	for _, existingConn := range conns {
+		if existingConn != conn {
+			newConns = append(newConns, existingConn)
+		}
+	}
+	return newConns
+}

lib/model/progressemitter_test.go

@@ -7,34 +7,46 @@
 package model
 
 import (
+	"fmt"
+	"path/filepath"
+	"runtime"
 	"testing"
 	"time"
 
 	"github.com/syncthing/syncthing/lib/config"
 	"github.com/syncthing/syncthing/lib/events"
+	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syncthing/syncthing/lib/sync"
 )
 
-var timeout = 10 * time.Millisecond
+var timeout = 100 * time.Millisecond
+
+func caller(skip int) string {
+	_, file, line, ok := runtime.Caller(skip + 1)
+	if !ok {
+		return "unknown"
+	}
+	return fmt.Sprintf("%s:%d", filepath.Base(file), line)
+}
 
 func expectEvent(w *events.Subscription, t *testing.T, size int) {
 	event, err := w.Poll(timeout)
 	if err != nil {
-		t.Fatal("Unexpected error:", err)
+		t.Fatal("Unexpected error:", err, "at", caller(1))
 	}
 	if event.Type != events.DownloadProgress {
-		t.Fatal("Unexpected event:", event)
+		t.Fatal("Unexpected event:", event, "at", caller(1))
 	}
 	data := event.Data.(map[string]map[string]*pullerProgress)
 	if len(data) != size {
-		t.Fatal("Unexpected event data size:", data)
+		t.Fatal("Unexpected event data size:", data, "at", caller(1))
 	}
 }
 
 func expectTimeout(w *events.Subscription, t *testing.T) {
 	_, err := w.Poll(timeout)
 	if err != events.ErrTimeout {
-		t.Fatal("Unexpected non-Timeout error:", err)
+		t.Fatal("Unexpected non-Timeout error:", err, "at", caller(1))
 	}
 }
 
@@ -52,14 +64,15 @@ func TestProgressEmitter(t *testing.T) {
 	expectTimeout(w, t)
 
 	s := sharedPullerState{
-		mut: sync.NewMutex(),
+		updated: time.Now(),
+		mut:     sync.NewRWMutex(),
 	}
 	p.Register(&s)
 
 	expectEvent(w, t, 1)
 	expectTimeout(w, t)
 
-	s.copyDone()
+	s.copyDone(protocol.BlockInfo{})
 
 	expectEvent(w, t, 1)
 	expectTimeout(w, t)
@@ -74,7 +87,7 @@ func TestProgressEmitter(t *testing.T) {
 	expectEvent(w, t, 1)
 	expectTimeout(w, t)
 
-	s.pullDone()
+	s.pullDone(protocol.BlockInfo{})
 
 	expectEvent(w, t, 1)
 	expectTimeout(w, t)
@@ -85,3 +98,335 @@ func TestProgressEmitter(t *testing.T) {
 	expectTimeout(w, t)
 
 }
+
+func TestSendDownloadProgressMessages(t *testing.T) {
+
+	c := config.Wrap("/tmp/test", config.Configuration{})
+	c.SetOptions(config.OptionsConfiguration{
+		ProgressUpdateIntervalS: 0,
+		TempIndexMinBlocks:      10,
+	})
+
+	fc := &FakeConnection{}
+
+	p := NewProgressEmitter(c)
+	p.temporaryIndexSubscribe(fc, []string{"folder", "folder2"})
+
+	expect := func(updateIdx int, state *sharedPullerState, updateType uint32, version protocol.Vector, blocks []int32, remove bool) {
+		messageIdx := -1
+		for i, msg := range fc.downloadProgressMessages {
+			if msg.folder == state.folder {
+				messageIdx = i
+				break
+			}
+		}
+		if messageIdx < 0 {
+			t.Errorf("Message for folder %s does not exist at %s", state.folder, caller(1))
+		}
+
+		msg := fc.downloadProgressMessages[messageIdx]
+
+		// Don't know the index (it's random due to iterating maps)
+		if updateIdx == -1 {
+			for i, upd := range msg.updates {
+				if upd.Name == state.file.Name {
+					updateIdx = i
+					break
+				}
+			}
+		}
+
+		if updateIdx == -1 {
+			t.Errorf("Could not find update for %s at %s", state.file.Name, caller(1))
+		}
+
+		if updateIdx > len(msg.updates)-1 {
+			t.Errorf("Update at index %d does not exist at %s", updateIdx, caller(1))
+		}
+
+		update := msg.updates[updateIdx]
+
+		if update.UpdateType != updateType {
+			t.Errorf("Wrong update type at %s", caller(1))
+		}
+
+		if !update.Version.Equal(version) {
+			t.Errorf("Wrong version at %s", caller(1))
+		}
+
+		if len(update.BlockIndexes) != len(blocks) {
+			t.Errorf("Wrong indexes. Have %d expect %d at %s", len(update.BlockIndexes), len(blocks), caller(1))
+		}
+		for i := range update.BlockIndexes {
+			if update.BlockIndexes[i] != blocks[i] {
+				t.Errorf("Index %d incorrect at %s", i, caller(1))
+			}
+		}
+
+		if remove {
+			fc.downloadProgressMessages = append(fc.downloadProgressMessages[:messageIdx], fc.downloadProgressMessages[messageIdx+1:]...)
+		}
+	}
+	expectEmpty := func() {
+		if len(fc.downloadProgressMessages) > 0 {
+			t.Errorf("Still have something at %s: %#v", caller(1), fc.downloadProgressMessages)
+		}
+	}
+
+	now := time.Now()
+	tick := func() time.Time {
+		now = now.Add(time.Second)
+		return now
+	}
+
+	if len(fc.downloadProgressMessages) != 0 {
+		t.Error("Expected no requests")
+	}
+
+	v1 := (protocol.Vector{}).Update(0)
+	v2 := (protocol.Vector{}).Update(1)
+
+	// Requires more than 10 blocks to work.
+	blocks := make([]protocol.BlockInfo, 11, 11)
+
+	state1 := &sharedPullerState{
+		folder: "folder",
+		file: protocol.FileInfo{
+			Name:    "state1",
+			Version: v1,
+			Blocks:  blocks,
+		},
+		mut:              sync.NewRWMutex(),
+		availableUpdated: time.Now(),
+	}
+	p.registry["1"] = state1
+
+	// Has no blocks, hence no message is sent
+	p.sendDownloadProgressMessages()
+	expectEmpty()
+
+	// Returns update for puller with new extra blocks
+	state1.available = []int32{1}
+	p.sendDownloadProgressMessages()
+
+	expect(0, state1, protocol.UpdateTypeAppend, v1, []int32{1}, true)
+	expectEmpty()
+
+	// Does nothing if nothing changes
+	p.sendDownloadProgressMessages()
+	expectEmpty()
+
+	// Does nothing if timestamp updated, but no new blocks (should never happen)
+	state1.availableUpdated = tick()
+
+	p.sendDownloadProgressMessages()
+	expectEmpty()
+
+	// Does not return an update if date blocks change but date does not (should never happen)
+	state1.available = []int32{1, 2}
+
+	p.sendDownloadProgressMessages()
+	expectEmpty()
+
+	// If the date and blocks changes, returns only the diff
+	state1.availableUpdated = tick()
+
+	p.sendDownloadProgressMessages()
+
+	expect(0, state1, protocol.UpdateTypeAppend, v1, []int32{2}, true)
+	expectEmpty()
+
+	// Returns forget and update if puller version has changed
+	state1.file.Version = v2
+
+	p.sendDownloadProgressMessages()
+
+	expect(0, state1, protocol.UpdateTypeForget, v1, nil, false)
+	expect(1, state1, protocol.UpdateTypeAppend, v2, []int32{1, 2}, true)
+	expectEmpty()
+
+	// Sends an empty update if new file exists, but does not have any blocks yet. (To indicate that the old blocks are no longer available)
+	state1.file.Version = v1
+	state1.available = nil
+	state1.availableUpdated = tick()
+
+	p.sendDownloadProgressMessages()
+
+	expect(0, state1, protocol.UpdateTypeForget, v2, nil, false)
+	expect(1, state1, protocol.UpdateTypeAppend, v1, nil, true)
+	expectEmpty()
+
+	// Updates for multiple files and folders can be combined
+	state1.available = []int32{1, 2, 3}
+	state1.availableUpdated = tick()
+
+	state2 := &sharedPullerState{
+		folder: "folder2",
+		file: protocol.FileInfo{
+			Name:    "state2",
+			Version: v1,
+			Blocks:  blocks,
+		},
+		mut:              sync.NewRWMutex(),
+		available:        []int32{1, 2, 3},
+		availableUpdated: time.Now(),
+	}
+	state3 := &sharedPullerState{
+		folder: "folder",
+		file: protocol.FileInfo{
+			Name:    "state3",
+			Version: v1,
+			Blocks:  blocks,
+		},
+		mut:              sync.NewRWMutex(),
+		available:        []int32{1, 2, 3},
+		availableUpdated: time.Now(),
+	}
+	state4 := &sharedPullerState{
+		folder: "folder2",
+		file: protocol.FileInfo{
+			Name:    "state4",
+			Version: v1,
+			Blocks:  blocks,
+		},
+		mut:              sync.NewRWMutex(),
+		available:        []int32{1, 2, 3},
+		availableUpdated: time.Now(),
+	}
+	p.registry["2"] = state2
+	p.registry["3"] = state3
+	p.registry["4"] = state4
+
+	p.sendDownloadProgressMessages()
+
+	expect(-1, state1, protocol.UpdateTypeAppend, v1, []int32{1, 2, 3}, false)
+	expect(-1, state3, protocol.UpdateTypeAppend, v1, []int32{1, 2, 3}, true)
+	expect(-1, state2, protocol.UpdateTypeAppend, v1, []int32{1, 2, 3}, false)
+	expect(-1, state4, protocol.UpdateTypeAppend, v1, []int32{1, 2, 3}, true)
+	expectEmpty()
+
+	// Returns forget if puller no longer exists, as well as updates if it has been updated.
+	state1.available = []int32{1, 2, 3, 4, 5}
+	state1.availableUpdated = tick()
+	state2.available = []int32{1, 2, 3, 4, 5}
+	state2.availableUpdated = tick()
+
+	delete(p.registry, "3")
+	delete(p.registry, "4")
+
+	p.sendDownloadProgressMessages()
+
+	expect(-1, state1, protocol.UpdateTypeAppend, v1, []int32{4, 5}, false)
+	expect(-1, state3, protocol.UpdateTypeForget, v1, nil, true)
+	expect(-1, state2, protocol.UpdateTypeAppend, v1, []int32{4, 5}, false)
+	expect(-1, state4, protocol.UpdateTypeForget, v1, nil, true)
+	expectEmpty()
+
+	// Deletions are sent only once (actual bug I found writing the tests)
+	p.sendDownloadProgressMessages()
+	p.sendDownloadProgressMessages()
+	expectEmpty()
+
+	// Not sent for "inactive" (symlinks, dirs, or wrong folder) pullers
+	// Directory
+	state5 := &sharedPullerState{
+		folder: "folder",
+		file: protocol.FileInfo{
+			Name:    "state5",
+			Version: v1,
+			Flags:   protocol.FlagDirectory,
+			Blocks:  blocks,
+		},
+		mut:              sync.NewRWMutex(),
+		available:        []int32{1, 2, 3},
+		availableUpdated: time.Now(),
+	}
+	// Symlink
+	state6 := &sharedPullerState{
+		folder: "folder",
+		file: protocol.FileInfo{
+			Name:    "state6",
+			Version: v1,
+			Flags:   protocol.FlagSymlink,
+		},
+		mut:              sync.NewRWMutex(),
+		available:        []int32{1, 2, 3},
+		availableUpdated: time.Now(),
+	}
+	// Some other directory
+	state7 := &sharedPullerState{
+		folder: "folderXXX",
+		file: protocol.FileInfo{
+			Name:    "state7",
+			Version: v1,
+			Blocks:  blocks,
+		},
+		mut:              sync.NewRWMutex(),
+		available:        []int32{1, 2, 3},
+		availableUpdated: time.Now(),
+	}
+	// Less than 10 blocks
+	state8 := &sharedPullerState{
+		folder: "folder",
+		file: protocol.FileInfo{
+			Name:    "state8",
+			Version: v1,
+			Blocks:  blocks[:3],
+		},
+		mut:              sync.NewRWMutex(),
+		available:        []int32{1, 2, 3},
+		availableUpdated: time.Now(),
+	}
+	p.registry["5"] = state5
+	p.registry["6"] = state6
+	p.registry["7"] = state7
+	p.registry["8"] = state8
+
+	p.sendDownloadProgressMessages()
+
+	expectEmpty()
+
+	// Device is no longer subscribed to a particular folder
+	delete(p.registry, "1") // Clean up first
+	delete(p.registry, "2") // Clean up first
+
+	p.sendDownloadProgressMessages()
+	expect(-1, state1, protocol.UpdateTypeForget, v1, nil, true)
+	expect(-1, state2, protocol.UpdateTypeForget, v1, nil, true)
+
+	expectEmpty()
+
+	p.registry["1"] = state1
+	p.registry["2"] = state2
+	p.registry["3"] = state3
+	p.registry["4"] = state4
+
+	p.sendDownloadProgressMessages()
+
+	expect(-1, state1, protocol.UpdateTypeAppend, v1, []int32{1, 2, 3, 4, 5}, false)
+	expect(-1, state3, protocol.UpdateTypeAppend, v1, []int32{1, 2, 3}, true)
+	expect(-1, state2, protocol.UpdateTypeAppend, v1, []int32{1, 2, 3, 4, 5}, false)
+	expect(-1, state4, protocol.UpdateTypeAppend, v1, []int32{1, 2, 3}, true)
+	expectEmpty()
+
+	p.temporaryIndexUnsubscribe(fc)
+	p.temporaryIndexSubscribe(fc, []string{"folder"})
+
+	p.sendDownloadProgressMessages()
+
+	// See progressemitter.go for explanation why this is commented out.
+	// Search for state.cleanup
+	//expect(-1, state2, protocol.UpdateTypeForget, v1, nil, false)
+	//expect(-1, state4, protocol.UpdateTypeForget, v1, nil, true)
+
+	expectEmpty()
+
+	// Cleanup when device no longer exists
+	p.temporaryIndexUnsubscribe(fc)
+
+	p.sendDownloadProgressMessages()
+	_, ok := p.sentDownloadStates[fc.ID()]
+	if ok {
+		t.Error("Should not be there")
+	}
+}

lib/model/rwfolder.go

@@ -970,9 +970,9 @@ func (p *rwFolder) handleFile(file protocol.FileInfo, copyChan chan<- copyBlocks
 
 	scanner.PopulateOffsets(file.Blocks)
 
-	reused := 0
 	var blocks []protocol.BlockInfo
 	var blocksSize int64
+	var reused []int32
 
 	// Check for an old temporary file which might have some blocks we could
 	// reuse.
@@ -988,25 +988,27 @@ func (p *rwFolder) handleFile(file protocol.FileInfo, copyChan chan<- copyBlocks
 		}
 
 		// Since the blocks are already there, we don't need to get them.
-		for _, block := range file.Blocks {
+		for i, block := range file.Blocks {
 			_, ok := existingBlocks[block.String()]
 			if !ok {
 				blocks = append(blocks, block)
 				blocksSize += int64(block.Size)
+			} else {
+				reused = append(reused, int32(i))
 			}
 		}
 
 		// 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 {
+		if len(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
+		// Copy the blocks, as we don't want to shuffle them on the FileInfo
+		blocks = append(blocks, file.Blocks...)
 		blocksSize = file.Size()
 	}
 
@@ -1018,6 +1020,12 @@ func (p *rwFolder) handleFile(file protocol.FileInfo, copyChan chan<- copyBlocks
 		}
 	}
 
+	// Shuffle the blocks
+	for i := range blocks {
+		j := rand.Intn(i + 1)
+		blocks[i], blocks[j] = blocks[j], blocks[i]
+	}
+
 	events.Default.Log(events.ItemStarted, map[string]string{
 		"folder": p.folder,
 		"item":   file.Name,
@@ -1026,17 +1034,20 @@ func (p *rwFolder) handleFile(file protocol.FileInfo, copyChan chan<- copyBlocks
 	})
 
 	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,
+		file:             file,
+		folder:           p.folder,
+		tempName:         tempName,
+		realName:         realName,
+		copyTotal:        len(blocks),
+		copyNeeded:       len(blocks),
+		reused:           len(reused),
+		updated:          time.Now(),
+		available:        reused,
+		availableUpdated: time.Now(),
+		ignorePerms:      p.ignorePermissions(file),
+		version:          curFile.Version,
+		mut:              sync.NewRWMutex(),
+		sparse:           p.allowSparse,
 	}
 
 	l.Debugf("%v need file %s; copy %d, reused %v", p, file.Name, len(blocks), reused)
@@ -1184,7 +1195,7 @@ func (p *rwFolder) copierRoutine(in <-chan copyBlocksState, pullChan chan<- pull
 				}
 				pullChan <- ps
 			} else {
-				state.copyDone()
+				state.copyDone(block)
 			}
 		}
 		out <- state.sharedPullerState
@@ -1210,19 +1221,19 @@ func (p *rwFolder) pullerRoutine(in <-chan pullBlockState, out chan<- *sharedPul
 		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()
+			state.pullDone(state.block)
 			out <- state.sharedPullerState
 			continue
 		}
 
 		var lastError error
-		potentialDevices := p.model.Availability(p.folder, state.file.Name)
+		candidates := p.model.Availability(p.folder, state.file.Name, state.file.Version, state.block)
 		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{}) {
+			selected, found := activity.leastBusy(candidates)
+			if !found {
 				if lastError != nil {
 					state.fail("pull", lastError)
 				} else {
@@ -1231,12 +1242,12 @@ func (p *rwFolder) pullerRoutine(in <-chan pullBlockState, out chan<- *sharedPul
 				break
 			}
 
-			potentialDevices = removeDevice(potentialDevices, selected)
+			candidates = removeAvailability(candidates, 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)
+			buf, lastError := p.model.requestGlobal(selected.ID, p.folder, state.file.Name, state.block.Offset, int(state.block.Size), state.block.Hash, selected.FromTemporary)
 			activity.done(selected)
 			if lastError != nil {
 				l.Debugln("request:", p.folder, state.file.Name, state.block.Offset, state.block.Size, "returned error:", lastError)
@@ -1256,7 +1267,7 @@ func (p *rwFolder) pullerRoutine(in <-chan pullBlockState, out chan<- *sharedPul
 			if err != nil {
 				state.fail("save", err)
 			} else {
-				state.pullDone()
+				state.pullDone(state.block)
 			}
 			break
 		}
@@ -1481,14 +1492,24 @@ func (p *rwFolder) inConflict(current, replacement protocol.Vector) bool {
 	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]
+func invalidateFolder(cfg *config.Configuration, folderID string, err error) {
+	for i := range cfg.Folders {
+		folder := &cfg.Folders[i]
+		if folder.ID == folderID {
+			folder.Invalid = err.Error()
+			return
+		}
+	}
+}
+
+func removeAvailability(availabilities []Availability, availability Availability) []Availability {
+	for i := range availabilities {
+		if availabilities[i] == availability {
+			availabilities[i] = availabilities[len(availabilities)-1]
+			return availabilities[:len(availabilities)-1]
 		}
 	}
-	return devices
+	return availabilities
 }
 
 func (p *rwFolder) moveForConflict(name string) error {

lib/model/rwfolder_test.go

@@ -104,9 +104,16 @@ func TestHandleFile(t *testing.T) {
 		t.Errorf("Unexpected count of copy blocks: %d != 8", len(toCopy.blocks))
 	}
 
-	for i, block := range toCopy.blocks {
-		if string(block.Hash) != string(blocks[i+1].Hash) {
-			t.Errorf("Block mismatch: %s != %s", block.String(), blocks[i+1].String())
+	for _, block := range blocks[1:] {
+		found := false
+		for _, toCopyBlock := range toCopy.blocks {
+			if string(toCopyBlock.Hash) == string(block.Hash) {
+				found = true
+				break
+			}
+		}
+		if !found {
+			t.Errorf("Did not find block %s", block.String())
 		}
 	}
 }
@@ -138,9 +145,17 @@ func TestHandleFileWithTemp(t *testing.T) {
 		t.Errorf("Unexpected count of copy blocks: %d != 4", len(toCopy.blocks))
 	}
 
-	for i, eq := range []int{1, 5, 6, 8} {
-		if string(toCopy.blocks[i].Hash) != string(blocks[eq].Hash) {
-			t.Errorf("Block mismatch: %s != %s", toCopy.blocks[i].String(), blocks[eq].String())
+	for _, idx := range []int{1, 5, 6, 8} {
+		found := false
+		block := blocks[idx]
+		for _, toCopyBlock := range toCopy.blocks {
+			if string(toCopyBlock.Hash) == string(block.Hash) {
+				found = true
+				break
+			}
+		}
+		if !found {
+			t.Errorf("Did not find block %s", block.String())
 		}
 	}
 }
@@ -187,13 +202,22 @@ func TestCopierFinder(t *testing.T) {
 	default:
 	}
 
-	// Verify that the right blocks went into the pull list
-	for i, eq := range []int{1, 5, 6, 8} {
-		if string(pulls[i].block.Hash) != string(blocks[eq].Hash) {
-			t.Errorf("Block %d mismatch: %s != %s", eq, pulls[i].block.String(), blocks[eq].String())
+	// Verify that the right blocks went into the pull list.
+	// They are pulled in random order.
+	for _, idx := range []int{1, 5, 6, 8} {
+		found := false
+		block := blocks[idx]
+		for _, pulledBlock := range pulls {
+			if string(pulledBlock.block.Hash) == string(block.Hash) {
+				found = true
+				break
+			}
+		}
+		if !found {
+			t.Errorf("Did not find block %s", block.String())
 		}
-		if string(finish.file.Blocks[eq-1].Hash) != string(blocks[eq].Hash) {
-			t.Errorf("Block %d mismatch: %s != %s", eq, finish.file.Blocks[eq-1].String(), blocks[eq].String())
+		if string(finish.file.Blocks[idx-1].Hash) != string(blocks[idx].Hash) {
+			t.Errorf("Block %d mismatch: %s != %s", idx, finish.file.Blocks[idx-1].String(), blocks[idx].String())
 		}
 	}
 

lib/model/sentdownloadstate.go

@@ -0,0 +1,184 @@
+// Copyright (C) 2015 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 (
+	"time"
+
+	"github.com/syncthing/syncthing/lib/protocol"
+)
+
+// sentFolderFileDownloadState represents a state of what we've announced as available
+// to some remote device for a specific file.
+type sentFolderFileDownloadState struct {
+	blockIndexes []int32
+	version      protocol.Vector
+	updated      time.Time
+}
+
+// sentFolderDownloadState represents a state of what we've announced as available
+// to some remote device for a specific folder.
+type sentFolderDownloadState struct {
+	files map[string]*sentFolderFileDownloadState
+}
+
+// update takes a set of currently active sharedPullerStates, and returns a list
+// of updates which we need to send to the client to become up to date.
+func (s *sentFolderDownloadState) update(pullers []*sharedPullerState) []protocol.FileDownloadProgressUpdate {
+	var name string
+	var updates []protocol.FileDownloadProgressUpdate
+	seen := make(map[string]struct{}, len(pullers))
+
+	for _, puller := range pullers {
+		name = puller.file.Name
+
+		seen[name] = struct{}{}
+
+		pullerBlockIndexes := puller.Available()
+		pullerVersion := puller.file.Version
+		pullerBlockIndexesUpdated := puller.AvailableUpdated()
+
+		localFile, ok := s.files[name]
+
+		// New file we haven't seen before
+		if !ok {
+			// Only send an update if the file actually has some blocks.
+			if len(pullerBlockIndexes) > 0 {
+				s.files[name] = &sentFolderFileDownloadState{
+					blockIndexes: pullerBlockIndexes,
+					updated:      pullerBlockIndexesUpdated,
+					version:      pullerVersion,
+				}
+
+				updates = append(updates, protocol.FileDownloadProgressUpdate{
+					Name:         name,
+					Version:      pullerVersion,
+					UpdateType:   protocol.UpdateTypeAppend,
+					BlockIndexes: pullerBlockIndexes,
+				})
+			}
+			continue
+		}
+
+		// Existing file we've already sent an update for.
+		if pullerBlockIndexesUpdated.Equal(localFile.updated) && pullerVersion.Equal(localFile.version) {
+			// The file state hasn't changed, go to next.
+			continue
+		}
+
+		if !pullerVersion.Equal(localFile.version) {
+			// The version has changed, clean up whatever we had for the old
+			// file, and advertise the new file.
+			updates = append(updates, protocol.FileDownloadProgressUpdate{
+				Name:       name,
+				Version:    localFile.version,
+				UpdateType: protocol.UpdateTypeForget,
+			})
+			updates = append(updates, protocol.FileDownloadProgressUpdate{
+				Name:         name,
+				Version:      pullerVersion,
+				UpdateType:   protocol.UpdateTypeAppend,
+				BlockIndexes: pullerBlockIndexes,
+			})
+			localFile.blockIndexes = pullerBlockIndexes
+			localFile.updated = pullerBlockIndexesUpdated
+			localFile.version = pullerVersion
+			continue
+		}
+
+		// Relies on the fact that sharedPullerState.Available() should always
+		// append.
+		newBlocks := pullerBlockIndexes[len(localFile.blockIndexes):]
+
+		localFile.blockIndexes = append(localFile.blockIndexes, newBlocks...)
+		localFile.updated = pullerBlockIndexesUpdated
+
+		// If there are new blocks, send the update.
+		if len(newBlocks) > 0 {
+			updates = append(updates, protocol.FileDownloadProgressUpdate{
+				Name:         name,
+				Version:      localFile.version,
+				UpdateType:   protocol.UpdateTypeAppend,
+				BlockIndexes: newBlocks,
+			})
+		}
+	}
+
+	// For each file that we are tracking, see if there still is a puller for it
+	// if not, the file completed or errored out.
+	for name, info := range s.files {
+		_, ok := seen[name]
+		if !ok {
+			updates = append(updates, protocol.FileDownloadProgressUpdate{
+				Name:       name,
+				Version:    info.version,
+				UpdateType: protocol.UpdateTypeForget,
+			})
+			delete(s.files, name)
+		}
+	}
+
+	return updates
+}
+
+// destroy removes all stored state, and returns a set of updates we need to
+// dispatch to clean up the state on the remote end.
+func (s *sentFolderDownloadState) destroy() []protocol.FileDownloadProgressUpdate {
+	updates := make([]protocol.FileDownloadProgressUpdate, 0, len(s.files))
+	for name, info := range s.files {
+		updates = append(updates, protocol.FileDownloadProgressUpdate{
+			Name:       name,
+			Version:    info.version,
+			UpdateType: protocol.UpdateTypeForget,
+		})
+		delete(s.files, name)
+	}
+	return updates
+}
+
+// sentDownloadState represents a state of what we've announced as available
+// to some remote device. It is used from within the progress emitter
+// which only has one routine, hence is deemed threadsafe.
+type sentDownloadState struct {
+	folderStates map[string]*sentFolderDownloadState
+}
+
+// update receives a folder, and a slice of pullers that are currently available
+// for the given folder, and according to the state of what we've seen before
+// returns a set of updates which we should send to the remote device to make
+// it aware of everything that we currently have available.
+func (s *sentDownloadState) update(folder string, pullers []*sharedPullerState) []protocol.FileDownloadProgressUpdate {
+	fs, ok := s.folderStates[folder]
+	if !ok {
+		fs = &sentFolderDownloadState{
+			files: make(map[string]*sentFolderFileDownloadState),
+		}
+		s.folderStates[folder] = fs
+	}
+	return fs.update(pullers)
+}
+
+// folders returns a set of folders this state is currently aware off.
+func (s *sentDownloadState) folders() []string {
+	folders := make([]string, 0, len(s.folderStates))
+	for key := range s.folderStates {
+		folders = append(folders, key)
+	}
+	return folders
+}
+
+// cleanup cleans up all state related to a folder, and returns a set of updates
+// which would clean up the state on the remote device.
+func (s *sentDownloadState) cleanup(folder string) []protocol.FileDownloadProgressUpdate {
+	fs, ok := s.folderStates[folder]
+	if ok {
+		updates := fs.destroy()
+		delete(s.folderStates, folder)
+		return updates
+	}
+	return nil
+}

lib/model/sharedpullerstate.go

@@ -10,6 +10,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"time"
 
 	"github.com/syncthing/syncthing/lib/db"
 	"github.com/syncthing/syncthing/lib/protocol"
@@ -30,15 +31,18 @@ type sharedPullerState struct {
 	sparse      bool
 
 	// Mutable, must be locked for access
-	err        error      // The first error we hit
-	fd         *os.File   // The fd of the temp file
-	copyTotal  int        // Total number of copy actions for the whole job
-	pullTotal  int        // Total number of pull actions for the whole job
-	copyOrigin int        // Number of blocks copied from the original file
-	copyNeeded int        // Number of copy actions still pending
-	pullNeeded int        // Number of block pulls still pending
-	closed     bool       // True if the file has been finalClosed.
-	mut        sync.Mutex // Protects the above
+	err              error        // The first error we hit
+	fd               *os.File     // The fd of the temp file
+	copyTotal        int          // Total number of copy actions for the whole job
+	pullTotal        int          // Total number of pull actions for the whole job
+	copyOrigin       int          // Number of blocks copied from the original file
+	copyNeeded       int          // Number of copy actions still pending
+	pullNeeded       int          // Number of block pulls still pending
+	updated          time.Time    // Time when any of the counters above were last updated
+	closed           bool         // True if the file has been finalClosed.
+	available        []int32      // Indexes of the blocks that are available in the temporary file
+	availableUpdated time.Time    // Time when list of available blocks was last updated
+	mut              sync.RWMutex // Protects the above
 }
 
 // A momentary state representing the progress of the puller
@@ -56,7 +60,7 @@ type pullerProgress struct {
 // A lockedWriterAt synchronizes WriteAt calls with an external mutex.
 // WriteAt() is goroutine safe by itself, but not against for example Close().
 type lockedWriterAt struct {
-	mut *sync.Mutex
+	mut *sync.RWMutex
 	wr  io.WriterAt
 }
 
@@ -196,15 +200,19 @@ func (s *sharedPullerState) failLocked(context string, err error) {
 }
 
 func (s *sharedPullerState) failed() error {
-	s.mut.Lock()
-	defer s.mut.Unlock()
+	s.mut.RLock()
+	err := s.err
+	s.mut.RUnlock()
 
-	return s.err
+	return err
 }
 
-func (s *sharedPullerState) copyDone() {
+func (s *sharedPullerState) copyDone(block protocol.BlockInfo) {
 	s.mut.Lock()
 	s.copyNeeded--
+	s.updated = time.Now()
+	s.available = append(s.available, int32(block.Offset/protocol.BlockSize))
+	s.availableUpdated = time.Now()
 	l.Debugln("sharedPullerState", s.folder, s.file.Name, "copyNeeded ->", s.copyNeeded)
 	s.mut.Unlock()
 }
@@ -212,6 +220,7 @@ func (s *sharedPullerState) copyDone() {
 func (s *sharedPullerState) copiedFromOrigin() {
 	s.mut.Lock()
 	s.copyOrigin++
+	s.updated = time.Now()
 	s.mut.Unlock()
 }
 
@@ -221,13 +230,17 @@ func (s *sharedPullerState) pullStarted() {
 	s.copyNeeded--
 	s.pullTotal++
 	s.pullNeeded++
+	s.updated = time.Now()
 	l.Debugln("sharedPullerState", s.folder, s.file.Name, "pullNeeded start ->", s.pullNeeded)
 	s.mut.Unlock()
 }
 
-func (s *sharedPullerState) pullDone() {
+func (s *sharedPullerState) pullDone(block protocol.BlockInfo) {
 	s.mut.Lock()
 	s.pullNeeded--
+	s.updated = time.Now()
+	s.available = append(s.available, int32(block.Offset/protocol.BlockSize))
+	s.availableUpdated = time.Now()
 	l.Debugln("sharedPullerState", s.folder, s.file.Name, "pullNeeded done ->", s.pullNeeded)
 	s.mut.Unlock()
 }
@@ -265,10 +278,10 @@ func (s *sharedPullerState) finalClose() (bool, error) {
 	return true, s.err
 }
 
-// Returns the momentarily progress for the puller
+// Progress returns the momentarily progress for the puller
 func (s *sharedPullerState) Progress() *pullerProgress {
-	s.mut.Lock()
-	defer s.mut.Unlock()
+	s.mut.RLock()
+	defer s.mut.RUnlock()
 	total := s.reused + s.copyTotal + s.pullTotal
 	done := total - s.copyNeeded - s.pullNeeded
 	return &pullerProgress{
@@ -282,3 +295,27 @@ func (s *sharedPullerState) Progress() *pullerProgress {
 		BytesDone:           db.BlocksToSize(done),
 	}
 }
+
+// Updated returns the time when any of the progress related counters was last updated.
+func (s *sharedPullerState) Updated() time.Time {
+	s.mut.RLock()
+	t := s.updated
+	s.mut.RUnlock()
+	return t
+}
+
+// AvailableUpdated returns the time last time list of available blocks was updated
+func (s *sharedPullerState) AvailableUpdated() time.Time {
+	s.mut.RLock()
+	t := s.availableUpdated
+	s.mut.RUnlock()
+	return t
+}
+
+// Available returns blocks available in the current temporary file
+func (s *sharedPullerState) Available() []int32 {
+	s.mut.RLock()
+	blocks := s.available
+	s.mut.RUnlock()
+	return blocks
+}

lib/model/sharedpullerstate_test.go

@@ -16,7 +16,7 @@ import (
 func TestSourceFileOK(t *testing.T) {
 	s := sharedPullerState{
 		realName: "testdata/foo",
-		mut:      sync.NewMutex(),
+		mut:      sync.NewRWMutex(),
 	}
 
 	fd, err := s.sourceFile()
@@ -45,7 +45,7 @@ func TestSourceFileOK(t *testing.T) {
 func TestSourceFileBad(t *testing.T) {
 	s := sharedPullerState{
 		realName: "nonexistent",
-		mut:      sync.NewMutex(),
+		mut:      sync.NewRWMutex(),
 	}
 
 	fd, err := s.sourceFile()
@@ -71,7 +71,7 @@ func TestReadOnlyDir(t *testing.T) {
 
 	s := sharedPullerState{
 		tempName: "testdata/read_only_dir/.temp_name",
-		mut:      sync.NewMutex(),
+		mut:      sync.NewRWMutex(),
 	}
 
 	fd, err := s.tempFile()

lib/protocol/common_test.go

@@ -49,6 +49,9 @@ func (t *TestModel) Close(deviceID DeviceID, err error) {
 func (t *TestModel) ClusterConfig(deviceID DeviceID, config ClusterConfigMessage) {
 }
 
+func (t *TestModel) DownloadProgress(DeviceID, string, []FileDownloadProgressUpdate, uint32, []Option) {
+}
+
 func (t *TestModel) closedError() error {
 	select {
 	case <-t.closedCh:

lib/protocol/message.go

@@ -138,6 +138,13 @@ type ClusterConfigMessage struct {
 	Options []Option // max:64
 }
 
+type DownloadProgressMessage struct {
+	Folder  string                       // max:64
+	Updates []FileDownloadProgressUpdate // max:1000000
+	Flags   uint32
+	Options []Option // max:64
+}
+
 func (o *ClusterConfigMessage) GetOption(key string) string {
 	for _, option := range o.Options {
 		if option.Key == key {
@@ -166,6 +173,13 @@ type Device struct {
 	Options         []Option // max:64
 }
 
+type FileDownloadProgressUpdate struct {
+	UpdateType   uint32
+	Name         string // max:8192
+	Version      Vector
+	BlockIndexes []int32 // max:1000000
+}
+
 type Option struct {
 	Key   string // max:64
 	Value string // max:1024

lib/protocol/message_xdr.go

@@ -690,6 +690,135 @@ func (o *ClusterConfigMessage) UnmarshalXDRFrom(u *xdr.Unmarshaller) error {
 
 /*
 
+DownloadProgressMessage Structure:
+
+ 0                   1                   2                   3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+/                                                               /
+\                 Folder (length + padded data)                 \
+/                                                               /
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+|                       Number of Updates                       |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+/                                                               /
+\      Zero or more FileDownloadProgressUpdate Structures       \
+/                                                               /
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+|                             Flags                             |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+|                       Number of Options                       |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+/                                                               /
+\                Zero or more Option Structures                 \
+/                                                               /
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+
+struct DownloadProgressMessage {
+	string Folder<64>;
+	FileDownloadProgressUpdate Updates<1000000>;
+	unsigned int Flags;
+	Option Options<64>;
+}
+
+*/
+
+func (o DownloadProgressMessage) XDRSize() int {
+	return 4 + len(o.Folder) + xdr.Padding(len(o.Folder)) +
+		4 + xdr.SizeOfSlice(o.Updates) + 4 +
+		4 + xdr.SizeOfSlice(o.Options)
+}
+
+func (o DownloadProgressMessage) MarshalXDR() ([]byte, error) {
+	buf := make([]byte, o.XDRSize())
+	m := &xdr.Marshaller{Data: buf}
+	return buf, o.MarshalXDRInto(m)
+}
+
+func (o DownloadProgressMessage) MustMarshalXDR() []byte {
+	bs, err := o.MarshalXDR()
+	if err != nil {
+		panic(err)
+	}
+	return bs
+}
+
+func (o DownloadProgressMessage) MarshalXDRInto(m *xdr.Marshaller) error {
+	if l := len(o.Folder); l > 64 {
+		return xdr.ElementSizeExceeded("Folder", l, 64)
+	}
+	m.MarshalString(o.Folder)
+	if l := len(o.Updates); l > 1000000 {
+		return xdr.ElementSizeExceeded("Updates", l, 1000000)
+	}
+	m.MarshalUint32(uint32(len(o.Updates)))
+	for i := range o.Updates {
+		if err := o.Updates[i].MarshalXDRInto(m); err != nil {
+			return err
+		}
+	}
+	m.MarshalUint32(o.Flags)
+	if l := len(o.Options); l > 64 {
+		return xdr.ElementSizeExceeded("Options", l, 64)
+	}
+	m.MarshalUint32(uint32(len(o.Options)))
+	for i := range o.Options {
+		if err := o.Options[i].MarshalXDRInto(m); err != nil {
+			return err
+		}
+	}
+	return m.Error
+}
+
+func (o *DownloadProgressMessage) UnmarshalXDR(bs []byte) error {
+	u := &xdr.Unmarshaller{Data: bs}
+	return o.UnmarshalXDRFrom(u)
+}
+func (o *DownloadProgressMessage) UnmarshalXDRFrom(u *xdr.Unmarshaller) error {
+	o.Folder = u.UnmarshalStringMax(64)
+	_UpdatesSize := int(u.UnmarshalUint32())
+	if _UpdatesSize < 0 {
+		return xdr.ElementSizeExceeded("Updates", _UpdatesSize, 1000000)
+	} else if _UpdatesSize == 0 {
+		o.Updates = nil
+	} else {
+		if _UpdatesSize > 1000000 {
+			return xdr.ElementSizeExceeded("Updates", _UpdatesSize, 1000000)
+		}
+		if _UpdatesSize <= len(o.Updates) {
+			o.Updates = o.Updates[:_UpdatesSize]
+		} else {
+			o.Updates = make([]FileDownloadProgressUpdate, _UpdatesSize)
+		}
+		for i := range o.Updates {
+			(&o.Updates[i]).UnmarshalXDRFrom(u)
+		}
+	}
+	o.Flags = u.UnmarshalUint32()
+	_OptionsSize := int(u.UnmarshalUint32())
+	if _OptionsSize < 0 {
+		return xdr.ElementSizeExceeded("Options", _OptionsSize, 64)
+	} else if _OptionsSize == 0 {
+		o.Options = nil
+	} else {
+		if _OptionsSize > 64 {
+			return xdr.ElementSizeExceeded("Options", _OptionsSize, 64)
+		}
+		if _OptionsSize <= len(o.Options) {
+			o.Options = o.Options[:_OptionsSize]
+		} else {
+			o.Options = make([]Option, _OptionsSize)
+		}
+		for i := range o.Options {
+			(&o.Options[i]).UnmarshalXDRFrom(u)
+		}
+	}
+	return u.Error
+}
+
+/*
+
 Folder Structure:
 
  0                   1                   2                   3
@@ -996,6 +1125,109 @@ func (o *Device) UnmarshalXDRFrom(u *xdr.Unmarshaller) error {
 
 /*
 
+FileDownloadProgressUpdate Structure:
+
+ 0                   1                   2                   3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+|                          Update Type                          |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+/                                                               /
+\                  Name (length + padded data)                  \
+/                                                               /
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+/                                                               /
+\                       Vector Structure                        \
+/                                                               /
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+|                    Number of Block Indexes                    |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+/                                                               /
+|                    Block Indexes (n items)                    |
+/                                                               /
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+
+struct FileDownloadProgressUpdate {
+	unsigned int UpdateType;
+	string Name<8192>;
+	Vector Version;
+	int BlockIndexes<1000000>;
+}
+
+*/
+
+func (o FileDownloadProgressUpdate) XDRSize() int {
+	return 4 +
+		4 + len(o.Name) + xdr.Padding(len(o.Name)) +
+		o.Version.XDRSize() +
+		4 + len(o.BlockIndexes)*4
+}
+
+func (o FileDownloadProgressUpdate) MarshalXDR() ([]byte, error) {
+	buf := make([]byte, o.XDRSize())
+	m := &xdr.Marshaller{Data: buf}
+	return buf, o.MarshalXDRInto(m)
+}
+
+func (o FileDownloadProgressUpdate) MustMarshalXDR() []byte {
+	bs, err := o.MarshalXDR()
+	if err != nil {
+		panic(err)
+	}
+	return bs
+}
+
+func (o FileDownloadProgressUpdate) MarshalXDRInto(m *xdr.Marshaller) error {
+	m.MarshalUint32(o.UpdateType)
+	if l := len(o.Name); l > 8192 {
+		return xdr.ElementSizeExceeded("Name", l, 8192)
+	}
+	m.MarshalString(o.Name)
+	if err := o.Version.MarshalXDRInto(m); err != nil {
+		return err
+	}
+	if l := len(o.BlockIndexes); l > 1000000 {
+		return xdr.ElementSizeExceeded("BlockIndexes", l, 1000000)
+	}
+	m.MarshalUint32(uint32(len(o.BlockIndexes)))
+	for i := range o.BlockIndexes {
+		m.MarshalUint32(uint32(o.BlockIndexes[i]))
+	}
+	return m.Error
+}
+
+func (o *FileDownloadProgressUpdate) UnmarshalXDR(bs []byte) error {
+	u := &xdr.Unmarshaller{Data: bs}
+	return o.UnmarshalXDRFrom(u)
+}
+func (o *FileDownloadProgressUpdate) UnmarshalXDRFrom(u *xdr.Unmarshaller) error {
+	o.UpdateType = u.UnmarshalUint32()
+	o.Name = u.UnmarshalStringMax(8192)
+	(&o.Version).UnmarshalXDRFrom(u)
+	_BlockIndexesSize := int(u.UnmarshalUint32())
+	if _BlockIndexesSize < 0 {
+		return xdr.ElementSizeExceeded("BlockIndexes", _BlockIndexesSize, 1000000)
+	} else if _BlockIndexesSize == 0 {
+		o.BlockIndexes = nil
+	} else {
+		if _BlockIndexesSize > 1000000 {
+			return xdr.ElementSizeExceeded("BlockIndexes", _BlockIndexesSize, 1000000)
+		}
+		if _BlockIndexesSize <= len(o.BlockIndexes) {
+			o.BlockIndexes = o.BlockIndexes[:_BlockIndexesSize]
+		} else {
+			o.BlockIndexes = make([]int32, _BlockIndexesSize)
+		}
+		for i := range o.BlockIndexes {
+			o.BlockIndexes[i] = int32(u.UnmarshalUint32())
+		}
+	}
+	return u.Error
+}
+
+/*
+
 Option Structure:
 
  0                   1                   2                   3

lib/protocol/nativemodel_darwin.go

@@ -9,32 +9,24 @@ package protocol
 import "golang.org/x/text/unicode/norm"
 
 type nativeModel struct {
-	next Model
+	Model
 }
 
 func (m nativeModel) Index(deviceID DeviceID, folder string, files []FileInfo, flags uint32, options []Option) {
 	for i := range files {
 		files[i].Name = norm.NFD.String(files[i].Name)
 	}
-	m.next.Index(deviceID, folder, files, flags, options)
+	m.Model.Index(deviceID, folder, files, flags, options)
 }
 
 func (m nativeModel) IndexUpdate(deviceID DeviceID, folder string, files []FileInfo, flags uint32, options []Option) {
 	for i := range files {
 		files[i].Name = norm.NFD.String(files[i].Name)
 	}
-	m.next.IndexUpdate(deviceID, folder, files, flags, options)
+	m.Model.IndexUpdate(deviceID, folder, files, flags, options)
 }
 
 func (m nativeModel) Request(deviceID DeviceID, folder string, name string, offset int64, hash []byte, flags uint32, options []Option, buf []byte) error {
 	name = norm.NFD.String(name)
-	return m.next.Request(deviceID, folder, name, offset, hash, flags, options, buf)
-}
-
-func (m nativeModel) ClusterConfig(deviceID DeviceID, config ClusterConfigMessage) {
-	m.next.ClusterConfig(deviceID, config)
-}
-
-func (m nativeModel) Close(deviceID DeviceID, err error) {
-	m.next.Close(deviceID, err)
+	return m.Model.Request(deviceID, folder, name, offset, hash, flags, options, buf)
 }

lib/protocol/nativemodel_unix.go

@@ -7,25 +7,5 @@ package protocol
 // Normal Unixes uses NFC and slashes, which is the wire format.
 
 type nativeModel struct {
-	next Model
-}
-
-func (m nativeModel) Index(deviceID DeviceID, folder string, files []FileInfo, flags uint32, options []Option) {
-	m.next.Index(deviceID, folder, files, flags, options)
-}
-
-func (m nativeModel) IndexUpdate(deviceID DeviceID, folder string, files []FileInfo, flags uint32, options []Option) {
-	m.next.IndexUpdate(deviceID, folder, files, flags, options)
-}
-
-func (m nativeModel) Request(deviceID DeviceID, folder string, name string, offset int64, hash []byte, flags uint32, options []Option, buf []byte) error {
-	return m.next.Request(deviceID, folder, name, offset, hash, flags, options, buf)
-}
-
-func (m nativeModel) ClusterConfig(deviceID DeviceID, config ClusterConfigMessage) {
-	m.next.ClusterConfig(deviceID, config)
-}
-
-func (m nativeModel) Close(deviceID DeviceID, err error) {
-	m.next.Close(deviceID, err)
+	Model
 }

lib/protocol/nativemodel_windows.go

@@ -21,30 +21,22 @@ var disallowedCharacters = string([]rune{
 })
 
 type nativeModel struct {
-	next Model
+	Model
 }
 
 func (m nativeModel) Index(deviceID DeviceID, folder string, files []FileInfo, flags uint32, options []Option) {
 	fixupFiles(folder, files)
-	m.next.Index(deviceID, folder, files, flags, options)
+	m.Model.Index(deviceID, folder, files, flags, options)
 }
 
 func (m nativeModel) IndexUpdate(deviceID DeviceID, folder string, files []FileInfo, flags uint32, options []Option) {
 	fixupFiles(folder, files)
-	m.next.IndexUpdate(deviceID, folder, files, flags, options)
+	m.Model.IndexUpdate(deviceID, folder, files, flags, options)
 }
 
 func (m nativeModel) Request(deviceID DeviceID, folder string, name string, offset int64, hash []byte, flags uint32, options []Option, buf []byte) error {
 	name = filepath.FromSlash(name)
-	return m.next.Request(deviceID, folder, name, offset, hash, flags, options, buf)
-}
-
-func (m nativeModel) ClusterConfig(deviceID DeviceID, config ClusterConfigMessage) {
-	m.next.ClusterConfig(deviceID, config)
-}
-
-func (m nativeModel) Close(deviceID DeviceID, err error) {
-	m.next.Close(deviceID, err)
+	return m.Model.Request(deviceID, folder, name, offset, hash, flags, options, buf)
 }
 
 func fixupFiles(folder string, files []FileInfo) {

lib/protocol/protocol.go

@@ -24,13 +24,14 @@ const (
 )
 
 const (
-	messageTypeClusterConfig = 0
-	messageTypeIndex         = 1
-	messageTypeRequest       = 2
-	messageTypeResponse      = 3
-	messageTypePing          = 4
-	messageTypeIndexUpdate   = 6
-	messageTypeClose         = 7
+	messageTypeClusterConfig    = 0
+	messageTypeIndex            = 1
+	messageTypeRequest          = 2
+	messageTypeResponse         = 3
+	messageTypePing             = 4
+	messageTypeIndexUpdate      = 6
+	messageTypeClose            = 7
+	messageTypeDownloadProgress = 8
 )
 
 const (
@@ -52,22 +53,29 @@ const (
 	SymlinkTypeMask = FlagDirectory | FlagSymlinkMissingTarget
 )
 
-// IndexMessage message flags (for IndexUpdate)
+// Request message flags
 const (
-	FlagIndexTemporary uint32 = 1 << iota
+	FlagFromTemporary uint32 = 1 << iota
 )
 
-// Request message flags
+// FileDownloadProgressUpdate update types
+const (
+	UpdateTypeAppend uint32 = iota
+	UpdateTypeForget
+)
+
+// CLusterConfig flags
 const (
-	FlagRequestTemporary uint32 = 1 << iota
+	FlagClusterConfigTemporaryIndexes uint32 = 1 << 0
 )
 
 // ClusterConfigMessage.Folders flags
 const (
-	FlagFolderReadOnly     uint32 = 1 << 0
-	FlagFolderIgnorePerms         = 1 << 1
-	FlagFolderIgnoreDelete        = 1 << 2
-	FlagFolderAll                 = 1<<3 - 1
+	FlagFolderReadOnly            uint32 = 1 << 0
+	FlagFolderIgnorePerms                = 1 << 1
+	FlagFolderIgnoreDelete               = 1 << 2
+	FlagFolderDisabledTempIndexes        = 1 << 3
+	FlagFolderAll                        = 1<<4 - 1
 )
 
 // ClusterConfigMessage.Folders.Devices flags
@@ -97,6 +105,8 @@ type Model interface {
 	ClusterConfig(deviceID DeviceID, config ClusterConfigMessage)
 	// The peer device closed the connection
 	Close(deviceID DeviceID, err error)
+	// The peer device sent progress updates for the files it is currently downloading
+	DownloadProgress(deviceID DeviceID, folder string, updates []FileDownloadProgressUpdate, flags uint32, options []Option)
 }
 
 type Connection interface {
@@ -105,8 +115,9 @@ type Connection interface {
 	Name() string
 	Index(folder string, files []FileInfo, flags uint32, options []Option) error
 	IndexUpdate(folder string, files []FileInfo, flags uint32, options []Option) error
-	Request(folder string, name string, offset int64, size int, hash []byte, flags uint32, options []Option) ([]byte, error)
+	Request(folder string, name string, offset int64, size int, hash []byte, fromTemporary bool) ([]byte, error)
 	ClusterConfig(config ClusterConfigMessage)
+	DownloadProgress(folder string, updates []FileDownloadProgressUpdate, flags uint32, options []Option)
 	Statistics() Statistics
 	Closed() bool
 }
@@ -242,7 +253,7 @@ func (c *rawConnection) IndexUpdate(folder string, idx []FileInfo, flags uint32,
 }
 
 // Request returns the bytes for the specified block after fetching them from the connected peer.
-func (c *rawConnection) Request(folder string, name string, offset int64, size int, hash []byte, flags uint32, options []Option) ([]byte, error) {
+func (c *rawConnection) Request(folder string, name string, offset int64, size int, hash []byte, fromTemporary bool) ([]byte, error) {
 	var id int
 	select {
 	case id = <-c.nextID:
@@ -250,6 +261,12 @@ func (c *rawConnection) Request(folder string, name string, offset int64, size i
 		return nil, ErrClosed
 	}
 
+	var flags uint32
+
+	if fromTemporary {
+		flags |= FlagFromTemporary
+	}
+
 	c.awaitingMut.Lock()
 	if ch := c.awaiting[id]; ch != nil {
 		panic("id taken")
@@ -265,7 +282,7 @@ func (c *rawConnection) Request(folder string, name string, offset int64, size i
 		Size:    int32(size),
 		Hash:    hash,
 		Flags:   flags,
-		Options: options,
+		Options: nil,
 	}, nil)
 	if !ok {
 		return nil, ErrClosed
@@ -292,6 +309,16 @@ func (c *rawConnection) Closed() bool {
 	}
 }
 
+// DownloadProgress sends the progress updates for the files that are currently being downloaded.
+func (c *rawConnection) DownloadProgress(folder string, updates []FileDownloadProgressUpdate, flags uint32, options []Option) {
+	c.send(-1, messageTypeDownloadProgress, DownloadProgressMessage{
+		Folder:  folder,
+		Updates: updates,
+		Flags:   flags,
+		Options: options,
+	}, nil)
+}
+
 func (c *rawConnection) ping() bool {
 	var id int
 	select {
@@ -359,6 +386,12 @@ func (c *rawConnection) readerLoop() (err error) {
 			}
 			c.handleResponse(hdr.msgID, msg)
 
+		case DownloadProgressMessage:
+			if state != stateReady {
+				return fmt.Errorf("protocol error: response message in state %d", state)
+			}
+			c.receiver.DownloadProgress(c.id, msg.Folder, msg.Updates, msg.Flags, msg.Options)
+
 		case pingMessage:
 			if state != stateReady {
 				return fmt.Errorf("protocol error: ping message in state %d", state)
@@ -469,6 +502,14 @@ func (c *rawConnection) readMessage() (hdr header, msg encodable, err error) {
 		err = cm.UnmarshalXDR(msgBuf)
 		msg = cm
 
+	case messageTypeDownloadProgress:
+		var dp DownloadProgressMessage
+		err := dp.UnmarshalXDR(msgBuf)
+		if xdrErr, ok := err.(isEofer); ok && xdrErr.IsEOF() {
+			err = nil
+		}
+		msg = dp
+
 	default:
 		err = fmt.Errorf("protocol error: %s: unknown message type %#x", c.id, hdr.msgType)
 	}

lib/protocol/protocol_test.go

@@ -183,7 +183,7 @@ func TestClose(t *testing.T) {
 	c0.Index("default", nil, 0, nil)
 	c0.Index("default", nil, 0, nil)
 
-	if _, err := c0.Request("default", "foo", 0, 0, nil, 0, nil); err == nil {
+	if _, err := c0.Request("default", "foo", 0, 0, nil, false); err == nil {
 		t.Error("Request should return an error")
 	}
 }

lib/protocol/wireformat.go

@@ -34,7 +34,7 @@ func (c wireFormatConnection) IndexUpdate(folder string, fs []FileInfo, flags ui
 	return c.Connection.IndexUpdate(folder, myFs, flags, options)
 }
 
-func (c wireFormatConnection) Request(folder, name string, offset int64, size int, hash []byte, flags uint32, options []Option) ([]byte, error) {
+func (c wireFormatConnection) Request(folder, name string, offset int64, size int, hash []byte, fromTemporary bool) ([]byte, error) {
 	name = norm.NFC.String(filepath.ToSlash(name))
-	return c.Connection.Request(folder, name, offset, size, hash, flags, options)
+	return c.Connection.Request(folder, name, offset, size, hash, fromTemporary)
 }