lib/upnp: Exit quicker (#6339)

During NAT discovery we block for 10s (NatTimeoutS) before returning.
This is mostly noticeable when Ctrl-C:ing a Syncthing directly after
startup as we wait for those ten seconds before shutting down. This
makes it check the context a little bit more frequently.

cmd/stfinddevice/main.go

@@ -7,6 +7,7 @@
 package main
 
 import (
+	"context"
 	"crypto/tls"
 	"errors"
 	"flag"
@@ -95,7 +96,7 @@ func checkServer(deviceID protocol.DeviceID, server string) checkResult {
 	})
 
 	go func() {
-		addresses, err := disco.Lookup(deviceID)
+		addresses, err := disco.Lookup(context.Background(), deviceID)
 		res <- checkResult{addresses: addresses, error: err}
 	}()
 

lib/api/mocked_discovery_test.go

@@ -7,6 +7,7 @@
 package api
 
 import (
+	"context"
 	"time"
 
 	"github.com/syncthing/syncthing/lib/discover"
@@ -26,7 +27,7 @@ func (m *mockedCachingMux) Stop() {
 
 // from events.Finder
 
-func (m *mockedCachingMux) Lookup(deviceID protocol.DeviceID) (direct []string, err error) {
+func (m *mockedCachingMux) Lookup(ctx context.Context, deviceID protocol.DeviceID) (direct []string, err error) {
 	return nil, nil
 }
 

lib/connections/service.go

@@ -360,6 +360,12 @@ func (s *service) connect(ctx context.Context) {
 		var seen []string
 
 		for _, deviceCfg := range cfg.Devices {
+			select {
+			case <-ctx.Done():
+				return
+			default:
+			}
+
 			deviceID := deviceCfg.DeviceID
 			if deviceID == s.myID {
 				continue
@@ -380,7 +386,7 @@ func (s *service) connect(ctx context.Context) {
 			for _, addr := range deviceCfg.Addresses {
 				if addr == "dynamic" {
 					if s.discoverer != nil {
-						if t, err := s.discoverer.Lookup(deviceID); err == nil {
+						if t, err := s.discoverer.Lookup(ctx, deviceID); err == nil {
 							addrs = append(addrs, t...)
 						}
 					}

lib/db/backend/backend.go

@@ -48,10 +48,15 @@ type ReadTransaction interface {
 // purposes of saving memory when transactions are in-RAM. Note that
 // transactions may be checkpointed *anyway* even if this is not called, due to
 // resource constraints, but this gives you a chance to decide when.
+//
+// Functions can be passed to Checkpoint. These are run if and only if the
+// checkpoint will result in a flush, and will run before the flush. The
+// transaction can be accessed via a closure. If an error is returned from
+// these functions the flush will be aborted and the error bubbled.
 type WriteTransaction interface {
 	ReadTransaction
 	Writer
-	Checkpoint() error
+	Checkpoint(...func() error) error
 	Commit() error
 }
 

lib/db/backend/leveldb_backend.go

@@ -150,8 +150,8 @@ func (t *leveldbTransaction) Put(key, val []byte) error {
 	return t.checkFlush(dbFlushBatchMax)
 }
 
-func (t *leveldbTransaction) Checkpoint() error {
-	return t.checkFlush(dbFlushBatchMin)
+func (t *leveldbTransaction) Checkpoint(preFlush ...func() error) error {
+	return t.checkFlush(dbFlushBatchMin, preFlush...)
 }
 
 func (t *leveldbTransaction) Commit() error {
@@ -167,10 +167,15 @@ func (t *leveldbTransaction) Release() {
 }
 
 // checkFlush flushes and resets the batch if its size exceeds the given size.
-func (t *leveldbTransaction) checkFlush(size int) error {
+func (t *leveldbTransaction) checkFlush(size int, preFlush ...func() error) error {
 	if len(t.batch.Dump()) < size {
 		return nil
 	}
+	for _, hook := range preFlush {
+		if err := hook(); err != nil {
+			return err
+		}
+	}
 	return t.flush()
 }
 

lib/db/lowlevel.go

@@ -124,11 +124,17 @@ func (db *Lowlevel) updateRemoteFiles(folder, device []byte, fs []protocol.FileI
 			return err
 		}
 
-		if err := t.Checkpoint(); err != nil {
+		if err := t.Checkpoint(func() error {
+			return meta.toDB(t, folder)
+		}); err != nil {
 			return err
 		}
 	}
 
+	if err := meta.toDB(t, folder); err != nil {
+		return err
+	}
+
 	return t.Commit()
 }
 
@@ -227,11 +233,17 @@ func (db *Lowlevel) updateLocalFiles(folder []byte, fs []protocol.FileInfo, meta
 			}
 		}
 
-		if err := t.Checkpoint(); err != nil {
+		if err := t.Checkpoint(func() error {
+			return meta.toDB(t, folder)
+		}); err != nil {
 			return err
 		}
 	}
 
+	if err := meta.toDB(t, folder); err != nil {
+		return err
+	}
+
 	return t.Commit()
 }
 

lib/db/meta.go

@@ -28,8 +28,8 @@ type metadataTracker struct {
 }
 
 type metaKey struct {
-	dev   protocol.DeviceID
-	flags uint32
+	dev  protocol.DeviceID
+	flag uint32
 }
 
 func newMetadataTracker() *metadataTracker {
@@ -62,8 +62,8 @@ func (m *metadataTracker) Marshal() ([]byte, error) {
 
 // toDB saves the marshalled metadataTracker to the given db, under the key
 // corresponding to the given folder
-func (m *metadataTracker) toDB(db *Lowlevel, folder []byte) error {
-	key, err := db.keyer.GenerateFolderMetaKey(nil, folder)
+func (m *metadataTracker) toDB(t readWriteTransaction, folder []byte) error {
+	key, err := t.keyer.GenerateFolderMetaKey(nil, folder)
 	if err != nil {
 		return err
 	}
@@ -79,7 +79,7 @@ func (m *metadataTracker) toDB(db *Lowlevel, folder []byte) error {
 	if err != nil {
 		return err
 	}
-	err = db.Put(key, bs)
+	err = t.Put(key, bs)
 	if err == nil {
 		m.dirty = false
 	}
@@ -103,14 +103,18 @@ func (m *metadataTracker) fromDB(db *Lowlevel, folder []byte) error {
 
 // countsPtr returns a pointer to the corresponding Counts struct, if
 // necessary allocating one in the process
-func (m *metadataTracker) countsPtr(dev protocol.DeviceID, flags uint32) *Counts {
+func (m *metadataTracker) countsPtr(dev protocol.DeviceID, flag uint32) *Counts {
 	// must be called with the mutex held
 
-	key := metaKey{dev, flags}
+	if bits.OnesCount32(flag) > 1 {
+		panic("incorrect usage: set at most one bit in flag")
+	}
+
+	key := metaKey{dev, flag}
 	idx, ok := m.indexes[key]
 	if !ok {
 		idx = len(m.counts.Counts)
-		m.counts.Counts = append(m.counts.Counts, Counts{DeviceID: dev[:], LocalFlags: flags})
+		m.counts.Counts = append(m.counts.Counts, Counts{DeviceID: dev[:], LocalFlags: flag})
 		m.indexes[key] = idx
 	}
 	return &m.counts.Counts[idx]
@@ -157,8 +161,8 @@ func (m *metadataTracker) updateSeqLocked(dev protocol.DeviceID, f FileIntf) {
 	}
 }
 
-func (m *metadataTracker) addFileLocked(dev protocol.DeviceID, flags uint32, f FileIntf) {
-	cp := m.countsPtr(dev, flags)
+func (m *metadataTracker) addFileLocked(dev protocol.DeviceID, flag uint32, f FileIntf) {
+	cp := m.countsPtr(dev, flag)
 
 	switch {
 	case f.IsDeleted():
@@ -196,8 +200,8 @@ func (m *metadataTracker) removeFile(dev protocol.DeviceID, f FileIntf) {
 	}
 }
 
-func (m *metadataTracker) removeFileLocked(dev protocol.DeviceID, flags uint32, f FileIntf) {
-	cp := m.countsPtr(dev, f.FileLocalFlags())
+func (m *metadataTracker) removeFileLocked(dev protocol.DeviceID, flag uint32, f FileIntf) {
+	cp := m.countsPtr(dev, flag)
 
 	switch {
 	case f.IsDeleted():

lib/db/set.go

@@ -71,7 +71,7 @@ func init() {
 }
 
 func NewFileSet(folder string, fs fs.Filesystem, db *Lowlevel) *FileSet {
-	var s = FileSet{
+	var s = &FileSet{
 		folder:      folder,
 		fs:          fs,
 		db:          db,
@@ -79,26 +79,34 @@ func NewFileSet(folder string, fs fs.Filesystem, db *Lowlevel) *FileSet {
 		updateMutex: sync.NewMutex(),
 	}
 
-	if err := s.meta.fromDB(db, []byte(folder)); err != nil {
-		l.Infof("No stored folder metadata for %q: recalculating", folder)
-		if err := s.recalcCounts(); backend.IsClosed(err) {
-			return nil
-		} else if err != nil {
-			panic(err)
-		}
-	} else if age := time.Since(s.meta.Created()); age > databaseRecheckInterval {
-		l.Infof("Stored folder metadata for %q is %v old; recalculating", folder, age)
-		if err := s.recalcCounts(); backend.IsClosed(err) {
+	recalc := func() *FileSet {
+		if err := s.recalcMeta(); backend.IsClosed(err) {
 			return nil
 		} else if err != nil {
 			panic(err)
 		}
+		return s
 	}
 
-	return &s
+	if err := s.meta.fromDB(db, []byte(folder)); err != nil {
+		l.Infof("No stored folder metadata for %q; recalculating", folder)
+		return recalc()
+	}
+
+	if metaOK := s.verifyLocalSequence(); !metaOK {
+		l.Infof("Stored folder metadata for %q is out of date after crash; recalculating", folder)
+		return recalc()
+	}
+
+	if age := time.Since(s.meta.Created()); age > databaseRecheckInterval {
+		l.Infof("Stored folder metadata for %q is %v old; recalculating", folder, age)
+		return recalc()
+	}
+
+	return s
 }
 
-func (s *FileSet) recalcCounts() error {
+func (s *FileSet) recalcMeta() error {
 	s.meta = newMetadataTracker()
 
 	if err := s.db.checkGlobals([]byte(s.folder), s.meta); err != nil {
@@ -109,6 +117,8 @@ func (s *FileSet) recalcCounts() error {
 	if err != nil {
 		return err
 	}
+	defer t.close()
+
 	var deviceID protocol.DeviceID
 	err = t.withAllFolderTruncated([]byte(s.folder), func(device []byte, f FileInfoTruncated) bool {
 		copy(deviceID[:], device)
@@ -120,7 +130,36 @@ func (s *FileSet) recalcCounts() error {
 	}
 
 	s.meta.SetCreated()
-	return s.meta.toDB(s.db, []byte(s.folder))
+	if err := s.meta.toDB(t, []byte(s.folder)); err != nil {
+		return err
+	}
+	return t.Commit()
+}
+
+// Verify the local sequence number from actual sequence entries. Returns
+// true if it was all good, or false if a fixup was necessary.
+func (s *FileSet) verifyLocalSequence() bool {
+	// Walk the sequence index from the current (supposedly) highest
+	// sequence number and raise the alarm if we get anything. This recovers
+	// from the occasion where we have written sequence entries to disk but
+	// not yet written new metadata to disk.
+	//
+	// Note that we can have the same thing happen for remote devices but
+	// there it's not a problem -- we'll simply advertise a lower sequence
+	// number than we've actually seen and receive some duplicate updates
+	// and then be in sync again.
+
+	curSeq := s.meta.Sequence(protocol.LocalDeviceID)
+
+	snap := s.Snapshot()
+	ok := true
+	snap.WithHaveSequence(curSeq+1, func(fi FileIntf) bool {
+		ok = false // we got something, which we should not have
+		return false
+	})
+	snap.Release()
+
+	return ok
 }
 
 func (s *FileSet) Drop(device protocol.DeviceID) {
@@ -150,7 +189,20 @@ func (s *FileSet) Drop(device protocol.DeviceID) {
 		s.meta.resetAll(device)
 	}
 
-	if err := s.meta.toDB(s.db, []byte(s.folder)); backend.IsClosed(err) {
+	t, err := s.db.newReadWriteTransaction()
+	if backend.IsClosed(err) {
+		return
+	} else if err != nil {
+		panic(err)
+	}
+	defer t.close()
+
+	if err := s.meta.toDB(t, []byte(s.folder)); backend.IsClosed(err) {
+		return
+	} else if err != nil {
+		panic(err)
+	}
+	if err := t.Commit(); backend.IsClosed(err) {
 		return
 	} else if err != nil {
 		panic(err)
@@ -168,12 +220,6 @@ func (s *FileSet) Update(device protocol.DeviceID, fs []protocol.FileInfo) {
 	s.updateMutex.Lock()
 	defer s.updateMutex.Unlock()
 
-	defer func() {
-		if err := s.meta.toDB(s.db, []byte(s.folder)); err != nil && !backend.IsClosed(err) {
-			panic(err)
-		}
-	}()
-
 	if device == protocol.LocalDeviceID {
 		// For the local device we have a bunch of metadata to track.
 		if err := s.db.updateLocalFiles([]byte(s.folder), fs, s.meta); err != nil && !backend.IsClosed(err) {

lib/discover/cache.go

@@ -7,6 +7,7 @@
 package discover
 
 import (
+	"context"
 	"sort"
 	stdsync "sync"
 	"time"
@@ -73,7 +74,7 @@ func (m *cachingMux) Add(finder Finder, cacheTime, negCacheTime time.Duration) {
 
 // Lookup attempts to resolve the device ID using any of the added Finders,
 // while obeying the cache settings.
-func (m *cachingMux) Lookup(deviceID protocol.DeviceID) (addresses []string, err error) {
+func (m *cachingMux) Lookup(ctx context.Context, deviceID protocol.DeviceID) (addresses []string, err error) {
 	m.mut.RLock()
 	for i, finder := range m.finders {
 		if cacheEntry, ok := m.caches[i].Get(deviceID); ok {
@@ -99,7 +100,7 @@ func (m *cachingMux) Lookup(deviceID protocol.DeviceID) (addresses []string, err
 		}
 
 		// Perform the actual lookup and cache the result.
-		if addrs, err := finder.Lookup(deviceID); err == nil {
+		if addrs, err := finder.Lookup(ctx, deviceID); err == nil {
 			l.Debugln("lookup for", deviceID, "at", finder)
 			l.Debugln("  addresses:", addrs)
 			addresses = append(addresses, addrs...)

lib/discover/cache_test.go

@@ -7,6 +7,7 @@
 package discover
 
 import (
+	"context"
 	"reflect"
 	"testing"
 	"time"
@@ -39,7 +40,9 @@ func TestCacheUnique(t *testing.T) {
 	f1 := &fakeDiscovery{addresses0}
 	c.Add(f1, time.Minute, 0)
 
-	addr, err := c.Lookup(protocol.LocalDeviceID)
+	ctx := context.Background()
+
+	addr, err := c.Lookup(ctx, protocol.LocalDeviceID)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -53,7 +56,7 @@ func TestCacheUnique(t *testing.T) {
 	f2 := &fakeDiscovery{addresses1}
 	c.Add(f2, time.Minute, 0)
 
-	addr, err = c.Lookup(protocol.LocalDeviceID)
+	addr, err = c.Lookup(ctx, protocol.LocalDeviceID)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -66,7 +69,7 @@ type fakeDiscovery struct {
 	addresses []string
 }
 
-func (f *fakeDiscovery) Lookup(deviceID protocol.DeviceID) (addresses []string, err error) {
+func (f *fakeDiscovery) Lookup(_ context.Context, deviceID protocol.DeviceID) (addresses []string, err error) {
 	return f.addresses, nil
 }
 
@@ -96,7 +99,7 @@ func TestCacheSlowLookup(t *testing.T) {
 	// Start a lookup, which will take at least a second
 
 	t0 := time.Now()
-	go c.Lookup(protocol.LocalDeviceID)
+	go c.Lookup(context.Background(), protocol.LocalDeviceID)
 	<-started // The slow lookup method has been called so we're inside the lock
 
 	// It should be possible to get ChildErrors while it's running
@@ -116,7 +119,7 @@ type slowDiscovery struct {
 	started chan struct{}
 }
 
-func (f *slowDiscovery) Lookup(deviceID protocol.DeviceID) (addresses []string, err error) {
+func (f *slowDiscovery) Lookup(_ context.Context, deviceID protocol.DeviceID) (addresses []string, err error) {
 	close(f.started)
 	time.Sleep(f.delay)
 	return nil, nil

lib/discover/discover.go

@@ -7,6 +7,7 @@
 package discover
 
 import (
+	"context"
 	"time"
 
 	"github.com/syncthing/syncthing/lib/protocol"
@@ -15,7 +16,7 @@ import (
 
 // A Finder provides lookup services of some kind.
 type Finder interface {
-	Lookup(deviceID protocol.DeviceID) (address []string, err error)
+	Lookup(ctx context.Context, deviceID protocol.DeviceID) (address []string, err error)
 	Error() error
 	String() string
 	Cache() map[protocol.DeviceID]CacheEntry

lib/discover/global.go

@@ -41,8 +41,8 @@ type globalClient struct {
 }
 
 type httpClient interface {
-	Get(url string) (*http.Response, error)
-	Post(url, ctype string, data io.Reader) (*http.Response, error)
+	Get(ctx context.Context, url string) (*http.Response, error)
+	Post(ctx context.Context, url, ctype string, data io.Reader) (*http.Response, error)
 }
 
 const (
@@ -89,7 +89,7 @@ func NewGlobal(server string, cert tls.Certificate, addrList AddressLister, evLo
 	// The http.Client used for announcements. It needs to have our
 	// certificate to prove our identity, and may or may not verify the server
 	// certificate depending on the insecure setting.
-	var announceClient httpClient = &http.Client{
+	var announceClient httpClient = &contextClient{&http.Client{
 		Timeout: requestTimeout,
 		Transport: &http.Transport{
 			DialContext: dialer.DialContext,
@@ -99,14 +99,14 @@ func NewGlobal(server string, cert tls.Certificate, addrList AddressLister, evLo
 				Certificates:       []tls.Certificate{cert},
 			},
 		},
-	}
+	}}
 	if opts.id != "" {
 		announceClient = newIDCheckingHTTPClient(announceClient, devID)
 	}
 
 	// The http.Client used for queries. We don't need to present our
 	// certificate here, so lets not include it. May be insecure if requested.
-	var queryClient httpClient = &http.Client{
+	var queryClient httpClient = &contextClient{&http.Client{
 		Timeout: requestTimeout,
 		Transport: &http.Transport{
 			DialContext: dialer.DialContext,
@@ -115,7 +115,7 @@ func NewGlobal(server string, cert tls.Certificate, addrList AddressLister, evLo
 				InsecureSkipVerify: opts.insecure,
 			},
 		},
-	}
+	}}
 	if opts.id != "" {
 		queryClient = newIDCheckingHTTPClient(queryClient, devID)
 	}
@@ -139,7 +139,7 @@ func NewGlobal(server string, cert tls.Certificate, addrList AddressLister, evLo
 }
 
 // Lookup returns the list of addresses where the given device is available
-func (c *globalClient) Lookup(device protocol.DeviceID) (addresses []string, err error) {
+func (c *globalClient) Lookup(ctx context.Context, device protocol.DeviceID) (addresses []string, err error) {
 	if c.noLookup {
 		return nil, lookupError{
 			error:    errors.New("lookups not supported"),
@@ -156,7 +156,7 @@ func (c *globalClient) Lookup(device protocol.DeviceID) (addresses []string, err
 	q.Set("device", device.String())
 	qURL.RawQuery = q.Encode()
 
-	resp, err := c.queryClient.Get(qURL.String())
+	resp, err := c.queryClient.Get(ctx, qURL.String())
 	if err != nil {
 		l.Debugln("globalClient.Lookup", qURL, err)
 		return nil, err
@@ -211,7 +211,7 @@ func (c *globalClient) serve(ctx context.Context) {
 			timer.Reset(2 * time.Second)
 
 		case <-timer.C:
-			c.sendAnnouncement(timer)
+			c.sendAnnouncement(ctx, timer)
 
 		case <-ctx.Done():
 			return
@@ -219,7 +219,7 @@ func (c *globalClient) serve(ctx context.Context) {
 	}
 }
 
-func (c *globalClient) sendAnnouncement(timer *time.Timer) {
+func (c *globalClient) sendAnnouncement(ctx context.Context, timer *time.Timer) {
 	var ann announcement
 	if c.addrList != nil {
 		ann.Addresses = c.addrList.ExternalAddresses()
@@ -239,7 +239,7 @@ func (c *globalClient) sendAnnouncement(timer *time.Timer) {
 
 	l.Debugf("Announcement: %s", postData)
 
-	resp, err := c.announceClient.Post(c.server, "application/json", bytes.NewReader(postData))
+	resp, err := c.announceClient.Post(ctx, c.server, "application/json", bytes.NewReader(postData))
 	if err != nil {
 		l.Debugln("announce POST:", err)
 		c.setError(err)
@@ -362,8 +362,8 @@ func (c *idCheckingHTTPClient) check(resp *http.Response) error {
 	return nil
 }
 
-func (c *idCheckingHTTPClient) Get(url string) (*http.Response, error) {
-	resp, err := c.httpClient.Get(url)
+func (c *idCheckingHTTPClient) Get(ctx context.Context, url string) (*http.Response, error) {
+	resp, err := c.httpClient.Get(ctx, url)
 	if err != nil {
 		return nil, err
 	}
@@ -374,8 +374,8 @@ func (c *idCheckingHTTPClient) Get(url string) (*http.Response, error) {
 	return resp, nil
 }
 
-func (c *idCheckingHTTPClient) Post(url, ctype string, data io.Reader) (*http.Response, error) {
-	resp, err := c.httpClient.Post(url, ctype, data)
+func (c *idCheckingHTTPClient) Post(ctx context.Context, url, ctype string, data io.Reader) (*http.Response, error) {
+	resp, err := c.httpClient.Post(ctx, url, ctype, data)
 	if err != nil {
 		return nil, err
 	}
@@ -403,3 +403,32 @@ func (e *errorHolder) Error() error {
 	e.mut.Unlock()
 	return err
 }
+
+type contextClient struct {
+	*http.Client
+}
+
+func (c *contextClient) Get(ctx context.Context, url string) (*http.Response, error) {
+	// For <go1.13 compatibility. Use the following commented line once that
+	// isn't required anymore.
+	// req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
+	req, err := http.NewRequest("GET", url, nil)
+	if err != nil {
+		return nil, err
+	}
+	req.Cancel = ctx.Done()
+	return c.Client.Do(req)
+}
+
+func (c *contextClient) Post(ctx context.Context, url, ctype string, data io.Reader) (*http.Response, error) {
+	// For <go1.13 compatibility. Use the following commented line once that
+	// isn't required anymore.
+	// req, err := http.NewRequestWithContext(ctx, "POST", url, data)
+	req, err := http.NewRequest("POST", url, data)
+	if err != nil {
+		return nil, err
+	}
+	req.Cancel = ctx.Done()
+	req.Header.Set("Content-Type", ctype)
+	return c.Client.Do(req)
+}

lib/discover/global_test.go

@@ -7,6 +7,7 @@
 package discover
 
 import (
+	"context"
 	"crypto/tls"
 	"io/ioutil"
 	"net"
@@ -225,7 +226,7 @@ func testLookup(url string) ([]string, error) {
 	go disco.Serve()
 	defer disco.Stop()
 
-	return disco.Lookup(protocol.LocalDeviceID)
+	return disco.Lookup(context.Background(), protocol.LocalDeviceID)
 }
 
 type fakeDiscoveryServer struct {

lib/discover/local.go

@@ -91,7 +91,7 @@ func NewLocal(id protocol.DeviceID, addr string, addrList AddressLister, evLogge
 }
 
 // Lookup returns a list of addresses the device is available at.
-func (c *localClient) Lookup(device protocol.DeviceID) (addresses []string, err error) {
+func (c *localClient) Lookup(_ context.Context, device protocol.DeviceID) (addresses []string, err error) {
 	if cache, ok := c.Get(device); ok {
 		if time.Since(cache.when) < CacheLifeTime {
 			addresses = cache.Addresses

lib/upnp/upnp.go

@@ -160,12 +160,6 @@ USER-AGENT: syncthing/1.0
 	}
 	defer socket.Close() // Make sure our socket gets closed
 
-	err = socket.SetDeadline(time.Now().Add(timeout))
-	if err != nil {
-		l.Debugln("UPnP discovery: setting socket deadline:", err)
-		return
-	}
-
 	l.Debugln("Sending search request for device type", deviceType, "on", intf.Name)
 
 	_, err = socket.WriteTo(search, ssdp)
@@ -178,16 +172,33 @@ USER-AGENT: syncthing/1.0
 
 	l.Debugln("Listening for UPnP response for device type", deviceType, "on", intf.Name)
 
-	// Listen for responses until a timeout is reached
+	ctx, cancel := context.WithTimeout(ctx, timeout)
+	defer cancel()
+
+	// Listen for responses until a timeout is reached or the context is
+	// cancelled
+	resp := make([]byte, 65536)
+loop:
 	for {
-		resp := make([]byte, 65536)
-		n, _, err := socket.ReadFrom(resp)
-		if err != nil {
-			if e, ok := err.(net.Error); !ok || !e.Timeout() {
-				l.Infoln("UPnP read:", err) //legitimate error, not a timeout.
-			}
+		if err := socket.SetDeadline(time.Now().Add(250 * time.Millisecond)); err != nil {
+			l.Infoln("UPnP socket:", err)
 			break
 		}
+
+		n, _, err := socket.ReadFrom(resp)
+		if err != nil {
+			select {
+			case <-ctx.Done():
+				break loop
+			default:
+			}
+			if e, ok := err.(net.Error); ok && e.Timeout() {
+				continue // continue reading
+			}
+			l.Infoln("UPnP read:", err) //legitimate error, not a timeout.
+			break
+		}
+
 		igds, err := parseResponse(ctx, deviceType, resp[:n])
 		if err != nil {
 			switch err.(type) {