Potential race between folder being added and scan (potentially fixes #1986)

cmd/syncthing/gui.go

@@ -428,7 +428,10 @@ func folderSummary(m *model.Model, folder string) map[string]interface{} {
 		res["error"] = err.Error()
 	}
 
-	res["version"] = m.CurrentLocalVersion(folder) + m.RemoteLocalVersion(folder)
+	lv, _ := m.CurrentLocalVersion(folder)
+	rv, _ := m.RemoteLocalVersion(folder)
+
+	res["version"] = lv + rv
 
 	ignorePatterns, _, _ := m.GetIgnores(folder)
 	res["ignorePatterns"] = false

internal/model/model.go

@@ -1554,23 +1554,23 @@ func (m *Model) Override(folder string) {
 // CurrentLocalVersion returns the change version for the given folder.
 // This is guaranteed to increment if the contents of the local folder has
 // changed.
-func (m *Model) CurrentLocalVersion(folder string) int64 {
+func (m *Model) CurrentLocalVersion(folder string) (int64, bool) {
 	m.fmut.RLock()
 	fs, ok := m.folderFiles[folder]
 	m.fmut.RUnlock()
 	if !ok {
 		// The folder might not exist, since this can be called with a user
 		// specified folder name from the REST interface.
-		return 0
+		return 0, false
 	}
 
-	return fs.LocalVersion(protocol.LocalDeviceID)
+	return fs.LocalVersion(protocol.LocalDeviceID), true
 }
 
 // RemoteLocalVersion returns the change version for the given folder, as
 // sent by remote peers. This is guaranteed to increment if the contents of
 // the remote or global folder has changed.
-func (m *Model) RemoteLocalVersion(folder string) int64 {
+func (m *Model) RemoteLocalVersion(folder string) (int64, bool) {
 	m.fmut.RLock()
 	defer m.fmut.RUnlock()
 
@@ -1578,7 +1578,7 @@ func (m *Model) RemoteLocalVersion(folder string) int64 {
 	if !ok {
 		// The folder might not exist, since this can be called with a user
 		// specified folder name from the REST interface.
-		return 0
+		return 0, false
 	}
 
 	var ver int64
@@ -1586,7 +1586,7 @@ func (m *Model) RemoteLocalVersion(folder string) int64 {
 		ver += fs.LocalVersion(n)
 	}
 
-	return ver
+	return ver, true
 }
 
 func (m *Model) GlobalDirectoryTree(folder, prefix string, levels int, dirsonly bool) map[string]interface{} {
@@ -1695,7 +1695,7 @@ func (m *Model) CheckFolderHealth(id string) error {
 	}
 
 	fi, err := os.Stat(folder.Path())
-	if m.CurrentLocalVersion(id) > 0 {
+	if v, ok := m.CurrentLocalVersion(id); ok && v > 0 {
 		// Safety check. If the cached index contains files but the
 		// folder doesn't exist, we have a problem. We would assume
 		// that all files have been deleted which might not be the case,

internal/model/rwfolder.go

@@ -204,10 +204,10 @@ func (p *rwFolder) Serve() {
 			}
 
 			// RemoteLocalVersion() is a fast call, doesn't touch the database.
-			curVer := p.model.RemoteLocalVersion(p.folder)
+			curVer, ok := p.model.RemoteLocalVersion(p.folder)
-			if curVer == prevVer {
+			if !ok || curVer == prevVer {
 				if debug {
-					l.Debugln(p, "skip (curVer == prevVer)", prevVer)
+					l.Debugln(p, "skip (curVer == prevVer)", prevVer, ok)
 				}
 				p.pullTimer.Reset(nextPullIntv)
 				continue
@@ -231,7 +231,7 @@ func (p *rwFolder) Serve() {
 					// sync. Remember the local version number and
 					// schedule a resync a little bit into the future.
 
-					if lv := p.model.RemoteLocalVersion(p.folder); lv < curVer {
+					if lv, ok := p.model.RemoteLocalVersion(p.folder); ok && lv < curVer {
 						// There's a corner case where the device we needed
 						// files from disconnected during the puller
 						// iteration. The files will have been removed from