gui, lib/config, lib/model: Add ability to ignore folders offered by other nodes (fixes #3993)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4179
LGTM: AudriusButkevicius, calmh

lib/config/config.go

@@ -155,6 +155,7 @@ type Configuration struct {
 	GUI            GUIConfiguration      `xml:"gui" json:"gui"`
 	Options        OptionsConfiguration  `xml:"options" json:"options"`
 	IgnoredDevices []protocol.DeviceID   `xml:"ignoredDevice" json:"ignoredDevices"`
+	IgnoredFolders []string              `xml:"ignoredFolder" json:"ignoredFolders"`
 	XMLName        xml.Name              `xml:"configuration" json:"-"`
 
 	MyID            protocol.DeviceID `xml:"-" json:"-"` // Provided by the instantiator.
@@ -182,6 +183,10 @@ func (cfg Configuration) Copy() Configuration {
 	newCfg.IgnoredDevices = make([]protocol.DeviceID, len(cfg.IgnoredDevices))
 	copy(newCfg.IgnoredDevices, cfg.IgnoredDevices)
 
+	// FolderConfiguraion.ID is type string
+	newCfg.IgnoredFolders = make([]string, len(cfg.IgnoredFolders))
+	copy(newCfg.IgnoredFolders, cfg.IgnoredFolders)
+
 	return newCfg
 }
 
@@ -238,6 +243,9 @@ func (cfg *Configuration) clean() error {
 	if cfg.IgnoredDevices == nil {
 		cfg.IgnoredDevices = []protocol.DeviceID{}
 	}
+	if cfg.IgnoredFolders == nil {
+		cfg.IgnoredFolders = []string{}
+	}
 	if cfg.Options.AlwaysLocalNets == nil {
 		cfg.Options.AlwaysLocalNets = []string{}
 	}

lib/config/wrapper.go

@@ -321,6 +321,19 @@ func (w *Wrapper) IgnoredDevice(id protocol.DeviceID) bool {
 	return false
 }
 
+// IgnoredFolder returns whether or not share attempts for the given
+// folder should be silently ignored.
+func (w *Wrapper) IgnoredFolder(folder string) bool {
+	w.mut.Lock()
+	defer w.mut.Unlock()
+	for _, nfolder := range w.cfg.IgnoredFolders {
+		if folder == nfolder {
+			return true
+		}
+	}
+	return false
+}
+
 // Device returns the configuration for the given device and an "ok" bool.
 func (w *Wrapper) Device(id protocol.DeviceID) (DeviceConfiguration, bool) {
 	w.mut.Lock()

lib/model/model.go

@@ -809,6 +809,11 @@ func (m *Model) ClusterConfig(deviceID protocol.DeviceID, cm protocol.ClusterCon
 			continue
 		}
 
+		if m.cfg.IgnoredFolder(folder.ID) {
+			l.Infof("Ignoring folder %s from device %s since we are configured to", folder.Description(), deviceID)
+			continue
+		}
+
 		if !m.folderSharedWithLocked(folder.ID, deviceID) {
 			events.Default.Log(events.FolderRejected, map[string]string{
 				"folder":      folder.ID,