cmd/syncthing: Allow custom event subscriptions (fixes #1879)

This adds a parameter "events" to the /rest/events endpoint. It should
be a comma separated list of the events the consumer is interested in.
When not given it defaults to the current set of events, so it's
backwards compatible.

The API service then manages subscriptions, creating them as required
for each requested event mask. Old subscriptions are not "garbage
collected" - it's assumed that in normal usage the set of event
subscriptions will be small enough. Possibly lower than before, as we
will not set up the disk event subscription unless it's actually used.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4092

lib/events/events.go

@@ -118,6 +118,67 @@ func (t EventType) MarshalText() ([]byte, error) {
 	return []byte(t.String()), nil
 }
 
+func UnmarshalEventType(s string) EventType {
+	switch s {
+	case "Starting":
+		return Starting
+	case "StartupComplete":
+		return StartupComplete
+	case "DeviceDiscovered":
+		return DeviceDiscovered
+	case "DeviceConnected":
+		return DeviceConnected
+	case "DeviceDisconnected":
+		return DeviceDisconnected
+	case "DeviceRejected":
+		return DeviceRejected
+	case "LocalChangeDetected":
+		return LocalChangeDetected
+	case "RemoteChangeDetected":
+		return RemoteChangeDetected
+	case "LocalIndexUpdated":
+		return LocalIndexUpdated
+	case "RemoteIndexUpdated":
+		return RemoteIndexUpdated
+	case "ItemStarted":
+		return ItemStarted
+	case "ItemFinished":
+		return ItemFinished
+	case "StateChanged":
+		return StateChanged
+	case "FolderRejected":
+		return FolderRejected
+	case "ConfigSaved":
+		return ConfigSaved
+	case "DownloadProgress":
+		return DownloadProgress
+	case "RemoteDownloadProgress":
+		return RemoteDownloadProgress
+	case "FolderSummary":
+		return FolderSummary
+	case "FolderCompletion":
+		return FolderCompletion
+	case "FolderErrors":
+		return FolderErrors
+	case "DevicePaused":
+		return DevicePaused
+	case "DeviceResumed":
+		return DeviceResumed
+	case "FolderScanProgress":
+		return FolderScanProgress
+	case "FolderPaused":
+		return FolderPaused
+	case "FolderResumed":
+		return FolderResumed
+	case "ListenAddressesChanged":
+		return ListenAddressesChanged
+	case "LoginAttempt":
+		return LoginAttempt
+	default:
+		return 0
+	}
+}
+
 const BufferSize = 64
 
 type Logger struct {