multi: wrap logger to request shutdown from signal on critical error

This commit adds a shutdown logger which will send a request for
shutdown on critical errors. It uses the signal package to request safe
shutdown of the daemon. Since we init our logs in config validation,
we add a started channel to the signal package to prevent the case where
we have a critical log after the ShutdownLogger has started but before
the daemon has started listening for intercepts. In this case, we just
ignore the shutdown request.

build/log_shutdown.go

@@ -0,0 +1,53 @@
+package build
+
+import (
+	"github.com/btcsuite/btclog"
+	"github.com/lightningnetwork/lnd/signal"
+)
+
+// ShutdownLogger wraps an existing logger with a shutdown function which will
+// be called on Critical/Criticalf to prompt shutdown.
+type ShutdownLogger struct {
+	btclog.Logger
+}
+
+// NewShutdownLogger creates a shutdown logger for the log provided which will
+// use the signal package to request shutdown on critical errors.
+func NewShutdownLogger(logger btclog.Logger) *ShutdownLogger {
+	return &ShutdownLogger{
+		Logger: logger,
+	}
+}
+
+// Criticalf formats message according to format specifier and writes to
+// log with LevelCritical. It will then call the shutdown logger's shutdown
+// function to prompt safe shutdown.
+//
+// Note: it is part of the btclog.Logger interface.
+func (s *ShutdownLogger) Criticalf(format string, params ...interface{}) {
+	s.Logger.Criticalf(format, params...)
+	s.shutdown()
+}
+
+// Critical formats message using the default formats for its operands
+// and writes to log with LevelCritical. It will then call the shutdown
+// logger's shutdown function to prompt safe shutdown.
+//
+// Note: it is part of the btclog.Logger interface.
+func (s *ShutdownLogger) Critical(v ...interface{}) {
+	s.Logger.Critical(v)
+	s.shutdown()
+}
+
+// shutdown checks whether we are listening for interrupts, since a shutdown
+// request to the signal package will block if it is not running, and requests
+// shutdown if possible.
+func (s *ShutdownLogger) shutdown() {
+	if !signal.Listening() {
+		s.Logger.Info("Request for shutdown ignored")
+		return
+	}
+
+	s.Logger.Info("Sending request for shutdown")
+	signal.RequestShutdown()
+}

build/logrotator.go

@@ -39,7 +39,10 @@ func NewRotatingLogWriter() *RotatingLogWriter {
 	logWriter := &LogWriter{}
 	backendLog := btclog.NewBackend(logWriter)
 	return &RotatingLogWriter{
-		GenSubLogger:     backendLog.Logger,
+		GenSubLogger: func(tag string) btclog.Logger {
+			logger := backendLog.Logger(tag)
+			return NewShutdownLogger(logger)
+		},
 		logWriter:        logWriter,
 		backendLog:       backendLog,
 		subsystemLoggers: SubLoggers{},