Allow to rotate logs on demand

Log file can be rotated sending a SIGUSR1 signal on Unix based systems and
using "sftpgo service rotatelogs" on Windows

Fixes #133

service/sigusr1_unix.go

@@ -0,0 +1,25 @@
+// +build !windows
+
+package service
+
+import (
+	"os"
+	"os/signal"
+	"syscall"
+
+	"github.com/drakkan/sftpgo/logger"
+)
+
+func registerSigUSR1() {
+	sig := make(chan os.Signal, 1)
+	signal.Notify(sig, syscall.SIGUSR1)
+	go func() {
+		for range sig {
+			logger.Debug(logSender, "", "Received log file rotation request")
+			err := logger.RotateLogFile()
+			if err != nil {
+				logger.Warn(logSender, "", "error rotating log file: %v", err)
+			}
+		}
+	}()
+}