utils/log: support max days of keeping log files

src/frp/models/server/config.go

@@ -32,6 +32,7 @@ var (
 	LogFile          string = "console"
 	LogWay           string = "console" // console or file
 	LogLevel         string = "info"
+	LogMaxDays       int64  = 3
 	HeartBeatTimeout int64  = 90
 	UserConnTimeout  int64  = 10
 
@@ -82,6 +83,11 @@ func LoadConf(confFile string) (err error) {
 		LogLevel = tmpStr
 	}
 
+	tmpStr, ok = conf.Get("common", "log_max_days")
+	if ok {
+		LogMaxDays, _ = strconv.ParseInt(tmpStr, 10, 64)
+	}
+
 	// servers
 	for name, section := range conf {
 		if name != "common" {