Fix syslog output containing duplicated timestamps (netbirdio#2292)

```console
journalctl
```
```diff
- Jul 19 14:41:01 rpi /usr/bin/netbird[614]: 2024-07-19T14:41:01+02:00 ERRO %!s(<nil>): error while handling message of Peer [key: REDACTED] error: [wrongly addressed message REDACTED]
- Jul 19 21:53:03 rpi /usr/bin/netbird[614]: 2024-07-19T21:53:03+02:00 WARN %!s(<nil>): disconnected from the Signal service but will retry silently. Reason: rpc error: code = Internal desc = server closed the stream without sending trailers
- Jul 19 21:53:04 rpi /usr/bin/netbird[614]: 2024-07-19T21:53:04+02:00 INFO %!s(<nil>): connected to the Signal Service stream
- Jul 19 22:24:10 rpi /usr/bin/netbird[614]: 2024-07-19T22:24:10+02:00 WARN [error: read udp 192.168.1.11:48398->9.9.9.9:53: i/o timeout, upstream: 9.9.9.9:53] %!s(<nil>): got an error while connecting to upstream
+ Jul 19 14:41:01 rpi /usr/bin/netbird[614]: error while handling message of Peer [key: REDACTED] error: [wrongly addressed message REDACTED]
+ Jul 19 21:53:03 rpi /usr/bin/netbird[614]: disconnected from the Signal service but will retry silently. Reason: rpc error: code = Internal desc = server closed the stream without sending trailers
+ Jul 19 21:53:04 rpi /usr/bin/netbird[614]: connected to the Signal Service stream
+ Jul 19 22:24:10 rpi /usr/bin/netbird[614]: [error: read udp 192.168.1.11:48398->9.9.9.9:53: i/o timeout, upstream: 9.9.9.9:53] got an error while connecting to upstream
```

please notice that although log level is no longer present in the syslog
message it is still respected by syslog logger, so the log levels are
not lost:
```console
journalctl -p 3
```
```diff
- Jul 19 14:41:01 rpi /usr/bin/netbird[614]: 2024-07-19T14:41:01+02:00 ERRO %!s(<nil>): error while handling message of Peer [key: REDACTED] error: [wrongly addressed message REDACTED]
+ Jul 19 14:41:01 rpi /usr/bin/netbird[614]: error while handling message of Peer [key: REDACTED] error: [wrongly addressed message REDACTED]
```

.editorconfig

@@ -0,0 +1,8 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+
+[*.go]
+indent_style = tab

formatter/formatter.go

@@ -14,14 +14,29 @@ type TextFormatter struct {
 	levelDesc       []string
 }
 
+// SyslogFormatter formats logs into text
+type SyslogFormatter struct {
+	levelDesc []string
+}
+
+var validLevelDesc = []string{"PANC", "FATL", "ERRO", "WARN", "INFO", "DEBG", "TRAC"}
+
+
 // NewTextFormatter create new MyTextFormatter instance
 func NewTextFormatter() *TextFormatter {
 	return &TextFormatter{
-		levelDesc:       []string{"PANC", "FATL", "ERRO", "WARN", "INFO", "DEBG", "TRAC"},
+		levelDesc:       validLevelDesc,
 		timestampFormat: time.RFC3339, // or RFC3339
 	}
 }
 
+// NewSyslogFormatter create new MySyslogFormatter instance
+func NewSyslogFormatter() *SyslogFormatter {
+	return &SyslogFormatter{
+		levelDesc: validLevelDesc,
+	}
+}
+
 // Format renders a single log entry
 func (f *TextFormatter) Format(entry *logrus.Entry) ([]byte, error) {
 	var fields string
@@ -49,3 +64,20 @@ func (f *TextFormatter) parseLevel(level logrus.Level) string {
 
 	return f.levelDesc[level]
 }
+
+// Format renders a single log entry
+func (f *SyslogFormatter) Format(entry *logrus.Entry) ([]byte, error) {
+	var fields string
+	keys := make([]string, 0, len(entry.Data))
+	for k, v := range entry.Data {
+		if k == "source" {
+			continue
+		}
+		keys = append(keys, fmt.Sprintf("%s: %v", k, v))
+	}
+
+	if len(keys) > 0 {
+		fields = fmt.Sprintf("[%s] ", strings.Join(keys, ", "))
+	}
+	return []byte(fmt.Sprintf("%s%s\n", fields, entry.Message)), nil
+}

formatter/formatter_test.go

@@ -8,7 +8,7 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func TestLogMessageFormat(t *testing.T) {
+func TestLogTextFormat(t *testing.T) {
 
 	someEntry := &logrus.Entry{
 		Data:    logrus.Fields{"att1": 1, "att2": 2, "source": "some/fancy/path.go:46"},
@@ -24,3 +24,20 @@ func TestLogMessageFormat(t *testing.T) {
 	expectedString := "^2021-02-21T01:10:30Z WARN \\[(att1: 1, att2: 2|att2: 2, att1: 1)\\] some/fancy/path.go:46: Some Message\\s+$"
 	assert.Regexp(t, expectedString, parsedString)
 }
+
+func TestLogSyslogFormat(t *testing.T) {
+
+	someEntry := &logrus.Entry{
+		Data:    logrus.Fields{"att1": 1, "att2": 2, "source": "some/fancy/path.go:46"},
+		Time:    time.Date(2021, time.Month(2), 21, 1, 10, 30, 0, time.UTC),
+		Level:   3,
+		Message: "Some Message",
+	}
+
+	formatter := NewSyslogFormatter()
+	result, _ := formatter.Format(someEntry)
+
+	parsedString := string(result)
+	expectedString := "^\\[(att1: 1, att2: 2|att2: 2, att1: 1)\\] Some Message\\s+$"
+	assert.Regexp(t, expectedString, parsedString)
+}

formatter/set.go

@@ -10,6 +10,12 @@ func SetTextFormatter(logger *logrus.Logger) {
 	logger.ReportCaller = true
 	logger.AddHook(NewContextHook())
 }
+// SetSyslogFormatter set the text formatter for given logger.
+func SetSyslogFormatter(logger *logrus.Logger) {
+	logger.Formatter = NewSyslogFormatter()
+	logger.ReportCaller = true
+	logger.AddHook(NewContextHook())
+}
 
 // SetJSONFormatter set the JSON formatter for given logger.
 func SetJSONFormatter(logger *logrus.Logger) {

util/log.go

@@ -35,8 +35,11 @@ func InitLog(logLevel string, logPath string) error {
 		AddSyslogHook()
 	}
 
+	//nolint:gocritic
 	if os.Getenv("NB_LOG_FORMAT") == "json" {
 		formatter.SetJSONFormatter(log.StandardLogger())
+	} else if logPath == "syslog" {
+		formatter.SetSyslogFormatter(log.StandardLogger())
 	} else {
 		formatter.SetTextFormatter(log.StandardLogger())
 	}