Addressed review remarks

clients/pkg/promtail/scrapeconfig/scrapeconfig.go

@@ -174,6 +174,15 @@ type JournalTargetConfig struct {
 	Matches string `yaml:"matches"`
 }
 
+type SyslogFormat string
+
+const (
+	// A modern Syslog RFC
+	SyslogFormatRFC5424 = "rfc5424"
+	// A legacy Syslog RFC also known as BSD-syslog
+	SyslogFormatRFC3164 = "rfc3164"
+)
+
 // SyslogTargetConfig describes a scrape config that listens for log lines over syslog.
 type SyslogTargetConfig struct {
 	// ListenAddress is the address to listen on for syslog messages.
@@ -202,15 +211,19 @@ type SyslogTargetConfig struct {
 	// message should be pushed to Loki
 	UseRFC5424Message bool `yaml:"use_rfc5424_message"`
 
-	// IsRFC3164Message defines wether the log is formated as RFC3164
-	IsRFC3164Message bool `yaml:"is_rfc3164_message"`
+	// Used Sylog format at the target.
+	SyslogFormat SyslogFormat `yaml:"syslog_format"`
 
 	// MaxMessageLength sets the maximum limit to the length of syslog messages
 	MaxMessageLength int `yaml:"max_message_length"`
 
 	TLSConfig promconfig.TLSConfig `yaml:"tls_config,omitempty"`
 }
 
+func (config SyslogTargetConfig) IsRFC3164Message() bool {
+    return config.SyslogFormat == SyslogFormatRFC3164
+}
+
 // WindowsEventsTargetConfig describes a scrape config that listen for windows event logs.
 type WindowsEventsTargetConfig struct {
 

clients/pkg/promtail/targets/syslog/syslogtarget.go

@@ -225,7 +225,7 @@ func (t *SyslogTarget) handleMessageRFC3164(connLabels labels.Labels, msg syslog
 }
 
 func (t *SyslogTarget) handleMessage(connLabels labels.Labels, msg syslog.Message) {
-	if t.config.IsRFC3164Message {
+	if t.config.IsRFC3164Message() {
 		t.handleMessageRFC3164(connLabels, msg)
 	} else {
 		t.handleMessageRFC5424(connLabels, msg)

clients/pkg/promtail/targets/syslog/transport.go

@@ -272,7 +272,7 @@ func (t *TCPTransport) handleConnection(cn net.Conn) {
 
 	lbs := t.connectionLabels(ipFromConn(c).String())
 
-	err := syslogparser.ParseStream(t.config.IsRFC3164Message, c, func(result *syslog.Result) {
+	err := syslogparser.ParseStream(t.config.IsRFC3164Message(), c, func(result *syslog.Result) {
 		if err := result.Error; err != nil {
 			t.handleMessageError(err)
 			return
@@ -397,7 +397,7 @@ func (t *UDPTransport) handleRcv(c *ConnPipe) {
 
 		r := bytes.NewReader(datagram[:n])
 
-		err = syslogparser.ParseStream(t.config.IsRFC3164Message, r, func(result *syslog.Result) {
+		err = syslogparser.ParseStream(t.config.IsRFC3164Message(), r, func(result *syslog.Result) {
 			if err := result.Error; err != nil {
 				t.handleMessageError(err)
 			} else {

docs/sources/send-data/promtail/configuration.md

@@ -865,9 +865,10 @@ Priority label is available as both value and keyword. For example, if `priority
 ### syslog
 
 The `syslog` block configures a syslog listener allowing users to push
-logs to Promtail with the syslog protocol.
-Currently supported is [IETF Syslog (RFC5424)](https://tools.ietf.org/html/rfc5424)
-with and without octet counting.
+logs to Promtail with the syslog protocol. Currently supported both
+[BSD syslog Protocol](https://datatracker.ietf.org/doc/html/rfc3164) and
+[IETF Syslog (RFC5424)](https://tools.ietf.org/html/rfc5424) with and
+without octet counting.
 
 The recommended deployment is to have a dedicated syslog forwarder like **syslog-ng** or **rsyslog**
 in front of Promtail. The forwarder can take care of the various specifications
@@ -918,6 +919,13 @@ use_incoming_timestamp: <bool>
 
 # Sets the maximum limit to the length of syslog messages
 max_message_length: <int>
+
+# Defines used Sylog format at the target. 
+syslog_format:
+ [type: <string> | default = "rfc5424"]
+
+# Defines whether the full RFC5424 formatted syslog message should be pushed to Loki
+use_rfc5424_message: <bool>
 ```
 
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