syslog-ng-ctl: workaround invalid escaping in syslog-ng/AxoSyslog metrics

Signed-off-by: László Várady <laszlo.varady@axoflow.com>

Author: MrAnno

pkg/syslog-ng-ctl/stats_prometheus.go

@@ -154,6 +154,39 @@ func transformEventDelayMetric(delayMetric *io_prometheus_client.MetricFamily, d
 	delayMetric.Type = io_prometheus_client.MetricType_GAUGE.Enum()
 }
 
+// Workaround for a bug in older syslog-ng/AxoSyslog versions where the output of STATS PROMETHEUS was overescaped.
+// Escapes \ as \\ everywhere except for the allowed sequences: \\, \n, \"
+func sanitizeBuggyFormat(output string) string {
+	var fixedOutput strings.Builder
+
+	length := len(output)
+	for i := 0; i < length; i++ {
+		c := output[i]
+
+		if c != '\\' {
+			fixedOutput.WriteByte(c)
+			continue
+		}
+
+		if i+1 >= length {
+			fixedOutput.WriteString("\\\\")
+			break
+		}
+
+		next := output[i+1]
+		if next == '\\' || next == 'n' || next == '"' {
+			fixedOutput.WriteByte(c)
+			fixedOutput.WriteByte(next)
+			i++
+			continue
+		}
+
+		fixedOutput.WriteString("\\\\")
+	}
+
+	return fixedOutput.String()
+}
+
 func StatsPrometheus(ctx context.Context, cc ControlChannel, lastMetricQueryTime *time.Time) ([]*io_prometheus_client.MetricFamily, error) {
 	rsp, err := cc.SendCommand(ctx, "STATS PROMETHEUS")
 	if err != nil {
@@ -169,6 +202,7 @@ func StatsPrometheus(ctx context.Context, cc ControlChannel, lastMetricQueryTime
 		return maps.Values(mfs), err
 	}
 
+	rsp = sanitizeBuggyFormat(rsp)
 	mfs, err = new(expfmt.TextParser).TextToMetricFamilies(strings.NewReader(rsp))
 
 	var delayMetric *io_prometheus_client.MetricFamily