Moved the collection of stats into its own go routine

postfix_exporter.go

@@ -16,6 +16,7 @@ package main
 import (
 	"bufio"
 	"bytes"
+	"context"
 	"errors"
 	"fmt"
 	"github.com/alecthomas/kingpin"
@@ -293,7 +294,7 @@ var (
 )
 
 // CollectFromLogline collects metrict from a Postfix log line.
-func (e *PostfixExporter) CollectFromLogline(line string) {
+func (e *PostfixExporter) CollectFromLogLine(line string) {
 	// Strip off timestamp, hostname, etc.
 	if logMatches := logLine.FindStringSubmatch(line); logMatches != nil {
 		// Group patterns to check by Postfix service.
@@ -397,7 +398,7 @@ func (e *PostfixExporter) CollectFromLogline(line string) {
 				}
 				e.smtpDelays.WithLabelValues("transmission").Observe(xdelay)
 
-				if smtpMatches := smtpStatusDeferredLine.FindStringSubmatch(logMatches[2]) ; smtpMatches != nil {
+				if smtpMatches := smtpStatusDeferredLine.FindStringSubmatch(logMatches[2]); smtpMatches != nil {
 					e.smtpStatusDeferred.Inc()
 				}
 			} else if smtpTLSMatches := smtpTLSLine.FindStringSubmatch(logMatches[2]); smtpTLSMatches != nil {
@@ -438,14 +439,25 @@ func (e *PostfixExporter) CollectFromLogline(line string) {
 }
 
 // CollectLogfileFromFile tails a Postfix log file and collects entries from it.
-func (e *PostfixExporter) CollectLogfileFromFile() error {
+func (e *PostfixExporter) CollectLogfileFromFile(ctx context.Context) {
+	gaugeVec := prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: "postfix",
+			Subsystem: "",
+			Name:      "up",
+			Help:      "Whether scraping Postfix's metrics was successful.",
+		},
+		[]string{"path"})
+	gauge := gaugeVec.With(prometheus.Labels{"path": e.tailer.Filename})
 	for {
 		select {
 		case line := <-e.tailer.Lines:
-			e.CollectFromLogline(line.Text)
-		default:
-			return nil
+			e.CollectFromLogLine(line.Text)
+		case <-ctx.Done():
+			gauge.Set(0)
+			return
 		}
+		gauge.Set(1)
 	}
 }
 
@@ -596,7 +608,6 @@ func NewPostfixExporter(showqPath string, logfilePath string, journal *Journal)
 			Name:      "smtp_status_deferred",
 			Help:      "Total number of messages deferred.",
 		}),
-
 	}, nil
 }
 
@@ -627,6 +638,48 @@ func (e *PostfixExporter) Describe(ch chan<- *prometheus.Desc) {
 	e.unsupportedLogEntries.Describe(ch)
 }
 
+func (e *PostfixExporter) foreverCollectFromJournal(ctx context.Context) {
+	gauge := prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: "postfix",
+			Subsystem: "",
+			Name:      "up",
+			Help:      "Whether scraping Postfix's metrics was successful.",
+		},
+		[]string{"path"}).With(prometheus.Labels{"path": e.journal.Path})
+	select {
+	case <-ctx.Done():
+		gauge.Set(0)
+		return
+	default:
+		err := e.CollectLogfileFromJournal()
+		if err != nil {
+			log.Printf("Couldn't read journal: %v", err)
+			gauge.Set(0)
+		} else {
+			gauge.Set(1)
+		}
+	}
+}
+
+func (e *PostfixExporter) StartMetricCollection(ctx context.Context) {
+	if e.journal != nil {
+		e.foreverCollectFromJournal(ctx)
+	} else {
+		e.CollectLogfileFromFile(ctx)
+	}
+
+	prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: "postfix",
+			Subsystem: "",
+			Name:      "up",
+			Help:      "Whether scraping Postfix's metrics was successful.",
+		},
+		[]string{"path"})
+	return
+}
+
 // Collect metrics from Postfix's showq socket and its log file.
 func (e *PostfixExporter) Collect(ch chan<- prometheus.Metric) {
 	err := CollectShowqFromSocket(e.showqPath, ch)
@@ -645,29 +698,6 @@ func (e *PostfixExporter) Collect(ch chan<- prometheus.Metric) {
 			e.showqPath)
 	}
 
-	var src string
-	if e.journal != nil {
-		err = e.CollectLogfileFromJournal()
-		src = e.journal.Path
-	} else {
-		err = e.CollectLogfileFromFile()
-		src = e.tailer.Filename
-	}
-	if err == nil {
-		ch <- prometheus.MustNewConstMetric(
-			postfixUpDesc,
-			prometheus.GaugeValue,
-			1.0,
-			src)
-	} else {
-		log.Printf("Failed to scrape log: %s", err)
-		ch <- prometheus.MustNewConstMetric(
-			postfixUpDesc,
-			prometheus.GaugeValue,
-			0.0,
-			src)
-	}
-
 	ch <- e.cleanupProcesses
 	ch <- e.cleanupRejects
 	ch <- e.cleanupNotAccepted
@@ -742,7 +772,9 @@ func main() {
 			panic(err)
 		}
 	})
-
+	ctx, cancelFunc := context.WithCancel(context.Background())
+	defer cancelFunc()
+	go exporter.StartMetricCollection(ctx)
 	log.Print("Listening on ", *listenAddress)
 	log.Fatal(http.ListenAndServe(*listenAddress, nil))
 }