Add text file exporter

This allows static metrics (e.g. an attributes collector replacement),
and cronjobs to expose stats by echoing into a file.

For example:

echo "my_metric 123" > mycronjob.prom.$$
mv mycronjob.prom.$$ mycronjob.prom

collector/textfile.go

@@ -0,0 +1,125 @@
+// +build !notextfile
+
+package collector
+
+import (
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	dto "github.com/prometheus/client_model/go"
+
+	"code.google.com/p/goprotobuf/proto"
+	"github.com/golang/glog"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/text"
+)
+
+var (
+	textFileDirectory = flag.String("textfile.directory", "", "Directory to read text files with metrics from.")
+)
+
+type textFileCollector struct {
+}
+
+func init() {
+	Factories["textfile"] = NewTextFileCollector
+}
+
+// Takes a config struct and registers a
+// SetMetricFamilyInjectionHook.
+func NewTextFileCollector(config Config) (Collector, error) {
+	if *textFileDirectory == "" {
+		// This collector is enabled by default, so do not fail if
+		// the flag is not passed.
+		glog.Infof("No directory specified, see --textfile.directory")
+	} else {
+		prometheus.SetMetricFamilyInjectionHook(parseTextFiles)
+	}
+
+	return &textFileCollector{}, nil
+}
+
+// textFile collector works via SetMetricFamilyInjectionHook in parseTextFiles.
+func (c *textFileCollector) Update(ch chan<- prometheus.Metric) (err error) {
+	return nil
+}
+
+func parseTextFiles() []*dto.MetricFamily {
+	var parser text.Parser
+	error := 0.0
+	metricFamilies := make([]*dto.MetricFamily, 0)
+	mtimes := map[string]time.Time{}
+
+	// Iterate over files and accumulate their metrics.
+	files, _ := ioutil.ReadDir(*textFileDirectory)
+	for _, f := range files {
+		if !strings.HasSuffix(f.Name(), ".prom") {
+			continue
+		}
+		path := filepath.Join(*textFileDirectory, f.Name())
+		file, err := os.Open(path)
+		if err != nil {
+			glog.Errorf("Error opening %s: %v", path, err)
+			error = 1.0
+			continue
+		}
+		parsedFamilies, err := parser.TextToMetricFamilies(file)
+		if err != nil {
+			glog.Errorf("Error parsing %s: %v", path, err)
+			error = 1.0
+			continue
+		}
+		// Only set this once it has been parsed, so that
+		// a failure does not appear fresh.
+		mtimes[f.Name()] = f.ModTime()
+		for _, mf := range parsedFamilies {
+			if mf.Help == nil {
+				help := fmt.Sprintf("Metric read from %s", path)
+				mf.Help = &help
+			}
+			metricFamilies = append(metricFamilies, mf)
+		}
+	}
+
+	// Export the mtimes of the successful files.
+	if len(mtimes) > 0 {
+		mtimeMetricFamily := dto.MetricFamily{
+			Name:   proto.String("node_textfile_mtime"),
+			Help:   proto.String("Unixtime mtime of textfiles successfully read."),
+			Type:   dto.MetricType_GAUGE.Enum(),
+			Metric: []*dto.Metric{},
+		}
+		for name, mtime := range mtimes {
+			mtimeMetricFamily.Metric = append(mtimeMetricFamily.Metric,
+				&dto.Metric{
+					Label: []*dto.LabelPair{
+						&dto.LabelPair{
+							Name:  proto.String("file"),
+							Value: &name,
+						},
+					},
+					Gauge: &dto.Gauge{Value: proto.Float64(float64(mtime.UnixNano()) / 1e9)},
+				},
+			)
+		}
+		metricFamilies = append(metricFamilies, &mtimeMetricFamily)
+	}
+	// Export if there were errors.
+	metricFamilies = append(metricFamilies, &dto.MetricFamily{
+		Name: proto.String("node_textfile_scrape_error"),
+		Help: proto.String("1 if there was an error opening or reading a file, 0 otherwise"),
+		Type: dto.MetricType_GAUGE.Enum(),
+		Metric: []*dto.Metric{
+			&dto.Metric{
+				Gauge: &dto.Gauge{Value: &error},
+			},
+		},
+	})
+
+	return metricFamilies
+}

node_exporter.go

@@ -25,7 +25,7 @@ var (
 	configFile        = flag.String("config", "", "Path to config file.")
 	memProfile        = flag.String("memprofile", "", "Write memory profile to this file.")
 	listeningAddress  = flag.String("listen", ":8080", "Address to listen on.")
-	enabledCollectors = flag.String("enabledCollectors", "attributes,diskstats,filesystem,loadavg,meminfo,stat,time,netdev,netstat", "Comma-separated list of collectors to use.")
+	enabledCollectors = flag.String("enabledCollectors", "attributes,diskstats,filesystem,loadavg,meminfo,stat,textfile,time,netdev,netstat", "Comma-separated list of collectors to use.")
 	printCollectors   = flag.Bool("printCollectors", false, "If true, print available collectors and exit.")
 	authUser          = flag.String("auth.user", "", "Username for basic auth.")
 	authPass          = flag.String("auth.pass", "", "Password for basic auth.")