switch to go-kit logger

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

log/logger.go

@@ -0,0 +1,90 @@
+package log
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/go-kit/log"
+	"github.com/prometheus-community/windows_exporter/log/eventlog"
+	"github.com/prometheus/common/promlog"
+	goeventlog "golang.org/x/sys/windows/svc/eventlog"
+)
+
+// AllowedFile is a settable identifier for the output file that the logger can have.
+type AllowedFile struct {
+	s string
+	w io.Writer
+}
+
+func (f *AllowedFile) String() string {
+	return f.s
+}
+
+// Set updates the value of the allowed format.
+func (f *AllowedFile) Set(s string) error {
+	switch s {
+	case "stdout":
+		f.w = os.Stdout
+	case "stderr":
+		f.w = os.Stderr
+	case "eventlog":
+		f.w = nil
+	default:
+		file, err := os.OpenFile(s, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0640)
+		if err != nil {
+			return err
+		}
+		f.w = file
+	}
+	return nil
+}
+
+// Config is a struct containing configurable settings for the logger
+type Config struct {
+	promlog.Config
+
+	File *AllowedFile
+}
+
+func New(config *Config) (log.Logger, error) {
+	if config.File == nil {
+		return nil, errors.New("log file undefined")
+	}
+
+	if config.Format == nil {
+		return nil, errors.New("log format undefined")
+	}
+
+	var (
+		l          log.Logger
+		loggerFunc func(io.Writer) log.Logger
+	)
+
+	switch config.Format.String() {
+	case "json":
+		loggerFunc = log.NewJSONLogger
+	case "logfmt":
+		loggerFunc = log.NewLogfmtLogger
+	default:
+		return nil, fmt.Errorf("unsupported log.format %q", config.Format.String())
+	}
+
+	if config.File.s == "eventlog" {
+		w, err := goeventlog.Open("windows_exporter")
+		if err != nil {
+			return nil, err
+		}
+		l = eventlog.NewEventLogLogger(w, loggerFunc)
+	} else {
+		l = loggerFunc(log.NewSyncWriter(config.File.w))
+	}
+
+	promlogConfig := promlog.Config{
+		Format: config.Format,
+		Level:  config.Level,
+	}
+
+	return promlog.NewWithLogger(l, &promlogConfig), nil
+}