feat(elog) Option

License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>

util/elog/option.go

+package elog
+
+import (
+	"io"
+
+	"github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/Sirupsen/logrus"
+	"github.com/jbenet/go-ipfs/Godeps/_workspace/src/gopkg.in/natefinch/lumberjack.v2"
+)
+
+type Option func()
+
+func SetOption(o Option) {
+	o()
+}
+
+var JSONFormatter = func() {
+	logrus.SetFormatter(&logrus.JSONFormatter{})
+}
+
+var TextFormatter = func() {
+	logrus.SetFormatter(&logrus.TextFormatter{})
+}
+
+type LogRotatorConfig struct {
+	File       string
+	MaxSizeMB  uint64
+	MaxBackups uint64
+	MaxAgeDays uint64
+}
+
+func Output(w io.Writer) Option {
+	return func() {
+		logrus.SetOutput(w)
+		// TODO return previous Output option
+	}
+}
+
+func OutputRotatingLogFile(config LogRotatorConfig) Option {
+	return func() {
+		logrus.SetOutput(
+			&lumberjack.Logger{
+				Filename:   config.File,
+				MaxSize:    int(config.MaxSizeMB),
+				MaxBackups: int(config.MaxBackups),
+				MaxAge:     int(config.MaxAgeDays),
+			})
+	}
+}
+
+// TODO log levels?  logrus.SetLevel(logrus.DebugLevel)