Logrus Wrapper

This is a wrapper of Logrus and the original work is of github.com/prometheus/common/log authors. I have added two functionalities on top of the existing code.

Features added in short

1. Log to a file/or basically to any io.Writer
2. Added WithFields functionality

Details

PS: The code which I changed refers to commit #61f87aac8082fa8c3c5655c7608d7478d46ac2ad.

Feature 1

This is an improvement for github.com/prometheus/common/log package where it lets you write logs to a file. Existing NewLogger function looked like

func NewLogger(w io.Writer) Logger {
	l := logrus.New()
	l.Out = w
	return logger{entry: logrus.NewEntry(l)}
}

But this implementation writes log to console only/stdout. See issue #82, #104 raising the same thing.

I changed the function to this:

func NewLogger() Logger {
	l := logrus.New()
	return logger{entry: logrus.NewEntry(l)}
}

and added a new SetOutput function for the purpose of setting output i.e., writing to a file.

func SetOutput(w io.Writer) {
	origLogger.Out = w
}

Feature 2

I have also added functionality to call WithFields function, so now you can do something like this:

log.WithFields(log.Fields{
    "animal": "walrus",
    "size":   10,
  }).Info("A group of walrus emerges from the ocean")

Usage

To use this package and log to a file, add the following lines in your package:

f, err := os.OpenFile("logs.log", os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0666)
if err != nil {
	log.Fatal(err)
}
defer f.Close()
log.NewLogger()
log.SetOutput(f)
log.WithFields(log.Fields{
    "animal": "walrus",
    "size":   10,
  }).Info("A group of walrus emerges from the ocean")