Log

Log is a logging interface for Go. That's it. Pass around the interface.

Rationale

Users want to standardise logging. Sometimes libraries log. We leave the underlying logging implementation to the user while allowing libraries to log by simply expecting something that satisfies the Logger interface. This leaves the user free to pre-configure structure, output, etc.

Interface

The interface is minimalistic on purpose

type Logger interface {
    Log(v ...interface{})
    Logf(format string, v ...interface{})
}

Example

Here's a logger that uses logrus and logs with predefined fields.

import (
	"github.com/go-log/log"
	"github.com/sirupsen/logrus"
)

type logrusLogger struct {
	*logrus.Entry
}

func (l *logrusLogger) Log(v ...interface{}) {
	l.Entry.Print(v...)
}

func (l *logrusLogger) Logf(format string, v ...interface{}) {
	l.Entry.Printf(format, v...)
}

func WithFields(f logrus.Fields) log.Logger {
	return &logrusLogger{logrus.WithFields(f)}	
}

The WithFields func returns a struct that satisfies the Logger interface.

Pre-configure a logger using WithFields and pass it as an option to a library.

import "github.com/lib/foo"

l := mylogger.WithFields(logrus.Fields{
	"library": "github.com/lib/foo",
})

f := foo.New(
	foo.WithLogger(l),
)