# README

logger

One logger to rule them all.

Motivation

I was using logrus for some times when I discovered zap. I wanted to try out zap in a project where I already used logrus. I was first thinking it should only be a matter of replacing all logrus occurence with zap's one modulo some renaming. But it was not that easy: interfaces were different, exposed API contained special types (for instance logrus.Field) or tooks differents parameters, logrus was handling standard output redirection differently than zap, etc. The cost of trying zap over logrus was high and the outcome was not that much a blast. All loggers are differents and no-one can expect one to work like another. Well, why the last sentence should be true ?

From that question is born this project which:

expose a unique abstract way of logging through a unique interface
expose a unique configuration
expose a unique way of redirect standard output
expose a unique way of writing to an io.Writer
is modulable (can use already built zap or logrus instances, or any other logger)
is easily mockable
help to test logs

Example

// var log = <some way of building one>

// same interface we are used to see
log.WithField(key, value).Info(args...)

// easy way to get a io.Writer to inject in every components that require a logger
logger.WriterLevel(log, logger.LevelError)

// easy way of redirecting golang log standard library
logger.RedirectStdLog(log, logger.LevelWarn)

Changing the underlying logger takes literraly one line.

package main

import (
    "github.com/krostar/logger"
    "github.com/krostar/logger/logrus"
    "github.com/krostar/logger/zap"
)

func main() {
    var config = logger.Config{
        Formatter: "json",
    }

    // create a logrus-based logger with configuration
    log := logrus.New(logrus.WithConfig(config))
    log.Info("i'm a logrus-based logger")

    // as any logger keep the same interface
    // switching to a zap-based logger with configuration is easy
    log = zap.New(zap.WithConfig(config))
    log.Info("i'm a zap-based logger")
}

You have a lot of code that:

is using io.Writer or
is logging directly with standard library log
takes a *log.Logger parameter

There is actually few methods to help with that:

func setupHTTP(addr string, logger *log.Logger) *http.Server {
    return &http.Server{
		Addr:     addr,
		ErrorLog: logger,
	}
}

func doSomethingElse(doIt func() error, errWriter io.Writer) {
    if err := doIt(); err != nil {
        io.WriteString(errWriter, err.String())
    }
}

func main() {
    var (
        log         logger.Logger // init it the way you want (zap, logrus, ...)
        stdlog    = logger.StdLog(log, logger.LevelError)
        writerlog = logger.WriterLevel(log, logger.LevelError)
    )

    setupHTTP(":80", stdlog)

    doSomethingElse(func()error{
        return errors.New("bim bam boum")
    }, stdlog)
}