Zap logger print both to console and to log file

Question

I have integrated Zap with my go application, we have logs getting printed in two log files and i am also using Lumberjack for log rotation. But i am trying to display the logs in console as well, but no luck for this case. Following is my code in logger.go

var (
    Logger *zap.Logger
    N2n    *zap.Logger
)

type WriteSyncer struct {
    io.Writer
}

func (ws WriteSyncer) Sync() error {
    return nil
}

func InitLogging(mode string) {
    var cfg zap.Config
    var logName = "abc.log"
    var slogName = "n2n.log"

    if mode == "production" {
        cfg = zap.NewProductionConfig()
        cfg.DisableCaller = true
    } else {
        cfg = zap.NewDevelopmentConfig()
        cfg.EncoderConfig.LevelKey = "level"
        cfg.EncoderConfig.NameKey = "name"
        cfg.EncoderConfig.MessageKey = "msg"
        cfg.EncoderConfig.CallerKey = "caller"
        cfg.EncoderConfig.StacktraceKey = "stacktrace"
    }

    cfg.Encoding = "json"
    cfg.EncoderConfig.TimeKey = "timestamp"
    cfg.EncoderConfig.EncodeTime = zapcore.ISO8601TimeEncoder
    cfg.OutputPaths = []string{logName}
    sw := getWriteSyncer(logName)
    swSugar := getWriteSyncer(slogName)

    l, err := cfg.Build(SetOutput(sw, cfg))
    if err != nil {
        panic(err)
    }
    defer l.Sync()

    ls, err := cfg.Build(SetOutput(swSugar, cfg))
    if err != nil {
        panic(err)
    }
    defer ls.Sync()

    Logger = l
    N2n = ls
}

// SetOutput replaces existing Core with new, that writes to passed WriteSyncer.
func SetOutput(ws zapcore.WriteSyncer, conf zap.Config) zap.Option {
    var enc zapcore.Encoder
    switch conf.Encoding {
    case "json":
        enc = zapcore.NewJSONEncoder(conf.EncoderConfig)
    case "console":
        enc = zapcore.NewConsoleEncoder(conf.EncoderConfig)
    default:
        panic("unknown encoding")
    }

    return zap.WrapCore(func(core zapcore.Core) zapcore.Core {
        return zapcore.NewCore(enc, ws, conf.Level)
    })
}

func getWriteSyncer(logName string) zapcore.WriteSyncer {
    var ioWriter = &lumberjack.Logger{
        Filename:   logName,
        MaxSize:    10, // MB
        MaxBackups: 3,  // number of backups
        MaxAge:     28, //days
        LocalTime:  true,
        Compress:   false, // disabled by default
    }
    var sw = WriteSyncer{
        ioWriter,
    }
    return sw
}

I have tried appending the output paths but it is not working.

Unsteady

Answer 1

Since this is one of the first things that appears after looking for this on Google, here's a simple example of how to make logs show on the Console and a log file, which can be any io.Writer as the one used by lumberjack:

func logInit(d bool, f *os.File) *zap.SugaredLogger {

    pe := zap.NewProductionEncoderConfig()

    fileEncoder := zapcore.NewJSONEncoder(pe)

    pe.EncodeTime = zapcore.ISO8601TimeEncoder # The encoder can be customized for each output
    consoleEncoder := zapcore.NewConsoleEncoder(pe)

    level := zap.InfoLevel
    if d {
        level = zap.DebugLevel
    }

    core := zapcore.NewTee(
        zapcore.NewCore(fileEncoder, zapcore.AddSync(f), level),
        zapcore.NewCore(consoleEncoder, zapcore.AddSync(os.Stdout), level),
    )

    l := zap.New(core) # Creating the logger

    return l.Sugar()
}

I used the default ProductionEncoderConfig but it could be a custom one like the one on OP's code.

Sidewalk

Answer 2

Figured out that zapcore has zapcore.NewMultiWriteSyncer which can write the logs in file and also on console using zapcore.addSync(os.stdout).

For example:

swSugar := zapcore.NewMultiWriteSyncer(
    zapcore.AddSync(os.Stdout), 
    getWriteSyncer(logfileName),
)

Unsteady

Answer 3

You can also use zap.CombineWriteSyncers:

CombineWriteSyncers is a utility that combines multiple WriteSyncers into a single, locked WriteSyncer. If no inputs are supplied, it returns a no-op WriteSyncer.

It's provided purely as a convenience; the result is no different from using zapcore.NewMultiWriteSyncer and zapcore.Lock individually.

    syncer := zap.CombineWriteSyncers(os.Stdout, getWriteSyncer(logfileName))

    core := zapcore.NewCore(enc, syncer, zap.NewAtomicLevelAt(zap.InfoLevel))
    zap.New(core)

Implausibility

Answer 4

Easiest way to log into multiple sources is to use zapper package. Create config.yml:

outputPaths:
  - stdout
  - /var/log/abc.log
  - /var/log/n2n.log

errorOutputPaths:
  - stderr
  - /var/log/abc.log
  - /var/log/n2n.log

Then initialize Zap logger:

package main

import "github.com/nafigator/zapper"

func main() {
    path := "/path/to/config.yml"
    log  := zapper.Must(&path, nil)

    log.Info("Log into multiple sources: OK")
}

Viscoid