Go logging with Zap

logger_dev.go

// +build test

package main

import "go.uber.org/zap"

func makeLogger() (*zap.Logger, error) {
    return zap.NewDevelopment()
}

logger_prod.go

// +build !test

package main

import (
    "go.uber.org/zap"
    "go.uber.org/zap/zapcore"
)

func makeLogger() (*zap.Logger, error) {
    prodConfig := zap.NewProductionConfig()
    prodConfig.Encoding = "console"
    prodConfig.EncoderConfig.EncodeTime = zapcore.ISO8601TimeEncoder
    prodConfig.EncoderConfig.EncodeDuration= zapcore.StringDurationEncoder

    return prodConfig.Build()
}

logging-example.go

package main

import (
    "go.uber.org/zap"
)

func main() {
    logger, err := makeLogger()
    if err != nil {
        panic(err)
    }
    defer logger.Sync()
    undo := zap.ReplaceGlobals(logger)
    defer undo()

    logger.Debug("Only in testing!")
    logger.Warn("Always!")
}

run_example.sh

#!/usr/bin/env bash

set -u

go get -u 'go.uber.org/zap'

go build -tags test -o example
echo "TEST:" && ./example
# See two messages!

go build -o example
echo "PROD:" && ./example

Runs like this (Go 1.14.4, zap v1.15.0):

$ ./run_example.sh 
TEST:
2020-06-15T22:17:33.811+0200	DEBUG	foo/logging-example.go:16	Only in testing!
2020-06-15T22:17:33.811+0200	WARN	foo/logging-example.go:17	Always!
main.main
	/<snip>/foo/logging-example.go:17
runtime.main
	/usr/local/go/src/runtime/proc.go:203
PROD:
2020-06-15T22:17:34.387+0200	warn	foo/logging-example.go:17	Always!