Extract out log package

internal/log/log.go

@@ -0,0 +1,36 @@
+// Copyright 2020 Kentaro Hibino. All rights reserved.
+// Use of this source code is governed by a MIT license
+// that can be found in the LICENSE file.
+
+// Package log exports logging related types and functions.
+package log
+
+import (
+	"io"
+	stdlog "log"
+)
+
+func NewLogger(out io.Writer) *Logger {
+	return &Logger{
+		stdlog.New(out, "", stdlog.Ldate|stdlog.Ltime|stdlog.Lmicroseconds|stdlog.LUTC),
+	}
+}
+
+type Logger struct {
+	*stdlog.Logger
+}
+
+func (l *Logger) Info(format string, args ...interface{}) {
+	format = "INFO: " + format
+	l.Printf(format, args...)
+}
+
+func (l *Logger) Warn(format string, args ...interface{}) {
+	format = "WARN: " + format
+	l.Printf(format, args...)
+}
+
+func (l *Logger) Error(format string, args ...interface{}) {
+	format = "ERROR: " + format
+	l.Printf(format, args...)
+}