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// Copyright 2017 The go-hep Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package fwk
import (
// WriteSyncer is an io.Writer which can be sync'ed/flushed.
type WriteSyncer interface {
Sync() error
type msgstream struct {
lvl Level
w WriteSyncer
n string
// NewMsgStream creates a new MsgStream value with name name and minimum
// verbosity level lvl.
// This MsgStream will print messages into w.
func NewMsgStream(name string, lvl Level, w WriteSyncer) MsgStream {
return newMsgStream(name, lvl, w)
func newMsgStream(name string, lvl Level, w WriteSyncer) msgstream {
if w == nil {
w = os.Stdout
return msgstream{
lvl: lvl,
w: w,
n: fmt.Sprintf("%-20s ", name),
// Debugf displays a (formated) DBG message
func (msg msgstream) Debugf(format string, a ...interface{}) (int, error) {
return msg.Msg(LvlDebug, format, a...)
// Infof displays a (formated) INFO message
func (msg msgstream) Infof(format string, a ...interface{}) (int, error) {
return msg.Msg(LvlInfo, format, a...)
// Warnf displays a (formated) WARN message
func (msg msgstream) Warnf(format string, a ...interface{}) (int, error) {
defer msg.flush()
return msg.Msg(LvlWarning, format, a...)
// Errorf displays a (formated) ERR message
func (msg msgstream) Errorf(format string, a ...interface{}) (int, error) {
defer msg.flush()
return msg.Msg(LvlError, format, a...)
// Msg displays a (formated) message with level lvl.
func (msg msgstream) Msg(lvl Level, format string, a ...interface{}) (int, error) {
if lvl < msg.lvl {
return 0, nil
format = msg.n + msg.lvl.msgstring() + " " + format
return fmt.Fprintf(msg.w, format, a...)
func (msg msgstream) flush() error {
return msg.w.Sync()