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// Copyright (c) 2019 The Decred developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package main
import (
// logWriter implements an io.Writer that outputs to both standard output and
// the write-end pipe of an initialized log rotator.
type logWriter struct{}
func (logWriter) Write(p []byte) (n int, err error) {
return len(p), nil
// Loggers per subsystem. A single backend logger is created and all subsytem
// loggers created from it will write to the backend. When adding new
// subsystems, add the subsystem logger variable here and to the
// subsystemLoggers map.
// Loggers can not be used before the log rotator has been initialized with a
// log file. This must be performed early during application startup by calling
// initLogRotator.
var (
// backendLog is the logging backend used to create all subsystem loggers.
// The backend must not be used before the log rotator has been initialized,
// or data races and/or nil pointer dereferences will occur.
backendLog = slog.NewBackend(logWriter{})
// logRotator is one of the logging outputs. It should be closed on
// application shutdown.
logRotator *rotator.Rotator
log = backendLog.Logger("FAUC")
// Initialize package-global logger variables.
func init() {
// subsystemLoggers maps each subsystem identifier to its associated logger.
var subsystemLoggers = map[string]slog.Logger{
"FAUC": log,
// initLogRotator initializes the logging rotater to write logs to logFile and
// create roll files in the same directory. It must be called before the
// package-global log rotater variables are used.
func initLogRotator(logFile string) {
logDir, _ := filepath.Split(logFile)
err := os.MkdirAll(logDir, 0700)
if err != nil {
fmt.Fprintf(os.Stderr, "failed to create log directory: %v\n", err)
r, err := rotator.New(logFile, 10*1024, false, 3)
if err != nil {
fmt.Fprintf(os.Stderr, "failed to create file rotator: %v\n", err)
logRotator = r
// setLogLevel sets the logging level for provided subsystem. Invalid
// subsystems are ignored. Uninitialized subsystems are dynamically created as
// needed.
func setLogLevel(subsystemID string, logLevel string) {
// Ignore invalid subsystems.
logger, ok := subsystemLoggers[subsystemID]
if !ok {
// Defaults to info if the log level is invalid.
level, _ := slog.LevelFromString(logLevel)
// setLogLevels sets the log level for all subsystem loggers to the passed
// level. It also dynamically creates the subsystem loggers as needed, so it
// can be used to initialize the logging system.
func setLogLevels(logLevel string) {
// Configure all sub-systems with the new logging level. Dynamically
// create loggers as needed.
for subsystemID := range subsystemLoggers {
setLogLevel(subsystemID, logLevel)
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