logrus

package
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 Go to latest Published: Jan 15, 2016 License: MIT, Apache-2.0 Imports: 15 Imported by: 0

README

Logrus  Build Status godoc reference

Logrus is a structured logger for Go (golang), completely API compatible with the standard library logger. Godoc. Please note the Logrus API is not yet stable (pre 1.0), the core API is unlikely to change much but please version control your Logrus to make sure you aren't fetching latest master on every build.

Nicely color-coded in development (when a TTY is attached, otherwise just plain text):

Colored

With log.Formatter = new(logrus.JSONFormatter), for easy parsing by logstash or Splunk:

{"animal":"walrus","level":"info","msg":"A group of walrus emerges from the
ocean","size":10,"time":"2014-03-10 19:57:38.562264131 -0400 EDT"}

{"level":"warning","msg":"The group's number increased tremendously!",
"number":122,"omg":true,"time":"2014-03-10 19:57:38.562471297 -0400 EDT"}

{"animal":"walrus","level":"info","msg":"A giant walrus appears!",
"size":10,"time":"2014-03-10 19:57:38.562500591 -0400 EDT"}

{"animal":"walrus","level":"info","msg":"Tremendously sized cow enters the ocean.",
"size":9,"time":"2014-03-10 19:57:38.562527896 -0400 EDT"}

{"level":"fatal","msg":"The ice breaks!","number":100,"omg":true,
"time":"2014-03-10 19:57:38.562543128 -0400 EDT"}

With the default log.Formatter = new(logrus.TextFormatter) when a TTY is not attached, the output is compatible with the logfmt format:

time="2014-04-20 15:36:23.830442383 -0400 EDT" level="info" msg="A group of walrus emerges from the ocean" animal="walrus" size=10
time="2014-04-20 15:36:23.830584199 -0400 EDT" level="warning" msg="The group's number increased tremendously!" omg=true number=122
time="2014-04-20 15:36:23.830596521 -0400 EDT" level="info" msg="A giant walrus appears!" animal="walrus" size=10
time="2014-04-20 15:36:23.830611837 -0400 EDT" level="info" msg="Tremendously sized cow enters the ocean." animal="walrus" size=9
time="2014-04-20 15:36:23.830626464 -0400 EDT" level="fatal" msg="The ice breaks!" omg=true number=100
Example

The simplest way to use Logrus is simply the package-level exported logger:

package main

import (
  log "github.com/Sirupsen/logrus"
)

func main() {
  log.WithFields(log.Fields{
    "animal": "walrus",
  }).Info("A walrus appears")
}

Note that it's completely api-compatible with the stdlib logger, so you can replace your log imports everywhere with log "github.com/Sirupsen/logrus" and you'll now have the flexibility of Logrus. You can customize it all you want:

package main

import (
  "os"
  log "github.com/Sirupsen/logrus"
  "github.com/Sirupsen/logrus/hooks/airbrake"
)

func init() {
  // Log as JSON instead of the default ASCII formatter.
  log.SetFormatter(&log.JSONFormatter{})

  // Use the Airbrake hook to report errors that have Error severity or above to
  // an exception tracker. You can create custom hooks, see the Hooks section.
  log.AddHook(&logrus_airbrake.AirbrakeHook{})

  // Output to stderr instead of stdout, could also be a file.
  log.SetOutput(os.Stderr)

  // Only log the warning severity or above.
  log.SetLevel(log.WarnLevel)
}

func main() {
  log.WithFields(log.Fields{
    "animal": "walrus",
    "size":   10,
  }).Info("A group of walrus emerges from the ocean")

  log.WithFields(log.Fields{
    "omg":    true,
    "number": 122,
  }).Warn("The group's number increased tremendously!")

  log.WithFields(log.Fields{
    "omg":    true,
    "number": 100,
  }).Fatal("The ice breaks!")
}

For more advanced usage such as logging to multiple locations from the same application, you can also create an instance of the logrus Logger:

package main

import (
  "github.com/Sirupsen/logrus"
)

// Create a new instance of the logger. You can have any number of instances.
var log = logrus.New()

func main() {
  // The API for setting attributes is a little different than the package level
  // exported logger. See Godoc.
  log.Out = os.Stderr

  log.WithFields(logrus.Fields{
    "animal": "walrus",
    "size":   10,
  }).Info("A group of walrus emerges from the ocean")
}
Fields

Logrus encourages careful, structured logging though logging fields instead of long, unparseable error messages. For example, instead of: log.Fatalf("Failed to send event %s to topic %s with key %d"), you should log the much more discoverable:

log.WithFields(log.Fields{
  "event": event,
  "topic": topic,
  "key": key,
}).Fatal("Failed to send event")

We've found this API forces you to think about logging in a way that produces much more useful logging messages. We've been in countless situations where just a single added field to a log statement that was already there would've saved us hours. The WithFields call is optional.

In general, with Logrus using any of the printf-family functions should be seen as a hint you should add a field, however, you can still use the printf-family functions with Logrus.

Hooks

You can add hooks for logging levels. For example to send errors to an exception tracking service on Error, Fatal and Panic, info to StatsD or log to multiple places simultaneously, e.g. syslog.

// Not the real implementation of the Airbrake hook. Just a simple sample.
import (
  log "github.com/Sirupsen/logrus"
)

func init() {
  log.AddHook(new(AirbrakeHook))
}

type AirbrakeHook struct{}

// `Fire()` takes the entry that the hook is fired for. `entry.Data[]` contains
// the fields for the entry. See the Fields section of the README.
func (hook *AirbrakeHook) Fire(entry *logrus.Entry) error {
  err := airbrake.Notify(entry.Data["error"].(error))
  if err != nil {
    log.WithFields(log.Fields{
      "source":   "airbrake",
      "endpoint": airbrake.Endpoint,
    }).Info("Failed to send error to Airbrake")
  }

  return nil
}

// `Levels()` returns a slice of `Levels` the hook is fired for.
func (hook *AirbrakeHook) Levels() []log.Level {
  return []log.Level{
    log.ErrorLevel,
    log.FatalLevel,
    log.PanicLevel,
  }
}

Logrus comes with built-in hooks. Add those, or your custom hook, in init:

import (
  log "github.com/Sirupsen/logrus"
  "github.com/Sirupsen/logrus/hooks/airbrake"
  "github.com/Sirupsen/logrus/hooks/syslog"
  "log/syslog"
)

func init() {
  log.AddHook(new(logrus_airbrake.AirbrakeHook))

  hook, err := logrus_syslog.NewSyslogHook("udp", "localhost:514", syslog.LOG_INFO, "")
  if err != nil {
    log.Error("Unable to connect to local syslog daemon")
  } else {
    log.AddHook(hook)
  }
}
Level logging

Logrus has six logging levels: Debug, Info, Warning, Error, Fatal and Panic.

log.Debug("Useful debugging information.")
log.Info("Something noteworthy happened!")
log.Warn("You should probably take a look at this.")
log.Error("Something failed but I'm not quitting.")
// Calls os.Exit(1) after logging
log.Fatal("Bye.")
// Calls panic() after logging
log.Panic("I'm bailing.")

You can set the logging level on a Logger, then it will only log entries with that severity or anything above it:

// Will log anything that is info or above (warn, error, fatal, panic). Default.
log.SetLevel(log.InfoLevel)

It may be useful to set log.Level = logrus.DebugLevel in a debug or verbose environment if your application has that.

Entries

Besides the fields added with WithField or WithFields some fields are automatically added to all logging events:

  1. time. The timestamp when the entry was created.
  2. msg. The logging message passed to {Info,Warn,Error,Fatal,Panic} after the AddFields call. E.g. Failed to send event.
  3. level. The logging level. E.g. info.
Environments

Logrus has no notion of environment.

If you wish for hooks and formatters to only be used in specific environments, you should handle that yourself. For example, if your application has a global variable Environment, which is a string representation of the environment you could do:

import (
  log "github.com/Sirupsen/logrus"
)

init() {
  // do something here to set environment depending on an environment variable
  // or command-line flag
  if Environment == "production" {
    log.SetFormatter(logrus.JSONFormatter)
  } else {
    // The TextFormatter is default, you don't actually have to do this.
    log.SetFormatter(logrus.TextFormatter)
  }
}

This configuration is how logrus was intended to be used, but JSON in production is mostly only useful if you do log aggregation with tools like Splunk or Logstash.

Formatters

The built-in logging formatters are:

  • logrus.TextFormatter. Logs the event in colors if stdout is a tty, otherwise without colors.
    • Note: to force colored output when there is no TTY, set the ForceColors field to true. To force no colored output even if there is a TTY set the DisableColors field to true
  • logrus.JSONFormatter. Logs fields as JSON.

Third party logging formatters:

  • zalgo: invoking the P͉̫o̳̼̊w̖͈̰͎e̬͔̭͂r͚̼̹̲ ̫͓͉̳͈ō̠͕͖̚f̝͍̠ ͕̲̞͖͑Z̖̫̤̫ͪa͉̬͈̗l͖͎g̳̥o̰̥̅!̣͔̲̻͊̄ ̙̘̦̹̦.

You can define your formatter by implementing the Formatter interface, requiring a Format method. Format takes an *Entry. entry.Data is a Fields type (map[string]interface{}) with all your fields as well as the default ones (see Entries section above):

type MyJSONFormatter struct {
}

log.SetFormatter(new(MyJSONFormatter))

func (f *JSONFormatter) Format(entry *Entry) ([]byte, error) {
  // Note this doesn't include Time, Level and Message which are available on
  // the Entry. Consult `godoc` on information about those fields or read the
  // source of the official loggers.
  serialized, err := json.Marshal(entry.Data)
    if err != nil {
      return nil, fmt.Errorf("Failed to marshal fields to JSON, %v", err)
    }
  return append(serialized, '\n'), nil
}
Logger as an io.Writer

Logrus can be transormed into an io.Writer. That writer is the end of an io.Pipe and it is your responsability to close it.

w := logger.Writer()
defer w.Close()

srv := http.Server{
    // create a stdlib log.Logger that writes to
    // logrus.Logger.
    ErrorLog: log.New(w, "", 0),
}

Each line written to that writer will be printed the usual way, using formatters and hooks. The level for those entries is info.

Rotation

Log rotation is not provided with Logrus. Log rotation should be done by an external program (like logrotated(8)) that can compress and delete old log entries. It should not be a feature of the application-level logger.

Documentation

Index

Constants

This section is empty.

Variables

This section is empty.

Functions

func AddHook 

func AddHook(hook Hook)

AddHook adds a hook to the standard logger hooks.

func Debug 

func Debug(args ...interface{})

Debug logs a message at level Debug on the standard logger.

func Debugf 

func Debugf(format string, args ...interface{})

Debugf logs a message at level Debug on the standard logger.

func Debugln 

func Debugln(args ...interface{})

Debugln logs a message at level Debug on the standard logger.

func Error 

func Error(args ...interface{})

Error logs a message at level Error on the standard logger.

func Errorf 

func Errorf(format string, args ...interface{})

Errorf logs a message at level Error on the standard logger.

func Errorln 

func Errorln(args ...interface{})

Errorln logs a message at level Error on the standard logger.

func Fatal 

func Fatal(args ...interface{})

Fatal logs a message at level Fatal on the standard logger.

func Fatalf 

func Fatalf(format string, args ...interface{})

Fatalf logs a message at level Fatal on the standard logger.

func Fatalln 

func Fatalln(args ...interface{})

Fatalln logs a message at level Fatal on the standard logger.

func Info 

func Info(args ...interface{})

Info logs a message at level Info on the standard logger.

func Infof 

func Infof(format string, args ...interface{})

Infof logs a message at level Info on the standard logger.

func Infoln 

func Infoln(args ...interface{})

Infoln logs a message at level Info on the standard logger.

func IsTerminal 

func IsTerminal() bool

IsTerminal returns true if the given file descriptor is a terminal.

func Panic 

func Panic(args ...interface{})

Panic logs a message at level Panic on the standard logger.

func Panicf 

func Panicf(format string, args ...interface{})

Panicf logs a message at level Panic on the standard logger.

func Panicln 

func Panicln(args ...interface{})

Panicln logs a message at level Panic on the standard logger.

func Print 

func Print(args ...interface{})

Print logs a message at level Info on the standard logger.

func Printf 

func Printf(format string, args ...interface{})

Printf logs a message at level Info on the standard logger.

func Println 

func Println(args ...interface{})

Println logs a message at level Info on the standard logger.

func SetFormatter 

func SetFormatter(formatter Formatter)

SetFormatter sets the standard logger formatter.

func SetLevel 

func SetLevel(level Level)

SetLevel sets the standard logger level.

func SetOutput 

func SetOutput(out io.Writer)

SetOutput sets the standard logger output.

func Warn 

func Warn(args ...interface{})

Warn logs a message at level Warn on the standard logger.

func Warnf 

func Warnf(format string, args ...interface{})

Warnf logs a message at level Warn on the standard logger.

func Warning 

func Warning(args ...interface{})

Warning logs a message at level Warn on the standard logger.

func Warningf 

func Warningf(format string, args ...interface{})

Warningf logs a message at level Warn on the standard logger.

func Warningln 

func Warningln(args ...interface{})

Warningln logs a message at level Warn on the standard logger.

func Warnln 

func Warnln(args ...interface{})

Warnln logs a message at level Warn on the standard logger.

Types

type Entry 

type Entry struct {
	Logger *Logger

	// Contains all the fields set by the user.
	Data Fields

	// Time at which the log entry was created
	Time time.Time

	// Level the log entry was logged at: Debug, Info, Warn, Error, Fatal or Panic
	Level Level

	// Message passed to Debug, Info, Warn, Error, Fatal or Panic
	Message string
}

An entry is the final or intermediate Logrus logging entry. It contains all the fields passed with WithField{,s}. It's finally logged when Debug, Info, Warn, Error, Fatal or Panic is called on it. These objects can be reused and passed around as much as you wish to avoid field duplication.

func NewEntry 

func NewEntry(logger *Logger) *Entry

func WithField 

func WithField(key string, value interface{}) *Entry

WithField creates an entry from the standard logger and adds a field to it. If you want multiple fields, use `WithFields`.

Note that it doesn't log until you call Debug, Print, Info, Warn, Fatal or Panic on the Entry it returns.

func WithFields 

func WithFields(fields Fields) *Entry

WithFields creates an entry from the standard logger and adds multiple fields to it. This is simply a helper for `WithField`, invoking it once for each field.

Note that it doesn't log until you call Debug, Print, Info, Warn, Fatal or Panic on the Entry it returns.

func (*Entry) Debug 

func (entry *Entry) Debug(args ...interface{})

func (*Entry) Debugf 

func (entry *Entry) Debugf(format string, args ...interface{})

func (*Entry) Debugln 

func (entry *Entry) Debugln(args ...interface{})

func (*Entry) Error 

func (entry *Entry) Error(args ...interface{})

func (*Entry) Errorf 

func (entry *Entry) Errorf(format string, args ...interface{})

func (*Entry) Errorln 

func (entry *Entry) Errorln(args ...interface{})

func (*Entry) Fatal 

func (entry *Entry) Fatal(args ...interface{})

func (*Entry) Fatalf 

func (entry *Entry) Fatalf(format string, args ...interface{})

func (*Entry) Fatalln 

func (entry *Entry) Fatalln(args ...interface{})

func (*Entry) Info 

func (entry *Entry) Info(args ...interface{})

func (*Entry) Infof 

func (entry *Entry) Infof(format string, args ...interface{})

func (*Entry) Infoln 

func (entry *Entry) Infoln(args ...interface{})

func (*Entry) Panic 

func (entry *Entry) Panic(args ...interface{})

func (*Entry) Panicf 

func (entry *Entry) Panicf(format string, args ...interface{})

func (*Entry) Panicln 

func (entry *Entry) Panicln(args ...interface{})

func (*Entry) Print 

func (entry *Entry) Print(args ...interface{})

func (*Entry) Printf 

func (entry *Entry) Printf(format string, args ...interface{})

func (*Entry) Println 

func (entry *Entry) Println(args ...interface{})

func (*Entry) Reader 

func (entry *Entry) Reader() (*bytes.Buffer, error)

Returns a reader for the entry, which is a proxy to the formatter.

func (*Entry) String 

func (entry *Entry) String() (string, error)

Returns the string representation from the reader and ultimately the formatter.

func (*Entry) Warn 

func (entry *Entry) Warn(args ...interface{})

func (*Entry) Warnf 

func (entry *Entry) Warnf(format string, args ...interface{})

func (*Entry) Warning 

func (entry *Entry) Warning(args ...interface{})

func (*Entry) Warningf 

func (entry *Entry) Warningf(format string, args ...interface{})

func (*Entry) Warningln 

func (entry *Entry) Warningln(args ...interface{})

func (*Entry) Warnln 

func (entry *Entry) Warnln(args ...interface{})

func (*Entry) WithField 

func (entry *Entry) WithField(key string, value interface{}) *Entry

Add a single field to the Entry.

func (*Entry) WithFields 

func (entry *Entry) WithFields(fields Fields) *Entry

Add a map of fields to the Entry.

type Fields 

type Fields map[string]interface{}

Fields type, used to pass to `WithFields`.

type Formatter 

type Formatter interface {
	Format(*Entry) ([]byte, error)
}

The Formatter interface is used to implement a custom Formatter. It takes an `Entry`. It exposes all the fields, including the default ones:

* `entry.Data["msg"]`. The message passed from Info, Warn, Error .. * `entry.Data["time"]`. The timestamp. * `entry.Data["level"]. The level the entry was logged at.

Any additional fields added with `WithField` or `WithFields` are also in `entry.Data`. Format is expected to return an array of bytes which are then logged to `logger.Out`.

type Hook 

type Hook interface {
	Levels() []Level
	Fire(*Entry) error
}

A hook to be fired when logging on the logging levels returned from `Levels()` on your implementation of the interface. Note that this is not fired in a goroutine or a channel with workers, you should handle such functionality yourself if your call is non-blocking and you don't wish for the logging calls for levels returned from `Levels()` to block.

type JSONFormatter 

type JSONFormatter struct{}

func (*JSONFormatter) Format 

func (f *JSONFormatter) Format(entry *Entry) ([]byte, error)

type Level 

type Level uint8

Level type 

const (
	// PanicLevel level, highest level of severity. Logs and then calls panic with the
	// message passed to Debug, Info, ...
	PanicLevel Level = iota
	// FatalLevel level. Logs and then calls `os.Exit(1)`. It will exit even if the
	// logging level is set to Panic.
	FatalLevel
	// ErrorLevel level. Logs. Used for errors that should definitely be noted.
	// Commonly used for hooks to send errors to an error tracking service.
	ErrorLevel
	// WarnLevel level. Non-critical entries that deserve eyes.
	WarnLevel
	// InfoLevel level. General operational entries about what's going on inside the
	// application.
	InfoLevel
	// DebugLevel level. Usually only enabled when debugging. Very verbose logging.
	DebugLevel
)

These are the different logging levels. You can set the logging level to log on your instance of logger, obtained with `logrus.New()`.

func GetLevel 

func GetLevel() Level

GetLevel returns the standard logger level.

func ParseLevel 

func ParseLevel(lvl string) (Level, error)

ParseLevel takes a string level and returns the Logrus log level constant.

func (Level) String 

func (level Level) String() string

Convert the Level to a string. E.g. PanicLevel becomes "panic".

type Logger 

type Logger struct {
	// The logs are `io.Copy`'d to this in a mutex. It's common to set this to a
	// file, or leave it default which is `os.Stdout`. You can also set this to
	// something more adventorous, such as logging to Kafka.
	Out io.Writer
	// Hooks for the logger instance. These allow firing events based on logging
	// levels and log entries. For example, to send errors to an error tracking
	// service, log to StatsD or dump the core on fatal errors.
	Hooks levelHooks
	// All log entries pass through the formatter before logged to Out. The
	// included formatters are `TextFormatter` and `JSONFormatter` for which
	// TextFormatter is the default. In development (when a TTY is attached) it
	// logs with colors, but to a file it wouldn't. You can easily implement your
	// own that implements the `Formatter` interface, see the `README` or included
	// formatters for examples.
	Formatter Formatter
	// The logging level the logger should log at. This is typically (and defaults
	// to) `logrus.Info`, which allows Info(), Warn(), Error() and Fatal() to be
	// logged. `logrus.Debug` is useful in
	Level Level
	// contains filtered or unexported fields
}

func New 

func New() *Logger

Creates a new logger. Configuration should be set by changing `Formatter`, `Out` and `Hooks` directly on the default logger instance. You can also just instantiate your own: 

var log = &Logger{
  Out: os.Stderr,
  Formatter: new(JSONFormatter),
  Hooks: make(levelHooks),
  Level: logrus.DebugLevel,
}

It's recommended to make this a global instance called `log`.

func StandardLogger 

func StandardLogger() *Logger

func (*Logger) Debug 

func (logger *Logger) Debug(args ...interface{})

func (*Logger) Debugf 

func (logger *Logger) Debugf(format string, args ...interface{})

func (*Logger) Debugln 

func (logger *Logger) Debugln(args ...interface{})

func (*Logger) Error 

func (logger *Logger) Error(args ...interface{})

func (*Logger) Errorf 

func (logger *Logger) Errorf(format string, args ...interface{})

func (*Logger) Errorln 

func (logger *Logger) Errorln(args ...interface{})

func (*Logger) Fatal 

func (logger *Logger) Fatal(args ...interface{})

func (*Logger) Fatalf 

func (logger *Logger) Fatalf(format string, args ...interface{})

func (*Logger) Fatalln 

func (logger *Logger) Fatalln(args ...interface{})

func (*Logger) Info 

func (logger *Logger) Info(args ...interface{})

func (*Logger) Infof 

func (logger *Logger) Infof(format string, args ...interface{})

func (*Logger) Infoln 

func (logger *Logger) Infoln(args ...interface{})

func (*Logger) Panic 

func (logger *Logger) Panic(args ...interface{})

func (*Logger) Panicf 

func (logger *Logger) Panicf(format string, args ...interface{})

func (*Logger) Panicln 

func (logger *Logger) Panicln(args ...interface{})

func (*Logger) Print 

func (logger *Logger) Print(args ...interface{})

func (*Logger) Printf 

func (logger *Logger) Printf(format string, args ...interface{})

func (*Logger) Println 

func (logger *Logger) Println(args ...interface{})

func (*Logger) Warn 

func (logger *Logger) Warn(args ...interface{})

func (*Logger) Warnf 

func (logger *Logger) Warnf(format string, args ...interface{})

func (*Logger) Warning 

func (logger *Logger) Warning(args ...interface{})

func (*Logger) Warningf 

func (logger *Logger) Warningf(format string, args ...interface{})

func (*Logger) Warningln 

func (logger *Logger) Warningln(args ...interface{})

func (*Logger) Warnln 

func (logger *Logger) Warnln(args ...interface{})

func (*Logger) WithField 

func (logger *Logger) WithField(key string, value interface{}) *Entry

Adds a field to the log entry, note that you it doesn't log until you call Debug, Print, Info, Warn, Fatal or Panic. It only creates a log entry. Ff you want multiple fields, use `WithFields`.

func (*Logger) WithFields 

func (logger *Logger) WithFields(fields Fields) *Entry

Adds a struct of fields to the log entry. All it does is call `WithField` for each `Field`.

func (*Logger) Writer 

func (logger *Logger) Writer() *io.PipeWriter

type StdLogger 

type StdLogger interface {
	Print(...interface{})
	Printf(string, ...interface{})
	Println(...interface{})

	Fatal(...interface{})
	Fatalf(string, ...interface{})
	Fatalln(...interface{})

	Panic(...interface{})
	Panicf(string, ...interface{})
	Panicln(...interface{})
}

StdLogger is what your logrus-enabled library should take, that way it'll accept a stdlib logger and a logrus logger. There's no standard interface, this is the closest we get, unfortunately.

type Termios 

type Termios syscall.Termios

type TextFormatter 

type TextFormatter struct {
	// Set to true to bypass checking for a TTY before outputting colors.
	ForceColors   bool
	DisableColors bool
	// Set to true to disable timestamp logging (useful when the output
	// is redirected to a logging system already adding a timestamp)
	DisableTimestamp bool
}

func (*TextFormatter) Format 

func (f *TextFormatter) Format(entry *Entry) ([]byte, error)

Source Files

View all Source files

Directories

Path Synopsis
examples
basic
hook
hooks
airbrake
papertrail
sentry
syslog

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