README

Logrus  Build Status

Logrus is a structured logger for Go (golang), completely API compatible with the standard library logger. Godoc.

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 l2met 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

Note again that Logrus is API compatible with the standardlib logger, so if you remove the log import and create a global log variable as below it will just work.

package main

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

var log = logrus.New()

func init() {
  log.Formatter = new(logrus.JSONFormatter)
  log.Formatter = new(logrus.TextFormatter) // default
}

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

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

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

Logrus encourages careful, structured logging. It encourages the use of 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 = logrus.New()

log.WithFields(logrus.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 want to 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 or info to StatsD.

log = logrus.New()
log.Hooks.Add(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(logrus.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() []logrus.Level {
  return []logrus.Level{
    logrus.Error,
    logrus.Fatal,
    logrus.Panic,
  }
}
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.Level = logrus.Info

It may be useful to set log.Level = logrus.Debug 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:

init() {
  // do something here to set environment depending on an environment variable
  // or command-line flag
  log := logrus.New()

  if Environment == "production" {
    log.Formatter = new(logrus.JSONFormatter)
  } else {
    // The TextFormatter is default, you don't actually have to do this.
    log.Formatter = new(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.
  • 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.Formatter = new(MyJSONFormatter)

func (f *JSONFormatter) Format(entry *Entry) ([]byte, error) {
  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
}
TODO
  • Performance
  • Default fields for an instance and inheritance
  • Default available hooks (airbrake, statsd, dump cores)
Expand ▾ Collapse ▴

Documentation

Index

Constants

This section is empty.

Variables

This section is empty.

Functions

This section is empty.

Types

type Entry

type Entry struct {
	Data Fields
	// contains filtered or unexported fields
}

func NewEntry

func NewEntry(logger *Logger) *Entry

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)

func (*Entry) String

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

func (*Entry) Warn

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

func (*Entry) Warnf

func (entry *Entry) Warnf(format string, 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

func (*Entry) WithFields

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

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

            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.Debug,
              }
              

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

              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`.

                  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 TextFormatter

                    type TextFormatter struct {
                    	// Set to true to bypass checking for a TTY before outputting colors.
                    	ForceColors bool
                    }

                    func (*TextFormatter) AppendKeyValue

                    func (f *TextFormatter) AppendKeyValue(serialized []byte, key, value interface{}) []byte

                    func (*TextFormatter) Format

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

                    Directories

                    Path Synopsis