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logrus |
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language: go | ||
go: | ||
- 1.1 | ||
- 1.2 | ||
- tip | ||
before_script: | ||
- go get github.com/stretchr/testify |
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The MIT License (MIT) | ||
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Copyright (c) 2014 Simon Eskildsen | ||
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Permission is hereby granted, free of charge, to any person obtaining a copy | ||
of this software and associated documentation files (the "Software"), to deal | ||
in the Software without restriction, including without limitation the rights | ||
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell | ||
copies of the Software, and to permit persons to whom the Software is | ||
furnished to do so, subject to the following conditions: | ||
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The above copyright notice and this permission notice shall be included in | ||
all copies or substantial portions of the Software. | ||
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | ||
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, | ||
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE | ||
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER | ||
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, | ||
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN | ||
THE SOFTWARE. |
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# Logrus <img src="http://i.imgur.com/hTeVwmJ.png" width="40" height="40" alt=":walrus:" class="emoji" title=":walrus:"/> [![Build Status](https://travis-ci.org/Sirupsen/logrus.svg?branch=master)](https://travis-ci.org/Sirupsen/logrus) | ||
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Logrus is a structured logger for Go (golang), completely API compatible with | ||
the standard library logger. [Godoc][godoc]. **Please note the Logrus API is not | ||
yet stable (pre 1.0), the core API is unlikely change much but please version | ||
control your Logrus to make sure you aren't fetching latest `master` on every | ||
build.** | ||
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Nicely color-coded in development (when a TTY is attached, otherwise just | ||
plain text): | ||
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![Colored](http://i.imgur.com/PY7qMwd.png) | ||
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With `log.Formatter = new(logrus.JSONFormatter)`, for easy parsing by logstash | ||
or Splunk: | ||
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```json | ||
{"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"} | ||
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{"level":"warning","msg":"The group's number increased tremendously!", | ||
"number":122,"omg":true,"time":"2014-03-10 19:57:38.562471297 -0400 EDT"} | ||
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{"animal":"walrus","level":"info","msg":"A giant walrus appears!", | ||
"size":10,"time":"2014-03-10 19:57:38.562500591 -0400 EDT"} | ||
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{"animal":"walrus","level":"info","msg":"Tremendously sized cow enters the ocean.", | ||
"size":9,"time":"2014-03-10 19:57:38.562527896 -0400 EDT"} | ||
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{"level":"fatal","msg":"The ice breaks!","number":100,"omg":true, | ||
"time":"2014-03-10 19:57:38.562543128 -0400 EDT"} | ||
``` | ||
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With the default `log.Formatter = new(logrus.TextFormatter)` when a TTY is not | ||
attached, the output is compatible with the | ||
[l2met](http://r.32k.io/l2met-introduction) format: | ||
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```text | ||
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 | ||
``` | ||
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#### Example | ||
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The simplest way to use Logrus is simply the package-level exported logger: | ||
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```go | ||
package main | ||
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import ( | ||
log "github.com/Sirupsen/logrus" | ||
) | ||
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func main() { | ||
log.WithFields(log.Fields{ | ||
"animal": "walrus", | ||
}).Info("A walrus appears") | ||
} | ||
``` | ||
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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: | ||
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```go | ||
package main | ||
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import ( | ||
"os" | ||
log "github.com/Sirupsen/logrus" | ||
"github.com/Sirupsen/logrus/hooks/airbrake" | ||
) | ||
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func init() { | ||
// Log as JSON instead of the default ASCII formatter. | ||
log.SetFormatter(&log.JSONFormatter{}) | ||
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// 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) | ||
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// Output to stderr instead of stdout, could also be a file. | ||
log.SetOutput(os.Stderr) | ||
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// Only log the warning severity or above. | ||
log.SetLevel(log.WarnLevel) | ||
} | ||
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func main() { | ||
log.WithFields(log.Fields{ | ||
"animal": "walrus", | ||
"size": 10, | ||
}).Info("A group of walrus emerges from the ocean") | ||
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log.WithFields(log.Fields{ | ||
"omg": true, | ||
"number": 122, | ||
}).Warn("The group's number increased tremendously!") | ||
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log.WithFields(log.Fields{ | ||
"omg": true, | ||
"number": 100, | ||
}).Fatal("The ice breaks!") | ||
} | ||
``` | ||
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For more advanced usage such as logging to multiple locations from the same | ||
application, you can also create an instance of the `logrus` Logger: | ||
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```go | ||
package main | ||
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import ( | ||
"github.com/Sirupsen/logrus" | ||
) | ||
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// Create a new instance of the logger. You can have any number of instances. | ||
var log = logrus.New() | ||
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func main() { | ||
// The API for setting attributes is a little different than the package level | ||
// exported logger. See Godoc. | ||
log.Out = os.Stderr | ||
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log.WithFields(log.Fields{ | ||
"animal": "walrus", | ||
"size": 10, | ||
}).Info("A group of walrus emerges from the ocean") | ||
} | ||
``` | ||
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#### Fields | ||
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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: | ||
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```go | ||
log.WithFields(log.Fields{ | ||
"event": event, | ||
"topic": topic, | ||
"key": key, | ||
}).Fatal("Failed to send event") | ||
``` | ||
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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. | ||
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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. | ||
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#### Hooks | ||
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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. | ||
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```go | ||
// Not the real implementation of the Airbrake hook. Just a simple sample. | ||
import ( | ||
log "github.com/Sirupsen/logrus" | ||
) | ||
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func init() { | ||
log.AddHook(new(AirbrakeHook)) | ||
} | ||
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type AirbrakeHook struct{} | ||
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// `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") | ||
} | ||
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return nil | ||
} | ||
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// `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, | ||
} | ||
} | ||
``` | ||
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Logrus comes with built-in hooks. Add those, or your custom hook, in `init`: | ||
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```go | ||
import ( | ||
log "github.com/Sirupsen/logrus" | ||
"github.com/Sirupsen/logrus/hooks/airbrake" | ||
"github.com/Sirupsen/logrus/hooks/syslog" | ||
) | ||
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func init() { | ||
log.AddHook(new(logrus_airbrake.AirbrakeHook)) | ||
log.AddHook(logrus_syslog.NewSyslogHook("udp", "localhost:514", syslog.LOG_INFO, "")) | ||
} | ||
``` | ||
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* [`github.com/Sirupsen/logrus/hooks/airbrake`](https://github.com/Sirupsen/logrus/blob/master/hooks/airbrake/airbrake.go). | ||
Send errors to an exception tracking service compatible with the Airbrake API. | ||
Uses [`airbrake-go`](https://github.com/tobi/airbrake-go) behind the scenes. | ||
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* [`github.com/Sirupsen/logrus/hooks/syslog`](https://github.com/Sirupsen/logrus/blob/master/hooks/syslog/syslog.go). | ||
Send errors to remote syslog server. | ||
Uses standard library `log/syslog` behind the scenes. | ||
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#### Level logging | ||
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Logrus has six logging levels: Debug, Info, Warning, Error, Fatal and Panic. | ||
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```go | ||
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.") | ||
``` | ||
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You can set the logging level on a `Logger`, then it will only log entries with | ||
that severity or anything above it: | ||
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```go | ||
// Will log anything that is info or above (warn, error, fatal, panic). Default. | ||
log.SetLevel(log.InfoLevel) | ||
``` | ||
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It may be useful to set `log.Level = logrus.DebugLevel` in a debug or verbose | ||
environment if your application has that. | ||
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#### Entries | ||
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Besides the fields added with `WithField` or `WithFields` some fields are | ||
automatically added to all logging events: | ||
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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`. | ||
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#### Environments | ||
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Logrus has no notion of environment. | ||
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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: | ||
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```go | ||
import ( | ||
log "github.com/Sirupsen/logrus" | ||
) | ||
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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) | ||
} | ||
} | ||
``` | ||
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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. | ||
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#### Formatters | ||
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The built-in logging formatters are: | ||
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* `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. | ||
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Third party logging formatters: | ||
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* [`zalgo`](https://github.com/aybabtme/logzalgo): invoking the P͉̫o̳̼̊w̖͈̰͎e̬͔̭͂r͚̼̹̲ ̫͓͉̳͈ō̠͕͖̚f̝͍̠ ͕̲̞͖͑Z̖̫̤̫ͪa͉̬͈̗l͖͎g̳̥o̰̥̅!̣͔̲̻͊̄ ̙̘̦̹̦. | ||
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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): | ||
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```go | ||
type MyJSONFormatter struct { | ||
} | ||
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log.SetFormatter(new(MyJSONFormatter)) | ||
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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 | ||
} | ||
``` | ||
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#### Rotation | ||
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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. | ||
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[godoc]: https://godoc.org/github.com/Sirupsen/logrus |
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