zerolog

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 Go to latest Published: Aug 6, 2017 License: MIT Imports: 14 Imported by: 0

README

Zero Allocation JSON Logger

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The zerolog package provides a fast and simple logger dedicated to JSON output.

Zerolog's API is designed to provide both a great developer experience and stunning performance. Its unique chaining API allows zerolog to write JSON log events by avoiding allocations and reflection.

The uber's zap library pioneered this approach. Zerolog is taking this concept to the next level with simpler to use API and even better performance.

To keep the code base and the API simple, zerolog focuses on JSON logging only. Pretty logging on the console is made possible using the provided zerolog.ConsoleWriter.

Features

  • Blazing fast
  • Low to zero allocation
  • Level logging
  • Sampling
  • Contextual fields
  • context.Context integration
  • net/http helpers
  • Pretty logging for development

Usage

import "github.com/rs/zerolog/log"
A global logger can be use for simple logging
log.Info().Msg("hello world")

// Output: {"level":"info","time":1494567715,"message":"hello world"}

NOTE: To import the global logger, import the log subpackage github.com/rs/zerolog/log.

log.Fatal().
    Err(err).
    Str("service", service).
    Msgf("Cannot start %s", service)

// Output: {"level":"fatal","time":1494567715,"message":"Cannot start myservice","error":"some error","service":"myservice"}
// Exit 1

NOTE: Using Msgf generates one allocation even when the logger is disabled.

Fields can be added to log messages
log.Info().
    Str("foo", "bar").
    Int("n", 123).
    Msg("hello world")

// Output: {"level":"info","time":1494567715,"foo":"bar","n":123,"message":"hello world"}
Create logger instance to manage different outputs
logger := zerolog.New(os.Stderr).With().Timestamp().Logger()

logger.Info().Str("foo", "bar").Msg("hello world")

// Output: {"level":"info","time":1494567715,"message":"hello world","foo":"bar"}
Sub-loggers let you chain loggers with additional context
sublogger := log.With().
                 Str("component": "foo").
                 Logger()
sublogger.Info().Msg("hello world")

// Output: {"level":"info","time":1494567715,"message":"hello world","component":"foo"}
Level logging
zerolog.SetGlobalLevel(zerolog.InfoLevel)

log.Debug().Msg("filtered out message")
log.Info().Msg("routed message")

if e := log.Debug(); e.Enabled() {
    // Compute log output only if enabled.
    value := compute()
    e.Str("foo": value).Msg("some debug message")
}

// Output: {"level":"info","time":1494567715,"message":"routed message"}
Pretty logging
if isConsole {
    log.Logger = log.Output(zerolog.ConsoleWriter{Out: os.Stderr})
}

log.Info().Str("foo", "bar").Msg("Hello world")

// Output: 1494567715 |INFO| Hello world foo=bar
Sub dictionary
log.Info().
    Str("foo", "bar").
    Dict("dict", zerolog.Dict().
        Str("bar", "baz").
        Int("n", 1)
    ).Msg("hello world")

// Output: {"level":"info","time":1494567715,"foo":"bar","dict":{"bar":"baz","n":1},"message":"hello world"}
Customize automatic field names
zerolog.TimestampFieldName = "t"
zerolog.LevelFieldName = "l"
zerolog.MessageFieldName = "m"

log.Info().Msg("hello world")

// Output: {"l":"info","t":1494567715,"m":"hello world"}
Log with no level nor message
log.Log().Str("foo","bar").Msg("")

// Output: {"time":1494567715,"foo":"bar"}
Add contextual fields to the global logger
log.Logger = log.With().Str("foo", "bar").Logger()
Log Sampling
sampled := log.Sample(10)
sampled.Info().Msg("will be logged every 10 messages")

// Output: {"time":1494567715,"sample":10,"message":"will be logged every 10 messages"}
Pass a sub-logger by context
ctx := log.With("component", "module").Logger().WithContext(ctx)

log.Ctx(ctx).Info().Msg("hello world")

// Output: {"component":"module","level":"info","message":"hello world"}
Set as standard logger output
log := zerolog.New(os.Stdout).With().
    Str("foo", "bar").
    Logger()

stdlog.SetFlags(0)
stdlog.SetOutput(log)

stdlog.Print("hello world")

// Output: {"foo":"bar","message":"hello world"}
Integration with net/http

The github.com/rs/zerolog/hlog package provides some helpers to integrate zerolog with http.Handler.

In this example we use alice to install logger for better readability.

log := zerolog.New(os.Stdout).With().
    Timestamp().
    Str("role", "my-service").
    Str("host", host).
    Logger()

c := alice.New()

// Install the logger handler with default output on the console
c = c.Append(hlog.NewHandler(log))

// Install some provided extra handler to set some request's context fields.
// Thanks to those handler, all our logs will come with some pre-populated fields.
c = c.Append(hlog.AccessHandler(func(r *http.Request, status, size int, duration time.Duration) {
    hlog.FromRequest(r).Info().
        Str("method", r.Method).
        Str("url", r.URL.String()).
        Int("status", status).
        Int("size", size).
        Dur("duration", duration).
        Msg("")
}))
c = c.Append(hlog.RemoteAddrHandler("ip"))
c = c.Append(hlog.UserAgentHandler("user_agent"))
c = c.Append(hlog.RefererHandler("referer"))
c = c.Append(hlog.RequestIDHandler("req_id", "Request-Id"))

// Here is your final handler
h := c.Then(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    // Get the logger from the request's context. You can safely assume it
    // will be always there: if the handler is removed, hlog.FromRequest
    // will return a no-op logger.
    hlog.FromRequest(r).Info().
        Str("user", "current user").
        Str("status", "ok").
        Msg("Something happened")

    // Output: {"level":"info","time":"2001-02-03T04:05:06Z","role":"my-service","host":"local-hostname","req_id":"b4g0l5t6tfid6dtrapu0","user":"current user","status":"ok","message":"Something happened"}
}))
http.Handle("/", h)

if err := http.ListenAndServe(":8080", nil); err != nil {
    log.Fatal().Err(err).Msg("Startup failed")
}

Global Settings

Some settings can be changed and will by applied to all loggers:

  • log.Logger: You can set this value to customize the global logger (the one used by package level methods).
  • zerolog.SetGlobalLevel: Can raise the minimum level of all loggers. Set this to zerolog.Disable to disable logging altogether (quiet mode).
  • zerolog.DisableSampling: If argument is true, all sampled loggers will stop sampling and issue 100% of their log events.
  • zerolog.TimestampFieldName: Can be set to customize Timestamp field name.
  • zerolog.LevelFieldName: Can be set to customize level field name.
  • zerolog.MessageFieldName: Can be set to customize message field name.
  • zerolog.ErrorFieldName: Can be set to customize Err field name.
  • zerolog.SampleFieldName: Can be set to customize the field name added when sampling is enabled.
  • zerolog.TimeFieldFormat: Can be set to customize Time field value formatting. If set with an empty string, times are formated as UNIX timestamp. // DurationFieldUnit defines the unit for time.Duration type fields added // using the Dur method.
  • DurationFieldUnit: Sets the unit of the fields added by Dur (default: time.Millisecond).
  • DurationFieldInteger: If set to true, Dur fields are formatted as integers instead of floats.

Field Types

Standard Types
  • Str
  • Bool
  • Int, Int8, Int16, Int32, Int64
  • Uint, Uint8, Uint16, Uint32, Uint64
  • Float32, Float64
Advanced Fields
  • Err: Takes an error and render it as a string using the zerolog.ErrorFieldName field name.
  • Timestamp: Insert a timestamp field with zerolog.TimestampFieldName field name and formatted using zerolog.TimeFieldFormat.
  • Time: Adds a field with the time formated with the zerolog.TimeFieldFormat.
  • Dur: Adds a field with a time.Duration.
  • Dict: Adds a sub-key/value as a field of the event.
  • Interface: Uses reflection to marshal the type.

Performance

All operations are allocation free (those numbers include JSON encoding):

BenchmarkLogEmpty-8        100000000    19.1 ns/op	   0 B/op       0 allocs/op
BenchmarkDisabled-8        500000000     4.07 ns/op	   0 B/op       0 allocs/op
BenchmarkInfo-8            30000000	    42.5 ns/op	   0 B/op       0 allocs/op
BenchmarkContextFields-8   30000000	    44.9 ns/op	   0 B/op       0 allocs/op
BenchmarkLogFields-8       10000000	   184 ns/op	   0 B/op       0 allocs/op

Using Uber's zap comparison benchmark:

Log a message and 10 fields:

Library Time Bytes Allocated Objects Allocated
zerolog 767 ns/op 552 B/op 6 allocs/op
⚡ zap 848 ns/op 704 B/op 2 allocs/op
⚡ zap (sugared) 1363 ns/op 1610 B/op 20 allocs/op
go-kit 3614 ns/op 2895 B/op 66 allocs/op
lion 5392 ns/op 5807 B/op 63 allocs/op
logrus 5661 ns/op 6092 B/op 78 allocs/op
apex/log 15332 ns/op 3832 B/op 65 allocs/op
log15 20657 ns/op 5632 B/op 93 allocs/op

Log a message with a logger that already has 10 fields of context:

Library Time Bytes Allocated Objects Allocated
zerolog 52 ns/op 0 B/op 0 allocs/op
⚡ zap 283 ns/op 0 B/op 0 allocs/op
⚡ zap (sugared) 337 ns/op 80 B/op 2 allocs/op
lion 2702 ns/op 4074 B/op 38 allocs/op
go-kit 3378 ns/op 3046 B/op 52 allocs/op
logrus 4309 ns/op 4564 B/op 63 allocs/op
apex/log 13456 ns/op 2898 B/op 51 allocs/op
log15 14179 ns/op 2642 B/op 44 allocs/op

Log a static string, without any context or printf-style templating:

Library Time Bytes Allocated Objects Allocated
zerolog 50 ns/op 0 B/op 0 allocs/op
⚡ zap 236 ns/op 0 B/op 0 allocs/op
standard library 453 ns/op 80 B/op 2 allocs/op
⚡ zap (sugared) 337 ns/op 80 B/op 2 allocs/op
go-kit 508 ns/op 656 B/op 13 allocs/op
lion 771 ns/op 1224 B/op 10 allocs/op
logrus 1244 ns/op 1505 B/op 27 allocs/op
apex/log 2751 ns/op 584 B/op 11 allocs/op
log15 5181 ns/op 1592 B/op 26 allocs/op

Documentation

Overview

Package zerolog provides a lightweight logging library dedicated to JSON logging.

A global Logger can be use for simple logging: 

import "github.com/rs/zerolog/log"

log.Info().Msg("hello world")
// Output: {"time":1494567715,"level":"info","message":"hello world"}

NOTE: To import the global logger, import the "log" subpackage "github.com/rs/zerolog/log".

Fields can be added to log messages: 

log.Info().Str("foo", "bar").Msg("hello world")
// Output: {"time":1494567715,"level":"info","message":"hello world","foo":"bar"}

Create logger instance to manage different outputs: 

logger := zerolog.New(os.Stderr).With().Timestamp().Logger()
logger.Info().
       Str("foo", "bar").
       Msg("hello world")
// Output: {"time":1494567715,"level":"info","message":"hello world","foo":"bar"}

Sub-loggers let you chain loggers with additional context: 

sublogger := log.With().Str("component": "foo").Logger()
sublogger.Info().Msg("hello world")
// Output: {"time":1494567715,"level":"info","message":"hello world","component":"foo"}

Level logging 

zerolog.SetGlobalLevel(zerolog.InfoLevel)

log.Debug().Msg("filtered out message")
log.Info().Msg("routed message")

if e := log.Debug(); e.Enabled() {
    // Compute log output only if enabled.
    value := compute()
    e.Str("foo": value).Msg("some debug message")
}
// Output: {"level":"info","time":1494567715,"routed message"}

Customize automatic field names: 

log.TimestampFieldName = "t"
log.LevelFieldName = "p"
log.MessageFieldName = "m"

log.Info().Msg("hello world")
// Output: {"t":1494567715,"p":"info","m":"hello world"}

Log with no level and message: 

log.Log().Str("foo","bar").Msg("")
// Output: {"time":1494567715,"foo":"bar"}

Add contextual fields to global Logger: 

log.Logger = log.With().Str("foo", "bar").Logger()

Sample logs: 

sampled := log.Sample(10)
sampled.Info().Msg("will be logged every 10 messages")

Index

Examples

Constants

View Source 
const (
	// Often samples log every 10 events.
	Often = 10
	// Sometimes samples log every 100 events.
	Sometimes = 100
	// Rarely samples log every 1000 events.
	Rarely = 1000
)

Variables

View Source 
var (
	// TimestampFieldName is the field name used for the timestamp field.
	TimestampFieldName = "time"

	// LevelFieldName is the field name used for the level field.
	LevelFieldName = "level"

	// MessageFieldName is the field name used for the message field.
	MessageFieldName = "message"

	// ErrorFieldName is the field name used for error fields.
	ErrorFieldName = "error"

	// SampleFieldName is the name of the field used to report sampling.
	SampleFieldName = "sample"

	// TimeFieldFormat defines the time format of the Time field type.
	// If set to an empty string, the time is formatted as an UNIX timestamp
	// as integer.
	TimeFieldFormat = time.RFC3339

	// TimestampFunc defines the function called to generate a timestamp.
	TimestampFunc = time.Now

	// DurationFieldUnit defines the unit for time.Duration type fields added
	// using the Dur method.
	DurationFieldUnit = time.Millisecond

	// DurationFieldInteger renders Dur fields as integer instead of float if
	// set to true.
	DurationFieldInteger = false
)

Functions

func DisableSampling 

func DisableSampling(v bool)

DisableSampling will disable sampling in all Loggers if true.

func SetGlobalLevel 

func SetGlobalLevel(l Level)

SetGlobalLevel sets the global override for log level. If this values is raised, all Loggers will use at least this value.

To globally disable logs, set GlobalLevel to Disabled.

func SyncWriter 

func SyncWriter(w io.Writer) io.Writer

SyncWriter wraps w so that each call to Write is synchronized with a mutex. This syncer can be the call to writer's Write method is not thread safe. Note that os.File Write operation is using write() syscall which is supposed to be thread-safe on POSIX systems. So there is no need to use this with os.File on such systems as zerolog guaranties to issue a single Write call per log event.

Types

type Array added in v1.1.0 

type Array struct {
	// contains filtered or unexported fields
}

func Arr added in v1.1.0 

func Arr() *Array

Arr creates an array to be added to an Event or Context.

func (*Array) Bool added in v1.1.0 

func (a *Array) Bool(b bool) *Array

Bool append the val as a bool to the array.

func (*Array) Bytes added in v1.1.0 

func (a *Array) Bytes(val []byte) *Array

Bytes append the val as a string to the array.

func (*Array) Dur added in v1.1.0 

func (a *Array) Dur(d time.Duration) *Array

Dur append d to the array.

func (*Array) Err added in v1.1.0 

func (a *Array) Err(err error) *Array

Err append the err as a string to the array.

func (*Array) Float32 added in v1.1.0 

func (a *Array) Float32(f float32) *Array

Float32 append f as a float32 to the array.

func (*Array) Float64 added in v1.1.0 

func (a *Array) Float64(f float64) *Array

Float64 append f as a float64 to the array.

func (*Array) Int added in v1.1.0 

func (a *Array) Int(i int) *Array

Int append i as a int to the array.

func (*Array) Int16 added in v1.1.0 

func (a *Array) Int16(i int16) *Array

Int16 append i as a int16 to the array.

func (*Array) Int32 added in v1.1.0 

func (a *Array) Int32(i int32) *Array

Int32 append i as a int32 to the array.

func (*Array) Int64 added in v1.1.0 

func (a *Array) Int64(i int64) *Array

Int64 append i as a int64 to the array.

func (*Array) Int8 added in v1.1.0 

func (a *Array) Int8(i int8) *Array

Int8 append i as a int8 to the array.

func (*Array) Interface added in v1.1.0 

func (a *Array) Interface(i interface{}) *Array

Interface append i marshaled using reflection.

func (*Array) MarshalZerologArray added in v1.1.0 

func (*Array) MarshalZerologArray(*Array)

func (*Array) Object added in v1.1.0 

func (a *Array) Object(obj LogObjectMarshaler) *Array

Object marshals an object that implement the LogObjectMarshaler interface and append it to the array.

func (*Array) Str added in v1.1.0 

func (a *Array) Str(val string) *Array

Str append the val as a string to the array.

func (*Array) Time added in v1.1.0 

func (a *Array) Time(t time.Time) *Array

Time append t formated as string using zerolog.TimeFieldFormat.

func (*Array) Uint added in v1.1.0 

func (a *Array) Uint(i uint) *Array

Uint append i as a uint to the array.

func (*Array) Uint16 added in v1.1.0 

func (a *Array) Uint16(i uint16) *Array

Uint16 append i as a uint16 to the array.

func (*Array) Uint32 added in v1.1.0 

func (a *Array) Uint32(i uint32) *Array

Uint32 append i as a uint32 to the array.

func (*Array) Uint64 added in v1.1.0 

func (a *Array) Uint64(i uint64) *Array

Uint64 append i as a uint64 to the array.

func (*Array) Uint8 added in v1.1.0 

func (a *Array) Uint8(i uint8) *Array

Uint8 append i as a uint8 to the array.

type ConsoleWriter added in v1.2.1 

type ConsoleWriter struct {
	Out     io.Writer
	NoColor bool
}

ConsoleWriter reads a JSON object per write operation and output an optionally colored human readable version on the Out writer.

func (ConsoleWriter) Write added in v1.2.1 

func (w ConsoleWriter) Write(p []byte) (n int, err error)

type Context 

type Context struct {
	// contains filtered or unexported fields
}

Context configures a new sub-logger with contextual fields.

func (Context) AnErr 

func (c Context) AnErr(key string, err error) Context

AnErr adds the field key with err as a string to the logger context.

func (Context) Array added in v1.1.0 

func (c Context) Array(key string, arr LogArrayMarshaler) Context

Array adds the field key with an array to the event context. Use zerolog.Arr() to create the array or pass a type that implement the LogArrayMarshaler interface.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout).With().
		Str("foo", "bar").
		Array("array", zerolog.Arr().
			Str("baz").
			Int(1),
		).Logger()

	log.Log().Msg("hello world")

}

Output:

{"foo":"bar","array":["baz",1],"message":"hello world"}
Example (Object) 
package main

import (
	"os"
	"time"

	"github.com/rs/zerolog"
)

type User struct {
	Name    string
	Age     int
	Created time.Time
}

func (u User) MarshalZerologObject(e *zerolog.Event) {
	e.Str("name", u.Name).
		Int("age", u.Age).
		Time("created", u.Created)
}

type Users []User

func (uu Users) MarshalZerologArray(a *zerolog.Array) {
	for _, u := range uu {
		a.Object(u)
	}
}

func main() {
	// Users implements zerolog.LogArrayMarshaler
	u := Users{
		User{"John", 35, time.Time{}},
		User{"Bob", 55, time.Time{}},
	}

	log := zerolog.New(os.Stdout).With().
		Str("foo", "bar").
		Array("users", u).
		Logger()

	log.Log().Msg("hello world")

}

Output:

{"foo":"bar","users":[{"name":"John","age":35,"created":"0001-01-01T00:00:00Z"},{"name":"Bob","age":55,"created":"0001-01-01T00:00:00Z"}],"message":"hello world"}

func (Context) Bool 

func (c Context) Bool(key string, b bool) Context

Bool adds the field key with val as a bool to the logger context.

func (Context) Bools added in v1.0.1 

func (c Context) Bools(key string, b []bool) Context

Bools adds the field key with val as a []bool to the logger context.

func (Context) Bytes added in v1.0.1 

func (c Context) Bytes(key string, val []byte) Context

Bytes adds the field key with val as a []byte to the logger context.

func (Context) Dict 

func (c Context) Dict(key string, dict *Event) Context

Dict adds the field key with the dict to the logger context.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout).With().
		Str("foo", "bar").
		Dict("dict", zerolog.Dict().
			Str("bar", "baz").
			Int("n", 1),
		).Logger()

	log.Log().Msg("hello world")

}

Output:

{"foo":"bar","dict":{"bar":"baz","n":1},"message":"hello world"}

func (Context) Dur 

func (c Context) Dur(key string, d time.Duration) Context

Dur adds the fields key with d divided by unit and stored as a float.

Example 
package main

import (
	"os"
	"time"

	"github.com/rs/zerolog"
)

func main() {
	d := time.Duration(10 * time.Second)

	log := zerolog.New(os.Stdout).With().
		Str("foo", "bar").
		Dur("dur", d).
		Logger()

	log.Log().Msg("hello world")

}

Output:

{"foo":"bar","dur":10000,"message":"hello world"}

func (Context) Durs added in v1.0.1 

func (c Context) Durs(key string, d []time.Duration) Context

Durs adds the fields key with d divided by unit and stored as a float.

Example 
package main

import (
	"os"
	"time"

	"github.com/rs/zerolog"
)

func main() {
	d := []time.Duration{
		time.Duration(10 * time.Second),
		time.Duration(20 * time.Second),
	}

	log := zerolog.New(os.Stdout).With().
		Str("foo", "bar").
		Durs("durs", d).
		Logger()

	log.Log().Msg("hello world")

}

Output:

{"foo":"bar","durs":[10000,20000],"message":"hello world"}

func (Context) Err 

func (c Context) Err(err error) Context

Err adds the field "error" with err as a string to the logger context. To customize the key name, change zerolog.ErrorFieldName.

func (Context) Errs added in v1.0.1 

func (c Context) Errs(key string, errs []error) Context

Errs adds the field key with errs as an array of strings to the logger context.

func (Context) Fields added in v1.0.1 

func (c Context) Fields(fields map[string]interface{}) Context

Fields is a helper function to use a map to set fields using type assertion.

func (Context) Float32 

func (c Context) Float32(key string, f float32) Context

Float32 adds the field key with f as a float32 to the logger context.

func (Context) Float64 

func (c Context) Float64(key string, f float64) Context

Float64 adds the field key with f as a float64 to the logger context.

func (Context) Floats32 added in v1.0.1 

func (c Context) Floats32(key string, f []float32) Context

Floats32 adds the field key with f as a []float32 to the logger context.

func (Context) Floats64 added in v1.0.1 

func (c Context) Floats64(key string, f []float64) Context

Floats64 adds the field key with f as a []float64 to the logger context.

func (Context) Int 

func (c Context) Int(key string, i int) Context

Int adds the field key with i as a int to the logger context.

func (Context) Int16 

func (c Context) Int16(key string, i int16) Context

Int16 adds the field key with i as a int16 to the logger context.

func (Context) Int32 

func (c Context) Int32(key string, i int32) Context

Int32 adds the field key with i as a int32 to the logger context.

func (Context) Int64 

func (c Context) Int64(key string, i int64) Context

Int64 adds the field key with i as a int64 to the logger context.

func (Context) Int8 

func (c Context) Int8(key string, i int8) Context

Int8 adds the field key with i as a int8 to the logger context.

func (Context) Interface 

func (c Context) Interface(key string, i interface{}) Context

Interface adds the field key with obj marshaled using reflection.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	obj := struct {
		Name string `json:"name"`
	}{
		Name: "john",
	}

	log := zerolog.New(os.Stdout).With().
		Str("foo", "bar").
		Interface("obj", obj).
		Logger()

	log.Log().Msg("hello world")

}

Output:

{"foo":"bar","obj":{"name":"john"},"message":"hello world"}

func (Context) Ints added in v1.0.1 

func (c Context) Ints(key string, i []int) Context

Ints adds the field key with i as a []int to the logger context.

func (Context) Ints16 added in v1.0.1 

func (c Context) Ints16(key string, i []int16) Context

Ints16 adds the field key with i as a []int16 to the logger context.

func (Context) Ints32 added in v1.0.1 

func (c Context) Ints32(key string, i []int32) Context

Ints32 adds the field key with i as a []int32 to the logger context.

func (Context) Ints64 added in v1.0.1 

func (c Context) Ints64(key string, i []int64) Context

Ints64 adds the field key with i as a []int64 to the logger context.

func (Context) Ints8 added in v1.0.1 

func (c Context) Ints8(key string, i []int8) Context

Ints8 adds the field key with i as a []int8 to the logger context.

func (Context) Logger 

func (c Context) Logger() Logger

Logger returns the logger with the context previously set.

func (Context) Object added in v1.0.3 

func (c Context) Object(key string, obj LogObjectMarshaler) Context

Object marshals an object that implement the LogObjectMarshaler interface.

Example 
package main

import (
	"os"
	"time"

	"github.com/rs/zerolog"
)

type User struct {
	Name    string
	Age     int
	Created time.Time
}

func (u User) MarshalZerologObject(e *zerolog.Event) {
	e.Str("name", u.Name).
		Int("age", u.Age).
		Time("created", u.Created)
}

func main() {
	// User implements zerolog.LogObjectMarshaler
	u := User{"John", 35, time.Time{}}

	log := zerolog.New(os.Stdout).With().
		Str("foo", "bar").
		Object("user", u).
		Logger()

	log.Log().Msg("hello world")

}

Output:

{"foo":"bar","user":{"name":"John","age":35,"created":"0001-01-01T00:00:00Z"},"message":"hello world"}

func (Context) Str 

func (c Context) Str(key, val string) Context

Str adds the field key with val as a string to the logger context.

func (Context) Strs added in v1.0.1 

func (c Context) Strs(key string, vals []string) Context

Strs adds the field key with val as a string to the logger context.

func (Context) Time 

func (c Context) Time(key string, t time.Time) Context

Time adds the field key with t formated as string using zerolog.TimeFieldFormat.

func (Context) Times added in v1.0.1 

func (c Context) Times(key string, t []time.Time) Context

Times adds the field key with t formated as string using zerolog.TimeFieldFormat.

func (Context) Timestamp 

func (c Context) Timestamp() Context

Timestamp adds the current local time as UNIX timestamp to the logger context with the "time" key. To customize the key name, change zerolog.TimestampFieldName.

func (Context) Uint 

func (c Context) Uint(key string, i uint) Context

Uint adds the field key with i as a uint to the logger context.

func (Context) Uint16 

func (c Context) Uint16(key string, i uint16) Context

Uint16 adds the field key with i as a uint16 to the logger context.

func (Context) Uint32 

func (c Context) Uint32(key string, i uint32) Context

Uint32 adds the field key with i as a uint32 to the logger context.

func (Context) Uint64 

func (c Context) Uint64(key string, i uint64) Context

Uint64 adds the field key with i as a uint64 to the logger context.

func (Context) Uint8 

func (c Context) Uint8(key string, i uint8) Context

Uint8 adds the field key with i as a uint8 to the logger context.

func (Context) Uints added in v1.0.1 

func (c Context) Uints(key string, i []uint) Context

Uints adds the field key with i as a []uint to the logger context.

func (Context) Uints16 added in v1.0.1 

func (c Context) Uints16(key string, i []uint16) Context

Uints16 adds the field key with i as a []uint16 to the logger context.

func (Context) Uints32 added in v1.0.1 

func (c Context) Uints32(key string, i []uint32) Context

Uints32 adds the field key with i as a []uint32 to the logger context.

func (Context) Uints64 added in v1.0.1 

func (c Context) Uints64(key string, i []uint64) Context

Uints64 adds the field key with i as a []uint64 to the logger context.

func (Context) Uints8 added in v1.0.1 

func (c Context) Uints8(key string, i []uint8) Context

Uints8 adds the field key with i as a []uint8 to the logger context.

type Event 

type Event struct {
	// contains filtered or unexported fields
}

Event represents a log event. It is instanced by one of the level method of Logger and finalized by the Msg or Msgf method.

func Dict 

func Dict() *Event

Dict creates an Event to be used with the *Event.Dict method. Call usual field methods like Str, Int etc to add fields to this event and give it as argument the *Event.Dict method.

func (*Event) AnErr 

func (e *Event) AnErr(key string, err error) *Event

AnErr adds the field key with err as a string to the *Event context. If err is nil, no field is added.

func (*Event) Array added in v1.1.0 

func (e *Event) Array(key string, arr LogArrayMarshaler) *Event

Array adds the field key with an array to the event context. Use zerolog.Arr() to create the array or pass a type that implement the LogArrayMarshaler interface.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout)

	log.Log().
		Str("foo", "bar").
		Array("array", zerolog.Arr().
			Str("baz").
			Int(1),
		).
		Msg("hello world")

}

Output:

{"foo":"bar","array":["baz",1],"message":"hello world"}
Example (Object) 
package main

import (
	"os"
	"time"

	"github.com/rs/zerolog"
)

type User struct {
	Name    string
	Age     int
	Created time.Time
}

func (u User) MarshalZerologObject(e *zerolog.Event) {
	e.Str("name", u.Name).
		Int("age", u.Age).
		Time("created", u.Created)
}

type Users []User

func (uu Users) MarshalZerologArray(a *zerolog.Array) {
	for _, u := range uu {
		a.Object(u)
	}
}

func main() {
	log := zerolog.New(os.Stdout)

	// Users implements zerolog.LogArrayMarshaler
	u := Users{
		User{"John", 35, time.Time{}},
		User{"Bob", 55, time.Time{}},
	}

	log.Log().
		Str("foo", "bar").
		Array("users", u).
		Msg("hello world")

}

Output:

{"foo":"bar","users":[{"name":"John","age":35,"created":"0001-01-01T00:00:00Z"},{"name":"Bob","age":55,"created":"0001-01-01T00:00:00Z"}],"message":"hello world"}

func (*Event) Bool 

func (e *Event) Bool(key string, b bool) *Event

Bool adds the field key with val as a bool to the *Event context.

func (*Event) Bools added in v1.0.1 

func (e *Event) Bools(key string, b []bool) *Event

Bools adds the field key with val as a []bool to the *Event context.

func (*Event) Bytes added in v1.0.1 

func (e *Event) Bytes(key string, val []byte) *Event

Bytes adds the field key with val as a string to the *Event context.

Runes outside of normal ASCII ranges will be hex-encoded in the resulting JSON.

func (*Event) Dict 

func (e *Event) Dict(key string, dict *Event) *Event

Dict adds the field key with a dict to the event context. Use zerolog.Dict() to create the dictionary.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout)

	log.Log().
		Str("foo", "bar").
		Dict("dict", zerolog.Dict().
			Str("bar", "baz").
			Int("n", 1),
		).
		Msg("hello world")

}

Output:

{"foo":"bar","dict":{"bar":"baz","n":1},"message":"hello world"}

func (*Event) Dur 

func (e *Event) Dur(key string, d time.Duration) *Event

Dur adds the field key with duration d stored as zerolog.DurationFieldUnit. If zerolog.DurationFieldInteger is true, durations are rendered as integer instead of float.

Example 
package main

import (
	"os"
	"time"

	"github.com/rs/zerolog"
)

func main() {
	d := time.Duration(10 * time.Second)

	log := zerolog.New(os.Stdout)

	log.Log().
		Str("foo", "bar").
		Dur("dur", d).
		Msg("hello world")

}

Output:

{"foo":"bar","dur":10000,"message":"hello world"}

func (*Event) Durs added in v1.0.1 

func (e *Event) Durs(key string, d []time.Duration) *Event

Durs adds the field key with duration d stored as zerolog.DurationFieldUnit. If zerolog.DurationFieldInteger is true, durations are rendered as integer instead of float.

Example 
package main

import (
	"os"
	"time"

	"github.com/rs/zerolog"
)

func main() {
	d := []time.Duration{
		time.Duration(10 * time.Second),
		time.Duration(20 * time.Second),
	}

	log := zerolog.New(os.Stdout)

	log.Log().
		Str("foo", "bar").
		Durs("durs", d).
		Msg("hello world")

}

Output:

{"foo":"bar","durs":[10000,20000],"message":"hello world"}

func (*Event) Enabled 

func (e *Event) Enabled() bool

Enabled return false if the *Event is going to be filtered out by log level or sampling.

func (*Event) Err 

func (e *Event) Err(err error) *Event

Err adds the field "error" with err as a string to the *Event context. If err is nil, no field is added. To customize the key name, change zerolog.ErrorFieldName.

func (*Event) Errs added in v1.0.1 

func (e *Event) Errs(key string, errs []error) *Event

Errs adds the field key with errs as an array of strings to the *Event context. If err is nil, no field is added.

func (*Event) Fields added in v1.0.1 

func (e *Event) Fields(fields map[string]interface{}) *Event

Fields is a helper function to use a map to set fields using type assertion.

func (*Event) Float32 

func (e *Event) Float32(key string, f float32) *Event

Float32 adds the field key with f as a float32 to the *Event context.

func (*Event) Float64 

func (e *Event) Float64(key string, f float64) *Event

Float64 adds the field key with f as a float64 to the *Event context.

func (*Event) Floats32 added in v1.0.1 

func (e *Event) Floats32(key string, f []float32) *Event

Floats32 adds the field key with f as a []float32 to the *Event context.

func (*Event) Floats64 added in v1.0.1 

func (e *Event) Floats64(key string, f []float64) *Event

Floats64 adds the field key with f as a []float64 to the *Event context.

func (*Event) Int 

func (e *Event) Int(key string, i int) *Event

Int adds the field key with i as a int to the *Event context.

func (*Event) Int16 

func (e *Event) Int16(key string, i int16) *Event

Int16 adds the field key with i as a int16 to the *Event context.

func (*Event) Int32 

func (e *Event) Int32(key string, i int32) *Event

Int32 adds the field key with i as a int32 to the *Event context.

func (*Event) Int64 

func (e *Event) Int64(key string, i int64) *Event

Int64 adds the field key with i as a int64 to the *Event context.

func (*Event) Int8 

func (e *Event) Int8(key string, i int8) *Event

Int8 adds the field key with i as a int8 to the *Event context.

func (*Event) Interface 

func (e *Event) Interface(key string, i interface{}) *Event

Interface adds the field key with i marshaled using reflection.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout)

	obj := struct {
		Name string `json:"name"`
	}{
		Name: "john",
	}

	log.Log().
		Str("foo", "bar").
		Interface("obj", obj).
		Msg("hello world")

}

Output:

{"foo":"bar","obj":{"name":"john"},"message":"hello world"}

func (*Event) Ints added in v1.0.1 

func (e *Event) Ints(key string, i []int) *Event

Ints adds the field key with i as a []int to the *Event context.

func (*Event) Ints16 added in v1.0.1 

func (e *Event) Ints16(key string, i []int16) *Event

Ints16 adds the field key with i as a []int16 to the *Event context.

func (*Event) Ints32 added in v1.0.1 

func (e *Event) Ints32(key string, i []int32) *Event

Ints32 adds the field key with i as a []int32 to the *Event context.

func (*Event) Ints64 added in v1.0.1 

func (e *Event) Ints64(key string, i []int64) *Event

Ints64 adds the field key with i as a []int64 to the *Event context.

func (*Event) Ints8 added in v1.0.1 

func (e *Event) Ints8(key string, i []int8) *Event

Ints8 adds the field key with i as a []int8 to the *Event context.

func (*Event) Msg 

func (e *Event) Msg(msg string)

Msg sends the *Event with msg added as the message field if not empty.

NOTICE: once this method is called, the *Event should be disposed. Calling Msg twice can have unexpected result.

func (*Event) Msgf 

func (e *Event) Msgf(format string, v ...interface{})

Msgf sends the event with formated msg added as the message field if not empty.

NOTICE: once this methid is called, the *Event should be disposed. Calling Msg twice can have unexpected result.

func (*Event) Object added in v1.0.3 

func (e *Event) Object(key string, obj LogObjectMarshaler) *Event

Object marshals an object that implement the LogObjectMarshaler interface.

Example 
package main

import (
	"os"
	"time"

	"github.com/rs/zerolog"
)

type User struct {
	Name    string
	Age     int
	Created time.Time
}

func (u User) MarshalZerologObject(e *zerolog.Event) {
	e.Str("name", u.Name).
		Int("age", u.Age).
		Time("created", u.Created)
}

func main() {
	log := zerolog.New(os.Stdout)

	// User implements zerolog.LogObjectMarshaler
	u := User{"John", 35, time.Time{}}

	log.Log().
		Str("foo", "bar").
		Object("user", u).
		Msg("hello world")

}

Output:

{"foo":"bar","user":{"name":"John","age":35,"created":"0001-01-01T00:00:00Z"},"message":"hello world"}

func (*Event) Str 

func (e *Event) Str(key, val string) *Event

Str adds the field key with val as a string to the *Event context.

func (*Event) Strs added in v1.0.1 

func (e *Event) Strs(key string, vals []string) *Event

Strs adds the field key with vals as a []string to the *Event context.

func (*Event) Time 

func (e *Event) Time(key string, t time.Time) *Event

Time adds the field key with t formated as string using zerolog.TimeFieldFormat.

func (*Event) TimeDiff 

func (e *Event) TimeDiff(key string, t time.Time, start time.Time) *Event

TimeDiff adds the field key with positive duration between time t and start. If time t is not greater than start, duration will be 0. Duration format follows the same principle as Dur().

func (*Event) Times added in v1.0.1 

func (e *Event) Times(key string, t []time.Time) *Event

Times adds the field key with t formated as string using zerolog.TimeFieldFormat.

func (*Event) Timestamp 

func (e *Event) Timestamp() *Event

Timestamp adds the current local time as UNIX timestamp to the *Event context with the "time" key. To customize the key name, change zerolog.TimestampFieldName.

func (*Event) Uint 

func (e *Event) Uint(key string, i uint) *Event

Uint adds the field key with i as a uint to the *Event context.

func (*Event) Uint16 

func (e *Event) Uint16(key string, i uint16) *Event

Uint16 adds the field key with i as a uint16 to the *Event context.

func (*Event) Uint32 

func (e *Event) Uint32(key string, i uint32) *Event

Uint32 adds the field key with i as a uint32 to the *Event context.

func (*Event) Uint64 

func (e *Event) Uint64(key string, i uint64) *Event

Uint64 adds the field key with i as a uint64 to the *Event context.

func (*Event) Uint8 

func (e *Event) Uint8(key string, i uint8) *Event

Uint8 adds the field key with i as a uint8 to the *Event context.

func (*Event) Uints added in v1.0.1 

func (e *Event) Uints(key string, i []uint) *Event

Uints adds the field key with i as a []int to the *Event context.

func (*Event) Uints16 added in v1.0.1 

func (e *Event) Uints16(key string, i []uint16) *Event

Uints16 adds the field key with i as a []int16 to the *Event context.

func (*Event) Uints32 added in v1.0.1 

func (e *Event) Uints32(key string, i []uint32) *Event

Uints32 adds the field key with i as a []int32 to the *Event context.

func (*Event) Uints64 added in v1.0.1 

func (e *Event) Uints64(key string, i []uint64) *Event

Uints64 adds the field key with i as a []int64 to the *Event context.

func (*Event) Uints8 added in v1.0.1 

func (e *Event) Uints8(key string, i []uint8) *Event

Uints8 adds the field key with i as a []int8 to the *Event context.

type Level 

type Level uint8

Level defines log levels. 

const (
	// DebugLevel defines debug log level.
	DebugLevel Level = iota
	// InfoLevel defines info log level.
	InfoLevel
	// WarnLevel defines warn log level.
	WarnLevel
	// ErrorLevel defines error log level.
	ErrorLevel
	// FatalLevel defines fatal log level.
	FatalLevel
	// PanicLevel defines panic log level.
	PanicLevel
	// Disabled disables the logger.
	Disabled
)

func (Level) String 

func (l Level) String() string

type LevelWriter 

type LevelWriter interface {
	io.Writer
	WriteLevel(level Level, p []byte) (n int, err error)
}

LevelWriter defines as interface a writer may implement in order to receive level information with payload.

func MultiLevelWriter 

func MultiLevelWriter(writers ...io.Writer) LevelWriter

MultiLevelWriter creates a writer that duplicates its writes to all the provided writers, similar to the Unix tee(1) command. If some writers implement LevelWriter, their WriteLevel method will be used instead of Write.

func SyslogLevelWriter 

func SyslogLevelWriter(w SyslogWriter) LevelWriter

SyslogLevelWriter wraps a SyslogWriter and call the right syslog level method matching the zerolog level.

type LogArrayMarshaler added in v1.1.0 

type LogArrayMarshaler interface {
	MarshalZerologArray(a *Array)
}

LogArrayMarshaler provides a strongly-typed and encoding-agnostic interface to be implemented by types used with Event/Context's Array methods.

type LogObjectMarshaler added in v1.0.3 

type LogObjectMarshaler interface {
	MarshalZerologObject(e *Event)
}

LogObjectMarshaler provides a strongly-typed and encoding-agnostic interface to be implemented by types used with Event/Context's Object methods.

type Logger 

type Logger struct {
	// contains filtered or unexported fields
}

A Logger represents an active logging object that generates lines of JSON output to an io.Writer. Each logging operation makes a single call to the Writer's Write method. There is no guaranty on access serialization to the Writer. If your Writer is not thread safe, you may consider a sync wrapper.

func Ctx 

func Ctx(ctx context.Context) Logger

Ctx returns the Logger associated with the ctx. If no logger is associated, a disabled logger is returned.

func New 

func New(w io.Writer) Logger

New creates a root logger with given output writer. If the output writer implements the LevelWriter interface, the WriteLevel method will be called instead of the Write one.

Each logging operation makes a single call to the Writer's Write method. There is no guaranty on access serialization to the Writer. If your Writer is not thread safe, you may consider using sync wrapper.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout)

	log.Info().Msg("hello world")

}

Output:

{"level":"info","message":"hello world"}

func Nop 

func Nop() Logger

Nop returns a disabled logger for which all operation are no-op.

func (Logger) Debug 

func (l Logger) Debug() *Event

Debug starts a new message with debug level.

You must call Msg on the returned event in order to send the event.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout)

	log.Debug().
		Str("foo", "bar").
		Int("n", 123).
		Msg("hello world")

}

Output:

{"level":"debug","foo":"bar","n":123,"message":"hello world"}

func (Logger) Error 

func (l Logger) Error() *Event

Error starts a new message with error level.

You must call Msg on the returned event in order to send the event.

Example 
package main

import (
	"errors"
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout)

	log.Error().
		Err(errors.New("some error")).
		Msg("error doing something")

}

Output:

{"level":"error","error":"some error","message":"error doing something"}

func (Logger) Fatal 

func (l Logger) Fatal() *Event

Fatal starts a new message with fatal level. The os.Exit(1) function is called by the Msg method.

You must call Msg on the returned event in order to send the event.

func (Logger) Info 

func (l Logger) Info() *Event

Info starts a new message with info level.

You must call Msg on the returned event in order to send the event.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout)

	log.Info().
		Str("foo", "bar").
		Int("n", 123).
		Msg("hello world")

}

Output:

{"level":"info","foo":"bar","n":123,"message":"hello world"}

func (Logger) Level 

func (l Logger) Level(lvl Level) Logger

Level creates a child logger with the minimum accepted level set to level.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout).Level(zerolog.WarnLevel)

	log.Info().Msg("filtered out message")
	log.Error().Msg("kept message")

}

Output:

{"level":"error","message":"kept message"}

func (Logger) Log 

func (l Logger) Log() *Event

Log starts a new message with no level. Setting GlobalLevel to Disabled will still disable events produced by this method.

You must call Msg on the returned event in order to send the event.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout)

	log.Log().
		Str("foo", "bar").
		Str("bar", "baz").
		Msg("")

}

Output:

{"foo":"bar","bar":"baz"}

func (Logger) Output added in v1.2.0 

func (l Logger) Output(w io.Writer) Logger

Output duplicates the current logger and sets w as its output.

func (Logger) Panic 

func (l Logger) Panic() *Event

Panic starts a new message with panic level. The message is also sent to the panic function.

You must call Msg on the returned event in order to send the event.

func (Logger) Sample 

func (l Logger) Sample(every int) Logger

Sample returns a logger that only let one message out of every to pass thru.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout).Sample(2)

	log.Info().Msg("message 1")
	log.Info().Msg("message 2")
	log.Info().Msg("message 3")
	log.Info().Msg("message 4")

}

Output:

{"level":"info","sample":2,"message":"message 2"}
{"level":"info","sample":2,"message":"message 4"}

func (Logger) Warn 

func (l Logger) Warn() *Event

Warn starts a new message with warn level.

You must call Msg on the returned event in order to send the event.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout)

	log.Warn().
		Str("foo", "bar").
		Msg("a warning message")

}

Output:

{"level":"warn","foo":"bar","message":"a warning message"}

func (Logger) With 

func (l Logger) With() Context

With creates a child logger with the field added to its context.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout).
		With().
		Str("foo", "bar").
		Logger()

	log.Info().Msg("hello world")

}

Output:

{"level":"info","foo":"bar","message":"hello world"}

func (Logger) WithContext 

func (l Logger) WithContext(ctx context.Context) context.Context

WithContext returns a copy of ctx with l associated.

func (Logger) WithLevel added in v1.0.1 

func (l Logger) WithLevel(level Level) *Event

WithLevel starts a new message with level.

You must call Msg on the returned event in order to send the event.

Example 
package main

import (
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout)

	log.WithLevel(zerolog.InfoLevel).
		Msg("hello world")

}

Output:

{"level":"info","message":"hello world"}

func (Logger) Write 

func (l Logger) Write(p []byte) (n int, err error)

Write implements the io.Writer interface. This is useful to set as a writer for the standard library log.

Example 
package main

import (
	stdlog "log"
	"os"

	"github.com/rs/zerolog"
)

func main() {
	log := zerolog.New(os.Stdout).With().
		Str("foo", "bar").
		Logger()

	stdlog.SetFlags(0)
	stdlog.SetOutput(log)

	stdlog.Print("hello world")

}

Output:

{"foo":"bar","message":"hello world"}

type SyslogWriter 

type SyslogWriter interface {
	io.Writer
	Debug(m string) error
	Info(m string) error
	Warning(m string) error
	Err(m string) error
	Emerg(m string) error
	Crit(m string) error
}

SyslogWriter is an interface matching a syslog.Writer struct.

Source Files

View all Source files

Directories

Path Synopsis
Package hlog provides a set of http.Handler helpers for zerolog.
 Package hlog provides a set of http.Handler helpers for zerolog.
internal
json
Package log provides a global logger for zerolog.
 Package log provides a global logger for zerolog.

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