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Package zap

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Published: Feb 7, 2017 | License: MIT | Module:


Package zap provides fast, structured, leveled logging in Go.



package main

import (

func main() {
	// Log in JSON, using zap's reflection-free JSON encoder. By default, loggers
	// write all InfoLevel and above logs to standard out.
	logger := zap.New(
		zap.NewJSONEncoder(zap.NoTime()), // drop timestamps in tests

	logger.Warn("Log without structured data...")
		"Or use strongly-typed wrappers to add structured context.",
		zap.String("library", "zap"),
		zap.Duration("latency", time.Nanosecond),

	// Avoid re-serializing the same data repeatedly by creating a child logger
	// with some attached context. That context is added to all the child's
	// log output, but doesn't affect the parent.
	child := logger.With(
		zap.String("user", ""),
		zap.Int("visits", 42),
	child.Error("Oh no!")

{"level":"warn","msg":"Log without structured data..."}
{"level":"warn","msg":"Or use strongly-typed wrappers to add structured context.","library":"zap","latency":1}
{"level":"error","msg":"Oh no!","user":"","visits":42}
Example (FileOutput)


package main

import (

func main() {
	// Create a temporary file to output logs to.
	f, err := ioutil.TempFile("", "log")
	if err != nil {
		panic("failed to create temporary file")
	defer os.Remove(f.Name())

	logger := zap.New(
		zap.NewJSONEncoder(zap.NoTime()), // drop timestamps in tests
		// Write the logging output to the specified file instead of stdout.
		// Any type implementing zap.WriteSyncer or zap.WriteFlusher can be used.

	logger.Info("This is an info log.", zap.Int("foo", 42))

	// Sync the file so logs are written to disk, and print the file contents.
	// zap will call Sync automatically when logging at FatalLevel or PanicLevel.
	contents, err := ioutil.ReadFile(f.Name())
	if err != nil {
		panic("failed to read temporary file")

{"level":"info","msg":"This is an info log.","foo":42}




var (
	// Discard is a convenience wrapper around ioutil.Discard.
	Discard = AddSync(ioutil.Discard)
	// DiscardOutput is an Option that discards logger output.
	DiscardOutput = Output(Discard)

type AtomicLevel

type AtomicLevel struct {
	// contains filtered or unexported fields

AtomicLevel wraps an atomically change-able Level value. It must be created by the DynamicLevel() function to allocate the internal atomic pointer.

func DynamicLevel

func DynamicLevel() AtomicLevel

DynamicLevel creates an atomically changeable dynamic logging level. The returned level can be passed as a logger option just like a concrete level.

The value's SetLevel() method may be called later to change the enabled logging level of all loggers that were passed the value (either explicitly, or by creating sub-loggers with Logger.With).

func (AtomicLevel) Enabled

func (lvl AtomicLevel) Enabled(l Level) bool

Enabled loads the level value, and calls its Enabled method.

func (AtomicLevel) Level

func (lvl AtomicLevel) Level() Level

Level returns the minimum enabled log level.

func (AtomicLevel) ServeHTTP

func (lvl AtomicLevel) ServeHTTP(w http.ResponseWriter, r *http.Request)

ServeHTTP supports changing logging level with an HTTP request.

GET requests return a JSON description of the current logging level. PUT requests change the logging level and expect a payload like:


func (AtomicLevel) SetLevel

func (lvl AtomicLevel) SetLevel(l Level)

SetLevel alters the logging level.

type CheckedMessage

type CheckedMessage struct {
	// contains filtered or unexported fields

A CheckedMessage is the result of a call to Logger.Check, which allows especially performance-sensitive applications to avoid allocations for disabled or heavily sampled log levels.



package main

import (

func main() {
	logger := zap.New(
		zap.NewJSONEncoder(zap.NoTime()), // drop timestamps in tests

	// By default, the debug logging level is disabled. However, calls to
	// logger.Debug will still allocate a slice to hold any passed fields.
	// Particularly performance-sensitive applications can avoid paying this
	// penalty by using checked messages.
	if cm := logger.Check(zap.DebugLevel, "This is a debug log."); cm.OK() {
		// Debug-level logging is disabled, so we won't get here.
		cm.Write(zap.Int("foo", 42), zap.Stack())

	if cm := logger.Check(zap.InfoLevel, "This is an info log."); cm.OK() {
		// Since info-level logging is enabled, we expect to write out this message.

{"level":"info","msg":"This is an info log."}

func NewCheckedMessage

func NewCheckedMessage(logger Logger, lvl Level, msg string) *CheckedMessage

NewCheckedMessage constructs a CheckedMessage. It's only intended for use by wrapper libraries, and shouldn't be necessary in application code.

func (*CheckedMessage) Chain

func (m *CheckedMessage) Chain(ms ...*CheckedMessage) *CheckedMessage

Chain combines two or more CheckedMessages. If the receiver message is not OK(), the passed message is returned. Otherwise if the passed message is OK(), then it is retained such that its Write() will be called after the receiver's Write(), and any previously Chain()'ed messages already so retained.

func (*CheckedMessage) OK

func (m *CheckedMessage) OK() bool

OK checks whether it's safe to call Write.

func (*CheckedMessage) Write

func (m *CheckedMessage) Write(fields ...Field)

Write logs the pre-checked message with the supplied fields. It will call the underlying level method (Debug, Info, Warn, Error, DPanic, Panic, and Fatal) for the defined levels; the Log method is only called for unknown logging levels.

It MUST be called at most once, since Write will return the *CheckedMessage to an internal pool for potentially immediate re-use; re-using a *CheckedMessage after calling Write() will result in data races or other undefined behavior. An attempt is made to detect and DPanic log any re-use, but such detection is not guaranteed due to race conditions.

type Encoder

type Encoder interface {

	// Copy the encoder, ensuring that adding fields to the copy doesn't affect
	// the original.
	Clone() Encoder
	// Return the encoder to the appropriate sync.Pool. Unpooled encoder
	// implementations can no-op this method.
	// Write the supplied message, level, and timestamp to the writer, along with
	// any accumulated context.
	WriteEntry(io.Writer, string, Level, time.Time) error

Encoder is a format-agnostic interface for all log entry marshalers. Since log encoders don't need to support the same wide range of use cases as general-purpose marshalers, it's possible to make them much faster and lower-allocation.

Implementations of the KeyValue interface's methods can, of course, freely modify the receiver. However, the Clone and WriteEntry methods will be called concurrently and shouldn't modify the receiver.

func NewJSONEncoder

func NewJSONEncoder(options ...JSONOption) Encoder

NewJSONEncoder creates a fast, low-allocation JSON encoder. By default, JSON encoders put the log message under the "msg" key, the timestamp (as floating-point seconds since epoch) under the "ts" key, and the log level under the "level" key. The encoder appropriately escapes all field keys and values.

Note that the encoder doesn't deduplicate keys, so it's possible to produce a message like


This is permitted by the JSON specification, but not encouraged. Many libraries will ignore duplicate key-value pairs (typically keeping the last pair) when unmarshaling, but users should attempt to avoid adding duplicate keys.



package main

import (

func main() {
	// An encoder with the default settings.

	// Dropping timestamps is often useful in tests.

	// In production, customize the encoder to work with your log aggregation
	// system.
		zap.RFC3339Formatter("@timestamp"), // human-readable timestamps
		zap.MessageKey("@message"),         // customize the message key
		zap.LevelString("@level"),          // stringify the log level

func NewTextEncoder

func NewTextEncoder(options ...TextOption) Encoder

NewTextEncoder creates a line-oriented text encoder whose output is optimized for human, rather than machine, consumption. By default, the encoder uses RFC3339-formatted timestamps.



package main

import (

func main() {
	// A text encoder with the default settings.

	// Dropping timestamps is often useful in tests.

	// If you don't like the default timestamp formatting, choose another.

func NullEncoder

func NullEncoder() Encoder

NullEncoder returns the fast, no-allocation encoder.

type Entry

type Entry struct {
	Level   Level
	Time    time.Time
	Message string
	// contains filtered or unexported fields

An Entry represents a complete log message. The entry's structured context is already serialized, but the log level, time, and message are available for inspection and modification.

Entries are pooled, so any functions that accept them must be careful not to retain references to them.

func (Entry) Fields

func (e Entry) Fields() KeyValue

Fields returns a mutable reference to the entry's accumulated context.

type Field

type Field struct {
	// contains filtered or unexported fields

A Field is a marshaling operation used to add a key-value pair to a logger's context. Most fields are lazily marshaled, so it's inexpensive to add fields to disabled debug-level log statements.

func Base64

func Base64(key string, val []byte) Field

Base64 constructs a field that encodes the given value as a padded base64 string. The byte slice is converted to a base64 string eagerly.

func Bool

func Bool(key string, val bool) Field

Bool constructs a Field with the given key and value. Bools are marshaled lazily.

func Duration

func Duration(key string, val time.Duration) Field

Duration constructs a Field with the given key and value. It represents durations as an integer number of nanoseconds.

func Error

func Error(err error) Field

Error constructs a Field that lazily stores err.Error() under the key "error". If passed a nil error, the field is a no-op.

func Float64

func Float64(key string, val float64) Field

Float64 constructs a Field with the given key and value. The way the floating-point value is represented is encoder-dependent, so marshaling is necessarily lazy.

func Int

func Int(key string, val int) Field

Int constructs a Field with the given key and value. Marshaling ints is lazy.

func Int64

func Int64(key string, val int64) Field

Int64 constructs a Field with the given key and value. Like ints, int64s are marshaled lazily.

func Marshaler

func Marshaler(key string, val LogMarshaler) Field

Marshaler constructs a field with the given key and zap.LogMarshaler. It provides a flexible, but still type-safe and efficient, way to add user-defined types to the logging context. The LogMarshaler's MarshalLog method is called lazily.



package main

import (


type Auth struct {
	ExpiresAt time.Time `json:"expires_at"`
	// Since we'll need to send the token to the browser, we include it in the
	// struct's JSON representation.
	Token string `json:"token"`

func (a Auth) MarshalLog(kv zap.KeyValue) error {
	kv.AddInt64("expires_at", a.ExpiresAt.UnixNano())
	// We don't want to log sensitive data.
	kv.AddString("token", "---")
	return nil

type User struct {
	Name string `json:"name"`
	Age  int    `json:"age"`
	Auth Auth   `auth:"auth"`

func (u User) MarshalLog(kv zap.KeyValue) error {
	kv.AddString("name", u.Name)
	kv.AddInt("age", u.Age)
	return kv.AddMarshaler("auth", u.Auth)

func main() {
	jane := User{
		Name: "Jane Doe",
		Age:  42,
		Auth: Auth{
			ExpiresAt: time.Unix(0, 100),
			Token:     "super secret",

	logger := zap.New(zap.NewJSONEncoder(zap.NoTime()))
	logger.Info("Successful login.", zap.Marshaler("user", jane))

{"level":"info","msg":"Successful login.","user":{"name":"Jane Doe","age":42,"auth":{"expires_at":100,"token":"---"}}}

func Nest

func Nest(key string, fields ...Field) Field

Nest takes a key and a variadic number of Fields and creates a nested namespace.



package main

import (

func main() {
	logger := zap.New(
		zap.NewJSONEncoder(zap.NoTime()), // drop timestamps in tests

	// We'd like the logging context to be {"outer":{"inner":42}}
	nest := zap.Nest("outer", zap.Int("inner", 42))
	logger.Info("Logging a nested field.", nest)

{"level":"info","msg":"Logging a nested field.","outer":{"inner":42}}

func Object

func Object(key string, val interface{}) Field

Object constructs a field with the given key and an arbitrary object. It uses an encoding-appropriate, reflection-based function to lazily serialize nearly any object into the logging context, but it's relatively slow and allocation-heavy.

If encoding fails (e.g., trying to serialize a map[int]string to JSON), Object includes the error message in the final log output.

func Skip

func Skip() Field

Skip constructs a no-op Field.

func Stack

func Stack() Field

Stack constructs a Field that stores a stacktrace of the current goroutine under the key "stacktrace". Keep in mind that taking a stacktrace is eager and extremely expensive (relatively speaking); this function both makes an allocation and takes ~10 microseconds.

func String

func String(key string, val string) Field

String constructs a Field with the given key and value.

func Stringer

func Stringer(key string, val fmt.Stringer) Field

Stringer constructs a Field with the given key and the output of the value's String method. The Stringer's String method is called lazily.

func Time

func Time(key string, val time.Time) Field

Time constructs a Field with the given key and value. It represents a time.Time as a floating-point number of seconds since epoch. Conversion to a float64 happens eagerly.

func Uint

func Uint(key string, val uint) Field

Uint constructs a Field with the given key and value.

func Uint64

func Uint64(key string, val uint64) Field

Uint64 constructs a Field with the given key and value.

func Uintptr

func Uintptr(key string, val uintptr) Field

Uintptr constructs a Field with the given key and value.

func (Field) AddTo

func (f Field) AddTo(kv KeyValue)

AddTo exports a field through the KeyValue interface. It's primarily useful to library authors, and shouldn't be necessary in most applications.

type Hook

type Hook func(*Entry) error

A Hook is executed each time the logger writes an Entry. It can modify the entry (including adding context to Entry.Fields()), but must not retain references to the entry or any of its contents. Returned errors are written to the logger's error output.

Hooks implement the Option interface.

type JSONOption

type JSONOption interface {
	// contains filtered or unexported methods

JSONOption is used to set options for a JSON encoder. MessageFormatters, TimeFormatters, and LevelFormatters all implement the JSONOption interface.

type KeyValue

type KeyValue interface {
	AddBool(key string, value bool)
	AddFloat64(key string, value float64)
	AddInt(key string, value int)
	AddInt64(key string, value int64)
	AddUint(key string, value uint)
	AddUint64(key string, value uint64)
	AddUintptr(key string, value uintptr)
	AddMarshaler(key string, marshaler LogMarshaler) error
	// AddObject uses reflection to serialize arbitrary objects, so it's slow and
	// allocation-heavy. Consider implementing the LogMarshaler interface instead.
	AddObject(key string, value interface{}) error
	AddString(key, value string)

KeyValue is an encoding-agnostic interface to add structured data to the logging context. Like maps, KeyValues aren't safe for concurrent use (though typical use shouldn't require locks).

See Marshaler for an example.

type Level

type Level int32

A Level is a logging priority. Higher levels are more important.

Note that Level satisfies the Option interface, so any Level can be passed to New to override the default logging priority.

const (

	// DebugLevel logs are typically voluminous, and are usually disabled in
	// production.
	DebugLevel Level
	// InfoLevel is the default logging priority.
	// WarnLevel logs are more important than Info, but don't need individual
	// human review.
	// ErrorLevel logs are high-priority. If an application is running smoothly,
	// it shouldn't generate any error-level logs.
	// DPanicLevel logs are particularly important errors. In development the
	// logger panics after writing the message.
	// PanicLevel logs a message, then panics.
	// FatalLevel logs a message, then calls os.Exit(1).

func LevelFlag

func LevelFlag(name string, defaultLevel Level, usage string) *Level

LevelFlag defines a Level flag with specified name, default value and usage string. The return value is the address of a Level value that stores the value of the flag.

func (Level) Enabled

func (l Level) Enabled(lvl Level) bool

Enabled returns true if the given level is at or above this level.

func (*Level) Get

func (l *Level) Get() interface{}

Get gets the level for the flag.Getter interface.

func (*Level) MarshalText

func (l *Level) MarshalText() ([]byte, error)

MarshalText marshals the Level to text. Note that the text representation drops the -Level suffix (see example).



package main

import (

func main() {
	level := zap.ErrorLevel
	s := struct {
		Level *zap.Level `json:"level"`
	bytes, _ := json.Marshal(s)


func (*Level) Set

func (l *Level) Set(s string) error

Set sets the level for the flag.Value interface.

func (Level) String

func (l Level) String() string

String returns a lower-case ASCII representation of the log level.

func (*Level) UnmarshalText

func (l *Level) UnmarshalText(text []byte) error

UnmarshalText unmarshals text to a level. Like MarshalText, UnmarshalText expects the text representation of a Level to drop the -Level suffix (see example).

In particular, this makes it easy to configure logging levels using YAML, TOML, or JSON files.



package main

import (

func main() {
	var s struct {
		Level zap.Level `json:"level"`
	// The zero value for a zap.Level is zap.InfoLevel.

	json.Unmarshal([]byte(`{"level":"error"}`), &s)


type LevelEnabler

type LevelEnabler interface {
	Enabled(Level) bool

LevelEnabler decides whether a given logging level is enabled when logging a message.

Enablers are intended to be used to implement deterministic filters; concerns like sampling are better implemented as a Logger implementation.

Each concrete Level value implements a static LevelEnabler which returns true for itself and all higher logging levels. For example WarnLevel.Enabled() will return true for WarnLevel, ErrorLevel, PanicLevel, and FatalLevel, but return false for InfoLevel and DebugLevel.

type LevelEnablerFunc

type LevelEnablerFunc func(Level) bool

LevelEnablerFunc is a convenient way to implement LevelEnabler around an anonymous function. It is also a valid Option to pass to a logger.

func (LevelEnablerFunc) Enabled

func (f LevelEnablerFunc) Enabled(lvl Level) bool

Enabled calls the wrapped function.

type LevelFormatter

type LevelFormatter func(Level) Field

A LevelFormatter defines how to convert an entry's logging level into a Field. LevelFormatters implement the JSONOption interface.

func LevelString

func LevelString(key string) LevelFormatter

LevelString encodes the entry's level under the provided key. It uses the level's String method to serialize it.

type LogMarshaler

type LogMarshaler interface {
	MarshalLog(KeyValue) error

LogMarshaler allows user-defined types to efficiently add themselves to the logging context, and to selectively omit information which shouldn't be included in logs (e.g., passwords).

type LogMarshalerFunc

type LogMarshalerFunc func(KeyValue) error

LogMarshalerFunc is a type adapter that allows using a function as a LogMarshaler.

func (LogMarshalerFunc) MarshalLog

func (f LogMarshalerFunc) MarshalLog(kv KeyValue) error

MarshalLog calls the underlying function.

type Logger

type Logger interface {
	// Create a child logger, and optionally add some context to that logger.
	With(...Field) Logger

	// Check returns a CheckedMessage if logging a message at the specified level
	// is enabled. It's a completely optional optimization; in high-performance
	// applications, Check can help avoid allocating a slice to hold fields.
	// See CheckedMessage for an example.
	Check(Level, string) *CheckedMessage

	// Log a message at the given level. Messages include any context that's
	// accumulated on the logger, as well as any fields added at the log site.
	// Calling Panic should panic() and calling Fatal should terminate the
	// process, but calling Log(PanicLevel, ...) or Log(FatalLevel, ...) should
	// not. It may not be possible for compatibility wrappers to comply with
	// this last part (e.g. the bark wrapper).
	Log(Level, string, ...Field)
	Debug(string, ...Field)
	Info(string, ...Field)
	Warn(string, ...Field)
	Error(string, ...Field)
	DPanic(string, ...Field)
	Panic(string, ...Field)
	Fatal(string, ...Field)

A Logger enables leveled, structured logging. All methods are safe for concurrent use.

func New

func New(enc Encoder, options ...Option) Logger

New constructs a logger that uses the provided encoder. By default, the logger will write Info logs or higher to standard out. Any errors during logging will be written to standard error.

Options can change the log level, the output location, the initial fields that should be added as context, and many other behaviors.



package main

import (

func main() {
	// The default logger outputs to standard out and only writes logs that are
	// Info level or higher.
	logger := zap.New(zap.NewJSONEncoder(
		zap.NoTime(), // drop timestamps in tests

	// The default logger does not print Debug logs.
	logger.Debug("This won't be printed.")
	logger.Info("This is an info log.")

{"level":"info","msg":"This is an info log."}
Example (Options)


package main

import (

func main() {
	// We can pass multiple options to the New method to configure the logging
	// level, output location, or even the initial context.
	logger := zap.New(
		zap.NewJSONEncoder(zap.NoTime()), // drop timestamps in tests
		zap.Fields(zap.Int("count", 1)),

	logger.Debug("This is a debug log.")
	logger.Info("This is an info log.")

{"level":"debug","msg":"This is a debug log.","count":1}
{"level":"info","msg":"This is an info log.","count":1}
Example (TextEncoder)


package main

import (

func main() {
	// For more human-readable output in the console, use a TextEncoder.
	textLogger := zap.New(zap.NewTextEncoder(
		zap.TextNoTime(), // drop timestamps in tests.

	textLogger.Info("This is a text log.", zap.Int("foo", 42))

[I] This is a text log. foo=42

func Tee

func Tee(logs ...Logger) Logger

Tee creates a Logger that duplicates its log calls to two or more loggers. It is similar to io.MultiWriter.

For each logging level method (.Debug, .Info, etc), the Tee calls each sub-logger's level method.

Exceptions are made for the DPanic, Panic, and Fatal methods: the returned logger calls .Log(DPanicLevel, ...), .Log(PanicLevel, ...), and .Log(FatalLevel, ...) respectively. Only after all sub-loggers have received the message, then the Tee terminates the process (using os.Exit or panic() per usual semantics).

NOTE: DPanic will currently never panic, since the Tee Logger does not accept options (nor even have a development flag).

Check returns a CheckedMessage chain of any OK CheckedMessages returned by all sub-loggers. The returned message is OK if any of the sub-messages are. An exception is made for FatalLevel and PanicLevel, where a CheckedMessage is returned against the Tee itself. This is so that tlog.Check(PanicLevel, ...).Write(...) is equivalent to tlog.Panic(...) (likewise for FatalLevel).



package main

import (

func main() {
	// Multiple loggers can be combine using Tee.
	output := zap.Output(os.Stdout)
	logger := zap.Tee(
		zap.New(zap.NewTextEncoder(zap.TextNoTime()), output),
		zap.New(zap.NewJSONEncoder(zap.NoTime()), output),

	logger.Info("this log gets encoded twice, differently", zap.Int("foo", 42))
[I] this log gets encoded twice, differently foo=42
{"level":"info","msg":"this log gets encoded twice, differently","foo":42}

type MessageFormatter

type MessageFormatter func(string) Field

A MessageFormatter defines how to convert a log message into a Field. MessageFormatters implement the JSONOption interface.

func MessageKey

func MessageKey(key string) MessageFormatter

MessageKey encodes log messages under the provided key.

type Meta

type Meta struct {

	Development bool
	Encoder     Encoder
	Hooks       []Hook
	Output      WriteSyncer
	ErrorOutput WriteSyncer

Meta is implementation-agnostic state management for Loggers. Most Logger implementations can reduce the required boilerplate by embedding a Meta.

Note that while the level-related fields and methods are safe for concurrent use, the remaining fields are not.

func MakeMeta

func MakeMeta(enc Encoder, options ...Option) Meta

MakeMeta returns a new meta struct with sensible defaults: logging at InfoLevel, development mode off, and writing to standard error and standard out.

func (Meta) Check

func (m Meta) Check(log Logger, lvl Level, msg string) *CheckedMessage

Check returns a CheckedMessage logging the given message is Enabled, nil otherwise.

func (Meta) Clone

func (m Meta) Clone() Meta

Clone creates a copy of the meta struct. It deep-copies the encoder, but not the hooks (since they rarely change).

func (Meta) Encode

func (m Meta) Encode(w io.Writer, t time.Time, lvl Level, msg string, fields []Field) error

Encode runs any Hook functions and then writes an encoded log entry to the given io.Writer, returning any error.

func (Meta) InternalError

func (m Meta) InternalError(cause string, err error)

InternalError prints an internal error message to the configured ErrorOutput. This method should only be used to report internal logger problems and should not be used to report user-caused problems.

type Option

type Option interface {
	// contains filtered or unexported methods

Option is used to set options for the logger.

func AddCaller

func AddCaller() Option

AddCaller configures the Logger to annotate each message with the filename and line number of zap's caller.

func AddStacks

func AddStacks(lvl Level) Option

AddStacks configures the Logger to record a stack trace for all messages at or above a given level. Keep in mind that this is (relatively speaking) quite expensive.

func Development

func Development() Option

Development puts the logger in development mode, which alters the behavior of the DPanic method.

func ErrorOutput

func ErrorOutput(w WriteSyncer) Option

ErrorOutput sets the destination for errors generated by the logger. The supplied WriteSyncer is automatically wrapped with a mutex, so it need not be safe for concurrent use.

func Fields

func Fields(fields ...Field) Option

Fields sets the initial fields for the logger.

func Output

func Output(w WriteSyncer) Option

Output sets the destination for the logger's output. The supplied WriteSyncer is automatically wrapped with a mutex, so it need not be safe for concurrent use.

type TextOption

type TextOption interface {
	// contains filtered or unexported methods

A TextOption is used to set options for a text encoder.

func TextNoTime

func TextNoTime() TextOption

TextNoTime omits timestamps from the serialized log entries.

func TextTimeFormat

func TextTimeFormat(layout string) TextOption

TextTimeFormat sets the format for log timestamps, using the same layout strings supported by time.Parse.

type TimeFormatter

type TimeFormatter func(time.Time) Field

A TimeFormatter defines how to convert the time of a log entry into a Field. TimeFormatters implement the JSONOption interface.

func EpochFormatter

func EpochFormatter(key string) TimeFormatter

EpochFormatter uses the Time field (floating-point seconds since epoch) to encode the entry time under the provided key.

func NoTime

func NoTime() TimeFormatter

NoTime drops the entry time altogether. It's often useful in testing, since it removes the need to stub time.Now.

func RFC3339Formatter

func RFC3339Formatter(key string) TimeFormatter

RFC3339Formatter encodes the entry time as an RFC3339-formatted string under the provided key.

func RFC3339NanoFormatter

func RFC3339NanoFormatter(key string) TimeFormatter

RFC3339NanoFormatter encodes the entry time as an RFC3339-formatted string with nanosecond precision under the provided key.

func UnixNanoFormatter

func UnixNanoFormatter(key string) TimeFormatter

UnixNanoFormatter encodes the entry time as a single int64 with nanosecond precision under the provided key.

type WriteFlusher

type WriteFlusher interface {
	Flush() error

A WriteFlusher is an io.Writer that can also flush any buffered data.

type WriteSyncer

type WriteSyncer interface {
	Sync() error

A WriteSyncer is an io.Writer that can also flush any buffered data. Note that *os.File (and thus, os.Stderr and os.Stdout) implement WriteSyncer.

func AddSync

func AddSync(w io.Writer) WriteSyncer

AddSync converts an io.Writer to a WriteSyncer. It attempts to be intelligent: if the concrete type of the io.Writer implements WriteSyncer or WriteFlusher, we'll use the existing Sync or Flush methods. If it doesn't, we'll add a no-op Sync method.

func MultiWriteSyncer

func MultiWriteSyncer(ws ...WriteSyncer) WriteSyncer

MultiWriteSyncer creates a WriteSyncer that duplicates its writes and sync calls, similarly to to io.MultiWriter.



package main

import (

func main() {
	// To send output to multiple outputs, use MultiWriteSyncer.
	textLogger := zap.New(
		zap.Output(zap.MultiWriteSyncer(os.Stdout, os.Stdout)),

	textLogger.Info("One becomes two")
[I] One becomes two
[I] One becomes two

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