zap

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README

⚡ zap

Blazing fast, structured, leveled logging in Go.

Zap logo

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Installation

go get -u go.uber.org/zap

Note that zap only supports the two most recent minor versions of Go.

Quick Start

In contexts where performance is nice, but not critical, use the SugaredLogger. It's 4-10x faster than other structured logging packages and includes both structured and printf-style APIs.

logger, _ := zap.NewProduction()
defer logger.Sync() // flushes buffer, if any
sugar := logger.Sugar()
sugar.Infow("failed to fetch URL",
  // Structured context as loosely typed key-value pairs.
  "url", url,
  "attempt", 3,
  "backoff", time.Second,
)
sugar.Infof("Failed to fetch URL: %s", url)

When performance and type safety are critical, use the Logger. It's even faster than the SugaredLogger and allocates far less, but it only supports structured logging.

logger, _ := zap.NewProduction()
defer logger.Sync()
logger.Info("failed to fetch URL",
  // Structured context as strongly typed Field values.
  zap.String("url", url),
  zap.Int("attempt", 3),
  zap.Duration("backoff", time.Second),
)

See the documentation and FAQ for more details.

Performance

For applications that log in the hot path, reflection-based serialization and string formatting are prohibitively expensive — they're CPU-intensive and make many small allocations. Put differently, using encoding/json and fmt.Fprintf to log tons of interface{}s makes your application slow.

Zap takes a different approach. It includes a reflection-free, zero-allocation JSON encoder, and the base Logger strives to avoid serialization overhead and allocations wherever possible. By building the high-level SugaredLogger on that foundation, zap lets users choose when they need to count every allocation and when they'd prefer a more familiar, loosely typed API.

As measured by its own benchmarking suite, not only is zap more performant than comparable structured logging packages — it's also faster than the standard library. Like all benchmarks, take these with a grain of salt.1

Log a message and 10 fields:

Package Time Time % to zap Objects Allocated
⚡ zap 656 ns/op +0% 5 allocs/op
⚡ zap (sugared) 935 ns/op +43% 10 allocs/op
zerolog 380 ns/op -42% 1 allocs/op
go-kit 2249 ns/op +243% 57 allocs/op
slog (LogAttrs) 2479 ns/op +278% 40 allocs/op
slog 2481 ns/op +278% 42 allocs/op
apex/log 9591 ns/op +1362% 63 allocs/op
log15 11393 ns/op +1637% 75 allocs/op
logrus 11654 ns/op +1677% 79 allocs/op

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

Package Time Time % to zap Objects Allocated
⚡ zap 67 ns/op +0% 0 allocs/op
⚡ zap (sugared) 84 ns/op +25% 1 allocs/op
zerolog 35 ns/op -48% 0 allocs/op
slog 193 ns/op +188% 0 allocs/op
slog (LogAttrs) 200 ns/op +199% 0 allocs/op
go-kit 2460 ns/op +3572% 56 allocs/op
log15 9038 ns/op +13390% 70 allocs/op
apex/log 9068 ns/op +13434% 53 allocs/op
logrus 10521 ns/op +15603% 68 allocs/op

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

Package Time Time % to zap Objects Allocated
⚡ zap 63 ns/op +0% 0 allocs/op
⚡ zap (sugared) 81 ns/op +29% 1 allocs/op
zerolog 32 ns/op -49% 0 allocs/op
standard library 124 ns/op +97% 1 allocs/op
slog 196 ns/op +211% 0 allocs/op
slog (LogAttrs) 200 ns/op +217% 0 allocs/op
go-kit 213 ns/op +238% 9 allocs/op
apex/log 771 ns/op +1124% 5 allocs/op
logrus 1439 ns/op +2184% 23 allocs/op
log15 2069 ns/op +3184% 20 allocs/op

Development Status: Stable

All APIs are finalized, and no breaking changes will be made in the 1.x series of releases. Users of semver-aware dependency management systems should pin zap to ^1.

Contributing

We encourage and support an active, healthy community of contributors — including you! Details are in the contribution guide and the code of conduct. The zap maintainers keep an eye on issues and pull requests, but you can also report any negative conduct to oss-conduct@uber.com. That email list is a private, safe space; even the zap maintainers don't have access, so don't hesitate to hold us to a high standard.

Released under the MIT License.

1 In particular, keep in mind that we may be benchmarking against slightly older versions of other packages. Versions are pinned in the benchmarks/go.mod file. ↩

Documentation

Overview

Package zap provides fast, structured, leveled logging.

For applications that log in the hot path, reflection-based serialization and string formatting are prohibitively expensive - they're CPU-intensive and make many small allocations. Put differently, using json.Marshal and fmt.Fprintf to log tons of interface{} makes your application slow.

Zap takes a different approach. It includes a reflection-free, zero-allocation JSON encoder, and the base Logger strives to avoid serialization overhead and allocations wherever possible. By building the high-level SugaredLogger on that foundation, zap lets users choose when they need to count every allocation and when they'd prefer a more familiar, loosely typed API.

Choosing a Logger

In contexts where performance is nice, but not critical, use the SugaredLogger. It's 4-10x faster than other structured logging packages and supports both structured and printf-style logging. Like log15 and go-kit, the SugaredLogger's structured logging APIs are loosely typed and accept a variadic number of key-value pairs. (For more advanced use cases, they also accept strongly typed fields - see the SugaredLogger.With documentation for details.) 

sugar := zap.NewExample().Sugar()
defer sugar.Sync()
sugar.Infow("failed to fetch URL",
  "url", "http://example.com",
  "attempt", 3,
  "backoff", time.Second,
)
sugar.Infof("failed to fetch URL: %s", "http://example.com")

By default, loggers are unbuffered. However, since zap's low-level APIs allow buffering, calling Sync before letting your process exit is a good habit.

In the rare contexts where every microsecond and every allocation matter, use the Logger. It's even faster than the SugaredLogger and allocates far less, but it only supports strongly-typed, structured logging. 

logger := zap.NewExample()
defer logger.Sync()
logger.Info("failed to fetch URL",
  zap.String("url", "http://example.com"),
  zap.Int("attempt", 3),
  zap.Duration("backoff", time.Second),
)

Choosing between the Logger and SugaredLogger doesn't need to be an application-wide decision: converting between the two is simple and inexpensive. 

logger := zap.NewExample()
defer logger.Sync()
sugar := logger.Sugar()
plain := sugar.Desugar()

Configuring Zap

The simplest way to build a Logger is to use zap's opinionated presets: NewExample, NewProduction, and NewDevelopment. These presets build a logger with a single function call: 

logger, err := zap.NewProduction()
if err != nil {
  log.Fatalf("can't initialize zap logger: %v", err)
}
defer logger.Sync()

Presets are fine for small projects, but larger projects and organizations naturally require a bit more customization. For most users, zap's Config struct strikes the right balance between flexibility and convenience. See the package-level BasicConfiguration example for sample code.

More unusual configurations (splitting output between files, sending logs to a message queue, etc.) are possible, but require direct use of go.uber.org/zap/zapcore. See the package-level AdvancedConfiguration example for sample code.

Extending Zap

The zap package itself is a relatively thin wrapper around the interfaces in go.uber.org/zap/zapcore. Extending zap to support a new encoding (e.g., BSON), a new log sink (e.g., Kafka), or something more exotic (perhaps an exception aggregation service, like Sentry or Rollbar) typically requires implementing the zapcore.Encoder, zapcore.WriteSyncer, or zapcore.Core interfaces. See the zapcore documentation for details.

Similarly, package authors can use the high-performance Encoder and Core implementations in the zapcore package to build their own loggers.

Frequently Asked Questions

An FAQ covering everything from installation errors to design decisions is available at https://github.com/uber-go/zap/blob/master/FAQ.md.

Example (AdvancedConfiguration) 
package main

import (
	"io"
	"os"

	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
)

func main() {
	// The bundled Config struct only supports the most common configuration
	// options. More complex needs, like splitting logs between multiple files
	// or writing to non-file outputs, require use of the zapcore package.
	//
	// In this example, imagine we're both sending our logs to Kafka and writing
	// them to the console. We'd like to encode the console output and the Kafka
	// topics differently, and we'd also like special treatment for
	// high-priority logs.

	// First, define our level-handling logic.
	highPriority := zap.LevelEnablerFunc(func(lvl zapcore.Level) bool {
		return lvl >= zapcore.ErrorLevel
	})
	lowPriority := zap.LevelEnablerFunc(func(lvl zapcore.Level) bool {
		return lvl < zapcore.ErrorLevel
	})

	// Assume that we have clients for two Kafka topics. The clients implement
	// zapcore.WriteSyncer and are safe for concurrent use. (If they only
	// implement io.Writer, we can use zapcore.AddSync to add a no-op Sync
	// method. If they're not safe for concurrent use, we can add a protecting
	// mutex with zapcore.Lock.)
	topicDebugging := zapcore.AddSync(io.Discard)
	topicErrors := zapcore.AddSync(io.Discard)

	// High-priority output should also go to standard error, and low-priority
	// output should also go to standard out.
	consoleDebugging := zapcore.Lock(os.Stdout)
	consoleErrors := zapcore.Lock(os.Stderr)

	// Optimize the Kafka output for machine consumption and the console output
	// for human operators.
	kafkaEncoder := zapcore.NewJSONEncoder(zap.NewProductionEncoderConfig())
	consoleEncoder := zapcore.NewConsoleEncoder(zap.NewDevelopmentEncoderConfig())

	// Join the outputs, encoders, and level-handling functions into
	// zapcore.Cores, then tee the four cores together.
	core := zapcore.NewTee(
		zapcore.NewCore(kafkaEncoder, topicErrors, highPriority),
		zapcore.NewCore(consoleEncoder, consoleErrors, highPriority),
		zapcore.NewCore(kafkaEncoder, topicDebugging, lowPriority),
		zapcore.NewCore(consoleEncoder, consoleDebugging, lowPriority),
	)

	// From a zapcore.Core, it's easy to construct a Logger.
	logger := zap.New(core)
	defer logger.Sync()
	logger.Info("constructed a logger")
}

Output:
Example (BasicConfiguration) 
package main

import (
	"encoding/json"

	"go.uber.org/zap"
)

func main() {
	// For some users, the presets offered by the NewProduction, NewDevelopment,
	// and NewExample constructors won't be appropriate. For most of those
	// users, the bundled Config struct offers the right balance of flexibility
	// and convenience. (For more complex needs, see the AdvancedConfiguration
	// example.)
	//
	// See the documentation for Config and zapcore.EncoderConfig for all the
	// available options.
	rawJSON := []byte(`{
	  "level": "debug",
	  "encoding": "json",
	  "outputPaths": ["stdout", "/tmp/logs"],
	  "errorOutputPaths": ["stderr"],
	  "initialFields": {"foo": "bar"},
	  "encoderConfig": {
	    "messageKey": "message",
	    "levelKey": "level",
	    "levelEncoder": "lowercase"
	  }
	}`)

	var cfg zap.Config
	if err := json.Unmarshal(rawJSON, &cfg); err != nil {
		panic(err)
	}
	logger := zap.Must(cfg.Build())
	defer logger.Sync()

	logger.Info("logger construction succeeded")
}

Output:

{"level":"info","message":"logger construction succeeded","foo":"bar"}
Example (Presets) 
package main

import (
	"time"

	"go.uber.org/zap"
)

func main() {
	// Using zap's preset constructors is the simplest way to get a feel for the
	// package, but they don't allow much customization.
	logger := zap.NewExample() // or NewProduction, or NewDevelopment
	defer logger.Sync()

	const url = "http://example.com"

	// In most circumstances, use the SugaredLogger. It's 4-10x faster than most
	// other structured logging packages and has a familiar, loosely-typed API.
	sugar := logger.Sugar()
	sugar.Infow("Failed to fetch URL.",
		// Structured context as loosely typed key-value pairs.
		"url", url,
		"attempt", 3,
		"backoff", time.Second,
	)
	sugar.Infof("Failed to fetch URL: %s", url)

	// In the unusual situations where every microsecond matters, use the
	// Logger. It's even faster than the SugaredLogger, but only supports
	// structured logging.
	logger.Info("Failed to fetch URL.",
		// Structured context as strongly typed fields.
		zap.String("url", url),
		zap.Int("attempt", 3),
		zap.Duration("backoff", time.Second),
	)
}

Output:

{"level":"info","msg":"Failed to fetch URL.","url":"http://example.com","attempt":3,"backoff":"1s"}
{"level":"info","msg":"Failed to fetch URL: http://example.com"}
{"level":"info","msg":"Failed to fetch URL.","url":"http://example.com","attempt":3,"backoff":"1s"}

Index

Examples

Constants

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

Variables

This section is empty.

Functions

func CombineWriteSyncers 

func CombineWriteSyncers(writers ...zapcore.WriteSyncer) zapcore.WriteSyncer

CombineWriteSyncers is a utility that combines multiple WriteSyncers into a single, locked WriteSyncer. If no inputs are supplied, it returns a no-op WriteSyncer.

It's provided purely as a convenience; the result is no different from using zapcore.NewMultiWriteSyncer and zapcore.Lock individually.

func LevelFlag 

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

LevelFlag uses the standard library's flag.Var to declare a global flag with the specified name, default, and usage guidance. The returned value is a pointer to the value of the flag.

If you don't want to use the flag package's global state, you can use any non-nil *Level as a flag.Value with your own *flag.FlagSet.

func NewDevelopmentEncoderConfig 

func NewDevelopmentEncoderConfig() zapcore.EncoderConfig

NewDevelopmentEncoderConfig returns an opinionated EncoderConfig for development environments.

Messages encoded with this configuration will use Zap's console encoder intended to print human-readable output. It will print log messages with the following information:

  • The log level (e.g. "INFO", "ERROR").
  • The time in ISO8601 format (e.g. "2017-01-01T12:00:00Z").
  • The message passed to the log statement.
  • If available, a short path to the file and line number where the log statement was issued. The logger configuration determines whether this field is captured.
  • If available, a stacktrace from the line where the log statement was issued. The logger configuration determines whether this field is captured.

By default, the following formats are used for different types:

  • Time is formatted in ISO8601 format (e.g. "2017-01-01T12:00:00Z").
  • Duration is formatted as a string (e.g. "1.234s").

You may change these by setting the appropriate fields in the returned object. For example, use the following to change the time encoding format: 

cfg := zap.NewDevelopmentEncoderConfig()
cfg.EncodeTime = zapcore.ISO8601TimeEncoder

func NewProductionEncoderConfig 

func NewProductionEncoderConfig() zapcore.EncoderConfig

NewProductionEncoderConfig returns an opinionated EncoderConfig for production environments.

Messages encoded with this configuration will be JSON-formatted and will have the following keys by default:

  • "level": The logging level (e.g. "info", "error").
  • "ts": The current time in number of seconds since the Unix epoch.
  • "msg": The message passed to the log statement.
  • "caller": If available, a short path to the file and line number where the log statement was issued. The logger configuration determines whether this field is captured.
  • "stacktrace": If available, a stack trace from the line where the log statement was issued. The logger configuration determines whether this field is captured.

By default, the following formats are used for different types:

  • Time is formatted as floating-point number of seconds since the Unix epoch.
  • Duration is formatted as floating-point number of seconds.

You may change these by setting the appropriate fields in the returned object. For example, use the following to change the time encoding format: 

cfg := zap.NewProductionEncoderConfig()
cfg.EncodeTime = zapcore.ISO8601TimeEncoder

func NewStdLog 

func NewStdLog(l *Logger) *log.Logger

NewStdLog returns a *log.Logger which writes to the supplied zap Logger at InfoLevel. To redirect the standard library's package-global logging functions, use RedirectStdLog instead.

Example 
package main

import (
	"go.uber.org/zap"
)

func main() {
	logger := zap.NewExample()
	defer logger.Sync()

	std := zap.NewStdLog(logger)
	std.Print("standard logger wrapper")
}

Output:

{"level":"info","msg":"standard logger wrapper"}

func NewStdLogAt added in v1.7.0 

func NewStdLogAt(l *Logger, level zapcore.Level) (*log.Logger, error)

NewStdLogAt returns *log.Logger which writes to supplied zap logger at required level.

func Open 

func Open(paths ...string) (zapcore.WriteSyncer, func(), error)

Open is a high-level wrapper that takes a variadic number of URLs, opens or creates each of the specified resources, and combines them into a locked WriteSyncer. It also returns any error encountered and a function to close any opened files.

Passing no URLs returns a no-op WriteSyncer. Zap handles URLs without a scheme and URLs with the "file" scheme. Third-party code may register factories for other schemes using RegisterSink.

URLs with the "file" scheme must use absolute paths on the local filesystem. No user, password, port, fragments, or query parameters are allowed, and the hostname must be empty or "localhost".

Since it's common to write logs to the local filesystem, URLs without a scheme (e.g., "/var/log/foo.log") are treated as local file paths. Without a scheme, the special paths "stdout" and "stderr" are interpreted as os.Stdout and os.Stderr. When specified without a scheme, relative file paths also work.

func RedirectStdLog 

func RedirectStdLog(l *Logger) func()

RedirectStdLog redirects output from the standard library's package-global logger to the supplied logger at InfoLevel. Since zap already handles caller annotations, timestamps, etc., it automatically disables the standard library's annotations and prefixing.

It returns a function to restore the original prefix and flags and reset the standard library's output to os.Stderr.

Example 
package main

import (
	"log"

	"go.uber.org/zap"
)

func main() {
	logger := zap.NewExample()
	defer logger.Sync()

	undo := zap.RedirectStdLog(logger)
	defer undo()

	log.Print("redirected standard library")
}

Output:

{"level":"info","msg":"redirected standard library"}

func RedirectStdLogAt added in v1.8.0 

func RedirectStdLogAt(l *Logger, level zapcore.Level) (func(), error)

RedirectStdLogAt redirects output from the standard library's package-global logger to the supplied logger at the specified level. Since zap already handles caller annotations, timestamps, etc., it automatically disables the standard library's annotations and prefixing.

It returns a function to restore the original prefix and flags and reset the standard library's output to os.Stderr.

func RegisterEncoder 

func RegisterEncoder(name string, constructor func(zapcore.EncoderConfig) (zapcore.Encoder, error)) error

RegisterEncoder registers an encoder constructor, which the Config struct can then reference. By default, the "json" and "console" encoders are registered.

Attempting to register an encoder whose name is already taken returns an error.

func RegisterSink added in v1.9.0 

func RegisterSink(scheme string, factory func(*url.URL) (Sink, error)) error

RegisterSink registers a user-supplied factory for all sinks with a particular scheme.

All schemes must be ASCII, valid under section 0.1 of RFC 3986 (https://tools.ietf.org/html/rfc3983#section-3.1), and must not already have a factory registered. Zap automatically registers a factory for the "file" scheme.

func ReplaceGlobals 

func ReplaceGlobals(logger *Logger) func()

ReplaceGlobals replaces the global Logger and SugaredLogger, and returns a function to restore the original values. It's safe for concurrent use.

Example 
package main

import (
	"go.uber.org/zap"
)

func main() {
	logger := zap.NewExample()
	defer logger.Sync()

	undo := zap.ReplaceGlobals(logger)
	defer undo()

	zap.L().Info("replaced zap's global loggers")
}

Output:

{"level":"info","msg":"replaced zap's global loggers"}

Types

type AtomicLevel 

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

An AtomicLevel is an atomically changeable, dynamic logging level. It lets you safely change the log level of a tree of loggers (the root logger and any children created by adding context) at runtime.

The AtomicLevel itself is an http.Handler that serves a JSON endpoint to alter its level.

AtomicLevels must be created with the NewAtomicLevel constructor to allocate their internal atomic pointer.

Example 
package main

import (
	"os"

	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
)

func main() {
	atom := zap.NewAtomicLevel()

	// To keep the example deterministic, disable timestamps in the output.
	encoderCfg := zap.NewProductionEncoderConfig()
	encoderCfg.TimeKey = ""

	logger := zap.New(zapcore.NewCore(
		zapcore.NewJSONEncoder(encoderCfg),
		zapcore.Lock(os.Stdout),
		atom,
	))
	defer logger.Sync()

	logger.Info("info logging enabled")

	atom.SetLevel(zap.ErrorLevel)
	logger.Info("info logging disabled")
}

Output:

{"level":"info","msg":"info logging enabled"}
Example (Config) 
package main

import (
	"encoding/json"

	"go.uber.org/zap"
)

func main() {
	// The zap.Config struct includes an AtomicLevel. To use it, keep a
	// reference to the Config.
	rawJSON := []byte(`{
		"level": "info",
		"outputPaths": ["stdout"],
		"errorOutputPaths": ["stderr"],
		"encoding": "json",
		"encoderConfig": {
			"messageKey": "message",
			"levelKey": "level",
			"levelEncoder": "lowercase"
		}
	}`)
	var cfg zap.Config
	if err := json.Unmarshal(rawJSON, &cfg); err != nil {
		panic(err)
	}
	logger := zap.Must(cfg.Build())
	defer logger.Sync()

	logger.Info("info logging enabled")

	cfg.Level.SetLevel(zap.ErrorLevel)
	logger.Info("info logging disabled")
}

Output:

{"level":"info","message":"info logging enabled"}

func NewAtomicLevel 

func NewAtomicLevel() AtomicLevel

NewAtomicLevel creates an AtomicLevel with InfoLevel and above logging enabled.

func NewAtomicLevelAt added in v1.3.0 

func NewAtomicLevelAt(l zapcore.Level) AtomicLevel

NewAtomicLevelAt is a convenience function that creates an AtomicLevel and then calls SetLevel with the given level.

func ParseAtomicLevel added in v1.21.0 

func ParseAtomicLevel(text string) (AtomicLevel, error)

ParseAtomicLevel parses an AtomicLevel based on a lowercase or all-caps ASCII representation of the log level. If the provided ASCII representation is invalid an error is returned.

This is particularly useful when dealing with text input to configure log levels.

func (AtomicLevel) Enabled 

func (lvl AtomicLevel) Enabled(l zapcore.Level) bool

Enabled implements the zapcore.LevelEnabler interface, which allows the AtomicLevel to be used in place of traditional static levels.

func (AtomicLevel) Level 

func (lvl AtomicLevel) Level() zapcore.Level

Level returns the minimum enabled log level.

func (AtomicLevel) MarshalText added in v1.3.0 

func (lvl AtomicLevel) MarshalText() (text []byte, err error)

MarshalText marshals the AtomicLevel to a byte slice. It uses the same text representation as the static zapcore.Levels ("debug", "info", "warn", "error", "dpanic", "panic", and "fatal").

func (AtomicLevel) ServeHTTP 

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

ServeHTTP is a simple JSON endpoint that can report on or change the current logging level.

GET

The GET request returns a JSON description of the current logging level like: 

{"level":"info"}

PUT

The PUT request changes the logging level. It is perfectly safe to change the logging level while a program is running. Two content types are supported: 

Content-Type: application/x-www-form-urlencoded

With this content type, the level can be provided through the request body or a query parameter. The log level is URL encoded like: 

level=debug

The request body takes precedence over the query parameter, if both are specified.

This content type is the default for a curl PUT request. Following are two example curl requests that both set the logging level to debug. 

curl -X PUT localhost:8080/log/level?level=debug
curl -X PUT localhost:8080/log/level -d level=debug

For any other content type, the payload is expected to be JSON encoded and look like: 

{"level":"info"}

An example curl request could look like this: 

curl -X PUT localhost:8080/log/level -H "Content-Type: application/json" -d '{"level":"debug"}'

func (AtomicLevel) SetLevel 

func (lvl AtomicLevel) SetLevel(l zapcore.Level)

SetLevel alters the logging level.

func (AtomicLevel) String added in v1.4.0 

func (lvl AtomicLevel) String() string

String returns the string representation of the underlying Level.

func (*AtomicLevel) UnmarshalText 

func (lvl *AtomicLevel) UnmarshalText(text []byte) error

UnmarshalText unmarshals the text to an AtomicLevel. It uses the same text representations as the static zapcore.Levels ("debug", "info", "warn", "error", "dpanic", "panic", and "fatal").

type Config 

type Config struct {
	// Level is the minimum enabled logging level. Note that this is a dynamic
	// level, so calling Config.Level.SetLevel will atomically change the log
	// level of all loggers descended from this config.
	Level AtomicLevel `json:"level" yaml:"level"`
	// Development puts the logger in development mode, which changes the
	// behavior of DPanicLevel and takes stacktraces more liberally.
	Development bool `json:"development" yaml:"development"`
	// DisableCaller stops annotating logs with the calling function's file
	// name and line number. By default, all logs are annotated.
	DisableCaller bool `json:"disableCaller" yaml:"disableCaller"`
	// DisableStacktrace completely disables automatic stacktrace capturing. By
	// default, stacktraces are captured for WarnLevel and above logs in
	// development and ErrorLevel and above in production.
	DisableStacktrace bool `json:"disableStacktrace" yaml:"disableStacktrace"`
	// Sampling sets a sampling policy. A nil SamplingConfig disables sampling.
	Sampling *SamplingConfig `json:"sampling" yaml:"sampling"`
	// Encoding sets the logger's encoding. Valid values are "json" and
	// "console", as well as any third-party encodings registered via
	// RegisterEncoder.
	Encoding string `json:"encoding" yaml:"encoding"`
	// EncoderConfig sets options for the chosen encoder. See
	// zapcore.EncoderConfig for details.
	EncoderConfig zapcore.EncoderConfig `json:"encoderConfig" yaml:"encoderConfig"`
	// OutputPaths is a list of URLs or file paths to write logging output to.
	// See Open for details.
	OutputPaths []string `json:"outputPaths" yaml:"outputPaths"`
	// ErrorOutputPaths is a list of URLs to write internal logger errors to.
	// The default is standard error.
	//
	// Note that this setting only affects internal errors; for sample code that
	// sends error-level logs to a different location from info- and debug-level
	// logs, see the package-level AdvancedConfiguration example.
	ErrorOutputPaths []string `json:"errorOutputPaths" yaml:"errorOutputPaths"`
	// InitialFields is a collection of fields to add to the root logger.
	InitialFields map[string]interface{} `json:"initialFields" yaml:"initialFields"`
}

Config offers a declarative way to construct a logger. It doesn't do anything that can't be done with New, Options, and the various zapcore.WriteSyncer and zapcore.Core wrappers, but it's a simpler way to toggle common options.

Note that Config intentionally supports only the most common options. More unusual logging setups (logging to network connections or message queues, splitting output between multiple files, etc.) are possible, but require direct use of the zapcore package. For sample code, see the package-level BasicConfiguration and AdvancedConfiguration examples.

For an example showing runtime log level changes, see the documentation for AtomicLevel.

func NewDevelopmentConfig 

func NewDevelopmentConfig() Config

NewDevelopmentConfig builds a reasonable default development logging configuration. Logging is enabled at DebugLevel and above, and uses a console encoder. Logs are written to standard error. Stacktraces are included on logs of WarnLevel and above. DPanicLevel logs will panic.

See NewDevelopmentEncoderConfig for information on the default encoder configuration.

func NewProductionConfig 

func NewProductionConfig() Config

NewProductionConfig builds a reasonable default production logging configuration. Logging is enabled at InfoLevel and above, and uses a JSON encoder. Logs are written to standard error. Stacktraces are included on logs of ErrorLevel and above. DPanicLevel logs will not panic, but will write a stacktrace.

Sampling is enabled at 100:100 by default, meaning that after the first 100 log entries with the same level and message in the same second, it will log every 100th entry with the same level and message in the same second. You may disable this behavior by setting Sampling to nil.

See NewProductionEncoderConfig for information on the default encoder configuration.

func (Config) Build 

func (cfg Config) Build(opts ...Option) (*Logger, error)

Build constructs a logger from the Config and Options.

type Field added in v1.8.0 

type Field = zapcore.Field

Field is an alias for Field. Aliasing this type dramatically improves the navigability of this package's API documentation.

func Any 

func Any(key string, value interface{}) Field

Any takes a key and an arbitrary value and chooses the best way to represent them as a field, falling back to a reflection-based approach only if necessary.

Since byte/uint8 and rune/int32 are aliases, Any can't differentiate between them. To minimize surprises, []byte values are treated as binary blobs, byte values are treated as uint8, and runes are always treated as integers.

func Array 

func Array(key string, val zapcore.ArrayMarshaler) Field

Array constructs a field with the given key and ArrayMarshaler. It provides a flexible, but still type-safe and efficient, way to add array-like types to the logging context. The struct's MarshalLogArray method is called lazily.

func Binary 

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

Binary constructs a field that carries an opaque binary blob.

Binary data is serialized in an encoding-appropriate format. For example, zap's JSON encoder base64-encodes binary blobs. To log UTF-8 encoded text, use ByteString.

func Bool 

func Bool(key string, val bool) Field

Bool constructs a field that carries a bool.

func Boolp added in v1.13.0 

func Boolp(key string, val *bool) Field

Boolp constructs a field that carries a *bool. The returned Field will safely and explicitly represent `nil` when appropriate.

func Bools 

func Bools(key string, bs []bool) Field

Bools constructs a field that carries a slice of bools.

func ByteString 

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

ByteString constructs a field that carries UTF-8 encoded text as a []byte. To log opaque binary blobs (which aren't necessarily valid UTF-8), use Binary.

func ByteStrings 

func ByteStrings(key string, bss [][]byte) Field

ByteStrings constructs a field that carries a slice of []byte, each of which must be UTF-8 encoded text.

func Complex128 

func Complex128(key string, val complex128) Field

Complex128 constructs a field that carries a complex number. Unlike most numeric fields, this costs an allocation (to convert the complex128 to interface{}).

func Complex128p added in v1.13.0 

func Complex128p(key string, val *complex128) Field

Complex128p constructs a field that carries a *complex128. The returned Field will safely and explicitly represent `nil` when appropriate.

func Complex128s 

func Complex128s(key string, nums []complex128) Field

Complex128s constructs a field that carries a slice of complex numbers.

func Complex64 

func Complex64(key string, val complex64) Field

Complex64 constructs a field that carries a complex number. Unlike most numeric fields, this costs an allocation (to convert the complex64 to interface{}).

func Complex64p added in v1.13.0 

func Complex64p(key string, val *complex64) Field

Complex64p constructs a field that carries a *complex64. The returned Field will safely and explicitly represent `nil` when appropriate.

func Complex64s 

func Complex64s(key string, nums []complex64) Field

Complex64s constructs a field that carries a slice of complex numbers.

func Dict added in v1.26.0 

func Dict(key string, val ...Field) Field

Dict constructs a field containing the provided key-value pairs. It acts similar to Object, but with the fields specified as arguments.

Example 
package main

import (
	"go.uber.org/zap"
)

func main() {
	logger := zap.NewExample()
	defer logger.Sync()

	logger.Info("login event",
		zap.Dict("event",
			zap.Int("id", 123),
			zap.String("name", "jane"),
			zap.String("status", "pending")))
}

Output:

{"level":"info","msg":"login event","event":{"id":123,"name":"jane","status":"pending"}}

func Duration 

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

Duration constructs a field with the given key and value. The encoder controls how the duration is serialized.

func Durationp added in v1.13.0 

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

Durationp constructs a field that carries a *time.Duration. The returned Field will safely and explicitly represent `nil` when appropriate.

func Durations 

func Durations(key string, ds []time.Duration) Field

Durations constructs a field that carries a slice of time.Durations.

func Error 

func Error(err error) Field

Error is shorthand for the common idiom NamedError("error", err).

func Errors 

func Errors(key string, errs []error) Field

Errors constructs a field that carries a slice of errors.

func Float32 

func Float32(key string, val float32) Field

Float32 constructs a field that carries a float32. The way the floating-point value is represented is encoder-dependent, so marshaling is necessarily lazy.

func Float32p added in v1.13.0 

func Float32p(key string, val *float32) Field

Float32p constructs a field that carries a *float32. The returned Field will safely and explicitly represent `nil` when appropriate.

func Float32s 

func Float32s(key string, nums []float32) Field

Float32s constructs a field that carries a slice of floats.

func Float64 

func Float64(key string, val float64) Field

Float64 constructs a field that carries a float64. The way the floating-point value is represented is encoder-dependent, so marshaling is necessarily lazy.

func Float64p added in v1.13.0 

func Float64p(key string, val *float64) Field

Float64p constructs a field that carries a *float64. The returned Field will safely and explicitly represent `nil` when appropriate.

func Float64s 

func Float64s(key string, nums []float64) Field

Float64s constructs a field that carries a slice of floats.

func Inline added in v1.17.0 

func Inline(val zapcore.ObjectMarshaler) Field

Inline constructs a Field that is similar to Object, but it will add the elements of the provided ObjectMarshaler to the current namespace.

func Int 

func Int(key string, val int) Field

Int constructs a field with the given key and value.

func Int16 

func Int16(key string, val int16) Field

Int16 constructs a field with the given key and value.

func Int16p added in v1.13.0 

func Int16p(key string, val *int16) Field

Int16p constructs a field that carries a *int16. The returned Field will safely and explicitly represent `nil` when appropriate.

func Int16s 

func Int16s(key string, nums []int16) Field

Int16s constructs a field that carries a slice of integers.

func Int32 

func Int32(key string, val int32) Field

Int32 constructs a field with the given key and value.

func Int32p added in v1.13.0 

func Int32p(key string, val *int32) Field

Int32p constructs a field that carries a *int32. The returned Field will safely and explicitly represent `nil` when appropriate.

func Int32s 

func Int32s(key string, nums []int32) Field

Int32s constructs a field that carries a slice of integers.

func Int64 

func Int64(key string, val int64) Field

Int64 constructs a field with the given key and value.

func Int64p added in v1.13.0 

func Int64p(key string, val *int64) Field

Int64p constructs a field that carries a *int64. The returned Field will safely and explicitly represent `nil` when appropriate.

func Int64s 

func Int64s(key string, nums []int64) Field

Int64s constructs a field that carries a slice of integers.

func Int8 

func Int8(key string, val int8) Field

Int8 constructs a field with the given key and value.

func Int8p added in v1.13.0 

func Int8p(key string, val *int8) Field

Int8p constructs a field that carries a *int8. The returned Field will safely and explicitly represent `nil` when appropriate.

func Int8s 

func Int8s(key string, nums []int8) Field

Int8s constructs a field that carries a slice of integers.

func Intp added in v1.13.0 

func Intp(key string, val *int) Field

Intp constructs a field that carries a *int. The returned Field will safely and explicitly represent `nil` when appropriate.

func Ints 

func Ints(key string, nums []int) Field

Ints constructs a field that carries a slice of integers.

func NamedError 

func NamedError(key string, err error) Field

NamedError constructs a field that lazily stores err.Error() under the provided key. Errors which also implement fmt.Formatter (like those produced by github.com/pkg/errors) will also have their verbose representation stored under key+"Verbose". If passed a nil error, the field is a no-op.

For the common case in which the key is simply "error", the Error function is shorter and less repetitive.

func Namespace 

func Namespace(key string) Field

Namespace creates a named, isolated scope within the logger's context. All subsequent fields will be added to the new namespace.

This helps prevent key collisions when injecting loggers into sub-components or third-party libraries.

Example 
package main

import (
	"go.uber.org/zap"
)

func main() {
	logger := zap.NewExample()
	defer logger.Sync()

	logger.With(
		zap.Namespace("metrics"),
		zap.Int("counter", 1),
	).Info("tracked some metrics")
}

Output:

{"level":"info","msg":"tracked some metrics","metrics":{"counter":1}}

func Object 

func Object(key string, val zapcore.ObjectMarshaler) Field

Object constructs a field with the given key and ObjectMarshaler. It provides a flexible, but still type-safe and efficient, way to add map- or struct-like user-defined types to the logging context. The struct's MarshalLogObject method is called lazily.

Example 
package main

import (
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
)

type addr struct {
	IP   string
	Port int
}

type request struct {
	URL    string
	Listen addr
	Remote addr
}

func (a addr) MarshalLogObject(enc zapcore.ObjectEncoder) error {
	enc.AddString("ip", a.IP)
	enc.AddInt("port", a.Port)
	return nil
}

func (r *request) MarshalLogObject(enc zapcore.ObjectEncoder) error {
	enc.AddString("url", r.URL)
	zap.Inline(r.Listen).AddTo(enc)
	return enc.AddObject("remote", r.Remote)
}

func main() {
	logger := zap.NewExample()
	defer logger.Sync()

	req := &request{
		URL:    "/test",
		Listen: addr{"127.0.0.1", 8080},
		Remote: addr{"127.0.0.1", 31200},
	}
	logger.Info("new request, in nested object", zap.Object("req", req))
	logger.Info("new request, inline", zap.Inline(req))
}

Output:

{"level":"info","msg":"new request, in nested object","req":{"url":"/test","ip":"127.0.0.1","port":8080,"remote":{"ip":"127.0.0.1","port":31200}}}
{"level":"info","msg":"new request, inline","url":"/test","ip":"127.0.0.1","port":8080,"remote":{"ip":"127.0.0.1","port":31200}}

func ObjectValues added in v1.22.0 

func ObjectValues[T any, P ObjectMarshalerPtr[T]](key string, values []T) Field

ObjectValues constructs a field with the given key, holding a list of the provided objects, where pointers to these objects can be marshaled by Zap.

Note that pointers to these objects must implement zapcore.ObjectMarshaler. That is, if you're trying to marshal a []Request, the MarshalLogObject method must be declared on the *Request type, not the value (Request). If it's on the value, use Objects.

Given an object that implements MarshalLogObject on the pointer receiver, you can log a slice of those objects with ObjectValues like so: 

type Request struct{ ... }
func (r *Request) MarshalLogObject(enc zapcore.ObjectEncoder) error

var requests []Request = ...
logger.Info("sending requests", zap.ObjectValues("requests", requests))

If instead, you have a slice of pointers of such an object, use the Objects field constructor. 

var requests []*Request = ...
logger.Info("sending requests", zap.Objects("requests", requests))
Example 
package main

import (
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
)

type addr struct {
	IP   string
	Port int
}

type request struct {
	URL    string
	Listen addr
	Remote addr
}

func (a addr) MarshalLogObject(enc zapcore.ObjectEncoder) error {
	enc.AddString("ip", a.IP)
	enc.AddInt("port", a.Port)
	return nil
}

func (r *request) MarshalLogObject(enc zapcore.ObjectEncoder) error {
	enc.AddString("url", r.URL)
	zap.Inline(r.Listen).AddTo(enc)
	return enc.AddObject("remote", r.Remote)
}

func main() {
	logger := zap.NewExample()
	defer logger.Sync()

	// Use the ObjectValues field constructor when you have a list of
	// objects that do not implement zapcore.ObjectMarshaler directly,
	// but on their pointer receivers.
	logger.Debug("starting tunnels",
		zap.ObjectValues("addrs", []request{
			{
				URL:    "/foo",
				Listen: addr{"127.0.0.1", 8080},
				Remote: addr{"123.45.67.89", 4040},
			},
			{
				URL:    "/bar",
				Listen: addr{"127.0.0.1", 8080},
				Remote: addr{"127.0.0.1", 31200},
			},
		}))
}

Output:

{"level":"debug","msg":"starting tunnels","addrs":[{"url":"/foo","ip":"127.0.0.1","port":8080,"remote":{"ip":"123.45.67.89","port":4040}},{"url":"/bar","ip":"127.0.0.1","port":8080,"remote":{"ip":"127.0.0.1","port":31200}}]}

func Objects added in v1.22.0 

func Objects[T zapcore.ObjectMarshaler](key string, values []T) Field

Objects constructs a field with the given key, holding a list of the provided objects that can be marshaled by Zap.

Note that these objects must implement zapcore.ObjectMarshaler directly. That is, if you're trying to marshal a []Request, the MarshalLogObject method must be declared on the Request type, not its pointer (*Request). If it's on the pointer, use ObjectValues.

Given an object that implements MarshalLogObject on the value receiver, you can log a slice of those objects with Objects like so: 

type Author struct{ ... }
func (a Author) MarshalLogObject(enc zapcore.ObjectEncoder) error

var authors []Author = ...
logger.Info("loading article", zap.Objects("authors", authors))

Similarly, given a type that implements MarshalLogObject on its pointer receiver, you can log a slice of pointers to that object with Objects like so: 

type Request struct{ ... }
func (r *Request) MarshalLogObject(enc zapcore.ObjectEncoder) error

var requests []*Request = ...
logger.Info("sending requests", zap.Objects("requests", requests))

If instead, you have a slice of values of such an object, use the ObjectValues constructor. 

var requests []Request = ...
logger.Info("sending requests", zap.ObjectValues("requests", requests))
Example 
package main

import (
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
)

type addr struct {
	IP   string
	Port int
}

func (a addr) MarshalLogObject(enc zapcore.ObjectEncoder) error {
	enc.AddString("ip", a.IP)
	enc.AddInt("port", a.Port)
	return nil
}

func main() {
	logger := zap.NewExample()
	defer logger.Sync()

	// Use the Objects field constructor when you have a list of objects,
	// all of which implement zapcore.ObjectMarshaler.
	logger.Debug("opening connections",
		zap.Objects("addrs", []addr{
			{IP: "123.45.67.89", Port: 4040},
			{IP: "127.0.0.1", Port: 4041},
			{IP: "192.168.0.1", Port: 4042},
		}))
}

Output:

{"level":"debug","msg":"opening connections","addrs":[{"ip":"123.45.67.89","port":4040},{"ip":"127.0.0.1","port":4041},{"ip":"192.168.0.1","port":4042}]}

func Reflect 

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

Reflect 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. Outside tests, Any is always a better choice.

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

func Skip 

func Skip() Field

Skip constructs a no-op field, which is often useful when handling invalid inputs in other Field constructors.

func Stack 

func Stack(key string) Field

Stack constructs a field that stores a stacktrace of the current goroutine under provided key. Keep in mind that taking a stacktrace is eager and expensive (relatively speaking); this function both makes an allocation and takes about two microseconds.

func StackSkip added in v1.16.0 

func StackSkip(key string, skip int) Field

StackSkip constructs a field similarly to Stack, but also skips the given number of frames from the top of the stacktrace.

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 Stringers added in v1.23.0 

func Stringers[T fmt.Stringer](key string, values []T) Field

Stringers constructs a field with the given key, holding a list of the output provided by the value's String method

Given an object that implements String on the value receiver, you can log a slice of those objects with Objects like so: 

type Request struct{ ... }
func (a Request) String() string

var requests []Request = ...
logger.Info("sending requests", zap.Stringers("requests", requests))

Note that these objects must implement fmt.Stringer directly. That is, if you're trying to marshal a []Request, the String method must be declared on the Request type, not its pointer (*Request).

func Stringp added in v1.13.0 

func Stringp(key string, val *string) Field

Stringp constructs a field that carries a *string. The returned Field will safely and explicitly represent `nil` when appropriate.

func Strings 

func Strings(key string, ss []string) Field

Strings constructs a field that carries a slice of strings.

func Time 

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

Time constructs a Field with the given key and value. The encoder controls how the time is serialized.

func Timep added in v1.13.0 

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

Timep constructs a field that carries a *time.Time. The returned Field will safely and explicitly represent `nil` when appropriate.

func Times 

func Times(key string, ts []time.Time) Field

Times constructs a field that carries a slice of time.Times.

func Uint 

func Uint(key string, val uint) Field

Uint constructs a field with the given key and value.

func Uint16 

func Uint16(key string, val uint16) Field

Uint16 constructs a field with the given key and value.

func Uint16p added in v1.13.0 

func Uint16p(key string, val *uint16) Field

Uint16p constructs a field that carries a *uint16. The returned Field will safely and explicitly represent `nil` when appropriate.

func Uint16s 

func Uint16s(key string, nums []uint16) Field

Uint16s constructs a field that carries a slice of unsigned integers.

func Uint32 

func Uint32(key string, val uint32) Field

Uint32 constructs a field with the given key and value.

func Uint32p added in v1.13.0 

func Uint32p(key string, val *uint32) Field

Uint32p constructs a field that carries a *uint32. The returned Field will safely and explicitly represent `nil` when appropriate.

func Uint32s 

func Uint32s(key string, nums []uint32) Field

Uint32s constructs a field that carries a slice of unsigned integers.

func Uint64 

func Uint64(key string, val uint64) Field

Uint64 constructs a field with the given key and value.

func Uint64p added in v1.13.0 

func Uint64p(key string, val *uint64) Field

Uint64p constructs a field that carries a *uint64. The returned Field will safely and explicitly represent `nil` when appropriate.

func Uint64s 

func Uint64s(key string, nums []uint64) Field

Uint64s constructs a field that carries a slice of unsigned integers.

func Uint8 

func Uint8(key string, val uint8) Field

Uint8 constructs a field with the given key and value.

func Uint8p added in v1.13.0 

func Uint8p(key string, val *uint8) Field

Uint8p constructs a field that carries a *uint8. The returned Field will safely and explicitly represent `nil` when appropriate.

func Uint8s 

func Uint8s(key string, nums []uint8) Field

Uint8s constructs a field that carries a slice of unsigned integers.

func Uintp added in v1.13.0 

func Uintp(key string, val *uint) Field

Uintp constructs a field that carries a *uint. The returned Field will safely and explicitly represent `nil` when appropriate.

func Uintptr 

func Uintptr(key string, val uintptr) Field

Uintptr constructs a field with the given key and value.

func Uintptrp added in v1.13.0 

func Uintptrp(key string, val *uintptr) Field

Uintptrp constructs a field that carries a *uintptr. The returned Field will safely and explicitly represent `nil` when appropriate.

func Uintptrs 

func Uintptrs(key string, us []uintptr) Field

Uintptrs constructs a field that carries a slice of pointer addresses.

func Uints 

func Uints(key string, nums []uint) Field

Uints constructs a field that carries a slice of unsigned integers.

type LevelEnablerFunc 

type LevelEnablerFunc func(zapcore.Level) bool

LevelEnablerFunc is a convenient way to implement zapcore.LevelEnabler with an anonymous function.

It's particularly useful when splitting log output between different outputs (e.g., standard error and standard out). For sample code, see the package-level AdvancedConfiguration example.

func (LevelEnablerFunc) Enabled 

func (f LevelEnablerFunc) Enabled(lvl zapcore.Level) bool

Enabled calls the wrapped function.

type Logger 

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

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

The Logger is designed for contexts in which every microsecond and every allocation matters, so its API intentionally favors performance and type safety over brevity. For most applications, the SugaredLogger strikes a better balance between performance and ergonomics.

func L 

func L() *Logger

L returns the global Logger, which can be reconfigured with ReplaceGlobals. It's safe for concurrent use.

func Must added in v1.22.0 

func Must(logger *Logger, err error) *Logger

Must is a helper that wraps a call to a function returning (*Logger, error) and panics if the error is non-nil. It is intended for use in variable initialization such as: 

var logger = zap.Must(zap.NewProduction())

func New 

func New(core zapcore.Core, options ...Option) *Logger

New constructs a new Logger from the provided zapcore.Core and Options. If the passed zapcore.Core is nil, it falls back to using a no-op implementation.

This is the most flexible way to construct a Logger, but also the most verbose. For typical use cases, the highly-opinionated presets (NewProduction, NewDevelopment, and NewExample) or the Config struct are more convenient.

For sample code, see the package-level AdvancedConfiguration example.

func NewDevelopment 

func NewDevelopment(options ...Option) (*Logger, error)

NewDevelopment builds a development Logger that writes DebugLevel and above logs to standard error in a human-friendly format.

It's a shortcut for NewDevelopmentConfig().Build(...Option).

func NewExample added in v1.5.0 

func NewExample(options ...Option) *Logger

NewExample builds a Logger that's designed for use in zap's testable examples. It writes DebugLevel and above logs to standard out as JSON, but omits the timestamp and calling function to keep example output short and deterministic.

func NewNop 

func NewNop() *Logger

NewNop returns a no-op Logger. It never writes out logs or internal errors, and it never runs user-defined hooks.

Using WithOptions to replace the Core or error output of a no-op Logger can re-enable logging.

func NewProduction 

func NewProduction(options ...Option) (*Logger, error)

NewProduction builds a sensible production Logger that writes InfoLevel and above logs to standard error as JSON.

It's a shortcut for NewProductionConfig().Build(...Option).

func (*Logger) Check 

func (log *Logger) Check(lvl zapcore.Level, msg string) *zapcore.CheckedEntry

Check returns a CheckedEntry 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.

Example 
package main

import (
	"go.uber.org/zap"
)

func main() {
	logger := zap.NewExample()
	defer logger.Sync()

	if ce := logger.Check(zap.DebugLevel, "debugging"); ce != nil {
		// If debug-level log output isn't enabled or if zap's sampling would have
		// dropped this log entry, we don't allocate the slice that holds these
		// fields.
		ce.Write(
			zap.String("foo", "bar"),
			zap.String("baz", "quux"),
		)
	}

}

Output:

{"level":"debug","msg":"debugging","foo":"bar","baz":"quux"}

func (*Logger) Core 

func (log *Logger) Core() zapcore.Core

Core returns the Logger's underlying zapcore.Core.

func (*Logger) DPanic 

func (log *Logger) DPanic(msg string, fields ...Field)

DPanic logs a message at DPanicLevel. The message includes any fields passed at the log site, as well as any fields accumulated on the logger.

If the logger is in development mode, it then panics (DPanic means "development panic"). This is useful for catching errors that are recoverable, but shouldn't ever happen.

func (*Logger) Debug 

func (log *Logger) Debug(msg string, fields ...Field)

Debug logs a message at DebugLevel. The message includes any fields passed at the log site, as well as any fields accumulated on the logger.

func (*Logger) Error 

func (log *Logger) Error(msg string, fields ...Field)

Error logs a message at ErrorLevel. The message includes any fields passed at the log site, as well as any fields accumulated on the logger.

func (*Logger) Fatal 

func (log *Logger) Fatal(msg string, fields ...Field)

Fatal logs a message at FatalLevel. The message includes any fields passed at the log site, as well as any fields accumulated on the logger.

The logger then calls os.Exit(1), even if logging at FatalLevel is disabled.

func (*Logger) Info 

func (log *Logger) Info(msg string, fields ...Field)

Info logs a message at InfoLevel. The message includes any fields passed at the log site, as well as any fields accumulated on the logger.

func (*Logger) Level added in v1.24.0 

func (log *Logger) Level() zapcore.Level

Level reports the minimum enabled level for this logger.

For NopLoggers, this is zapcore.InvalidLevel.

func (*Logger) Log added in v1.22.0 

func (log *Logger) Log(lvl zapcore.Level, msg string, fields ...Field)

Log logs a message at the specified level. The message includes any fields passed at the log site, as well as any fields accumulated on the logger. Any Fields that require evaluation (such as Objects) are evaluated upon invocation of Log.

func (*Logger) Name added in v1.25.0 

func (log *Logger) Name() string

Name returns the Logger's underlying name, or an empty string if the logger is unnamed.

func (*Logger) Named 

func (log *Logger) Named(s string) *Logger

Named adds a new path segment to the logger's name. Segments are joined by periods. By default, Loggers are unnamed.

Example 
package main

import (
	"go.uber.org/zap"
)

func main() {
	logger := zap.NewExample()
	defer logger.Sync()

	// By default, Loggers are unnamed.
	logger.Info("no name")

	// The first call to Named sets the Logger name.
	main := logger.Named("main")
	main.Info("main logger")

	// Additional calls to Named create a period-separated path.
	main.Named("subpackage").Info("sub-logger")
}

Output:

{"level":"info","msg":"no name"}
{"level":"info","logger":"main","msg":"main logger"}
{"level":"info","logger":"main.subpackage","msg":"sub-logger"}

func (*Logger) Panic 

func (log *Logger) Panic(msg string, fields ...Field)

Panic logs a message at PanicLevel. The message includes any fields passed at the log site, as well as any fields accumulated on the logger.

The logger then panics, even if logging at PanicLevel is disabled.

func (*Logger) Sugar 

func (log *Logger) Sugar() *SugaredLogger

Sugar wraps the Logger to provide a more ergonomic, but slightly slower, API. Sugaring a Logger is quite inexpensive, so it's reasonable for a single application to use both Loggers and SugaredLoggers, converting between them on the boundaries of performance-sensitive code.

func (*Logger) Sync 

func (log *Logger) Sync() error

Sync calls the underlying Core's Sync method, flushing any buffered log entries. Applications should take care to call Sync before exiting.

func (*Logger) Warn 

func (log *Logger) Warn(msg string, fields ...Field)

Warn logs a message at WarnLevel. The message includes any fields passed at the log site, as well as any fields accumulated on the logger.

func (*Logger) With 

func (log *Logger) With(fields ...Field) *Logger

With creates a child logger and adds structured context to it. Fields added to the child don't affect the parent, and vice versa. Any fields that require evaluation (such as Objects) are evaluated upon invocation of With.

func (*Logger) WithLazy added in v1.26.0 

func (log *Logger) WithLazy(fields ...Field) *Logger

WithLazy creates a child logger and adds structured context to it lazily.

The fields are evaluated only if the logger is further chained with [With] or is written to with any of the log level methods. Until that occurs, the logger may retain references to objects inside the fields, and logging will reflect the state of an object at the time of logging, not the time of WithLazy().

WithLazy provides a worthwhile performance optimization for contextual loggers when the likelihood of using the child logger is low, such as error paths and rarely taken branches.

Similar to [With], fields added to the child don't affect the parent, and vice versa.

func (*Logger) WithOptions 

func (log *Logger) WithOptions(opts ...Option) *Logger

WithOptions clones the current Logger, applies the supplied Options, and returns the resulting Logger. It's safe to use concurrently.

type ObjectMarshalerPtr added in v1.24.0 

type ObjectMarshalerPtr[T any] interface {
	*T
	zapcore.ObjectMarshaler
}

ObjectMarshalerPtr is a constraint that specifies that the given type implements zapcore.ObjectMarshaler on a pointer receiver.

type Option 

type Option interface {
	// contains filtered or unexported methods
}

An Option configures a Logger.

func AddCaller 

func AddCaller() Option

AddCaller configures the Logger to annotate each message with the filename, line number, and function name of zap's caller. See also WithCaller.

func AddCallerSkip 

func AddCallerSkip(skip int) Option

AddCallerSkip increases the number of callers skipped by caller annotation (as enabled by the AddCaller option). When building wrappers around the Logger and SugaredLogger, supplying this Option prevents zap from always reporting the wrapper code as the caller.

func AddStacktrace 

func AddStacktrace(lvl zapcore.LevelEnabler) Option

AddStacktrace configures the Logger to record a stack trace for all messages at or above a given level.

func Development 

func Development() Option

Development puts the logger in development mode, which makes DPanic-level logs panic instead of simply logging an error.

func ErrorOutput 

func ErrorOutput(w zapcore.WriteSyncer) Option

ErrorOutput sets the destination for errors generated by the Logger. Note that this option only affects internal errors; for sample code that sends error-level logs to a different location from info- and debug-level logs, see the package-level AdvancedConfiguration example.

The supplied WriteSyncer must be safe for concurrent use. The Open and zapcore.Lock functions are the simplest ways to protect files with a mutex.

func Fields 

func Fields(fs ...Field) Option

Fields adds fields to the Logger.

func Hooks 

func Hooks(hooks ...func(zapcore.Entry) error) Option

Hooks registers functions which will be called each time the Logger writes out an Entry. Repeated use of Hooks is additive.

Hooks are useful for simple side effects, like capturing metrics for the number of emitted logs. More complex side effects, including anything that requires access to the Entry's structured fields, should be implemented as a zapcore.Core instead. See zapcore.RegisterHooks for details.

func IncreaseLevel added in v1.14.0 

func IncreaseLevel(lvl zapcore.LevelEnabler) Option

IncreaseLevel increase the level of the logger. It has no effect if the passed in level tries to decrease the level of the logger.

func OnFatal deprecated added in v1.16.0 

func OnFatal(action zapcore.CheckWriteAction) Option

OnFatal sets the action to take on fatal logs.

Deprecated: Use WithFatalHook instead.

func WithCaller added in v1.15.0 

func WithCaller(enabled bool) Option

WithCaller configures the Logger to annotate each message with the filename, line number, and function name of zap's caller, or not, depending on the value of enabled. This is a generalized form of AddCaller.

func WithClock added in v1.18.0 

func WithClock(clock zapcore.Clock) Option

WithClock specifies the clock used by the logger to determine the current time for logged entries. Defaults to the system clock with time.Now.

func WithFatalHook added in v1.22.0 

func WithFatalHook(hook zapcore.CheckWriteHook) Option

WithFatalHook sets a CheckWriteHook to run on fatal logs. Zap will call this hook after writing a log statement with a Fatal level.

For example, the following builds a logger that will exit the current goroutine after writing a fatal log message, but it will not exit the program. 

zap.New(core, zap.WithFatalHook(zapcore.WriteThenGoexit))

It is important that the provided CheckWriteHook stops the control flow at the current statement to meet expectations of callers of the logger. We recommend calling os.Exit or runtime.Goexit inside custom hooks at minimum.

func WithPanicHook added in v1.27.0 

func WithPanicHook(hook zapcore.CheckWriteHook) Option

WithPanicHook sets a CheckWriteHook to run on Panic/DPanic logs. Zap will call this hook after writing a log statement with a Panic/DPanic level.

For example, the following builds a logger that will exit the current goroutine after writing a Panic/DPanic log message, but it will not start a panic. 

zap.New(core, zap.WithPanicHook(zapcore.WriteThenGoexit))

This is useful for testing Panic/DPanic log output.

func WrapCore 

func WrapCore(f func(zapcore.Core) zapcore.Core) Option

WrapCore wraps or replaces the Logger's underlying zapcore.Core.

Example (Replace) 
package main

import (
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
)

func main() {
	// Replacing a Logger's core can alter fundamental behaviors.
	// For example, it can convert a Logger to a no-op.
	nop := zap.WrapCore(func(zapcore.Core) zapcore.Core {
		return zapcore.NewNopCore()
	})

	logger := zap.NewExample()
	defer logger.Sync()

	logger.Info("working")
	logger.WithOptions(nop).Info("no-op")
	logger.Info("original logger still works")
}

Output:

{"level":"info","msg":"working"}
{"level":"info","msg":"original logger still works"}
Example (Wrap) 
package main

import (
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
)

func main() {
	// Wrapping a Logger's core can extend its functionality. As a trivial
	// example, it can double-write all logs.
	doubled := zap.WrapCore(func(c zapcore.Core) zapcore.Core {
		return zapcore.NewTee(c, c)
	})

	logger := zap.NewExample()
	defer logger.Sync()

	logger.Info("single")
	logger.WithOptions(doubled).Info("doubled")
}

Output:

{"level":"info","msg":"single"}
{"level":"info","msg":"doubled"}
{"level":"info","msg":"doubled"}

type SamplingConfig 

type SamplingConfig struct {
	Initial    int                                           `json:"initial" yaml:"initial"`
	Thereafter int                                           `json:"thereafter" yaml:"thereafter"`
	Hook       func(zapcore.Entry, zapcore.SamplingDecision) `json:"-" yaml:"-"`
}

SamplingConfig sets a sampling strategy for the logger. Sampling caps the global CPU and I/O load that logging puts on your process while attempting to preserve a representative subset of your logs.

If specified, the Sampler will invoke the Hook after each decision.

Values configured here are per-second. See zapcore.NewSamplerWithOptions for details.

type Sink added in v1.9.0 

type Sink interface {
	zapcore.WriteSyncer
	io.Closer
}

Sink defines the interface to write to and close logger destinations.

type SugaredLogger 

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

A SugaredLogger wraps the base Logger functionality in a slower, but less verbose, API. Any Logger can be converted to a SugaredLogger with its Sugar method.

Unlike the Logger, the SugaredLogger doesn't insist on structured logging. For each log level, it exposes four methods:

  • methods named after the log level for log.Print-style logging
  • methods ending in "w" for loosely-typed structured logging
  • methods ending in "f" for log.Printf-style logging
  • methods ending in "ln" for log.Println-style logging

For example, the methods for InfoLevel are: 

Info(...any)           Print-style logging
Infow(...any)          Structured logging (read as "info with")
Infof(string, ...any)  Printf-style logging
Infoln(...any)         Println-style logging

func S 

func S() *SugaredLogger

S returns the global SugaredLogger, which can be reconfigured with ReplaceGlobals. It's safe for concurrent use.

func (*SugaredLogger) DPanic 

func (s *SugaredLogger) DPanic(args ...interface{})

DPanic logs the provided arguments at DPanicLevel. In development, the logger then panics. (See DPanicLevel for details.) Spaces are added between arguments when neither is a string.

func (*SugaredLogger) DPanicf 

func (s *SugaredLogger) DPanicf(template string, args ...interface{})

DPanicf formats the message according to the format specifier and logs it at DPanicLevel. In development, the logger then panics. (See DPanicLevel for details.)

func (*SugaredLogger) DPanicln added in v1.22.0 

func (s *SugaredLogger) DPanicln(args ...interface{})

DPanicln logs a message at DPanicLevel. In development, the logger then panics. (See DPanicLevel for details.) Spaces are always added between arguments.

func (*SugaredLogger) DPanicw 

func (s *SugaredLogger) DPanicw(msg string, keysAndValues ...interface{})

DPanicw logs a message with some additional context. In development, the logger then panics. (See DPanicLevel for details.) The variadic key-value pairs are treated as they are in With.

func (*SugaredLogger) Debug 

func (s *SugaredLogger) Debug(args ...interface{})

Debug logs the provided arguments at DebugLevel. Spaces are added between arguments when neither is a string.

func (*SugaredLogger) Debugf 

func (s *SugaredLogger) Debugf(template string, args ...interface{})

Debugf formats the message according to the format specifier and logs it at DebugLevel.

func (*SugaredLogger) Debugln added in v1.22.0 

func (s *SugaredLogger) Debugln(args ...interface{})

Debugln logs a message at DebugLevel. Spaces are always added between arguments.

func (*SugaredLogger) Debugw 

func (s *SugaredLogger) Debugw(msg string, keysAndValues ...interface{})

Debugw logs a message with some additional context. The variadic key-value pairs are treated as they are in With.

When debug-level logging is disabled, this is much faster than 

s.With(keysAndValues).Debug(msg)

func (*SugaredLogger) Desugar 

func (s *SugaredLogger) Desugar() *Logger

Desugar unwraps a SugaredLogger, exposing the original Logger. Desugaring is quite inexpensive, so it's reasonable for a single application to use both Loggers and SugaredLoggers, converting between them on the boundaries of performance-sensitive code.

func (*SugaredLogger) Error 

func (s *SugaredLogger) Error(args ...interface{})

Error logs the provided arguments at ErrorLevel. Spaces are added between arguments when neither is a string.

func (*SugaredLogger) Errorf 

func (s *SugaredLogger) Errorf(template string, args ...interface{})

Errorf formats the message according to the format specifier and logs it at ErrorLevel.

func (*SugaredLogger) Errorln added in v1.22.0 

func (s *SugaredLogger) Errorln(args ...interface{})

Errorln logs a message at ErrorLevel. Spaces are always added between arguments.

func (*SugaredLogger) Errorw 

func (s *SugaredLogger) Errorw(msg string, keysAndValues ...interface{})

Errorw logs a message with some additional context. The variadic key-value pairs are treated as they are in With.

func (*SugaredLogger) Fatal 

func (s *SugaredLogger) Fatal(args ...interface{})

Fatal constructs a message with the provided arguments and calls os.Exit. Spaces are added between arguments when neither is a string.

func (*SugaredLogger) Fatalf 

func (s *SugaredLogger) Fatalf(template string, args ...interface{})

Fatalf formats the message according to the format specifier and calls os.Exit.

func (*SugaredLogger) Fatalln added in v1.22.0 

func (s *SugaredLogger) Fatalln(args ...interface{})

Fatalln logs a message at FatalLevel and calls os.Exit. Spaces are always added between arguments.

func (*SugaredLogger) Fatalw 

func (s *SugaredLogger) Fatalw(msg string, keysAndValues ...interface{})

Fatalw logs a message with some additional context, then calls os.Exit. The variadic key-value pairs are treated as they are in With.

func (*SugaredLogger) Info 

func (s *SugaredLogger) Info(args ...interface{})

Info logs the provided arguments at InfoLevel. Spaces are added between arguments when neither is a string.

func (*SugaredLogger) Infof 

func (s *SugaredLogger) Infof(template string, args ...interface{})

Infof formats the message according to the format specifier and logs it at InfoLevel.

func (*SugaredLogger) Infoln added in v1.22.0 

func (s *SugaredLogger) Infoln(args ...interface{})

Infoln logs a message at InfoLevel. Spaces are always added between arguments.

func (*SugaredLogger) Infow 

func (s *SugaredLogger) Infow(msg string, keysAndValues ...interface{})

Infow logs a message with some additional context. The variadic key-value pairs are treated as they are in With.

func (*SugaredLogger) Level added in v1.24.0 

func (s *SugaredLogger) Level() zapcore.Level

Level reports the minimum enabled level for this logger.

For NopLoggers, this is zapcore.InvalidLevel.

func (*SugaredLogger) Log added in v1.27.0 

func (s *SugaredLogger) Log(lvl zapcore.Level, args ...interface{})

Log logs the provided arguments at provided level. Spaces are added between arguments when neither is a string.

func (*SugaredLogger) Logf added in v1.27.0 

func (s *SugaredLogger) Logf(lvl zapcore.Level, template string, args ...interface{})

Logf formats the message according to the format specifier and logs it at provided level.

func (*SugaredLogger) Logln added in v1.27.0 

func (s *SugaredLogger) Logln(lvl zapcore.Level, args ...interface{})

Logln logs a message at provided level. Spaces are always added between arguments.

func (*SugaredLogger) Logw added in v1.27.0 

func (s *SugaredLogger) Logw(lvl zapcore.Level, msg string, keysAndValues ...interface{})

Logw logs a message with some additional context. The variadic key-value pairs are treated as they are in With.

func (*SugaredLogger) Named 

func (s *SugaredLogger) Named(name string) *SugaredLogger

Named adds a sub-scope to the logger's name. See Logger.Named for details.

func (*SugaredLogger) Panic 

func (s *SugaredLogger) Panic(args ...interface{})

Panic constructs a message with the provided arguments and panics. Spaces are added between arguments when neither is a string.

func (*SugaredLogger) Panicf 

func (s *SugaredLogger) Panicf(template string, args ...interface{})

Panicf formats the message according to the format specifier and panics.

func (*SugaredLogger) Panicln added in v1.22.0 

func (s *SugaredLogger) Panicln(args ...interface{})

Panicln logs a message at PanicLevel and panics. Spaces are always added between arguments.

func (*SugaredLogger) Panicw 

func (s *SugaredLogger) Panicw(msg string, keysAndValues ...interface{})

Panicw logs a message with some additional context, then panics. The variadic key-value pairs are treated as they are in With.

func (*SugaredLogger) Sync 

func (s *SugaredLogger) Sync() error

Sync flushes any buffered log entries.

func (*SugaredLogger) Warn 

func (s *SugaredLogger) Warn(args ...interface{})

Warn logs the provided arguments at WarnLevel. Spaces are added between arguments when neither is a string.

func (*SugaredLogger) Warnf 

func (s *SugaredLogger) Warnf(template string, args ...interface{})

Warnf formats the message according to the format specifier and logs it at WarnLevel.

func (*SugaredLogger) Warnln added in v1.22.0 

func (s *SugaredLogger) Warnln(args ...interface{})

Warnln logs a message at WarnLevel. Spaces are always added between arguments.

func (*SugaredLogger) Warnw 

func (s *SugaredLogger) Warnw(msg string, keysAndValues ...interface{})

Warnw logs a message with some additional context. The variadic key-value pairs are treated as they are in With.

func (*SugaredLogger) With 

func (s *SugaredLogger) With(args ...interface{}) *SugaredLogger

With adds a variadic number of fields to the logging context. It accepts a mix of strongly-typed Field objects and loosely-typed key-value pairs. When processing pairs, the first element of the pair is used as the field key and the second as the field value.

For example, 

 sugaredLogger.With(
   "hello", "world",
   "failure", errors.New("oh no"),
   Stack(),
   "count", 42,
   "user", User{Name: "alice"},
)

is the equivalent of 

unsugared.With(
  String("hello", "world"),
  String("failure", "oh no"),
  Stack(),
  Int("count", 42),
  Object("user", User{Name: "alice"}),
)

Note that the keys in key-value pairs should be strings. In development, passing a non-string key panics. In production, the logger is more forgiving: a separate error is logged, but the key-value pair is skipped and execution continues. Passing an orphaned key triggers similar behavior: panics in development and errors in production.

func (*SugaredLogger) WithLazy added in v1.27.0 

func (s *SugaredLogger) WithLazy(args ...interface{}) *SugaredLogger

WithLazy adds a variadic number of fields to the logging context lazily. The fields are evaluated only if the logger is further chained with [With] or is written to with any of the log level methods. Until that occurs, the logger may retain references to objects inside the fields, and logging will reflect the state of an object at the time of logging, not the time of WithLazy().

Similar to [With], fields added to the child don't affect the parent, and vice versa. Also, the keys in key-value pairs should be strings. In development, passing a non-string key panics, while in production it logs an error and skips the pair. Passing an orphaned key has the same behavior.

func (*SugaredLogger) WithOptions added in v1.22.0 

func (s *SugaredLogger) WithOptions(opts ...Option) *SugaredLogger

WithOptions clones the current SugaredLogger, applies the supplied Options, and returns the result. It's safe to use concurrently.

Source Files

View all Source files

Directories

Path Synopsis
benchmarks module
Package buffer provides a thin wrapper around a byte slice.
 Package buffer provides a thin wrapper around a byte slice.
exp module
Package internal and its subpackages hold types and functionality that are not part of Zap's public API.
 Package internal and its subpackages hold types and functionality that are not part of Zap's public API.
bufferpool
Package bufferpool houses zap's shared internal buffer pool.
 Package bufferpool houses zap's shared internal buffer pool.
color
Package color adds coloring functionality for TTY output.
 Package color adds coloring functionality for TTY output.
exit
Package exit provides stubs so that unit tests can exercise code that calls os.Exit(1).
 Package exit provides stubs so that unit tests can exercise code that calls os.Exit(1).
pool
Package pool provides internal pool utilities.
 Package pool provides internal pool utilities.
readme
readme generates Zap's README from a template.
 readme generates Zap's README from a template.
stacktrace
Package stacktrace provides support for gathering stack traces efficiently.
 Package stacktrace provides support for gathering stack traces efficiently.
ztest
Package ztest provides low-level helpers for testing log output.
 Package ztest provides low-level helpers for testing log output.
Package zapcore defines and implements the low-level interfaces upon which zap is built.
 Package zapcore defines and implements the low-level interfaces upon which zap is built.
Package zapgrpc provides a logger that is compatible with grpclog.
 Package zapgrpc provides a logger that is compatible with grpclog.
internal/test Module
Package zapio provides tools for interacting with IO streams through Zap.
 Package zapio provides tools for interacting with IO streams through Zap.
Package zaptest provides a variety of helpers for testing log output.
 Package zaptest provides a variety of helpers for testing log output.
observer
Package observer provides a zapcore.Core that keeps an in-memory, encoding-agnostic representation of log entries.
 Package observer provides a zapcore.Core that keeps an in-memory, encoding-agnostic representation of log entries.

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