7d8f9e5cf0 | ||
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hlog | ||
internal/json | ||
log | ||
.gitignore | ||
.travis.yml | ||
LICENSE | ||
README.md | ||
array.go | ||
array_test.go | ||
benchmark_test.go | ||
console.go | ||
context.go | ||
ctx.go | ||
ctx_test.go | ||
event.go | ||
fields.go | ||
globals.go | ||
hook.go | ||
hook_test.go | ||
log.go | ||
log_example_test.go | ||
log_test.go | ||
pretty.png | ||
sampler.go | ||
sampler_test.go | ||
syslog.go | ||
syslog_test.go | ||
writer.go | ||
writer_test.go |
README.md
Zero Allocation JSON Logger
The zerolog package provides a fast and simple logger dedicated to JSON output.
Zerolog's API is designed to provide both a great developer experience and stunning performance. Its unique chaining API allows zerolog to write JSON log events by avoiding allocations and reflection.
Uber's zap library pioneered this approach. Zerolog is taking this concept to the next level with a simpler to use API and even better performance.
To keep the code base and the API simple, zerolog focuses on JSON logging only. Pretty logging on the console is made possible using the provided (but inefficient) zerolog.ConsoleWriter
.
Features
- Blazing fast
- Low to zero allocation
- Level logging
- Sampling
- Hooks
- Contextual fields
context.Context
integrationnet/http
helpers- Pretty logging for development
Installation
go get -u github.com/rs/zerolog/log
Getting Started
Simple Logging Example
For simple logging, import the global logger package github.com/rs/zerolog/log
package main
import (
"github.com/rs/zerolog"
"github.com/rs/zerolog/log"
)
func main() {
// UNIX Time is faster and smaller than most timestamps
// If you set zerolog.TimeFieldFormat to an empty string,
// logs will write with UNIX time
zerolog.TimeFieldFormat = ""
log.Print("hello world")
}
// Output: {"time":1516134303,"level":"debug","message":"hello world"}
Note: The default log level for
log.Print
is debug
Leveled Logging
Simple Leveled Logging Example
package main
import (
"github.com/rs/zerolog"
"github.com/rs/zerolog/log"
)
func main() {
zerolog.TimeFieldFormat = ""
log.Info().Msg("hello world")
}
// Output: {"time":1516134303,"level":"info","message":"hello world"}
zerolog allows for logging at the following levels (from highest to lowest):
- panic (
zerolog.PanicLevel
, 5) - fatal (
zerolog.FatalLevel
, 4) - error (
zerolog.ErrorLevel
, 3) - warn (
zerolog.WarnLevel
, 2) - info (
zerolog.InfoLevel
, 1) - debug (
zerolog.DebugLevel
, 0)
You can set the Global logging level to any of these options using the SetGlobalLevel
function in the zerolog package, passing in one of the given constants above, e.g. zerolog.InfoLevel
would be the "info" level. Whichever level is chosen, all logs with a level greater than or equal to that level will be written. To turn off logging entirely, pass the zerolog.Disabled
constant.
Setting Global Log Level
This example uses command-line flags to demonstrate various outputs depending on the chosen log level.
package main
import (
"flag"
"github.com/rs/zerolog"
"github.com/rs/zerolog/log"
)
func main() {
zerolog.TimeFieldFormat = ""
debug := flag.Bool("debug", false, "sets log level to debug")
flag.Parse()
// Default level for this example is info, unless debug flag is present
zerolog.SetGlobalLevel(zerolog.InfoLevel)
if *debug {
zerolog.SetGlobalLevel(zerolog.DebugLevel)
}
log.Debug().Msg("This message appears only when log level set to Debug")
log.Info().Msg("This message appears when log level set to Debug or Info")
if e := log.Debug(); e.Enabled() {
// Compute log output only if enabled.
value := "bar"
e.Str("foo", value).Msg("some debug message")
}
}
Info Output (no flag)
$ ./logLevelExample
{"time":1516387492,"level":"info","message":"This message appears when log level set to Debug or Info"}
Debug Output (debug flag set)
$ ./logLevelExample -debug
{"time":1516387573,"level":"debug","message":"This message appears only when log level set to Debug"}
{"time":1516387573,"level":"info","message":"This message appears when log level set to Debug or Info"}
{"time":1516387573,"level":"debug","foo":"bar","message":"some debug message"}
Logging Fatal Messages
package main
import (
"errors"
"github.com/rs/zerolog"
"github.com/rs/zerolog/log"
)
func main() {
err := errors.New("A repo man spends his life getting into tense situations")
service := "myservice"
zerolog.TimeFieldFormat = ""
log.Fatal().
Err(err).
Str("service", service).
Msgf("Cannot start %s", service)
}
// Output: {"time":1516133263,"level":"fatal","error":"A repo man spends his life getting into tense situations","service":"myservice","message":"Cannot start myservice"}
// exit status 1
NOTE: Using
Msgf
generates one allocation even when the logger is disabled.
Contextual Logging
Fields can be added to log messages
log.Info().
Str("foo", "bar").
Int("n", 123).
Msg("hello world")
// Output: {"level":"info","time":1494567715,"foo":"bar","n":123,"message":"hello world"}
Create logger instance to manage different outputs
logger := zerolog.New(os.Stderr).With().Timestamp().Logger()
logger.Info().Str("foo", "bar").Msg("hello world")
// Output: {"level":"info","time":1494567715,"message":"hello world","foo":"bar"}
Sub-loggers let you chain loggers with additional context
sublogger := log.With().
Str("component": "foo").
Logger()
sublogger.Info().Msg("hello world")
// Output: {"level":"info","time":1494567715,"message":"hello world","component":"foo"}
Pretty logging
if isConsole {
log.Logger = log.Output(zerolog.ConsoleWriter{Out: os.Stderr})
}
log.Info().Str("foo", "bar").Msg("Hello world")
// Output: 1494567715 |INFO| Hello world foo=bar
Sub dictionary
log.Info().
Str("foo", "bar").
Dict("dict", zerolog.Dict().
Str("bar", "baz").
Int("n", 1)
).Msg("hello world")
// Output: {"level":"info","time":1494567715,"foo":"bar","dict":{"bar":"baz","n":1},"message":"hello world"}
Customize automatic field names
zerolog.TimestampFieldName = "t"
zerolog.LevelFieldName = "l"
zerolog.MessageFieldName = "m"
log.Info().Msg("hello world")
// Output: {"l":"info","t":1494567715,"m":"hello world"}
Log with no level nor message
log.Log().Str("foo","bar").Msg("")
// Output: {"time":1494567715,"foo":"bar"}
Add contextual fields to the global logger
log.Logger = log.With().Str("foo", "bar").Logger()
Log Sampling
sampled := log.Sample(&zerolog.BasicSampler{N: 10})
sampled.Info().Msg("will be logged every 10 messages")
// Output: {"time":1494567715,"level":"info","message":"will be logged every 10 messages"}
More advanced sampling:
// Will let 5 debug messages per period of 1 second.
// Over 5 debug message, 1 every 100 debug messages are logged.
// Other levels are not sampled.
sampled := log.Sample(zerolog.LevelSampler{
DebugSampler: &zerolog.BurstSampler{
Burst: 5,
Period: 1*time.Second,
NextSampler: &zerolog.BasicSampler{N: 100},
},
})
sampled.Debug().Msg("hello world")
// Output: {"time":1494567715,"level":"debug","message":"hello world"}
Hooks
type SeverityHook struct{}
func (h SeverityHook) Run(e *zerolog.Event, level zerolog.Level, msg string) {
if level != zerolog.NoLevel {
e.Str("severity", level.String())
}
}
hooked := log.Hook(SeverityHook{})
hooked.Warn().Msg("")
// Output: {"level":"warn","severity":"warn"}
Pass a sub-logger by context
ctx := log.With("component", "module").Logger().WithContext(ctx)
log.Ctx(ctx).Info().Msg("hello world")
// Output: {"component":"module","level":"info","message":"hello world"}
Set as standard logger output
log := zerolog.New(os.Stdout).With().
Str("foo", "bar").
Logger()
stdlog.SetFlags(0)
stdlog.SetOutput(log)
stdlog.Print("hello world")
// Output: {"foo":"bar","message":"hello world"}
Integration with net/http
The github.com/rs/zerolog/hlog
package provides some helpers to integrate zerolog with http.Handler
.
In this example we use alice to install logger for better readability.
log := zerolog.New(os.Stdout).With().
Timestamp().
Str("role", "my-service").
Str("host", host).
Logger()
c := alice.New()
// Install the logger handler with default output on the console
c = c.Append(hlog.NewHandler(log))
// Install some provided extra handler to set some request's context fields.
// Thanks to those handler, all our logs will come with some pre-populated fields.
c = c.Append(hlog.AccessHandler(func(r *http.Request, status, size int, duration time.Duration) {
hlog.FromRequest(r).Info().
Str("method", r.Method).
Str("url", r.URL.String()).
Int("status", status).
Int("size", size).
Dur("duration", duration).
Msg("")
}))
c = c.Append(hlog.RemoteAddrHandler("ip"))
c = c.Append(hlog.UserAgentHandler("user_agent"))
c = c.Append(hlog.RefererHandler("referer"))
c = c.Append(hlog.RequestIDHandler("req_id", "Request-Id"))
// Here is your final handler
h := c.Then(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
// Get the logger from the request's context. You can safely assume it
// will be always there: if the handler is removed, hlog.FromRequest
// will return a no-op logger.
hlog.FromRequest(r).Info().
Str("user", "current user").
Str("status", "ok").
Msg("Something happened")
// Output: {"level":"info","time":"2001-02-03T04:05:06Z","role":"my-service","host":"local-hostname","req_id":"b4g0l5t6tfid6dtrapu0","user":"current user","status":"ok","message":"Something happened"}
}))
http.Handle("/", h)
if err := http.ListenAndServe(":8080", nil); err != nil {
log.Fatal().Err(err).Msg("Startup failed")
}
Global Settings
Some settings can be changed and will by applied to all loggers:
log.Logger
: You can set this value to customize the global logger (the one used by package level methods).zerolog.SetGlobalLevel
: Can raise the minimum level of all loggers. Set this tozerolog.Disable
to disable logging altogether (quiet mode).zerolog.DisableSampling
: If argument istrue
, all sampled loggers will stop sampling and issue 100% of their log events.zerolog.TimestampFieldName
: Can be set to customizeTimestamp
field name.zerolog.LevelFieldName
: Can be set to customize level field name.zerolog.MessageFieldName
: Can be set to customize message field name.zerolog.ErrorFieldName
: Can be set to customizeErr
field name.zerolog.TimeFieldFormat
: Can be set to customizeTime
field value formatting. If set with an empty string, times are formated as UNIX timestamp. // DurationFieldUnit defines the unit for time.Duration type fields added // using the Dur method.DurationFieldUnit
: Sets the unit of the fields added byDur
(default:time.Millisecond
).DurationFieldInteger
: If set to true,Dur
fields are formatted as integers instead of floats.
Field Types
Standard Types
Str
Bool
Int
,Int8
,Int16
,Int32
,Int64
Uint
,Uint8
,Uint16
,Uint32
,Uint64
Float32
,Float64
Advanced Fields
Err
: Takes anerror
and render it as a string using thezerolog.ErrorFieldName
field name.Timestamp
: Insert a timestamp field withzerolog.TimestampFieldName
field name and formatted usingzerolog.TimeFieldFormat
.Time
: Adds a field with the time formated with thezerolog.TimeFieldFormat
.Dur
: Adds a field with atime.Duration
.Dict
: Adds a sub-key/value as a field of the event.Interface
: Uses reflection to marshal the type.
Benchmarks
All operations are allocation free (those numbers include JSON encoding):
BenchmarkLogEmpty-8 100000000 19.1 ns/op 0 B/op 0 allocs/op
BenchmarkDisabled-8 500000000 4.07 ns/op 0 B/op 0 allocs/op
BenchmarkInfo-8 30000000 42.5 ns/op 0 B/op 0 allocs/op
BenchmarkContextFields-8 30000000 44.9 ns/op 0 B/op 0 allocs/op
BenchmarkLogFields-8 10000000 184 ns/op 0 B/op 0 allocs/op
There are a few Go logging benchmarks and comparisons that include zerolog.
Using Uber's zap comparison benchmark:
Log a message and 10 fields:
Library | Time | Bytes Allocated | Objects Allocated |
---|---|---|---|
zerolog | 767 ns/op | 552 B/op | 6 allocs/op |
⚡ zap | 848 ns/op | 704 B/op | 2 allocs/op |
⚡ zap (sugared) | 1363 ns/op | 1610 B/op | 20 allocs/op |
go-kit | 3614 ns/op | 2895 B/op | 66 allocs/op |
lion | 5392 ns/op | 5807 B/op | 63 allocs/op |
logrus | 5661 ns/op | 6092 B/op | 78 allocs/op |
apex/log | 15332 ns/op | 3832 B/op | 65 allocs/op |
log15 | 20657 ns/op | 5632 B/op | 93 allocs/op |
Log a message with a logger that already has 10 fields of context:
Library | Time | Bytes Allocated | Objects Allocated |
---|---|---|---|
zerolog | 52 ns/op | 0 B/op | 0 allocs/op |
⚡ zap | 283 ns/op | 0 B/op | 0 allocs/op |
⚡ zap (sugared) | 337 ns/op | 80 B/op | 2 allocs/op |
lion | 2702 ns/op | 4074 B/op | 38 allocs/op |
go-kit | 3378 ns/op | 3046 B/op | 52 allocs/op |
logrus | 4309 ns/op | 4564 B/op | 63 allocs/op |
apex/log | 13456 ns/op | 2898 B/op | 51 allocs/op |
log15 | 14179 ns/op | 2642 B/op | 44 allocs/op |
Log a static string, without any context or printf
-style templating:
Library | Time | Bytes Allocated | Objects Allocated |
---|---|---|---|
zerolog | 50 ns/op | 0 B/op | 0 allocs/op |
⚡ zap | 236 ns/op | 0 B/op | 0 allocs/op |
standard library | 453 ns/op | 80 B/op | 2 allocs/op |
⚡ zap (sugared) | 337 ns/op | 80 B/op | 2 allocs/op |
go-kit | 508 ns/op | 656 B/op | 13 allocs/op |
lion | 771 ns/op | 1224 B/op | 10 allocs/op |
logrus | 1244 ns/op | 1505 B/op | 27 allocs/op |
apex/log | 2751 ns/op | 584 B/op | 11 allocs/op |
log15 | 5181 ns/op | 1592 B/op | 26 allocs/op |