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🚨 slog: Attribute formatting
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samber/slog-formatter
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Common formatters forslog library + helpers for building your own.
Sponsored by:
Cloud-native search engine for observability - An OSS alternative to Splunk, Elasticsearch, Loki, and Tempo.
Handlers:
- NewFormatterHandler: main handler
- NewFormatterMiddleware: compatible with
slog-multimiddlewares - RecoverHandlerError: catch panics and error from handlers
Common formatters:
- TimeFormatter: transforms a
time.Timeinto a readable string - UnixTimestampFormatter: transforms a
time.Timeinto a unix timestamp. - TimezoneConverter: set a
time.Timeto a different timezone - ErrorFormatter: transforms a go error into a readable error
- HTTPRequestFormatter: transforms a *http.Request into a readable object
- HTTPResponseFormatter: transforms a *http.Response into a readable object
- PIIFormatter: hide private Personal Identifiable Information (PII)
- IPAddressFormatter: hide ip address from logs
- FlattenFormatterMiddleware: returns a formatter middleware that flatten attributes recursively
Custom formatter:
- Format: pass any attribute into a formatter
- FormatByKind: pass attributes matching
slog.Kindinto a formatter - FormatByType: pass attributes matching generic type into a formatter
- FormatByKey: pass attributes matching key into a formatter
- FormatByFieldType: pass attributes matching both key and generic type into a formatter
- FormatByGroup: pass attributes under a group into a formatter
- FormatByGroupKey: pass attributes under a group and matching key, into a formatter
- FormatByGroupKeyType: pass attributes under a group, matching key and matching a generic type, into a formatter
See also:
- slog-multi:
slog.Handlerchaining, fanout, routing, failover, load balancing... - slog-formatter:
slogattribute formatting - slog-sampling:
slogsampling policy - slog-mock:
slog.Handlerfor test purposes
HTTP middlewares:
- slog-gin: Gin middleware for
sloglogger - slog-echo: Echo middleware for
sloglogger - slog-fiber: Fiber middleware for
sloglogger - slog-chi: Chi middleware for
sloglogger - slog-http:
net/httpmiddleware forsloglogger
Loggers:
- slog-zap: A
sloghandler forZap - slog-zerolog: A
sloghandler forZerolog - slog-logrus: A
sloghandler forLogrus
Log sinks:
- slog-datadog: A
sloghandler forDatadog - slog-betterstack: A
sloghandler forBetterstack - slog-rollbar: A
sloghandler forRollbar - slog-loki: A
sloghandler forLoki - slog-sentry: A
sloghandler forSentry - slog-syslog: A
sloghandler forSyslog - slog-logstash: A
sloghandler forLogstash - slog-fluentd: A
sloghandler forFluentd - slog-graylog: A
sloghandler forGraylog - slog-quickwit: A
sloghandler forQuickwit - slog-slack: A
sloghandler forSlack - slog-telegram: A
sloghandler forTelegram - slog-mattermost: A
sloghandler forMattermost - slog-microsoft-teams: A
sloghandler forMicrosoft Teams - slog-webhook: A
sloghandler forWebhook - slog-kafka: A
sloghandler forKafka - slog-nats: A
sloghandler forNATS - slog-parquet: A
sloghandler forParquet+Object Storage - slog-channel: A
sloghandler for Go channels
go get github.com/samber/slog-formatter
Compatibility: go >= 1.21
No breaking changes will be made to exported APIs before v2.0.0.
- in some case, you should consider implementing
slog.LogValuerinstead of using this library. - use this library carefully, log processing can be very costly (!)
The following example has 3 formatters that anonymize data, format errors and format user. 👇
import (slogformatter"github.com/samber/slog-formatter""log/slog")formatter1:=slogformatter.FormatByKey("very_private_data",func(v slog.Value) slog.Value {returnslog.StringValue("***********")})formatter2:=slogformatter.ErrorFormatter("error")formatter3:=slogformatter.FormatByType(func(uUser) slog.Value {returnslog.StringValue(fmt.Sprintf("%s %s",u.firstname,u.lastname))})logger:=slog.New(slogformatter.NewFormatterHandler(formatter1,formatter2,formatter3)(slog.NewTextHandler(os.Stdout,nil), ),)err:=fmt.Errorf("an error")logger.Error("a message",slog.Any("very_private_data","abcd"),slog.Any("user",user),slog.Any("err",err))// outputs:// time=2023-04-10T14:00:0.000000+00:00 level=ERROR msg="a message" error.message="an error" error.type="*errors.errorString" user="John doe" very_private_data="********"
GoDoc:https://pkg.go.dev/github.com/samber/slog-formatter
Returns a slog.Handler that applies formatters to.
import (slogformatter"github.com/samber/slog-formatter""log/slog")typeUserstruct {emailstringfirstnamestringlastnamestring}formatter1:=slogformatter.FormatByKey("very_private_data",func(v slog.Value) slog.Value {returnslog.StringValue("***********")})formatter2:=slogformatter.ErrorFormatter("error")formatter3:=slogformatter.FormatByType(func(uUser) slog.Value {returnslog.StringValue(fmt.Sprintf("%s %s",u.firstname,u.lastname))})logger:=slog.New(slogformatter.NewFormatterHandler(formatter1,formatter2,formatter3)(slog.NewTextHandler(os.StdErr,nil), ),)err:=fmt.Errorf("an error")logger.Error("a message",slog.Any("very_private_data","abcd"),slog.Any("user",user),slog.Any("err",err))// outputs:// time=2023-04-10T14:00:0.000000+00:00 level=ERROR msg="a message" error.message="an error" error.type="*errors.errorString" user="John doe" very_private_data="********"
Returns aslog-multi middleware that applies formatters to.
import (slogformatter"github.com/samber/slog-formatter"slogmulti"github.com/samber/slog-multi""log/slog")formatter1:=slogformatter.FormatByKey("very_private_data",func(v slog.Value) slog.Value {returnslog.StringValue("***********")})formatter2:=slogformatter.ErrorFormatter("error")formatter3:=slogformatter.FormatByType(func(uUser) slog.Value {returnslog.StringValue(fmt.Sprintf("%s %s",u.firstname,u.lastname))})formattingMiddleware:=slogformatter.NewFormatterHandler(formatter1,formatter2,formatter3)sink:=slog.NewJSONHandler(os.Stderr, slog.HandlerOptions{})logger:=slog.New(slogmulti.Pipe(formattingMiddleware).Handler(sink),)err:=fmt.Errorf("an error")logger.Error("a message",slog.Any("very_private_data","abcd"),slog.Any("user",user),slog.Any("err",err))// outputs:// time=2023-04-10T14:00:0.000000+00:00 level=ERROR msg="a message" error.message="an error" error.type="*errors.errorString" user="John doe" very_private_data="********"
Returns aslog.Handler that recovers from panics or error of the chain of handlers.
import (slogformatter"github.com/samber/slog-formatter"slogmulti"github.com/samber/slog-multi""log/slog")recovery:=slogformatter.RecoverHandlerError(func(ctx context.Context,record slog.Record,errerror) {// will be called only if subsequent handlers fail or return an errorlog.Println(err.Error()) },)sink:=NewSinkHandler(...)logger:=slog.New(slogmulti.Pipe(recovery).Handler(sink),)err:=fmt.Errorf("an error")logger.Error("a message",slog.Any("very_private_data","abcd"),slog.Any("user",user),slog.Any("err",err))// outputs:// time=2023-04-10T14:00:0.000000+00:00 level=ERROR msg="a message" error.message="an error" error.type="*errors.errorString" user="John doe" very_private_data="********"
Transforms atime.Time into a readable string.
slogformatter.NewFormatterHandler(slogformatter.TimeFormatter(time.DateTime,time.UTC),)
Transforms atime.Time into a unix timestamp.
slogformatter.NewFormatterHandler(slogformatter.UnixTimestampFormatter(time.Millisecond),)
Set atime.Time to a different timezone.
slogformatter.NewFormatterHandler(slogformatter.TimezoneConverter(time.UTC),)
Transforms a Go error into a readable error.
import (slogformatter"github.com/samber/slog-formatter""log/slog")logger:=slog.New(slogformatter.NewFormatterHandler(slogformatter.ErrorFormatter("error"), )(slog.NewTextHandler(os.Stdout,nil), ),)err:=fmt.Errorf("an error")logger.Error("a message",slog.Any("error",err))// outputs:// {// "time":"2023-04-10T14:00:0.000000+00:00",// "level": "ERROR",// "msg": "a message",// "error": {// "message": "an error",// "type": "*errors.errorString"// "stacktrace": "main.main()\n\t/Users/samber/src/github.com/samber/slog-formatter/example/example.go:108 +0x1c\n"// }// }
Transforms *http.Request and *http.Response into readable objects.
import (slogformatter"github.com/samber/slog-formatter""log/slog")logger:=slog.New(slogformatter.NewFormatterHandler(slogformatter.HTTPRequestFormatter(false),slogformatter.HTTPResponseFormatter(false), )(slog.NewJSONHandler(os.Stdout,nil), ),)req,_:=http.NewRequest(http.MethodGet,"https://api.screeb.app",nil)req.Header.Set("Content-Type","application/json")req.Header.Set("X-TOKEN","1234567890")res,_:=http.DefaultClient.Do(req)logger.Error("a message",slog.Any("request",req),slog.Any("response",res))
Hides private Personal Identifiable Information (PII).
IDs are kept as is. Values longer than 5 characters have a plain text prefix.
import (slogformatter"github.com/samber/slog-formatter""log/slog")logger:=slog.New(slogformatter.NewFormatterHandler(slogformatter.PIIFormatter("user"), )(slog.NewTextHandler(os.Stdout,nil), ),)logger.With(slog.Group("user",slog.String("id","bd57ffbd-8858-4cc4-a93b-426cef16de61"),slog.String("email","foobar@example.com"),slog.Group("address",slog.String("street","1st street"),slog.String("city","New York"),slog.String("country","USA"),slog.Int("zip",12345), ), ), ).Error("an error")// outputs:// {// "time":"2023-04-10T14:00:0.000000+00:00",// "level": "ERROR",// "msg": "an error",// "user": {// "id": "bd57ffbd-8858-4cc4-a93b-426cef16de61",// "email": "foob*******",// "address": {// "street": "1st *******",// "city": "New *******",// "country": "*******",// "zip": "*******"// }// }// }
Transforms an IP address into "********".
import (slogformatter"github.com/samber/slog-formatter""log/slog")logger:=slog.New(slogformatter.NewFormatterHandler(slogformatter.IPAddressFormatter("ip_address"), )(slog.NewTextHandler(os.Stdout,nil), ),)logger.With("ip_address","1.2.3.4").Error("an error")// outputs:// {// "time":"2023-04-10T14:00:0.000000+00:00",// "level": "ERROR",// "msg": "an error",// "ip_address": "*******",// }
A formatter middleware that flatten attributes recursively.
import (slogformatter"github.com/samber/slog-formatter"slogmulti"github.com/samber/slog-multi""log/slog")logger:=slog.New(slogmulti.Pipe(slogformatter.FlattenFormatterMiddlewareOptions{Separator:".",Prefix:"attrs",IgnorePath:false}.NewFlattenFormatterMiddlewareOptions()).Handler(slog.NewJSONHandler(os.Stdout,nil)),)logger.With("email","samuel@acme.org").With("environment","dev").WithGroup("group1").With("hello","world").WithGroup("group2").With("hello","world").Error("A message","foo","bar")// outputs:// {// "time": "2023-05-20T22:14:55.857065+02:00",// "level": "ERROR",// "msg": "A message",// "attrs.email": "samuel@acme.org",// "attrs.environment": "dev",// "attrs.group1.hello": "world",// "attrs.group1.group2.hello": "world",// "foo": "bar"// }
Pass every attributes into a formatter.
slogformatter.NewFormatterHandler(slogformatter.Format(func(groups []string,keystring,value slog.Value) slog.Value {// hide everything under "user" groupiflo.Contains(groups,"user") {returnslog.StringValue("****") }returnvalue }),)
Pass attributes matchingslog.Kind into a formatter.
slogformatter.NewFormatterHandler(slogformatter.FormatByKind(slog.KindDuration,func(value slog.Value) slog.Value {return... }),)
Pass attributes matching generic type into a formatter.
slogformatter.NewFormatterHandler(// format a custom error type slogformatter.FormatByType[*customError](func(err*customError) slog.Value {returnslog.GroupValue(slog.Int("code",err.code),slog.String("message",err.msg), ) }),// format other errors slogformatter.FormatByType[error](func(errerror) slog.Value {returnslog.GroupValue(slog.Int("code",err.Error()),slog.String("type",reflect.TypeOf(err).String()), ) }),)
slog.LogValuer when possible:
typecustomErrorstruct {...}func (customError)Error()string {...}// implements slog.LogValuerfunc (customError)LogValue() slog.Value {return slog.StringValue(...)}
Pass attributes matching key into a formatter.
slogformatter.NewFormatterHandler(slogformatter.FormatByKey("abcd",func(value slog.Value) slog.Value {return... }),)
Pass attributes matching both key and generic type into a formatter.
slogformatter.NewFormatterHandler(slogformatter.FormatByFieldType[User]("user",func(uUser) slog.Value {return... }),)
Pass attributes under a group into a formatter.
slogformatter.NewFormatterHandler(slogformatter.FormatByGroup([]{"user","address"},func(attr []slog.Attr) slog.Value {return... }),)
Pass attributes under a group and matching key, into a formatter.
slogformatter.NewFormatterHandler(slogformatter.FormatByGroupKey([]{"user","address"},"country",func(value slog.Value) slog.Value {return... }),)
Pass attributes under a group, matching key and matching a generic type, into a formatter.
slogformatter.NewFormatterHandler(slogformatter.FormatByGroupKeyType[string]([]{"user","address"},"country",func(valuestring) slog.Value {return... }),)
- Ping me on twitter@samuelberthe (DMs, mentions, whatever :))
- Fork theproject
- Fixopen issues or request new features
Don't hesitate ;)
# Install some dev dependenciesmake tools# Run testsmaketest# ormake watch-test
Give a ⭐️ if this project helped you!
Copyright © 2023Samuel Berthe.
This project isMIT licensed.
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