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slog: Syslog handler

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A Syslog Handler for slog Go library.

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See also:

HTTP middlewares:

Loggers:

Log sinks:

🚀 Install

go get github.com/samber/slog-syslog/v2

Compatibility: go >= 1.21

No breaking changes will be made to exported APIs before v3.0.0.

💡 Usage

GoDoc: https://pkg.go.dev/github.com/samber/slog-syslog/v2

Handler options

type Option struct {
	// log level (default: debug)
	Level slog.Leveler

	// connection to syslog server
	Writer *syslog.Writer

	// optional: customize json payload builder
	Converter Converter
	// optional: custom marshaler
	Marshaler func(v any) ([]byte, error)
	// optional: fetch attributes from context
	AttrFromContext []func(ctx context.Context) []slog.Attr

	// optional: see slog.HandlerOptions
	AddSource   bool
	ReplaceAttr func(groups []string, a slog.Attr) slog.Attr
}

Attributes will be injected in log payload.

Other global parameters:

slogsyslog.SourceKey = "source"
slogsyslog.ContextKey = "extra"
slogsyslog.ErrorKeys = []string{"error", "err"}

Example

import (
	"fmt"
	"log"
	"log/slog"
	"net"
	"time"

	slogsyslog "github.com/samber/slog-syslog/v2"
)

func main() {
	// ncat -u -l 9999 -k
	writer, err := net.Dial("udp", "localhost:9999")
	if err != nil {
		log.Fatal(err)
	}

	logger := slog.New(slogsyslog.Option{Level: slog.LevelDebug, Writer: writer}.NewSyslogHandler())
	logger = logger.
		With("environment", "dev").
		With("release", "v1.0.0")

	// log error
	logger.
		With("category", "sql").
		With("query.statement", "SELECT COUNT(*) FROM users;").
		With("query.duration", 1*time.Second).
		With("error", fmt.Errorf("could not count users")).
		Error("caramba!")

	// log user signup
	logger.
		With(
			slog.Group("user",
				slog.String("id", "user-123"),
				slog.Time("created_at", time.Now()),
			),
		).
		Info("user registration")
}

Output:

@cee: {"timestamp":"2023-04-10T14:00:0.000000", "level":"ERROR", "message":"caramba!", "error":{ "error":"could not count users", "kind":"*errors.errorString", "stack":null }, "extra":{ "environment":"dev", "release":"v1.0.0", "category":"sql", "query.statement":"SELECT COUNT(*) FROM users;", "query.duration": "1s" }}

@cee: {"timestamp":"2023-04-10T14:00:0.000000", "level":"INFO", "message":"user registration", "error":null, "extra":{ "environment":"dev", "release":"v1.0.0", "user":{ "id":"user-123", "created_at":"2023-04-10T14:00:0.000000+00:00"}}}

Tracing

Import the samber/slog-otel library.

import (
	slogsyslog "github.com/samber/slog-syslog"
	slogotel "github.com/samber/slog-otel"
	"go.opentelemetry.io/otel/sdk/trace"
)

func main() {
	tp := trace.NewTracerProvider(
		trace.WithSampler(trace.AlwaysSample()),
	)
	tracer := tp.Tracer("hello/world")

	ctx, span := tracer.Start(context.Background(), "foo")
	defer span.End()

	span.AddEvent("bar")

	logger := slog.New(
		slogsyslog.Option{
			// ...
			AttrFromContext: []func(ctx context.Context) []slog.Attr{
				slogotel.ExtractOtelAttrFromContext([]string{"tracing"}, "trace_id", "span_id"),
			},
		}.NewSyslogHandler(),
	)

	logger.ErrorContext(ctx, "a message")
}

🤝 Contributing

Don't hesitate ;)

# Install some dev dependencies
make tools

# Run tests
make test
# or
make watch-test

👤 Contributors

Contributors

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📝 License

Copyright © 2023 Samuel Berthe.

This project is MIT licensed.