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A Loki Handler for slog Go library.

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See also:

HTTP middlewares:

Loggers:

Log sinks:

🚀 Install

go get github.com/samber/slog-loki/v3

Compatibility: go >= 1.21

No breaking changes will be made to exported APIs before v4.0.0.

💡 Usage

GoDoc: https://pkg.go.dev/github.com/samber/slog-loki/v3

Handler options

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

	// loki
	Client *loki.Client

	// optional: customize webhook event builder
	Converter Converter
	// 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:

slogloki.SourceKey = "source"
slogloki.ErrorKeys = []string{"error", "err"}
slogloki.SubAttributeSeparator = "__"
slogloki.AttributeKeyInvalidCharReplacement = "_"

Example

import (
	"github.com/grafana/loki-client-go/loki"
	slogloki "github.com/samber/slog-loki/v3"
	"log/slog"
)

func main() {
	// setup loki client
	config, _ := loki.NewDefaultConfig("http://localhost:3100/loki/api/v1/push")
	config.TenantID = "xyz"
	client, _ := loki.New(config)

	logger := slog.New(slogloki.Option{Level: slog.LevelDebug, Client: client}.NewLokiHandler())
	logger = logger.
		With("environment", "dev").
		With("release", "v1.0.0")

	// log error
	logger.Error("caramba!")

	// log user signup
	logger.Info("user registration")

	// stop loki client and purge buffers
	client.Stop()
}

Tracing

Import the samber/slog-otel library.

import (
	slogloki "github.com/samber/slog-loki"
	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(
		slogloki.Option{
			// ...
			AttrFromContext: []func(ctx context.Context) []slog.Attr{
				slogotel.ExtractOtelAttrFromContext([]string{"tracing"}, "trace_id", "span_id"),
			},
		}.NewLokiHandler(),
	)

	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.