go get github.com/samber/slog-nats

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

	// NATS client
	EncodedConnection *nats.EncodedConn
	Subject           string

	// optional: customize NATS 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
}

slognats.SourceKey = "source"
slognats.ContextKey = "extra"
slognats.RequestKey = "request"
slognats.ErrorKeys = []string{"error", "err"}
slognats.RequestIgnoreHeaders = false

slog.Group("user",
    slog.String("id", "user-123"),
    slog.String("username", "samber"),
    slog.Time("created_at", time.Now()),
)

import (
	"context"
	"fmt"
	"time"

	slognats "github.com/samber/slog-nats"
	"github.com/nats-io/nats.go"

	"log/slog"
)

func main() {
	// docker-compose up -d
	// brew tap nats-io/nats-tools
	// brew install nats-io/nats-tools/nats
	// nats subscribe test

	uri := "nats://127.0.0.1:4222"

	nc, err := nats.Connect(uri)
	if err != nil {
		panic(err)
	}

	ec, err := nats.NewEncodedConn(nc, nats.JSON_ENCODER)
	if err != nil {
		panic(err)
	}

	defer nc.Flush()
	defer nc.Close()

	logger := slog.New(slognats.Option{Level: slog.LevelDebug, EncodedConnection: ec, Subject: "test"}.NewNATSHandler())
	logger = logger.With("release", "v1.0.0")

	logger.
		With(
			slog.Group("user",
				slog.String("id", "user-123"),
				slog.Time("created_at", time.Now()),
			),
		).
		With("error", fmt.Errorf("an error")).
		Error("a message")
}

{
  	"level": "ERROR",
	"logger.name": "samber/slog-nats",
	"logger.version": "1.0.0",
	"message": "a message",
	"timestamp": "2023-04-30T01:33:21.676768Z",
	"error": {
		"error": "an error",
		"kind": "*errors.errorString",
		"stack": null
	},
	"extra": {
		"release": "v1.0.0"
	},
	"user": {
		"created_at": "2023-04-30T01:33:21.676704Z",
		"id": "user-123"
	}
}

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

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

# Install some dev dependencies
make tools

# Run tests
make test
# or
make watch-test