slog: NATS handler

A NATS Handler for slog Go library.

---

^{Sponsored by:}

Cloud-native search engine for observability - An OSS alternative to Splunk, Elasticsearch, Loki, and Tempo.

---

See also:

• slog-multi: slog.Handler chaining, fanout, routing, failover, load balancing...
• slog-formatter: slog attribute formatting
• slog-sampling: slog sampling policy
• slog-mock: slog.Handler for test purposes

HTTP middlewares:

• slog-gin: Gin middleware for slog logger
• slog-echo: Echo middleware for slog logger
• slog-fiber: Fiber middleware for slog logger
• slog-chi: Chi middleware for slog logger
• slog-http: net/http middleware for slog logger

Loggers:

• slog-zap: A slog handler for Zap
• slog-zerolog: A slog handler for Zerolog
• slog-logrus: A slog handler for Logrus

Log sinks:

• slog-datadog: A slog handler for Datadog
• slog-betterstack: A slog handler for Betterstack
• slog-rollbar: A slog handler for Rollbar
• slog-loki: A slog handler for Loki
• slog-sentry: A slog handler for Sentry
• slog-syslog: A slog handler for Syslog
• slog-logstash: A slog handler for Logstash
• slog-fluentd: A slog handler for Fluentd
• slog-graylog: A slog handler for Graylog
• slog-quickwit: A slog handler for Quickwit
• slog-slack: A slog handler for Slack
• slog-telegram: A slog handler for Telegram
• slog-mattermost: A slog handler for Mattermost
• slog-microsoft-teams: A slog handler for Microsoft Teams
• slog-webhook: A slog handler for Webhook
• slog-kafka: A slog handler for Kafka
• slog-nats: A slog handler for NATS
• slog-parquet: A slog handler for Parquet + Object Storage
• slog-channel: A slog handler for Go channels

🚀 Install

go get github.com/samber/slog-nats

Compatibility: go >= 1.21

No breaking changes will be made to exported APIs before v1.0.0.

💡 Usage

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

Handler options

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
}

Other global parameters:

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

Supported attributes

The following attributes are interpreted by slognats.DefaultConverter:

Atribute name	slog.Kind	Underlying type
"user"	group (see below)
"error"	any	error
"request"	any	*http.Request
other attributes	*

Other attributes will be injected in extra field.

Users must be of type slog.Group. Eg:

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

Example

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")
}

NATS 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"
	}
}

Tracing

Import the samber/slog-otel library.

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")
}

🤝 Contributing

• Ping me on twitter @samuelberthe (DMs, mentions, whatever :))
• Fork the project
• Fix open issues or request new features

Don't hesitate ;)

# Install some dev dependencies
make tools

# Run tests
make test
# or
make watch-test

👤 Contributors

💫 Show your support

Give a ⭐️ if this project helped you!

📝 License

Copyright © 2023 Samuel Berthe.

This project is MIT licensed.