slog: NATS handler

A NATS Handler for slog Go library.

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^{Sponsored by:}

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

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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:

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.