slog: Fiber middleware

Fiber middleware to log http requests using slog.

---

^{Sponsored by:}

Cut Kubernetes & AI costs, boost application stability

100% OpenTelemetry-native observability platform
Simple to use, built on open standards, and designed for full cost control

---

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

# Fiber v3 (current)
go get github.com/samber/slog-fiber

# Fiber v2 (beta)
go get github.com/samber/slog-fiber@fiber-v2

Compatibility: go >= 1.25

No breaking changes will be made to exported APIs before v2.0.0.

💡 Usage

Handler options

type Config struct {
	DefaultLevel     slog.Level
	ClientErrorLevel slog.Level
	ServerErrorLevel slog.Level

	WithUserAgent      bool
	WithRequestID      bool
	WithRequestBody    bool
	WithRequestHeader  bool
	WithResponseBody   bool
	WithResponseHeader bool
	WithSpanID         bool
	WithTraceID        bool
	WithClientIP       bool
	WithCustomMessage  func(c fiber.Ctx, err error) string

	Filters []Filter
}

Attributes will be injected in log payload.

Other global parameters:

slogfiber.TraceIDKey = "trace_id"
slogfiber.SpanIDKey = "span_id"
slogfiber.RequestBodyMaxSize  = 64 * 1024 // 64KB
slogfiber.ResponseBodyMaxSize = 64 * 1024 // 64KB
slogfiber.HiddenRequestHeaders = map[string]struct{}{ ... }
slogfiber.HiddenResponseHeaders = map[string]struct{}{ ... }
slogfiber.RequestIDContextKey = "request-id"
slogfiber.RequestIDHeaderKey = "X-Request-Id"

Minimal

import (
	"github.com/gofiber/fiber/v3"
	"github.com/gofiber/fiber/v3/middleware/recover"
	slogfiber "github.com/samber/slog-fiber"
	"log/slog"
)

// Create a slog logger, which:
//   - Logs to stdout.
logger := slog.New(slog.NewTextHandler(os.Stdout, nil))

app := fiber.New()

app.Use(slogfiber.New(logger))
app.Use(recover.New())

app.Get("/", func(c fiber.Ctx) error {
	return c.SendString("Hello, World 👋!")
})

app.Listen(":4242")

// output:
// time=2023-10-15T20:32:58.926+02:00 level=INFO msg="Incoming request" env=production request.time=2023-10-15T20:32:58.626+02:00 request.method=GET request.path=/ request.route="" request.ip=127.0.0.1:63932 request.length=0 response.time=2023-10-15T20:32:58.926+02:00 response.latency=100ms response.status=200 response.length=7 id=229c7fc8-64f5-4467-bc4a-940700503b0d

OTEL

logger := slog.New(slog.NewTextHandler(os.Stdout, nil))

config := slogfiber.Config{
	WithSpanID:  true,
	WithTraceID: true,
}

app := fiber.New()
app.Use(slogfiber.NewWithConfig(logger, config))

Custom log levels

logger := slog.New(slog.NewTextHandler(os.Stdout, nil))

config := slogfiber.Config{
	DefaultLevel:     slog.LevelInfo,
	ClientErrorLevel: slog.LevelWarn,
	ServerErrorLevel: slog.LevelError,
}

app := fiber.New()
app.Use(slogfiber.NewWithConfig(logger, config))

Verbose

logger := slog.New(slog.NewTextHandler(os.Stdout, nil))

config := slogfiber.Config{
	WithRequestBody: true,
	WithResponseBody: true,
	WithRequestHeader: true,
	WithResponseHeader: true,
}

app := fiber.New()
app.Use(slogfiber.NewWithConfig(logger, config))

Filters

logger := slog.New(slog.NewTextHandler(os.Stdout, nil))

app := fiber.New()
app.Use(
	slogfiber.NewWithFilters(
		logger,
		slogfiber.Accept(func (c fiber.Ctx) bool {
			return xxx
		}),
		slogfiber.IgnoreStatus(401, 404),
	),
)
app.Use(recover.New())

Available filters:

• Accept / Ignore
• AcceptMethod / IgnoreMethod
• AcceptStatus / IgnoreStatus
• AcceptStatusGreaterThan / IgnoreStatusGreaterThan
• AcceptStatusLessThan / IgnoreStatusLessThan
• AcceptStatusGreaterThanOrEqual / IgnoreStatusGreaterThanOrEqual
• AcceptStatusLessThanOrEqual / IgnoreStatusLessThanOrEqual
• AcceptPath / IgnorePath
• AcceptPathContains / IgnorePathContains
• AcceptPathPrefix / IgnorePathPrefix
• AcceptPathSuffix / IgnorePathSuffix
• AcceptPathMatch / IgnorePathMatch
• AcceptHost / IgnoreHost
• AcceptHostContains / IgnoreHostContains
• AcceptHostPrefix / IgnoreHostPrefix
• AcceptHostSuffix / IgnoreHostSuffix
• AcceptHostMatch / IgnoreHostMatch

Using custom time formatters

// Create a slog logger, which:
//   - Logs to stdout.
//   - RFC3339 with UTC time format.
logger := slog.New(
	slogformatter.NewFormatterHandler(
		slogformatter.TimezoneConverter(time.UTC),
		slogformatter.TimeFormatter(time.RFC3339, nil),
	)(
		slog.NewTextHandler(os.Stdout, nil),
	),
)

app := fiber.New()

app.Use(slogfiber.New(logger))
app.Use(recover.New())

app.Get("/", func(c fiber.Ctx) error {
	return c.SendString("Hello, World 👋!")
})

app.Listen(":4242")

// output:
// time=2023-10-15T20:32:58.926+02:00 level=INFO msg="Incoming request" env=production request.time=2023-10-15T20:32:58Z request.method=GET request.path=/ request.route="" request.ip=127.0.0.1:63932 request.length=0 response.time=2023-10-15T20:32:58Z response.latency=100ms response.status=200 response.length=7 id=229c7fc8-64f5-4467-bc4a-940700503b0d

Using custom logger sub-group

logger := slog.New(slog.NewTextHandler(os.Stdout, nil))

app := fiber.New()

app.Use(slogfiber.New(logger.WithGroup("http")))
app.Use(recover.New())

app.Get("/", func(c fiber.Ctx) error {
	return c.SendString("Hello, World 👋!")
})

app.Listen(":4242")

// output:
// time=2023-10-15T20:32:58.926+02:00 level=INFO msg="Incoming request" env=production http.request.time=2023-10-15T20:32:58.626+02:00 http.request.method=GET http.request.path=/ http.request.route="" http.request.ip=127.0.0.1:63932 http.request.length=0 http.response.time=2023-10-15T20:32:58.926+02:00 http.response.latency=100ms http.response.status=200 http.response.length=7 http.id=229c7fc8-64f5-4467-bc4a-940700503b0d

Add logger to a single route

logger := slog.New(slog.NewTextHandler(os.Stdout, nil))

app := fiber.New()

app.Use(recover.New())

app.Get("/", slogfiber.New(logger), func(c fiber.Ctx) error {
	return c.SendString("Hello, World 👋!")
})

app.Listen(":4242")

Adding custom attributes

logger := slog.New(slog.NewTextHandler(os.Stdout, nil))

// Add an attribute to all log entries made through this logger.
logger = logger.With("env", "production")

app := fiber.New()

app.Use(slogfiber.New(logger))
app.Use(recover.New())

app.Get("/", func(c fiber.Ctx) error {
	// Add an attribute to a single log entry.
	slogfiber.AddCustomAttributes(c, slog.String("foo", "bar"))
	return c.SendString("Hello, World 👋!")
})

app.Listen(":4242")

// output:
// time=2023-10-15T20:32:58.926+02:00 level=INFO msg="Incoming request" env=production request.time=2023-10-15T20:32:58.626+02:00 request.method=GET request.path=/ request.route="" request.ip=127.0.0.1:63932 request.length=0 response.time=2023-10-15T20:32:58.926+02:00 response.latency=100ms response.status=200 response.length=7 id=229c7fc8-64f5-4467-bc4a-940700503b0d foo=bar

JSON output

logger := slog.New(slog.NewJSONHandler(os.Stdout, nil)),

app := fiber.New()

app.Use(slogfiber.New(logger))
app.Use(recover.New())

app.Get("/", func(c fiber.Ctx) error {
	return c.SendString("Hello, World 👋!")
})

app.Listen(":4242")

// output:
// {"time":"2023-10-15T20:32:58.926+02:00","level":"INFO","msg":"Incoming request","env":"production","http":{"request":{"time":"2023-10-15T20:32:58.626+02:00","method":"GET","path":"/","route":"","ip":"127.0.0.1:55296","length":0},"response":{"time":"2023-10-15T20:32:58.926+02:00","latency":100000,"status":200,"length":7},"id":"04201917-d7ba-4b20-a3bb-2fffba5f2bd9"}}

🤝 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.