slog: Fiber middleware

Fiber middleware to log http requests using slog.

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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

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

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

Compatibility: go >= 1.21

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

	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.RequestIDHeaderKey = "X-Request-Id"

Minimal

import (
	"github.com/gofiber/fiber/v2"
	"github.com/gofiber/fiber/v2/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 / IgnoreStatusLessThan
• AcceptStatusGreaterThanOrEqual / 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.