slog: net/http middleware

net/http handler 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

go get github.com/samber/slog-http

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:

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

Minimal

import (
	"net/http"
	"os"
	"time"

	sloghttp "github.com/samber/slog-http"
	"log/slog"
)

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

// mux router
mux := http.NewServeMux()

// Routes
mux.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("Hello, World!"))
}))
mux.Handle("/error", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
	http.Error(w,  "I'm angry" http.StatusInternalServerError)
}))

// Middleware
handler := sloghttp.Recovery(mux)
handler = sloghttp.New(logger)(handler)

// Start server
http.ListenAndServe(":4242", handler)

// output:
// time=2023-10-15T20:32:58.926+02:00 level=INFO msg="Success" 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 := sloghttp.Config{
	WithSpanID:  true,
	WithTraceID: true,
}

mux := http.NewServeMux()

// Middleware
handler := sloghttp.Recovery(mux)
handler = sloghttp.NewWithConfig(logger, config)(handler)

// Start server
http.ListenAndServe(":4242", handler)

Custom log levels

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

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

mux := http.NewServeMux()

// Middleware
handler := sloghttp.Recovery(mux)
handler = sloghttp.NewWithConfig(logger, config)(handler)

// Start server
http.ListenAndServe(":4242", handler)

Verbose

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

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

mux := http.NewServeMux()

// Middleware
handler := sloghttp.Recovery(mux)
handler = sloghttp.NewWithConfig(logger, config)(handler)

// Start server
http.ListenAndServe(":4242", handler)

Filters

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

mux := http.NewServeMux()

// Middleware
handler := sloghttp.Recovery(mux)
handler = sloghttp.NewWithFilters(
	logger,
	sloghttp.Accept(func (w sloghttp.WrapResponseWriter, r *http.Request) bool {
		return xxx
	}),
	sloghttp.IgnoreStatus(401, 404),
)(handler)

// Start server
http.ListenAndServe(":4242", handler)

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

import (
	"net/http"
	"log/slog"

	sloghttp "github.com/samber/slog-http"
	slogformatter "github.com/samber/slog-formatter"
)

// 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.DateTime, nil),
	)(
		slog.NewTextHandler(os.Stdout, nil),
	),
)

// mux router
mux := http.NewServeMux()

// Routes
mux.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("Hello, World!"))
}))
mux.Handle("/error", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
	http.Error(w, "I'm angry" http.StatusInternalServerError)
}))

// Middleware
handler := sloghttp.Recovery(mux)
handler = sloghttp.New(logger)(handler)

// Start server
http.ListenAndServe(":4242", handler)

// output:
// time=2023-10-15T20:32:58.926+02:00 level=INFO msg="Success" 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))

// mux router
mux := http.NewServeMux()

// Routes
mux.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("Hello, World!"))
}))
mux.Handle("/error", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
	http.Error(w,  "I'm angry" http.StatusInternalServerError)
}))

// Middleware
handler := sloghttp.Recovery(mux)
handler = sloghttp.New(logger.WithGroup("http"))(handler)

// Start server
http.ListenAndServe(":4242", handler)

// output:
// time=2023-10-15T20:32:58.926+02:00 level=INFO msg="Success" 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))

// mux router
mux := http.NewServeMux()

// Routes
mux.Handler("/", sloghttp.New(logger)(
	http.HandlerFunc(
		func(w http.ResponseWriter, r *http.Request) {
			return c.String(http.StatusOK, "Hello, World!")
		},
	),
	sloghttp.New(logger),
))

// Start server
http.ListenAndServe(":4242", handler)

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")

// mux router
mux := http.NewServeMux()

// Routes
mux.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
	sloghttp.AddCustomAttributes(r, slog.String("foo", "bar"))
	w.Write([]byte("Hello, World!"))
}))

// Middleware
handler := sloghttp.Recovery(mux)
handler = sloghttp.New(logger)(handler)

// Start server
http.ListenAndServe(":4242", handler)

// output:
// time=2023-10-15T20:32:58.926+02:00 level=INFO msg="Success" 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))

// mux router
mux := http.NewServeMux()

// Routes
mux.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("Hello, World!"))
}))

// Middleware
handler := sloghttp.Recovery(mux)
handler = sloghttp.New(logger)(handler)

// Start server
http.ListenAndServe(":4242", handler)

// output:
// {"time":"2023-10-15T20:32:58.926+02:00","level":"INFO","msg":"Success","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.