feat: structured logging

cmd/dns.go

@@ -2,9 +2,12 @@ package cmd
 
 import (
 	"context"
+	"log/slog"
 	"time"
 
+	appconfig "github.com/lachlanharrisdev/gonetsim/internal/config"
 	"github.com/lachlanharrisdev/gonetsim/internal/dnsserver"
+	"github.com/lachlanharrisdev/gonetsim/internal/observability"
 	"github.com/lachlanharrisdev/gonetsim/internal/service"
 	"github.com/lachlanharrisdev/gonetsim/internal/utils"
 	"github.com/spf13/cobra"
@@ -48,7 +51,12 @@ var dnsCmd = &cobra.Command{
 		ctx, stop := utils.SignalContext(context.Background())
 		defer stop()
 
-		manager := service.NewManager(5 * time.Second)
+		logger, err := observability.NewLogger(appconfig.Default().Logging)
+		if err != nil {
+			return err
+		}
+		slog.SetDefault(logger)
+		manager := service.NewManager(5*time.Second, logger)
 		return manager.RunSingleService(ctx, dnsserver.NewService(conf))
 	},
 }

cmd/http.go

@@ -2,9 +2,12 @@ package cmd
 
 import (
 	"context"
+	"log/slog"
 	"time"
 
+	appconfig "github.com/lachlanharrisdev/gonetsim/internal/config"
 	"github.com/lachlanharrisdev/gonetsim/internal/httpserver"
+	"github.com/lachlanharrisdev/gonetsim/internal/observability"
 	"github.com/lachlanharrisdev/gonetsim/internal/service"
 	"github.com/lachlanharrisdev/gonetsim/internal/utils"
 	"github.com/spf13/cobra"
@@ -27,7 +30,12 @@ var httpCmd = &cobra.Command{
 		ctx, stop := utils.SignalContext(context.Background())
 		defer stop()
 
-		manager := service.NewManager(5 * time.Second)
+		logger, err := observability.NewLogger(appconfig.Default().Logging)
+		if err != nil {
+			return err
+		}
+		slog.SetDefault(logger)
+		manager := service.NewManager(5*time.Second, logger)
 
 		return manager.RunSingleService(ctx,
 			httpserver.NewHTTPService(

cmd/https.go

@@ -2,9 +2,12 @@ package cmd
 
 import (
 	"context"
+	"log/slog"
 	"time"
 
+	appconfig "github.com/lachlanharrisdev/gonetsim/internal/config"
 	"github.com/lachlanharrisdev/gonetsim/internal/httpserver"
+	"github.com/lachlanharrisdev/gonetsim/internal/observability"
 	"github.com/lachlanharrisdev/gonetsim/internal/service"
 	"github.com/lachlanharrisdev/gonetsim/internal/utils"
 	"github.com/spf13/cobra"
@@ -29,7 +32,12 @@ var httpsCmd = &cobra.Command{
 		ctx, stop := utils.SignalContext(context.Background())
 		defer stop()
 
-		manager := service.NewManager(5 * time.Second)
+		logger, err := observability.NewLogger(appconfig.Default().Logging)
+		if err != nil {
+			return err
+		}
+		slog.SetDefault(logger)
+		manager := service.NewManager(5*time.Second, logger)
 		return manager.RunSingleService(ctx,
 			httpserver.NewHTTPSService(
 				httpserver.Config{Addr: listen, StatusCode: httpsStatus},

cmd/root.go

@@ -3,12 +3,13 @@ package cmd
 import (
 	"context"
 	"fmt"
-	"log"
+	"log/slog"
 	"os"
 
 	appconfig "github.com/lachlanharrisdev/gonetsim/internal/config"
 	"github.com/lachlanharrisdev/gonetsim/internal/dnsserver"
 	"github.com/lachlanharrisdev/gonetsim/internal/httpserver"
+	"github.com/lachlanharrisdev/gonetsim/internal/observability"
 	"github.com/lachlanharrisdev/gonetsim/internal/service"
 	"github.com/lachlanharrisdev/gonetsim/internal/utils"
 	"github.com/spf13/cobra"
@@ -17,28 +18,35 @@ import (
 var rootConfigPath string
 
 var rootCmd = &cobra.Command{
-	Use:          "gonetsim",
-	Short:        "Network service simulator (dns + http + https)",
-	Args:         cobra.NoArgs,
-	SilenceUsage: true,
+	Use:           "gonetsim",
+	Short:         "Network service simulator (dns + http + https)",
+	Args:          cobra.NoArgs,
+	SilenceUsage:  true,
+	SilenceErrors: true,
 	RunE: func(cmd *cobra.Command, args []string) error {
 		cfgRes, err := appconfig.LoadOrCreate(rootConfigPath)
 		if err != nil {
 			return err
 		}
+		cfg := cfgRes.Config
+
+		logger, err := observability.NewLogger(cfg.Logging)
+		if err != nil {
+			return err
+		}
+		slog.SetDefault(logger)
 		if cfgRes.Created {
-			log.Printf("config: created default config at %s", cfgRes.Path)
+			logger.Info("config created", "path", cfgRes.Path)
 		}
-		log.Printf("config: using %s", cfgRes.Path)
-		cfg := cfgRes.Config
+		logger.Info("config loaded", "path", cfgRes.Path)
 
 		ctx, stop := utils.SignalContext(context.Background())
 		defer stop()
 
 		runCtx, cancel := context.WithCancel(ctx)
 		defer cancel()
 
-		manager := service.NewManager(cfg.General.ShutdownTimeout)
+		manager := service.NewManager(cfg.General.ShutdownTimeout, logger)
 
 		if cfg.DNS.Enabled {
 			listen, err := parseAddrPort(cfg.DNS.Listen)
@@ -85,20 +93,16 @@ var rootCmd = &cobra.Command{
 			manager.Add(httpserver.NewHTTPSService(conf, tlsOpts))
 		}
 
-		log.Printf("root: running (dns=%t http=%t https=%t)", cfg.DNS.Enabled, cfg.HTTP.Enabled, cfg.HTTPS.Enabled)
+		logger.Info("running", "dns", cfg.DNS.Enabled, "http", cfg.HTTP.Enabled, "https", cfg.HTTPS.Enabled)
 
 		return manager.RunAll(runCtx)
 	},
 }
 
-func exitError(msg interface{}) {
-	fmt.Fprintln(os.Stderr, msg)
-	os.Exit(1)
-}
-
 func Execute() {
 	if err := rootCmd.Execute(); err != nil {
-		exitError(err)
+		slog.Error("fatal error", "err", err)
+		os.Exit(1)
 	}
 }
 

go.mod

@@ -7,11 +7,15 @@ require (
 	github.com/knadh/koanf/providers/file v1.2.1
 	github.com/knadh/koanf/providers/structs v1.0.0
 	github.com/knadh/koanf/v2 v2.3.4
+	github.com/lmittmann/tint v1.1.3
+	github.com/mattn/go-colorable v0.1.14
+	github.com/mattn/go-isatty v0.0.20
 	github.com/miekg/dns v1.1.72
 	github.com/spf13/cobra v1.10.2
 )
 
 require (
+	github.com/fatih/color v1.19.0 // indirect
 	github.com/fatih/structs v1.1.0 // indirect
 	github.com/fsnotify/fsnotify v1.9.0 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // indirect
@@ -24,6 +28,6 @@ require (
 	golang.org/x/mod v0.31.0 // indirect
 	golang.org/x/net v0.48.0 // indirect
 	golang.org/x/sync v0.19.0 // indirect
-	golang.org/x/sys v0.39.0 // indirect
+	golang.org/x/sys v0.42.0 // indirect
 	golang.org/x/tools v0.40.0 // indirect
 )

go.sum

@@ -1,6 +1,8 @@
 github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/fatih/color v1.19.0 h1:Zp3PiM21/9Ld6FzSKyL5c/BULoe/ONr9KlbYVOfG8+w=
+github.com/fatih/color v1.19.0/go.mod h1:zNk67I0ZUT1bEGsSGyCZYZNrHuTkJJB+r6Q9VuMi0LE=
 github.com/fatih/structs v1.1.0 h1:Q7juDM0QtcnhCpeyLGQKyg4TOIghuNXrkL32pHAUMxo=
 github.com/fatih/structs v1.1.0/go.mod h1:9NiDSp5zOcgEDl+j00MP/WkGVPOlPRLejGD8Ga6PJ7M=
 github.com/fsnotify/fsnotify v1.9.0 h1:2Ml+OJNzbYCTzsxtv8vKSFD9PbJjmhYF14k/jKC7S9k=
@@ -21,6 +23,12 @@ github.com/knadh/koanf/providers/structs v1.0.0 h1:DznjB7NQykhqCar2LvNug3MuxEQsZ
 github.com/knadh/koanf/providers/structs v1.0.0/go.mod h1:kjo5TFtgpaZORlpoJqcbeLowM2cINodv8kX+oFAeQ1w=
 github.com/knadh/koanf/v2 v2.3.4 h1:fnynNSDlujWE+v83hAp8wKr/cdoxHLO0629SN+U8Urc=
 github.com/knadh/koanf/v2 v2.3.4/go.mod h1:gRb40VRAbd4iJMYYD5IxZ6hfuopFcXBpc9bbQpZwo28=
+github.com/lmittmann/tint v1.1.3 h1:Hv4EaHWXQr+GTFnOU4VKf8UvAtZgn0VuKT+G0wFlO3I=
+github.com/lmittmann/tint v1.1.3/go.mod h1:HIS3gSy7qNwGCj+5oRjAutErFBl4BzdQP6cJZ0NfMwE=
+github.com/mattn/go-colorable v0.1.14 h1:9A9LHSqF/7dyVVX6g0U9cwm9pG3kP9gSzcuIPHPsaIE=
+github.com/mattn/go-colorable v0.1.14/go.mod h1:6LmQG8QLFO4G5z1gPvYEzlUgJ2wF+stgPZH1UqBm1s8=
+github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWEY=
+github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
 github.com/miekg/dns v1.1.72 h1:vhmr+TF2A3tuoGNkLDFK9zi36F2LS+hKTRW0Uf8kbzI=
 github.com/miekg/dns v1.1.72/go.mod h1:+EuEPhdHOsfk6Wk5TT2CzssZdqkmFhf8r+aVyDEToIs=
 github.com/mitchellh/copystructure v1.2.0 h1:vpKXTN4ewci03Vljg/q9QvCGUDttBOGBIa15WveJJGw=
@@ -45,8 +53,11 @@ golang.org/x/net v0.48.0 h1:zyQRTTrjc33Lhh0fBgT/H3oZq9WuvRR5gPC70xpDiQU=
 golang.org/x/net v0.48.0/go.mod h1:+ndRgGjkh8FGtu1w1FGbEC31if4VrNVMuKTgcAAnQRY=
 golang.org/x/sync v0.19.0 h1:vV+1eWNmZ5geRlYjzm2adRgW2/mcpevXNg50YZtPCE4=
 golang.org/x/sync v0.19.0/go.mod h1:9KTHXmSnoGruLpwFjVSX0lNNA75CykiMECbovNTZqGI=
+golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.39.0 h1:CvCKL8MeisomCi6qNZ+wbb0DN9E5AATixKsvNtMoMFk=
 golang.org/x/sys v0.39.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
+golang.org/x/sys v0.42.0 h1:omrd2nAlyT5ESRdCLYdm3+fMfNFE/+Rf4bDIQImRJeo=
+golang.org/x/sys v0.42.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
 golang.org/x/tools v0.40.0 h1:yLkxfA+Qnul4cs9QA3KnlFu0lVmd8JJfoq+E41uSutA=
 golang.org/x/tools v0.40.0/go.mod h1:Ik/tzLRlbscWpqqMRjyWYDisX8bG13FrdXp3o4Sr9lc=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

internal/config/config.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"path/filepath"
 	"runtime"
+	"strings"
 	"time"
 
 	"github.com/knadh/koanf/parsers/toml/v2"
@@ -28,6 +29,7 @@ type Config struct {
 	DNS     DNSConfig     `koanf:"dns"`
 	HTTP    HTTPConfig    `koanf:"http"`
 	HTTPS   HTTPSConfig   `koanf:"https"`
+	Logging LoggingConfig `koanf:"logging"`
 }
 
 type GeneralConfig struct {
@@ -60,6 +62,11 @@ type HTTPSConfig struct {
 	Key     string `koanf:"key"`
 }
 
+type LoggingConfig struct {
+	LogFormat string `koanf:"format"`
+	Level     string `koanf:"level"`
+}
+
 func Default() Config {
 	return Config{
 		General: GeneralConfig{ShutdownTimeout: 2 * time.Second},
@@ -84,6 +91,10 @@ func Default() Config {
 			Listen:  ":8443",
 			Status:  200,
 		},
+		Logging: LoggingConfig{
+			LogFormat: "text",
+			Level:     "info",
+		},
 	}
 }
 
@@ -122,6 +133,24 @@ func (c Config) Validate() error {
 	if !c.DNS.Enabled && !c.HTTP.Enabled && !c.HTTPS.Enabled {
 		return errors.New("at least one service must be enabled")
 	}
+
+	// logging
+	logFormat := strings.ToLower(strings.TrimSpace(c.Logging.LogFormat))
+	switch logFormat {
+	case "", "text", "json":
+		// ok
+	default:
+		return fmt.Errorf("logging.format must be one of: text, json")
+	}
+	// default is "info" (see Default()); allow empty for backwards compat
+	logLevel := strings.ToLower(strings.TrimSpace(c.Logging.Level))
+	switch logLevel {
+	case "", "debug", "info", "warn", "warning", "error":
+		// ok
+	default:
+		return fmt.Errorf("logging.level must be one of: debug, info, warn, error")
+	}
+
 	return nil
 }
 

internal/config/default_config.toml

@@ -51,3 +51,9 @@ status = 200
 # ephemeral self-signed certificate at startup.
 cert = ""
 key = ""
+
+[logging]
+# Log output format: "text" (fixed-width columns) or "json".
+format = "text"
+# Minimum log level: "debug", "info", "warn", "error".
+level = "info"

internal/dnsserver/config.go

@@ -2,6 +2,7 @@ package dnsserver
 
 import (
 	"errors"
+	"log/slog"
 	"net/netip"
 
 	"github.com/miekg/dns"
@@ -16,12 +17,17 @@ func (s *Server) Name() string {
 type Server struct {
 	conf Config
 	srv  *dns.Server
+	log  *slog.Logger
 }
 
 func NewService(conf Config) service.Service {
 	return &Server{conf: conf}
 }
 
+func (s *Server) SetLogger(logger *slog.Logger) {
+	s.log = logger
+}
+
 type Config struct {
 	Addr string
 	Net  string