feat: replace log with rs/zerolog for structured logging

Switch from the standard library log package to rs/zerolog with
ConsoleWriter for colorful terminal output in dev mode and JSON
output in production. Users can now provide their own logger via
Options.Logger or set the level via Options.LogLevel.

configuration.go

@@ -1,15 +1,17 @@
 package via
 
-import "github.com/alexedwards/scs/v2"
+import (
+	"github.com/alexedwards/scs/v2"
+	"github.com/rs/zerolog"
+)
 
-type LogLevel int
+func ptr(l zerolog.Level) *zerolog.Level { return &l }
 
-const (
-	undefined LogLevel = iota
-	LogLevelError
-	LogLevelWarn
-	LogLevelInfo
-	LogLevelDebug
+var (
+	LogLevelDebug = ptr(zerolog.DebugLevel)
+	LogLevelInfo  = ptr(zerolog.InfoLevel)
+	LogLevelWarn  = ptr(zerolog.WarnLevel)
+	LogLevelError = ptr(zerolog.ErrorLevel)
 )
 
 // Plugin is a func that can mutate the given *via.V app runtime. It is useful to integrate popular JS/CSS UI libraries or tools.
@@ -23,9 +25,12 @@ type Options struct {
 	// The http server address. e.g. ':3000'
 	ServerAddress string
 
-	// Level of the logs to write to stdout.
-	// Options: Error, Warn, Info, Debug.
-	LogLvl LogLevel
+	// LogLevel sets the minimum log level. nil keeps the default (Info).
+	LogLevel *zerolog.Level
+
+	// Logger overrides the default logger entirely. When set, LogLevel and
+	// DevMode have no effect on logging.
+	Logger *zerolog.Logger
 
 	// The title of the HTML document.
 	DocumentTitle string

context.go

@@ -5,7 +5,6 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"log"
 	"maps"
 	"reflect"
 	"sync"
@@ -456,7 +455,7 @@ func (c *Context) unsubscribeAll() {
 
 func newContext(id string, route string, v *V) *Context {
 	if v == nil {
-		log.Fatal("create context failed: app pointer is nil")
+		panic("create context failed: app pointer is nil")
 	}
 
 	return &Context{

go.mod

@@ -11,6 +11,7 @@ require (
 	github.com/delaneyj/toolbelt v0.9.1
 	github.com/mattn/go-sqlite3 v1.14.32
 	github.com/nats-io/nats.go v1.48.0
+	github.com/rs/zerolog v1.34.0
 	github.com/starfederation/datastar-go v1.0.3
 	github.com/stretchr/testify v1.11.1
 )
@@ -24,6 +25,8 @@ require (
 	github.com/google/go-tpm v0.9.7 // indirect
 	github.com/klauspost/compress v1.18.2 // indirect
 	github.com/kr/text v0.2.0 // indirect
+	github.com/mattn/go-colorable v0.1.13 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/minio/highwayhash v1.0.4-0.20251030100505-070ab1a87a76 // indirect
 	github.com/nats-io/jwt/v2 v2.8.0 // indirect
 	github.com/nats-io/nats-server/v2 v2.12.2 // indirect

go.sum

@@ -13,6 +13,7 @@ github.com/antithesishq/antithesis-sdk-go v0.5.0 h1:cudCFF83pDDANcXFzkQPUHHedfnn
 github.com/antithesishq/antithesis-sdk-go v0.5.0/go.mod h1:IUpT2DPAKh6i/YhSbt6Gl3v2yvUZjmKncl7U91fup7E=
 github.com/cenkalti/backoff v2.2.1+incompatible h1:tNowT99t7UNflLxfYYSlKYsBpXdEet03Pg2g16Swow4=
 github.com/cenkalti/backoff v2.2.1+incompatible/go.mod h1:90ReRw6GdpyfrHakVjL/QHaoyV4aDUVVkXQJJJ3NXXM=
+github.com/coreos/go-systemd/v22 v22.5.0/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
 github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
@@ -20,6 +21,7 @@ github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc h1:U9qPSI2PIWSS1
 github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/delaneyj/toolbelt v0.9.1 h1:QJComn2qoaQ4azl5uRkGpdHSO9e+JtoxDTXCiQHvH8o=
 github.com/delaneyj/toolbelt v0.9.1/go.mod h1:eNXpPuThjTD4tpRNCBl4JEz9jdg9LpyzNuyG+stnIbs=
+github.com/godbus/dbus/v5 v5.0.4/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
 github.com/google/brotli/go/cbrotli v0.0.0-20230829110029-ed738e842d2f h1:jopqB+UTSdJGEJT8tEqYyE29zN91fi2827oLET8tl7k=
 github.com/google/brotli/go/cbrotli v0.0.0-20230829110029-ed738e842d2f/go.mod h1:nOPhAkwVliJdNTkj3gXpljmWhjc4wCaVqbMJcPKWP4s=
 github.com/google/go-tpm v0.9.7 h1:u89J4tUUeDTlH8xxC3CTW7OHZjbjKoHdQ9W7gCUhtxA=
@@ -33,6 +35,12 @@ github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
+github.com/mattn/go-colorable v0.1.13 h1:fFA4WZxdEF4tXPZVKMLwD8oUnCTTo08duU7wxecdEvA=
+github.com/mattn/go-colorable v0.1.13/go.mod h1:7S9/ev0klgBDR4GtXTXX8a3vIGJpMovkB8vQcUbaXHg=
+github.com/mattn/go-isatty v0.0.16/go.mod h1:kYGgaQfpe5nmfYZH+SKPsOc2e4SrIfOl2e/yFXSvRLM=
+github.com/mattn/go-isatty v0.0.19/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
+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/mattn/go-sqlite3 v1.14.6/go.mod h1:NyWgC/yNuGj7Q9rpYnZvas74GogHl5/Z4A/KQRfk6bU=
 github.com/mattn/go-sqlite3 v1.14.32 h1:JD12Ag3oLy1zQA+BNn74xRgaBbdhbNIDYvQUEuuErjs=
 github.com/mattn/go-sqlite3 v1.14.32/go.mod h1:Uh1q+B4BYcTPb+yiD3kU8Ct7aC0hY9fxUwlHK0RXw+Y=
@@ -50,11 +58,15 @@ github.com/nats-io/nuid v1.0.1 h1:5iA8DT8V7q8WK2EScv2padNa/rTESc1KdnPw4TC2paw=
 github.com/nats-io/nuid v1.0.1/go.mod h1:19wcPz3Ph3q0Jbyiqsd0kePYG7A95tJPxeL+1OSON2c=
 github.com/pierrec/lz4/v4 v4.1.18 h1:xaKrnTkyoqfh1YItXl56+6KJNVYWlEEPuAQW9xsplYQ=
 github.com/pierrec/lz4/v4 v4.1.18/go.mod h1:gZWDp/Ze/IJXGXf23ltt2EXimqmTUXEy0GFuRQyBid4=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 h1:Jamvg5psRIccs7FGNTlIRMkT8wgtp5eCXdBlqhYGL6U=
 github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/rogpeppe/go-internal v1.14.1 h1:UQB4HGPB6osV0SQTLymcB4TgvyWu6ZyliaW0tI/otEQ=
 github.com/rogpeppe/go-internal v1.14.1/go.mod h1:MaRKkUm5W0goXpeCfT7UZI6fk/L7L7so1lCWt35ZSgc=
+github.com/rs/xid v1.6.0/go.mod h1:7XoLgs4eV+QndskICGsho+ADou8ySMSjJKDIan90Nz0=
+github.com/rs/zerolog v1.34.0 h1:k43nTLIwcTVQAncfCw4KZ2VY6ukYoZaBPNOE8txlOeY=
+github.com/rs/zerolog v1.34.0/go.mod h1:bJsvje4Z08ROH4Nhs5iH600c3IkWhwp44iRc54W6wYQ=
 github.com/starfederation/datastar-go v1.0.3 h1:DnzgsJ6tDHDM6y5Nxsk0AGW/m8SyKch2vQg3P1xGTcU=
 github.com/starfederation/datastar-go v1.0.3/go.mod h1:stm83LQkhZkwa5GzzdPEN6dLuu8FVwxIv0w1DYkbD3w=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
@@ -74,6 +86,9 @@ github.com/xyproto/randomstring v1.0.5 h1:YtlWPoRdgMu3NZtP45drfy1GKoojuR7hmRcnhZ
 github.com/xyproto/randomstring v1.0.5/go.mod h1:rgmS5DeNXLivK7YprL0pY+lTuhNQW3iGxZ18UQApw/E=
 golang.org/x/crypto v0.45.0 h1:jMBrvKuj23MTlT0bQEOBcAE0mjg8mK9RXFhRH6nyF3Q=
 golang.org/x/crypto v0.45.0/go.mod h1:XTGrrkGJve7CYK7J8PEww4aY7gM3qMCElcJQ8n8JdX4=
+golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.21.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/sys v0.38.0 h1:3yZWxaJjBmCWXqhN1qh02AkOnCQ1poK6oF+a7xWL6Gc=
 golang.org/x/sys v0.38.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=

internal/examples/chatroom/main.go

@@ -22,7 +22,7 @@ func main() {
 	v.Config(via.Options{
 		DevMode:       true,
 		DocumentTitle: "ViaChat",
-		LogLvl:        via.LogLevelInfo,
+		LogLevel:      via.LogLevelInfo,
 	})
 
 	v.AppendToHead(

internal/examples/livereload/main.go

@@ -14,7 +14,7 @@ func main() {
 	v.Config(via.Options{
 		DocumentTitle: "Live Reload Demo",
 		DevMode:       true,
-		LogLvl:        via.LogLevelDebug,
+		LogLevel:      via.LogLevelDebug,
 		Plugins:       []via.Plugin{
 			// picocss.Default
 		},

internal/examples/nats-chatroom/main.go

@@ -60,7 +60,7 @@ func main() {
 	v.Config(via.Options{
 		DevMode:       true,
 		DocumentTitle: "NATS Chat",
-		LogLvl:        via.LogLevelInfo,
+		LogLevel:      via.LogLevelInfo,
 		ServerAddress: ":7331",
 		PubSub:        ps,
 	})

internal/examples/realtimechart/main.go

@@ -14,7 +14,7 @@ func main() {
 	v := via.New()
 
 	v.Config(via.Options{
-		LogLvl:  via.LogLevelDebug,
+		LogLevel: via.LogLevelDebug,
 		DevMode: true,
 		Plugins: []via.Plugin{
 			// picocss.Default,

internal/examples/shakespeare/main.go

@@ -54,7 +54,7 @@ func main() {
 	v.Config(via.Options{
 		DevMode:       true,
 		DocumentTitle: "Search",
-		LogLvl:        via.LogLevelWarn,
+		LogLevel:      via.LogLevelWarn,
 	})
 
 	v.AppendToHead(

via.go

@@ -13,7 +13,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"log"
 	"net/http"
 	"net/url"
 	"os"
@@ -22,6 +21,7 @@ import (
 	"sync"
 
 	"github.com/alexedwards/scs/v2"
+	"github.com/rs/zerolog"
 	"github.com/ryanhamamura/via/h"
 	"github.com/starfederation/datastar-go/datastar"
 )
@@ -34,6 +34,7 @@ var datastarJS []byte
 type V struct {
 	cfg                       Options
 	mux                       *http.ServeMux
+	logger                    zerolog.Logger
 	contextRegistry           map[string]*Context
 	contextRegistryMutex      sync.RWMutex
 	documentHeadIncludes      []h.H
@@ -46,52 +47,52 @@ type V struct {
 	datastarOnce    sync.Once
 }
 
+func (v *V) logEvent(evt *zerolog.Event, c *Context) *zerolog.Event {
+	if c != nil && c.id != "" {
+		evt = evt.Str("via-ctx", c.id)
+	}
+	return evt
+}
+
 func (v *V) logFatal(format string, a ...any) {
-	log.Printf("[fatal] msg=%q", fmt.Sprintf(format, a...))
+	v.logEvent(v.logger.WithLevel(zerolog.FatalLevel), nil).Msgf(format, a...)
 }
 
 func (v *V) logErr(c *Context, format string, a ...any) {
-	cRef := ""
-	if c != nil && c.id != "" {
-		cRef = fmt.Sprintf("via-ctx=%q ", c.id)
-	}
-	log.Printf("[error] %smsg=%q", cRef, fmt.Sprintf(format, a...))
+	v.logEvent(v.logger.Error(), c).Msgf(format, a...)
 }
 
 func (v *V) logWarn(c *Context, format string, a ...any) {
-	cRef := ""
-	if c != nil && c.id != "" {
-		cRef = fmt.Sprintf("via-ctx=%q ", c.id)
-	}
-	if v.cfg.LogLvl >= LogLevelWarn {
-		log.Printf("[warn] %smsg=%q", cRef, fmt.Sprintf(format, a...))
-	}
+	v.logEvent(v.logger.Warn(), c).Msgf(format, a...)
 }
 
 func (v *V) logInfo(c *Context, format string, a ...any) {
-	cRef := ""
-	if c != nil && c.id != "" {
-		cRef = fmt.Sprintf("via-ctx=%q ", c.id)
-	}
-	if v.cfg.LogLvl >= LogLevelInfo {
-		log.Printf("[info] %smsg=%q", cRef, fmt.Sprintf(format, a...))
-	}
+	v.logEvent(v.logger.Info(), c).Msgf(format, a...)
 }
 
 func (v *V) logDebug(c *Context, format string, a ...any) {
-	cRef := ""
-	if c != nil && c.id != "" {
-		cRef = fmt.Sprintf("via-ctx=%q ", c.id)
-	}
-	if v.cfg.LogLvl == LogLevelDebug {
-		log.Printf("[debug] %smsg=%q", cRef, fmt.Sprintf(format, a...))
-	}
+	v.logEvent(v.logger.Debug(), c).Msgf(format, a...)
+}
+
+func newConsoleLogger(level zerolog.Level) zerolog.Logger {
+	return zerolog.New(zerolog.ConsoleWriter{Out: os.Stderr, TimeFormat: "15:04:05"}).
+		With().Timestamp().Logger().Level(level)
 }
 
 // Config overrides the default configuration with the given options.
 func (v *V) Config(cfg Options) {
-	if cfg.LogLvl != undefined {
-		v.cfg.LogLvl = cfg.LogLvl
+	if cfg.Logger != nil {
+		v.logger = *cfg.Logger
+	} else if cfg.LogLevel != nil || cfg.DevMode != v.cfg.DevMode {
+		level := zerolog.InfoLevel
+		if cfg.LogLevel != nil {
+			level = *cfg.LogLevel
+		}
+		if cfg.DevMode {
+			v.logger = newConsoleLogger(level)
+		} else {
+			v.logger = zerolog.New(os.Stderr).With().Timestamp().Logger().Level(level)
+		}
 	}
 	if cfg.DocumentTitle != "" {
 		v.cfg.DocumentTitle = cfg.DocumentTitle
@@ -260,7 +261,7 @@ func (v *V) Start() {
 	if v.sessionManager != nil {
 		handler = v.sessionManager.LoadAndSave(v.mux)
 	}
-	log.Fatalf("[fatal] %v", http.ListenAndServe(v.cfg.ServerAddress, handler))
+	v.logger.Fatal().Err(http.ListenAndServe(v.cfg.ServerAddress, handler)).Msg("http server failed")
 }
 
 // HTTPServeMux returns the underlying HTTP request multiplexer to enable user extentions, middleware and
@@ -284,7 +285,7 @@ func (v *V) ensureDatastarHandler() {
 func (v *V) devModePersist(c *Context) {
 	p := filepath.Join(".via", "devmode", "ctx.json")
 	if err := os.MkdirAll(filepath.Dir(p), 0755); err != nil {
-		log.Fatalf("failed to create directory for devmode files: %v", err)
+		v.logFatal("failed to create directory for devmode files: %v", err)
 	}
 
 	// load persisted list from file, or empty list if file not found
@@ -398,6 +399,7 @@ func New() *V {
 
 	v := &V{
 		mux:                  mux,
+		logger:               newConsoleLogger(zerolog.InfoLevel),
 		contextRegistry:      make(map[string]*Context),
 		devModePageInitFnMap: make(map[string]func(*Context)),
 		sessionManager:       scs.New(),
@@ -406,7 +408,6 @@ func New() *V {
 		cfg: Options{
 			DevMode:       false,
 			ServerAddress: ":3000",
-			LogLvl:        LogLevelInfo,
 			DocumentTitle: "⚡ Via",
 		},
 	}
@@ -518,7 +519,7 @@ func New() *V {
 	v.mux.HandleFunc("POST /_session/close", func(w http.ResponseWriter, r *http.Request) {
 		body, err := io.ReadAll(r.Body)
 		if err != nil {
-			log.Printf("Error reading body: %v", err)
+			v.logErr(nil, "error reading body: %v", err)
 			w.WriteHeader(http.StatusBadRequest)
 			return
 		}