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.

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
 		}