refactor: replace zap with slog (#2421)

This PR replaces the third-party Zap logging library with Go's standard library slog package for structured logging. This change reduced the number of dependencies while maintaining the same logging functionality and format.

Fixes #2120

Changes:
- Removed dependencies on go.uber.org/zap and go.uber.org/zap/zapcore
- Added usage of Go's standard library log/slog package
- Simplified the StdLogger structure by combining infoLog and debugLog into a single stdLog
- Refactored the StructuredLogger to use slog.Logger instead of Zap's SugaredLogger
- Modified the NewStructuredLogger function to use slog handlers and configuration
- Added a new replaceAttr function to maintain compatibility with Google Cloud Logging format
- Ensured that log messages continue to adhere to the LogEntry format for Google Cloud Logging

Author: danielandersson

cmd/root.go

@@ -579,7 +579,7 @@ func loadConfig(c *Command, args []string, opts []Option) error {
 
 	// Handle logger separately from config
 	if c.conf.StructuredLogs {
-		c.logger, c.cleanup = log.NewStructuredLogger(c.conf.Quiet)
+		c.logger = log.NewStructuredLogger(c.conf.Quiet)
 	}
 
 	if c.conf.Quiet {

go.mod

@@ -16,7 +16,6 @@ require (
 	github.com/spf13/pflag v1.0.7
 	github.com/spf13/viper v1.20.1
 	go.opencensus.io v0.24.0
-	go.uber.org/zap v1.27.0
 	golang.org/x/oauth2 v0.30.0
 	golang.org/x/sys v0.35.0
 	google.golang.org/api v0.247.0
@@ -73,7 +72,6 @@ require (
 	go.opentelemetry.io/otel v1.37.0 // indirect
 	go.opentelemetry.io/otel/metric v1.37.0 // indirect
 	go.opentelemetry.io/otel/trace v1.37.0 // indirect
-	go.uber.org/multierr v1.11.0 // indirect
 	golang.org/x/crypto v0.41.0 // indirect
 	golang.org/x/net v0.43.0 // indirect
 	golang.org/x/sync v0.16.0 // indirect

go.sum

@@ -389,10 +389,6 @@ go.opentelemetry.io/otel/trace v1.37.0 h1:HLdcFNbRQBE2imdSEgm/kwqmQj1Or1l/7bW6mx
 go.opentelemetry.io/otel/trace v1.37.0/go.mod h1:TlgrlQ+PtQO5XFerSPUYG0JSgGyryXewPGyayAWSBS0=
 go.uber.org/goleak v1.3.0 h1:2K3zAYmnTNqV73imy9J1T3WC+gmCePx2hEGkimedGto=
 go.uber.org/goleak v1.3.0/go.mod h1:CoHD4mav9JJNrW/WLlf7HGZPjdw8EucARQHekz1X6bE=
-go.uber.org/multierr v1.11.0 h1:blXXJkSxSSfBVBlC76pxqeO+LN3aDfLQo+309xJstO0=
-go.uber.org/multierr v1.11.0/go.mod h1:20+QtiLqy0Nd6FdQB9TLXag12DsQkrbs3htMFfDN80Y=
-go.uber.org/zap v1.27.0 h1:aJMhYGrd5QSmlpLMr2MftRKl7t8J8PTZPA732ud/XR8=
-go.uber.org/zap v1.27.0/go.mod h1:GB2qFLM7cTU87MWRP2mPIjqfIDnGu+VIO4V/SdhGo2E=
 golang.org/x/crypto v0.0.0-20180904163835-0709b304e793/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20190510104115-cbcb75029529/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=

internal/log/log.go

@@ -15,36 +15,35 @@
 package log
 
 import (
+	"fmt"
 	"io"
 	llog "log"
+	"log/slog"
 	"os"
+	"time"
 
 	"github.com/GoogleCloudPlatform/cloud-sql-proxy/v2/cloudsql"
-	"go.uber.org/zap"
-	"go.uber.org/zap/zapcore"
 )
 
 // StdLogger is the standard logger that distinguishes between info and error
 // logs.
 type StdLogger struct {
-	infoLog  *llog.Logger
-	debugLog *llog.Logger
-	errLog   *llog.Logger
+	stdLog *llog.Logger
+	errLog *llog.Logger
 }
 
 // NewStdLogger create a Logger that uses out and err for informational and
 // error messages.
 func NewStdLogger(out, err io.Writer) cloudsql.Logger {
 	return &StdLogger{
-		infoLog:  llog.New(out, "", llog.LstdFlags),
-		debugLog: llog.New(out, "", llog.LstdFlags),
-		errLog:   llog.New(err, "", llog.LstdFlags),
+		stdLog: llog.New(out, "", llog.LstdFlags),
+		errLog: llog.New(err, "", llog.LstdFlags),
 	}
 }
 
 // Infof logs informational messages
 func (l *StdLogger) Infof(format string, v ...interface{}) {
-	l.infoLog.Printf(format, v...)
+	l.stdLog.Printf(format, v...)
 }
 
 // Errorf logs error messages
@@ -54,61 +53,72 @@ func (l *StdLogger) Errorf(format string, v ...interface{}) {
 
 // Debugf logs debug messages
 func (l *StdLogger) Debugf(format string, v ...interface{}) {
-	l.debugLog.Printf(format, v...)
+	l.stdLog.Printf(format, v...)
 }
 
 // StructuredLogger writes log messages in JSON.
 type StructuredLogger struct {
-	logger *zap.SugaredLogger
+	stdLog *slog.Logger
+	errLog *slog.Logger
 }
 
 // Infof logs informational messages
 func (l *StructuredLogger) Infof(format string, v ...interface{}) {
-	l.logger.Infof(format, v...)
+	l.stdLog.Info(fmt.Sprintf(format, v...))
 }
 
 // Errorf logs error messages
 func (l *StructuredLogger) Errorf(format string, v ...interface{}) {
-	l.logger.Errorf(format, v...)
+	l.errLog.Error(fmt.Sprintf(format, v...))
 }
 
 // Debugf logs debug messages
 func (l *StructuredLogger) Debugf(format string, v ...interface{}) {
-	l.logger.Debugf(format, v...)
+	l.stdLog.Debug(fmt.Sprintf(format, v...))
 }
 
 // NewStructuredLogger creates a Logger that logs messages using JSON.
-func NewStructuredLogger(quiet bool) (cloudsql.Logger, func() error) {
-	// Configure structured logs to adhere to LogEntry format
-	// https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry
-	c := zap.NewProductionEncoderConfig()
-	c.LevelKey = "severity"
-	c.MessageKey = "message"
-	c.TimeKey = "timestamp"
-	c.EncodeLevel = zapcore.CapitalLevelEncoder
-	c.EncodeTime = zapcore.ISO8601TimeEncoder
-
-	enc := zapcore.NewJSONEncoder(c)
-
-	var syncer zapcore.WriteSyncer
-	// quiet disables writing to the info log
+func NewStructuredLogger(quiet bool) cloudsql.Logger {
+	var infoHandler, errorHandler slog.Handler
 	if quiet {
-		syncer = zapcore.AddSync(io.Discard)
+		infoHandler = slog.DiscardHandler
 	} else {
-		syncer = zapcore.Lock(os.Stdout)
+		infoHandler = slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
+			Level:       slog.LevelDebug,
+			ReplaceAttr: replaceAttr,
+		})
 	}
-	core := zapcore.NewTee(
-		zapcore.NewCore(enc, syncer, zap.LevelEnablerFunc(func(l zapcore.Level) bool {
-			// Anything below error, goes to the info log.
-			return l < zapcore.ErrorLevel
-		})),
-		zapcore.NewCore(enc, zapcore.Lock(os.Stderr), zap.LevelEnablerFunc(func(l zapcore.Level) bool {
-			// Anything at error or higher goes to the error log.
-			return l >= zapcore.ErrorLevel
-		})),
-	)
+	errorHandler = slog.NewJSONHandler(os.Stderr, &slog.HandlerOptions{
+		Level:       slog.LevelError,
+		ReplaceAttr: replaceAttr,
+	})
+
 	l := &StructuredLogger{
-		logger: zap.New(core).Sugar(),
+		stdLog: slog.New(infoHandler),
+		errLog: slog.New(errorHandler),
+	}
+	return l
+}
+
+// replaceAttr remaps default Go logging keys to adhere to LogEntry format
+// https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry
+func replaceAttr(groups []string, a slog.Attr) slog.Attr {
+	if groups != nil {
+		return a
+	}
+
+	switch a.Key {
+	case slog.LevelKey:
+		a.Key = "severity"
+	case slog.MessageKey:
+		a.Key = "message"
+	case slog.SourceKey:
+		a.Key = "sourceLocation"
+	case slog.TimeKey:
+		a.Key = "timestamp"
+		if a.Value.Kind() == slog.KindTime {
+			a.Value = slog.StringValue(a.Value.Time().Format(time.RFC3339))
+		}
 	}
-	return l, l.logger.Sync
+	return a
 }