feat: add log-local-time flag for local timezone in logs

Add a --log-local-time flag that configures cloudflared to use local
timezone for log timestamps instead of the default UTC.

This helps users correlate logs with local system events and other
services running in their timezone.

The flag can also be set via the TUNNEL_LOG_LOCAL_TIME environment
variable.

Closes #1530

cmd/cloudflared/cliutil/logger.go

@@ -54,6 +54,12 @@ func ConfigureLoggingFlags(shouldHide bool) []cli.Flag {
 			EnvVars: []string{"TUNNEL_TRACE_OUTPUT"},
 			Hidden:  shouldHide,
 		}),
+		altsrc.NewBoolFlag(&cli.BoolFlag{
+			Name:    flags.LogLocalTime,
+			Usage:   "Use local timezone for log timestamps instead of UTC.",
+			EnvVars: []string{"TUNNEL_LOG_LOCAL_TIME"},
+			Hidden:  shouldHide,
+		}),
 		FlagLogOutput,
 	}
 }

cmd/cloudflared/flags/flags.go

@@ -143,6 +143,9 @@ const (
 	LogFormatOutputValueDefault = "default"
 	LogFormatOutputValueJSON    = "json"
 
+	// LogLocalTime uses local timezone instead of UTC for log timestamps.
+	LogLocalTime = "log-local-time"
+
 	// TraceOutput is the command line flag to set the name of trace output file
 	TraceOutput = "trace-output"
 

cmd/cloudflared/tunnel/cmd.go

@@ -115,6 +115,7 @@ var (
 		cfdflags.LogFile,
 		cfdflags.LogDirectory,
 		cfdflags.TraceOutput,
+		cfdflags.LogLocalTime,
 		cfdflags.ProxyDns,
 		"proxy-dns-port",
 		"proxy-dns-address",

logger/create.go

@@ -44,6 +44,16 @@ func utcNow() time.Time {
 	return time.Now().UTC()
 }
 
+func localNow() time.Time {
+	return time.Now()
+}
+
+func configureTimestampFunc(useLocalTime bool) {
+	if useLocalTime {
+		zerolog.TimestampFunc = localNow
+	}
+}
+
 func fallbackLogger(err error) *zerolog.Logger {
 	failLog := fallbacklog.With().Logger()
 	fallbacklog.Error().Msgf("Falling back to a default logger due to logger setup failure: %s", err)
@@ -146,6 +156,8 @@ func createFromContext(
 	logDirectoryFlagName string,
 	disableTerminal bool,
 ) *zerolog.Logger {
+	configureTimestampFunc(c.Bool(cfdflags.LogLocalTime))
+
 	logLevel := c.String(logLevelFlagName)
 	logFile := c.String(cfdflags.LogFile)
 	logDirectory := c.String(logDirectoryFlagName)

logger/create_test.go

@@ -3,6 +3,7 @@ package logger
 import (
 	"io"
 	"testing"
+	"time"
 
 	"github.com/pkg/errors"
 	"github.com/rs/zerolog"
@@ -130,3 +131,28 @@ func TestResilientMultiWriter_Management(t *testing.T) {
 		})
 	}
 }
+
+func TestTimestampFunctions(t *testing.T) {
+	t.Run("utcNow returns UTC", func(t *testing.T) {
+		ts := utcNow()
+		_, offset := ts.Zone()
+		assert.Equal(t, 0, offset)
+	})
+
+	t.Run("localNow returns local timezone", func(t *testing.T) {
+		ts := localNow()
+		expected := time.Now()
+		_, expectedOffset := expected.Zone()
+		_, actualOffset := ts.Zone()
+		assert.Equal(t, expectedOffset, actualOffset)
+	})
+
+	t.Run("configureTimestampFunc sets local time when true", func(t *testing.T) {
+		configureTimestampFunc(true)
+		ts := zerolog.TimestampFunc()
+		expected := time.Now()
+		_, expectedOffset := expected.Zone()
+		_, actualOffset := ts.Zone()
+		assert.Equal(t, expectedOffset, actualOffset)
+	})
+}