From 8102d662e3c8585d09a6aaffc55c872141838d96 Mon Sep 17 00:00:00 2001
From: Alistair Mackay <34012094+fireflycons@users.noreply.github.com>
Date: Mon, 22 Apr 2024 10:22:16 +0100
Subject: [PATCH] Switch to allow header timestamps to be UTC (#65)

* Don't test syslog on windows

* Allow selecting UTC time in timestamp header

* Declare func for UTC time outside the method

May save a few ns.

* Removed headerTimeZone

timeZone var isn't accessed if offest is zero
---
 logger.go      | 22 ++++++++++++++++++----
 syslog_test.go |  3 +++
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/logger.go b/logger.go
index f5d128a8..5c73f9e2 100644
--- a/logger.go
+++ b/logger.go
@@ -78,13 +78,16 @@ type Logger struct {
 	// If Caller is negative, adds the full /path/to/file:line of the "caller" key.
 	Caller int
 
-	// TimeField defines the time filed name in output.  It uses "time" in if empty.
+	// TimeField defines the time field name in output.  It uses "time" in if empty.
 	TimeField string
 
 	// TimeFormat specifies the time format in output. It uses time.RFC3339 with milliseconds if empty.
 	// If set with `TimeFormatUnix`, `TimeFormatUnixMs`, times are formated as UNIX timestamp.
 	TimeFormat string
 
+	// TimeUTC specifices that the timestamps should be UTC instead of system local time.
+	TimeUTC bool
+
 	// Context specifies an optional context of logger.
 	Context Context
 
@@ -438,6 +441,9 @@ const smallsString = "00010203040506070809" +
 	"90919293949596979899"
 
 var timeNow = time.Now
+var timeUtcNow = func() time.Time {
+	return time.Now().UTC()
+}
 var timeOffset, timeZone = func() (int64, string) {
 	now := timeNow()
 	_, n := now.Zone()
@@ -450,6 +456,14 @@ func (l *Logger) silent(level Level) bool {
 }
 
 func (l *Logger) header(level Level) *Entry {
+	headerTimeFunc := timeNow
+	headerTimeOffset := timeOffset
+
+	if l.TimeUTC {
+		headerTimeFunc = timeUtcNow
+		headerTimeOffset = 0
+	}
+
 	e := epool.Get().(*Entry)
 	e.buf = e.buf[:0]
 	e.Level = level
@@ -471,7 +485,7 @@ func (l *Logger) header(level Level) *Entry {
 		sec, nsec, _ := now()
 		var tmp [32]byte
 		var buf []byte
-		if timeOffset == 0 {
+		if headerTimeOffset == 0 {
 			// "2006-01-02T15:04:05.999Z"
 			tmp[25] = '"'
 			tmp[24] = 'Z'
@@ -488,7 +502,7 @@ func (l *Logger) header(level Level) *Entry {
 			buf = tmp[:31]
 		}
 		// date time
-		sec += 9223372028715321600 + timeOffset // unixToInternal + internalToAbsolute + timeOffset
+		sec += 9223372028715321600 + headerTimeOffset // unixToInternal + internalToAbsolute + timeOffset
 		year, month, day, _ := absDate(uint64(sec), true)
 		hour, minute, second := absClock(uint64(sec))
 		// year
@@ -626,7 +640,7 @@ func (l *Logger) header(level Level) *Entry {
 		e.buf = append(e.buf, tmp[:]...)
 	default:
 		e.buf = append(e.buf, '"')
-		e.buf = timeNow().AppendFormat(e.buf, l.TimeFormat)
+		e.buf = headerTimeFunc().AppendFormat(e.buf, l.TimeFormat)
 		e.buf = append(e.buf, '"')
 	}
 	// level
diff --git a/syslog_test.go b/syslog_test.go
index b83f6f27..e89d8bb4 100644
--- a/syslog_test.go
+++ b/syslog_test.go
@@ -1,3 +1,6 @@
+//go:build !windows
+// +build !windows
+
 package log
 
 import (