Merge branch 'master' of https://github.com/sirupsen/logrus

Conflicts:
	CHANGELOG.md

text_formatter.go

@@ -3,9 +3,9 @@ package logrus
 import (
 	"bytes"
 	"fmt"
-	"runtime"
 	"sort"
 	"strings"
+	"sync"
 	"time"
 )
 
@@ -20,12 +20,10 @@ const (
 
 var (
 	baseTimestamp time.Time
-	isTerminal    bool
 )
 
 func init() {
 	baseTimestamp = time.Now()
-	isTerminal = IsTerminal()
 }
 
 type TextFormatter struct {
@@ -50,6 +48,10 @@ type TextFormatter struct {
 	// that log extremely frequently and don't use the JSON formatter this may not
 	// be desired.
 	DisableSorting bool
+
+	// Whether the logger's out is to a terminal
+	isTerminal   bool
+	terminalOnce sync.Once
 }
 
 func (f *TextFormatter) Format(entry *Entry) ([]byte, error) {
@@ -70,8 +72,13 @@ func (f *TextFormatter) Format(entry *Entry) ([]byte, error) {
 
 	prefixFieldClashes(entry.Data, entry.HasCaller())
 
-	isColorTerminal := isTerminal && (runtime.GOOS != "windows")
-	isColored := (f.ForceColors || isColorTerminal) && !f.DisableColors
+	f.terminalOnce.Do(func() {
+		if entry.Logger != nil {
+			f.isTerminal = IsTerminal(entry.Logger.Out)
+		}
+	})
+
+	isColored := (f.ForceColors || f.isTerminal) && !f.DisableColors
 
 	timestampFormat := f.TimestampFormat
 	if timestampFormat == "" {