log: improve prefix handling (#5489)

pkg/util/xlog/xlog.go

@@ -96,21 +96,21 @@ func (l *Logger) Spawn() *Logger {
 }
 
 func (l *Logger) Errorf(format string, v ...any) {
-	log.Logger.Errorf(l.prefixString+format, v...)
+	log.Logger.WithPrefix(l.prefixString).Errorf(format, v...)
 }
 
 func (l *Logger) Warnf(format string, v ...any) {
-	log.Logger.Warnf(l.prefixString+format, v...)
+	log.Logger.WithPrefix(l.prefixString).Warnf(format, v...)
 }
 
 func (l *Logger) Infof(format string, v ...any) {
-	log.Logger.Infof(l.prefixString+format, v...)
+	log.Logger.WithPrefix(l.prefixString).Infof(format, v...)
 }
 
 func (l *Logger) Debugf(format string, v ...any) {
-	log.Logger.Debugf(l.prefixString+format, v...)
+	log.Logger.WithPrefix(l.prefixString).Debugf(format, v...)
 }
 
 func (l *Logger) Tracef(format string, v ...any) {
-	log.Logger.Tracef(l.prefixString+format, v...)
+	log.Logger.WithPrefix(l.prefixString).Tracef(format, v...)
 }

pkg/util/xlog/xlog_test.go

@@ -0,0 +1,76 @@
+// Copyright 2026 The frp Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package xlog
+
+import (
+	"bytes"
+	"testing"
+
+	goliblog "github.com/fatedier/golib/log"
+	"github.com/stretchr/testify/require"
+
+	frplog "github.com/fatedier/frp/pkg/util/log"
+)
+
+func TestPrefixIsNotPartOfFormatString(t *testing.T) {
+	tests := []struct {
+		name string
+		log  func(*Logger)
+	}{
+		{name: "error", log: func(xl *Logger) { xl.Errorf("value [%s]", "ok") }},
+		{name: "warn", log: func(xl *Logger) { xl.Warnf("value [%s]", "ok") }},
+		{name: "info", log: func(xl *Logger) { xl.Infof("value [%s]", "ok") }},
+		{name: "debug", log: func(xl *Logger) { xl.Debugf("value [%s]", "ok") }},
+		{name: "trace", log: func(xl *Logger) { xl.Tracef("value [%s]", "ok") }},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			output := captureLogs(t)
+
+			tt.log(New().AppendPrefix("%1000000s"))
+
+			require.Contains(t, output.String(), "[%1000000s] value [ok]")
+			require.Less(t, output.Len(), 1024)
+		})
+	}
+}
+
+func TestFormattingSemanticsArePreserved(t *testing.T) {
+	output := captureLogs(t)
+	xl := New().AppendPrefix("run")
+
+	xl.Infof("%[2]s %[1]s", "first", "second")
+	xl.Infof("100% complete")
+
+	require.Contains(t, output.String(), "[run] second first")
+	require.Contains(t, output.String(), "[run] 100% complete")
+}
+
+func captureLogs(t *testing.T) *bytes.Buffer {
+	t.Helper()
+
+	output := bytes.NewBuffer(nil)
+	oldLogger := frplog.Logger
+	frplog.Logger = goliblog.New(
+		goliblog.WithOutput(output),
+		goliblog.WithLevel(goliblog.TraceLevel),
+		goliblog.WithCaller(false),
+	)
+	t.Cleanup(func() {
+		frplog.Logger = oldLogger
+	})
+	return output
+}