From bca3cd84d1e08dd91a3151307636fb29edd24333 Mon Sep 17 00:00:00 2001
From: yusing <yusing@6uo.me>
Date: Tue, 29 Apr 2025 00:46:30 +0800
Subject: [PATCH] fix(accesslog): os: invalid use of WriteAt on file opened
 with O_APPEND

---
 internal/logging/accesslog/access_logger.go |  6 +++
 internal/logging/accesslog/file_logger.go   | 43 +++++++++++++++++----
 internal/logging/accesslog/rotate.go        | 19 +++++++--
 3 files changed, 58 insertions(+), 10 deletions(-)

diff --git a/internal/logging/accesslog/access_logger.go b/internal/logging/accesslog/access_logger.go
index c5feb28..14f2f55 100644
--- a/internal/logging/accesslog/access_logger.go
+++ b/internal/logging/accesslog/access_logger.go
@@ -43,6 +43,12 @@ type (
 		Name() string // file name or path
 	}
 
+	SupportRotate interface {
+		io.Writer
+		supportRotate
+		Name() string
+	}
+
 	RequestFormatter interface {
 		// AppendRequestLog appends a log line to line with or without a trailing newline
 		AppendRequestLog(line []byte, req *http.Request, res *http.Response) []byte
diff --git a/internal/logging/accesslog/file_logger.go b/internal/logging/accesslog/file_logger.go
index b1691a3..f887271 100644
--- a/internal/logging/accesslog/file_logger.go
+++ b/internal/logging/accesslog/file_logger.go
@@ -2,8 +2,9 @@ package accesslog
 
 import (
 	"fmt"
+	"io"
 	"os"
-	pathPkg "path"
+	"path/filepath"
 	"sync"
 
 	"github.com/yusing/go-proxy/internal/logging"
@@ -11,7 +12,7 @@ import (
 )
 
 type File struct {
-	*os.File
+	f *os.File
 
 	// os.File.Name() may not equal to key of `openedFiles`.
 	// Store it for later delete from `openedFiles`.
@@ -25,21 +26,25 @@ var (
 	openedFilesMu sync.Mutex
 )
 
-func newFileIO(path string) (WriterWithName, error) {
+func newFileIO(path string) (SupportRotate, error) {
 	openedFilesMu.Lock()
 	defer openedFilesMu.Unlock()
 
 	var file *File
-	path = pathPkg.Clean(path)
+	path = filepath.Clean(path)
 	if opened, ok := openedFiles[path]; ok {
 		opened.refCount.Add()
 		return opened, nil
 	} else {
-		f, err := os.OpenFile(path, os.O_APPEND|os.O_CREATE|os.O_RDWR, 0o644)
+		// cannot open as O_APPEND as we need Seek and WriteAt
+		f, err := os.OpenFile(path, os.O_CREATE|os.O_RDWR, 0o644)
 		if err != nil {
 			return nil, fmt.Errorf("access log open error: %w", err)
 		}
-		file = &File{File: f, path: path, refCount: utils.NewRefCounter()}
+		if _, err := f.Seek(0, io.SeekEnd); err != nil {
+			return nil, fmt.Errorf("access log seek error: %w", err)
+		}
+		file = &File{f: f, path: path, refCount: utils.NewRefCounter()}
 		openedFiles[path] = file
 		go file.closeOnZero()
 	}
@@ -47,6 +52,30 @@ func newFileIO(path string) (WriterWithName, error) {
 	return file, nil
 }
 
+func (f *File) Name() string {
+	return f.f.Name()
+}
+
+func (f *File) Write(p []byte) (n int, err error) {
+	return f.f.Write(p)
+}
+
+func (f *File) ReadAt(p []byte, off int64) (n int, err error) {
+	return f.f.ReadAt(p, off)
+}
+
+func (f *File) WriteAt(p []byte, off int64) (n int, err error) {
+	return f.f.WriteAt(p, off)
+}
+
+func (f *File) Seek(offset int64, whence int) (int64, error) {
+	return f.f.Seek(offset, whence)
+}
+
+func (f *File) Truncate(size int64) error {
+	return f.f.Truncate(size)
+}
+
 func (f *File) Close() error {
 	f.refCount.Sub()
 	return nil
@@ -62,5 +91,5 @@ func (f *File) closeOnZero() {
 	openedFilesMu.Lock()
 	delete(openedFiles, f.path)
 	openedFilesMu.Unlock()
-	f.File.Close()
+	f.f.Close()
 }
diff --git a/internal/logging/accesslog/rotate.go b/internal/logging/accesslog/rotate.go
index f21348c..b004472 100644
--- a/internal/logging/accesslog/rotate.go
+++ b/internal/logging/accesslog/rotate.go
@@ -12,7 +12,7 @@ import (
 )
 
 type supportRotate interface {
-	io.ReadSeeker
+	io.Seeker
 	io.ReaderAt
 	io.WriterAt
 	Truncate(size int64) error
@@ -66,9 +66,23 @@ var rotateBytePool = synk.NewBytesPool(0, 16*1024*1024)
 // If the file does not need to be rotated, it returns nil, nil.
 func rotateLogFile(file supportRotate, config *Retention) (result *RotateResult, err error) {
 	if config.KeepSize > 0 {
-		return rotateLogFileBySize(file, config)
+		result, err = rotateLogFileBySize(file, config)
+	} else {
+		result, err = rotateLogFileByPolicy(file, config)
 	}
 
+	if err != nil {
+		return nil, err
+	}
+
+	if _, err := file.Seek(0, io.SeekEnd); err != nil {
+		return nil, err
+	}
+
+	return result, nil
+}
+
+func rotateLogFileByPolicy(file supportRotate, config *Retention) (result *RotateResult, err error) {
 	var shouldStop func() bool
 	t := utils.TimeNow()
 
@@ -234,7 +248,6 @@ var timeJSON = []byte(`"time":"`)
 //
 // The returned time is not validated.
 func ExtractTime(line []byte) []byte {
-	//TODO: optimize this
 	switch line[0] {
 	case '{': // JSON format
 		if i := bytes.Index(line, timeJSON); i != -1 {