From e44ecc0cccd4ae8ae38dd71ba8b083ee83fc67a8 Mon Sep 17 00:00:00 2001
From: yusing <yusing.wys@gmail.com>
Date: Tue, 16 Dec 2025 17:20:59 +0800
Subject: [PATCH] fix(access_log): fix slice out-of-bound panic on log rotation

---
 internal/logging/accesslog/access_logger.go |  1 +
 internal/logging/accesslog/rotate.go        | 50 ++++++++++++---------
 2 files changed, 31 insertions(+), 20 deletions(-)

diff --git a/internal/logging/accesslog/access_logger.go b/internal/logging/accesslog/access_logger.go
index 911e7a04..a18b9ba2 100644
--- a/internal/logging/accesslog/access_logger.go
+++ b/internal/logging/accesslog/access_logger.go
@@ -94,6 +94,7 @@ const (
 )
 
 var bytesPool = synk.GetUnsizedBytesPool()
+var sizedPool = synk.GetSizedBytesPool()
 
 func NewAccessLogger(parent task.Parent, cfg AnyConfig) (AccessLogger, error) {
 	writers, err := cfg.Writers()
diff --git a/internal/logging/accesslog/rotate.go b/internal/logging/accesslog/rotate.go
index 083443d9..054b2c85 100644
--- a/internal/logging/accesslog/rotate.go
+++ b/internal/logging/accesslog/rotate.go
@@ -3,12 +3,11 @@ package accesslog
 import (
 	"bytes"
 	"errors"
+	"fmt"
 	"io"
-	"slices"
 	"time"
 
 	"github.com/rs/zerolog"
-	gperr "github.com/yusing/goutils/errs"
 	"github.com/yusing/goutils/mockable"
 	strutils "github.com/yusing/goutils/strings"
 )
@@ -164,31 +163,14 @@ func rotateLogFileByPolicy(file supportRotate, config *Retention, result *Rotate
 
 	// Read each line and write it to the beginning of the file
 	writePos := int64(0)
-	buf := bytesPool.Get()
-	defer func() {
-		bytesPool.Put(buf)
-	}()
-
 	// in reverse order to keep the order of the lines (from old to new)
 	for i := len(linesToKeep) - 1; i >= 0; i-- {
 		line := linesToKeep[i]
 		n := line.Size
-		if cap(buf) < int(n) {
-			buf = slices.Grow(buf, int(n)-cap(buf))
-		}
-		buf = buf[:n]
 
-		// Read the line from its original position
-		if _, err := file.ReadAt(buf, line.Pos); err != nil {
+		if err := fileContentMove(file, line.Pos, writePos, int(n)); err != nil {
 			return false, err
 		}
-
-		// Write it to the new position
-		if _, err := file.WriteAt(buf, writePos); err != nil {
-			return false, err
-		} else if n < line.Size {
-			return false, gperr.Errorf("%w, writing %d bytes, only %d written", io.ErrShortWrite, line.Size, n)
-		}
 		writePos += n
 	}
 
@@ -199,6 +181,34 @@ func rotateLogFileByPolicy(file supportRotate, config *Retention, result *Rotate
 	return true, nil
 }
 
+// fileContentMove moves the content of the file from the source position to the destination position.
+//
+// this is only used for moving from the back to the front of the file.
+func fileContentMove(file supportRotate, srcPos, dstPos int64, size int) error {
+	buf := sizedPool.GetSized(size)
+	defer sizedPool.Put(buf)
+
+	// Read the line from its original position
+	nRead, err := file.ReadAt(buf, srcPos)
+	if err != nil {
+		return err
+	}
+	if nRead != size {
+		return fmt.Errorf("%w, reading %d bytes, only %d read", io.ErrShortBuffer, size, nRead)
+	}
+
+	// Write it to the new position
+	nWritten, err := file.WriteAt(buf, dstPos)
+	if err != nil {
+		return err
+	}
+	if nWritten != size {
+		return fmt.Errorf("%w, writing %d bytes, only %d written", io.ErrShortWrite, size, nWritten)
+	}
+
+	return nil
+}
+
 // rotateLogFileBySize rotates the log file by size.
 // It returns the result of the rotation and an error if any.
 //