feat(attach): 附件可配置限额、流式落盘与分阶段上传

管理端可配类型/体积；上传改流式避免整文件进内存；发帖先选再传并拦截未上传提交；提高 Next proxy 体积上限。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/service/upload.go

@@ -8,9 +8,11 @@ import (
 	"image"
 	_ "image/jpeg"
 	_ "image/png"
+	"io"
 	"log"
 	"os"
 	"path/filepath"
+	"strconv"
 	"strings"
 
 	"github.com/freefire/jiang13-bbs/model"
@@ -31,14 +33,32 @@ const (
 
 // UploadService 附件上传：落盘到 data/uploads，元信息入库 attachments
 type UploadService struct {
-	db  *gorm.DB
-	dir string // 上传根目录（如 data/uploads）
+	db      *gorm.DB
+	dir     string // 上传根目录（如 data/uploads）
+	setting *SettingService
 }
 
 func NewUploadService(db *gorm.DB, uploadDir string) *UploadService {
 	return &UploadService{db: db, dir: uploadDir}
 }
 
+// WithSetting 注入站点设置（插图体积上限）
+func (s *UploadService) WithSetting(setting *SettingService) *UploadService {
+	s.setting = setting
+	return s
+}
+
+func (s *UploadService) imageMaxBytes() int64 {
+	if s.setting == nil {
+		return ImageMaxBytes
+	}
+	n, err := s.setting.ImageMaxBytes()
+	if err != nil || n < 1 {
+		return ImageMaxBytes
+	}
+	return n
+}
+
 // EnsureDir 启动时确保上传目录存在
 func (s *UploadService) EnsureDir() error {
 	if err := os.MkdirAll(filepath.Join(s.dir, "avatars"), 0o755); err != nil {
@@ -125,8 +145,7 @@ func detectImageFormat(data []byte) (imageFormat, error) {
 	return imageFormat{}, errors.New("仅支持 JPEG / PNG / WebP")
 }
 
-func decodeImageSize(data []byte, mime string) (w, h int, err error) {
-	r := bytes.NewReader(data)
+func decodeImageSizeReader(r io.Reader, mime string) (w, h int, err error) {
 	var cfg image.Config
 	switch mime {
 	case "image/webp":
@@ -140,28 +159,33 @@ func decodeImageSize(data []byte, mime string) (w, h int, err error) {
 	return cfg.Width, cfg.Height, nil
 }
 
-// SaveImage 保存帖子插图：校验格式/大小/尺寸 → 落盘 → 写 attachments（kind=image）
-func (s *UploadService) SaveImage(userID uint, data []byte) (*model.Attachment, error) {
-	if len(data) == 0 {
+// SaveImage 流式保存帖子插图：校验格式/大小/尺寸 → 落盘 → 写 attachments（kind=image）
+func (s *UploadService) SaveImage(userID uint, src io.Reader) (*model.Attachment, error) {
+	if src == nil {
 		return nil, errors.New("文件为空")
 	}
-	if len(data) > ImageMaxBytes {
-		return nil, errors.New("图片不能超过 5MB")
+	maxB := s.imageMaxBytes()
+	tooLarge := func() error {
+		mb := int(maxB >> 20)
+		if mb < 1 {
+			mb = 1
+		}
+		return errors.New("图片不能超过 " + strconv.Itoa(mb) + "MB")
 	}
-	format, err := detectImageFormat(data)
+
+	// 先读魔数头，再与剩余流合并落盘，整图不进内存
+	head := make([]byte, 12)
+	n, err := io.ReadFull(src, head)
+	if err != nil && !errors.Is(err, io.ErrUnexpectedEOF) && !errors.Is(err, io.EOF) {
+		return nil, errors.New("读取图片失败")
+	}
+	if n == 0 {
+		return nil, errors.New("文件为空")
+	}
+	format, err := detectImageFormat(head[:n])
 	if err != nil {
 		return nil, err
 	}
-	w, h, err := decodeImageSize(data, format.mime)
-	if err != nil {
-		return nil, err
-	}
-	if w < 1 || h < 1 {
-		return nil, errors.New("无效的图片尺寸")
-	}
-	if w > ImageMaxDim || h > ImageMaxDim {
-		return nil, errors.New("图片边长不能超过 4096px")
-	}
 
 	nameBytes := make([]byte, 16)
 	if _, err := rand.Read(nameBytes); err != nil {
@@ -169,7 +193,61 @@ func (s *UploadService) SaveImage(userID uint, data []byte) (*model.Attachment,
 	}
 	filename := hex.EncodeToString(nameBytes) + format.ext
 	fullPath := filepath.Join(s.dir, "images", filename)
-	if err := os.WriteFile(fullPath, data, 0o644); err != nil {
+	tmp := fullPath + ".partial"
+
+	f, err := os.OpenFile(tmp, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o644)
+	if err != nil {
+		return nil, err
+	}
+	remain := maxB + 1 - int64(n)
+	if remain < 0 {
+		_ = f.Close()
+		_ = os.Remove(tmp)
+		return nil, tooLarge()
+	}
+	writtenHead, err := f.Write(head[:n])
+	if err != nil {
+		_ = f.Close()
+		_ = os.Remove(tmp)
+		return nil, err
+	}
+	writtenRest, copyErr := io.Copy(f, io.LimitReader(src, remain))
+	_ = f.Close()
+	if copyErr != nil {
+		_ = os.Remove(tmp)
+		return nil, copyErr
+	}
+	total := int64(writtenHead) + writtenRest
+	if total == 0 {
+		_ = os.Remove(tmp)
+		return nil, errors.New("文件为空")
+	}
+	if total > maxB {
+		_ = os.Remove(tmp)
+		return nil, tooLarge()
+	}
+
+	rf, err := os.Open(tmp)
+	if err != nil {
+		_ = os.Remove(tmp)
+		return nil, err
+	}
+	w, h, err := decodeImageSizeReader(rf, format.mime)
+	_ = rf.Close()
+	if err != nil {
+		_ = os.Remove(tmp)
+		return nil, err
+	}
+	if w < 1 || h < 1 {
+		_ = os.Remove(tmp)
+		return nil, errors.New("无效的图片尺寸")
+	}
+	if w > ImageMaxDim || h > ImageMaxDim {
+		_ = os.Remove(tmp)
+		return nil, errors.New("图片边长不能超过 4096px")
+	}
+	if err := os.Rename(tmp, fullPath); err != nil {
+		_ = os.Remove(tmp)
 		return nil, err
 	}
 
@@ -178,7 +256,7 @@ func (s *UploadService) SaveImage(userID uint, data []byte) (*model.Attachment,
 		Kind:   model.AttachmentKindImage,
 		URL:    "/uploads/images/" + filename,
 		MIME:   format.mime,
-		Size:   len(data),
+		Size:   int(total),
 		Width:  w,
 		Height: h,
 	}