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/handler/post.go

@@ -2,7 +2,6 @@ package handler
 
 import (
 	"errors"
-	"io"
 	"net/http"
 	"net/url"
 	"path/filepath"
@@ -282,11 +281,46 @@ func (h *Handlers) AdminPointsStats(c *gin.Context) {
 // UploadPostFile 上传帖子附件（草稿态）
 func (h *Handlers) UploadPostFile(c *gin.Context) {
 	claims := middleware.CurrentUser(c)
+
+	maxBytes, err := h.Setting.AttachmentMaxBytes()
+	if err != nil || maxBytes < 1 {
+		maxBytes = service.FileMaxBytes
+	}
+	overhead := int64(64 << 10) // multipart 边界开销
+	limit := maxBytes + overhead
+
+	if c.Request.ContentLength > limit {
+		mb := int(maxBytes >> 20)
+		if mb < 1 {
+			mb = 1
+		}
+		c.JSON(http.StatusRequestEntityTooLarge, gin.H{"error": "附件不能超过 " + strconv.Itoa(mb) + "MB"})
+		return
+	}
+	c.Request.Body = http.MaxBytesReader(c.Writer, c.Request.Body, limit)
+
 	file, err := c.FormFile("file")
 	if err != nil {
+		var maxErr *http.MaxBytesError
+		if errors.As(err, &maxErr) {
+			mb := int(maxBytes >> 20)
+			if mb < 1 {
+				mb = 1
+			}
+			c.JSON(http.StatusRequestEntityTooLarge, gin.H{"error": "附件不能超过 " + strconv.Itoa(mb) + "MB"})
+			return
+		}
 		c.JSON(http.StatusBadRequest, gin.H{"error": "请选择文件"})
 		return
 	}
+	if file.Size > maxBytes {
+		mb := int(maxBytes >> 20)
+		if mb < 1 {
+			mb = 1
+		}
+		c.JSON(http.StatusRequestEntityTooLarge, gin.H{"error": "附件不能超过 " + strconv.Itoa(mb) + "MB"})
+		return
+	}
 	price, _ := strconv.Atoi(c.DefaultPostForm("price_points", "0"))
 	f, err := file.Open()
 	if err != nil {
@@ -294,13 +328,18 @@ func (h *Handlers) UploadPostFile(c *gin.Context) {
 		return
 	}
 	defer f.Close()
-	data, err := io.ReadAll(io.LimitReader(f, service.FileMaxBytes+1))
-	if err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": "读取文件失败"})
-		return
-	}
-	att, err := h.PostFile.SaveDraftFile(claims.ID, file.Filename, data, price)
+
+	att, err := h.PostFile.SaveDraftFile(claims.ID, file.Filename, f, price)
 	if err != nil {
+		var maxErr *http.MaxBytesError
+		if errors.As(err, &maxErr) || errors.Is(err, service.ErrAttachmentTooLarge) {
+			mb := int(maxBytes >> 20)
+			if mb < 1 {
+				mb = 1
+			}
+			c.JSON(http.StatusRequestEntityTooLarge, gin.H{"error": "附件不能超过 " + strconv.Itoa(mb) + "MB"})
+			return
+		}
 		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
 		return
 	}
@@ -399,7 +438,14 @@ func (h *Handlers) DownloadPostAttachment(c *gin.Context) {
 	path := h.PostFile.FilePath(att)
 	h.PostFile.IncDownload(att.ID)
 	c.Header("Content-Disposition", "attachment; filename*=UTF-8''"+url.PathEscape(att.Name))
-	c.Header("Content-Type", att.MIME)
+	c.Header("X-Content-Type-Options", "nosniff")
+	c.Header("Content-Security-Policy", "sandbox")
+	ct := att.MIME
+	ext := service.ExtOfFilename(att.Name)
+	if service.IsActiveContentExt(ext) || ct == "" {
+		ct = "application/octet-stream"
+	}
+	c.Header("Content-Type", ct)
 	c.File(path)
 	_ = filepath.Base(path)
 }