feat(share): add OG preview for home route share links

Intercept /home route for social media bots viewing cloudreve://share
paths and render OG preview directly.

middleware/frontend.go

@@ -1,12 +1,17 @@
 package middleware
 
 import (
-	"github.com/cloudreve/Cloudreve/v4/application/dependency"
-	"github.com/cloudreve/Cloudreve/v4/pkg/util"
-	"github.com/gin-gonic/gin"
 	"io"
 	"net/http"
+	"net/url"
 	"strings"
+
+	"github.com/cloudreve/Cloudreve/v4/application/constants"
+	"github.com/cloudreve/Cloudreve/v4/application/dependency"
+	filemanagerfs "github.com/cloudreve/Cloudreve/v4/pkg/filemanager/fs"
+	"github.com/cloudreve/Cloudreve/v4/pkg/sharepreview"
+	"github.com/cloudreve/Cloudreve/v4/pkg/util"
+	"github.com/gin-gonic/gin"
 )
 
 // FrontendFileHandler 前端静态文件处理
@@ -50,8 +55,12 @@ func FrontendFileHandler(dep dependency.Dep) gin.HandlerFunc {
 			return
 		}
 
+		if renderSharePreviewForBot(c) {
+			return
+		}
+
 		// 不存在的路径和index.html均返回index.html
-		if (path == "/index.html") || (path == "/") || !fs.Exists("/", path) {
+		if path == "/index.html" || path == "/" || !fs.Exists("/", path) {
 			// 读取、替换站点设置
 			settingClient := dep.SettingProvider()
 			siteBasic := settingClient.SiteBasic(c)
@@ -84,3 +93,95 @@ func FrontendFileHandler(dep dependency.Dep) gin.HandlerFunc {
 		c.Abort()
 	}
 }
+
+func renderSharePreviewForBot(c *gin.Context) bool {
+	path := c.Request.URL.Path
+	if path != "/home" && path != "/home/" {
+		return false
+	}
+	if !util.IsSocialMediaBot(c.GetHeader("User-Agent")) {
+		return false
+	}
+	shareURI := parseShareURI(c.Query("path"))
+	if shareURI == nil {
+		return false
+	}
+	shareID := shareURI.ID("")
+	if shareID == "" {
+		return false
+	}
+
+	html, err := sharepreview.RenderOGPage(c, sharepreview.Options{
+		ID:        shareID,
+		Password:  shareURI.Password(),
+		SharePath: shareURI.PathTrimmed(),
+	})
+	if err != nil {
+		return false
+	}
+	c.Header("Content-Type", "text/html; charset=utf-8")
+	c.String(http.StatusOK, html)
+	c.Abort()
+	return true
+}
+
+func parseShareURI(raw string) *filemanagerfs.URI {
+	if raw == "" {
+		return nil
+	}
+	shareURI, err := filemanagerfs.NewUriFromString(raw)
+	if err != nil {
+		sanitized := sanitizeInvalidPercentEscapes(raw)
+		if sanitized != raw {
+			shareURI, err = filemanagerfs.NewUriFromString(sanitized)
+		}
+	}
+	if err != nil && strings.Contains(raw, "%") {
+		unescaped, err := url.QueryUnescape(raw)
+		if err == nil {
+			shareURI, err = filemanagerfs.NewUriFromString(unescaped)
+			if err != nil {
+				sanitized := sanitizeInvalidPercentEscapes(unescaped)
+				if sanitized != unescaped {
+					shareURI, err = filemanagerfs.NewUriFromString(sanitized)
+				}
+			}
+		}
+	}
+	if err != nil {
+		return nil
+	}
+	if shareURI.FileSystem() != constants.FileSystemShare {
+		return nil
+	}
+	return shareURI
+}
+
+func sanitizeInvalidPercentEscapes(raw string) string {
+	if !strings.Contains(raw, "%") {
+		return raw
+	}
+
+	var b strings.Builder
+	b.Grow(len(raw))
+	for i := 0; i < len(raw); i++ {
+		if raw[i] != '%' {
+			b.WriteByte(raw[i])
+			continue
+		}
+		if i+2 < len(raw) && isHexDigit(raw[i+1]) && isHexDigit(raw[i+2]) {
+			b.WriteByte('%')
+			b.WriteByte(raw[i+1])
+			b.WriteByte(raw[i+2])
+			i += 2
+			continue
+		}
+		// Replace stray % to avoid url.Parse failures.
+		b.WriteString("%25")
+	}
+	return b.String()
+}
+
+func isHexDigit(b byte) bool {
+	return ('0' <= b && b <= '9') || ('a' <= b && b <= 'f') || ('A' <= b && b <= 'F')
+}