初始提交：姜十三论坛 Jiang13 Forum

轻量自用论坛，Go 单二进制 + React SPA 内嵌 + SQLite。

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

middleware/presence.go

@@ -0,0 +1,39 @@
+package middleware
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+
+	"github.com/gin-gonic/gin"
+	"github.com/jiang13/forum/service"
+)
+
+const VisitorCookieName = "j13_vid"
+
+// PresenceMiddleware 记录当前请求的浏览活跃（会员或游客）
+func PresenceMiddleware(online *service.OnlineService) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		if uid, ok := c.Get(CtxUserID); ok {
+			if id, ok := uid.(uint); ok && id > 0 {
+				online.Ping(id)
+				c.Next()
+				return
+			}
+		}
+		vid, err := c.Cookie(VisitorCookieName)
+		if err != nil || vid == "" {
+			vid = newVisitorID()
+			c.SetCookie(VisitorCookieName, vid, 86400, "/", "", false, true)
+		}
+		online.PingGuest(vid)
+		c.Next()
+	}
+}
+
+func newVisitorID() string {
+	b := make([]byte, 16)
+	if _, err := rand.Read(b); err != nil {
+		return hex.EncodeToString([]byte("fallback-visitor-id"))
+	}
+	return hex.EncodeToString(b)
+}