重組前檢查點:根目錄 main package

logout.go

@@ -0,0 +1,68 @@
+package main
+
+import (
+	"log"
+	"net/http"
+	"strings"
+
+	"gorm.io/gorm"
+)
+
+// logoutHandler 處理 POST /logout，依 Content-Type 分流（與登入一致）：
+// 表單走瀏覽器流程（需通過 CSRF 驗證，失敗時以 403 重繪目前狀態頁），
+// JSON 走 API 流程。登出為冪等操作——查無 Session 亦視為成功；資料庫
+// 刪除失敗僅記錄，仍清除 Cookie 並回應成功（Session 最遲於效期到期失效）。
+func logoutHandler(db *gorm.DB) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		ct := r.Header.Get("Content-Type")
+		var isForm bool
+		switch {
+		case strings.HasPrefix(ct, "application/json"):
+		case strings.HasPrefix(ct, "application/x-www-form-urlencoded"),
+			strings.HasPrefix(ct, "multipart/form-data"):
+			isForm = true
+		default:
+			writeError(w, http.StatusUnsupportedMediaType, "Content-Type 須為 application/json 或表單")
+			return
+		}
+
+		if isForm {
+			if err := r.ParseForm(); err != nil {
+				renderAccountPage(w, r, db, http.StatusBadRequest, "無法解析表單內容")
+				return
+			}
+			if !verifyCSRF(r) {
+				renderAccountPage(w, r, db, http.StatusForbidden, "表單驗證失敗，請重新整理頁面後再試")
+				return
+			}
+		}
+
+		if c, err := r.Cookie(sessionCookieName); err == nil {
+			if err := deleteSession(db, c.Value); err != nil {
+				log.Printf("logout: %v", err)
+			}
+		}
+		clearSessionCookie(w, r)
+
+		if isForm {
+			// PRG：以 303 導向 /login 顯示登入表單，避免重新整理重複送出。
+			http.Redirect(w, r, "/login", http.StatusSeeOther)
+			return
+		}
+		w.WriteHeader(http.StatusNoContent)
+	}
+}
+
+// clearSessionCookie 以 Max-Age=0 清除瀏覽器的 Session Cookie（與
+// setSessionCookie 對稱，屬性一致以免因 Path 或 Secure 差異清不掉）。
+func clearSessionCookie(w http.ResponseWriter, r *http.Request) {
+	http.SetCookie(w, &http.Cookie{
+		Name:     sessionCookieName,
+		Value:    "",
+		Path:     "/",
+		MaxAge:   -1,
+		HttpOnly: true,
+		SameSite: http.SameSiteLaxMode,
+		Secure:   r.TLS != nil,
+	})
+}