优化JWT解码逻辑，添加错误处理以防止空用户ID导致的权限拒绝

src/jwt/jwt.cpp

@@ -1,6 +1,8 @@
 #include "jwt.h"
 
 #include <chrono>
+#include <print>
+
 #include <jwt-cpp/jwt.h>
 
 
@@ -23,9 +25,13 @@ extern "C"
 
     auto get_payload(const char* token) -> char*
     {
-        auto decoded_token = jwt::decode(token);
-        auto payload       = decoded_token.get_payload_claim("user_id").as_string();
-        return strdup(payload.c_str());
+        try {
+            auto decoded_token = jwt::decode(token);
+            auto payload       = decoded_token.get_payload_claim("user_id").as_string();
+            return strdup(payload.c_str());
+        } catch (...) {
+            return nullptr;
+        }
     }
 
     auto verify_token(const char* token, const char* secret) -> int

src/server/auth/delete.c

@@ -82,6 +82,11 @@ int user_delete_handler(mg_connection* conn, void* cbdata)
     }
 
     char* user_id = get_payload(form.token);
+    if (!user_id) {
+        res_permission_denied(conn);
+        delete_form_dtor(&form);
+        return 1;
+    }
 
     if (form.user_id && strcmp(user_id, form.user_id)) {
         int perm1;

src/server/auth/repasswd.c

@@ -150,6 +150,11 @@ int user_repasswd_handler(mg_connection* conn, void* cbdata)
     }
 
     char* user_id = get_payload(form.token);
+    if (!user_id) {
+        res_permission_denied(conn);
+        repasswd_form_dtor(&form);
+        return 1;
+    }
 
     if (form.user_id && strcmp(user_id, form.user_id)) {
         impl_others(conn, user_id, &form);

src/server/study/problems.c

@@ -255,6 +255,11 @@ int problems_handler(mg_connection* conn, void* cbdata)
         res_need_token(conn);
     } else {
         char* user_id = get_payload(form.token);
+        if (!user_id) {
+            res_permission_denied(conn);
+            problem_form_dtor(&form);
+            return 1;
+        }
         int result;
         int flag = get_user_permission(user_id, &result);
         if (!flag) {

src/server/study/sets.c

@@ -204,6 +204,11 @@ int sets_handler(mg_connection* conn, void* cbdata)
         res_need_token(conn);
     } else {
         char* user_id = get_payload(form.token);
+        if (!user_id) {
+            res_permission_denied(conn);
+            set_form_dtor(&form);
+            return 1;
+        }
         int result;
         int flag = get_user_permission(user_id, &result);
         if (!flag) {