add cache for gen msg

src/plugins/nonebot_hk_reporter/post.py

@@ -19,9 +19,10 @@ class Post:
     target_name: Optional[str] = None
     compress: bool = False
     override_use_pic: Optional[bool] = None
-
     pics: list[str] = field(default_factory=list)
 
+    _message: Optional[list] = None
+
     def _use_pic(self):
         if not self.override_use_pic is None:
             return self.override_use_pic
@@ -97,6 +98,7 @@ class Post:
         self.pics.insert(0, b64image)
 
     async def generate_messages(self):
+        if self._message is None:
             await self._pic_merge()
             msgs = []
             text = ''
@@ -117,7 +119,8 @@ class Post:
                 msgs.append("[CQ:image,file={url}]".format(url=pic))
             if self.compress:
                 msgs = [''.join(msgs)]
-        return msgs
+            self._message = msgs
+        return self._message
 
     def __str__(self):
         return 'type: {}\nfrom: {}\ntext: {}\nurl: {}\npic: {}'.format(