某些情况下用户离开无法触发defer_call/ defer_call Not Triggered for Some Situations

[ChemInCode]

亲爱的wang0618，

祝您一切顺利。我想咨询一下我们的一些用户在访问我们的pywebio应用程序时偶尔遇到的问题。他们偶尔会遇到 tornado.websocket.WebSocketClosedError，这导致无法触发 defer_call。

根据我的观察，我猜测这个问题可能与用户离开应用的方式有关，如果用户在断开网络连接后关闭或刷新浏览器页面，则无法触发 defer_call。

如果您能友好地帮助我找到解决这个问题的办法，我将不胜感激。如果有任何建议或修复措施，请告知我们，这将有助于用户能够更加顺利地使用我们的应用。

非常感谢您的关注和支持。期待您宝贵的指导。

此致，
ChemInCode

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Dear Wang0618,

I hope this message finds you well. I would like to inquire about an occasional issue that some of our users are experiencing while accessing our pywebio application. It seems that they are encountering a tornado.websocket.WebSocketClosedError, which is preventing the defer_call from being triggered.

Based on my observations, I suspect that this issue might be related to the way users are leaving the application, specifically when they close or refresh the browser page. If a user closes or refreshes the browser page after disconnecting their internet connection, the defer_call does not get triggered.

I would greatly appreciate it if you could kindly assist me in finding a solution to this matter. If there are any suggested steps or fixes, please let me know, as it would be of great help to ensure a smoother experience for our users.

Thank you very much for your attention and support. Looking forward to your valuable guidance.

Best regards,
ChemInCode

Traceback (most recent call last):
conn.write_message(msg)
self.context.write_message(json.dumps(message))
raise WebSocketClosedError()
tornado.websocket.WebSocketClosedError

[wang0618]

defer_call() is designed to be triggered no matter how the session ends. If the reality is that it will not be triggered in some cases, then this should be a bug.
Are you using the latest version of pywebio? If not, please upgrade the pywebio version first. If you have used the latest version of pywebio, please let me know and I will troubleshoot the bug in the code

[wang0618]

I got it!

In your code, you actually call defer_call() after put_buttons(). That is to say the on_close() callback is registered to pywebio after put_buttons().

If you put defer_call at the beginning of the pywebio app function, it will work as expected

def index():    
    @pywebio.session.defer_call
    def on_close():
        print('someone left')

content = pywebio.input.input()
pywebio.output.put_buttons(['show'],[lambda:pywebio.output.put_text(content)])

[wang0618]

@pywebio.session.defer_call is just a syntax sugar for on_close = pywebio.session.defer_call(on_close), so the defer_call() is registered to pywebio only when the code run to here.

[ChemInCode]

非常感谢您的回复！您的答案非常有帮助！只要我把defer_call放到app pywebio app function 的开头，那么无论我在会话中途断开网络连接还是以其它非正常手段关闭会话，on_close都能被执行。只不过断开网络连接的话，on_close会在一分钟左右之后才被执行而不是立刻被执行。但如果我加入了SSL并且在会话中途断开网络连接，那么似乎无论我等待多久，on_close还是不会被执行。如下面代码所示：

---

Thank you very much for your response! Your answer has been extremely helpful! By placing defer_call at the beginning of the pywebio app function, no matter if I disconnect the network connection or close the session using other unconventional means during the session, on_close can still be executed. The only difference is that if I disconnect the network connection, on_close will be executed after about a minute instead of immediately. However, if I add SSL and disconnect the network connection during the session, it seems that no matter how long I wait, on_close will not be executed, as shown in the code below:

import tornado.ioloop
from pywebio.platform.tornado import webio_handler
import pywebio,os

def index():
    @pywebio.session.defer_call
    def on_close():
        print('someone left')
        
    content = pywebio.input.input()
    pywebio.output.put_buttons(['show'],[lambda:pywebio.output.put_text(content)])
    
def make_app():
    return tornado.web.Application([
        (r"/", webio_handler(index)),
    ])

if __name__ == '__main__':
    http_server = tornado.httpserver.HTTPServer(make_app(), ssl_options={
           "certfile": os.path.join(os.path.abspath("."), "1_test_domain.crt"),
           "keyfile": os.path.join(os.path.abspath("."), "2_test_domain.key"),
    })
    http_server.listen(443)
    tornado.ioloop.IOLoop.instance().start()

[wang0618]

You need add websocket_ping_interval config to tornado.web.Application:

tornado.web.Application(
        [
            (r"/", webio_handler(index)),
        ],
        websocket_ping_interval=10,
 )

Accroding to tornado's doc, it enable tornado to detect if the websocket has failed without being properly closed.

If you use start_server() to start your pywebio app, pywebio will add this parameter to tornado for you.

[ChemInCode]

非常感谢您耐心的回答！现在pywebio 应用程序可以正常工作了！

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Thank you very much for your patient assistance! The pywebio app is now working perfectly!