Sockets of multi connect server's client do not close on minor change from eco server to normal server and normal client

ℹ️
After I use it (https://github.com/realpython/materials/blob/master/python-sockets-tutorial/multiconn-client.py) with a small change (minor change from echo server to normal server) -

- after sending and receiving messages from the client and server, the client does not close; or
- all data.messages have been exausted, the client does not close.

https://stackoverflow.com/questions/70640602/sockets-in-python-client-not-closing-after-event-read-write-events-in-multi-conn

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Describe the bug
After minor change from echo server to normal server:

- after sending and receiving messages from the client and server, the client does not close; or
- all data.messages have been exausted, the client does not close.

To Reproduce
Provided in the stackoverflow question

Expected behavior
The client should close. Looks like it does not get into the if not recv_data code while I was checking. The program should reach the code. No major changes to the code has been made other than sending data from messages section. :

if not recv_data:
    print("closing connection", data.connid)
    sel.unregister(sock)
    sock.close()

Screenshots
Added to link:
https://stackoverflow.com/questions/70640602/sockets-in-python-client-not-closing-after-event-read-write-events-in-multi-conn

Desktop (please complete the following information):

• OS: [e.g. iOS] Win, Linux

Additional context
NA

从 python-sockets-tutorial/multiconn-client.py 和链接的 Stack Overflow 复现开始；将 echo-server 的更改与所描述的 normal-server 流程进行比较。确认消息耗尽后，客户端会到达所示的 if not recv_data 分支并关闭。完成意味着客户端在所描述的两种情况下都能可靠地关闭。