Re: [lwip-devel] lwip_recvfrom(sock == 0)

[address@hidden]

Am 24.09.2020 um 18:05 schrieb Gisle Vanem:
> Hello list.
>
> I have patched MicroPython [1] with LwIP support on Windows.
> And running some tcp/ip related test shows a funny
> behaviour in LwIP. E.g. from:
>    
> https://github.com/micropython/micropython/blob/master/tests/extmod/usocket_tcp_basic.py
>
>    # recv() on a fresh socket should raise ENOTCONN
>    s = socket.socket()
>    try:
>      s.recv(1)
>    except OSError as er:
>
>      print("ENOTCONN:", er.args[0] == errno.ENOTCONN)
>
> The trace in LwIP shows:
>    src/api/sockets.c(1754): lwip_socket(PF_INET, SOCK_STREAM, 0) = 0
>    src/api/sockets.c(1243): lwip_recvfrom(0, 0E88A030, 1, 0x0, ..)
>    src/api/sockets.c(976): lwip_recv_tcp: top while sock->lastdata=00000000
>
> Now the MicroPython test hangs forever. Nothing happens
> with this socket 0. It's unconnected, so how could this socket
> ever receive a single byte?

It should indeed not wait here, but return an error. Would you mind
adding a bug in our savannah bugtracker to ensure this does not get
forgotten?

>
> Using the same .py-test in the real CPython 3.6, it immediately
> returns the expected:
>    py -3 extmod\usocket_tcp_basic.py
>    ENOTCONN: True
>
> Could it be some of my 'LWIP_x' options are messed up?

Hmm, while this could change with options, it still should not behave
like you saw.

Regards,
Simon

>
> [1] https://github.com/micropython/micropython