select() seems to signal data to read from a shut down socket [solved]

[DrSegatron]

I use select() to catch read and exception events:

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returncount=select(max_socket,&read,NULL,&exception,NULL);

This has worked fine before, recv()ing at read events and disconnecting at exception events. But now after a few months I need to build on this code for another project I have some problems.

Connections to server socket and reads from connection sockets work fine, but If I do a graceful disconnect (FIN), instead of immediately getting an exception event as before, it instead sets a read event, which fails as there is no data to recv():

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V (268658) wifi.c: tcp_server_task(): 2 socket(s)
V (269268) wifi.c: tcp_server_task(): select (1 sockets active)
W (269268) wifi.c: tcp_server_task(): Recv returned 0! ESP_OK

This flag is never cleared and the program is in an infinite select()-recv()-select()-recv() loop for quite some while until something times out and the exception event is flagged.

Has an update broken something or is my program flawed in some way?

[WiFive]

Your code should recognize zero length read as a graceful disconnect.

[DrSegatron]

I do that as a "workaround" now, are you saying this is fine and by design? Why this change, it certainly gave me exceptions before.

But if it's the intended behaviour, I'm a bit more at ease

Edit: Perhaps there's a difference between graceful shutdown and a connection reset?

[WiFive]

Yes graceful shutdown can allow you to finish writing before you close. Basically other side is politely saying "I'm done writing, are you done writing?"