espressif: always make new client sockets be non-blocking

[dhalbert]

Fixes #7431.

• The new client socket returned by accept() was not set to O_NON_BLOCK all the time, causing it to block until a request was made. Now ensure that it is always set to non-blocking.

Other fixes:

• write()s to eventfds should always be 8 bytes. There was a write that was only 4 bytes (writing the fd). This should actually return an error, but it wasn't checked. @tannewt I don't see that the results of these writes are used anywhere, so I think this change is OK, but you can take a look. Internally they are added to a counter associated with the eventfd.
• Added a check for ctrl-C interrupts in loop where it was not present.

I tested this on a Metro ESP32-S2, and saw that requests from Chrome were not hanging. It is also now possible to ctrl-C the HTTPServer. Before this fix, it was blocking internally on an lwip_recv(), and could not be interrupted.

Also tested the web workflow, which seems to work the same as before. Using HTTPServer on port 80 can cause issues with the web workflow, as might be expected, but these issues are not worse with this fix.

@yousafs and @michalpokusa and anyone else: testing appreciated.

I think this makes adafruit/Adafruit_CircuitPython_HTTPServer#32 not be needed.

[jepler]

Makes sense, didn't test

[michalpokusa]

I can confirm that in my testing on ESP32-S2 TFT Feather, these changes seem to fix the blocking behaviour in Chrome.
Thanks @dhalbert!

The adafruit/Adafruit_CircuitPython_HTTPServer#32 was an experimental way to fix the issue before fix in CircuitPython itself. Right now it is indeed not needed to merge it anymore.

[Sinai]

CircuitPython 8.2.0 , adafruit_wiznet5k 3.0.0 ,
cs = digitalio.DigitalInOut(board.D10)
spi_bus = busio.SPI(board.SCK, MOSI=board.MOSI, MISO=board.MISO)
eth = WIZNET5K(spi_bus, cs)
socket.set_interface(eth)
socket.setdefaulttimeout(0.0) ------>>>>>> timeout
server = Server(socket, "/test")
server.poll()
Hangs and the timeout dont work.

[dhalbert]

@Sinai The choice of non-blocking here is internal; we do timeouts outselves.

[Sinai]

@dhalbert Thank you for your answer.
Yes i know. but it doesnt work and server.poll() hangs forever....

I think when you setup a Server using Wifi is different than using eth.
I have to built my own socket class. and set a timeout on that..