micropython-samples/uasyncio_iostream/poll

Context: uasyncio StreamReader and StreamWriter objects hang indefinitely under fault conditions.

Under fault conditions uasyncio expects to receive POLLERR or POLLHUP conditions from the poll instance. In my testing this never occurs.

Testing was of client connections. Socket type was SOCK_STREAM. Two fault conditions were tested:

1. Server outage.
2. Socket closed by another coroutine.

Testing was performed with a server running under the Unix build. Clients were tested on:

1. Unix build (on same machine as server).
2. ESP8266.
3. ESP32.

Results were as follows. Numbers represent the event no. received from the poll instance. "No trigger" means that the poll instance produced no response after the fault. On all platforms where the client was reading, a server outage produced a POLLIN (1) response. On all but ESP32 this repeated indefinitely causing the client endlessly to read empty bytes objects.

Numbers are base 10. Mode refers to the client mode. Expected refers to uasyncio.

Mode	Platform	Outage	Closure	Expected
Read	Unix	1	32	9 or 17
Read	ESP8266	1	No trigger	9 or 17
Read	ESP32	1 (once)	No trigger	9 or 17
Write	Unix	OSError	32	12 or 20
Write	ESP8266	OSError	No trigger	12 or 20
Write	ESP832	OSError	No trigger	12 or 20

1 == POLLIN
4 == POLLOUT
9 == (POLLIN & POLLERR)
17 == (POLLIN & POLLHUP)
12 == (POLLOUT & POLLERR)
20 == (POLLOUT & POLLHUP)
32 == I have no idea.

Test scripts may be found here:
Server - can run in read or write mode
Read client
Write client