Fix assertion errors

[Bmooij]

I don't know if it is correct.

For my project I'm using the Async Event Source Plugin from ESPAsyncWebServer.

My client contained a bug that initialized a SSE connection every second. After some time my ESP32 crashes and reboots. Needless to say I had to fix that bug in my client.

But from my opinion, the server should not crash/reboot from that issue. So I tried to pin point the problem.

A little background, when a SSE client connects, a welcome message is send back:

void Events::onLocalWebSocketConnected(AsyncEventSourceClient *client) {
    client->send("welcome", "message", getId());
}

First I wrote a python script that simulates my client bug. (Connect every second to the ESP32, for 500 times)

from sseclient import SSEClient
import threading
import time

def main():
    for x in range(0, 500):
        print("Connnection %d" % x)
        x = threading.Thread(target=sseClient)
        x.start()
        time.sleep(1)

def sseClient():
    messages = SSEClient('http://{ip}/events')

if __name__ == "__main__":
    main()

And indeed after some time the ESP32 crashes. I figured out that there where 2 issues. 1 is ESPAsyncWebServer related (I will open a pull request for that too) and 1 is AsyncTCP related.

The error that occurred that is AsyncTCP related:
assertion "invalid socket state for sent callback" failed: file "/home/runner/work/esp32-arduino-lib-builder/esp32-arduino-lib-builder/esp-idf/components/lwip/lwip/src/core/tcp.c", line 1842, function: tcp_sent

0x4008e2dc: invoke_abort at /home/runner/work/esp32-arduino-lib-builder/esp32-arduino-lib-builder/esp-idf/components/esp32/panic.c line 155
0x4008e50d: abort at /home/runner/work/esp32-arduino-lib-builder/esp32-arduino-lib-builder/esp-idf/components/esp32/panic.c line 170
0x401214bb: __assert_func at ../../../.././newlib/libc/stdlib/assert.c line 63
0x4013b6da: tcp_sent at /home/runner/work/esp32-arduino-lib-builder/esp32-arduino-lib-builder/esp-idf/components/lwip/lwip/src/core/tcp.c line 1842
0x40176640: AsyncClient::_error(signed char) at .pio\libdeps\development\AsyncTCP\src\AsyncTCP.cpp line 851
0x4017694b: _async_service_task(void*) at .pio\libdeps\development\AsyncTCP\src\AsyncTCP.cpp line 1211
0x4008a991: vPortTaskWrapper at /home/runner/work/esp32-arduino-lib-builder/esp32-arduino-lib-builder/esp-idf/components/freertos/port.c line 143

The problem was that an error occurred and the socket state was not LISTEN. When tcp_sent is called without the state LISTEN, an assertion error is thrown.

[Bmooij]

With this fix, the fix in ESPAsyncWebServer is irrelevant

[me-no-dev]

ha! those are changes in LwIP that I was not aware of :) definitely no need to call the functions with NULL anymore. But also interesting how nobody else had that error