Fast writing into a socket causes hang

[leoshusar]

I'm using this library in PlatformIO on STM32F401 with both W5100 and W5500. In my application I'm using HTTP server and WebSocket server - that's where I've discovered this issue. When I have WS connected and I'm sending some HTTP requests, it randomly gets stuck in this loop, just stays there forever. SnIR returns 0 and SnSR returns 0x14.

I've managed to replicate the issue with just this piece of code:

#include <Ethernet.h>

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };

EthernetServer server{23};

void setup() {
  Ethernet.init(PB6);
  Ethernet.begin(mac);

  server.begin();
}

void loop() {
  auto client = server.accept();

  while (true) {
    if (client) {
      client.write("xxx");
      client.write("xxx");
    } else {
      break;
    }
    delay(10);
  }
}

This fails 100% of the time, just quicker than my main app, like in 1-10 seconds.

My observations:

• when I keep only one client.write("xxx");, it looks like it works just fine (I waited for just like 20 minutes, not too long)
• when I connected two clients and was alternating the writing between them, it also looked stable

I don't know if I'm just doing something wrong or if this is a bug in this library / in STM SPI / in Wiznet / ...

Any ideas please?
Thanks!