A bad connection causes an inifinite loop (at least on an ESP32 but I think also on an Arduino)

[Jeroen88]

The problem of #56 is even bigger: ::ClientRead() and ::ClientWrite() are called in bearssl ssl_io.c. If the socket client connection (Client *c) is lost or reset by the peer, both c->read(buf, len) and c->write(buf, len) will return a 0 (at least on the ESP32 but I think this is standard behavior also on an Arduino) thus causing an infinite loop in static int run_until(br_sslio_context *ctx, unsigned target) in ssl_io.c.

In my situation this problem occurs on a bad WiFi connection, but I think it may also occur on a bad tcp/ip connection or if the peer closes the connection.

One solution would be to add a timeout in the run_until() function, but I think it is better not to touch the original library. So I made adaptations to ::ClientRead() and ::ClientWrite() that involve static variables, which I think is a bad programming habit, but this is the only way to record a state between calls to these functions.
I did not introduce a new timeout value, but use the value of the socket client c->getTimeout().

int BearSSLClient::clientRead(void *ctx, unsigned char *buf, size_t len)
{
  static bool notAvailableFlag = false;
  static uint32_t lastNotAvailableMillis;

  Client* c = (Client*)ctx;

  if (!c->connected() && !c->available()) {

    return -1;			// connection lost or closed by peer (in ssl_io.c low_read, which points to this function, fails on a -1. which it should if a connection is lost)
  }

  int result = c->read(buf, len);
  if (result == 0) {
    if(notAvailableFlag) {
      if(millis() - lastNotAvailableMillis > c->getTimeout()) {
        notAvailableFlag = false;  // for the next round

        return -1;		// timout read (in ssl_io.c low_read, which points to this function, fails on a -1. which it should if a connection is lost or closed by peer)
      }
    } else {
      notAvailableFlag = true; // First time no data available
      lastNotAvailableMillis = millis();
    }
  
    delay(10);			// Needed?
  } else {
    notAvailableFlag = false; // This flag was set but new data is available, so start again
  }

#ifdef DEBUGSERIAL
  DEBUGSERIAL.print("BearSSLClient::clientRead - ");
  DEBUGSERIAL.print(result);
  DEBUGSERIAL.print(" - ");  
  for (size_t i = 0; i < result; i++) {
    byte b = buf[i];

    if (b < 16) {
      DEBUGSERIAL.print("0");
    }
    DEBUGSERIAL.print(b, HEX);
  }
  DEBUGSERIAL.println();
#endif

  return result;
}

int BearSSLClient::clientWrite(void *ctx, const unsigned char *buf, size_t len)
{
  static bool notAvailableForWriteFlag = false;
  static uint32_t lastNotAvailableForWriteMillis;

  Client* c = (Client*)ctx;

  if (!c->connected()) {

    return -1;			// connection lost or closed by peer (in ssl_io.c low_write, which points to this function, fails on a -1. which it should if a connection is lost)
  }

  int result = c->write(buf, len);
  if (result == 0) {

    if(notAvailableForWriteFlag) {
      if(millis() - lastNotAvailableForWriteMillis > c->getTimeout()) {
        notAvailableForWriteFlag = false;  // for the next round

        return -1;		// timout write (in ssl_io.c low_write, which points to this function, fails on a -1. which it should if a connection is lost or closed by peer)
      }
    } else {
      notAvailableForWriteFlag = true; // First time impossible to write data to peer
      lastNotAvailableForWriteMillis = millis();
    }

    delay(10);			// Needed?
  } else {
    notAvailableForWriteFlag = false; // This flag was set but new data was written, so start again
  }

#ifdef DEBUGSERIAL
  DEBUGSERIAL.print("BearSSLClient::clientWrite - ");
  DEBUGSERIAL.print(len);
  DEBUGSERIAL.print(" - ");
  for (size_t i = 0; i < len; i++) {
    byte b = buf[i];

    if (b < 16) {
      DEBUGSERIAL.print("0");
    }
    DEBUGSERIAL.print(b, HEX);
  }
  DEBUGSERIAL.println();
#endif

  return result;
}

[Jeroen88]

Here also should be added: if(errorCode() != BR_ERR_OK) return 0; This will check for (among others) the connection being dropped during SSL negotiation.

[jhochs]

This issue is causing poor performance of a program I'm running on a MKR 1500 to communicate via MQTT: about half the time when connecting to MQTT the program hangs indefinitely. I tried implementing @Jeroen88's clientRead() and clientWrite() but then it invariably won't connect at all. Any ideas why this is?