AsyncEventSourceMessage::send() fails when message size > TCP_SND_BUF

[ul-gh]

Hi,

In file AsyncEventSource.cpp: When the SSE message size is greater than the size reported by AsyncClient::space(), which is the LWIP TCP send buffer space (CONFIG_LWIP_TCP_SND_BUF_DEFAULT, set to 5744 bytes), the event message is not sent correctly.

In function AsyncEventSourceMessage::send(), the call to "client->add()" is made using the "_data" message buffer.
While "client->add()" has a maximum message size limit of TCP_SND_BUF size, this is only added to the "_sent" bytes data member, but that property is never evaluated. There is no offset added to the _data buffer index, nor is the _data buffer ever consumed. (Until deletion, that is).

From the code:

  const size_t len = _len - _sent;
  if(client->space() < len){
    return 0;
  }
  size_t sent = client->add((const char *)_data, len);  <====== No offset, always starts from beginning of buffer
  if(client->canSend())
    client->send();
  _sent += sent;
  return sent; 
}

This simply does not work.

The following code does, this was just now tested with SSE messages of 16 kB size:

// This could also return void as the return value is not used.
// Leaving as-is for compatibility...
size_t AsyncEventSourceMessage::send(AsyncClient *client) {
    if (_sent >= _len) {
      return 0;
    }
    const size_t len_to_send = _len - _sent;
    auto position = reinterpret_cast<const char*>(_data + _sent * sizeof(*_data));
    const size_t sent_now = client->write(position, len_to_send);
    _sent += sent_now;
    return sent_now;
}

PR follows; please let me know if there are any issues.

[ul-gh]

Please find a test bench header file containing plain C strings of 1...16 kB size for testing:
dummy_text.h

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