incomplete message received

[sanderkob]

AsyncTelegram2 version 2.2.1 and 2.2.2
board ESP8266
No change to default format style, so it is HTML.
Built with VisualStudioCode PlatformIO, default board params.

I occasionally get an incomplete error, generated in this code

AsyncTelegram2/src/AsyncTelegram2.cpp

Lines 240 to 253 in 5260273

	if (err)
	{
	log_error("deserializeJson() failed\n");
	log_debug("%s", err.c_str());
	log_error();
	log_error(m_rxbuffer);
	// Skip this message id due to the impossibility to parse correctly
	m_lastUpdateId = m_rxbuffer.substring(m_rxbuffer.indexOf(F("\"update_id\":")) + strlen("\"update_id\":")).toInt() + 1;
	// int64_t chat_id = m_rxbuffer.substring( m_rxbuffer.indexOf("{\"id\":") + strlen("{\"id\":")).toInt();
	m_rxbuffer = "";
	// Inform the user about parsing error (blocking)
	sendTo(message.chatId, "[ERROR] - No memory: inrease buffer size with \"setJsonBufferSize(buf_size)\" method");
	return MessageNoData;

The json buffer is large enough, I checked this by sending additional info to my chat (the code added to AsyncTelegram2.cpp is in https://gist.github.com/sanderkob/693cf1c7664d2048fde183263edff221 )
I try to solve this without serial logging.
The output from the additional code is:

[ERROR] - No memory: inrease buffer size with "setJsonBufferSize(buf_size)" method
[ERROR] - deserializeJson() failed
IncompleteInput
[ERROR] - rxbuffer

{"ok":true,"result":[
[ERROR] - JsonBufferSize
4096
[ERROR] - rxbuffer len msg
23
[ERROR] - content len msg
23

It appears that the intended message to be received is {"ok": true,"result": []} (with 25 chars) and deserialization fails because the last two chars are actually missing.
The content of m_rxbuffer as sent to my chat is {"ok": true,"result": [ with 21 chars
However, m_rxbuffer len and content len are both 23 chars.

So, the primary question is: why is the message truncated (]} missing)?
In addition, why are spaces missing in the message that shows the content of m_rxbuffer?

To further investigate, I looked at the code
https://github.com/cotestatnt/AsyncTelegram2/blob/526027396a3ac208d36c54f8eea09c06a51a866d/src/AsyncTelegram2.cpp#L164C9-L173

If the intent is to timeout after one sec, I would expect the code to be
for (uint32_t timeout = millis(); (millis() - timeout < 1000) && pos < len;)
to ensure that the loop exits after 1000 milliseconds or when pos reaches len.
However, I do not think this is relevant to the problem at hand.

[sanderkob]

Some additional information.
I have two telegram bots on ESP8266 that use AsyncTelegram2; the error occurs in both.
Occurrence is of the order of 1 in 10^5 (10 ppm), i.e. once in every 100.000 getUpdates..
The error is independent of :
rx,tx buffersize - setBufferSizes() 512, 2048
json buffersize - setJsonBufferSize() 1024, 2048
TCP_MSS size - lwip version 2.0.3, low memory (default) TCP_MSS = 536, high bandwith TCP_MSS = 1460
CPU frequenty - 80, 160 MHz

Are there any other factors to check?
Since the error is not detrimental to my applicatrion I could safely ignore it.