large session names will silently fail

[folkertvanheusden]

When the initiator uses a large session-name (more than 48 bytes, including 0x00) causing the applesession-data to be more than 64 bytes (see static const size_t MaxBufferSize = 64; in AppleMIDI/src/AppleMIDI_Settings.h) then the library will not respond to the request, not even a reject will be send.

See this zip-file for network traces (included are text-dumps):

network-traces.zip

[lathoub]

Thanks for reporting @folkertvanheusden and some initial checking

I have initiated a fix in this branch using MSVS (I don't have a device at hand here). Can you do a quick check?

Beware: the long session name will be truncated to DefaultSettings::MaxSessionNameLen, but processing should continue (ignoring the remainder of the packet)

[folkertvanheusden]

Yes, that fixes the problem.
Thank you very much for the fast response!

[lathoub]

@folkertvanheusden
Can you also check with shorter session names?

[folkertvanheusden]

Hi, With short (e.g. "aseqdump (129:0)") names it crashes.

[lathoub]

tested with short and long names on an ESP32
@folkertvanheusden pls check again

[lathoub]

Some additional context, if you read this later: the parser is designed to have a minimal memory footprint: small code and memory footprint. The parser buffer is only 64 bytes. Even for longer MIDI messages, 64 bytes is enough - the packet is sliced in 64 bytes and processed in pieces.

For the initial AppleMIDI handshake, the session name can be longer than the 64 bytes buffer, the parser will truncate the session name (DefaultSettings::MaxSessionNameLen) and discard the remainder of the packet.

Arduino-AppleMIDI-Library/src/AppleMIDI_Parser.h

Lines 79 to 102 in be0be95

	#ifdef KEEP_SESSION_NAME
	uint16_t bi = 0;
	while (i < buffer.size())
	{
	if (bi < DefaultSettings::MaxSessionNameLen)
	invitation.sessionName[bi++] = buffer[i++];
	else
	i++;
	}
	invitation.sessionName[bi++] = '\0';
	#else
	while (i < buffer.size())
	i++;
	#endif
	auto retVal = parserReturn::Processed;
	// when given a Session Name and the buffer has been fully processed and the
	// last character is not 'endl', then we got a very long sessionName. It will
	// continue in the next memory chunk of the packet. We don't care, so indicated
	// flush the remainder of the packet.
	// First part if the session name is kept, processing continues
	if (i > minimumLen)
	if (i == buffer.size() && buffer[i] != 0x00)
	retVal = parserReturn::SessionNameVeryLong;

Arduino-AppleMIDI-Library/src/AppleMIDI.hpp

Lines 41 to 45 in be0be95

	else if (retVal == parserReturn::SessionNameVeryLong)
	{
	// purge the rest of the data in controlPort
	while (controlPort.read() >= 0) {}
	}

[folkertvanheusden]

Thanks for the explanation.

I've tested be0be95 and it works fine now with both long and short names.