Questions about SPDM message read/write between requester and responder

[owen126315]

I am trying to understand how requester send SPDM message over MCTP to responder through using wireshark to capture the tcp packets between requester and responder.

And I found that the captured packets seem mismatched from the SPDM message format and MCTP message format.

Is SOCKET_SPDM_COMMAND_NORMAL necessary for SPDM request/respond?
Why the write function would split the request into four packets?
Why the mctp header information is not included in the packet payload?

spdm-emu/spdm_emu/spdm_emu_common/command.c

Lines 258 to 315 in c8ac4ca

	bool send_platform_data(const SOCKET socket, uint32_t command,
	const uint8_t *send_buffer, size_t bytes_to_send)
	{
	bool result;
	uint32_t request;
	uint32_t transport_type;
	request = command;
	result = write_data32(socket, request);
	if (!result) {
	return result;
	}
	printf("Platform port Transmit command: ");
	request = htonl(request);
	dump_data((uint8_t *)&request, sizeof(uint32_t));
	printf("\n");
	result = write_data32(socket, m_use_transport_layer);
	if (!result) {
	return result;
	}
	printf("Platform port Transmit transport_type: ");
	transport_type = ntohl(m_use_transport_layer);
	dump_data((uint8_t *)&transport_type, sizeof(uint32_t));
	printf("\n");
	result = write_multiple_bytes(socket, send_buffer,
	(uint32_t)bytes_to_send);
	if (!result) {
	return result;
	}
	switch (command) {
	case SOCKET_SPDM_COMMAND_SHUTDOWN:
	close_pcap_packet_file();
	break;
	case SOCKET_SPDM_COMMAND_NORMAL:
	if (m_use_transport_layer == SOCKET_TRANSPORT_TYPE_MCTP) {
	/* Append mctp_header_t for PCAP*/
	mctp_header_t mctp_header;
	mctp_header.header_version = 0;
	mctp_header.destination_id = 0;
	mctp_header.source_id = 0;
	mctp_header.message_tag = 0xC0;
	append_pcap_packet_data(&mctp_header,
	sizeof(mctp_header),
	send_buffer, bytes_to_send);
	} else {
	append_pcap_packet_data(NULL, 0, send_buffer,
	bytes_to_send);
	}
	break;
	}
	return true;
	}

[jyao1]

SPDM-EMU implements a mechanism to send message via socket, not MCTP.

MCTP or DOE is just treated as payload in the TCP socket message.

[owen126315]

(Please correct me if I am wrong :))
Therefore, SPDM-EMU does not construct complete MCTP packets.
Instead, it just adding the MCTP message header to the front of SPDM messages to construct MCTP messages, the MCTP transport header is not included. Only the green block is constructed.

If I want to encode the SPDM messages into complete MCTP packets, do I need to construct it by myself?

[jyao1]

yes, you are right. In current implementation, we just add MCTP message header. There is no MCTP transport header. The purpose of the SPDM-EMU is to test SPDM, not MCTP.

Feel free to proposal a patch to add MCTP transport header, if you see there is such need.

[maxwell652]

yes, you are right. In current implementation, we just add MCTP message header. There is no MCTP transport header. The purpose of the SPDM-EMU is to test SPDM, not MCTP.

Feel free to proposal a patch to add MCTP transport header, if you see there is such need.

Hi Yao，
Do you know where the official MCTP protocol source code library is located? Because I couldn't find any relevant repository under the DMTF organization

[jyao1]

Do you know where the official MCTP protocol source code library is located? Because I couldn't find any relevant repository under the DMTF organization

No. I don't know.