EthernetUDP in Multicast - packet are sent to EthernetUDP source port instead of the destination port

[NeyVian]

How to reproduce the issue :

EthernetUDP mcast_udp;
IPAddress mcast_group(230, 1, 1, 1);
uint16_t recv_port = 49500;
uint16_t dest_port = 49600;
mcast_udp.beginMulticast(mcast_group, recv_port);
mcast_udp.beginPacket(mcast_group, dest_port);
mcast_udp.write("some data");
mcast_udp.endPacket();

with this code the packet is sent from recv_port to recv_port, and not to dest_port.

This can be fixed in
socket.cpp > bool EthernetClass::socketSendUDP(uint8_t s)
by replacing
W5100.execCmdSn(s, Sock_SEND);
with
W5100.execCmdSn(s, ((W5100.readSnMR(s) & SnMR::MULTI) == SnMR::MULTI) ? Sock_SEND_MAC : Sock_SEND);

[JAndrassy]

it is designed to use the same port for receiving and sending

[NeyVian]

it is designed to use the same port for receiving and sending

can you provide a source please ?

[JAndrassy]

that is not a right use of SEND_MAC. from W5500 datasheet

SEND_MAC transmits data without the automatic ARP-process. In this case, the destination hardware address is acquired from Sn_DHAR configured by host, instead of APR-process.

[NeyVian]

that is not a right use of SEND_MAC. from W5500 datasheet

SEND_MAC transmits data without the automatic ARP-process. In this case, the destination hardware address is acquired from Sn_DHAR configured by host, instead of APR-process.

Multicast don't rely on ARP-process. no need to match an IP to a MAC as the group defines the destination MAC.