Data transferring between peers on the localhost doesn't work on macOS

[kovewnikov]

Hey team, first of all, I want to thank you for adding IPv6 support and other features to the original ENet—nicely done! However, I'm encountering an issue on my Mac

Minimum repro steps:

Server code

#include <iostream>
#define ENET_IMPLEMENTATION
#include <enet.h>

int main(int argc, const char * argv[])
{
    if (enet_initialize() != 0)
    {
        return 1;
    }
    
    ENetAddress localAddress;
    memset(&localAddress, 0, sizeof(ENetAddress));
    enet_address_set_host (&localAddress, "127.0.0.1");
    localAddress.port = 1234;
    ENetHost* server = enet_host_create (&localAddress, 32, 2, 0, 0);
    if (!server)
    {
        exit (1);
    }
    
    while (true)
    {
        ENetEvent event;
        if (enet_host_service (server, &event, 1000) > 0)
        {
            printf("Got event %d\n", event.type);
        }
    }
    
    enet_host_destroy(server);
    enet_deinitialize();
    return 0;
}

Client code

#include <iostream>
#define ENET_IMPLEMENTATION
#include <enet.h>

int main(int argc, const char * argv[])
{
    if (enet_initialize () != 0)
    {
        return 1;
    }
    
    ENetAddress localAddress;
    memset(&localAddress, 0, sizeof(ENetAddress));
    enet_address_set_host (&localAddress, "127.0.0.1");
    localAddress.port = 8973;
    ENetHost* client = enet_host_create (&localAddress, 1, 2, 0, 0);
    if (client == NULL)
    {
        exit (1);
    }
    
    ENetAddress remoteAddress = localAddress;
    remoteAddress.port = 1234;
    ENetPeer* remoteServer = enet_host_connect (client, &remoteAddress, 2, 0);
    if (remoteServer == NULL)
    {
        exit (1);
    }
    
    ENetEvent event;
    /* Wait up to 5 seconds for the connection attempt to succeed. */
    if (enet_host_service (client, & event, 5000) > 0 &&
        event.type == ENET_EVENT_TYPE_CONNECT)
    {
        std::printf("Connection to server is succeeded.\n");
    }
    else
    {
        enet_peer_reset (remoteServer);
        std::printf("Connection to server is failed. Either the 5 seconds are up or a disconnect event was received.\n");
    }

    enet_host_destroy(client);
    enet_deinitialize();
    return 0;
}

Client output

Connection to server is failed. Either the 5 seconds are up or a disconnect event was received.

So, as you can see, the client never connects to the server.

Notes:

• It seems like the culprit is enet_socket_receive - because after receiving the message via recvmsg the sockaddr_in6 sin actually contains sockaddr_in (the field sin6_family is set to AF_INET instead of AF_INET6) ¯\_(ツ)_/¯
• Explicitly setting the IPv6 localAddress during socket creation/binding, like this:
  enet_address_set_host (&localAddress, "::ffff:127.0.0.1"); doesn't help
• Explicitly setting the localAddress as "any" like this:
  localAddress.host = ENET_HOST_ANY;
  instead of
  enet_address_set_host (&localAddress, "127.0.0.1"); doesn't help.

Environment:

• macOS: Sequoia 15.2
• Xcode 16.2
• Apple M1 max

[zpl-zak]

Hey,

I don't have a way to validate this issue on IPv6 stack right now unfortunately, but if the proposed fix works well and does not affect IPv4-only set up anyhow, we'd gladly accept a PR to get it merged in.

Thank you for looking into the issue!