Binding to IPV4_UNSPECIFIED/IPV6_UNSPECIFIED

[manekinekko]

Hi. I am working on implementing wasi-sockets for jco. I'd like to make sure I understand this UDP test program correctly.

In crates/test-programs/src/bin/preview2_udp_sample_application.rs:49:

assert_eq!(datagrams[0].remote_address, client_addr);

We are checking the remote_address received from the remote socket matches the client_addr used in the bind call. However, when client is bound to unspecified_addr (0.0.0.0), the resolved remote_address of the remote client ends up being 127.0.0.1 (this is probably spec'ed out in an ietf rfc but I couldn't find which one).

So, the test case is failing because of this:

left: IpSocketAddress::Ipv4(Ipv4SocketAddress { port: 52726, address: (127, 0, 0, 1) })
right: IpSocketAddress::Ipv4(Ipv4SocketAddress { port: 52726, address: (0, 0, 0, 0) })

Also, I tried patching the remote socket resolved address making sure it's 0.0.0.0, which passes the test above, however this breaks the test_udp_dual_stack_conversation:111 test case, because we cannot send a UDP packet to remote address which value is 0.0.0.0 (triggering a -65 errno):

   server_outgoing
        .blocking_send(&[OutgoingDatagram {
            data: msg.data.clone(),
            remote_address: Some(msg.remote_address), // cannot send to 0.0.0.0
        }])
        .unwrap();

Can you please help adding some clarity?

cc @badeend @pchickey @guybedford

[badeend]

I have only skimmed the JCO implementation so I could be wrong, but: my guess is that it has to with the fact that you cache the local address, but don't update it after a stream call.

"connect"ing a socket updates the local binding. This is documented on the stream method in udp.wit:

This function only changes the local socket configuration and does not generate any network traffic. On success, the remote-address of the socket is updated. The local-address may be updated as well, based on the best network path to remote-address.

[guybedford]

I can confirm that this is resolved in the JCO implementation now.