sip/transp: add win32 local transport addr fallback

[sreimers]

tcp_conn_local_get function does not always return information about the host address when the socket has been bound to an unspecified address.

fixes baresip/baresip#2797

[sreimers]

@cspiel1 on windows tcp_conn_local_get returns any address if tcp connection is not connected or accepted. So looks like connh is called to early.

https://github.com/baresip/re/blob/main/src/sip/transp.c#L795-L796

(btw. looks like connh err is ignored and overriden by secure path).

The getsockname function does not always return information about the host address when the socket has been bound to an unspecified address, unless the socket has been connected with connect or accept (for example, using ADDR_ANY). A Windows Sockets application must not assume that the address will be specified unless the socket is connected. The address that will be used for the socket is unknown unless the socket is connected when used in a multihomed host. If the socket is using a connectionless protocol, the address may not be available until I/O occurs on the socket.

https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-getsockname

[alfredh]

/**
 * Get local network address of TCP Connection
 *
 * @param tc    TCP Connection
 * @param local Returned local network address
 *
 * @return 0 if success, otherwise errorcode
 */
int tcp_conn_local_get(const struct tcp_conn *tc, struct sa *local)
{
	int err;

	if (!tc || !local)
		return EINVAL;

	sa_init(local, AF_UNSPEC);
	err = getsockname(tc->fdc, &local->u.sa, &local->len);

	if (err < 0) {
		err = RE_ERRNO_SOCK;
		DEBUG_WARNING("conn local get: getsockname(): %m\n", err);
	}

	return err;
}

This only works if the TCP connection is "connected".

[cspiel1]

@cspiel1 on windows tcp_conn_local_get returns any address if tcp connection is not connected or accepted. So looks like connh is called to early.

So, this PR is only a workaround where a fallback address is assigned?

Should we add some kind of wait condition for the TCP connection?

[sreimers]

Looks like pjsip does a similiar fallback, so not sure if there is a reliable way (other than waiting for tcp_estab_handler):

        /* Update (again) local address, just in case local address currently
         * set is different now that asynchronous connect() is started.
         */
        addr_len = sizeof(local_addr);
        if (pj_sock_getsockname(sock, &local_addr, &addr_len)==PJ_SUCCESS) {
            pj_sockaddr *tp_addr = &tcp->base.local_addr;

            /* Some systems (like old Win32 perhaps) may not set local address
             * properly before socket is fully connected.
             */
            if (pj_sockaddr_cmp(tp_addr, &local_addr) &&
                pj_sockaddr_has_addr(&local_addr) &&
                pj_sockaddr_get_port(&local_addr) != 0)
            {
                pj_sockaddr_cp(tp_addr, &local_addr);
                sockaddr_to_host_port(tcp->base.pool, &tcp->base.local_name,
                                      &local_addr);
            }
        }