Listening on same IPv4 and IPv6 port?

[jcorporation]

I am using the http-server from the example and run it with ./example -l http://[::]:8080. Should mongoose listen also on IPv4 0.0.0.0:8080 in this case?

Plattform is: Linux t14 6.2.0-25-generic #25-Ubuntu SMP PREEMPT_DYNAMIC Fri Jun 16 17:05:07 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

cat /proc/sys/net/ipv6/bindv6only
0

wget http://127.0.0.1:8080 -O - 
--2023-07-18 23:16:14--  http://127.0.0.1:8080/
Connecting to 127.0.0.1:8080... failed: Connection refused.

[cpq]

@jcorporation why should it, if you have specified the ipv6 listening address ?

[jcorporation]

Older versions of mongoose had this behavior.

As I understand the socket code: not setting IPV6_V6ONLY enables ipv4 and ipv6 connections.

I looked into the mongoose source: If I remove this code from mg_open_listener() function:

#if defined(IPV6_V6ONLY)
    } else if (c->loc.is_ip6 &&
               (rc = setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, (char *) &on,
                                sizeof(on))) != 0) {
      // See #2089. Allow to bind v4 and v6 sockets on the same port
      MG_ERROR(("setsockopt(IPV6_V6ONLY): %d", MG_SOCK_ERR(rc)));
#endif

Mongoose accepts IPv6 and IPv4 connections. It would be great if you could add an compile time option to enable/disable this behavior.

It was changed with #2089.

[comburent]

The description in #2089 seems contradictory: it fixes "not listening to the same port on both ipv4 and ipv6" by not listening to both? It's unclear what exactly was the original issue there

[comburent]

@jcorporation why should it, if you have specified the ipv6 listening address ?

Per https://www.rfc-editor.org/rfc/rfc3493#section-5.3

This socket option restricts AF_INET6 sockets to IPv6 communications
only. As stated in section <3.7 Compatibility with IPv4 Nodes>,
AF_INET6 sockets may be used for both IPv4 and IPv6 communications.

Reading the RFC, the IPV6_V6ONLY is oriented for specific scenarios, not as a default.

Further references:

• https://www.kernel.org/doc/html/latest/networking/ip-sysctl.html#proc-sys-net-ipv6-variables

[jcorporation]

Should I maintain my own patch or is there any chance that this behavior will change? A compile time option would be perfect for me.

[cpq]

@jcorporation

What if we change :

#if defined(IPV6_V6ONLY)

to

#if MG_IPV6_V6ONLY

And define MG_IPV6_V6ONLY as 0 by default, would that work ?

[jcorporation]

This sounds good!