Socket::ttl and Socket::set_ttl don't work with IPv6 sockets.

[dvolodin7]

ttl and set_ttl methods return an error on IPv6 sockets.

Current implementations are limited to IPv4 only:

pub fn ttl(&self) -> io::Result<u32> {
        unsafe {
            getsockopt::<c_int>(self.as_raw(), sys::IPPROTO_IP, sys::IP_TTL).map(|ttl| ttl as u32)
        }
    }
}

and

 pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
     unsafe { setsockopt(self.as_raw(), sys::IPPROTO_IP, sys::IP_TTL, ttl as c_int) }
}

For IPv6 address family the proper implementations should be like

pub fn ttl(&self) -> io::Result<u32> {
        unsafe {
            getsockopt::<c_int>(self.as_raw(), sys::IPPROTO_IPV6, sys::IP_TTL).map(|ttl| ttl as u32)
        }
    }
}

and

 pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
     unsafe { setsockopt(self.as_raw(), sys::IPPROTO_IPV6, sys::IP_TTL, ttl as c_int) }
}

Unfortunately, I haven't found a reliable way to get the address family/domain of the socket instance, something like

pub fn domain(&self) -> io::Result<Domain>

So the possible solutions are:

1. To implement Socket::domain method, which is very system-dependent and may include:

• Socket::local_addr check, which may fail for unbound sockets on some systems
• Using getsockopt with SO_DOMAIN option, which is not available on some systems.

3. Add methods like Socket::ttl_v6 and Socket::set_ttl_v6 - and leave the problem of detecting the proper address family to a library user.

[Thomasdezeeuw]

Basically the same issue as #413, we need IPv4 and IPv6 versions.

We should just give everything in the IPPROTO_IP group (

socket2/src/socket.rs

Lines 1077 to 1082 in 4c55898

	/// Socket options for IPv4 sockets, get/set using `IPPROTO_IP`.
	///
	/// Additional documentation can be found in documentation of the OS.
	/// * Linux: <https://man7.org/linux/man-pages/man7/ip.7.html>
	/// * Windows: <https://docs.microsoft.com/en-us/windows/win32/winsock/ipproto-ip-socket-options>
	impl Socket {

) a _ipv4 suffix. Same for IPPROTO_IPV6 (

socket2/src/socket.rs

Lines 1529 to 1534 in 4c55898

	/// Socket options for IPv6 sockets, get/set using `IPPROTO_IPV6`.
	///
	/// Additional documentation can be found in documentation of the OS.
	/// * Linux: <https://man7.org/linux/man-pages/man7/ipv6.7.html>
	/// * Windows: <https://docs.microsoft.com/en-us/windows/win32/winsock/ipproto-ipv6-socket-options>
	impl Socket {

).

[dvolodin7]

Looks like a proper solution.

[famfo]

The IPv6 equivalent of IP_TTL is IPV6_UNICAST_HOPS (by RFC 3493). The option is implemented in socket2.
Finding that option took me very long, so I think some more documentation would be required.