Provide bind_device_by_index_v{4|6} methods for linux.

[Frostie314159]

Hi, it would be nice if we had the functionality for binding a socket to an interface under linux, since that functionality is available.

[Thomasdezeeuw]

A pr to add this would be welcome.

[Frostie314159]

Sure, I'll get to this next week.

[carlocorradini]

Any update?
This is super useful ☺️🥳

[Thomasdezeeuw]

Any update? This is super useful ☺️🥳

No pr was made, but they're still welcome.

[Frostie314159]

I'm in the progress of writing one, however I'm not entirely sure how to go about it.

[Thomasdezeeuw]

I just look at the code and we have Socket::bind_device_by_index_v4:

socket2/src/sys/unix.rs

Lines 2006 to 2045 in c93cdcc

	pub fn bind_device_by_index_v4(&self, interface: Option<NonZeroU32>) -> io::Result<()> {
	let index = interface.map_or(0, NonZeroU32::get);
	unsafe { setsockopt(self.as_raw(), IPPROTO_IP, libc::IP_BOUND_IF, index) }
	}
	/// Sets the value for `IPV6_BOUND_IF` option on this socket.
	///
	/// If a socket is bound to an interface, only packets received from that
	/// particular interface are processed by the socket.
	///
	/// If `interface` is `None`, the binding is removed. If the `interface`
	/// index is not valid, an error is returned.
	///
	/// One can use [`libc::if_nametoindex`] to convert an interface alias to an
	/// index.
	#[cfg(all(
	feature = "all",
	any(
	target_os = "ios",
	target_os = "macos",
	target_os = "tvos",
	target_os = "watchos",
	)
	))]
	#[cfg_attr(
	docsrs,
	doc(cfg(all(
	feature = "all",
	any(
	target_os = "ios",
	target_os = "macos",
	target_os = "tvos",
	target_os = "watchos",
	)
	)))
	)]
	pub fn bind_device_by_index_v6(&self, interface: Option<NonZeroU32>) -> io::Result<()> {
	let index = interface.map_or(0, NonZeroU32::get);
	unsafe { setsockopt(self.as_raw(), IPPROTO_IPV6, libc::IPV6_BOUND_IF, index) }
	}

. Or is this about another setting then IP_BOUND_IF?

[Frostie314159]

That setting is Apple specific, this is about the Linux socket option.

[sciguy16]

I had a similar question and was about to add it myself when I found that SO_BINDTODEVICE option has already been implemented! It was added in 2020 in 6780944, but isn't shown on docs.rs by default due to their platform filtering options.

The default platform is unhelpfully the alphabetically first aarch64-apple-ios, but if we swap it to linux then the full API list is displayed: https://docs.rs/socket2/latest/x86_64-unknown-linux-gnu/socket2/struct.Socket.html#method.bind_device