Linux: UDP listen: Receive broadcasts (mimic Windows behavior) #149

kgraefe · 2023-03-22T07:48:49Z

On Windows, when listening on a specific IP address, you also receive corresponding subnet broadcasts and global broadcasts (Ipv4Addr::BROADCAST) received on the interface matching the IP.

In order to mimic that behavior on Linux, this change adds ingress filters to UDP/Listen so one can listen on Ipv4Addr::UNSPECIFIED but drop any packet that is not received on the specified interface or any of the specified IP addresses.

@lemunozm As I said in #142 I'm not sure if that's too much code for a too specific problem to be merged upstream. But I'll leave it here for you to decide.

lemunozm · 2023-03-22T08:12:24Z

Ok, I'll check later, but I think your PR goes with the message-io philosophy of abstracting different platform behaviors

lemunozm · 2023-03-22T08:15:18Z

I mean, with this change, a Linux user can achieve the same behavior that a Windows user, isn't it?

kgraefe · 2023-03-22T08:19:46Z

I mean, with this change, a Linux user can achieve the same behavior that a Windows user, isn't it?

yes

lemunozm · 2023-03-22T08:21:49Z

I'm ok with this PR if we extend the option docs to highlight just that.

kgraefe · 2023-03-22T08:27:27Z

but in the application I still have to use compile conditions:

// Listen on any IP but filter to only allow packets incoming on the specific interface and
// with one of the following destination addresses:
// - the interface's local IP,
// - the corresponding subnet broadcast IP, or
// - the global broadcast IP
#[cfg(target_os = "linux")]
let (socket_id, _) = node_handler.network().listen_with(
    TransportListen::Udp(UdpListenConfig {
        broadcast: true,
        ingress_addresses: vec![
            interface.local_ip.into(),
            interface.broadcast_ip.into(),
            Ipv4Addr::BROADCAST.into(),
        ],
        ingress_interface: Some(interface.index),
        ..Default::default()
    }),
    SocketAddrV4::new(Ipv4Addr::UNSPECIFIED, port),
)?;

// Windows does all of the above automatically for sockets listening on the interface's
// local IP.
#[cfg(target_os = "windows")]
let (socket_id, _) = node_handler.network().listen_with(
    TransportListen::Udp(UdpListenConfig {
        broadcast: true,
        ..Default::default()
    }),
    SocketAddrV4::new(interface.local_ip, port),
)?;

kgraefe · 2023-03-22T08:31:39Z

where interface is of a custom type with the information retrieved from nix::ifaddrs::getifaddrs() and nix::net::if_::if_nametoindex()

kgraefe · 2023-03-22T08:39:36Z

maybe I can rework that to a flag mimic_windows or sth. (I don't have a good name yet) where message-io tries to figure out the ingress filter parameters internally

lemunozm · 2023-03-22T09:21:48Z

I really like the last idea! In that way, your app code will be really simple; that is what we looking for.

If the nix dependency is significantly big or annoying, it could exist under a feature. But for now, I think we can live with it.

lemunozm · 2023-03-22T09:22:37Z

By the way, feel free to add your project to the README open-source list if you want.

Signed-off-by: Konrad Gräfe <kgraefe@paktolos.net>

kgraefe · 2023-03-23T08:14:26Z

I'm done :-)

lemunozm · 2023-03-23T09:39:38Z

src/adapters/udp.rs

+ #[cfg(target_os = "linux")]
+ fn accept(&self, mut accept_remote: impl FnMut(AcceptedType<'_, Self::Remote>)) {


I get a little lost here; why the Linux behavior changes so much now?

The reason is that I need to use nix::sys::socket::recvmsg() in order to pass the control_buffer which receives the ingress IP address. And as that's the core of the function it affects the rest of the function as well.

Ok, I see.

I'm thinking, that maybe we can use the non-linux accept() for all platforms (as before), and only if the ingress config is enabled and we are in linux run this accept() as a special case.

The main advantage of this is that the normal use case (99% of time) will use the usual accept() which are probably a little bit faster and simple to debug/understand if, in the future, any user finds an issue.

lemunozm · 2023-03-23T09:40:50Z

src/adapters/udp.rs

@@ -231,6 +324,66 @@ impl Local for LocalResource {
 }
 }

+ #[cfg(target_os = "linux")]
+ fn accept(&self, mut accept_remote: impl FnMut(AcceptedType<'_, Self::Remote>)) {
+ let mut input_buffer = vec![0; MAX_LOCAL_PAYLOAD_LEN];


Do we really need this to be a vector? Could it be an array to avoid allocations?

probably not, I will change that

lemunozm

Looks good! I left a last minor comment change, but not mandatory.

lemunozm · 2023-03-23T15:46:37Z

src/adapters/udp.rs

+ #[cfg(target_os = "linux")]
+ if !self.ingress_addresses.is_empty() {
+ self.accept_filtered(accept_remote);
+ return
+ }


lemunozm · 2023-03-23T15:50:23Z

src/adapters/udp.rs

+ #[cfg(target_os = "linux")]
+ match addr {
+ SocketAddr::V4 { .. } => {
+ socket::setsockopt(socket.as_raw_fd(), sockopt::Ipv4PacketInfo, &true)?
+ }
+ SocketAddr::V6 { .. } => {
+ socket::setsockopt(socket.as_raw_fd(), sockopt::Ipv6RecvPacketInfo, &true)?
+ }
+ }
+
+ #[cfg(target_os = "linux")]
+ let mut ingress_addresses = vec![];
+
+ #[cfg(target_os = "linux")]
+ if config.receive_broadcasts {


Minor last change, don't mandatory. Could the match addr { part and the let mut ingress_addresses = vec![]; be under the if config.receive_broadcasts { condition?

Yes for the match addr and it should be as the setsockopt()s are not necessary otherwise

No for the ingress_addresses as it has to land in the LocalResource later on. Do you think it would be better to use an Option<Vec<..>> here? Currently I'm using ingress_addresses.is_empty() as an indicator whether or not the option has been set. I'm not sure if it's better allocation-wise, but semantically it probably would be.

I have no strong opinion but it makes sense!

This option mimics the Windows behavior to also receive broadcasts on sockets bound to a specific IP. Signed-off-by: Konrad Gräfe <kgraefe@paktolos.net>

lemunozm · 2023-03-23T16:47:05Z

Thanks for this @kgraefe !

kgraefe changed the title ~~Udp listen ingress filter~~ Linux: UDP listen: Add ingress filters Mar 22, 2023

kgraefe force-pushed the udp-listen-ingress-filter branch 2 times, most recently from 6df858a to 97eb83a Compare March 22, 2023 12:53

udp: listen: Rename broadcast config entry to send_broadcasts

480a7fb

Signed-off-by: Konrad Gräfe <kgraefe@paktolos.net>

kgraefe force-pushed the udp-listen-ingress-filter branch from 97eb83a to c785981 Compare March 22, 2023 12:54

lemunozm reviewed Mar 23, 2023

View reviewed changes

kgraefe changed the title ~~Linux: UDP listen: Add ingress filters~~ Linux: UDP listen: Receive broadcasts (mimic Windows behavior) Mar 23, 2023

kgraefe force-pushed the udp-listen-ingress-filter branch from c785981 to 1e62022 Compare March 23, 2023 12:18

kgraefe requested a review from lemunozm March 23, 2023 12:19

lemunozm approved these changes Mar 23, 2023

View reviewed changes

udp: listen: linux: Implement receive_broadcasts option

b746f33

This option mimics the Windows behavior to also receive broadcasts on sockets bound to a specific IP. Signed-off-by: Konrad Gräfe <kgraefe@paktolos.net>

kgraefe force-pushed the udp-listen-ingress-filter branch from 1e62022 to b746f33 Compare March 23, 2023 16:19

kgraefe requested a review from lemunozm March 23, 2023 16:20

lemunozm approved these changes Mar 23, 2023

View reviewed changes

lemunozm merged commit e6c01b8 into lemunozm:master Mar 23, 2023

kgraefe deleted the udp-listen-ingress-filter branch March 23, 2023 19:05

lemunozm mentioned this pull request Mar 24, 2023

Release v0.15.0 #142

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Linux: UDP listen: Receive broadcasts (mimic Windows behavior) #149

Linux: UDP listen: Receive broadcasts (mimic Windows behavior) #149

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lemunozm commented Mar 23, 2023

		#[cfg(target_os = "linux")]
		fn accept(&self, mut accept_remote: impl FnMut(AcceptedType<'_, Self::Remote>)) {

Linux: UDP listen: Receive broadcasts (mimic Windows behavior) #149

Linux: UDP listen: Receive broadcasts (mimic Windows behavior) #149

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