Adds bind_device_by_index to android and linux

This PR adds bind_device_by_index to android and linux OS, which binds a
socket to a device by its interface index.

Author: ningyuan-wang

Cargo.toml

@@ -51,7 +51,7 @@ targets = [
 features = ["all"]
 
 [target."cfg(unix)".dependencies]
-libc = "0.2.171"
+libc = "0.2.172"
 
 [target.'cfg(windows)'.dependencies.windows-sys]
 version = "0.52"

src/sys/unix.rs

@@ -17,8 +17,10 @@ use std::net::{Ipv4Addr, Ipv6Addr};
 #[cfg(all(
     feature = "all",
     any(
+        target_os = "android",
         target_os = "ios",
         target_os = "visionos",
+        target_os = "linux",
         target_os = "macos",
         target_os = "tvos",
         target_os = "watchos",
@@ -1805,6 +1807,38 @@ impl crate::Socket {
         .map(|_| ())
     }
 
+    /// Gets the value for the `SO_BINDTOIFINDEX` option on this socket.
+    ///
+    /// This value gets the socket binded device's interface index.
+    #[cfg(all(feature = "all", any(target_os = "android", target_os = "linux")))]
+    pub fn device_index(&self) -> io::Result<Option<NonZeroU32>> {
+        let index_raw = unsafe {
+            getsockopt::<libc::c_uint>(self.as_raw(), libc::SOL_SOCKET, libc::SO_BINDTOIFINDEX)?
+        };
+        Ok(NonZeroU32::new(index_raw))
+    }
+
+    /// Sets the value for `SO_BINDTOIFINDEX` option on this socket.
+    ///
+    /// If a socket is bound to an interface, only packets received from that
+    /// particular interface are processed by the socket. Note that this only
+    /// works for some socket types, particularly `AF_INET` sockets.
+    ///
+    /// If `interface` is `None`, the binding is removed. If the `interface`
+    /// index is not valid, an error is returned.
+    #[cfg(all(feature = "all", any(target_os = "android", target_os = "linux")))]
+    pub fn bind_device_by_index(&self, interface: Option<NonZeroU32>) -> io::Result<()> {
+        let index = interface.map_or(0, NonZeroU32::get);
+        unsafe {
+            setsockopt(
+                self.as_raw(),
+                libc::SOL_SOCKET,
+                libc::SO_BINDTOIFINDEX,
+                index as c_int,
+            )
+        }
+    }
+
     /// Sets the value for the `SO_SETFIB` option on this socket.
     ///
     /// Bind socket to the specified forwarding table (VRF) on a FreeBSD.

tests/socket.rs

@@ -982,6 +982,38 @@ fn device() {
     panic!("failed to bind to any device.");
 }
 
+#[cfg(all(feature = "all", any(target_os = "android", target_os = "linux")))]
+#[test]
+#[ignore = "setting `SO_BINDTOIFINDEX` requires the `CAP_NET_RAW` capability (works when running as root)"]
+fn device_by_index() {
+    const INTERFACE_INDICES: &[u32; 3] = &[1, 2, 3];
+
+    let socket = Socket::new(Domain::IPV4, Type::STREAM, None).unwrap();
+    assert_eq!(socket.device().unwrap(), None);
+
+    for if_index in INTERFACE_INDICES {
+        if let Err(err) = socket.bind_device_by_index(std::num::NonZeroU32::new(*if_index)) {
+            if matches!(err.raw_os_error(), Some(libc::ENODEV)) {
+                eprintln!("error binding to interface index (`{if_index}`): {err}");
+                continue;
+            } else {
+                panic!("unexpected error binding device: {}", err);
+            }
+        }
+        assert_eq!(
+            socket.device_index().unwrap(),
+            std::num::NonZeroU32::new(*if_index)
+        );
+
+        socket.bind_device_by_index(None).unwrap();
+        assert_eq!(socket.device_index().unwrap(), None);
+        // Just need to do it with one interface.
+        return;
+    }
+
+    panic!("failed to bind to any device by IFINDEX.");
+}
+
 #[cfg(all(
     feature = "all",
     any(