commit 3851430dec41c204d6219a84c47ca6885622a98e
Author: kolapapa <kola@kolapapas-MacBook-Pro.local>
Date:   Sun Dec 20 14:02:52 2020 +0100

    Add Socket::(bind_)device
    
    Co-authored-by: Thomas de Zeeuw <thomasdezeeuw@gmail.com>

diff --git a/src/sys/unix.rs b/src/sys/unix.rs
index 72097ae..1a0f24e 100644
--- a/src/sys/unix.rs
+++ b/src/sys/unix.rs
@@ -7,6 +7,8 @@
 // except according to those terms.
 
 use std::cmp::min;
+#[cfg(all(feature = "all", target_os = "linux"))]
+use std::ffi::{CStr, CString};
 #[cfg(not(target_os = "redox"))]
 use std::io::{IoSlice, IoSliceMut};
 use std::mem::{self, size_of, MaybeUninit};
@@ -19,6 +21,8 @@
 use std::os::unix::net::{UnixDatagram, UnixListener, UnixStream};
 #[cfg(feature = "all")]
 use std::path::Path;
+#[cfg(all(feature = "all", target_os = "linux"))]
+use std::slice;
 use std::time::Duration;
 use std::{io, ptr};
 
@@ -867,6 +871,73 @@ pub fn set_mark(&self, mark: u32) -> io::Result<()> {
         unsafe { setsockopt::<c_int>(self.inner, libc::SOL_SOCKET, libc::SO_MARK, mark as c_int) }
     }
 
+    /// Gets the value for the `SO_BINDTODEVICE` option on this socket.
+    ///
+    /// This value gets the socket binded device's interface name.
+    ///
+    /// This function is only available on Linux.
+    #[cfg(all(feature = "all", target_os = "linux"))]
+    pub fn device(&self) -> io::Result<Option<CString>> {
+        // TODO: replace with `MaybeUninit::uninit_array` once stable.
+        let mut buf: [MaybeUninit<u8>; libc::IFNAMSIZ] =
+            unsafe { MaybeUninit::<[MaybeUninit<u8>; libc::IFNAMSIZ]>::uninit().assume_init() };
+        let mut len = buf.len() as libc::socklen_t;
+        unsafe {
+            syscall!(getsockopt(
+                self.inner,
+                libc::SOL_SOCKET,
+                libc::SO_BINDTODEVICE,
+                buf.as_mut_ptr().cast(),
+                &mut len,
+            ))?;
+        }
+        if len == 0 {
+            Ok(None)
+        } else {
+            // Allocate a buffer for `CString` with the length including the
+            // null terminator.
+            let len = len as usize;
+            let mut name = Vec::with_capacity(len);
+
+            // TODO: use `MaybeUninit::slice_assume_init_ref` once stable.
+            // Safety: `len` bytes are writen by the OS, this includes a null
+            // terminator. However we don't copy the null terminator because
+            // `CString::from_vec_unchecked` adds its own null terminator.
+            let buf = unsafe { slice::from_raw_parts(buf.as_ptr().cast(), len - 1) };
+            name.extend_from_slice(buf);
+
+            // Safety: the OS initialised the string for us, which shouldn't
+            // include any null bytes.
+            Ok(Some(unsafe { CString::from_vec_unchecked(name) }))
+        }
+    }
+
+    /// Sets the value for the `SO_BINDTODEVICE` 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` or an empty string it removes the binding.
+    ///
+    /// This function is only available on Linux.
+    #[cfg(all(feature = "all", target_os = "linux"))]
+    pub fn bind_device(&self, interface: Option<&CStr>) -> io::Result<()> {
+        let (value, len) = if let Some(interface) = interface {
+            (interface.as_ptr(), interface.to_bytes_with_nul().len())
+        } else {
+            (ptr::null(), 0)
+        };
+        syscall!(setsockopt(
+            self.inner,
+            libc::SOL_SOCKET,
+            libc::SO_BINDTODEVICE,
+            value.cast(),
+            len as libc::socklen_t,
+        ))
+        .map(|_| ())
+    }
+
     /// Get the value of the `SO_REUSEPORT` option on this socket.
     ///
     /// For more information about this option, see [`set_reuse_port`].
diff --git a/tests/socket.rs b/tests/socket.rs
index 11a3d9c..75890af 100644
--- a/tests/socket.rs
+++ b/tests/socket.rs
@@ -1,3 +1,5 @@
+#[cfg(all(feature = "all", target_os = "linux"))]
+use std::ffi::CStr;
 #[cfg(any(windows, target_vendor = "apple"))]
 use std::io;
 #[cfg(unix)]
@@ -271,3 +273,19 @@ fn keepalive() {
     ))]
     assert_eq!(socket.keepalive_retries().unwrap(), 10);
 }
+
+#[cfg(all(feature = "all", target_os = "linux"))]
+#[test]
+fn device() {
+    const INTERFACE: &str = "lo0\0";
+    let interface = CStr::from_bytes_with_nul(INTERFACE.as_bytes()).unwrap();
+    let socket = Socket::new(Domain::IPV4, Type::STREAM, None).unwrap();
+
+    assert_eq!(socket.device().unwrap(), None);
+
+    socket.bind_device(Some(interface)).unwrap();
+    assert_eq!(socket.device().unwrap().as_deref(), Some(interface));
+
+    socket.bind_device(None).unwrap();
+    assert_eq!(socket.device().unwrap(), None);
+}