From 1dfd15d8f3626eb91ff6238155d3bfbfaed59cf5 Mon Sep 17 00:00:00 2001
From: Thomas de Zeeuw <thomasdezeeuw@gmail.com>
Date: Mon, 21 Dec 2020 12:18:07 +0100
Subject: [PATCH] Add Socket::(bind_)device

Backport of commit 3851430dec41c204d6219a84c47ca6885622a98e.
---
 src/socket.rs   | 26 ++++++++++++++++++++
 src/sys/unix.rs | 64 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 90 insertions(+)

diff --git a/src/socket.rs b/src/socket.rs
index c69262ca..1f1fcc92 100644
--- a/src/socket.rs
+++ b/src/socket.rs
@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(target_os = "linux")]
+use std::ffi::{CStr, CString};
 use std::fmt;
 use std::io::{self, Read, Write};
 use std::net::{self, Ipv4Addr, Ipv6Addr, Shutdown};
@@ -412,6 +414,30 @@ impl Socket {
         self.inner.set_mark(mark)
     }
 
+    /// 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(target_os = "linux")]
+    pub fn device(&self) -> io::Result<Option<CString>> {
+        self.inner.device()
+    }
+
+    /// 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(target_os = "linux")]
+    pub fn bind_device(&self, interface: Option<&CStr>) -> io::Result<()> {
+        self.inner.bind_device(interface)
+    }
+
     /// Gets the value of the `IPV6_UNICAST_HOPS` option for this socket.
     ///
     /// Specifies the hop limit for ipv6 unicast packets
diff --git a/src/sys/unix.rs b/src/sys/unix.rs
index 5f3c27c9..87794002 100644
--- a/src/sys/unix.rs
+++ b/src/sys/unix.rs
@@ -9,16 +9,24 @@
 // except according to those terms.
 
 use std::cmp;
+#[cfg(target_os = "linux")]
+use std::ffi::{CStr, CString};
 use std::fmt;
 use std::io;
 use std::io::{ErrorKind, Read, Write};
 use std::mem;
+#[cfg(target_os = "linux")]
+use std::mem::MaybeUninit;
 use std::net::Shutdown;
 use std::net::{self, Ipv4Addr, Ipv6Addr};
 use std::ops::Neg;
 #[cfg(feature = "unix")]
 use std::os::unix::net::{UnixDatagram, UnixListener, UnixStream};
 use std::os::unix::prelude::*;
+#[cfg(target_os = "linux")]
+use std::ptr;
+#[cfg(target_os = "linux")]
+use std::slice;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::time::{Duration, Instant};
 
@@ -563,6 +571,62 @@ impl Socket {
         unsafe { self.setsockopt(libc::SOL_SOCKET, libc::SO_MARK, mark as c_int) }
     }
 
+    #[cfg(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;
+        let len = unsafe {
+            cvt(libc::getsockopt(
+                self.fd,
+                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) }))
+        }
+    }
+
+    #[cfg(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)
+        };
+
+        unsafe {
+            cvt(libc::setsockopt(
+                self.fd,
+                libc::SOL_SOCKET,
+                libc::SO_BINDTODEVICE,
+                value.cast(),
+                len as libc::socklen_t,
+            ))
+            .map(|_| ())
+        }
+    }
+
     pub fn unicast_hops_v6(&self) -> io::Result<u32> {
         unsafe {
             let raw: c_int = self.getsockopt(libc::IPPROTO_IPV6, libc::IPV6_UNICAST_HOPS)?;