From fac3e82e24754c9a1a79b247c8a0a9a169c34a8c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Konrad=20Gr=C3=A4fe?= <kgraefe@paktolos.net>
Date: Wed, 3 May 2023 08:52:05 +0200
Subject: [PATCH] tcp: connect: Add bind_device option
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Add option to bind an outgoing TCP connection to a specific device,
identified by its name.

Signed-off-by: Konrad Gräfe <kgraefe@paktolos.net>
---
 src/adapters/tcp.rs | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/src/adapters/tcp.rs b/src/adapters/tcp.rs
index 9e9fc5a..66aec3b 100644
--- a/src/adapters/tcp.rs
+++ b/src/adapters/tcp.rs
@@ -10,7 +10,11 @@ use mio::event::{Source};
 use socket2::{Socket, Domain, TcpKeepalive, Type, Protocol};
 
 use std::net::{SocketAddr};
+#[cfg(unix)]
+use std::ffi::{CString};
 use std::io::{self, ErrorKind, Read, Write};
+#[cfg(target_os = "macos")]
+use std::num::NonZeroU32;
 use std::ops::{Deref};
 use std::mem::{forget, MaybeUninit};
 #[cfg(target_os = "windows")]
@@ -25,11 +29,19 @@ pub const INPUT_BUFFER_SIZE: usize = u16::MAX as usize; // 2^16 - 1
 
 #[derive(Clone, Debug, Default)]
 pub struct TcpConnectConfig {
+    bind_device: Option<String>,
     source_address: Option<SocketAddr>,
     keepalive: Option<TcpKeepalive>,
 }
 
 impl TcpConnectConfig {
+    /// Bind the TCP connection to a specific interface, identified by its name. On other systems
+    /// this opion will be ignored.
+    pub fn with_bind_device(mut self, device: String) -> Self {
+        self.bind_device = Some(device);
+        self
+    }
+
     /// Enables TCP keepalive settings on the socket.
     pub fn with_keepalive(mut self, keepalive: TcpKeepalive) -> Self {
         self.keepalive = Some(keepalive);
@@ -98,6 +110,25 @@ impl Remote for RemoteResource {
             socket.bind(&source_address.into())?;
         }
 
+        #[cfg(unix)]
+        if let Some(bind_device) = config.bind_device {
+            let device = CString::new(bind_device)?;
+
+            #[cfg(not(target_os = "macos"))]
+            socket.bind_device(Some(device.as_bytes()))?;
+
+            #[cfg(target_os = "macos")]
+            match NonZeroU32::new(unsafe { libc::if_nametoindex(device.as_ptr()) }) {
+                Some(index) => socket.bind_device_by_index(Some(index))?,
+                None => {
+                    return Err(io::Error::new(
+                        ErrorKind::NotFound,
+                        "Bind device interface not found",
+                    ))
+                }
+            }
+        }
+
         match socket.connect(&peer_addr.into()) {
             #[cfg(unix)]
             Err(e) if e.raw_os_error() != Some(libc::EINPROGRESS) => return Err(e),