feat(socket): support advanced routing configuration for client socket

Enable binding to a specific network interface, applying a firewall mark, or selecting a routing table (FIB) for outgoing packets on supported platforms.

crates/irtt-client/src/config.rs

@@ -231,6 +231,15 @@ pub struct SocketConfig {
     /// `None` binds to an unspecified address with an ephemeral port matching
     /// the selected remote address family.
     pub bind_addr: Option<SocketAddr>,
+    /// Network interface to bind this socket to (`SO_BINDTODEVICE`).
+    #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
+    pub bind_to_device: Option<String>,
+    /// Firewall mark applied to outgoing packets (`SO_MARK`).
+    #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
+    pub mark: Option<u32>,
+    /// FreeBSD FIB used for routing this socket (`SO_SETFIB`).
+    #[cfg(target_os = "freebsd")]
+    pub fib: Option<u32>,
     /// Optional IPv4 TTL or IPv6 hop limit applied to sent packets.
     ///
     /// `None` leaves the platform default unchanged. Values must fit in the

crates/irtt-client/src/socket.rs

@@ -12,6 +12,14 @@ use crate::{
     socket_options::apply_ttl_to_socket,
 };
 
+#[cfg(any(
+    target_os = "android",
+    target_os = "freebsd",
+    target_os = "fuchsia",
+    target_os = "linux"
+))]
+use crate::socket_options::apply_routing_options;
+
 pub(crate) fn validate_open_timeouts(timeouts: &[Duration]) -> Result<(), ClientError> {
     if timeouts.is_empty() {
         return Err(ClientError::NoOpenTimeouts);
@@ -115,6 +123,13 @@ fn create_connected_udp_socket(
     remote: SocketAddr,
 ) -> Result<UdpSocket, ClientError> {
     let socket = create_prebind_udp_socket(config, remote)?;
+    #[cfg(any(
+        target_os = "android",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "linux"
+    ))]
+    apply_routing_options(&socket, config, remote)?;
     let bind_addr = config.bind_addr.unwrap_or_else(|| {
         if remote.is_ipv4() {
             SocketAddr::from(([0, 0, 0, 0], 0))

crates/irtt-client/src/socket_options.rs

@@ -5,11 +5,64 @@ use std::{
 
 use socket2::SockRef;
 
+#[cfg(any(
+    target_os = "android",
+    target_os = "freebsd",
+    target_os = "fuchsia",
+    target_os = "linux"
+))]
+use socket2::Socket;
+
 use crate::{
     config::{MAX_DSCP_CODEPOINT, MAX_TTL},
     error::ClientError,
 };
 
+#[cfg(any(
+    target_os = "android",
+    target_os = "freebsd",
+    target_os = "fuchsia",
+    target_os = "linux"
+))]
+pub(crate) fn apply_routing_options(
+    socket: &Socket,
+    config: &crate::SocketConfig,
+    remote: SocketAddr,
+) -> Result<(), ClientError> {
+    #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
+    {
+        if let Some(device) = &config.bind_to_device {
+            socket
+                .bind_device(Some(device.as_bytes()))
+                .map_err(|source| ClientError::SocketOption {
+                    operation: "bind socket to device",
+                    remote,
+                    source,
+                })?;
+        }
+        if let Some(mark) = config.mark {
+            socket
+                .set_mark(mark)
+                .map_err(|source| ClientError::SocketOption {
+                    operation: "set firewall mark",
+                    remote,
+                    source,
+                })?;
+        }
+    }
+    #[cfg(target_os = "freebsd")]
+    if let Some(fib) = config.fib {
+        socket
+            .set_fib(fib)
+            .map_err(|source| ClientError::SocketOption {
+                operation: "set FIB",
+                remote,
+                source,
+            })?;
+    }
+    Ok(())
+}
+
 /// Converts a public DSCP codepoint (`0..=`[`MAX_DSCP_CODEPOINT`]) into the
 /// raw IP TOS / Traffic Class byte it occupies the upper six bits of.
 ///