Additional Linux socket options

Added support for setting/getting value of:
* TCP Maximum Segment Size (TCP_MAXSEG)
* Socket Mark (SO_MARK)

Signed-off-by: Ammar Zuberi <ammar@cloudflare.com>

src/socket.rs

@@ -369,6 +369,49 @@ impl Socket {
         self.inner.set_ttl(ttl)
     }
 
+    /// Gets the value of the `TCP_MAXSEG` option on this socket.
+    ///
+    /// The `TCP_MAXSEG` option denotes the TCP Maximum Segment
+    /// Size and is only available on TCP sockets.
+    #[cfg(unix)]
+    pub fn mss(&self) -> io::Result<u32> {
+        self.inner.mss()
+    }
+
+    /// Sets the value of the `TCP_MAXSEG` option on this socket.
+    ///
+    /// The `TCP_MAXSEG` option denotes the TCP Maximum Segment
+    /// Size and is only available on TCP sockets.
+    #[cfg(unix)]
+    pub fn set_mss(&self, mss: u32) -> io::Result<()> {
+        self.inner.set_mss(mss)
+    }
+
+    /// Gets the value for the `SO_MARK` option on this socket.
+    ///
+    /// This value gets the socket mark field for each packet sent through
+    /// this socket.
+    ///
+    /// This function is only available on Linux and requires the
+    /// `CAP_NET_ADMIN` capability.
+    #[cfg(target_os = "linux")]
+    pub fn mark(&self) -> io::Result<u32> {
+        self.inner.mark()
+    }
+
+    /// Sets the value for the `SO_MARK` option on this socket.
+    ///
+    /// This value sets the socket mark field for each packet sent through
+    /// this socket. Changing the mark can be used for mark-based routing
+    /// without netfilter or for packet filtering.
+    ///
+    /// This function is only available on Linux and requires the
+    /// `CAP_NET_ADMIN` capability.
+    #[cfg(target_os = "linux")]
+    pub fn set_mark(&self, mark: u32) -> io::Result<()> {
+        self.inner.set_mark(mark)
+    }
+
     /// Gets the value of the `IPV6_UNICAST_HOPS` option for this socket.
     ///
     /// Specifies the hop limit for ipv6 unicast packets

src/sys/unix.rs

@@ -534,6 +534,30 @@ impl Socket {
         unsafe { self.setsockopt(libc::IPPROTO_IP, libc::IP_TTL, ttl as c_int) }
     }
 
+    pub fn mss(&self) -> io::Result<u32> {
+        unsafe {
+            let raw: c_int = self.getsockopt(libc::IPPROTO_TCP, libc::TCP_MAXSEG)?;
+            Ok(raw as u32)
+        }
+    }
+
+    pub fn set_mss(&self, mss: u32) -> io::Result<()> {
+        unsafe { self.setsockopt(libc::IPPROTO_TCP, libc::TCP_MAXSEG, mss as c_int) }
+    }
+
+    #[cfg(target_os = "linux")]
+    pub fn mark(&self) -> io::Result<u32> {
+        unsafe {
+            let raw: c_int = self.getsockopt(libc::SOL_SOCKET, libc::SO_MARK)?;
+            Ok(raw as u32)
+        }
+    }
+
+    #[cfg(target_os = "linux")]
+    pub fn set_mark(&self, mark: u32) -> io::Result<()> {
+        unsafe { self.setsockopt(libc::SOL_SOCKET, libc::SO_MARK, mark as c_int) }
+    }
+
     pub fn unicast_hops_v6(&self) -> io::Result<u32> {
         unsafe {
             let raw: c_int = self.getsockopt(libc::IPPROTO_IPV6, libc::IPV6_UNICAST_HOPS)?;