Add read and write functions for TunInterface

This adds read and write functionality for TunInterface.

tun/src/unix/linux/mod.rs

@@ -2,7 +2,7 @@ use fehler::throws;
 
 use socket2::{Domain, SockAddr, Socket, Type};
 use std::fs::OpenOptions;
-use std::io::Error;
+use std::io::{Error, Write};
 use std::mem;
 use std::net::{Ipv4Addr, Ipv6Addr, SocketAddrV4, SocketAddrV6};
 use std::os::fd::RawFd;
@@ -140,6 +140,17 @@ impl TunInterface {
     }
 }
 
+impl Write for TunInterface {
+    #[throws]
+    fn write(&mut self, buf: &[u8]) -> usize {
+        self.socket.send(buf)?
+    }
+
+    fn flush(&mut self) -> std::io::Result<()> {
+        Ok(())
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::TunInterface;