Add read and write functions for TunInterface

This adds read and write functionality for TunInterface.

tun/src/unix/apple/mod.rs

@@ -1,9 +1,14 @@
+use byteorder::{ByteOrder, NetworkEndian};
 use fehler::throws;
-use libc::c_char;
+use libc::{c_char, iovec, writev, AF_INET, AF_INET6};
 use socket2::{Domain, SockAddr, Socket, Type};
+use std::io::{IoSlice, Write};
 use std::net::{Ipv4Addr, SocketAddrV4};
 use std::os::fd::{AsRawFd, RawFd};
-use std::{io::Error, mem};
+use std::{
+    io::{Error, Read},
+    mem,
+};
 
 mod kern_control;
 mod sys;
@@ -122,6 +127,36 @@ impl TunInterface {
     }
 }
 
+impl Write for TunInterface {
+    #[throws]
+    fn write(&mut self, buf: &[u8]) -> usize {
+        use std::io::ErrorKind;
+        let proto = match buf[0] >> 4 {
+            6 => Ok(AF_INET6),
+            4 => Ok(AF_INET),
+            _ => Err(Error::new(ErrorKind::InvalidInput, "Invalid IP version")),
+        }?;
+        let mut pbuf = [0; 4];
+        NetworkEndian::write_i32(&mut pbuf, proto);
+
+        let bufs = [IoSlice::new(&pbuf), IoSlice::new(buf)];
+        let bytes_written: isize = unsafe {
+            writev(
+                self.as_raw_fd(),
+                bufs.as_ptr() as *const iovec,
+                bufs.len() as i32,
+            )
+        };
+        bytes_written
+            .try_into()
+            .map_err(|_| Error::new(ErrorKind::Other, "Conversion error"))?
+    }
+
+    fn flush(&mut self) -> std::io::Result<()> {
+        Ok(())
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::*;