Enable the async feature of tun

Use `tun::AsyncDevice` instead of hand-rolling an async tunnel device
with `tun::Device` + sys calls.

talpid-tunnel/Cargo.toml

@@ -27,7 +27,7 @@ jnix = { version = "0.5.1", features = ["derive"] }
 log = { workspace = true }
 
 [target.'cfg(any(target_os = "linux", target_os = "macos"))'.dependencies]
-tun = "0.7"
+tun = { version = "0.7", features = ["async"] }
 
 [target.'cfg(windows)'.dependencies]
 talpid-windows = { path = "../talpid-windows" }

talpid-tunnel/src/tun_provider/unix.rs

@@ -111,7 +111,7 @@ impl Deref for UnixTun {
 
 /// A tunnel device
 pub struct TunnelDevice {
-    dev: tun::Device,
+    dev: tun::AsyncDevice,
 }
 
 /// A tunnel device builder.
@@ -125,15 +125,7 @@ pub struct TunnelDeviceBuilder {
 impl TunnelDeviceBuilder {
     /// Create a [`TunnelDevice`] from this builder.
     pub fn create(self) -> Result<TunnelDevice, Error> {
-        fn apply_async_flags(fd: RawFd) -> Result<(), nix::Error> {
-            fcntl::fcntl(fd, fcntl::FcntlArg::F_GETFL)?;
-            let arg = fcntl::FcntlArg::F_SETFL(fcntl::OFlag::O_RDWR | fcntl::OFlag::O_NONBLOCK);
-            fcntl::fcntl(fd, arg)?;
-            Ok(())
-        }
-
-        let dev = tun::create(&self.config).map_err(Error::CreateDevice)?;
-        apply_async_flags(dev.as_raw_fd()).map_err(Error::SetDeviceAsync)?;
+        let dev = tun::create_as_async(&self.config).map_err(Error::CreateDevice)?;
         Ok(TunnelDevice { dev })
     }
 
@@ -164,12 +156,6 @@ impl AsRawFd for TunnelDevice {
     }
 }
 
-impl IntoRawFd for TunnelDevice {
-    fn into_raw_fd(self) -> RawFd {
-        self.dev.into_raw_fd()
-    }
-}
-
 impl TunnelDevice {
     #[cfg(target_os = "linux")]
     fn set_ip(&mut self, ip: IpAddr) -> Result<(), Error> {