cros_async: Add AsyncWrapper type

This makes it easier to implement IntoAsync for foreign types.

BUG=none
TEST=Use it in a later change

Change-Id: I070fe3b63ac7458e21fa38b3a1b1bdb318c44d5b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2891120
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Chirantan Ekbote <chirantan@chromium.org>
Reviewed-by: Noah Gold <nkgold@google.com>
Reviewed-by: Keiichi Watanabe <keiichiw@chromium.org>

cros_async/src/io_ext.rs

@@ -16,7 +16,8 @@
 //! `URingExecutor` documentation for an explaination of why.
 
 use std::fs::File;
-use std::os::unix::io::AsRawFd;
+use std::ops::{Deref, DerefMut};
+use std::os::unix::io::{AsRawFd, RawFd};
 use std::sync::Arc;
 
 use async_trait::async_trait;
@@ -119,6 +120,43 @@ impl IntoAsync for File {}
 impl IntoAsync for UnixSeqpacket {}
 impl IntoAsync for &UnixSeqpacket {}
 
+/// Simple wrapper struct to implement IntoAsync on foreign types.
+pub struct AsyncWrapper<T>(T);
+
+impl<T> AsyncWrapper<T> {
+    /// Create a new `AsyncWrapper` that wraps `val`.
+    pub fn new(val: T) -> Self {
+        AsyncWrapper(val)
+    }
+
+    /// Consumes the `AsyncWrapper`, returning the inner struct.
+    pub fn into_inner(self) -> T {
+        self.0
+    }
+}
+
+impl<T> Deref for AsyncWrapper<T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        &self.0
+    }
+}
+
+impl<T> DerefMut for AsyncWrapper<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        &mut self.0
+    }
+}
+
+impl<T: AsRawFd> AsRawFd for AsyncWrapper<T> {
+    fn as_raw_fd(&self) -> RawFd {
+        self.0.as_raw_fd()
+    }
+}
+
+impl<T: AsRawFd> IntoAsync for AsyncWrapper<T> {}
+
 #[cfg(test)]
 mod tests {
     use std::fs::{File, OpenOptions};

cros_async/src/lib.rs

@@ -77,7 +77,8 @@ pub use event::EventAsync;
 pub use executor::Executor;
 pub use fd_executor::FdExecutor;
 pub use io_ext::{
-    Error as AsyncError, IntoAsync, IoSourceExt, ReadAsync, Result as AsyncResult, WriteAsync,
+    AsyncWrapper, Error as AsyncError, IntoAsync, IoSourceExt, ReadAsync, Result as AsyncResult,
+    WriteAsync,
 };
 pub use mem::{BackingMemory, MemRegion};
 pub use poll_source::PollSource;