Add a dedicated Future for retrieving the metadata of a file (#385)

tokio-fs/src/file/metadata.rs

@@ -0,0 +1,39 @@
+use super::File;
+
+use futures::{Future, Poll};
+
+use std::fs::File as StdFile;
+use std::fs::Metadata;
+use std::io;
+
+const POLL_AFTER_RESOLVE: &str = "Cannot poll MetadataFuture after it resolves";
+
+/// Future returned by `File::metadata` and resolves to a `(Metadata, File)` instance.
+#[derive(Debug)]
+pub struct MetadataFuture {
+    file: Option<File>,
+}
+
+impl MetadataFuture {
+    pub(crate) fn new(file: File) -> Self {
+        MetadataFuture { file: Some(file) }
+    }
+
+    fn std(&mut self) -> &mut StdFile {
+        self.file.as_mut().expect(POLL_AFTER_RESOLVE).std()
+    }
+}
+
+impl Future for MetadataFuture {
+    type Item = (File, Metadata);
+    type Error = io::Error;
+
+    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+        let metadata = try_ready!(::blocking_io(|| {
+            StdFile::metadata(self.std())
+        }));
+
+        let file = self.file.take().expect(POLL_AFTER_RESOLVE);
+        Ok((file, metadata).into())
+    }
+}

tokio-fs/src/file/mod.rs

@@ -3,10 +3,12 @@
 //! [`File`]: file/struct.File.html
 
 mod create;
+mod metadata;
 mod open;
 mod open_options;
 
 pub use self::create::CreateFuture;
+pub use self::metadata::MetadataFuture;
 pub use self::open::OpenFuture;
 pub use self::open_options::OpenOptions;
 
@@ -133,6 +135,11 @@ impl File {
         ::blocking_io(|| self.std().set_len(size))
     }
 
+    /// Queries metadata about the underlying file.
+    pub fn metadata(self) -> MetadataFuture {
+        MetadataFuture::new(self)
+    }
+
     /// Queries metadata about the underlying file.
     pub fn poll_metadata(&mut self) -> Poll<Metadata, io::Error> {
         ::blocking_io(|| self.std().metadata())