fs: use async fn instead of custom futures (#1381)

Also update all the doc examples.

tokio-fs/src/open_options.rs

@@ -0,0 +1,112 @@
+use super::File;
+
+use futures_util::future::poll_fn;
+use std::io;
+use std::path::Path;
+
+/// Options and flags which can be used to configure how a file is opened.
+///
+/// This is a specialized version of [`std::fs::OpenOptions`] for usage from
+/// the Tokio runtime.
+///
+/// `From<std::fs::OpenOptions>` is implemented for more advanced configuration
+/// than the methods provided here.
+///
+/// [`std::fs::OpenOptions`]: https://doc.rust-lang.org/std/fs/struct.OpenOptions.html
+#[derive(Clone, Debug)]
+pub struct OpenOptions(std::fs::OpenOptions);
+
+impl OpenOptions {
+    /// Creates a blank new set of options ready for configuration.
+    ///
+    /// All options are initially set to `false`.
+    ///
+    /// # Examples
+    ///
+    /// ```ignore
+    /// use tokio::fs::OpenOptions;
+    ///
+    /// let mut options = OpenOptions::new();
+    /// let future = options.read(true).open("foo.txt");
+    /// ```
+    pub fn new() -> OpenOptions {
+        OpenOptions(std::fs::OpenOptions::new())
+    }
+
+    /// See the underlying [`read`] call for details.
+    ///
+    /// [`read`]: https://doc.rust-lang.org/std/fs/struct.OpenOptions.html#method.read
+    pub fn read(&mut self, read: bool) -> &mut OpenOptions {
+        self.0.read(read);
+        self
+    }
+
+    /// See the underlying [`write`] call for details.
+    ///
+    /// [`write`]: https://doc.rust-lang.org/std/fs/struct.OpenOptions.html#method.write
+    pub fn write(&mut self, write: bool) -> &mut OpenOptions {
+        self.0.write(write);
+        self
+    }
+
+    /// See the underlying [`append`] call for details.
+    ///
+    /// [`append`]: https://doc.rust-lang.org/std/fs/struct.OpenOptions.html#method.append
+    pub fn append(&mut self, append: bool) -> &mut OpenOptions {
+        self.0.append(append);
+        self
+    }
+
+    /// See the underlying [`truncate`] call for details.
+    ///
+    /// [`truncate`]: https://doc.rust-lang.org/std/fs/struct.OpenOptions.html#method.truncate
+    pub fn truncate(&mut self, truncate: bool) -> &mut OpenOptions {
+        self.0.truncate(truncate);
+        self
+    }
+
+    /// See the underlying [`create`] call for details.
+    ///
+    /// [`create`]: https://doc.rust-lang.org/std/fs/struct.OpenOptions.html#method.create
+    pub fn create(&mut self, create: bool) -> &mut OpenOptions {
+        self.0.create(create);
+        self
+    }
+
+    /// See the underlying [`create_new`] call for details.
+    ///
+    /// [`create_new`]: https://doc.rust-lang.org/std/fs/struct.OpenOptions.html#method.create_new
+    pub fn create_new(&mut self, create_new: bool) -> &mut OpenOptions {
+        self.0.create_new(create_new);
+        self
+    }
+
+    /// Opens a file at `path` with the options specified by `self`.
+    ///
+    /// # Errors
+    ///
+    /// `OpenOptionsFuture` results in an error if called from outside of the
+    /// Tokio runtime or if the underlying [`open`] call results in an error.
+    ///
+    /// [`open`]: https://doc.rust-lang.org/std/fs/struct.OpenOptions.html#method.open
+    #[allow(clippy::needless_lifetimes)] // false positive: https://github.com/rust-lang/rust-clippy/issues/3988
+    pub async fn open<P>(&self, path: P) -> io::Result<File>
+    where
+        P: AsRef<Path> + Send + Unpin + 'static,
+    {
+        let std_file = poll_fn(|_| crate::blocking_io(|| self.0.open(&path))).await?;
+        Ok(File::from_std(std_file))
+    }
+}
+
+impl From<std::fs::OpenOptions> for OpenOptions {
+    fn from(options: std::fs::OpenOptions) -> OpenOptions {
+        OpenOptions(options)
+    }
+}
+
+impl Default for OpenOptions {
+    fn default() -> Self {
+        Self::new()
+    }
+}