fs: add read_to_string (#1664)

tokio-fs/src/read_to_string.rs

@@ -0,0 +1,27 @@
+use crate::asyncify;
+
+use std::{io, path::Path};
+
+/// Creates a future which will open a file for reading and read the entire
+/// contents into a string and return said string.
+///
+/// This is the async equivalent of `std::fs::read_to_string`.
+///
+/// # Examples
+///
+/// ```no_run
+/// use tokio::fs;
+///
+/// # async fn dox() -> std::io::Result<()> {
+/// let contents = fs::read_to_string("foo.txt").await?;
+/// println!("foo.txt contains {} bytes", contents.len());
+/// # Ok(())
+/// # }
+/// ```
+pub async fn read_to_string<P>(path: P) -> io::Result<String>
+where
+    P: AsRef<Path>,
+{
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::read_to_string(path)).await
+}