Vendor dependencies

Let's see how I like this workflow.

vendor/tokio/tests/io_read_to_string.rs

@@ -0,0 +1,63 @@
+#![warn(rust_2018_idioms)]
+#![cfg(feature = "full")]
+
+use std::io;
+use tokio::io::AsyncReadExt;
+use tokio_test::assert_ok;
+use tokio_test::io::Builder;
+
+#[tokio::test]
+async fn read_to_string() {
+    let mut buf = String::new();
+    let mut rd: &[u8] = b"hello world";
+
+    let n = assert_ok!(rd.read_to_string(&mut buf).await);
+    assert_eq!(n, 11);
+    assert_eq!(buf[..], "hello world"[..]);
+}
+
+#[tokio::test]
+async fn to_string_does_not_truncate_on_utf8_error() {
+    let data = vec![0xff, 0xff, 0xff];
+
+    let mut s = "abc".to_string();
+
+    match AsyncReadExt::read_to_string(&mut data.as_slice(), &mut s).await {
+        Ok(len) => panic!("Should fail: {} bytes.", len),
+        Err(err) if err.to_string() == "stream did not contain valid UTF-8" => {}
+        Err(err) => panic!("Fail: {}.", err),
+    }
+
+    assert_eq!(s, "abc");
+}
+
+#[tokio::test]
+async fn to_string_does_not_truncate_on_io_error() {
+    let mut mock = Builder::new()
+        .read(b"def")
+        .read_error(io::Error::new(io::ErrorKind::Other, "whoops"))
+        .build();
+    let mut s = "abc".to_string();
+
+    match AsyncReadExt::read_to_string(&mut mock, &mut s).await {
+        Ok(len) => panic!("Should fail: {} bytes.", len),
+        Err(err) if err.to_string() == "whoops" => {}
+        Err(err) => panic!("Fail: {}.", err),
+    }
+
+    assert_eq!(s, "abc");
+}
+
+#[tokio::test]
+async fn to_string_appends() {
+    let data = b"def".to_vec();
+
+    let mut s = "abc".to_string();
+
+    let len = AsyncReadExt::read_to_string(&mut data.as_slice(), &mut s)
+        .await
+        .unwrap();
+
+    assert_eq!(len, 3);
+    assert_eq!(s, "abcdef");
+}