io: add AsyncReadExt::{chain, take} (#1484)

tokio-io/tests/chain.rs

@@ -0,0 +1,16 @@
+#![warn(rust_2018_idioms)]
+#![feature(async_await)]
+
+use tokio_io::AsyncReadExt;
+use tokio_test::assert_ok;
+
+#[tokio::test]
+async fn chain() {
+    let mut buf = Vec::new();
+    let rd1: &[u8] = b"hello ";
+    let rd2: &[u8] = b"world";
+
+    let mut rd = rd1.chain(rd2);
+    assert_ok!(rd.read_to_end(&mut buf).await);
+    assert_eq!(buf, b"hello world");
+}

tokio-io/tests/take.rs

@@ -0,0 +1,16 @@
+#![warn(rust_2018_idioms)]
+#![feature(async_await)]
+
+use tokio_io::AsyncReadExt;
+use tokio_test::assert_ok;
+
+#[tokio::test]
+async fn take() {
+    let mut buf = [0; 6];
+    let rd: &[u8] = b"hello world";
+
+    let mut rd = rd.take(4);
+    let n = assert_ok!(rd.read(&mut buf).await);
+    assert_eq!(n, 4);
+    assert_eq!(&buf, &b"hell\0\0"[..]);
+}