Vendor dependencies

Let's see how I like this workflow.

vendor/tokio/tests/tcp_shutdown.rs

@@ -0,0 +1,28 @@
+#![warn(rust_2018_idioms)]
+#![cfg(all(feature = "full", not(tokio_wasi)))] // Wasi doesn't support bind
+
+use tokio::io::{self, AsyncReadExt, AsyncWriteExt};
+use tokio::net::{TcpListener, TcpStream};
+use tokio_test::assert_ok;
+
+#[tokio::test]
+async fn shutdown() {
+    let srv = assert_ok!(TcpListener::bind("127.0.0.1:0").await);
+    let addr = assert_ok!(srv.local_addr());
+
+    tokio::spawn(async move {
+        let mut stream = assert_ok!(TcpStream::connect(&addr).await);
+
+        assert_ok!(AsyncWriteExt::shutdown(&mut stream).await);
+
+        let mut buf = [0u8; 1];
+        let n = assert_ok!(stream.read(&mut buf).await);
+        assert_eq!(n, 0);
+    });
+
+    let (mut stream, _) = assert_ok!(srv.accept().await);
+    let (mut rd, mut wr) = stream.split();
+
+    let n = assert_ok!(io::copy(&mut rd, &mut wr).await);
+    assert_eq!(n, 0);
+}