Vendor dependencies

Let's see how I like this workflow.

vendor/tokio/tests/io_take.rs

@@ -0,0 +1,74 @@
+#![warn(rust_2018_idioms)]
+#![cfg(all(feature = "full", not(tokio_wasi)))] // Wasi does not support panic recovery
+
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use tokio::io::{self, AsyncRead, AsyncReadExt, ReadBuf};
+use tokio_test::assert_ok;
+
+mod support {
+    pub(crate) mod leaked_buffers;
+}
+use support::leaked_buffers::LeakedBuffers;
+
+#[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"[..]);
+}
+
+#[tokio::test]
+async fn issue_4435() {
+    let mut buf = [0; 8];
+    let rd: &[u8] = b"hello world";
+
+    let rd = rd.take(4);
+    tokio::pin!(rd);
+
+    let mut read_buf = ReadBuf::new(&mut buf);
+    read_buf.put_slice(b"AB");
+
+    futures::future::poll_fn(|cx| rd.as_mut().poll_read(cx, &mut read_buf))
+        .await
+        .unwrap();
+    assert_eq!(&buf, &b"ABhell\0\0"[..]);
+}
+
+struct BadReader {
+    leaked_buffers: LeakedBuffers,
+}
+
+impl BadReader {
+    fn new() -> Self {
+        Self {
+            leaked_buffers: LeakedBuffers::new(),
+        }
+    }
+}
+
+impl AsyncRead for BadReader {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        _cx: &mut Context<'_>,
+        read_buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        let mut buf = ReadBuf::new(unsafe { self.leaked_buffers.create(10) });
+        buf.put_slice(&[123; 10]);
+        *read_buf = buf;
+
+        Poll::Ready(Ok(()))
+    }
+}
+
+#[tokio::test]
+#[should_panic]
+async fn bad_reader_fails() {
+    let mut buf = Vec::with_capacity(10);
+
+    BadReader::new().take(10).read_buf(&mut buf).await.unwrap();
+}