Vendor dependencies

Let's see how I like this workflow.

vendor/tokio/tests/tcp_into_std.rs

@@ -0,0 +1,45 @@
+#![warn(rust_2018_idioms)]
+#![cfg(all(feature = "full", not(tokio_wasi)))] // Wasi doesn't support bind
+
+use std::io::Read;
+use std::io::Result;
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
+use tokio::net::TcpListener;
+use tokio::net::TcpStream;
+
+#[tokio::test]
+async fn tcp_into_std() -> Result<()> {
+    let mut data = [0u8; 12];
+    let listener = TcpListener::bind("127.0.0.1:0").await?;
+    let addr = listener.local_addr().unwrap().to_string();
+
+    let handle = tokio::spawn(async {
+        let stream: TcpStream = TcpStream::connect(addr).await.unwrap();
+        stream
+    });
+
+    let (tokio_tcp_stream, _) = listener.accept().await?;
+    let mut std_tcp_stream = tokio_tcp_stream.into_std()?;
+    std_tcp_stream
+        .set_nonblocking(false)
+        .expect("set_nonblocking call failed");
+
+    let mut client = handle.await.expect("The task being joined has panicked");
+    client.write_all(b"Hello world!").await?;
+
+    std_tcp_stream
+        .read_exact(&mut data)
+        .expect("std TcpStream read failed!");
+    assert_eq!(b"Hello world!", &data);
+
+    // test back to tokio stream
+    std_tcp_stream
+        .set_nonblocking(true)
+        .expect("set_nonblocking call failed");
+    let mut tokio_tcp_stream = TcpStream::from_std(std_tcp_stream)?;
+    client.write_all(b"Hello tokio!").await?;
+    let _size = tokio_tcp_stream.read_exact(&mut data).await?;
+    assert_eq!(b"Hello tokio!", &data);
+
+    Ok(())
+}