add: take_io method to LazyConfigAcceptor (#145)

* add: take_io method to LazyConfigAcceptor

The `take_io` method can be used to take back ownership of the client IO stream when an error occurs
during clientHello handshake.

An example of this is when a client tries to connect to an TLS socket expecting it to be plain text
connection. In this case take_io can be used to send a 400 response, "The plain HTTP request was
sent to HTTPS port", back to the client.

* rename test lazy_config_acceptor_take_io

tokio-rustls/src/lib.rs

@@ -203,6 +203,51 @@ where
             io: Some(io),
         }
     }
+
+    /// Takes back the client connection. Will return `None` if called more than once or if the
+    /// connection has been accepted.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # fn choose_server_config(
+    /// #     _: rustls::server::ClientHello,
+    /// # ) -> std::sync::Arc<rustls::ServerConfig> {
+    /// #     unimplemented!();
+    /// # }
+    /// # #[allow(unused_variables)]
+    /// # async fn listen() {
+    /// use tokio::io::AsyncWriteExt;
+    /// let listener = tokio::net::TcpListener::bind("127.0.0.1:4443").await.unwrap();
+    /// let (stream, _) = listener.accept().await.unwrap();
+    ///
+    /// let acceptor = tokio_rustls::LazyConfigAcceptor::new(rustls::server::Acceptor::default(), stream);
+    /// futures_util::pin_mut!(acceptor);
+    ///
+    /// match acceptor.as_mut().await {
+    ///     Ok(start) => {
+    ///         let clientHello = start.client_hello();
+    ///         let config = choose_server_config(clientHello);
+    ///         let stream = start.into_stream(config).await.unwrap();
+    ///         // Proceed with handling the ServerConnection...
+    ///     }
+    ///     Err(err) => {
+    ///         if let Some(mut stream) = acceptor.take_io() {
+    ///             stream
+    ///                 .write_all(
+    ///                     format!("HTTP/1.1 400 Invalid Input\r\n\r\n\r\n{:?}\n", err)
+    ///                         .as_bytes()
+    ///                 )
+    ///                 .await
+    ///                 .unwrap();
+    ///         }
+    ///     }
+    /// }
+    /// # }
+    /// ```
+    pub fn take_io(&mut self) -> Option<IO> {
+        self.io.take()
+    }
 }
 
 impl<IO> Future for LazyConfigAcceptor<IO>

tokio-rustls/tests/test.rs

@@ -11,6 +11,7 @@ use std::time::Duration;
 use std::{io, thread};
 use tokio::io::{copy, split, AsyncReadExt, AsyncWriteExt};
 use tokio::net::{TcpListener, TcpStream};
+use tokio::sync::oneshot;
 use tokio::{runtime, time};
 use tokio_rustls::{LazyConfigAcceptor, TlsAcceptor, TlsConnector};
 
@@ -215,5 +216,40 @@ async fn lazy_config_acceptor_eof() {
     }
 }
 
+#[tokio::test]
+async fn lazy_config_acceptor_take_io() -> Result<(), rustls::Error> {
+    let (mut cstream, sstream) = tokio::io::duplex(1200);
+
+    let (tx, rx) = oneshot::channel();
+
+    tokio::spawn(async move {
+        cstream.write_all(b"hello, world!").await.unwrap();
+
+        let mut buf = Vec::new();
+        cstream.read_to_end(&mut buf).await.unwrap();
+        tx.send(buf).unwrap();
+    });
+
+    let acceptor = LazyConfigAcceptor::new(rustls::server::Acceptor::default(), sstream);
+    futures_util::pin_mut!(acceptor);
+    if (acceptor.as_mut().await).is_ok() {
+        panic!("Expected Err(err)");
+    }
+
+    let server_msg = b"message from server";
+
+    let some_io = acceptor.take_io();
+    assert!(some_io.is_some(), "Expected Some(io)");
+    some_io.unwrap().write_all(server_msg).await.unwrap();
+
+    assert_eq!(rx.await.unwrap(), server_msg);
+
+    assert!(
+        acceptor.take_io().is_none(),
+        "Should not be able to take twice"
+    );
+    Ok(())
+}
+
 // Include `utils` module
 include!("utils.rs");