feat(client): Add connection capturing API to hyper-util

- rework features to allow enabling only tokio/sync for the client
- a `capture_connection` API

Cargo.toml

@@ -26,7 +26,7 @@ pin-project-lite = "0.2.4"
 futures-channel = { version = "0.3", optional = true }
 socket2 = { version = "0.5", optional = true, features = ["all"] }
 tracing = { version = "0.1", default-features = false, features = ["std"], optional = true }
-tokio = { version = "1", optional = true, features = ["net", "rt", "time"] }
+tokio = { version = "1", optional = true, default-features = false  }
 tower-service ={ version = "0.3", optional = true }
 tower = { version = "0.4.1", optional = true, features = ["make", "util"] }
 
@@ -57,7 +57,7 @@ full = [
 ]
 
 client = ["hyper/client", "dep:tracing", "dep:futures-channel", "dep:tower", "dep:tower-service"]
-client-legacy = ["client", "dep:socket2"]
+client-legacy = ["client", "dep:socket2", "tokio/sync"]
 
 server = ["hyper/server"]
 server-auto = ["server", "http1", "http2"]
@@ -67,7 +67,7 @@ service = ["dep:tower", "dep:tower-service"]
 http1 = ["hyper/http1"]
 http2 = ["hyper/http2"]
 
-tokio = ["dep:tokio"]
+tokio = ["dep:tokio", "tokio/net", "tokio/rt", "tokio/time"]
 
 # internal features used in CI
 __internal_happy_eyeballs_tests = []

src/client/legacy/client.rs

@@ -18,6 +18,7 @@ use hyper::rt::Timer;
 use hyper::{body::Body, Method, Request, Response, Uri, Version};
 use tracing::{debug, trace, warn};
 
+use super::connect::capture::CaptureConnectionExtension;
 #[cfg(feature = "tokio")]
 use super::connect::HttpConnector;
 use super::connect::{Alpn, Connect, Connected, Connection};
@@ -265,6 +266,10 @@ where
     ) -> Result<Response<hyper::body::Incoming>, Error> {
         let mut pooled = self.connection_for(pool_key).await?;
 
+        req.extensions_mut()
+            .get_mut::<CaptureConnectionExtension>()
+            .map(|conn| conn.set(&pooled.conn_info));
+
         if pooled.is_http1() {
             if req.version() == Version::HTTP_2 {
                 warn!("Connection is HTTP/1, but request requires HTTP/2");

src/client/legacy/connect/capture.rs

@@ -0,0 +1,191 @@
+use std::{ops::Deref, sync::Arc};
+
+use http::Request;
+use tokio::sync::watch;
+
+use super::Connected;
+
+/// [`CaptureConnection`] allows callers to capture [`Connected`] information
+///
+/// To capture a connection for a request, use [`capture_connection`].
+#[derive(Debug, Clone)]
+pub struct CaptureConnection {
+    rx: watch::Receiver<Option<Connected>>,
+}
+
+/// Capture the connection for a given request
+///
+/// When making a request with Hyper, the underlying connection must implement the [`Connection`] trait.
+/// [`capture_connection`] allows a caller to capture the returned [`Connected`] structure as soon
+/// as the connection is established.
+///
+/// *Note*: If establishing a connection fails, [`CaptureConnection::connection_metadata`] will always return none.
+///
+/// # Examples
+///
+/// **Synchronous access**:
+/// The [`CaptureConnection::connection_metadata`] method allows callers to check if a connection has been
+/// established. This is ideal for situations where you are certain the connection has already
+/// been established (e.g. after the response future has already completed).
+/// ```rust
+/// use hyper_util::client::legacy::connect::capture_connection;
+/// let mut request = http::Request::builder()
+///   .uri("http://foo.com")
+///   .body(())
+///   .unwrap();
+///
+/// let captured_connection = capture_connection(&mut request);
+/// // some time later after the request has been sent...
+/// let connection_info = captured_connection.connection_metadata();
+/// println!("we are connected! {:?}", connection_info.as_ref());
+/// ```
+///
+/// **Asynchronous access**:
+/// The [`CaptureConnection::wait_for_connection_metadata`] method returns a future resolves as soon as the
+/// connection is available.
+///
+/// ```rust
+/// # #[cfg(feature  = "tokio")]
+/// # async fn example() {
+/// use hyper_util::client::legacy::connect::capture_connection;
+/// use hyper_util::client::legacy::Client;
+/// use hyper_util::rt::TokioExecutor;
+/// use bytes::Bytes;
+/// use http_body_util::Empty;
+/// let mut request = http::Request::builder()
+///   .uri("http://foo.com")
+///   .body(Empty::<Bytes>::new())
+///   .unwrap();
+///
+/// let mut captured = capture_connection(&mut request);
+/// tokio::task::spawn(async move {
+///     let connection_info = captured.wait_for_connection_metadata().await;
+///     println!("we are connected! {:?}", connection_info.as_ref());
+/// });
+///
+/// let client = Client::builder(TokioExecutor::new()).build_http();
+/// client.request(request).await.expect("request failed");
+/// # }
+/// ```
+pub fn capture_connection<B>(request: &mut Request<B>) -> CaptureConnection {
+    let (tx, rx) = CaptureConnection::new();
+    request.extensions_mut().insert(tx);
+    rx
+}
+
+/// TxSide for [`CaptureConnection`]
+///
+/// This is inserted into `Extensions` to allow Hyper to back channel connection info
+#[derive(Clone)]
+pub(crate) struct CaptureConnectionExtension {
+    tx: Arc<watch::Sender<Option<Connected>>>,
+}
+
+impl CaptureConnectionExtension {
+    pub(crate) fn set(&self, connected: &Connected) {
+        self.tx.send_replace(Some(connected.clone()));
+    }
+}
+
+impl CaptureConnection {
+    /// Internal API to create the tx and rx half of [`CaptureConnection`]
+    pub(crate) fn new() -> (CaptureConnectionExtension, Self) {
+        let (tx, rx) = watch::channel(None);
+        (
+            CaptureConnectionExtension { tx: Arc::new(tx) },
+            CaptureConnection { rx },
+        )
+    }
+
+    /// Retrieve the connection metadata, if available
+    pub fn connection_metadata(&self) -> impl Deref<Target = Option<Connected>> + '_ {
+        self.rx.borrow()
+    }
+
+    /// Wait for the connection to be established
+    ///
+    /// If a connection was established, this will always return `Some(...)`. If the request never
+    /// successfully connected (e.g. DNS resolution failure), this method will never return.
+    pub async fn wait_for_connection_metadata(
+        &mut self,
+    ) -> impl Deref<Target = Option<Connected>> + '_ {
+        if self.rx.borrow().is_some() {
+            return self.rx.borrow();
+        }
+        let _ = self.rx.changed().await;
+        self.rx.borrow()
+    }
+}
+
+#[cfg(all(test, not(miri)))]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_sync_capture_connection() {
+        let (tx, rx) = CaptureConnection::new();
+        assert!(
+            rx.connection_metadata().is_none(),
+            "connection has not been set"
+        );
+        tx.set(&Connected::new().proxy(true));
+        assert_eq!(
+            rx.connection_metadata()
+                .as_ref()
+                .expect("connected should be set")
+                .is_proxied(),
+            true
+        );
+
+        // ensure it can be called multiple times
+        assert_eq!(
+            rx.connection_metadata()
+                .as_ref()
+                .expect("connected should be set")
+                .is_proxied(),
+            true
+        );
+    }
+
+    #[tokio::test]
+    async fn async_capture_connection() {
+        let (tx, mut rx) = CaptureConnection::new();
+        assert!(
+            rx.connection_metadata().is_none(),
+            "connection has not been set"
+        );
+        let test_task = tokio::spawn(async move {
+            assert_eq!(
+                rx.wait_for_connection_metadata()
+                    .await
+                    .as_ref()
+                    .expect("connection should be set")
+                    .is_proxied(),
+                true
+            );
+            // can be awaited multiple times
+            assert!(
+                rx.wait_for_connection_metadata().await.is_some(),
+                "should be awaitable multiple times"
+            );
+
+            assert_eq!(rx.connection_metadata().is_some(), true);
+        });
+        // can't be finished, we haven't set the connection yet
+        assert_eq!(test_task.is_finished(), false);
+        tx.set(&Connected::new().proxy(true));
+
+        assert!(test_task.await.is_ok());
+    }
+
+    #[tokio::test]
+    async fn capture_connection_sender_side_dropped() {
+        let (tx, mut rx) = CaptureConnection::new();
+        assert!(
+            rx.connection_metadata().is_none(),
+            "connection has not been set"
+        );
+        drop(tx);
+        assert!(rx.wait_for_connection_metadata().await.is_none());
+    }
+}

src/client/legacy/connect/mod.rs

@@ -74,6 +74,9 @@ pub mod dns;
 #[cfg(feature = "tokio")]
 mod http;
 
+pub(crate) mod capture;
+pub use capture::{capture_connection, CaptureConnection};
+
 pub use self::sealed::Connect;
 
 /// Describes a type returned by a connector.
@@ -169,7 +172,6 @@ impl Connected {
 
     // Don't public expose that `Connected` is `Clone`, unsure if we want to
     // keep that contract...
-    #[cfg(feature = "http2")]
     pub(super) fn clone(&self) -> Connected {
         Connected {
             alpn: self.alpn,

tests/legacy_client.rs

@@ -18,7 +18,7 @@ use http_body_util::{Empty, Full, StreamBody};
 use hyper::body::Bytes;
 use hyper::body::Frame;
 use hyper::Request;
-use hyper_util::client::legacy::connect::HttpConnector;
+use hyper_util::client::legacy::connect::{capture_connection, HttpConnector};
 use hyper_util::client::legacy::Client;
 use hyper_util::rt::{TokioExecutor, TokioIo};
 
@@ -876,3 +876,35 @@ fn alpn_h2() {
     );
     drop(client);
 }
+
+#[cfg(not(miri))]
+#[test]
+fn capture_connection_on_client() {
+    let _ = pretty_env_logger::try_init();
+
+    let rt = runtime();
+    let connector = DebugConnector::new();
+
+    let client = Client::builder(TokioExecutor::new()).build(connector);
+
+    let server = TcpListener::bind("127.0.0.1:0").unwrap();
+    let addr = server.local_addr().unwrap();
+    thread::spawn(move || {
+        let mut sock = server.accept().unwrap().0;
+        //drop(server);
+        sock.set_read_timeout(Some(Duration::from_secs(5))).unwrap();
+        sock.set_write_timeout(Some(Duration::from_secs(5)))
+            .unwrap();
+        let mut buf = [0; 4096];
+        sock.read(&mut buf).expect("read 1");
+        sock.write_all(b"HTTP/1.1 200 OK\r\nContent-Length: 0\r\n\r\n")
+            .expect("write 1");
+    });
+    let mut req = Request::builder()
+        .uri(&*format!("http://{}/a", addr))
+        .body(Empty::<Bytes>::new())
+        .unwrap();
+    let captured_conn = capture_connection(&mut req);
+    rt.block_on(client.request(req)).expect("200 OK");
+    assert!(captured_conn.connection_metadata().is_some());
+}