feat(ext): add ext::on_informational() callback extension (#3818)

This new function allows attaching a callback to a request, such that
when it is sent through a hyper client connection, and any 1xx
informational responses are received, they are passed to the callback.

This takes the unstable client informational feature (introduced in
#2594, tracking issue in #2565), and promotes it to a stable API.

Closes #2565

src/ext/informational.rs

@@ -0,0 +1,86 @@
+use std::sync::Arc;
+
+#[derive(Clone)]
+pub(crate) struct OnInformational(Arc<dyn OnInformationalCallback + Send + Sync>);
+
+/// Add a callback for 1xx informational responses.
+///
+/// # Example
+///
+/// ```
+/// # let some_body = ();
+/// let mut req = hyper::Request::new(some_body);
+///
+/// hyper::ext::on_informational(&mut req, |res| {
+///     println!("informational: {:?}", res.status());
+/// });
+///
+/// // send request on a client connection...
+/// ```
+pub fn on_informational<B, F>(req: &mut http::Request<B>, callback: F)
+where
+    F: Fn(Response<'_>) + Send + Sync + 'static,
+{
+    on_informational_raw(req, OnInformationalClosure(callback));
+}
+
+pub(crate) fn on_informational_raw<B, C>(req: &mut http::Request<B>, callback: C)
+where
+    C: OnInformationalCallback + Send + Sync + 'static,
+{
+    req.extensions_mut()
+        .insert(OnInformational(Arc::new(callback)));
+}
+
+// Sealed, not actually nameable bounds
+pub(crate) trait OnInformationalCallback {
+    fn on_informational(&self, res: http::Response<()>);
+}
+
+impl OnInformational {
+    pub(crate) fn call(&self, res: http::Response<()>) {
+        self.0.on_informational(res);
+    }
+}
+
+struct OnInformationalClosure<F>(F);
+
+impl<F> OnInformationalCallback for OnInformationalClosure<F>
+where
+    F: Fn(Response<'_>) + Send + Sync + 'static,
+{
+    fn on_informational(&self, res: http::Response<()>) {
+        let res = Response(&res);
+        (self.0)(res);
+    }
+}
+
+// A facade over http::Response.
+//
+// It purposefully hides being able to move the response out of the closure,
+// while also not being able to expect it to be a reference `&Response`.
+// (Otherwise, a closure can be written as `|res: &_|`, and then be broken if
+// we make the closure take ownership.)
+//
+// With the type not being nameable, we could change from being a facade to
+// being either a real reference, or moving the http::Response into the closure,
+// in a backwards-compatible change in the future.
+#[derive(Debug)]
+pub struct Response<'a>(&'a http::Response<()>);
+
+impl Response<'_> {
+    #[inline]
+    pub fn status(&self) -> http::StatusCode {
+        self.0.status()
+    }
+
+    #[inline]
+    pub fn version(&self) -> http::Version {
+        self.0.version()
+    }
+
+    #[inline]
+    pub fn headers(&self) -> &http::HeaderMap {
+        self.0.headers()
+    }
+}

src/ext/mod.rs

@@ -19,6 +19,15 @@ mod h1_reason_phrase;
 #[cfg(any(feature = "http1", feature = "ffi"))]
 pub use h1_reason_phrase::ReasonPhrase;
 
+#[cfg(all(feature = "http1", feature = "client"))]
+mod informational;
+#[cfg(all(feature = "http1", feature = "client"))]
+pub use informational::on_informational;
+#[cfg(all(feature = "http1", feature = "client"))]
+pub(crate) use informational::OnInformational;
+#[cfg(all(feature = "http1", feature = "client", feature = "ffi"))]
+pub(crate) use informational::{on_informational_raw, OnInformationalCallback};
+
 #[cfg(feature = "http2")]
 /// Represents the `:protocol` pseudo-header used by
 /// the [Extended CONNECT Protocol].

src/ffi/http_types.rs

@@ -70,7 +70,7 @@ pub struct hyper_headers {
 }
 
 #[derive(Clone)]
-pub(crate) struct OnInformational {
+struct OnInformational {
     func: hyper_request_on_informational_callback,
     data: UserDataPointer,
 }
@@ -268,13 +268,21 @@ ffi_fn! {
     /// be valid after the callback finishes. You must copy any data you wish
     /// to persist.
     fn hyper_request_on_informational(req: *mut hyper_request, callback: hyper_request_on_informational_callback, data: *mut c_void) -> hyper_code {
+        #[cfg(feature = "client")]
+        {
         let ext = OnInformational {
             func: callback,
             data: UserDataPointer(data),
         };
         let req = non_null!(&mut *req ?= hyper_code::HYPERE_INVALID_ARG);
-        req.0.extensions_mut().insert(ext);
+        crate::ext::on_informational_raw(&mut req.0, ext);
         hyper_code::HYPERE_OK
+        }
+        #[cfg(not(feature = "client"))]
+        {
+        drop((req, callback, data));
+        hyper_code::HYPERE_FEATURE_NOT_ENABLED
+        }
     }
 }
 
@@ -567,10 +575,12 @@ unsafe fn raw_name_value(
 
 // ===== impl OnInformational =====
 
-impl OnInformational {
-    pub(crate) fn call(&mut self, resp: Response<IncomingBody>) {
-        let mut resp = hyper_response::wrap(resp);
-        (self.func)(self.data.0, &mut resp);
+#[cfg(feature = "client")]
+impl crate::ext::OnInformationalCallback for OnInformational {
+    fn on_informational(&self, res: http::Response<()>) {
+        let res = res.map(|()| IncomingBody::empty());
+        let mut res = hyper_response::wrap(res);
+        (self.func)(self.data.0, &mut res);
     }
 }
 

src/proto/h1/conn.rs

@@ -73,7 +73,7 @@ where
                 preserve_header_order: false,
                 title_case_headers: false,
                 h09_responses: false,
-                #[cfg(feature = "ffi")]
+                #[cfg(feature = "client")]
                 on_informational: None,
                 notify_read: false,
                 reading: Reading::Init,
@@ -245,7 +245,7 @@ where
                 #[cfg(feature = "ffi")]
                 preserve_header_order: self.state.preserve_header_order,
                 h09_responses: self.state.h09_responses,
-                #[cfg(feature = "ffi")]
+                #[cfg(feature = "client")]
                 on_informational: &mut self.state.on_informational,
             },
         ) {
@@ -285,7 +285,7 @@ where
         self.state.h09_responses = false;
 
         // Drop any OnInformational callbacks, we're done there!
-        #[cfg(feature = "ffi")]
+        #[cfg(feature = "client")]
         {
             self.state.on_informational = None;
         }
@@ -635,10 +635,10 @@ where
                 debug_assert!(head.headers.is_empty());
                 self.state.cached_headers = Some(head.headers);
 
-                #[cfg(feature = "ffi")]
+                #[cfg(feature = "client")]
                 {
                     self.state.on_informational =
-                        head.extensions.remove::<crate::ffi::OnInformational>();
+                        head.extensions.remove::<crate::ext::OnInformational>();
                 }
 
                 Some(encoder)
@@ -942,8 +942,8 @@ struct State {
     /// If set, called with each 1xx informational response received for
     /// the current request. MUST be unset after a non-1xx response is
     /// received.
-    #[cfg(feature = "ffi")]
-    on_informational: Option<crate::ffi::OnInformational>,
+    #[cfg(feature = "client")]
+    on_informational: Option<crate::ext::OnInformational>,
     /// Set to true when the Dispatcher should poll read operations
     /// again. See the `maybe_notify` method for more.
     notify_read: bool,

src/proto/h1/io.rs

@@ -188,7 +188,7 @@ where
                     #[cfg(feature = "ffi")]
                     preserve_header_order: parse_ctx.preserve_header_order,
                     h09_responses: parse_ctx.h09_responses,
-                    #[cfg(feature = "ffi")]
+                    #[cfg(feature = "client")]
                     on_informational: parse_ctx.on_informational,
                 },
             )? {
@@ -710,7 +710,7 @@ mod tests {
                 #[cfg(feature = "ffi")]
                 preserve_header_order: false,
                 h09_responses: false,
-                #[cfg(feature = "ffi")]
+                #[cfg(feature = "client")]
                 on_informational: &mut None,
             };
             assert!(buffered

src/proto/h1/mod.rs

@@ -77,8 +77,8 @@ pub(crate) struct ParseContext<'a> {
     #[cfg(feature = "ffi")]
     preserve_header_order: bool,
     h09_responses: bool,
-    #[cfg(feature = "ffi")]
-    on_informational: &'a mut Option<crate::ffi::OnInformational>,
+    #[cfg(feature = "client")]
+    on_informational: &'a mut Option<crate::ext::OnInformational>,
 }
 
 /// Passed to Http1Transaction::encode