feat(conn/auto): allow serving connection with upgrade after config

When using hyper_util::server::conn::auto::Builder, if one wants to set
http1 or http2 options one has to specialize the struct into
Http1Builder or Http2Builder with .http1()/.http2() methods.

However, once the struct has been specialized there is no way to go back
to the inner Builder to call serve_connection_with_upgrades(): one would
need to either add make inner public, add an inner() method to get it
back, or add a stub that just calls the method on inner like we have
with serve_connection().

Since we already had one for serve_connection(), add an indentical one for
serve_connection_with_upgrades()
Note that it does not make sense for serve_connection_with_upgrades() to
be called without the http feature (I think?), so it has only been implemented
for http1 if the http2 feature is set.

src/server/conn/auto.rs

@@ -665,6 +665,27 @@ impl<E> Http1Builder<'_, E> {
     {
         self.inner.serve_connection(io, service).await
     }
+
+    /// Bind a connection together with a [`Service`], with the ability to
+    /// handle HTTP upgrades. This requires that the IO object implements
+    /// `Send`.
+    #[cfg(feature = "http2")]
+    pub fn serve_connection_with_upgrades<I, S, B>(
+        &self,
+        io: I,
+        service: S,
+    ) -> UpgradeableConnection<'_, I, S, E>
+    where
+        S: Service<Request<Incoming>, Response = Response<B>>,
+        S::Future: 'static,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        B: Body + 'static,
+        B::Error: Into<Box<dyn StdError + Send + Sync>>,
+        I: Read + Write + Unpin + Send + 'static,
+        E: HttpServerConnExec<S::Future, B>,
+    {
+        self.inner.serve_connection_with_upgrades(io, service)
+    }
 }
 
 /// Http2 part of builder.
@@ -824,6 +845,26 @@ impl<E> Http2Builder<'_, E> {
     {
         self.inner.serve_connection(io, service).await
     }
+
+    /// Bind a connection together with a [`Service`], with the ability to
+    /// handle HTTP upgrades. This requires that the IO object implements
+    /// `Send`.
+    pub fn serve_connection_with_upgrades<I, S, B>(
+        &self,
+        io: I,
+        service: S,
+    ) -> UpgradeableConnection<'_, I, S, E>
+    where
+        S: Service<Request<Incoming>, Response = Response<B>>,
+        S::Future: 'static,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        B: Body + 'static,
+        B::Error: Into<Box<dyn StdError + Send + Sync>>,
+        I: Read + Write + Unpin + Send + 'static,
+        E: HttpServerConnExec<S::Future, B>,
+    {
+        self.inner.serve_connection_with_upgrades(io, service)
+    }
 }
 
 #[cfg(test)]
@@ -971,7 +1012,9 @@ mod tests {
                 let stream = TokioIo::new(stream);
                 tokio::task::spawn(async move {
                     let _ = auto::Builder::new(TokioExecutor::new())
-                        .serve_connection(stream, service_fn(hello))
+                        .http2()
+                        .max_header_list_size(4096)
+                        .serve_connection_with_upgrades(stream, service_fn(hello))
                         .await;
                 });
             }