Add APIs to allow switching an HTTP1 connection to HTTP2 if H2 preface is seen

src/error.rs

@@ -192,6 +192,13 @@ impl Error {
         matches!(self.inner.kind, Kind::Parse(Parse::Status))
     }
 
+    /// Returns true if this was an HTTP parse error caused by HTTP2 preface sent over an HTTP1
+    /// connection.
+    #[cfg(all(any(feature = "client", feature = "server"), feature = "http1"))]
+    pub fn is_parse_version_h2(&self) -> bool {
+        matches!(self.inner.kind, Kind::Parse(Parse::VersionH2))
+    }
+
     /// Returns true if this error was caused by user code.
     pub fn is_user(&self) -> bool {
         matches!(self.inner.kind, Kind::User(_))

src/server/conn/http1.rs

@@ -522,6 +522,12 @@ where
             Pin::new(conn).graceful_shutdown()
         }
     }
+
+    /// Return the inner IO object, and additional information provided the connection
+    /// has not yet been upgraded.
+    pub fn into_parts(self) -> Option<Parts<I, S>> {
+        self.inner.map(|conn| conn.into_parts())
+    }
 }
 
 impl<I, B, S> Future for UpgradeableConnection<I, S>