fix(server): convert panic to error if Connection::without_shutdown called on HTTP/2 conn

src/error.rs

@@ -128,6 +128,10 @@ pub(super) enum User {
     #[cfg(feature = "http1")]
     ManualUpgrade,
 
+    /// User called `server::Connection::without_shutdown()` on an HTTP/2 conn.
+    #[cfg(feature = "server")]
+    WithoutShutdownNonHttp1,
+
     /// User aborted in an FFI callback.
     #[cfg(feature = "ffi")]
     AbortedByCallback,
@@ -355,6 +359,11 @@ impl Error {
         Error::new_user(User::Body).with(cause)
     }
 
+    #[cfg(feature = "server")]
+    pub(super) fn new_without_shutdown_not_h1() -> Error {
+        Error::new(Kind::User(User::WithoutShutdownNonHttp1))
+    }
+
     #[cfg(feature = "http1")]
     pub(super) fn new_shutdown(cause: std::io::Error) -> Error {
         Error::new(Kind::Shutdown).with(cause)
@@ -449,6 +458,10 @@ impl Error {
             Kind::User(User::NoUpgrade) => "no upgrade available",
             #[cfg(feature = "http1")]
             Kind::User(User::ManualUpgrade) => "upgrade expected but low level API in use",
+            #[cfg(feature = "server")]
+            Kind::User(User::WithoutShutdownNonHttp1) => {
+                "without_shutdown() called on a non-HTTP/1 connection"
+            }
             #[cfg(feature = "ffi")]
             Kind::User(User::AbortedByCallback) => "operation aborted by an application callback",
         }