Run pre_request_handler for WebSocket routes

The WebSocket upgrade path matched the route and switched protocols
without setting req.matched_route or calling pre_request_handler, so a
check placed there (e.g. authentication) never ran for WebSocket
routes. Set matched_route and run the handler before the upgrade; if it
handles the request, reply with a regular HTTP response instead of 101.

Also write rejected upgrade responses (from pre_routing_handler too)
with write_response_with_content, so they carry Content-Length. Without
it, a client reading the body waited until the keep-alive timeout.

httplib.h

@@ -14411,18 +14411,25 @@ Server::process_request(Stream &strm, const std::string &remote_addr,
   };
 
   // WebSocket upgrade
-  // Check pre_routing_handler_ before upgrading so that authentication
-  // and other middleware can reject the request with an HTTP response
-  // (e.g., 401) before the protocol switches.
+  // Run pre_routing_handler_ and pre_request_handler_ before upgrading so
+  // that authentication and other middleware can reject the request with an
+  // HTTP response (e.g., 401) before the protocol switches.
   if (detail::is_websocket_upgrade(req)) {
     if (pre_routing_handler_ &&
         pre_routing_handler_(req, res) == HandlerResponse::Handled) {
       if (res.status == -1) { res.status = StatusCode::OK_200; }
-      return write_response(strm, close_connection, req, res);
+      return write_response_with_content(strm, close_connection, req, res);
     }
     // Find matching WebSocket handler
     for (const auto &entry : websocket_handlers_) {
       if (entry.matcher->match(req)) {
+        req.matched_route = entry.matcher->pattern();
+        if (pre_request_handler_ &&
+            pre_request_handler_(req, res) == HandlerResponse::Handled) {
+          if (res.status == -1) { res.status = StatusCode::OK_200; }
+          return write_response_with_content(strm, close_connection, req, res);
+        }
+
         // Compute accept key
         auto client_key = req.get_header_value("Sec-WebSocket-Key");
         auto accept_key = detail::websocket_accept_key(client_key);