Adapt CROW_WEBSOCKET_ROUTE to accept app reference

[soehrl]

Hello,

I noticed today that it is not possible to use the CROW_WEBSOCKET_ROUTE macro to define WebSocket routes in other functions. E.g., something like this:

void define_endpoints(crow::SimpleApp& app) {
    CROW_ROUTE(app, "/") ([]() {
        return "Hello, world!";
    });
    CROW_WEBSOCKET_ROUTE(app, "/ws")
      .onaccept([&](const crow::request&, void**) {
          return true;
      })
      .onopen([](crow::websocket::connection&) {})
      .onclose([](crow::websocket::connection&, std::string_view) {});
}

Resulted in the error:

error: no matching member function for call to 'websocket'
    CROW_WEBSOCKET_ROUTE(app, "/ws")
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/simon/Code/Crow/include/crow/app.h:33:98: note: expanded from macro 'CROW_WEBSOCKET_ROUTE'
#define CROW_WEBSOCKET_ROUTE(app, url) app.route<crow::black_magic::get_parameter_tag(url)>(url).websocket<decltype(app)>(&app)
                                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
/Users/simon/Code/Crow/include/crow/routing.h:527:29: note: candidate template ignored: substitution failure [with App = crow::Crow<> &]: 'app' declared as a pointer to a reference of type 'crow::Crow<> &'
        WebSocketRule<App>& websocket(App* app)
                            ^            ~
1 error generated.

The issue was that decltype(app) then returned a reference. I fixed the problem by using std::remove_reference<decltype(app)>::type instead. I also added a test to assure that it is working.

[The-EDev]

In function 'void define_endpoints(crow::SimpleApp&)':

/drone/src/tests/external_definition/main.cpp:13:54: error: 'std::string_view' has not been declared

   13 |       .onclose([](crow::websocket::connection&, std::string_view) {});

[soehrl]

Didn't test it on an older compiler, should work now!

[crow-clang-format]

--- tests/external_definition/main.cpp	(before formatting)
+++ tests/external_definition/main.cpp	(after formatting)
@@ -1,8 +1,10 @@
 // Testing whether crow routes can be defined in an external function.
 #include "crow.h"
 
-void define_endpoints(crow::SimpleApp& app) {
-    CROW_ROUTE(app, "/") ([]() {
+void define_endpoints(crow::SimpleApp& app)
+{
+    CROW_ROUTE(app, "/")
+    ([]() {
         return "Hello, world!";
     });
     CROW_WEBSOCKET_ROUTE(app, "/ws")