MessageMetadata has no user-provided default constructor

[lshamis]

The following program fails to compile:

#include <App.h>

int main() {
  struct Unused {};
  uWS::App app;
  app.ws<Unused>("/", uWS::App::WebSocketBehavior{});
}

Compiler output:

INFO: From Compiling example.cc:
In file included from external/uwebsockets/src/WebSocket.h:24:0,
                 from external/uwebsockets/src/HttpResponse.h:30,
                 from external/uwebsockets/src/App.h:25,
                 from example.cc:1:
external/uwebsockets/src/WebSocketContextData.h: In instantiation of 'uWS::WebSocketContextData<<anonymous> >::WebSocketContextData()::<lambda(uWS::Subscriber*, std::pair<std::basic_string_view<char>, std::basic_string_view<char> >)> [with bool SSL = false]':
external/uwebsockets/src/WebSocketContextData.h:73:41:   required from 'struct uWS::WebSocketContextData<<anonymous> >::WebSocketContextData() [with bool SSL = false]::<lambda(struct uWS::Subscriber*, struct std::pair<std::basic_string_view<char>, std::basic_string_view<char> >)>'
external/uwebsockets/src/WebSocketContextData.h:144:6:   required from 'uWS::WebSocketContextData<<anonymous> >::WebSocketContextData() [with bool SSL = false]'
external/uwebsockets/src/WebSocketContext.h:388:9:   required from 'static uWS::WebSocketContext<<anonymous>, <anonymous> >* uWS::WebSocketContext<<anonymous>, <anonymous> >::create(uWS::Loop*, us_socket_context_t*) [with bool SSL = false; bool isServer = true]'
external/uwebsockets/src/App.h:143:69:   required from 'uWS::TemplatedApp<SSL>&& uWS::TemplatedApp<SSL>::ws(std::string, uWS::TemplatedApp<SSL>::WebSocketBehavior&&) [with UserData = main()::Unused; bool SSL = false; std::string = std::basic_string<char>]'
example.cc:6:52:   required from here
external/uwebsockets/src/WebSocketContextData.h:38:12: note: 'struct uWS::WebSocketContextData<false>::MessageMetadata' has no user-provided default constructor
     struct MessageMetadata {
            ^~~~~~~~~~~~~~~
external/uwebsockets/src/WebSocketContextData.h:39:22: note: and the implicitly-defined constructor does not initialize 'unsigned int uWS::WebSocketContextData<false>::MessageMetadata::length'
         unsigned int length;
                      ^~~~~~

This was built with: uwebsockets at commit 2d65df86c7988f5d9afa826cfbceda332f06f6a4 usockets at commit 7683672d87067cd75b854f4e36b9820f4809a4be

but the same error occurs going back at least v18.3.0

This was tested with the default gcc on Ubuntu Bionic (gcc version 7.5.0)

[ghost]

This is not an error - do you compile with warnings as errors?

[ghost]

external/uwebsockets/src/WebSocketContextData.h:39:22: note: and the implicitly-defined constructor does not initialize 'unsigned int uWS::WebSocketContextData<false>::MessageMetadata::length'
         unsigned int length;
                      ^~~~~~

That's the culprit. But this is totally allowed.

[lshamis]

I've gone through and confirmed that you fully populate all instances of MessageMetadata before reading the values, so no uninitialized-memory issues.

@alexhultman are you open to PRs that cleanup warnings?

Thanks, and we can close this.

[ghost]

All warnings (not pedantic) should be fixed, but not at the cost of adding overhead.

[ghost]

GCC 9 does not show this warning in -Wextra

[ghost]

Neither does Clang 10

[ghost]

Fixed on master