Fix example-chat

[keith-dev]

example-chat has runtime errors because std::function<> is assigned null in places.

This is a fix for that, with unittests.

[mrozigor]

What is the exact error? As far as I see in the code, these handlers are checked for null before calling them. Maybe problem is with example?

[keith-dev]

What is the exact error? As far as I see in the code, these handlers are checked for null before calling them. Maybe problem is with example?

The application crashes, segfaults. I ran it on Android 15 under Termux (clang) and Linux (probably clang again) where it crashed.

Using gdb, the crash is caused by assigning null to a std::function.

The crash can be reproduced on Lunux by compiling with clang and just using example-chat, the faulty code is in Crow, not the example.

The check for null isn't the problem, it's assigning null that's the problem.

[mrozigor]

Ok, thanks for info. So the only thing is that you can create lambda_wrapper with nullptr.

[dranikpg]

I don't really understand what lambda_wrapper does 🙂 After all, std just throws as well

https://en.cppreference.com/w/cpp/utility/functional/function/operator()

Exceptions
Throws std::bad_function_call if *this does not store a callable function target, i.e. !*this == true.

[rainhard]

I have encountered the same problem and don't know how to fix it yet.
here is the clue:

response::end()
  -> complete_request_handler
      -> Connection::complete_request
          -> Connection::prepare_buffers
              -> res.complete_request_handler = nullptr; //  operator = free captured `self` Connection, cause segfault