Crow currently does not decode the URL path.
Such a decoder could be added, but only makes sense in a few cases and adds additional runtime to request handling.
Therefore there is no plan to do the URL path decoding in crow.

Ok, I'm fine with this, however, is this typical for webservers? It seems like surprising behaviour.

Can we document this?
And add a nice obviously named function?

My route was coded something like:

CROW_ROUTE(app, "/<string>/<path>")
([]( const crow::request& req, crow::response& res, const string_view url_leaf, string url_path_partial )
{
   // decode URL path
   url_path_partial.resize( crow::qs_decode(&url_path_partial[0]) );
}

IF this is the correct approach, then it would be nice to have a function that accepts a string and in-place decodes it.

What do you think?

Yo are welcome to add the function and the documentation.

I've pushed a PR with test case. Was trying codespaces, is there a way to run the unit tests in there?

https://github.com/CrowCpp/Crow/pull/993/checks
they run now, I had to approve.

I've forced-pushed. Do you have to re-approve each time?

It seems. :)

Ok, I'm fine with this, however, is this typical for webservers? It seems like surprising behaviour.

Certainly surprised me, spent a long time assuming I was doing something wrong.
I'll be adding url_decode to my add_static_dir(), thanks!

Looking at the MSVC implementation of std::string::resize made me wrinkle my nose a bit for a non-changing case, so I'm using

      int decoded_length = url_decode(&url[0]);
      if (decoded_length != static_cast<int>(url.size()))
         url.resize(decoded_length);

I'm curious so I looked into this ...

    _CONSTEXPR20 void resize(_CRT_GUARDOVERFLOW const size_type _New_size, const _Elem _Ch = _Elem()) {
        // determine new length, padding with _Ch elements as needed
        const size_type _Old_size = size();
        if (_New_size <= _Old_size) {
            _Eos(_New_size);
        } else {
            append(_New_size - _Old_size, _Ch);
        }
    }

For non-changing it always calls _Eos()

    _CONSTEXPR20 void _Eos(const size_type _New_size) noexcept { // set new length and null terminator
        _ASAN_STRING_MODIFY(*this, _Mypair._Myval2._Mysize, _New_size);
        _Mypair._Myval2._Mysize = _New_size;
        _Traits::assign(_Mypair._Myval2._Myptr()[_New_size], _Elem());
    }

For the non-changing case,
So it always sets size=size and then assigns the null terminator.

I guess they are trying to avoid a second test to check for == (one extra branch costs more than 2 assigns?)
libc++ also implements resize the same way:
https://github.com/llvm-mirror/libcxx/blob/78d6a7767ed57b50122a161b91f59f19c9bd0d19/include/string#L3095

libstdc++ uses a second test:
https://github.com/gcc-mirror/gcc/blob/24a041ea863721f3181e4433195e7697bf52c413/libstdc%2B%2B-v3/include/bits/basic_string.tcc#L432