This adds an overlay port for curl that adds the features required for
HTTP/3.
This is not quite compatible with the upstream vcpkg.json, because
enabling HTTP/2 makes it use the default SSL backend, which is
sectransp for macOS and schannel on Windows. These backends are not
compatible with ngtcp2. Additionally, we can not build curl with
multiple SSL backends when using ngtcp2.
I couldn't find a way to selectively disable/enable dependencies based
on what features are enabled, so I made HTTP/2 pick OpenSSL in our
overlay port. Upstream vcpkg will likely want to support wolfSSL and
GnuTLS backends for ngtcp2, so they'll be additional work to get this
into upstream.
Instead of wrapping all non-movable members of TransportSocket in OwnPtr
to keep it movable, make TransportSocket itself non-movable and wrap it
in OwnPtr.
This has been a longstanding ergonomic issue with our IPC compiler. Non-
trivial types were previously passed by const&. So if we wanted to avoid
expensive copies, we would have to const_cast and move the data.
We now pass ownership of all transferred data to the client subclasses.
This allows us to remove const_cast from these methods, and allows us to
avoid some trivial expensive copies that we didn't bother to const_cast.
This implementation can be better improved in the future by ripping
out a lot of the manual logic in LibWebSocket and rely on libcurl to
parse our message payloads. But for now, this uses the 'raw mode' of
curl websockets in connect-only mode to allow for somewhat seamless
integration into our event loop.
