Update libcurl

Engine/lib/curl/docs/HYPER.md

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+# Hyper
+
+Hyper is a separate HTTP library written in Rust. curl can be told to use this
+library as a backend to deal with HTTP.
+
+## Experimental!
+
+Hyper support in curl is considered **EXPERIMENTAL** until further notice. It
+needs to be explicitly enabled at build-time.
+
+Further development and tweaking of the Hyper backend support in curl will
+happen in in the master branch using pull-requests, just like ordinary
+changes.
+
+## Hyper version
+
+The C API for Hyper is brand new and is still under development.
+
+## build curl with hyper
+
+Since March 3 2022, hyper needs the nightly rustc to build, which you may need
+to install first with:
+
+     % rustup toolchain install nightly
+
+Then build hyper and enable its C API like this:
+
+     % git clone https://github.com/hyperium/hyper
+     % cd hyper
+     % RUSTFLAGS="--cfg hyper_unstable_ffi" cargo +nightly rustc --features client,http1,http2,ffi -Z unstable-options --crate-type cdylib
+
+Build curl to use hyper's C API:
+
+     % git clone https://github.com/curl/curl
+     % cd curl
+     % autoreconf -fi
+     % ./configure --with-hyper=<hyper dir>
+     % make
+
+# using Hyper internally
+
+Hyper is a low level HTTP transport library. curl itself provides all HTTP
+headers and Hyper provides all received headers back to curl.
+
+Therefore, most of the "header logic" in curl as in responding to and acting
+on specific input and output headers are done the same way in curl code.
+
+The API in Hyper delivers received HTTP headers as (cleaned up) name=value
+pairs, making it impossible for curl to know the exact byte representation
+over the wire with Hyper.
+
+## Limitations
+
+The hyper backend does not support
+
+- `CURLOPT_IGNORE_CONTENT_LENGTH`
+- `--raw` and disabling `CURLOPT_HTTP_TRANSFER_DECODING`
+- RTSP
+- hyper is much stricter about what HTTP header contents it allows
+- HTTP/0.9
+- HTTP/2 upgrade using HTTP:// URLs. Aka 'h2c'
+
+## Remaining issues
+
+This backend is still not feature complete with the native backend. Areas that
+still need attention and verification include:
+
+- multiplexed HTTP/2
+- h2 Upgrade:
+- pausing transfers
+- receiving HTTP/1 trailers
+- sending HTTP/1 trailers
+