This defines an extension type used in requests for the client that is
used to setup a callback for receipt of informational (1xx) responses.
The type isn't currently public, and is only usable in the C API.
As I understand it, "cargo rustc" in gen_header.sh generates a ton of
errors, but still manages to generate an object that can be used by
cbindgen to generate hyper.h.
However, I tried to make a separate change to add more fields to
hyper.h, and learned that "cargo rustc" stops if it reaches 50 errors,
which I reached. I was able to buy some headroom and fix a number of
the compilation errors by adding imports to the fake Cargo.toml we
generate in gen_header.sh.
I wasn't sure how to resolve imports like "crate::Result" which appear
to reference the top-level src/error.rs, and print an error when they
are compiled in gen_header.sh. But I only need to buy headroom under
the 50 error count for now, which I was able to do by adding the
imports.
It is possible that someone more familiar with Rust than me could look
at this and know what to change to get the total number of errors to
zero.
Make C API functions that return pointers return null in case of a
panic, instead of aborting.
Add ffi_fn! macro rules that enable default error values to be returned
by writing "?= <value>" after an ffi function's body.
This adds an internal ability to copy the HTTP/1 reason-phrase and place
it in the `http::Extensions` of a response, if it doesn't match the
canonical reason. This could be exposed in the Rust API later, but for
now it is only used by the C API.
